Approval of Air Quality Implementation 

Plans; Navajo Nation; Regional Haze 

Requirements for Navajo Generating 

Station 

Final Rule 

Responses to Comments on Proposal and 

Supplemental Proposal 
This page intentionally left blank.
 Approval of Air Quality Implementation 

Plans; Navajo Nation; Regional Haze 

Requirements for Navajo Generating Station 

Final Rule 

Responses to Comments on Proposal and 

Supplemental Proposal 

Air Division 

Region IX 

U. S. Environmental Protection Agency 

San Francisco, CA 94105 

July 28, 2014 
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i 

Table of Contents 

Acronyms and Abbreviations ......................................................................................................... ii

1.0 Introduction ........................................................................................................................... 1

1.1 Background .................................................................................................................... 1

1.2 Public Comments ........................................................................................................... 1

1.3 Organization of This Document ..................................................................................... 2

2.0 Oral Testimony at the Public Hearings and Mass Comment Campaigns ............................. 3

2.1 Oral Testimony at the Public Hearings .......................................................................... 3

2.2 Mass Comment Campaigns ......................................................................................... 16

3.0 Comments on Factor One – Cost of Controls ..................................................................... 23

3.1 Comments on the Analysis of the Cost of SCR at NGS .............................................. 23

3.2 Other Comments on Factor One .................................................................................. 44

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

Impacts ................................................................................................................................ 44

4.1 Comments on Economic Impacts ................................................................................ 44

4.1.1 General Comments on Economic Impacts ......................................................... 45

4.1.2 Comments on the EPA’s Affordability Analysis ............................................... 57

4.2 Comments on Energy and Non-Air Quality Environmental Impacts .......................... 75

5.0 Comments on Factor Three – Existing Controls at NGS .................................................... 84

6.0 Comments on Factor Four – Remaining Useful Life of NGS ............................................. 87

7.0 Comments on Factor Five – Anticipated Visibility Improvements .................................... 90

8.0 Comments on BART Determinations ............................................................................... 120

8.1 Comments on the Proposed BART Determination for NOx ...................................... 120

8.2 Comments on BART for PM ..................................................................................... 154

8.3 Comments on BART for SO2 ..................................................................................... 157

8.4 Other Comments on BART ........................................................................................ 158

8.5 Comments on the EPA’s BART Alternative ............................................................. 160

8.6 Additional Alternatives to BART .............................................................................. 183

9.0 Comments on the TWG Alternative and EPA’s Supplemental Proposal ......................... 192

10.0 Other Comments ............................................................................................................... 226

Appendix A: List of Written Comments ..................................................................................... 246
ii 

Acronyms and Abbreviations 

Pollutants

CO2 Carbon dioxide 

H2SO4 Sulfuric acid 

HCl Hydrochloric acid 

HF Hydrogen fluoride 

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 

lb Pound 

MMBtu Million British thermal units 

MW Megawatt 

MWh Megawatt hour 

TBtu Trillion British thermal units 

tpy Tons per year 

Acronyms and Abbreviations 

ADEQ Arizona Department of Environmental Quality 

ANPR Advance Notice of Proposed Rulemaking 

ALA American Lung Association 

APA Administrative Procedure Act 

APS Arizona Public Service 

BACT Best Available Control Technology 

BART Best Available Retrofit Technology 

BAU Business as usual 

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

Acronyms and Abbreviations 

CAMD Clean Air Markets Division (EPA) 

CAP Central Arizona Project 

CAWCD Central Arizona Water Conservation District 

CEMS Continuous emissions monitoring system 

CFR Code of Federal Regulations 

CO Colorado 

COMS Continuous opacity monitoring system 

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

DOI Department of the Interior 

EGU Electric generating unit 

EPA U.S. Environmental Protection Agency 

EPRI Electric Power Research Institute 

ESA Endangered Species Act 

FCC Federal Communications Commission 

FCPP Four Corners Power Plant 

FIP Federal Implementation Plan 

FLM Federal Land Manager 

FR Federal Register 

GHG Greenhouse Gas Emissions

IWAQM Interagency Workgroup on Air Quality Modeling 

LADWP Los Angeles Department of Water and Power 

LCRBDF Lower Colorado River Basin Development Fund 

LNB Low NOx burner 

MACT Maximum Achievable Control Technology 

MATS Mercury and Air Toxics Standard 

MPP Mohave Power Project 

NAAQS National Ambient Air Quality Standards 

NGS Navajo Generating Station 

NM New Mexico 

NPDES National Pollutant Discharge Elimination System 

NREL National Renewable Energy Laboratory 
iv 

Acronyms and Abbreviations 

NSPS New Source Performance Standard 

NSR New Source Review 

NVE NV Energy 

OAR Office of Air and Radiation (EPA) 

PSD Prevention of Significant Deterioration 

RAVI BART Reasonably Attributable Visibility Impairment Best Available Retrofit 

Technology 

RHR Regional Haze Rule 

SCR Selective catalytic reduction 

SIP State Implementation Plan 

SJGS San Juan Generating Station 

SNCR Selective non-catalytic reduction 

SOFA Separated over-fire air 

SRP Salt River Project 

TAR Tribal Authority Rule 

TEP Tucson Electric Power Company 

TIP Tribal Implementation Plan 

TSD Technical Support Document 

TWG Technical Work Group on NGS 

U.S.C. United States Code 

UARG Utility Air Regulatory Group 

U.S. United States 

WRAP Western Regional Air Partnership 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

1.0 Introduction 

1.1 Background 

 On February 5, 2013, the U.S. Environmental Protection Agency (EPA or we) proposed a 

source-specific Federal Implementation Plan (FIP) requiring the Navajo Generating Station (NGS), 

located on the Navajo Nation, to achieve emissions reductions required by the Clean Air Act’s (CAA’s) 

Best Available Retrofit Technology (BART) provision.1 In addition to our proposed BART 

determination, EPA also proposed a BART Alternative, put forth a framework for evaluating additional 

alternatives to BART, and invited stakeholders to submit other alternatives to EPA for consideration. 

On July 26, 2013, a diverse group of stakeholders, known as the Technical Work Group on NGS 

(TWG), developed an agreement (TWG Agreement) that included an alternative to BART (Appendix B 

to the TWG Agreement) and submitted it to EPA. EPA independently evaluated Appendix B to the 

TWG Agreement to determine if it meets the requirements of the CAA and the Regional Haze Rule 

(RHR). In a Supplemental Proposal published in the Federal Register on October 22, 2013, EPA 

proposed to determine that requirements consistent with Appendix B to the TWG Agreement are “better 

than BART” because it would achieve greater reasonable progress than EPA’s proposed BART 

determination towards the national visibility goal.2

 Throughout this document and our Final Rule, we 

refer to the requirements put forth in our Supplemental Proposal as the “TWG Alternative.” 

1.2 Public Comments 

 In the February 2013 Proposed Rule, EPA provided a 90-day public comment period, to close on 

May 6, 2013. At the request of several stakeholders working to develop an alternative to BART, EPA 

provided several extensions of the public comment period.3 In our October 2013 Supplemental Proposal, 

EPA invited comment on the TWG Alternative concurrently with the open comment period on EPA’s 

Proposed Rule. The comment period for both proposals closed on January 6, 2014. 

The EPA held five public hearings on the Proposed Rule and Supplemental Proposal on the 

Navajo Nation, on the Hopi Reservation, and in Arizona on November 12 – 15, 2013. In all, 194 oral 

testimonies were presented at the five hearings, although several individuals spoke at more than one 

hearing. The oral testimony is discussed further in Section 2.1 of this document 

We received approximately 77,000 written comments. Of these, approximately 76,800 comments 

came from individuals who responded to mass comment campaigns by email or postcard. These 

comments are discussed further in Section 2.2 of this document. 

1

 The proposed BART determination published in the Federal Register on February 5, 2013, in Volume 78, beginning on 

page 8,274 (78 FR 8274, February 5, 2013). 

2

 78 FR 62509 (October 22, 2013). 

3

 See 78 FR 16825 (March 19, 2013) that extended the comment period to August 5, 2013, 78 FR 41012 (July 9, 2013) that 

extended the comment period to October 4, 2013, and 78 FR 58987 (September 25, 2013) that extended the comment period 

to January 6, 2014. On June 19, 2013, EPA also announced our intention to hold five public hearings throughout Arizona to 

accept oral comment on our proposed rulemaking (78 FR 36716). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 We received an additional 300 unique written comments, not including duplicates from 261 

different entities. These commenters can be broken down by type as follows: 8 tribal governments, 172 

private individuals, 9 environmental and public interest advocacy groups, 8 CAP water interest groups, 

26 industry/commerce entities, 1 federal agency, 24 state/local government entities, 12 elected officials, 

and the TWG. These comments are listed Appendix A. The comments are summarized by subject matter 

topics in Sections 3.0 through 10.0 of this document. 

In addition to the comments submitted in writing and to the oral comments provided at the public 

hearings that have been transcribed, EPA also received by mail a DVD of .mp4 files showing videos of 

eight individuals speaking about NGS. Two individuals were speaking in Diné, the Navajo language, 

with another individual interpreting into English. The eight individuals are the same eight individuals 

listed as signatories of written comment 0403 that expresses opposition to the current and proposed 

operation of NGS and associated activities.4

 The written comment from these individuals is addressed 

elsewhere in this document (section 10.0). These video files are not in the electronic docket for this 

rulemaking, and EPA is not providing separate responses to the video comments because the eight 

individuals did not raise any unique issues or concerns, related specifically to NGS and our proposed 

BART determination, that have not already been raised by other commenters through the public 

comment process.5

1.3 Organization 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 NGS 

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

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

 Section 8.0 – Comments on BART Determinations 

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

 Section 10.0 – Other Comments 

4

 Throughout this Response to Comments document, EPA refers to comments by the document number in the docket for this 

rule. For example, comment 0403 refers to document number 0403 in the docket at EPA-R09-OAR-2013-0009. See 

Appendix A for the full list of comments. 

5

 We note that one unique concern raised by several of the individuals was related to potential adverse air quality effects of 

coal fires at the Kayenta Mine that are allowed to burn or smolder. This comment is not related to EPA’s proposed BART 

determination for NGS. EPA notes that the Bureau of Reclamation has started its process to develop an Environmental 

Impact Statement (EIS) required under the National Environmental Protection Act (NEPA) for activities resulting from the 

continued operation of NGS and the Kayenta Mine. The on-going NEPA process provides numerous opportunities and the 

appropriate forum to raise concerns related to the impacts of coal fires at the Kayenta Mine. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

2.0 Oral Testimony at the Public Hearings and Mass Comment 

Campaigns 

2.1 Oral Testimony at the Public Hearings 

 EPA held five public hearings in Arizona on November 12, 13, 14, and 15, 2013. In conjunction 

with each hearing (generally before the hearing), EPA held an open-house style information session to 

provide time for members of the public to talk with representatives from EPA about the Proposed Rule 

and Supplemental Proposal for NGS. EPA summarized the Proposed Rule and Supplemental Proposal in 

posters and handouts that were displayed at each information session and hearing. EPA posted copies of 

the handouts and posters in the docket for the proposed rulemaking.6 An interpreter for speakers of Diné, 

the Navajo language, was present for the information sessions and public hearings at the LeChee 

Chapter House and at Page High School. 

 In all, a total of 194 oral testimonies were presented at the five hearings, although several 

individuals spoke at more than one hearing. Most speakers spoke as private individuals, but many spoke 

as representatives of the interested industries (e.g., the co-owners of NGS and operator of the Kayenta 

Mine), environmental advocacy groups, public interest advocacy groups, and local governments. 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 

Nov. 12 LeChee Chapter House 

LeChee, Arizona 

(EPA-R09-OAR-2013-0009-0426) 

10 a.m. – 1 p.m. 

(concurrent) 

Private individuals – 22 

Industry/Commerce – 1 

Government – 4 

Nov. 12 Page High Cultural Arts Building 

Page, Arizona 

(EPA-R09-OAR-2013-0009-0427 

3 – 5 

p.m. 

6 – 9 

p.m. 

Private individuals – 22 

Industry/Commerce – 10 

Government – 3 

Nov. 13 Hopi Day School 

Kykotsmovi, Arizona 

(EPA-R09-OAR-2013-0009-0428) 

3 – 5 

p.m. 

6 – 9 

p.m. 

Private individuals – 18 

Industry/ Commerce – 11 

Environmental/ Public 

interest – 7 

Government – 1 

Nov. 14 Phoenix Convention Center 

Phoenix, Arizona 

(EPA-R09-OAR-2013-0009-0429) 

3 – 5 

p.m. 

6 – 10 

p.m. 

Private individuals – 37 

Industry/Commerce – 16 

Environmental/ Public 

interest – 8 

Government – 8 

6

 See document number 0219 in the docket (docket number EPA-R09-OAR-2013-0009) for the proposed rulemaking at 

www.regulations.gov (i.e., EPA-R09-OAR-2013-0009-0219). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

PUBLIC HEARINGS AND INFORMATION SESSIONS 

Time

Date

Venue 

(with Transcript Docket Number)

Info 

Session 

Public 

Hearing Commenters 

Nov. 15 Pima Community College 

Tucson, Arizona 

(EPA-R09-OAR-2013-0009-0430) 

3 – 5 

p.m. 

6 – 9 

p.m. 

Private individuals – 26 

Industry/Commerce – 11 

Environmental/Public 

interest – 7 

Government – 1 

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

exception of comments from entities that submitted written comments for those cases where the written 

comments duplicated their oral testimony. For example, TWG submitted written comments that are 

summarized in the other sections of this document; therefore their oral comments on the same topics are 

not included in this section. Numerous individuals provided oral comments at the public hearings that 

are similar to or duplicative of comments made by different individuals or entities in writing. For 

example, during the public hearing, numerous individuals noted the contribution of NGS to the local and 

state economy, or supported the development of renewable energy to replace NGS. Because these 

comments were the same as the major topics from the public hearings, they are summarized in the 

Public Hearing section of this document. However, similar comments also appear in later sections of this 

document that describe comments submitted in writing (e.g., Section 4.0). The comments at all of the 

hearings followed similar themes and are generally treated together in the following summaries. 

Comment: Contribution of NGS to the local and state economy and support for TWG Alternative 

 Many commenters preferred the TWG Alternative because they believe that EPA’s proposed 

BART determination would force NGS and its associated mine (i.e., the Kayenta Mine) to close, causing 

economic harm to an area where the majority of residents are low-income and where opportunities for 

employment are limited, particularly for young people. Many of these commenters cautioned EPA to 

carefully balance the environmental benefit of any requirement for NGS with the potential economic 

harm to the Navajo Nation and Hopi Tribe. These commenters stressed that NGS employs over 500 

people and the Kayenta Mine has over 400 employees, and the loss of these jobs would only exacerbate 

the unemployment rate in the area, which currently ranges from 47 percent to 60 percent. A few 

commenters related personal experiences and described how the shutdown of other coal-fired power 

plants and mines (e.g., Mohave Power Project and the Black Mesa Mine) affected their ability to find 

employment and provide for their families. One commenter discussed how the lack of employment 

opportunities in the area combined with the closure of the NGS plant would increase the crime rate in 

the area, which currently stands at 24 percent. 

 Several commenters emphasized that in addition to offering employment opportunities, NGS 

provides substantial economic benefit to Tribes and the State of Arizona. Many commenters highlighted 

that NGS’s payments to the Navajo Nation make up a large portion of the Nation’s budget. However, 

some commenters challenged the claim that the Nation’s budget is limited and the Nation relies on coal 

revenues to function. One commenter asserted that only 36 percent of the general funds come from coal 

revenues. Another commenter mentioned two articles: one that reported that the Navajo Nation returned 

over $14.5 million of federal funding allocated for diabetes programs, and another article that reported 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

that the Navajo Nation returned over $16 million of federal funding allocated for workforce 

development. Several commenters cited an Arizona State University (ASU) economic impact study 

which projected that NGS and its associated mine will indirectly account for more than $20 billion in 

gross state product and over $679 million in adjusted state tax revenues between 2011 and 2044, while 

generating over 3,000 jobs annually. One commenter noted that NGS currently pays about $52 million 

per year in total wages to its 538 employees. Another commenter stated that the Kayenta Mine alone 

contributes roughly $117 million annually to the region through royalties, business payments, and 

wages. 

 A number of commenters discussed educational benefits from NGS contributions (e.g., 

scholarships for Native American students) and stressed that without this financial assistance many local 

residents would not be able to afford to send their children to college. Others discussed the potential 

impact to businesses and the real estate market if NGS were to close. One commenter reported that the 

gold industry contributes over $3.5 billion to the State of Arizona and would be heavily impacted if 

water rates increased as a result of NGS closing. The commenter projected that higher rates would force 

these institutions to shut down contributing to a loss of more than 20,000 jobs in the area. A few 

commenters contended that the decline in business revenue and property values in and around the NGS 

area is largely due to residents’ fear that NGS will shut down. According to one commenter, in 2007 the 

average home price was $255,000 and today it is $184,000. The commenter added that during the same 

period manufactured homes, which make up the majority of homes in the area declined from $122,000 

to $106,000. Another commenter added that a decline in housing prices would negatively impact 

property taxes which subsidize facilities, like Page Hospital. The commenter noted that Page Hospital 

currently contributes roughly $9.2 million annually to the city in both direct and indirect spending (e.g., 

salaries, housing, and utilities). 

 Several commenters favor the TWG Alternative because they believe that EPA’s proposed 

BART determination will make it economically impossible for NGS to continue to operate; thus, would 

impact their ability to receive affordable and reliable energy and water in the future. A number of these 

commenters noted that NGS currently supplies more than 90 percent of the energy used by Central 

Arizona Water Conservation District (CAWCD), which operates the Central Arizona Project (CAP) 

which transfers water from the Colorado River throughout Arizona. One commenter asserted that the 

EPA’s proposed regulation could potentially add $1.1 billion in costs to Arizona’s water and power 

bills. A co-owner of NGS argued that the installation of SCR would cost the plant $400 to $544 million, 

possibly up to $1 billion, of which $8 to $5 million would be passed down to its customers, resulting in 

higher rates during a time where most communities are still recovering from the recent recession. These 

commenters stressed that higher rates would be particularly damaging to those individuals living on 

fixed incomes, such as the elderly. A few commenters urged EPA to uphold its federal trust obligations 

and ensure that tribal communities continue to have access to affordable water, and advised EPA to 

make a decision consistent with the legal rights that the Gila River Indian Community and other 

stakeholders bargained for and that Congress granted under the Arizona Water Settlements Act of 2004. 

 A few commenters support the TWG Alternative because they believe it is a fair compromise 

created by a diverse group of stakeholders (e.g., the Navajo Nation, industry, and environmental 

groups), which provides a path for future operation at NGS by allowing for potential ownership changes 

and by providing an appropriate timeframe to install SCR technology, while still ensuring that the total 

emission reductions of NOx will be greater than those achieved under EPA’s proposed BART 

determination. On the other hand, some commenters, particularly Hopi, expressed frustration that they 

were not appropriately involved in the formation of the proposed alternative. However, many of the 

commenters at the hearings urged EPA to approve the TWG Alternative and move forward with the 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

final rule as soon as possible. Many of these commenters believe that EPA’s proposal is overreaching 

and represents a threat to states’ rights and hinders their ability to deal with environmental issues on a 

local level, and some urged the EPA to allow for Navajo EPA and the Navajo Nation Department of 

Justice to take on the role of regulator. 

Response:

EPA recognizes the contribution of NGS and the Kayenta Mine to the economy of the Navajo 

Nation, the Hopi Tribe, the city of Page, and the state of Arizona. In our notice of proposed rulemaking, 

EPA discussed the history of NGS and the relationship between NGS, the Central Arizona Project, and 

numerous tribes located in Arizona.7

 EPA also recognizes that NGS is a facility that is subject to the 

BART requirement of the Regional Haze Rule, and emissions from NGS affect visibility at 11 national 

parks and wilderness areas in the Southwest. As discussed in our Proposed Rule and in our 

Supplemental Proposal, for a number of reasons, including the importance of NGS to numerous Indian 

tribes located in Arizona and the federal government’s reliance on NGS to meet the requirements of 

water settlements with several tribes, EPA outlined a framework for considering “better than BART” 

alternatives that ensure emission reductions while providing additional flexibility in the compliance 

timeframe to the operator of NGS.8

 EPA disagrees with assertions that we are overreaching and threatening states’ rights and states’ 

ability to address environmental issues on a local level. As discussed in our Proposed Rule, NGS is 

located on the Navajo Nation and the state of Arizona does not have regulatory authority over facilities 

located on the Navajo Nation. EPA further noted in our proposals that the Navajo Nation EPA has not 

sought to develop a Tribal Implementation Plan to regulate NGS. Because NGS is a subject-to-BART 

source that would undergo a BART determination if located on state land, and based on the importance 

of visibility to the national parks and wilderness areas located in the Southwestern United States, EPA 

proposed to find that a BART determination was “necessary or appropriate” under the Tribal Authority 

Rule.9

 EPA understands the frustrations expressed by several commenters, including the Hopi Tribe, 

regarding limited stakeholder participation in the TWG. EPA was not involved in the formation of the 

TWG or in any of the discussions of the TWG.10 Our docket for this rulemaking includes letters that the 

Hope Tribe sent to the Department of the Interior following submittal of the TWG Alternative to EPA.11

EPA participated in a telephone conference with Hopi Tribal leaders to hear their concerns about the 

TWG as well as formal consultation following our Supplemental Proposal.12

 In our proposed rulemaking, EPA put forth a framework for “better than BART” alternatives and 

invited suggestions for other alternatives that reduce NOx emissions at NGS and its contribution to 

visibility impairment while providing long-term sustainable benefits to tribes. Although EPA recognizes 

that the members of the TWG did not invite all affected stakeholders to participate in their discussions, 

EPA does agree with comments that the TWG Agreement represents a compromise between diverse 

7

 See 78 FR at 8275 (February 5, 2013). 

8 Id. and 78 FR 62509 (October 22, 2013). 9

 See 78 FR at 8279 (February 5, 2013) and 40 CFR 49.11. 

10 At their request, EPA presented an overview of our proposed BART determination on March 21, 2013 to the stakeholders 

that formed the Technical Work Group. See EPA memo to file (document number 0033) in the docket for the proposed 

rulemaking at http://www.regulations.gov/#!documentDetail;D=EPA-R09-OAR-2013-0009-0033. 11 See, for example, document number 0151 in the docket for this rulemaking at EPA-R09-OAR-2013-0009. 

12See documents 0166 and 0303 in the docket for this rulemaking. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

stakeholders. Our Supplemental Proposal of the TWG Alternative, consistent with Appendix B of the 

TWG Agreement, provides certainty for future operation of NGS, flexibility in the compliance 

timeframe, and more emission reductions of NOx than would have been achieved under EPA’s proposed 

BART determination. Based on our analysis in our Supplemental Proposal and consideration of all 

comments received, EPA is taking action to finalize the TWG Alternative, including a cap in lifetime 

emissions of NOx from NGS over 2009-2044 (2009-2044 NOx Cap). EPA is also finalizing a BART 

Benchmark as the basis for the 2009-2044 NOx Cap in the TWG Alternative. The BART Benchmark is 

based on our proposed BART determination for NGS. 

Comment: Impact of air pollutants from NGS on public health and welfare and support for proposed 

BART determination

 Several commenters favor EPA’s proposed BART determination or more stringent requirements 

for NGS because they believe that emissions from the plant cause health problems in the area, such as 

respiratory illness and heart disease. These commenters noted that the Navajo and Hopi communities, 

particularly children and the elderly who live closest to the plant, are the most susceptible to the 

pollutants emitted. According to one commenter, approximately 213,000 children live near the NGS 

plant. One commenter asserted that 19 percent of the children living in Page, Arizona suffer from 

neurological complications, which is two times higher than average, and 98 percent of those children are 

Native Americans. Some commenters emphasized that Native Americans have the shortest life 

expectancies in this country, which they believe is a direct result of the pollution produced by nearby 

plants. One commenter cited a Clean Air Task Force study which states that NGS is responsible for 

approximately $127 million in health costs every year. Many of these commenters urged EPA to 

conduct health studies to determine the actual impact to health on these communities. 

 Many commenters spoke in support of stringent requirements and controls on NGS because they 

believe emissions from the plant contribute haze, which impairs air quality and visibility in the 11 

national parks (e.g., Grand Canyon and Petrified Forest) and wilderness areas surrounding the plant. 

Many discussed the importance of tourism to the economy of the area and claimed that the haze 

produced from NGS diminishes the beauty of the region and quality of life for residents. A few 

commenters highlighted the fact that the NGS plant is over 40 years old and urged EPA to require plant 

operators to update the plant with cleaner and more efficient technology. These commenters emphasized 

that NGS is one of the worst polluting coal-fired power plants in the United States. 

 Some commenters favor stringent requirements and controls on NGS because they believe that 

emissions from the plant are negatively impacting the land and the water in the area. Some living near 

the plant believe that it is responsible for killing native plants species that they depend on for their 

livestock, and has harmed traditional dry land farming. Others claimed that emissions from the plant can 

be linked to high levels of mercury found in fish species located in nearby lakes (e.g., Lake Powell and 

Wheat Fields Lake). Many commenters, particularly residents living on Black Mesa, expressed their 

concerns over the wellbeing of their sole source of drinking water, the Navajo Aquifer that, once 

contaminated, will force residents out of the area. A few commenters discussed how coal is transported 

to the NGS plant and noted that the pipeline used to transport a slurry of pulverized coal requires over 

3.3 million gallons per day of water often pulled from the Navajo Aquifer, which they believe is unfair 

considering most of the residents in the area do not have access to water and electricity. These 

commenters encouraged EPA to properly monitor local aquifers to ensure that the water quality remains 

high. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 A number of commenters favor stringent requirements and controls on NGS because they 

believe that emissions produced from the plant are contributing to climate change. Several of these 

commenters cited reports and studies, including the Intergovernmental Panel on Climate Change report 

and the Climate Vulnerability Monitor study, as proof that climate change is real and largely manmade. 

One commenter asserted that low levels of electricity production at Hoover Dam due to low water levels 

demonstrate that climate change is occurring. 

 A few commenters questioned the extent to which NGS emissions are impacting public health 

and the environment, instead blaming the haze on emissions from natural sources (e.g., volcanoes, 

wind/dust storms, and forest fires) and pollution from nearby cities (i.e., Phoenix, Los Angeles, and Las 

Vegas). One commenter noted that a single volcanic eruption has the potential to emit more emissions 

than 10,000 years of human activity. Another commenter stated that EPA’s website states that vehicles 

are the largest producers of NOx emissions in the country and implied that EPA is unfairly targeting 

power plants rather than addressing emissions from vehicles. The commenter added that in 2012 over 

4.5 million people visited the Grand Canyon, which meant 1.5 million vehicles traveled to and from the 

national park, assuming each car accommodated 3 people. The commenter further noted that EPA’s 

website states that NOx emissions have declined by more than 40 percent since 1980. 

 A limited number of commenters preferred EPA’s proposed BART determination over the TWG 

Alternative because they believe that the alternative is based on a false premise. They asserted that the 

shutdown of a single unit is not equivalent to cleaning up all three units, because the energy lost from 

the shutdown will ultimately need to be produced elsewhere, since the demand for power does not 

change. One commenter highlighted that the Navajo Nation is surrounded by seven coal-fired power 

plants that collectively produced 106,942 tons of NOx in 2011 and concluded that the shutdown of one 

unit at NGS will have no significant impact on visibility. 

 A few commenters support stringent requirements and controls on NGS because they believe 

that the TWG Alternative provides no certainty or commitment that any of the units will actually be 

retired early. Many argued that NGS has known about the possible change in ownership, NEPA 

requirements, and requirements to control emissions for years but chose not to address these issues until 

now. A few commenters added that FCPP was in a similar situation, but unlike NGS, EPA proposed a 

BART alternative with concrete compliance deadlines and a much shorter time frame. One commenter 

urged the EPA to use its discretion to improve the TWG Alternative by shortening the compliance time 

frame and provide a concrete pathway for emissions reduction that can be anticipated as they transition 

to clean, renewable energy in northern Arizona. Another commenter noted that neither EPA nor TWG 

has provided visibility modeling to compare the new proposal to EPA’s original proposal. Further, the 

U.S. Bureau of Reclamation has made a public commitment to reduce pollution emitted from NGS by 

eventually transitioning it from coal to cleaner energy, which should be considered. 

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 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

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 reduce visibility impairment, resulting from stationary sources, at National Parks and 

Wilderness Areas. EPA agrees that visibility-impairing pollutants are among the same pollutants that 

affect human and ecosystem health. Although health studies may provide useful information, these 

studies are beyond the scope of a BART analysis. 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. 

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). On April 15, 2014, the 

Court of Appeals for the District of Columbia Circuit upheld EPA’s promulgation of the Rule.13

EPA agrees with comments that mining and combustion of coal affect the environment. EPA 

notes that the Bureau of Reclamation has started its environmental impact review process required under 

the National Environmental Protection Act (NEPA) for activities resulting from the continued operation 

of NGS and the Kayenta Mine that is triggered by the renewal of various leases and other rights of 

way.14 The on-going NEPA process provides numerous opportunities and the appropriate forum to raise 

concerns related to the impacts of mining and use of water from the Navajo Aquifer. EPA further notes 

that coal is transported from the Kayenta Mine to NGS via a dedicated electric rail line. Regarding 

concerns raised over the use of water from the Navajo Aquifer to transport coal in a slurry, EPA notes 

that this practice was used to transport coal from the Black Mesa Mine to the Mohave Generating 

Station in Nevada and was discontinued when the Mohave Generating Station closed in 2005. 

EPA agrees that climate change is happening and humans are largely responsible for recent 

climate change.15 EPA notes that the RHR addresses pollutants that impair visibility and is not intended 

to address pollutants that contribute to climate change. EPA has developed various programs and 

activities to address emissions of greenhouse gases.16 For example, on June 2, 2014, EPA signed a 

proposal to cut carbon emissions from existing power plants.17

EPA also agrees that stationary sources, such as power plants, represent one of many sources that 

contribute to regional haze and visibility impairment at Class I areas. EPA notes that in Section 169A of 

the CAA, Congress directed EPA to develop regulations that, among other things, required major 

stationary sources, in existence between 1962 to 1977, to install BART. Several commenters asserted 

that mobile vehicle emissions contribute more to visibility impairment than stationary sources, and 

implied that EPA is unfairly targeting stationary source emissions while doing nothing to control mobile 

source emissions. EPA disagrees with the assertion that EPA is not controlling mobile sources of 

emissions. Consistent with title II of the CAA, the EPA Office of Transportation and Air Quality 

protects public health and air quality by, among other things, regulating air pollution from motor 

vehicles, engines, and the fuels to operate them.18 As a result of EPA’s actions and requirements, new 

cars and sport utility vehicles sold today have emission levels of hydrocarbons, NOx, and carbon 

13 See document titled “White Stallion Energy Center, LLC v. EPA” in the docket for this rulemaking. 

14 See www.ngskmc-eis.net 

15 http://www.epa.gov/climatechange/basics/ 

16 http://www.epa.gov/climatechange/EPAactivities.html 

17 See http://www2.epa.gov/carbon-pollution-standards. 18 http://www.epa.gov/otaq/ 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

monoxide that are 98 – 99 percent lower than new vehicles sold in the 1960s on a per mile basis.19

Similarly, standards established for heavy-duty highway and non-road sources require emission rate 

reductions on the order of 90 percent or more for particulate matter and NOx. In 2014, EPA finalized 

new vehicle emission standards and reduced the fuel sulfur content of gasoline to achieve additional 

reductions in tailpipe and evaporative emissions from passenger cars, light-duty vehicles, medium-duty 

passenger cars, and some heavy-duty vehicles starting in 2017.20

EPA agrees that forest fires and volcanic eruptions, when they occur, can impact visibility to a 

greater extent than anthropogenic sources of emissions. However, the possibility that sources outside of 

human control exist and can have large impacts on visibility on an episodic basis does not negate the 

fact that stationary sources contribute to visibility impairment, and that Congress directed EPA to 

develop rules to address these emissions for the purpose of remedying the existing impairment of 

visibility in Class I areas and restoring visibility to natural conditions. 

EPA disagrees with assertions that the TWG Alternative is based on a false premise because the 

closure or curtailment of one unit would just result in electricity produced elsewhere. EPA notes that the 

portion of the TWG Agreement that calls for closure of one unit or curtailment at NGS was possible 

because of decisions by the Los Angeles Department of Water and Power and NV Energy to exit NGS 

and replace that electricity with power generated by natural gas and renewable sources.21 Therefore, any 

additional electricity needed to replace lost generation from NGS associated with LADWP and NV 

Energy’s divestiture would come from energy sources that emit less air pollution than a conventional 

coal-fired power plant operating with SCR on all units. EPA agrees that there are several coal-fired 

power plants near the Navajo Nation, and EPA also agrees with the commenter that the closure of one 

unit alone will not be better than installation of SCR on Unit 1-3 at NGS. However, EPA notes that the 

TWG Alternative includes not only closure of one unit, but will achieve emission reductions through the 

installation of SCR on two units in 2030. Taken together, the TWG Alternative will achieve greater 

emission reductions over 2009-2044 than would have been achieved under our BART determination. 

Although some commenters requested that EPA shorten the timeframe for compliance under the TWG 

Alternative, other commenters requested that EPA extend the TWG Alternative compliance timeframe. 

As presented in our Supplemental Proposal and as discussed in Section 9.0 of this Response to 

Comments document, EPA’s analysis of the TWG Alternative shows that the timeframes for closure or 

curtailment, and installation of SCR are appropriate to allow the operator of NGS to maintain total NOx

emissions from the TWG Alternative below emissions that would have been achieved under BART. 

In addition, EPA disagrees with commenters that there is no certainty in the TWG Alternative. 

Our Supplemental Proposal defines various requirements in the TWG Alternative, including 

requirements to meet a cap in NOx emissions over 2009-2044 (2009-2044 NOx Cap) through one of four 

options: (1) permanently cease operation of one coal-fired unit by December 31, 2019 and comply with 

an emission limit of 0.07 lb/MMBtu on each of the two remaining coal-fired units by December 31, 

2030 (see proposed regulatory text in Supplemental Proposal for Alternative A1: 40 CFR 

49.5513(j)(3)(i)(A)); or (2) permanently cease operation of one coal-fired unit with the option to 

increase net generating capacity by no more than 189 MW by December 31, 2019 and comply with an 

19 See, e.g., 76 FR 74854, at 74900 (December 1, 2011) 20 See Fact Sheet for Tier 3 Standards available at http://www.epa.gov/otaq/documents/tier3/420f14010.pdf 

21 See document titled “LADWP-Navajo+IPP Coal Elimination Presentation 031913” in the docket for this rule. See also 

section 7 of Nevada SB 123 available at http://www.leg.state.nv.us/Session/77th2013/Bills/SB/SB123_EN.pdf, requiring NV 

Energy to retire or eliminate not less than 250 MW of generating capacity on or before December 31, 2019. NV Energy owns 

approximately 254 MW of generating capacity at NGS. See also: http://www.lasvegassun.com/news/2013/apr/02/nv-energydecommission-coal-plants-shift-gas-and-r/ 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

emission limit of 0.07 lb/MMBtu on each of the two remaining coal-fired units by December 31, 2030 

(see proposed regulatory text in Supplemental Proposal for Alternative A2: 40 CFR 49.5513(j)(3)(i)(B)); 

or (3) reduce net generating capacity of NGS by no less than 561 MW by December 31, 2019 and 

comply with an emission limit of 0.07 lb/MMBtu on two coal-fired units by December 31, 2030 (see 

proposed regulatory text in Supplemental Proposal for Alternative A3: 40 CFR 49.5513(j)(3)(i)(C)); or 

(4) in addition to the 2009-2044 NOx Cap, comply with a cap in NOx emissions that applies over 2009-

2029 that is equivalent to emissions over that period under Alternative A1 (2009-2029 NOx Cap) (see 

proposed regulatory text in Supplemental Proposal for Alternative B: 40 CFR 49.5513(j)(3)(i)(D)). The 

2009-2044 NOx Cap and the 2009-2029 NOx Cap are both enforceable, and thus, both ensure that NGS 

is operated in a manner such that total NOx emissions are lower than what would have been achieved 

under BART. 

EPA agrees with commenters that it seems likely that the operator and owners of NGS were 

aware of environmental requirements under development and that leases and other rights-of-way 

agreements needed to be renewed prior to expiration in 2019, raising the possibility of changes in 

ownership of NGS. EPA recognizes that the FIP for the Four Corners Power Plant included an 

alternative to BART that included closure of three units by 2014 and installation of SCR on the 

remaining two units by July 31, 2018. EPA notes that both NGS and FCPP are located on the Navajo 

Nation, and pursuant to the Tribal Authority Rule, EPA proposed to determine that a BART 

determination for NOx was necessary or appropriate. Both the FCPP and NGS contribute to the Navajo 

Nation in terms of revenue and employment, however, NGS is unique because of its critical importance 

to the Navajo Nation as well as other tribes, including the Hopi Tribe, and numerous tribes receiving 

CAP water through Congressional water settlement acts. EPA appreciates the sentiment expressed by 

several commenters requesting a transition to renewable energy sources in northern Arizona and 

acknowledges the commitments made by the Bureau of Reclamation regarding transitions to cleaner 

energy sources; however, EPA does not have authority through BART to redefine a source and require it 

to change its method of electricity generation. The comment regarding visibility modeling of the TWG 

Alternative is discussed in Section 9.0. 

Comment: Support for renewable energy to replace NGS

 A number of commenters consider the proposed BART requirements and controls on NGS as a 

first step in transitioning away from coal-fired power plants to renewable energy sources. Commenters 

enumerated many problems with coal as an energy source, including air pollution emissions (SO2, NOx, 

PM, mercury and other toxic compounds, acid gases, and GHGs) that harm ecosystems. 

 Several commenters favor stringent requirements and controls on NGS because they believe that 

the production of renewable energy could economically benefit the Navajo Nation. Some commenters 

asserted that 900 megawatts of renewable energy can create the same number of jobs and opportunities 

that one coal unit does. One commenter claimed that the production of coal averages about 6 jobs per 

million dollars invested, while solar and wind production generates about 13 jobs per million dollars 

invested. Another commenter stressed that the Black Mesa region’s 13,000 acres of already reclaimed 

mine land and 25,000 acres of land scheduled for reclamation could generate 6,000 megawatts of solar 

power; thus creating 2,800 operational jobs and 30,000 temporary jobs. One commenter mentioned that 

stock values in two of the largest U.S. coal producing companies, Peabody and Arch, has dropped by 75 

percent, which coincides with a drop in solar panel costs, and is proof that more and more utilities are 

switching to cost-efficient alternatives. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 A few commenters support stringent requirements and controls on NGS because they believe 

that Arizona is ideally suited for solar and wind energy projects. One commenter noted that Tucson 

Electric Power (TEP) currently has a 50-megawatt solar power plant in New Mexico Macho Springs that 

provides clean, efficient solar power to the area, which the commenter believes could be replicated in 

Arizona. By the same token, one commenter discussed how the military and universities are now taking 

advantage of “green” alternatives; specifically, ASU has installed solar panels across its four campuses 

and the ASU Research Park, allowing it to have 21-megawatts of solar capacity. A few commenters 

discussed the benefits they receive from solar panels on their homes and land, including lower electricity 

rates. A number of commenters cited a 2013 poll conducted by Colorado College that stated that 74 

percent of Arizona voters picked solar as their first or second choice of energy source, with 43 percent 

favoring wind, 20 percent natural gas, and only 6 percent coal. 

 On the other hand, a few commenters believe that the replacement of coal with alternative energy 

sources, particularly natural gas, is not a viable solution because of the unknowns associated with the 

use of these alternatives (e.g., cost and environment impacts). They noted that natural gas prices are 

higher and far more volatile than coal, which would only amplify as competition for gas rises in the 

future as companies switch to natural gas as restrictions on coal production continue to increase. One 

commenter noted that Arizona’s coal prices to produce power have reached $1.70 per million Btu 

compared to $5.40 for natural gas, since 2000, and currently over 40 percent of Arizona homes use 

natural gas for heating which causes demand for natural gas to rise seven-fold during the winter. The 

commenter emphasized that Arizona imports virtually all of its natural gas from New Mexico where 

production has plummeted by 75 percent since 2006, and the demand for gas by states like California 

and Nevada continues to grow. The commenter mentioned PIRA Energy Group, a leading energy 

analytic firm, which projected that the demand for gas could exceed 14 trillion cubic feet by 2025, while 

Dow Chemical forecasts 90 industrial projects alone using 2.6 trillion cubic feet more by 2020. The 

commenter warned that the demand for natural gas will also continue to expand globally as the demand 

for gas continues to surge in the United States. The commenter explained that the DOE has approved 20 

liquefied natural gas (LNG) export applications that will send 20 Bcf/day of gas to Europe and Asia, 

which is a third of all U.S. output, in addition to gas piped to Mexico which will triple to 6 Bcf/day by 

2020. Another commenter expressed concerns over the chemicals used to operate SCR, in particular 

ammonia, which has the potential to negatively impact the area if a spill were to occur. 

Response:

 EPA recognizes that numerous commenters support renewable energy development on the 

Navajo Nation or elsewhere in Arizona to replace NGS, however, we note that EPA does not have 

authority under BART to redefine a source, i.e., for the purposes of BART, EPA cannot require a coalfired power plant to convert to natural gas or renewable energy generation. We agree with commenters 

that coal-fired power plants emit numerous air pollutants that affect visibility, human health, and the 

environment. Through the RHR and BART, EPA and states are requiring stationary sources of a certain 

age that cause or contribute to visibility-impairment in Class I areas to install BART to reduce emissions 

of visibility-impairing pollution. 

 EPA also recognizes that some commenters do not support replacement of coal with natural gas 

due to the price volatility and increasing demand for natural gas. EPA notes that our analysis (as 

discussed in our Proposed Rule and in Section 4.1 of this Response to Comments document) indicates 

that EPA’s proposed BART determination would not force NGS to close, nor does our Proposed Rule or 

Supplemental Proposal require NGS to convert to natural gas. Decisions by two of the existing owners 

of NGS to divest from coal-fired power are related to state law in California and Nevada and are not a 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

requirement of EPA or the RHR. EPA understands the commenter’s concern over the use of ammonia to 

operate SCR. In the TSD for our Proposed Rule, EPA discussed the risks associated with transportation 

and storage of ammonia and noted that SCR is a widely used control technology and that a review of the 

National Toxic Substance Incidents Program of the U.S. Agency for Toxic Substances and Disease 

Registry shows that over 2005-2010, there were no accidents or spills involving transport or use of 

anhydrous ammonia at power plants. Of the 45 incidents reported over 2005 to 2010, all incidents of 

release were associated with agricultural use of anhydrous ammonia.22

Comment: Other Air Pollution Control Technologies

 One commenter discussed the benefits achieved by an alternative emissions control technology 

known as the CEFCO process, a practice of combining Ewan technology with the patented Cooper 

Process and encouraged EPA to consider this as a possible alternative practice. The commenter argued 

that this practice exceeds the current BACT compliance requirements by removing over 99 percent of 

mercury, PM, SOx, NOx, and other trace metals, along with removing over 90 percent of CO2 emissions. 

According to the commenter, this process is able to convert CO2 emissions into usable fuels, tertiaryenhanced oil recovery, or enhanced vegetable crop growth. In regards to NOx, the commenter claimed 

that this process could reduce emissions below 0.01 pounds per million Btu by converting the nitrogen 

oxides into potassium nitrate fertilizer, which could be sold for profit. 

Response:

 EPA notes that a BART determination is an emission limit, not a requirement to install a specific 

technology. The facility must comply with the emission limit within the required timeframe, and the 

operator of NGS may consider this, or any other technology, in developing its plan to cost-effectively 

comply with its NOx emission limit. 

Comment: Environmental and Social Justice

 Several commenters believe that the presence of NGS and several other power plants in and 

around the Navajo Nation represents an environmental and economic justice issue. Many noted that 

Navajo and Hopi communities were promised running water and electricity at the time the plant was 

constructed 40 years ago; however, these communities, which live closest to the plant and are the most 

susceptible to the pollutants emitted by the plant, still do not have access to running water and 

electricity. One commenter stated that he had to pay $6,000 in order to receive electricity in his home, 

while other families in the area enjoy free power. Some commenters argued that the Navajo Nation 

carries border towns on their backs by providing them energy and supporting their economy, and 

stressed that these residents living in areas categorized as desert should pay the true cost associated with 

receiving power and water. One commenter explained that a Navajo water hauler pays 10 to 20 times 

more for water than recipients in southern Arizona. The commenter added that Kaibeto, a Navajo 

community near Page, pays $13,034.04 per acre foot of water; meanwhile, Glendale residents and a 

farmer in Tempe can expect to pay $551 and $41 per acre feet, respectively. One commenter countered 

that a power line project is currently underway and will provide power to nearly 62 homes in the area, so 

the communities lacking electricity and running water will receive these commodities soon. 

22 See pages 60 to 61 of the TSD for the Proposed Rulemaking, document number 0014 in the docket for this rulemaking at 

EPA-R09-OAR-2013-0009. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 Some of these commenters expressed their frustrations that owners of NGS and the Kayenta 

Mine have reaped large profits (many investors recovering their capital costs by 2027), while reservation 

residents still live in poverty. One commenter noted that the CEO of APS made $11.5 million in 2012; 

likewise the CEO of Peabody made $10.2 million and received a bonus of $2.6 million. 

 Several commenters expressed frustration with the leaders of the Navajo Nation and EPA, who 

they believe have not protected the interests of the local population. A few expressed their concerns over 

how the alternatives were written; noting that many tribal residents do not understand the technical 

language used in the documents and therefore cannot adequately comment on the validity of the 

alternatives proposed. Some commenters argued that pollution emitted is preventable using existing 

technology and EPA should enforce the same regulations on NGS as it does to other coal-burning power 

plants (e.g., FCPP) throughout the United States. A few commenters argued that extending the time 

frame NGS has to comply demonstrates that the federal government believes it can be exempt from its 

own federal law. Several argued that tribal communities do not have the funds to develop proposals 

and/or conduct environmental assessments. The commenters stated that unlike industry, they cannot 

afford to hire university experts or engineers to speak on their behalf and urged EPA uphold federal trust 

responsibilities and create an equal playing field. 

Response: 

 EPA describes Environmental Justice as “the fair treatment and meaningful involvement of all 

people regardless of race, color, national origin, or income with respect to the development, 

implementation, and enforcement of environmental laws, regulations, and policies. EPA has this goal for 

all communities and persons across this Nation. It will be achieved when everyone enjoys the same 

degree of protection from environmental and health hazards and equal access to the decision-making 

process to have a healthy environment in which to live, learn, and work.”23

 EPA takes fair treatment and meaningful involvement seriously and provided numerous 

opportunities for tribal governments, environmental and tribal non-governmental organizations, 

residents in Indian country and other interested stakeholders to provide input in the development of our 

proposed, supplemental and final rulemaking for NGS. EPA began our public involvement process for a 

BART determination for NGS in 2009, when we published an Advanced Notice of Proposed 

Rulemaking (ANPR). In the ANPR, we presented our analyses of the cost and anticipated visibility 

benefits of controls for FCPP and NGS and solicited public comment.24 Although we initially provided a 

30-day public comment period, at the request of tribal governments and other interested stakeholders, 

we extended the comment period for tribes to October 28, 2009 and, to allow additional time for 

government-to-government consultation on NGS, exercised our discretion to accept comments from 

tribes until March 1, 2010. As discussed in the TSD for our proposed rulemaking, EPA received over 

6,000 comments on the ANPR.25 During 2009 through 2012, EPA met with various stakeholders, 

including tribal governments and Navajo environmental groups, at their request, to discuss NGS and 

hear their comments and concerns related to a BART determination for this facility.26 On February 5, 

2013, our Proposed Rule for NGS was published in the Federal Register. In the TSD for the Proposed 

Rule, we included discussion of the substantive comments we received that resulted in changes to the 

23 http://www.epa.gov/environmentaljustice/ 

24 74 FR 44313 (August 28, 2009). 

25 See page 25 of the TSD to the February 5, 2013 Proposed Rule. 

26 See, for example document number 0232 in the ANPR docket at EPA-R09-OAR-2009-0598, and document numbers 0008 

and 0009 in the docket for this rule at EPA-R09-OAR-2013-0009. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

analysis we had presented in the ANPR. We initially provided a 90-day comment period for the 

proposed rule, and at the request of various stakeholders, we provided several extensions of the public 

comment period, which closed on January 6, 2014. During the comment period, EPA continued to meet 

with stakeholders, at their request, to discuss our proposed BART determination for NGS and our 

framework for better-than-BART alternatives.27 Our docket for this final rule contains a record of each 

meeting we attended during this period. 

On July 26, 2013, the Technical Work Group submitted the TWG Agreement to EPA for 

consideration. EPA posted the TWG Agreement to our docket on the same day to provide the public an 

opportunity to review it.28 On September 25, 2013, EPA signed a Supplemental Proposal that, based on 

our review and analysis, proposed to approve requirements consistent with Appendix B of the TWG 

Agreement as “better than BART” (i.e., the TWG Alternative) and submitted it to the Federal Register 

for publication. EPA posted the pre-publication version of the Supplemental Proposal, along with 

supporting documents, to the docket on September 25, 2013 to allow for early review by interested 

parties.29 Due to the lapse in appropriations and resulting shutdown of the federal government from 

October 1 – 16, 2013, the Supplemental Proposal was published in the Federal Register nearly one 

month after signature, on October 22, 2013. The comment period for the Supplemental Proposal closed 

on January 6, 2014, the same day as the BART proposal. The Supplemental Proposal also included 

notice of five open house and public hearing events EPA scheduled throughout Arizona in November 

2013. The open houses were held concurrently with the public hearing (at one venue) or prior to the 

public hearing (at four venues), and allowed members of the public an opportunity to talk with 

representatives from EPA and ask questions. EPA held events at the LeChee Chapter House, located on 

the Navajo Nation, as well as in Page, Arizona, and provided oral interpretation services between 

English and Diné (the Navajo language). EPA also held an event at the Hopi Day School, located in 

Kykotsmovi, the seat of the Hopi tribal government. EPA engaged with the government of the Hopi 

Tribe to search for an oral interpreter between English and the Hopi language, but the Hopi Tribe was 

unable to locate anyone to provide those services. Finally, we also held events in Phoenix and in Tucson, 

Arizona, to allow stakeholders in central and southern Arizona, representing CAP water interests and 

several tribes receiving CAP water, the opportunity to provide comment and talk with representatives 

from EPA. Although EPA understands that the TSD, and to some extent, the Federal Register notices, 

include technical information that may be difficult for many individuals to understand, EPA did include 

Fact Sheets and handouts, written in plain language, with the Proposed Rule and Supplemental Proposal, 

and at the open house and public hearing events.30 EPA representatives were also present at the events to 

discuss and explain our Proposals. EPA recognizes that many tribal communities do not have the funds 

to develop alternative proposals or hire experts on their behalf; however, we note that EPA considers 

with equal weight all comments, regardless of the form of the comment or whether the commenter is a 

purported expert or not. 

As stated in our Proposed Rule and Supplemental Proposal, EPA has determined that these 

proposed rules, if finalized, will not have disproportionately high and adverse human health or 

environmental effects on minority or low-income populations because it increases the level of 

environmental protection for all affected populations (i.e., requires emission reductions from NGS).31

EPA recognizes that some commenters may view the timeframe for compliance under EPA’s framework 

27 See, for example, document number 0150, 0152, 0166, 0173, 0302, and 0303 in the docket for this rule at EPA-R09-OAR2013-0009. 

28 See document number 0122 in docket for this rulemaking at EPA-R09-OAR-2013-0009. 

29 See document numbers 0182, 0183, and 0184 in the docket for this rulemaking at EPA-R09-OAR-2013-0009. 

30 See document 0219 in the docket for this rulemaking at EPA-R09-OAR-2013-0009. 

31 See discussions under Executive Order 12898 in 78 FR at 8793 (February 5, 2013) and 78 FR at 62520 (October 22, 2013). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

for BART Alternatives as an environmental justice issue. We note that the LNB/SOFA credit was based 

on real, actual emission reductions achieved beginning in 2009 at NGS that were voluntary and not 

required by any rule or regulation. This LNB/SOFA credit is an important part of the framework for 

evaluating the compliance timeframe for BART Alternatives. However, we note that the TWG 

Alternative, which calls for closure of one unit by the end of 2019 (or equivalent curtailment) will result 

not only in reductions of NOx, but also reductions of several other pollutants, including SO2, PM, CO2, 

and hazardous air pollutants. Thus, although the TWG Alternative provides an alternative timeframe for 

compliance at NGS to 2030, ultimately the TWG Alternative will result in greater NOx reductions than 

would have been achieved under BART, will result in reductions of additional pollutants that affect 

visibility or human health, and will provide an enforceable mechanism to ensure that NGS ceases 

conventional coal-fired electricity generation at NGS by the end of 2044. Finally, while we recognize 

the individuals and tribal non-governmental organizations may have different perspectives from the 

elected tribal officials or governments, EPA’s determination that compliance flexibility is necessary or 

appropriate for NGS was based, in part, on significant comments we received from tribal governments 

about the direct importance of NGS on revenues to the Navajo Nation and Hopi Tribe, and the indirect 

relationship between NGS, CAP, and tribes that receive CAP water through water settlement 

agreements. 

EPA recognizes that numerous commenters expressed frustration regarding social inequities 

related to costs and benefits of coal mining and combustion and water availability and cost. We note that 

NGS and Kayenta Mine are undergoing a process to renew various leases and rights-of-way, and that 

these approvals are federal actions that are subject to NEPA. The joint EIS process for NGS and 

Kayenta Mine is the appropriate venue to raise more general concerns related to costs, benefits, and the 

environmental and social justice of coal mining and coal combustion at the Kayenta Mine and NGS. 

2.2 Mass Comment Campaigns 

 We received many comments from private individuals through email campaigns organized by 

several different environmental interest groups. Most of these commenters submitted the templates 

provided by the sponsoring organizations without change, but others customized the templates to 

varying degree. 

Comments: 

 Comment 0120 includes over 36,000 nearly identical comments that were submitted via a Sierra 

Club campaign. Comment 0436 includes 416 additional emails submitted via the Sierra Club campaign 

with individual variations. Most of these comments, including one private individual (0114) whose 

comment was posted as an individual comment to the docket incorporated some or all of the same points 

as Comment 0120, with some discussing the harmful effects of coal production on the environment, in 

particular the deterioration of air quality and visibility at national parks and wilderness areas, including 

Grand Canyon, due to haze. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Comments 0121 and 0375 represent a mass email campaign sponsored by Care2, which was 

identical to comment number 0120 and submitted by over 7,000 individuals. Most comments 

incorporated some or all of the same points as Comment 0120, although some comments included 

personal observations. Similarly, Comment 0198 represents an example of 11 form letters submitted in a 

campaign sponsored by an unknown organization; these letters were identical to Comment 0120, 

although some included personalized hand-written additions. 

 Comment 0120 reads as follows: 

Dear Region 9, 

I am concerned about the coal plant pollution that has harmed views at Grand 

Canyon National Park for decades. Navajo Generating Station (NGS) is one of the 

dirtiest coal plants in the country and has fouled the world-renowned Grand 

Canyon for too long. Located just 12 miles from the park, it also pollutes at least 

ten other special places, including other national parks and wilderness areas. 

Worse, the federal government owns the largest share of NGS. We can't delay 

ending the coal pollution that is harming the Grand Canyon, and the federal 

government should lead in protecting the park. 

I applaud your proposal to significantly reduce nitrogen oxide pollution from 

NGS with strong pollution controls (Selective Catalytic Reduction or SCR), but I 

am deeply worried because you are considering delaying cleanup by ten years or 

more. Other coal plants harming special places have had to clean up within five 

years and there's no reason it shouldn't happen at NGS, too. EPA proposed 

pollution controls for NGS that are the modern industry standard for NOx control. 

In fact, SCR is in use on more than 200 coal-fired units around the country. 

Please require Navajo Generating Station to reduce haze pollution through the 

installation of SCR within five years to protect Grand Canyon and other parks 

affected by NGS's coal pollution. We owe it to future generations to pass on a 

restored natural heritage. Thank you for considering my comments. 

 Comment 0294 represents an example of 82 postcards that the EPA received from the Black 

Mesa Water Coalition. The postcard reads as follows: 

The proposed BART ruling will not only reduce regional haze in the Grand 

Canyon, but also improve air quality for many people living around NGS. Enforce 

BART to protect the public’s health. 

 Comment 0374 represents a mass email campaign sponsored by Environment Arizona, which 

was submitted by 728 commenters. Most comments incorporated some or all of the same points; 

however, 17 comments were considered unique and were placed in Comment 0435. Most of these 

commenters discussed the harmful effects of coal production on the environment, in particular the 

deterioration of visibility at the Grand Canyon due to haze. 

 The comment reads as follows: 

Dear Ms. Lee, 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

I urge you to clean up the air at the Grand Canyon. Arizona is the Grand Canyon 

State. People come from across the globe to visit this amazing place, and it's right 

here in our backyard. It has been almost 40 years now that the Navajo Generating 

Station coal plant has been polluting the vistas that are the pride of our state. We 

can't let this continue to happen. 

Please make sure there is an enforceable and complete plan for this aging coal 

plant to clean up its air pollution as required under the Clean Air Act without 

delay. 

 Comment 0376 represents a mass email campaign sponsored by WildEarth Guardians, which 

was submitted by 1,226 commenters, including 6 comments that were considered unique. Comments 

0058 and 0438 include 121 additional emails submitted through WildEarth Guardians, and two 

individuals (0059, 0068) whose comment were posted as individual comments to the docket also 

submitted essentially the same comments. Most comments incorporated some or all of the same points. 

Other comments discussed the harmful effects of coal production on the human health and the 

environment, and argued the potential benefits to alternative energy sources. 

 The comment reads as follows: 

Dear Regional Administrator Blumenfeld, 

I support cleaning up the Navajo Generating Station's air pollution, but I believe 

there's a more reasonable path forward than requiring the owners of this power 

plant to spend millions just to make this coal-fired power plant less polluting. 

The Navajo Generating Station takes a tremendous toll on our clean air, our 

health, and on our well-being in the American West. The plant's air pollution must 

be curbed, but there are better alternatives. 

I call on the U.S. Environmental Protection Agency to explore clean energy 

alternatives that both curb coal use at the Navajo Generating Station and clear the 

air that we depend on. To this end, I call on the EPA to require the Navajo 

Generating Station to retire altogether by 2020. 

By setting a retirement date for the Navajo Generating Station, we can be assured 

that the plant's air pollution will be effectively curbed and that cleaner energy 

sources, including rooftop solar and efficiencies, will be able to replace this dirty 

energy. 

I support the EPA's efforts to safeguard our iconic and irreplaceable landscapes, 

like the Grand Canyon, and to keep our children and our communities safe from 

air pollution. Retiring the Navajo Generating Station by 2020 ensures both that 

our clean air will be protected and that clean energy will power our future. 

 Comment 0377 represents a mass email campaign with the subject line reading “Taxpayer from 

AZ,” which was submitted by 26 commenters, including 2 comments considered unique, and an 

additional 11 private individuals (0279, 0286, 0291,0309, 0311, 0319, 0322, 0378, 0379, 0422, 0423) 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

whose comment were posted separately to the docket. The majority of the comments submitted 

incorporated some or all of the same points. 

 An example comment reads as follows: 

Dear Dr. Lee, 

We, Thomas and Anita Christy have lived in Arizona since 1977. We are 

concerned about the EPA’s proposed rule regarding regional air visibility in areas 

surrounding the Navajo Generating Station in northern Arizona. 

In February 2013, the EPA issued a proposed rule aimed at limiting nitrogen 

oxide emissions at the plant. At an estimated cost of up to $1.1 billion, EPA's 

proposal to limit these emissions five years from now, with a possible extension 

to 2023, would place a tremendous financial burden on me and my family as well 

as on energy users in Arizona and water users that take Central Arizona Project 

(CAP) water. The owners of the plant have made clear that the short timeframes 

in the proposed rule could result in plant closure. Regardless of whether the plant 

closes or remains open, EPA's proposed rule could cause serious economic 

hardship in northern Arizona and will force unaffordable water and energy costs 

upon Arizona businesses and ratepayers. 

Because the EPA's proposed rule is unworkable on several levels, CAP and other 

key stakeholders formed a Technical Work Group (TWG) and developed a 

reasonable alternative that would protect regional air quality and also the future of 

NGS. The future economic wellbeing of Arizona, including the Navajo and Hopi 

people who depend on NGS for jobs and other income, is at stake. We urge the 

EPA to adopt the TWG BART Proposal as the final rule for NGS. 

 Comment 0380 represents a mass email campaign with the subject line reading “Do not delay 

Navajo Station Generation cleanup,” which was submitted by 114 commenters, including 6 comments 

that were considered unique. The majority of the comments, including 6 additional emails placed in 

Comment 0434, incorporated some or all of the same points; however, some comments stated that NGS 

should not be given an extension and discussed the harmful effects of coal production on the 

environment and the health of the Navajo people, along with the potential benefits of alternative energy 

sources. 

The comment reads as follows: 

Dear Environmental Protection Agency, 

You are requiring coal-fired power plants across the country to greatly reduce 

their harmful nitrogen oxide air pollution within five years. Navajo people and all 

residents of the Four Corners region need those safeguards as well, in the same 

time frame. 

The communities and people of northern Arizona and the Four Corners area 

cannot continue to endure the harmful effects of coal pollution. Our health should 

be just as important as those from other parts of the country. Please do not allow 

delays or extensions for the Navajo Generating Station. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

This plant should not get special polluting extensions because it is on tribal lands. 

I am Navajo and I do not want continued pollution. I do not want a coal 

dependent economy. Today we have ways to generate power cleanly and 

inexpensively from the sun and wind, and there is demand for it across the 

Southwest. The solar and wind industry can generate the same amount of jobs as 

coal. 

The longer you allow the Navajo Generating Station to keep polluting, the more 

you hold communities back from where we want to go — toward clean air and 

clean energy. Please stick to your original proposal for Navajo Generating 

Station: nitrogen oxide pollution must be cut within five years. 

 Comment 0385 represents a mass comment letter campaign organized by the National Parks 

Conservation Association, which was submitted essentially verbatim by 35,293 commenters. Comment 

0439 includes roughly 296 additional letters organized by the same organization. Two hundred and 

eighty-seven of the original 35,293 comments and one additional individual (0067) whose comment was 

posted as an individual comment to the docket were considered unique. The majority of the comments 

incorporated some or all of the same points; however some comments included personal experiences 

with worsening air pollution in the region and discussed the negative impacts associated with coal-fired 

power production. 

 The comment reads as follows: 

Dear Jared Blumenfeld, 

I'm writing as someone who believes that our national parks deserve clean air and 

knows that the law requires it. I'm concerned about the Navajo Generating Station 

(NGS)--it's one of the dirtiest coal-fired power plants in the nation, and it's just 12 

miles from Grand Canyon National Park! This antiquated polluter degrades air 

quality in the Grand Canyon and at least ten other beautiful national parks and 

wilderness areas in the region. 

I applaud your proposal to significantly reduce nitrogen oxide pollution from 

NGS with Selective Catalytic Reduction (SCR) but you are considering delaying 

cleanup by a decade or more. This plant's clean up should not be postponed; it 

should reduce its pollution within five years, just like other dirty old coal plants. 

The U.S. government is the plant's biggest owner and accordingly its cleanup plan 

should set an example; rather than delay reducing pollution that harms both lands 

and people. I urge you to require pollution controls within five years to protect 

Grand Canyon and other parks affected by NGS's pollution in a timely manner. 

The Grand Canyon alone creates nearly 7,000 direct and indirect jobs and brings 

over $428 million to the economy every year. Grand Canyon and the other 

national parks and wilderness areas in the region are major economic generators 

for local economies. These are places that people worldwide come to experience--

places we, our children, and grandchildren deserve to experience unimpaired. 

Please require Navajo Generating Station to reduce emissions through the use of 

SCR within five years. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 Comment 0386 represents a mass email campaign sponsored by Sierra Club that was submitted 

by 38,368 commenters. This mass email campaign included two different letters. The first letter was 

submitted by 37,485 commenters. Most of these comments incorporated some or all of the same points. 

The second letter was submitted by 594 commenters and was essentially verbatim to Comment 0120. 

Out of the 38,368 comments, 284 were considered unique and included personal observations. 

The first comment reads as follows: 

Dear Ms. Lee, 

I am concerned about the coal plant pollution that has harmed the health of people 

who live near Navajo Generating Station (NGS) and that has obscured the skies 

over Grand Canyon National Park, other parks, and wilderness areas for decades. 

NGS is one of the dirtiest coal plants in the country and has fouled worldrenowned Grand Canyon for too long. Located just 12 miles from the park, it also 

pollutes at least ten other special places, including other national parks and 

wilderness areas. Ironically, the federal government owns the largest share of 

NGS. 

While this docket is focused on regional haze, it is clear that cleaning up NGS 

will provide significant public health benefits, especially to those nearest the 

plant, whose voices have been ignored far too often. The Clean Air Task Force 

estimates that pollution from NGS contributed to 16 premature deaths, 25 heart 

attacks, 300 asthma attacks, and 15 asthma emergency room visits last year. This 

results in total annual health costs of more than $127 million. When the costs are 

evaluated, the health costs and cost in lives should be considered. 

I support EPA's proposal to significantly reduce nitrogen oxide (NOx) pollution 

from NGS with strong pollution controls (Selective Catalytic Reduction or SCR), 

but I am deeply worried because EPA is considering delaying cleanup by ten 

years or more. Other coal plants harming special places and public health have 

had to clean up within five years; NGS should as well. The EPA-proposed 

pollution controls for NGS are the modern industry standard for NOx control, and, 

in fact, SCR is in use on more than 200 coal-fired units around the country, 

including on other coal plants in Arizona. 

I cannot support the proposed Technical Work Group proposal that is being 

promoted by Salt River Project because it lacks a clear enforceable path to end 

coal's dirty legacy in the region and bring about development of renewable energy 

to tribal lands. The plant operators must comply with EPA's proposed rule or opt 

for a combination of retirement and retrofits that would meet the same reductions. 

The current TWG proposal does not do that. It does not meet the emissions 

reduction requirements in a timely manner and also includes huge question marks 

and several off-ramps, meaning no clear path. There is no guarantee that a unit 

will close. There is no commitment to stop burning coal. 

Arizonans and others in the region have waited far too long for clean air and clear 

skies over Grand Canyon. Our health has suffered for long enough. It is past time 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

for the plant operators to step up and agree to a clear and enforceable plan that 

includes the reductions in pollutants that meet the Clean Air Act requirements. 

The Clean Air Act's visibility protection provisions, enacted with strong bipartisan support, contain clear requirements that must be met to restore and 

protect air quality in our national parks and wilderness areas. Most important 

among these is the requirement to install modern pollution controls on outdated 

major pollution sources, such as coal-fired power plants, that demonstrably 

degrade air quality in Class I areas. It is uncontested that NGS lacks such modern 

pollution control equipment and that its emissions degrade air quality at many 

Class I areas in the region. 

We can't delay ending the coal pollution that is harming Grand Canyon, and the 

federal government should lead in protecting the park. Please require Navajo 

Generating Station to reduce haze pollution through the installation of SCR within 

five years to protect Grand Canyon and other parks affected by NGS's coal 

pollution. We owe it to future generations to pass on a restored natural heritage. 

 Comment 0424 represents an example of 51 postcards that the EPA received from the Navajo 

Nation. The postcard reads as follows: 

EPA’s proposal to cut nitrogen oxide pollution at NGS by 84% within five years 

will reduce Grand Canyon haze and improve air quality for nearby residents. 

Response:

EPA agrees with commenters that NGS affects visibility at numerous national parks and 

wilderness areas throughout the Southwest and we agree that an emission limit representing the 

installation and operation of SCR is BART for NGS. As discussed in more detail in Section 3.0, EPA 

disagrees with commenters that our proposed BART determination will cost over $1.1 billion. EPA also 

disagrees that NGS lacks modern pollution control equipment. As discussed in our Proposed Rule, NGS 

uses hot-side electrostatic precipitators to control PM and wet limestone FGDs to control SO2. In 

addition, over 2009-2011, NGS installed modern combustion controls to reduce NOx by approximately 

30 percent. Regarding comments on public health, EPA notes that many of the same pollutants that 

impair visibility are criteria pollutants that are regulated by different programs under the CAA for their 

effects on human health. 

EPA recognizes the many commenters support a five-year compliance timeframe for installation 

of SCR, and many other commenters supported the flexibility in the timeframe for compliance afforded 

under the TWG Alternative. EPA provides further discussion of the TWG Alternative and the 

compliance timeframes in Sections 8 and 9 of this response to comments document. 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 not consider BART as a requirement to redesign a source 

when considering available control alternatives (see specifically 70 FR 39164).32

32 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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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

3.0 Comments on Factor One – Cost of Controls 

3.1 Comments on the Analysis of the Cost of SCR at NGS 

Comment: General 

 Sixteen private individuals (0079, 0117, 0145, 0146, 0147, 0148, 0161, 0163, 0167, 0168, 0193, 

0200, 0203, 0205, 0212, 0226), government commenters (0287, 0297, 0324, 0406, 0443), a 

public/private coalition (0400), and an industry trade association (0278) argued that installing SCR 

could cost NGS over $1 billion without yielding any perceptible visibility improvements.33 One of these 

commenters (0079) emphasized that this system would be 15-20 times more expensive than the 

LNB/SOFA already installed, and warned that these costs may result in a 20 percent increase in CAP 

energy rates, or higher if the plant cannot finance the cost of this equipment over a 20-year period. 

 Another private individual (0020) strongly urged EPA not to delay the installation of controls 

because the cost to install them will only increase in the future. Similarly, one private individual (0180) 

considers the high cost of SCR technology as a good incentive for coal-power companies to pursue 

alternative energy sources. 

Response: 

EPA disagrees with the assertion that installing SCR would cost NGS over $1 billion. In Table 2 

of our proposed rulemaking (78 FR at 8280), we provided the total capital cost for SCR plus 

LNB/SOFA estimated by SRP, the facility operator ($589 million), and the cost estimated by EPA ($541 

million). The assertion of $1 billion dollars in cost for SCR is associated with the presumption by 

commenters that future permits or rules would require the installation and operation of baghouses at 

NGS. The response to that comment is provided later in this section (section 3.1). 

EPA disagrees with the assertion that there will be no perceptible visibility improvement from 

our proposed BART determination. The response to this comment is addressed in section 7.0. EPA 

agrees that SCR is more costly than LNB/SOFA. Using the estimates from our proposed rulemaking, 

SCR+LNB/SOFA is more costly than LNB/SOFA alone by approximate 12 times ($541 million versus 

$45 million). However, EPA disagrees that the costs associated with SCR would result in a 20 percent or 

greater increase in CAP energy rates. As discussed in Table 8 of our Proposed Rule, we project an 

increase of $8.40 per acre-foot of water, representing a 14 percent increase of the energy-only water rate 

(paid by tribes or Non-Indian Agriculture (NIA) water users), or a 6 percent increase over the energy 

and fixed OM&R costs paid by other CAP water users (e.g., municipal and commercial water users). 

 EPA agrees that costs to install controls may increase in the future (due to other factors, such as 

inflation), however, EPA disagrees that this is a reason to require installation of controls at NGS sooner 

than is practicable. EPA disagrees with the assertion that SCR is a “high cost” technology (we note that 

SCR is an industry standard for new coal and natural gas fired power plants). We disagree that SCR 

should serve as an incentive to pursue other energy sources (see e.g., section 4.1.2); we note that the 

purpose of the BART requirement under the provisions of 169A of the CAA is to protect visibility by 

33 Throughout this document, four digit numbers in parentheses represent the last four digits of the document ID number in 

the docket for this rule, e.g., 0079 refers to document number 0079 in EPA-R09-OAR-2013-0009, also referred to as EPAR09-OAR-2013-0009-0079. See also Appendix A for list of commenters by document ID number. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

requiring stationary sources of a certain size and age to install the “best available retrofit technology” to 

reduce emissions of visibility-impairing pollutants. This requirement does not require fuel-switching, or 

a redefinition of the source, nor is it intended to incentivize alternative energy sources. 

Comment: EPA underestimated SCR costs 

 Two of the owners of NGS (0314, 0348), a state agency (0017/0289/0320), and a CAP 

agricultural water users group (0305) commented that EPA underestimated the cost of compliance by 

disregarding real costs that would be incurred. One of the NGS owners (0348) noted that in the February 

2013 Proposal, EPA largely accepted the cost estimates developed for SRP by S&L in 2010; however, 

EPA revised or removed several of the line items within S&L’s cost estimates for installation of SCR at 

NGS, including interest rates, Owner’s Construction Management, O&M Support & Contracted 

Services, Owner’s Legal Support and Insurance, and Allowance for Funds Used During Construction 

(AFUDC). The commenter disagreed with several of EPA’s revisions to S&L’s work, commenting as 

follows: 

 On the basis that they are not included in the Control Cost Manual, EPA eliminated Owner’s 

Construction Management, and O&M Support & Contracted Services, despite the fact that 

these line items represent real costs incurred throughout the project by NGS Participants, 

such as project initiation, project management, owner’s onsite construction support and 

startup activities. The commenter disagreed that they are not included in the Control Cost 

Manual, stating that these items typically would be included in the “Construction 

Management and Field Engineering” line item in the S&L estimate – a line item that EPA 

accepted into the estimate. These items have been broken out into a separate line item due to 

the commenter’s preferred approach to performing major capital equipment installation 

projects. The commenter has consistently employed this approach throughout its fleet for a 

variety of installations, believing that this approach has resulted in improved design quality 

and overall equipment reliability versus current contracting trends (i.e., 

Engineer/Procure/Construct contracts). Accordingly, the commenter has continued to include 

this line item in its estimated installation costs for SCR at NGS. 

 Even if AFUDC is excluded in the Control Cost Manual, it is a real cost to the NGS 

Participants, and it therefore should be included in an evaluation of the cost of controls, in 

accordance with the BART Guidelines. 

 The EPA revised the interest rates for calculating the annualized cost of capital from 9.8 

percent down to 7 percent on the basis that the Control Cost Manual recommends the use of 

7 percent. The commenter objected to the use of a “one size fits all” approach for cost 

calculations and asserted that the EPA should accept cost estimates that are based on the real 

cost of borrowing money for power plant owners. 

 The CAP agricultural water users group (0305) quoted the BART Guidelines and the final RHR 

to assert that while the use of the Control Cost Manual is encouraged, it is not mandated, and that EPA 

has discretion to use additional sources of cost information. The commenter believes, therefore, that the 

SRP estimates for the excluded cost items are appropriate to use because they are more precise than the 

generic statements that EPA relied upon in the Control Cost Manual. The commenter asserted on this 

basis that because EPA has not provided specific reasons why the SRP estimates are inaccurate or 

unnecessary, it should use the SRP estimates rather than guidance in the Control Cost Manual. 

Response:
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

EPA disagrees with the comment that we improperly reworked and underestimated the SCR cost 

estimates; however we note that even if we only relied on the cost estimate provided by SRP, EPA still 

would have concluded that SCR is cost-effective at NGS. EPA used a hybrid approach for our cost 

analysis that relied primarily on the cost estimates provided by SRP, 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 Manual, where possible” to determine whether SRP included cost estimates 

for services or equipment associated with SCR that were not allowed under the EPA Control Cost 

Manual (e.g., owner’s costs or allowance for funds used during construction, or AFUDC).34 We note 

that the capital cost estimate EPA presented in the proposed rulemaking for SCR plus LNB/SOFA ($541 

million total for Units 1-3) is only 8 percent lower than the SRP cost estimate ($589 million) and that 

even if we had used SRP’s cost estimate, it would not have changed our determination under Factor 1 

that SCR is cost-effective at NGS. 

Our detailed, line-by-line analysis was included in the docket for this proposed rulemaking and 

provided an explanation for why we retained, modified, or rejected each line item in the SCR cost 

estimate for Units 1-3 at NGS.35 EPA used all of the direct capital costs as estimated by S&L. Direct 

capital costs are those costs that contribute directly to the physical capital of the installation (e.g., steel, 

concrete, mechanical equipment, etc). Indirect capital costs are associated with installation, for example, 

construction and contractor fees, startup, testing, and process contingency costs. The EPA Control Cost 

Manual calculates total indirect costs as a percentage of the total direct capital costs, and estimates that 

general facilities would be 5 percent of total direct capital costs, engineering and home office fees would 

be 10 percent of total direct capital costs, and process contingency would be 5 percent of total direct 

capital costs. Thus, the EPA Control Cost Manual calculates total indirect costs to be 20 percent of total 

direct capital costs. 

As discussed in the TSD to the proposed rulemaking, EPA made four adjustments to SRP’s cost 

estimates for SCR: two adjustments to total indirect capital costs, one adjustment to an additional capital 

cost, and one adjustment to the annual cost calculation.36 For example, using Unit 2 as an example, EPA 

excluded indirect capital costs of $8,163,050 that S&L attributed to “Owners Construction Management, 

O&M Support, Contract Services,” and a cost of $5,000,000 attributed to “Owners Legal Support and 

Insurance.” EPA also excluded a cost of $4,059,526 attributed to “Allowance for Funds Used During 

Construction” which is an additional component of total capital cost, and revised the interest rate from 

9.8 percent to 7 percent, which is used in the calculation of total annual cost. 

S&L estimated total indirect capital cost to be $49.7 million. EPA estimated indirect capital costs 

to be $36.5 million. We note that, had we used the calculation methodology exactly as prescribed in the 

EPA Control Cost Manual, the total indirect capital cost would have been roughly $18 million (based on 

20 percent of S&L’s estimate of total direct costs, which are already escalated compared to total direct 

costs using the EPA Control Cost Manual). The indirect capital cost S&L estimated is roughly 2.8 times 

higher, and the indirect capital cost estimated by EPA is roughly two times higher, than that estimated 

using the EPA Control Cost methodology. EPA notes that S&L did not provide information to identify 

and differentiate between costs included under “Engineering, Procurement, and Project Services” valued 

at $14 million, “Construction Management/Field Engineering” valued at $15 million, and “Owners 

Construction Management, O&M support and Contract Services”, valued at $8 million (these values 

34 The OAQPS Control Cost Manual is now referred to as the EPA Control Cost Manual. 

35 See MS Excel document titled “EPA cost analysis for NGS” in the docket for this rulemaking at EPA-R09-OAR-2013-

0009-0004. 

36 See Table 12 of the TSD to the February 5, 2013 Proposed Rulemaking at EPA-R09-OAR-2013-0009-0014. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

represent cost estimates for Unit 2). In particular, S&L did not provide sufficient detail to determine that 

these line-item costs do not represent redundant costs. EPA excluded the line item representing the $8 

million cost for “Owners Construction Management, O&M Support and Contract Services” as costs not 

included in the EPA Control Cost Manual. Although “contractor fees” are costs cited by the EPA 

Control Cost Manual as an appropriate indirect cost, these fees seem to be represented under existing 

line items costs, e.g., “project services” or “construction management/field engineering”. EPA also 

excluded legal support and insurance, a $5 million cost, as costs that are not included in the EPA Control 

Cost Manual (legal support) or that are noted as being minimal (insurance).37 EPA similarly excluded 

the additional capital cost for AFUDC, as the EPA Control Cost Manual specifically sets this value to 

zero.38 As asserted by commenters, although these costs (e.g., AFUDC or legal costs), may be real costs 

that could be borne by a utility, EPA notes that exclusion of these three line item costs, totaling $17 

million for Unit 2, resulted in an 8% difference in the total capital cost for Unit 2. This difference would 

not have changed our determination under Factor 1 that SCR is cost-effective for NGS. 

For calculating total annual cost, EPA used the values estimated by S&L for all line items, 

except for capital recovery (i.e., the interest rate). S&L used a capital recovery factor based on a 9.8 

percent interest rate and 20 year life (or recovery period), whereas EPA used a capital recovery factor 

based on a 7 percent interest rate and a 20 year life. Based on the difference in capital recovery, S&L 

estimated total annual cost for Unit 2 to be roughly $27.8 million and EPA estimated total annual cost 

for Unit 2 to be $21.8 million – a difference of $6 million, or 22 percent. As explained in Chapter 2 

(Cost Estimation: Concepts and Methodology), and as discussed in EPA’s line-by-line cost estimate that 

accompanied our proposed rule,39 the EPA Control Cost Manual uses a social interest rate, as 

determined by the Office of Management and Budget (OMB), which the EPA Control Cost Manual (in 

2002) cites as 7 percent.40 OMB states, in their Circular related to Regulatory Analysis, that: “As a 

default position, OMB Circular A-94 states that a real discount rate of 7 percent should be used as a 

base-case for regulatory analysis. The 7 percent rate is an estimate of the average before-tax rate of 

return to private capital in the U.S. economy.”41 Therefore, EPA’s use of a 7 percent interest rate is 

conservative and generally consistent with other cost analyses performed for other BART 

determinations nationally.42

In our Proposed Rule, we presented total capital and total annual cost estimates from EPA and 

SRP, as well as average and incremental cost-effectiveness values based on EPA and SRP assumptions 

for total annual cost and total annual NOx reductions. Based on SRP’s analysis, average costeffectiveness of SCR+LNB/SOFA at NGS was less than $3,000 per ton and incremental costeffectiveness of SCR+LNB/SOFA (compared to SNCR+LNB/SOFA) was approximately $5,300 per 

ton.43 EPA stated that the cost-effectiveness values calculated by both EPA and SRP for 

37 See page 2-48, discussion of indirect annual cost, of the EPA Control Cost Manual Section 4 – NOx Controls. 

38 Elsewhere, EPA discusses exclusion of AFUDC based on the “overnight” costing methodology used by the EPA Control 

Cost Manual. See e.g., Final Regional Haze Rule for Arizona (Phase 1) at 77 FR 72512 at 72531 (December 5, 2012) and 

footnote 94 and references therein. 

39 See MS Excel document titled “EPA cost analysis for NGS” in the docket for this rulemaking at EPA-R09-OAR-2013-

0009-0004, and EPA Control Cost Manual available at: http://www.epa.gov/ttncatc1/dir1/c_allchs.pdf 40 See page 2-13 of Chapter 2 of the EPA Control Cost Manual, available at: http://www.epa.gov/ttncatc1/dir1/c_allchs.pdf. 41 http://www.whitehouse.gov/omb/circulars_a004_a-4/#e 42 See, e.g., Final Regional Haze Rule for Arizona (Phase 1) at 77 FR 72512 at 72547 (December 5, 2012) and Final Regional 

Haze Rule for Wyoming at 79 FR 5032 at 5137 (January 30, 2014). We note however, that there are other BART 

determinations that have used lower interest rates, e.g., Final Regional Haze Rule for Oklahoma at 76 FR 81728 at 81745 

(December 28, 2011). 

43 See Table 3 of our Notice of Proposed Rulemaking, 78 FR at 8281 (February 5, 2013). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

SCR+LNB/SOFA are lower than or within the range of other BART evaluations that required SCR; and 

EPA has determined that SCR is cost-effective at NGS.44 Therefore, even if EPA accepted the S&L cost 

estimates submitted by SRP, as commenters suggest, EPA would still have determined that SCR is costeffective for NGS. 

Comment: EPA overestimated SCR costs 

 An environmental advocacy group (0373) stated that EPA overestimated the cost of installing 

SCR at NGS. In contrast to the previous comment, the commenter indicated that EPA properly adjusted 

the cost estimates submitted by one of the owners of NGS as improper or not allowed under accepted 

methodologies, including using a lower interest rate and excluding the costs of other pollutant control 

technology. However, the commenter believes that further revisions are appropriate. 

 The commenter (0373) (citing the Stamper report submitted with the comments) stated that EPA 

overestimated the cost of SCR at NGS in the following ways: 

 Overestimated outage costs associated with installation and “preinstallation” work that is 

unsupported, often inflated, and should have been excluded under the same rationale that the 

EPA excluded cost of other pollutant control technologies. 

 Overestimated catalyst costs that are almost twice the low end of the range that vendors have 

typically quoted. Accepting this high catalyst cost is inconsistent with BART determinations 

elsewhere; for example, in its analysis of BART for NOx control at Colstrip Units 1 and 2 in 

Montana, the EPA relied on a 2010 study showing catalyst prices as low as $4,000/m3

 with 

average prices at $5,000-6,000/m3, not the $8,000/m3 claimed by the NGS owner. 

 Improper statement of the cost of auxiliary power; the NGS owner relied on market rates which 

are in excess of the busbar cost (i.e., cost to the owner to generate electricity). 

 Assumed lifetime of an SCR system for NGS should be at least 30, not 20 years. Even a 30-year 

lifetime is itself very conservative as many SCRs installed in Europe in the 1980s are still in 

operation today, and an analysis prepared by Black & Veatch for another facility assumed a 40-

year lifetime for SCR. The lifetime of an SCR retrofit is generally set equal to the remaining 

useful life of the facility – in this case 2044. There is no support in the record for a 20-year 

lifetime and the cost assumptions associated with it. 

 Corrected interest rate is still too high. EPA used 7 percent, noting that it is the “social” interest 

rate, which is proper for analyzing BART. However, the Office of Management and Budget 

(OMB) has recently published a social interest rate of 2.8 percent for a 20-year amortization 

period, and the Control Cost Manual directs using the social interest rate set by OMB. In 

addition, it is uncertain that the social interest rate should be used in a BART determination 

because cost-effectiveness determinations for BART do not appear to fall within the scope of 

“cost analyses related to government regulations.” Rather, a source-specific rate of interest (i.e., 

the rate at which NGS can borrow) may be the correct rate to use, which appears to properly fall 

within a range of 2.9 percent (the cost of capital for SRP) and 4.9 percent (the cost of capital for 

Arizona Public Service). 

44 See our Notice of Proposed Rulemaking at 78 FR at 8281 (February 5, 2013). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 By correcting what the commenter (0373) believes are overestimated costs and underestimated 

SCR performance (see section 8.1), the commenter calculated that SCR is more cost effective than 

estimated by EPA. In these calculations, the commenter assumed 80 to 84 percent NOx pollutant 

removal at each of the three NGS units with the installation of SCR and adjusted costs to (according to 

the commenter): (1) make the method used consistent with the overnight costing methodology in the 

Control Cost Manual; (2) account for a more accurate catalyst cost; (3) move auxiliary power costs into 

operations and maintenance and use a more accurate cost per unit of electricity; (4) adjust the cost of 

reagent such that it is not inflated; (5) use a proper, lower interest rate of 4.9 percent (the most 

conservative rate that is correct); and (6) adjust the lifetime of the SCR controls to reflect 30, not 20 

years. While the commenter believes that EPA properly found that SCR plus LNB/SOFA is costeffective at NGS at $2,240 per ton of NOx removed (at an emission rate of 0.055 lb/MMBtu), the 

commenter asserted that its corrected cost-effectiveness calculations result in values of $1,412 per ton 

for Unit 1, $1,331 per ton for Unit 2, and $1,497 per ton for Unit 3. On this basis, the commenter 

contended that EPA’s determination that SCR plus LNB/SOFA is BART for NOx control at NGS is the 

correct, fully-supported and fully-supportable decision. 

Response:

We agree that our BART determination for NOx is fully-supported by our five-factor analysis, 

however, EPA disagrees with the commenter that any further revisions to the SCR cost estimate are 

necessary. Even if some of the costs projected by S&L and used by EPA may be overestimated (e.g., the 

commenter points primarily to capital recovery, catalyst replacement costs, and costs for lost power 

generation), EPA disagrees that we must correct every issue of concern raised by the commenters in 

order to support our BART determination. EPA made four specific corrections to the estimates provided 

by S&L and SRP to make the cost calculation methodology more consistent with methodologies used 

for BART cost calculations nationally.45 As noted in the response to comments that we underestimated 

the cost of SCR, EPA noted that even if we consider the average and incremental cost effectiveness of 

SCR using SRP and S&L’s full cost projections, EPA would still determine that SCR at NGS is costeffective. The cost-effectiveness values cited by the commenter, below $1,500 per ton, certainly suggest 

that SCR could be even more cost-effective than the values we relied upon in our proposal, but this 

would not change our overall determination that an emission limit achievable with SCR is BART for 

NGS. 

Comment: Updated SCR cost estimate from SRP 

 Because compliance with EPA’s proposed BART determination is achievable with SCR, one of 

the owners of NGS (0348) contracted with S&L in 2013 to review and update the SCR cost estimates 

that were prepared in 2010 (report attached to comments as Appendix U). According to the commenter, 

in addition to escalating the SCR cost estimate to reflect inflation, S&L incorporated other minor 

adjustments to its 2010 estimate as a result of changes in equipment needs based on recent experience 

with the SCR installation at SRP’s Coronado Generating Station and also made adjustments to ensure

that the lowest level of NOx emissions can be achieved based on design standards at this time, including 

modifications to the air baskets to address likely increases in ammonium bisulfate formation and sulfuric 

acid fouling and corrosion, deduction of economizer flue gas bypass, installation of sootblowers instead 

45 See, e.g., Final Regional Haze Plan for Arizona (Phase 1) at 77 FR 72512 at 72531 (December 5, 2012); Final Regional 

Haze Plan for North Dakota at 77 FR 20894 at 20916-17 (April 16, 2012); Final Regional Haze Plan for New Mexico at 76 

FR 52388 at 52399-400 (August 22, 2011); Final Regional Haze Plan for Wyoming at 79 FR 5032 at 5082 (January 30, 

2014). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

of sonic horns for improved online maintenance of dust and ash loading on the upper layer of the SCR, 

installation of a hot water recirculation system for greater reliability due to flue gas temperature 

increases, and installation of an extra layer of catalyst. The revised capital cost estimates for SCR 

installation submitted by the commenter are shown in Table 1. 

Table 1: Cost Estimates for SCR Provided by SRP in 2010 and 2013 Dollars 

Item Unit 1 Unit 2 Unit 3 

2010 Costs $151,825,000 $205,808,000 $186,528,000 

2013 Costs $162,896,000 $220,928,000 $199,760,000 

2013 Scope Adjustments $20,955,000 $24,533,000 $21,030,000 

2013 Total Costs $183,851,000 $245,461,000 $220,790,000 

Total Cost for all Units $650 million

Response:

EPA reviewed the updated 2013 cost estimates developed by S&L and provided by SRP.46 In its 

2013 cost report, S&L explains that it generally escalated labor costs by 8 percent and material costs by 

6.7 percent. In addition, S&L provided updated cost estimates based on a revised design target of 0.03 

lb/MMBtu (so that the SCR system is deployed as a 3+1 system rather than a 2+2 catalyst layer system), 

and other design features, including a low-load temperature control system to operate SCR at lower 

loads. S&L escalated several costs at rates above 6.7 or 8 percent (e.g., freight, scaffolding). S&L did 

not make any revisions to the components of variable annual costs, including maintenance labor, 

auxiliary power, steam, and catalyst replacement. To be consistent with the cost estimates in our 

proposed rulemaking, EPA accepted most of the line item costs as adjusted by S&L and made the same 

four adjustments to the 2013 cost estimates, namely, to exclude “Owners Construction Management, 

O&M Support and Contract Service,” “Owners Legal Support and Insurance,” and AFUDC, and to use 

an interest rate of 7 percent. These changes result in an 8 percent difference in total capital costs of SCR 

between EPA’s 2013 estimate and SRP’s 2013 estimate and a 21 percent difference in the total annual 

costs of SCR between the 2013 estimates from EPA and SRP (see Table 2). 

46 See document titled “2014_0304 EPA cost analysis for NGS_Revised for 2013.xlsx” in the docket for this rulemaking. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Table 2: Cost Estimates for SCR in 2010 and 2013 Dollars 

Unit 1 Unit 2 Unit 3 Total 

Costs 

Estimated by 

EPA 

Total Capital Cost 

in 2010 $ $137,527,000 $188,585,000 $170,294,000 $496 M 

Total Capital Cost 

in 2013 $ $168,391,000 $226,811,000 $203,297,000 $598 M 

Percent Change 21% 20% 19% 21% 

Total Annual Cost 

in 2010 $ $16,963,576 $21,783,090 $20,056,549 $58.8 M 

Total Annual Cost 

in 2013 $ $19,876,919 $26,165,354 $23,171,799 $69.2 M 

Percent Change 17% 20% 16% 18% 

Costs 

Estimated by 

SRP 

Total Capital Cost 

in 2010 $ $151,825,000 $205,808,000 $186,528,000 $544 M 

Total Capital Cost 

in 2013 $ $183,851,000 $245,461,000 $220,790,000 $650 M 

Percent Change 21% 19% 18% 19% 

Total Annual Cost 

in 2010 $ $21,579,000 $27,835,000 $25,601,000 $75.0 M 

Total Annual Cost 

in 2013 $ $25,290,000 $33,205,000 $29,572,000 $88.1 M 

Percent Change 17% 19% 16% 17% 

 In our proposed BART determination, EPA also presented the average and incremental costeffectiveness of controls, based on the combination of combustion controls (LNB/SOFA) and postcombustion controls (i.e., SNCR or SCR). Therefore, cost-effectiveness values presented in Table 3 of 

our proposed rule were based on total annual cost of SCR in combination with annual cost of 

LNB/SOFA (SCR+LNB/SOFA), SNCR in combination with LNB/SOFA (SNCR+LNB/SOFA) or 

LNB/SOFA alone.47 Based on the updated 2013 cost estimates for SCR, Table 3 shows the average and 

incremental cost-effectiveness of controls, in both 2010 and 2013 dollars, based on EPA and SRP 

assumptions for total annual cost and annual NOx reductions achieved by the three sets of technologies. 

SRP only provided updated costs (in 2013 dollars) for SCR. Therefore, SCR based on 2013 cost 

estimates and SNCR or LNB/SOFA based on 2010 cost estimates may not be directly comparable, but 

we still include calculations of incremental cost-effectiveness because it provides useful information, 

and it is based on the set of cost values that SRP has chosen to provide on our proposed rulemaking. 

47 78 FR at 8281, February 5, 2013 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Table 3: Cost Effectiveness of Controls in 2010 and 2013 dollars48

2010 $ 2013 $ 

EPA SRP EPA SRP 

LNB/SOFA 

Total Annual Cost $5.2 million 

SRP did not submit updated costs 

in 2013 $ 

Annual NOx reduced (tpy) 10,865 

NOx Limit (lb/MMBtu) 0.24 

Average Cost Effectiveness $486 per ton 

SNCR+ 

LNB/SOFA 

Total Annual Cost $28.8 million 

Annual NOx reduced (tpy) 16,608 

NOx Limit (lb/MMBtu) 0.18 

Average Cost Effectiveness* $1,745 per ton 

Incremental Cost Effectiveness $4,110 per ton 

SCR+ 

LNB/SOFA 

Total Annual Cost** $67.5 million $80.2 million $74.4 million $92.6 million 

Annual NOx reduced (tpy) 28,573 26,180 28,573 26,180 

NOx Limit (lb/MMBtu) 0.055 0.080 0.055 0.080 

Average Cost Effectiveness $2,369 per ton $3,069 per ton $2,605 per ton $3,537 per ton 

Incremental Cost Effectiveness 

(vs. LNB/SOFA) $3,522 per ton $4,889 per ton $3,899 per ton $5,695 per ton 

Incremental Cost Effectiveness 

(vs. SNCR+LNB/SOFA) $3,239 per ton $5,357 per ton $3,798 per ton $6,647 per ton 

* In Table 3 of our Notice of Proposed Rulemaking (NPR-Table 3), EPA reported the following values for SRP’s average 

and incremental cost effectiveness of SNCR+LNB/SOFA: $1,481 per ton (average) and $3,135 per ton (incremental). EPA 

also reported SRP’s incremental cost effectiveness of SCR+LNB/SOFA to be $5,282 per ton. These values were based on 

reported values in SRP’s Updated NGS BART Analysis dated January 20, 2012. These values were based only on SCR at 

0.08 or SNCR at 0.018 lb/MMBtu (not SCR or SNCR in combination with LNB/SOFA) and for SNCR, assume a smaller 

annual NOx reduction (approximately 15,896 tons per year) than EPA had estimated (16,608 tons per year). For an “apples 

to apples” comparison in NPR-Table 3, EPA could have reported the same average and incremental costs for SNCR to 

represent both EPA and SRP because EPA did not make any revisions to SRP’s cost estimates for SNCR. For the incremental 

cost of SCR+LNB/SOFA compared to SNCR+LNB/SOFA and SCR+LNB/SOFA compared to LNB/SOFA, EPA could have 

used the above values of $5,357 per ton and $4,889 per ton, to represent SRP cost estimates. 

** EPA’s cost effectiveness calculations represent SCR in combination with LNB/SOFA, rather than SCR alone. 

Based on the revised 2013 cost estimates for SCR presented in Table 2 of this response to 

comments document and the revised cost-effectiveness values presented in Table 3 of this document, 

EPA continues to determine that SCR+LNB/SOFA is cost-effective at NGS. In addition, we note that 

the values for average cost-effectiveness of SCR at NGS are comparable to average cost-effectiveness 

values for BART determinations elsewhere in the western U.S. where SCR was determined BART, 

ranging from $825 per ton to $6,300 per ton.49

Comment: Updated baghouse cost estimate from SRP

 One of the owners of NGS (0348), a tribal government (0039/0317), and a state agency 

(0017/0289/0320) indicated that there is a possibility that baghouses will be needed to address the 

increased PM emissions from NGS if the proposed BART determination is implemented. These 

commenters said that baghouses could increase the cost of compliance by over $500 million, and that 

EPA must consider these costs in its analysis. One of the commenters (0039/0317) stated that this would 

increase the cost of SCR by 108 percent, and another (0017/0289/0320) indicated that it would 

approximately double the electric and water rate impacts identified by EPA. 

48 See document titled “2014_0304 NGS emissions and incremental costs.xls” in the docket for this proposed rulemaking. 

49 See document titled: “Western Coal EGU BART Summary.xlsx” in the docket for this rule. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 One of the owners of NGS (0348) stated that in the TSD accompanying the February 2013 

Proposal, EPA indicated that it cannot know if a baghouse fabric filter would be required as part of a 

New Source Review Best Available Control Technology (BACT) determination for NGS and, as a 

result, EPA asserted that the potential costs of a baghouse cannot be considered as part of the BART 

determination. The commenter agreed that EPA cannot be certain as to whether baghouses will be 

required, but strongly disagreed with EPA’s argument that the potential cost cannot be considered as a 

result. Given the significance of the cost associated with baghouses, the commenter believes that EPA 

should consider this as a scenario in its cost-effectiveness evaluation. 

 An owner of NGS (0348) believes that because EPA proposed the more stringent NOx limit it is 

more likely that a future BACT determination would require installation of a baghouse because the 

introduction of additional layers of catalyst – required to achieve lower NOx emissions – creates 

additional oxidation of SO2 to SO3, which can generate more PM emissions and therefore make more 

stringent PM controls such as baghouses appear more cost-effective. The commenter added that 

concerns regarding the possible need for a baghouse should also have been recognized by EPA as 

additional support for a more reasonable and achievable NOx limit for SCR that is closer to 0.080 

lb/MMBtu. 

 The commenter (0348) submitted updated cost estimates prepared by S&L for adding baghouses 

along with SCR at NGS. The commenter asserted that EPA cannot dismiss these costs entirely unless it 

can provide assurance that baghouses would not be required as a result of its BART determination. The 

updated costs are presented in Table 4, including the escalation of the 2010 SCR plus baghouse cost for 

inflation and the scope adjustments for improved SCR performance list previously. 

Table 4: Cost Estimates for SCR plus Baghouses Provided by SRP in 2010 and 2013 Dollars 

Item Unit 1 SCR w/ 

Baghouse 

Unit 2 SCR w/ 

Baghouse 

Unit 3 SCR w/ 

Baghouse 

2010 Costs $372,184,000 $410,919,000 $347,869,000 

2013 Costs $403,442,000 $445,515,000 $376,825,000 

2013 Scope Adjustments $20,955,000 $24,533,000 $21,030,000 

2013 Total Costs $425,004,000 $470,487,000 $398,677,000 

Total Cost for all Units $1.3 billion

Response:

 EPA disagrees with the assertion that the estimated costs of our proposed BART determination 

must also include the cost of baghouses due to the potential that a BACT determination for sulfuric acid 

mist might require additional controls. As we indicated in the TSD that accompanied our Proposed Rule, 

EPA disagreed when this same comment was made on the ANPR. Specifically, in our TSD, EPA stated 

that “without undertaking a source-specific top-down PSD BACT analysis, EPA cannot determine what 

may be required as BACT for potential significant emission increases for sulfuric acid mist. Therefore, 

EPA cannot speculate what BACT for sulfuric acid might be in the event a PSD permit is required for 

NGS.” In addition, the BART Guidelines do not require the BART cost analysis to include costs 

associated with future potential requirements from other rules or regulations. EPA further noted that a 

2009 PSD permit for the Coronado Generating Station issued by the Arizona Department of 

Environmental Quality for increased emissions of sulfuric acid mist as a result of planned SCR 

installation required use of an ultra-low SO2 to SO3 conversion catalyst and a sulfuric acid mist 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

minimization analysis, but specifically did not require the installation of a new baghouse for control of 

sulfuric acid mist or particulate matter.50

 In addition, as discussed in our Proposed Rule, EPA did not propose that it is necessary or 

appropriate under the TAR to determine BART for PM emissions at NGS.51 EPA noted that the PM 

emissions are already controlled at NGS by hot-side ESPs, and that the Mercury and Air Toxics 

Standard (MATS) that was finalized on February 16, 2012 set a filterable PM emission limit of 0.03 

lb/MMBtu that NGS must comply with by 2015 or 2016. EPA understands that Units 1-3 at NGS can 

meet the MATS emission limit for PM without additional PM controls, and that SRP has been 

evaluating the ability of NGS to comply with the MATS emission limit for Hg without baghouses as 

well. 

 Because EPA is not setting a BART limit for PM that requires installation of baghouses or other 

PM controls, and because the BART Guidelines do not require BART analyses to include compliance 

costs associated with other potential requirements in the future, EPA disagrees with commenters and 

EPA is not including the potential costs associated with dry sorbent injection and baghouses in the cost 

estimate for SCR for the purposes of BART. 

Comment: Must consider $/deciview 

 Two of the owners of NGS (0314, 0348), a CAP agricultural water users group (0305), and the 

operator of the Kayenta Mine (0384) noted that EPA’s evaluation of the BART options considered costeffectiveness only in terms of dollars per ton of emissions removed ($/ton). One of these commenters 

(0348) asserted that the BART Guidelines and the courts have reaffirmed that the BART regulations 

require consideration of the degree of improvement in visibility when evaluating whether a technology 

is too costly for a particular source (citing 70 FR 39170; American Corn Growers Association v. EPA, 

F.3d1, 1 at 6-7). The commenter stated that at the very least EPA should have considered the costs of 

compliance in the context of both $/ton and dollars per deciview-improved ($/deciview) before reaching 

a conclusion regarding the impacts of BART compliance costs at NGS. 

 One commenter (0348) stated that exclusion of the degree of visibility improvement from the 

assessment omits critical information that EPA must consider in determining BART for NGS. The 

commenter calculated the $/deciview for each of the facilities EPA included in the average costeffectiveness comparison table in its TSD (citing Table 16, page 54, of the TSD for the proposed rule) 

and submitted a diagram purporting to consolidate the information into a single figure that shows the 

cost effectiveness values in both $/ton and $/deciview for each of the units. The commenter asserts that 

NGS is an outlier when the degree of visibility improvement is considered in evaluating costeffectiveness, and that the figure clearly demonstrates that if EPA had appropriately considered costeffectiveness, contemplating both the tons of NOx removed and the deciview improvement with respect 

to cost, it would have concluded that SCR at NGS is not cost-effective. 

 Another commenter (0314) stated that EPA lost sight of the overall purpose of the regional haze 

program by failing to compare the control costs as a function of visibility improvement. According to 

the commenter, the NGS operator estimated the incremental visibility cost effectiveness of the 

application of SCR at NGS at approximately $61 million per deciview, compared to a value of $13 

50 See page 54 of the TSD to the Proposed Rulemaking at EPA-R09-OAR-2013-0009-0014. EPA also notes that the 

modeling and cost analysis is based on the use of ultra-low SO2 to SO3 conversion catalyst for the SCR system. 51 See Proposed BART determination at 78 FR at 8279 (February 5, 2013). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

million per deciview for LNB/SOFA; including baghouses with SCR increases the incremental visibility 

cost effectiveness to approximately $13 billion per deciview. The commenter asserted that this is a 5- to 

10-fold difference in visibility cost effectiveness and demonstrates that only advanced combustion 

controls are cost effective in terms of regional haze BART. 

 The operator of the Kayenta Mine (0384) quoted the NREL report as saying that installation of 

SCR at NGS would cost $33 million per year per deciview improvement, a cost to benefit ratio larger 

than those calculated for BART controls proposed for other units in the region even if the other units 

were to install SCR. This commenter (0384) asserted that this conclusion is even stronger when one 

considers the significant cost if NGS were to close, which would increase the cost per deciview per year 

by an additional $571+ million (based on the ASU economic study of $20 billion economic benefit to 

Arizona between 2009-2044) and bring the total to almost $600 million per deciview per year, vastly 

exceeding any other comparable SCR installation. The commenter went on to contend that a closure of 

one-third of NGS under the Supplemental Proposal results in $153 million per deciview per year 

(assuming a $4.2 billion decrease in value due to the closing), which the commenter believes is also 

vastly in excess of any other comparable SCR installation. 

 The CAP agricultural water users group (0305) noted that the BART Guidelines define cost 

effectiveness as “a criterion used to assess the potential for achieving an objective in the most 

economical way” (citing 40 CFR part 51, Appendix Y, section IV.D4.b). The commenter stated that 

since the objective of CAA section 169A is the remediation and prevention of visibility impairment, a 

proper factor 1 analysis of cost effectiveness must assess the visibility improvements that result from the 

control alternatives as a result of emissions reductions. The commenter believes that EPA’s reliance on 

cost-effectiveness metrics alone to conclude that SCR is cost-effective is arbitrary. 

Response:

 EPA disagrees with the assertion that our analysis of Factor 1 (cost of compliance) is arbitrary 

because we focus on average and incremental cost-effectiveness. We also disagree that the BART 

Guidelines require consideration of $/deciview. While a $/deciview metric may provide some useful 

information to assess how pollution controls would benefit Class I areas, the BART Guidelines do not 

require consideration of $/deciview as a mandatory metric in a BART analysis. The BART Guidelines 

are clear that certain calculations must be included in consideration of the cost of controls, including 

total capital costs, total annual costs, and average and incremental cost effectiveness.52 The $/deciview 

metric is identified by the BART Guidelines as an example of “other cost-effectiveness measures” that 

can be considered under the cost of compliance. Specifically, under the section titled “How do I select 

the ‘best’ alternative, using the results of Steps 1 through 5?”, the BART Guidelines recommend 

developing a chart (or charts) displaying for each of the alternatives various pieces of information, 

including “Costs of compliance – total annualized costs ($), cost effectiveness ($/ton), and incremental 

cost effectiveness ($/ton), and/or any other cost effectiveness measures (such as $/deciview)” (emphasis 

added). Therefore, while $/deciview is another measure that can be considered in addition to the other 

metrics of cost-effectiveness, it is not required, and a methodology for calculating $/deciview was not 

described in any detail elsewhere in the BART Guidelines.53

52 See BART Guidelines, 70 FR 39104 at 39166-39167 (July 6, 2005), which describes the steps needed to evaluate the cost 

of controls. 

53 The BART Guidelines describe in great detail how incremental cost should be calculated. In contrast, the Guidelines 

provide no instruction on the calculation of $/deciview. Arguably, $/deciview can be calculated any number of ways using a 

combination of many cost and visibility metrics, including total capital cost, total annual cost, annual deciview improvement 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

EPA considered cost of controls by discussing the total capital costs, total annual costs, $/ton, 

and incremental $/ton, and considered visibility impacts by discussing the individual and cumulative 

deciview improvement resulting from SCR, as well as the percent change in improvement. We further 

note that EPA did calculate the anticipated $/deciview of the three control options in Table 10 of our 

Proposed Rule.54 EPA calculated the $/maximum deciview ($/max dv) based on the total annual cost of 

controls and the highest projected 98th percentile improvement in visibility at all 11 Class I areas 

modeled from that control technology, as well as the $/cumulative deciview based on the total annual 

cost of controls and the sum of all projected 98th percentile visibility improvements for all 11 Class I 

areas. For LNB/SOFA, the $/max dv was $2.5 million per maximum deciview and the $/cumulative dv 

was $0.3 million per cumulative deciview. For SNCR+LNB/SOFA, the $/max dv was $9.3 million and 

the $/cumulative dv was $1.3 million. For SCR, the $/max dv was $11.8 million and the $/cumulative dv 

was $1.8 million. Although EPA disagrees with commenters that we must consider $/deciview as a 

metric under Factor 1, we also disagree with commenters that we completely excluded consideration of 

the metric from our analysis. Rather than include calculations of $/deciview under Factor 1, we instead 

included $/deciview under Factor 5. 

One commenter cited to its calculated $/deciview for SCR at NGS to suggest that NGS is an 

outlier compared to other BART determinations where SCR was required (i.e., Naughton, Four Corners, 

San Juan, Hayden, and Craig Unit 2) when the degree of visibility improvement is considered in 

evaluating cost-effectiveness (i.e., the commenter plotted average cost-effectiveness in $ per ton on the 

x-axis and cost per decivew on the y-axis).55 The commenter calculated $/deciview for NGS for SCR 

controls at over $60 million per deciview and cost-effectiveness at nearly $3,000 per ton.56 The 

commenter suggests this $/deciview value is substantially higher than other BART determinations where 

average cost-effectiveness ranged from less than $2,000 per ton to nearly $5,000 per ton, and cost per 

deciview for all facilities was less than $20 million per deciview. As noted above, EPA reported in 

Table 10 of our Proposed Rule a $/deciview value for SCR+LNB/SOFA of $11.8 million per deciview 

(calculated from total annual cost of approximately $64 million per year and maximum modeled 

visibility improvement from SCR+LNB/SOFA of 5.4 deciviews). The commenter did not provide the 

basis for the $/deciview values it asserted in its letter, but a $/deciview value for SCR of over $60 

million per deciview was likely calculated assuming its own values of total annual cost of $80 million 

per year for SCR+LNB/SOFA and its own maximum modeled visibility improvement from 

SCR+LNB/SOFA of 1.27 dv.57 The commenter also did not provide the basis for the $/deciview and 

$/ton estimates it cited for other BART determinations, therefore the comment does not provide any 

basis for EPA to determine whether the comparisons offered by the commenter are “apples to apples”. 

EPA notes, however, that the $/deciview and $/ton estimates EPA provided in our Proposed Rule ($11.8 

million per deciview and less than $3,000 per ton) are entirely consistent with the range of costat the most impacted Class I area, annual deciview improvement at all impacted Class I areas, 98th percentile improvement at 

the most impacted area or all impacted Class I areas. EPA has reported $/deciview based on total annual cost divided by 

either the largest 98th percentile improvement and total annual cost divided by the sum of the 98th percentile improvements 

from all impacted Class I areas within 300 km of the source. See Table 10 in 78 FR at 8287 (February 5, 2013). 

54 See Table 10 in 78 FR at 8287 (February 5, 2013). 55 See Figure 8, page 43, of SRP comment letter dated January 6, 2014 at EPA-R09-OAR-2013-0009-0348. 

56 The commenter also plotted the SCR+Baghouse case at nearly $6,000 per ton and over $120 million per deciview. EPA is 

does not understand where the $13 billion per deciview for SCR+Baghouse, cited by one of the commenters (0314) and 

attributed to an analysis from SRP, comes from. 

57 See Table 2 in EPA’s Proposed Rule for total annual cost of SCR+LNB/SOFA projected by SRP. See SRP’s January 20, 

2012 Updated BART Analysis showing visibility benefits from SCR+LNB/SOFA (as sum of maximum incremental 

improvements of 0.54 dv (baseline to LNB/SOFA), 0.29 (LNB/SOFA to SNCR), and 0.44 (SNCR to SCR)). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

effectiveness values cited by the commenter for BART determinations for other facilities as shown in 

the commenter’s graph (i.e., average cost-effectiveness ranged from less than $2,000 per ton to nearly 

$5,000 per ton, and cost per deciview for all facilities was less than $20 million per deciview). 

EPA further notes that in previous EPA BART determinations (e.g., Four Corners Power Plant 

and San Juan Generating Station), EPA did not include $/deciview calculations, therefore, it is unclear 

how the commenter generated its values for $/deciview for these facilities.58 The commenter’s diagram 

included 8 data points representing five facilities, but did not identify which point corresponded to 

which facility, or provide the underlying data for its calculations. For Four Corners, EPA finalized a 

BART determination requiring SCR on Units 1-5 as well as a better than BART alternative that involved 

closure of Units 1-3 and installation of SCR on Units 4 and 5. EPA’s estimated total annual cost of 

BART was $93 million per year and SCR installation on Units 4 and 5 only was approximately $57.5 

million per year.59 EPA’s modeling analysis showed the largest anticipated visibility improvement from 

BART to be 2.85 dv and from the BART Alternative to be 3.76 dv.60 This corresponds to a $/deciview 

value of $33 million per deciview from BART at Four Corners and $15 million per deciview from the 

Four Corners BART Alternative. For San Juan Generating Station, EPA estimated the total annual cost 

of SCR on Units 1-4 to be approximately $30 million per year, and estimated the largest visibility 

improvement to be 3.11 dv, resulting in a $/deciview value of nearly $10 million per deciview.61

Although the $/deciview values for EPA’s BART Alternative for Four Corners and EPA’s BART 

determination for San Juan are generally consistent with the values depicted by the commenter, these 

values are based on EPA’s own estimates for cost and visibility improvement, which differed from those 

provided by the facilities.62 Thus, the commenter’s comparison between SRP’s cost and modeling 

results for NGS, with results for other facilities that are likely based on EPA cost and modeling, is 

misleading, particularly because the comparisons are not an apples to apples comparison and the 

commenter did not provide the basis for its depictions of $/deciview and $/ton estimates for SCR for any 

facility. Notwithstanding the uninformative nature of the commenter’s diagram, EPA notes that NGS is 

not an outlier in the commenter’s diagram because the $/deciview and $/ton estimates that EPA 

provided for SCR at NGS in our proposed rule are consistent with those depicted by the commenter as 

representing those of BART determinations for other facilities. 

Comment: Cost-Effectiveness of Presumptive BART 

 One of the owners of NGS (0348) stated that in establishing presumptive limits in its BART 

Guidelines, EPA recognized that SCR is not cost effective and that combustion controls such as 

LNB/SOFA represent the most cost-effective control options for most boiler types. The commenter 

pointed out that in establishing presumptive limits, EPA considered controls that cost less than 

$1,500/ton to be cost effective, and that the cost effectiveness in $/ton for SCR at NGS, which ranges 

from $3,000 $6,000 per ton based on 2010 estimates, is well above this threshold. The commenter 

58 In the final rulemakings for Four Corners and San Juan, EPA stated that, for several reasons, EPA was not using the 

$/deciview metric for BART purposes, and was considering cost-effectiveness in conjunction with our assessments of the 

modeled visibility benefits of BART controls. See 76 FR 52388 at 52395 (August 22, 2011) and 77 FR 51620 at 51623 

(August 24, 2012). 

59 See Table 15 of the TSD to EPA’s proposed BART determination for Four Corners Power Plant (dated October 19, 2010) 

available at EPA-R09-OAR-2010-0683-0002, at 

http://www.regulations.gov/#!docketBrowser;rpp=25;so=ASC;sb=docId;po=0;D=EPA-R09-OAR-2010-0683 60 See Table 10 in the Supplemental Proposal for Four Corners Power Plant, 76 FR 10530 at 10540 (February 25, 2011). 

61 See Tables 7 and 8 in EPA’s proposed rule for San Juan Generating Station, 76 FR 491 at 503 (January 5, 2011). 

62 See, for example, discussion in Final Rule for FCPP at 77 FR at 51622 and 51629 (August 24, 2012), and discussion in 

Final Rule for SJGS at 76 FR at 52392 to 52396 and 52427 (August 22, 2011). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

concluded on this basis that even if the cost of control options are compared on a $/ton basis alone, EPA 

should have rejected SCR and adopted LNB/SOFA as BART for NGS. 

 Another owner of NGS (0315) also compared EPA’s estimate for the cost-effectiveness of SCR 

to cost-effectiveness values published in EPA documents when the RHR was finalized in 2005. 

According to this commenter, EPA’s cost-effectiveness estimate for SCR+LNB/SOFA at NGS (which 

the commenter asserts is too low) is three to four times higher than the value the EPA determined 

through notice and comment rulemaking to be cost-effective controls (i.e., combustion controls with 

average cost effectiveness of $600 per ton of NOx removed), and significantly higher than the $1,600 per 

ton that EPA determined was not cost effective (citing 70 FR 39131 and the RHR TSD). The commenter 

asserts that this is an arbitrary shift in policy. 

Response:

EPA disagrees with the commenters’ assertion that the BART Guidelines established a threshold 

for cost-effectiveness against which all future BART determinations must compare. 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 costeffectiveness as a means to broadly compare control technologies, not as a threshold for rejecting 

controls for an individual unit or facility that exceed the average cost-effectiveness of combustion 

controls. 

In addition, a comparison of the average cost-effectiveness estimates in the 2005 BART 

Guidelines against EPA’s cost-effectiveness estimates for NGS (based on 2010 or 2013 dollars) is not an 

“apples to apples” comparison. The technical support documentation for the 2005 BART Guidelines63

indicates 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)64 or kilowatt-hour (kW-hr), and then scaled according to 

boiler size. The same commenter has previously dismissed the SCR cost estimates for NGS, developed 

by the National Park Service based on the EPA Control Cost Manual, as being too low (ranging from 

$88 – 96 per kW, which is only slightly lower than $100 per kW used in the 2005 BART Guidelines for 

the presumptive limit analysis) because it is outdated and does not include site-specific costs.65 In 

contrast, Table 5.1 in SRP’s 2009 comment letter estimates capital costs of SCR at NGS ranging from 

63 The technical supporting information is included in the docket for the final rulemaking for the BART Guidelines (EPAHQ-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). 

64 In the 2005 BART presumptive limit analysis, EPA estimated capital cost assuming SCR cost = $100/kW. 65 In the ANPR, in addition to reporting SRP’s cost estimates and EPA’s revisions to SRP’s cost estimates, for reference, 

EPA also reported results from a cost estimate analysis conducted by the National Park Service and provided to EPA during 

consultations with the FLMs prior to our ANPR. SRP provided comments to EPA on the NPS cost estimates reported in the 

ANPR, see section 5.1 (page 29) in document titled “Comment letter from Hayslip, Salt River Project” document ID number 

EPA-R09-OAR-2009-0598-0126. Available at: 

http://www.regulations.gov/#!docketBrowser;rpp=50;so=DESC;sb=docId;po=100;dct=PS;D=EPA-R09-OAR-2009-0598. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

$264 to 356 per kW. The commenter appears to be selectively choosing to accept the EPA Control Cost 

Manual in one case ( to establish the cost-effectiveness from the 2005 presumptive limit analysis to 

serve as a bright line threshold), and reject it in another (for determining cost effectiveness of postcombustion controls at NGS): 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” unrealistically low” value from the EPA Control Cost 

Manual as a threshold to reject post-combustion controls because its updated and 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 or 2013 cost 

estimates is inconsistent with its own criticisms of the EPA Control Cost Manual. 

Comment: Erroneous calculation of incremental cost effectiveness

 A CAP agricultural water users group (0305) asserted that EPA failed to follow the BART 

Guidelines’ procedure for calculating incremental cost effectiveness. The commenter stated that because 

of this failure, EPA erroneously overestimated the incremental cost effectiveness of SCR relative to 

SNCR, arbitrarily and capriciously biasing its factor 1 analysis in favor of SCR. The commenter asserted 

that EPA (1) incorrectly identified the dominant control options and (2) incorrectly calculated 

incremental cost effectiveness. 

 Regarding EPA’s alleged misidentification of the dominant control options, the commenter made 

the following arguments: 

 In its analysis, EPA identified the “least-cost envelope” (dominant) control options as 

LNB/SOFA, SNCR (at 0.015 lb/MMBtu), and SCR (at 0.055 lb/MMBtu), and identified SCR at 

0.08 lb/MMBtu and SNCR at 0.18 lb/MMBtu as inferior control options.

 Nevertheless, EPA did not consider the incremental cost effectiveness of SNCR at 0.015 

lb/MMBtu but rather evaluated the inferior control option of SNCR at 0.018 lb/MMBtu, 

justifying this decision on the fact that SRP indicated that SNCR at NGS would achieve roughly 

0.18 lb/MMBtu. This is arbitrary and capricious because it fails to follow the BART Guidelines’ 

instructions to consider dominant control options in calculating incremental cost effectiveness.

 EPA could properly determine that SNCR at 0.15 lb/MMBtu is not a technically achievable 

control option, and did so in the TSD by accepting SRP’s assertion that this is the case. However, 

EPA should have removed consideration of the control option from its entire five-factor analysis.

 In addition, EPA accepted SRP’s assertion that SNCR at 0.15 lb/MMBtu is not technically 

achievable, but arbitrarily rejected SRP’s assertion that SCR at 0.055 lb/MMBtu is not 

technically achievable. This inconsistency is arbitrary and capricious, and EPA should revise its 

incremental cost effectiveness analysis to ensure that it properly selects and considers only 

dominant control alternatives.

Regarding its contention that EPA incorrectly calculated incremental cost effectiveness, the commenter 

made the following assertions: 

 EPA’s underlying data show that installing SNCR at NGS would have a total annual cost of 

approximately $23.5 million and would reduce NOx emissions between 16,600 and 19,500 tpy, 

while installing SCR at NGS units would have a total annual cost of between $61 and $64 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

million with NOx emission reductions between 26,200 and 28,500 tpy. Thus, on a total 

annualized cost basis, SCR costs more than twice as much as SNCR, and reduces about 50 

percent more emissions. These data contradict EPA’s incremental cost effectiveness calculations, 

because if SCR is truly more efficient at the margin than SNCR, spending twice as much money 

on SCR should result in more than twice the level of emissions reductions. 

 EPA has failed to follow the procedure outlined in the BART Guidelines for proper calculation 

of incremental cost, which require calculation of incremental cost effectiveness between just the 

dominant control options that EPA has identified, and not the inferior options, using the leastcost envelope data. 

 Recalculating incremental cost effectiveness using EPA’s identified dominant control option of 

SNCR at 0.15 lb/MMBtu yields incremental cost effectiveness of $2,128/ton for SNCR versus 

LNB/SOFA and $4,451/ton for SCR versus SNCR. EPA’s erroneous calculations using the 

inferior control option of SNCR at 0.18 lb/MMBtu unduly bias EPA’s incremental cost estimates 

in favor of SCR and against SNCR. 

 The conclusion that EPA’s calculations are incorrect is also supported by EPA’s least-cost 

envelope, which contains a least-cost curve with increasing slope. This means the incremental 

cost effectiveness between dominant control options, which is calculated as the slope of the 

curve, should get progressively greater as they get more expensive. 

 EPA’s conclusion that that SCR is the most incrementally cost-effective control alternative, and 

the incremental cost-effectiveness data underlying it in Table 3 of the February 2013 Proposal, 

are erroneous. 

Response:

 EPA disagrees with the assertions that our calculations of incremental cost-effectiveness were 

erroneous and biased our analysis in favor of SCR. We reported values for incremental costeffectiveness in Table 3 of our Proposed Rule, in Table 15 of the TSD to our Proposed Rule, and 

included the underlying calculations in a worksheet in the docket for this rulemaking.66 The assertions 

stem from cost and cost-effectiveness calculations for SNCR based on two assumptions for the level of 

control SNCR may achieve, i.e., 0.15 lb/MMBtu and 0.18 lb/MMBtu. EPA’s TSD for the Proposed Rule 

included descriptions of the various submittals from SRP. In their original BART analysis, SRP assumed 

that SNCR could achieve an emission rate of 0.20 lb/MMBtu.67 In a subsequent submittal (dated January 

20, 2012), SRP described retaining Fuel Tech Incorporated to develop a computational fluid dynamics 

model to maximize NOx removal from SNCR. SRP included average and incremental cost calculations 

using two potential levels of control with SNCR (at equivalent cost): 0.15 lb/MMBtu and 0.18 

lb/MMBtu. Subsequently, in a letter dated July 20, 2012, SRP indicated that, based on initial testing, it 

expected SNCR to achieve an emission rate of roughly 0.18 lb/MMBtu, and recommended a limit of 

0.20 lb/MMBtu that includes a margin for compliance.68

In our cost-effectiveness analysis for our Proposed Rule, EPA included calculations for SNCR at 

0.15 and 0.18 lb/MMBtu; however, as stated in our TSD and as reflected in Table 3 of the Proposed 

Rule and Table 15 of the TSD, EPA evaluated and reported the average and incremental cost66 See TSD for the proposed rule at EPA-R09-OAR-2013-0009-0014, and document titled “2013_0101 NGS emissions and 

incremental costs.xlsx” in the docket for this rulemaking at EPA-R09-OAR-2013-0009-0004. 67 See, for example, Table 6 in the TSD for the Proposed Rule based on SRP’s January 2009 Revised BART Analysis. 

68 See document titled “2012_0120 SRP Updates NGS BART Report.pdf” in the docket for the proposed rule at EPA-R09-

OAR-2013-0009-0005. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

effectiveness of SNCR at a level of 0.18 lb/MMBtu. This value represents the approximate mid-point of 

the range of options SRP has provided to EPA related to SNCR over time (0.15-0.20 lb/MMBtu) and 

was the level SRP expected to achieve based on initial testing. Although our Proposed Rule and TSD 

evaluated SNCR at 0.18 lb/MMBtu, and our TSD provided an explanation of the chronology and history 

of SRP’s submittals related to SNCR and the rationale for our evaluation of SNCR at 0.18 lb/MMBtu 

instead of 0.15 lb/MMBtu, for completeness, our cost-effectiveness worksheets that we included in the 

docket for our Proposed Rule continued to include evaluations of SNCR at 0.15 lb/MMBtu and 0.18 

lb/MMBtu. 

 The commenter states that EPA evaluated the least-cost envelope for controls for NGS and 

determined the dominant controls to be LNB/SOFA, SNCR at 0.15 lb/MMBtu, and SCR at 0.055 

lb/MMBtu. This is consistent with the graph we developed on the tab titled “least cost envelope” in our 

cost-effectiveness worksheet. The commenters assert that because the graph of the least cost envelope 

excluded SNCR at 0.018 lb/MMBtu from the least cost envelope (i.e., indicating that SNCR at 0.018 

lb/MMBtu was an inferior control option), EPA should not have evaluated SNCR at this control level. 

Similarly, because SCR at 0.08 lb/MMBtu was also not on the least cost envelope, it was also an inferior 

control option that should not have been evaluated. The commenters assert that our decision to evaluate 

the inferior SNCR level (i.e., 0.18 lb/MMBtu) in lieu of the dominant control (i.e., 0.15 lb/MMBtu) was 

inconsistent with the BART Guidelines and arbitrary and capricious given our evaluation of SCR at both 

inferior and dominant levels (i.e., 0.08 and 0.055 lb/MMBtu). 

EPA disagrees with this assertion. SRP’s submissions indicated the possibility that, at equivalent 

cost, SNCR at NGS might achieve emission rates in the range of 0.15-0.18 lb/MMBtu. SRP later 

confirmed, based on initial testing, that SNCR did not perform as well as expected, and that it achieved 

emission rates of approximately 0.18 lb/MMBtu (and recommended a limit of 0.20 lb/MMBtu). The 

actual achievable emission rate associated with SNCR was expected to be controlled by the fluid 

dynamics of air flow in the flue gas and mixing of ammonia as well as acceptable levels of ammonia 

slip, and was not expected to be determined by cost.69 Therefore, for our proposed rule, EPA evaluated 

SNCR at the level SRP indicated was achievable based on their initial testing (i.e., 0.18 lb/MMBtu). 

This was not an arbitrary decision. For SCR, in the TSD for the proposed rulemaking, EPA articulated 

our rationale for determining that SCR systems could be designed for achieving either 0.08 lb/MMBtu 

or 0.055 lb/MMBtu, at differing cost, depending on the design target and the number of layers of 

catalyst initially deployed.70 Therefore, our evaluation of SCR at two different levels of control (at two 

different costs) was also not arbitrary. 

The commenter asserted that our evaluation of SNCR at 0.18 lb/MMBtu unduly biased EPA’s 

incremental cost-effectiveness estimates against SNCR.71 The commenter recalculated incremental costeffectiveness of SCR based on SNCR at 0.15 lb/MMBtu and asserted that the incremental costeffectiveness would have been $4,451 per ton and the incremental cost-effectiveness of SNCR versus 

LNB/SOFA would have been $2,128 per ton. EPA disagrees with the assertion that our evaluation of 

SNCR at 0.18 lb/MMBtu biased our evaluation of SCR or SNCR. As discussed above, EPA’s evaluation 

69 Id, page 3. 70 See Table 14 of the TSD for the Proposed Rule. EPA also notes that SRP had previously stated that it would design the 

SCR system as a 2+2 system with a target of 0.05 lb/MMBtu to meet a limit of 0.08 lb/MMBtu. EPA’s proposed BART limit 

of 0.055 lb/MMBtu was based on a 3+1 system. In their comment letter (as discussed in Section 8.1 of this response to 

comments document), SRP indicated it would design a 3+1 system to meet a design target of 0.03 lb/MMBtu but would still 

require a limit of 0.08 lb/MMBtu. Because EPA and SRP are now in agreement on the 3+1 design of the SCR system, the 

cost estimates for SCR for the final rule are not expected to differ based on the number of initial catalyst layers. 71 We note that EPA could have evaluated SNCR at 0.20 lb/MMBtu, and if we had done so, this level for SNCR would have 

resulted in incremental cost-effectiveness numbers that favored SCR to a greater extent. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

of SNCR at 0.18 lb/MMBtu was reasonable. However, even if we chose to accept the incremental costeffectiveness values calculated by the commenter, it would not change our determination that SCR is 

cost-effective at NGS. 

 The commenter asserts that our calculation of incremental cost-effectiveness is erroneous 

because we calculated incremental cost of SCR+LNB/SOFA to be lower than the incremental cost of 

SNCR+LNB/SOFA, whereas a least-cost curve should be one of increasing slope, therefore, the 

incremental cost of controls should get increasingly greater as the level of controls becomes more 

stringent. A least-cost curve of constantly increasing slope (as depicted in the BART Guidelines) is 

theoretical. EPA’s calculations for incremental cost-effectiveness were mathematically correct. Real 

data for annual cost and annual emission reductions could result in least cost envelopes that look like a 

straight line if incremental cost-effectiveness between controls is similar (e.g., if SNCR does not achieve 

an emission rate as low as expected).72

Similarly, the commenter also asserts that if SCR is truly more efficient at the margin than 

SNCR, spending twice as much on SCR should result in more than twice the level of emission 

reductions compared to SNCR. The commenter appears to confusing average cost-effectiveness and 

incremental cost-effectiveness. Although the commenter references incremental cost-effectiveness, the 

idea that spending twice as much should result in twice the level of emission reductions is actually 

related to average cost effectiveness, not incremental cost-effectiveness. EPA estimated the total annual 

cost of SCR+LNB/SOFA to be $64 million and result in emission reductions of 28,573 tons per year. 

EPA also estimated the total annual cost of SNCR+LNB/SOFA to be $29 million and result in emission 

reductions of 16,608 tons per year.73 EPA agrees that SCR is more than double the annual cost of SNCR 

but does not reduce NOx emissions by more than double that of SNCR. EPA’s calculations reflect this 

because the average cost-effectiveness of SCR ($2,240 per ton) is higher than the average costeffectiveness of SNCR ($1,745 per ton).74 The commenter appears to be concerned that EPA’s 

calculation of incremental cost-effectiveness of SNCR+LNB/SOFA ($4,110 per ton) is higher than 

incremental cost-effectiveness of SCR+LNB/SOFA ($2,933 per ton). The incremental cost-effectiveness 

is a comparison of the costs and performance between two levels of control. In other words, EPA 

calculated the incremental cost-effectiveness of going from LNB+SOFA to SNCR+LNB/SOFA as 

$4,110 per ton (i.e., annual cost of LNB/SOFA is $5 million and reduces NOx by 10,865 tons per year, 

therefore incremental cost-effectiveness between LNB/SOFA and SNCR+LNB/SOFA was calculated 

approximately as [$29 million per year minus $5 million per year] divided by [16,608 tons per year 

minus 10,865 tons per year]). The incremental cost-effectiveness of SNCR+LNB/SOFA is relatively 

high because the total annual cost of SNCR+LNB/SOFA is roughly 6 times higher than LNB/SOFA but 

the total emission reductions from SNCR+LNB/SOFA is only 1.5 times larger than LNB/SOFA. In 

contrast, the incremental cost of going from SNCR+LNB/SOFA to SCR+LNB/SOFA is lower because 

the total annual cost of SCR+LNB/SOFA is roughly 2.2 times higher than SNCR+LNB/SOFA and the 

total emission reductions from SCR+LNB/SOFA is roughly 1.72 times higher than SNCR+LNB/SOFA. 

The commenter is focusing only on the comparison between SCR and SNCR and neglecting the 

72 See “2013 Least Cost Envelope” Tab in the document titled “2014_0304 NGS emissions and incremental costs.xlsx” in the 

docket for this rulemaking. 

73 The commenter cites an approximate annual cost of SNCR at $23.5 million and emission reductions from SNCR between 

16,600 tons per year (i.e., SNCR at 0.18 lb/MMBtu) and 19,500 tons per year (SNCR at 0.15 lb/MMBtu). The commenter 

also cites an approximate annual cost of SCR between $61 to 64 million and emission reductions from SCR between 26,200 

tons per year (SCR at 0.08 lb/MMBtu) and 28,500 tons per year (SCR at 0.055 lb/MMBtu). The commenter’s citations differ 

from EPA’s because EPA evaluated SNCR+LNB/SOFA and SCR+LNB/SOFA. 

74 See Table 3 of EPA’s proposed rule (78 FR at 8281, February 5, 2013). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

comparison between SNCR and LNB/SOFA when attempting to understand incremental costeffectiveness. 

 The commenter recognizes that EPA could have determined SNCR at 0.15 lb/MMBtu was not 

technically achievable and removed it from our analysis. EPA agrees that this would have been less 

confusing. Therefore EPA has removed evaluation of SNCR at 0.15 lb/MMBtu from our revised costeffectiveness spreadsheets based on the updated 2013 cost estimates.75 However, EPA disagrees that our 

analysis was erroneous or arbitrary because it included additional information on SNCR, i.e., SNCR at 

0.15 lb/MMBtu that was generated over the course of our BART analysis, but was later determined to be 

unachievable. 

Comment: Apples-to-oranges comparison of costs

 A CAP agricultural water users group (0305) stated that EPA presented and compared 

inconsistent cost information from EPA and SRP, with the result that the figures appear more consistent 

with each other than they actually are. According to the commenter, it appears that the SRP cost 

information was generated using a theoretical NOx emission limit of 0.08 lb/MMBtu for SCR, while 

EPA used a 0.055 lb/MMBtu limit. To appropriately compare EPA and SRP cost data, EPA should 

revise its cost analysis to present its cost data relating to a NOx limit of 0.08 lb/MMBtu. 

Response: 

 EPA disagrees with the assertion that in our proposed rulemaking, we presented and compared 

inconsistent cost information from EPA and SRP in order to make the values appear more consistent 

with each other than they actually are. In our Rule, we noted that the average and incremental cost 

calculations that were attributed to SRP were indeed based on values submitted by SRP, based on the 

assumption that SCR would achieve an emission rate of 0.08 lb/MMBtu.76 In contrast, the values EPA 

reported for SCR were based on the assumption that SCR would meet an emission limit of 0.055 

lb/MMBtu. As discussed in the TSD for our proposed rule, EPA calculated total and annual costs of 

SCR assuming 3 layers of catalyst (equivalent to a limit of 0.08 lb/MMBtu) and 4 layers of catalyst 

(equivalent to a limit of 0.055 lb/MMBtu). EPA disagrees that it was inappropriate to compare EPA’s 

cost-effectiveness estimate for SCR at 0.055 lb/MMBtu with SRP’s cost-effectiveness for SCR at 0.08 

lb/MMBtu, because both estimates were based on an emission limit each entity has determined is 

achievable with that technology, and the cost associated with that level of control. EPA notes that in our 

cost-effectiveness worksheets included with our Proposed Rule, EPA did calculate cost-effectiveness of 

SCR at 0.08 lb/MMBtu, as recommended by the commenter.77 This value was $2,341 per ton, which is 

(contrary to what the commenter asserted) even closer to the value reported by SRP of $2,926 per ton. 

Therefore, even if we agreed with the commenter, this revised value would not change our 

determination that SCR is cost-effective at NGS. 

Comment: Conclusions on cost 

75 See “2013 Least Cost Envelope” Tab in the document titled “2014_0304 NGS emissions and incremental costs.xlsx” in the 

docket for this rulemaking. 

76 See proposed rule 78 FR 8274 at 8280 and footnote 31. 

77 See tab titled “2010-12 and EPA cost estimates” within document titled “2013_0101 NGS emissions and incremental 

costs.xlsx” at EPA-R09-OAR-2013-0009-0004. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 One of the owners of NGS (0348) stated that regardless of whether EPA considers the 

commenter’s 2010 or 2013 cost estimates, and whether the EPA excludes line items from the total costs, 

it is clear that SCR is not a cost-effective BART control option for NGS. The commenter asserted that 

its previous BART submittals (including the 2012 BART report attached to the comments as Appendix 

K), LNB/SOFA achieves greater incremental visibility improvement than post combustion controls, at a 

fraction of the cost. According to the commenter, the cost of SCR exceeds that of LNB/SOFA by more 

than a factor of 14, and by more than a factor of 28 if baghouses are also required, and LNB/SOFA also 

achieves an emission rate that is well below the presumptive BART limit of 0.28 lb/MMBtu established 

by the EPA for the type of boilers at NGS. The commenter asserted that if EPA had given adequate 

consideration to this information in developing its BART proposal, it would have concluded that SCR 

cannot be justified given its significant cost and the small degree of visibility improvement it would 

provide relative to other BART control options. 

 One tribal government (0039/0317) disagreed with the EPA determination that the average cost 

effectiveness of the combination of SCR+LNB/SOFA versus SNCR+LNB/SOFA, where SCR is nearly 

30 percent higher, is not substantial. 

Response:

 EPA agrees that consideration of 2010 versus 2013 costs and the inclusion of the line item costs 

that EPA excluded from SRP’s cost analysis do not change our overall conclusion on Factor 1. 

However, EPA disagrees with the commenter’s assertion that the conclusion on Factor 1 should be that 

SCR is not cost-effective. EPA proposed that SCR is cost-effective for NGS based on our evaluation of 

the average and incremental cost-effectiveness of SCR. 

Conclusions related to the anticipated visibility improvements (i.e., Factor 5) are discussed in 

more detail in Section 7 of this response to comments document. Although the commenter is correct in 

stating that their January 2012 Updated BART Analysis indicates the incremental visibility 

improvement of LNB/SOFA is greater than the incremental visibility improvement of post-combustion 

controls, EPA notes that the commenter provided incremental visibility improvement from (1) baseline 

to LNB/SOFA, (2) LNB/SOFA to SNCR, and (3), SNCR to SCR. It is also instructive to compare 

LNB/SOFA to SCR (as EPA has done for incremental cost in our proposed rule, e.g., Table 3 in our 

Proposed Rule). The commenter, using its preferred assumptions for the visibility modeling which differ 

from those used by EPA (see Section 7 of this response to comments document), modeled an average 

visibility benefit of 0.37 dv when going from baseline conditions to LNB/SOFA, an incremental 

visibility benefit of 0.15 dv when going from LNB/SOFA to SNCR (at 0.18 lb/MMBtu), and an 

incremental visibility benefit of 0.27 dv when going from SNCR (at 0.18 lb/MMBtu) to SCR (at 0.08 

lb/MMBtu). EPA notes that the commenter modeled an average visibility benefit when going from 

LNB/SOFA to SCR of 0.42 dv, which is greater than the visibility benefit of going from baseline to 

LNB/SOFA. The commenter also reported the largest improvement in visibility (i.e., maximum) was 

0.54 dv when going from baseline to LNB/SOFA, 0.29 dv when going from LNB/SOFA to SNCR (at 

0.18 lb/MMBtu), and 0.44 dv when going from SNCR to SCR (at 0.08 lb/MMBtu). Thus, when going 

from LNB/SOFA to SCR, the largest improvement in visibility is 0.73 dv, which is also larger than the 

visibility benefit of going from baseline to LNB/SOFA. Although incremental visibility improvement 

can be an informative metric, EPA does not find the results of the commenter’s modeling compelling to 

change our conclusion that SCR at NGS is cost-effective and will reduce the impact of NGS on visibility 

impairment at 11 Class I areas. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Regarding the comment that a 30 percent difference between the average cost-effectiveness of 

SNCR+LNB/SOFA and SCR+LNB/SOFA is substantial, EPA notes the average cost-effectiveness of 

SCR+LNB/SOFA at $2,240 per ton. Whether we consider the average cost-effectiveness of 

SCR+LNB/SOFA alone or in comparison to the average cost-effectiveness of SNCR+LNB/SOFA of 

$1,745 per ton, EPA’s determination that SCR is cost-effective at NGS does not change. 

3.2 Other Comments on Factor One 

Comment: Indirect costs should also be considered under Factor 1

 The Gila River Indian Community (0039/0317) asserted that EPA conducted the analysis of costeffectiveness incorrectly by excluding the indirect costs of the requirements and only considering the 

direct cost of the requirements. The commenter asserted that the indirect costs are profound. The 

commenter stated that EPA briefly discussed, but did give serious consideration to the costs associated 

with indirect impacts of our proposed BART determination. 

Response:

 EPA disagrees with the assertion that our cost-effectiveness analysis was incorrect because it did 

not include indirect costs. The BART Guidelines, in the discussion titled “How do I estimate the costs of 

controls?” focuses on the costs of the equipment and other capital and annual costs associated with the 

control technology alternatives, and specifically recommends use of the EPA Control Cost Manual in 

order to maintain and improve consistency, as the basis for equipment cost estimates.78 The EPA 

Control Cost Manual does include “indirect” costs, but these are costs associated with non-equipment 

costs of construction of a given control technology (e.g., engineering and project services, or labor 

costs). Neither the EPA Control Cost Manual nor the BART Guidelines require consideration of the 

monetary value associated with indirect effects in the manner recommended by the commenter (i.e., the 

impact of higher electricity generation costs on CAP water rates and surplus NGS power sales that 

contribute to the Lower Colorado River Basin Development Fund and tribal water settlement 

agreements). Therefore, EPA disagrees that our analysis for Factor 1 was incorrect or incomplete 

because it did not include indirect costs to tribes. 

 EPA further notes that under Factor 2, the energy and non-air quality impacts analysis, the 

BART Guidelines specifically require the energy impact analysis to consider only direct energy impacts 

(e.g., parasitic load from certain control technologies) and to generally exclude indirect energy impacts 

of controls (e.g., energy to produce raw materials for construction of control equipment) unless the 

indirect impact is unusual or significant. We note that under Factor 2, EPA did consider indirect effects 

of control alternatives to tribes and other entities in Arizona that rely on NGS for power, or CAP for 

water. EPA quantified the impact to electricity rates and CAP water rates, and also assessed whether 

installation of SCR would result in electricity generation costs at NGS that exceed the cost to purchase 

power on the wholesale market. Therefore, although EPA appropriately did not consider indirect costs to 

tribes in our analysis of Factor 1, EPA did include consideration of indirect impacts to tribes and other 

entities in our analysis of Factor 2. 

78 See Final BART Guidelines at 70 FR39104 at 39166-7 (July 6, 2005). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

4.0 Comments on Factor 2 – Economic, Energy, and Non-Air 

Quality Environmental Impacts 

4.1 Comments on Economic Impacts 

4.1.1 General Comments on Economic Impacts 

Comment: Comments on potential economic impacts 

 Numerous private individuals (0046, 0050, 0051, 0077, 0106, 0115, 0128, 0145, 0146, 0147, 

0148, 0161, 0167, 0168, 0169, 0193, 0195, 0200, 0203, 0205, 0212, 0221, 0222, 0233, 0224, 0226, 

0229, 0246, 0264.1, 0266, 0272, 0292, 0321, 0382), a public/private coalition (0400), and an industry 

trade association (0278) fear that the imposition of “cost-prohibitive” emission controls would result in 

the closure of NGS and its associated mine (i.e., Kayenta Mine), and many stressed that the loss of jobs 

as a result of these closures would be devastating to the Navajo Nation and Arizona’s economy. One 

commenter (0077) mentioned a study conducted by ASU that researched the economic impact of NGS, 

which revealed that the closure of the plant would shatter the Navajo Nation and Arizona’s economy. 

Other commenters (0233, 0292) noted that this study predicted that the plant will give rise to nearly $20 

billion in economic activity to Arizona and the tribal communities over the next 30 years. Four 

commenters (0229, 0233, 0266, 0292) noted that NGS and its associated mine collectively provide 

upwards of 1,000 jobs – most to members of the Hopi Tribe and Navajo Nation. One private individual 

(0284) stated that the unemployment rate for Native Americans in Arizona is 60 percent. 

 One private individual (0272) believes that the decline in property values in and around Page, 

Arizona is largely due to residents’ fear that NGS will shut down. In addition, two individuals (0138, 

0321) noted that NGS is a large supporter of school programs (e.g., scholarships for college), activities 

(e.g., basketball tournaments sponsor) in the area, and emphasized that without these financial 

contributions many of these programs and events would not be available to students. One of the 

commenters (0321) warned that the closure of NGS would force many families to move, which would 

have a ripple effect on the school system (e.g., reduction in enrollment) and local business that rely on 

plant employees to buy their goods and services. Furthermore, the commenter believes that the plant 

offers Native Americans the ability to bridge the gap between the work world and the traditional Navajo 

world. A community healthcare provider (0018) stated that closure of NGS could threaten the 

commenter’s ability to deliver care in the isolated communities the commenter serves because NGS is a 

strong partner in the community through its support of health outreach for the commenter and other 

social service agencies. 

 A number of commenters (0343, 0017/0289/0320, 0140, 0188, 0234, 0304, 0052, 0306, 0416), 

also described the economic importance of NGS and the Kayenta mine to the State of Arizona, the 

Navajo Nation, and the Hopi Tribe. The commenters typically noted that NGS and the mine provide 

many jobs to Native Americans, and the tribes receive significant revenues from payments associated 

with coal royalties, taxes, permits, lease fees, and scholarships. According to some of these commenters, 

mining activity has provided over 50 percent of the Navajo Nation’s operating expenses in recent years 

and over 80 percent of the Hopi Tribe’s 2009 operating budget. Some of the commenters cited a 2012 

ASU study that determined that NGS and the Kayenta Mine cumulatively will account for more than 

$679 million in adjusted state tax revenues from 2011 through 2044 and will provide 112,720 full-time 

equivalent job years in Arizona during that time period, while indirectly benefiting local businesses. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

One commenter (0142) noted some key points about NGS regarding its economic significance 

including that the plant employs about 520 people and the Kayenta mine employs more than 400 people, 

of which 85 and 90 percent are Native American. According to the commenter, NGS closure, with the 

impact on Kayenta mine, would lead to a loss of close to 3,400 jobs and more than $20 billion in lost 

economic contributions from 2011 to 2044. The commenter stated that EPA must consider these 

economic impacts the regulation will have one the Tribes and the State of Arizona, and the commenter 

said that closing NGS is not an option. In the commenter’s opinion, EPA should give NGS time in order 

to address problems with plant emissions. 

Another commenter (0223) expressed similar concerns about the potential impact of EPA’s 

BART proposal and Alternative 1, stating that associated costs will cripple existing Arizona businesses 

and completely deter others from participating. The commenter asserted that multi-billion dollar 

companies such as Lockheed Martin will not relocate to Arizona if there are any uncertainties with 

regard to the availability of affordable energy and water in the desert. One commenter (0258) also 

expressed concern about the economic impact of the increased costs for water and power in Arizona 

under EPA’s proposal, which the commenter believes would be a devastating blow to an economy that 

is just beginning to emerge from the recession. 

The Navajo Nation (0024/0098/0316/0326) strongly opposes the BART proposal and stated that 

it could threaten the economy and livelihood of the Navajo Nation. The commenter indicated that it has 

previously communicated to EPA that if SCR is required within 5 years, the worst possible outcome 

would be the shutdown of NGS. Should this be the case, the Navajo Nation would lose around $1.02 

billion (2013$) through 2044 in direct payments from NGS, plus additional millions in lost revenues 

from Kayenta Mine. These potential financial losses would be devastating to the Navajo Nation. On the 

other hand, if only one generator would shut down, the Navajo Nation could incur a loss of close to 

$300 million between now and 2044, the commenter said. If LADWP and NV Energy relinquish their 

ownership shares in NGS by 2019, which seems very likely, the commenter said that NGS may have to 

shut down one 750 MW unit and apply SCR to the other units if the Navajo Nation also elects to not 

exercise the option of purchasing a portion of the NGS ownership shares. If this does not happen, the 

commenter would have to use its limited funds and staff time to identify sufficient financial resources 

and support to use its right to acquire a portion of NGS. Due to various different variables, the 

commenter said that it could lose this opportunity to purchase part of NGS. The commenter indicated 

that it does expect to see a loss of about $11 million annually as a result of closing one unit or through 

curtailment of energy production at NGS, but the commenter has committed to making sure the plant 

remains economically viable and the Navajo Nation continues to receive about $33 million in revenue 

until 2044. 

In addition to strongly opposing the BART proposal, the commenter (0316) also indicated that 

the Agency has failed to perform an adequate 5-factor analysis, in particular as it relates to assessing the 

non-air quality impacts associated with coming into compliance. The commenter reiterated that despite 

previous communication from the commenter to EPA that may have been misleading in terms of the 

Navajo Nation’s position on the TWG Agreement, the commenter repeated its strong support of the 

TWG Alternative as a better alternative than the BART proposal and Alternative 1. 

One private individual (0025) asserted NGS does not benefit the Navajo Nation as they are 

paying very little for the use of Navajo land. The commenter believes that, though workers are being 

paid, the only people benefiting are CAP, APS, TEP, SRP, NV Energy, and LADWP. The commenter 

stated that NGS has easily used 20 percent of the electricity for profit instead of going to the CAP 

project. The commenter (0025/0135) also stated that 0177-13 used the old ASU economic study 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

(2/12/12) instead of the newer version that quoted $30 billion that the old ASU economic study said not 

to use on the Navajo Nation.79

A council delegate for several chapters of the Navajo Nation (0362) asserted that the Navajo 

Nation does not need NGS, indicating that in the first 25 years, the Navajo Nation was given only 

$160,000 a year for the use of about 766 acres of land, and the second 25 years began with $608,400 a 

year until 2011 when half of what was paid to the State of Arizona in taxes was provided to the Navajo 

Nation. The commenter concluded that the benefit to the Navajo Nation is now only about $3 million a 

year until 2020 and that the Navajo Nation does not critically need the NGS revenue. 

Response:

 Although there may be some disagreement by others about the relative importance of NGS to the 

Navajo Nation (contrasting comments from e.g., 0362 and 0316), EPA recognizes that NGS and the 

Kayenta Mine contribute economically to the Navajo Nation, the Hopi Tribe, tribes and communities 

that use CAP water, and other communities in Arizona, such as the city of Page. In our Proposed Rule, 

we recognized that the concerns expressed by numerous commenters on the ANPR was that a stringent 

BART determination would force NGS to close. In our Proposed Rule, under Factor 2, we included an 

analysis that showed that the installation of SCR on all three units by 2018 would not cause the cost of 

electricity generation at NGS to exceed the cost to purchase wholesale power on the open market. In 

other words, our analysis shows that it would be more economical for NGS to install SCR and continue 

operating than it would be to close and purchase power on the wholesale market. As described in 

responses to other comments on EPA’s Affordability Analysis, EPA has updated the analysis and the 

results still show that our final BART determination requiring compliance with an emission limit 

achievable with SCR in 2019 would not cause the cost of electricity generation at NGS to exceed the 

cost to purchase wholesale power on the open market. This analysis and supporting documents were in 

our docket for our proposal. Comments related to other aspects of our five-factor analysis and the TWG 

Agreement are discussed elsewhere in this responses to comments document. 

Comment: Contribution of Class I areas to local and state economy 

 Several individuals (0091, 0181, 0240, 0264.8, 0288, 0327, 0360, 0366, 0388, 0405, 0432) 

support additional controls on NGS because they believe that visibility at national parks and wilderness 

areas is important to safeguard tourism and the economic vitality of Arizona, local and tribal 

communities, and nearby states. 

 One environmental advocacy group (0373) stated that rigorously addressing visibility-impairing 

pollutants will have a positive impact on U.S. national parks and wilderness areas, which are of great 

natural and cultural value and are also engines for sustainable local capital. The commenter indicated 

that in 2008, National Park Service units received over 274 million visits accounting for over $2.5 

billion in revenue. Quoting an exhibit submitted with the comments, the commenter stated that national 

parks support $13.3 billion in local private-sector economic activity and 267,000 private-sector jobs; 

79 The commenter attached to Comment 0135 a proposed Navajo Nation Council resolution with tracking number 0177-13, 

the subject of which is the renewal of NGS’s lease. Attached to the resolution is the ASU economic study dated February 12, 

2012, which addresses the economic impact of NGS and Kayenta mine on the State of Arizona. In Comment 0025 the 

commenter presented quotes from this ASU report indicating that additional study would be needed to quantify the economic 

impact on the Navajo Nation. Such a study was subsequently carried out by ASU with findings published in an April 2013 

report. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

attract businesses and individuals to the local area, resulting in economic growth in areas near parks that 

is an average of 1 percent per year greater than statewide rates over the past three decades; and generate 

more than four dollars in value to the public for every tax dollar invested. The commenter asserted that 

tourism is a critical component of the economies of Arizona, Utah, and the Southwestern United States, 

giving the example that, in 2010, Grand Canyon National Park generated over 4.3 million recreation 

visits, in excess of $428 million in local spending, and more than 6,100 jobs (citing an exhibit submitted 

with the comments). 

 One public interest advocacy group (0404) representing the Taxpayer Association of Kane 

County, Utah, stated the largest economic source in the county is tourism. Tourists come to the area to 

visit Lake Powell and the Grand Canyon. However, the commenter asserts that the polluted air 

stemming from NGS has a negative impact on the tourism industry where the haze from NGS often 

covers the sky preventing people from viewing the beautiful vistas. 

Response:

 EPA agrees that National Parks and Wilderness Areas are important natural and cultural 

resources that contribute to tourism and economic vitality in the southwestern United States. Generally 

consistent with information provided by the commenters, in our Proposed Rule, we noted that the 11 

Class I areas located within 300 km of NGS support an active tourism industry drawing over 4 million 

visitors to the Grand Canyon National Parks alone in 2011.80

Comment: Give more consideration to economic impact of SCR

 Many private individuals (0026, 0036, 0042, 0044, 0045, 0046, 0048, 0050, 0051, 0053, 0054, 

0069, 0070, 0075, 0077,0078, 0079, 0081, 0086, 0088, 0099, 0109, 0115, 0117, 0119, 0128, 0132, 0133, 

0145, 0146, 0147, 0148, 0160, 0161, 0163, 0165, 0167, 0168, 0170, 0193, 0200, 0203, 0205, 0208, 

0212, 0221, 0226, 0232, 0233, 0266, 0298, 0307, 0329, 0330, 0335, 0346, 0358, 0437), a government 

commenter (0406), and a public/private coalition (0400) urged EPA to give more consideration to the 

economic impacts, especially increases in water and energy rates, that this rule will have on Arizona 

residents (i.e., users of CAP water, and agriculture and tribal communities), in addition to its impact on 

water policy in Arizona. One commenter (0221) indicated that the cost of installing SCR at NGS would 

increase the price of power by 0.39 to 0.48 cents per kilowatt-hour, and potentially raise water rates for 

CAP users as much as 13 to 16 percent. Another commenter (0088) suggested that the NPS increase its 

fees to pay for costs of controls, since regional haze rules are intended to improve visibility at parks, 

instead of requiring energy rates to increase for roughly 6 million Arizonans. One private individual 

(0212) stated that rate increases would negatively impact people living on fixed incomes. 

 Numerous private individuals (0046, 0086, 0088, 0145, 0146, 0147, 0148, 0161, 0163, 0165, 

0167, 0168, 0193, 0200, 0203, 0205, 0212, 0221, 0226, 0233, 0266, 0298, 0307, 0437), government 

commenters (0324, 0406, 0443), a public/private coalition (0400), and an industry trade association 

(0278) emphasized that NGS is responsible for supplying about 90 percent of the power used by CAP to 

pump water from the Colorado River across Arizona. One commenter (0307) stated that the plant sells 

its excess power to help defray the repayments to the federal government for the construction of the 

CAP system, and argued that EPA’s proposed rule would hinder the selling of this power; thus, 

increasing the financial burden of the plant and Arizonans. One of these commenters (0046), along with 

80 See Proposed Rule 78 FR at 8275 (February 5, 2013) and footnote 1. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

another private individual (0069), suggested that CAP has the opportunity to research alternative fuel 

sources, so that it can continue to supply Arizonans with reliable and affordable water. 

One commenter (0087) expressed concern about water rate increases as a result of the 

rulemaking. The commenter referred to the water settlement agreement between the U.S. and the Gila 

River Indian Community in 2004. The commenter stated that agreement entitled the Community to over 

300,000 acre-feet of water from CAP. In addition, the commenter stated that the agreement also 

committed substantial funds from the U.S. towards constructing and repairing irrigation infrastructure in 

order for the Community to use its CAP allocation. The commenter asserted that if EPA moves forward 

with the proposal it could make the investment useless by making the water too expensive for the 

Community to purchase. Other tribes with similar CAP allocations could also be negatively impacted 

because of the higher cost of water and also because tribal subsidies set aside to offset those costs would 

run out faster. Some commenters noted that not only will Native American communities be affected, but 

non-Indian communities, like farmers, will also be impacted by the regulation, and will be forced to use 

more groundwater. The commenter asserted that in some cases, it is possible that groundwater pumping 

will double, and counteract decades of sustainable water policy, the commenter said. Furthermore, 

families struggling to get back on their feet would also be negatively affected by the increase in water 

rates. 

 One private individual (0115) highlighted that Arizonans live in the desert and low water rates 

are essential for maintaining an overall quality of life, particularly for farmers and manufacturers. 

Similarly, one private individual (0117) argued that an increase in water rates would limit the financial 

resources that local businesses and utility companies have available to hire more employees. This 

commenter (0117) and another private individual (0168) warned that companies looking to relocate may 

look past Arizona for a state with an environment more conducive to businesses. In contrast, one private 

individual (0264.7) argued that prime agriculture land in Arizona has vanished over time due to urban 

sprawl and the desire for low water and electricity rates. 

 Six private individuals (0038, 0040, 0083, 0177, 0204, 0388) are willing to pay higher energy 

costs for a healthier environment. One of these commenters (0083) stated that NGS is not obligated to 

produce cheap power and suggested that they charge a rate that will pay for the true operating costs of 

producing the electricity, thus allowing the plant to stay in operation. 

 One public/private coalition (0381) in Pinal County, Arizona, expressed significant concern that 

the cost of SCR would represent a tremendous economic burden. The commenter asserted that Pinal 

County is the fastest growing county in Arizona, contains a significant amount of irrigate farmland and 

relies heavily on CAP. Therefore, commenter concludes that the cost implications of requiring SCR 

would hinder economic recovery and future development in Arizona and Pinal County. This sentiment 

was echoed by other comments, including comments from chamber of commerce representatives (0140, 

0188, 0234, 0304), an industry/commerce trade association (0084), two CAP water distributors (0194, 

0214), two associations of CAP water distributors (0252, 0398), and a consultant (0262), who expressed 

concern that EPA’s proposed rule would place a tremendous economic burden on energy and water 

users in Arizona. For example, one commenter (0234) noted that Flagstaff’s total cost of living is 

currently 15.6 percent above the national average, based on a cost of living index study prepared on a 

quarterly basis by the Greater Flagstaff Chamber, and 56.7 percent above the national average for the 

cost of housing, which they believe would worsen if NGS shuts down. Another commenter (0282) noted 

that many small businesses (i.e., mom-and-pop shops) depend on affordable energy and water rates and 

warned that these businesses may not be able to survive if these rates increased. One commenter (0304) 

claimed that EPA’s proposed rules would increase rates by 20 percent or more. The industry/commerce 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

trade association (0084) indicated that water rates could double or triple, which will prevent small 

businesses from hiring and reduce the disposable income of consumers, further harming small 

businesses. 

 The association of CAP water distributors (0398) stated that EPA discounted the economic 

consequences that will arise if NGS is forced to shut down due to regulatory costs and failed to properly 

assess the harm a shutdown would cause to the state. This commenter urged EPA to address what the 

commenter believes are incontrovertible economic impacts to central Arizona, central Arizona 

agriculture, and the Navajo and Hopi tribes. 

 Several local government commenters (0175, 0189, 0201, 0207, 0213, 0263, 0293, 0295), 

although supportive of clean energy initiatives, said the cost of installing and operating SCR would 

place a tremendous economic burden on energy users in the State of Arizona, and specifically on CAP 

users and could jeopardize the continued operation of NGS. One local government commenter (0220) 

said that costly additional controls to NGS should not be mandated by EPA at the expense of Arizona 

ratepayers. A number of Arizona local government commenters emphasized how in the recent years, 

many cities have faced severe economic challenges. 

One individual (0025/0125) asserted that although SRP says it cannot afford SCR, it just 

invested $371 million in the Mesquite Power in Arlington, Arizona, and is deliberately violating federal 

law by not installing the SCR. The commenter also urged EPA not to allow NGS 10 years to install 

SCR. 

One individual (0091) stated that although EPA’s cost analysis shows that the installation of 

SCR at NGS would increase the cost of electricity generation by 16 percent, the commenter believes that 

this is less costly than purchasing electricity on the wholesale market from elsewhere in the West, and 

suggested that NGS explore alternative energy sources, such as wind and solar to offset this rise in cost. 

 Several representatives of the Arizona state legislature (0082, 0085, 0087, 0095, 0097, 0104, 

0105) voiced concern over regulating NGS, which they believe will have devastating effects on the State 

of Arizona. Some of the commenters said that NGS is a vital component of the state, which provides 

affordable energy to CAP, which in turn provides affordable water to 80 percent of the population of 

Arizona. The commenters assert that requiring controls on NGS could cost as much as $1.1 billion and 

could cause the plant to shut down. Some of the commenters referred to the ASU report, which indicated 

that the regulation could cause a loss of 3,400 jobs per year and close to $20 billion in lost economic 

activity over the next three decades. One commenter (0105) said that it has reviewed the reports 

available on the expected benefits from the regulation in terms of decreasing NOx emissions and reduce 

haze over the Grand Canyon and said that it questions the projections and analysis stating that there is a 

lack of evidence that the regulation will have noticeable results. Other commenters also said that it is 

questionable whether NGS is responsible for perceptible haze above the Grand Canyon. Some of the 

commenters referred to the NREL report which did not conclusively indicate that additional controls 

would lead to improved perceptible visibility. One commenter (0085) was perplexed why EPA would 

require such costly controls on a plant so important to the livelihood of the State of Arizona without firm 

evidence that controls are guaranteed to improve visibility. One commenter (0087) stated that regardless 

of the actual visibility improvements that would be achieved, all parties agree that costs would increase 

substantially. In general, the commenters assert because NGS is vital to the State of Arizona and closure 

of the plant would impact the well-being of the state, commenters urged EPA to abandon the proposed 

rule and conduct a thorough analysis that considers the indirect economic implications of the regulation. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Response:

EPA recognizes that NGS and the Kayenta Mine contribute economically to the Navajo Nation, 

the Hopi Tribe, tribes and communities that use CAP water, and other communities in Arizona, such as 

the city of Page. As mentioned above, in our Proposed Rule, we recognized the concerns expressed by 

numerous commenters on the ANPR that a stringent BART determination would force NGS to close. In 

our Proposed Rule, under Factor 2, we included an analysis that showed that the installation of SCR on 

all three units by 2018 would not cause the cost of electricity generation at NGS to exceed the cost to 

purchase wholesale power on the open market. In other words, our analysis shows that it would be more 

economical for NGS to install SCR and continue operating than it would be to close and purchase power 

on the wholesale market. As described in responses to other comments on the affordability analysis, 

EPA has updated the analysis and the results still show that our final BART determination requiring 

compliance with an emission limit achievable with SCR in 2019 would not cause the cost of electricity 

generation at NGS to exceed the cost to purchase wholesale power on the open market. 

In our Proposed Rule, EPA also calculated and considered the cost increases associated with 

SCR on SRP electricity rates and CAP water rates. We projected an electricity rate increase to SRP 

customers of 0.66 percent, a water rate increase to CAP municipal and industrial (M&I) customers of 6 

percent, and a water rate increase to tribal and agricultural water users of 14 percent. Although the actual 

amount of the rate increase of $8.40 per acre-foot was projected to be the same for all users (i.e., M&I, 

tribal, and agricultural), the percent increase was higher for tribal and agricultural water users because 

these users pay less for water than M&I users.81 As stated in our Proposed Rule, EPA recognizes that 

water rate increases are critical issues to many stakeholders, including numerous tribes, and EPA 

considers the potential economic impacts to argue for flexibility in the compliance timeframe for NGS.82

Comments related to other aspects of our five-factor analysis, including consideration of indirect 

costs, and anticipated visibility benefits, as well as the TWG Agreement, are discussed elsewhere in this 

response to comments document. 

Comment: Impact to the Lower Colorado Basin Development Fund

One commenter (0348) stated that the increased cost of production (with the SCR capital cost 

included) would result in less competitive wholesale sales from surplus generation at NGS – revenue 

that flows into the Lower Colorado River Basin Development Fund (LCRBDF, or Development Fund). 

The commenter noted that CAP officials have estimated that the fund would be at risk of losing 

approximately $175 million over the 2016-2036 timeframe, and $1.2 million per year, thereafter. 

Another commenter (0384) stated that the increasing cost of production at NGS resulting from 

substantial SCR capital investment will likely have a negative impact on the Development Fund..The 

commenter asserted that increased cost will result in the need to raise NGS prices, thus lessening its 

competitiveness in the wholesale power market and that as less NGS surplus is sold due to its 

competitive disadvantage, less revenue flows into the Development Fund. The commenter stated that the 

annual loss to the Fund would be approximately $6.6 million with a NPV of over $82 million over a 25-

year time horizon. 

81 See Proposed Rule at 78 FR at 8283 and Table 6 (February 5, 2013). 

82 Id. at 8284. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Response:

 As discussed briefly in our Proposal Rule and in more detail in the TSD to our Proposed Rule, 

EPA recognizes that any electricity owned by Reclamation based on is 24.3 percent participation in 

NGS that is not used by CAP is sold and revenues are deposited into the Development Fund.83 This fund 

is authorized to pay the delivery portion of the cost of CAP water for certain Indian tribes and to pay the 

cost of constructing delivery systems to bring CAP water to certain Indian tribes.84 EPA considers the 

potential economic impacts to the Development Fund, in addition to other potential economic impacts to 

tribes, to argue for providing flexibility in the compliance timeframe for NGS. 

Comment: Impact to tribal agriculture is overstated 

 One private individual (0158) asserted that the Gila River Indian Community employs only two 

agricultural workers and that most of the Gila River farmland is not being used. The commenter added 

that the Salt River Indian Community does not employ any agricultural workers and that the Salt River 

Indian Community does not have a water crisis. The commenter asserted the Ak-Chin Indian 

Community employs five agricultural workers and that Ak-Chin is converting farmland for other uses 

(e.g., for its casino and resort). The commenter concluded that these tribes would not be economically 

impacted if SCR and baghouses are installed at NGS. 

Response:

 Although the commenter asserts that the importance of farming and agriculture to several tribes 

may have been overstated, EPA notes that regardless of the level of farming, the Gila River Indian 

Community, the Salt River Indian Community, and the Ak-Chin Indian Community all have allocations 

of CAP water through settlement agreements that were approved as acts of Congress, and that potential 

increases in CAP water rates are important economic considerations to these tribes. 

Comment: Economic impact on Arizona mining industry 

 One industry trade association (0306) indicated that the mining industry in Arizona would be 

particularly hard hit by the BART proposal because it is an energy-intensive industry and a significant 

water user. The commenter noted that the Arizona copper industry employed about 12,100 people and 

had an estimated direct and indirect impact on the Arizona economy of nearly $5 billion in 2012. The 

commenter believes that the increased electric and water costs associated with the proposed BART, and 

particularly with NGS closure, would adversely affect the mining industry and the Arizona economy as 

a whole. 

 The commenter (0306) stated that many of its member companies rely both on NGS electricity 

and CAP water, so increased water and electric rates would create a cumulative effect and adversely 

affect profitability. The commenter indicated that because its mining company members operate in a 

global market which determines the prices for their products, they cannot pass increased electricity and 

water costs on to their customers. According to the commenter, such price increases threaten the 

competitiveness of these companies on the global market. 

83 See Proposed Rule at 78 FR at 8282 (February 5, 2013) and TSD at pages 71-72. 

84 See Proposed Rule at 78 FR at 8283 (February 5, 2013). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Response:

 EPA did not specifically consider the potential economic impacts to the mining industry in 

Arizona in our Proposed Rule. Although we do not interpret the BART Guidelines to require 

consideration of indirect costs and impacts of controls, we recognize and acknowledge that other 

stakeholders may be affected by this rulemaking in addition to tribes and other groups discussed in our 

proposed rules. As stated elsewhere, EPA considers the potential economic impacts to tribes to argue for 

flexibility in the compliance timeframe for NGS. This flexibility also benefits other stakeholders, 

including the mining industry in Arizona. 

Comment: Specific Impacts to Tucson Electric Power (TEP) 

One of the owners of NGS (0314) stated that its share of installing SCR on all three NGS units 

would cost $49 million, which could double if permitting requires baghouses to reduce particulate 

emissions. The commenter indicated that it is also an owner participant in FCPP (7 percent of Units 4 

and 5) and SJGS (50 percent of Units 1 and 2), for which EPA has already finalized BART 

determinations requiring installation of SCR, so that the commenter is potentially facing about $320 

million in capital expenses over the next 5 years based on the conventional regulatory compliance 

schedule. The commenter believes that these costs would result in significantly higher electricity costs 

for its customers (a rate impact approaching a 4 percent increase) at a time when Tucson is struggling to 

recover from the economic stagnation of the recent recession, placing an economic hardship on the 

customers and making recovery more difficult. The commenter further noted that most of its customers 

are also customers of Tucson Water, which relies on CAP for over 75 percent of its water, and CAP has 

estimated that SCR at NGS could result in an increase in water rates of 33 percent. 

Response:

 EPA recognizes that Tucson Electric Power is a participant in other coal-fired power plants in 

the southwestern United States that are subject to BART. EPA notes that our BART determination does 

not require installation of baghouses and that in our Proposed Rule we estimated a six percent increase 

in water rates from SCR installation at NGS for industrial customers (assuming 100 percent reliance on 

CAP water). As stated elsewhere, EPA considers the potential economic impacts to tribes to argue for 

flexibility in the compliance timeframe for NGS. This flexibility also benefits other stakeholders, 

including the customers of Tucson Electric Power and Tucson Water. 

Comment: Installation of pollution controls creates jobs 

 One environmental advocacy group (0373) stated requiring installation of pollution control 

technologies creates jobs, noting that each installation creates short-term construction jobs as well as 

permanent operations and management positions (citing an exhibit submitted with the comments). 

Response:

 EPA agrees that jobs will likely be associated with construction and installation of air pollution 

control technologies. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Comment: Requiring SCR may force NGS to close

One commenter (0348), the operator and co-owner of NGS, stated that should EPA require SCR 

on all units, its decision will put at risk the future viability of the NGS units and threaten the delivered 

cost of water to CAP users since substitute and more costly power would be necessary to replace lost 

NGS power. The commenter (0348) disagreed with EPA’s assertion that should a BART determination 

require SCR, NGS would not shut down since the cost of market replacement power would be more 

expensive than the increased cost of production at the generating station. In the case of NGS closure, the 

commenter stated that the effective replacement substitute would be a new base load power plant, most 

likely gas-fired. The commenter suggested that EPA had relied on forecasted short-term (spot market) 

values in its comparison of substitute cost of NGS generated power. Thus, the commenter asserted that 

the more relevant cost comparison is that of a newly built power station and, thus, accordingly, the 

analysis of short-term market values as undertaken by EPA presented a skewed cost comparison 

outcome. 

The commenter (0348) noted the complexity of decision making at NGS because it has multiple 

owners, each with its own specific cost structure and factors that filter into its decision-making. The 

commenter asserted that EPA failed to acknowledge or recognize these diverse and complicating factor 

in arriving at any ‘consensus’ at to new and substantial capital investment at NGS. The commenter also 

asserted that the pending departure of LADWP and NV Energy (in 2019) was another factor in how 

decisions to meet required upgrades will be difficult to reach in a timely manner. The commenter 

claimed that, in addition to the complexities arising from multiple ownership, there exist considerable 

uncertainties regarding additional factors that will affect the plant’s operation and future cost and that 

items such as pending lease negotiations with the Navajo Nation, rights-of-way agreements, and other 

such factors make the timing of an SCR mandate critically important. 

The commenter (0348) added that the Bureau of Indian Affairs must also approve the amended 

lease but cannot do so until all Federal actions have been completed and that the required Federal review 

process will necessitate the coordination of 10 or more Federal agencies and 15 Native American Tribes. 

The commenter stated that only after these actions are completed will a Record of Decision (ROD) be 

issued and the Secretary of the Interior approval obtained, adding that the ROD is subject to litigation 

should any party of interest challenge the findings. The commenter asserted that before any NGS owner 

agrees to invest in environmental upgrades, all this will need to be resolved. Because of the complexities 

and number of parties involved, the commenter stated that a BART finding requiring SCR before the 

2024-26 timeframe is likely to result in NGS participants unwilling to invest since the likelihood of 

closure on the uncertainties is unlikely. 

Another owner of NGS (0314) stated the February 2013 Proposal presents significant challenges 

and risks with regard to the commenter’s resource planning by handicapping its ability to costeffectively respond to changing conditions. The commenter noted that some of these uncertainties have 

the potential to change the economic viability of its generating resources, such as the impacts of 

potential future regulations, future fuel prices, and customer load growth/decline (accounting for energy 

efficiency and distributed generation). The commenter indicated that implementation of the BART 

proposal would require the NGS owners to decide between making a significant capital investment in 

the plant or allowing the plant to close by 2019; if the NGS owners elected to install controls to meet 

BART, recovering that cost could only be achieved through long-term operation of NGS which would 

have the effect of locking NGS into the commenter’s generation portfolio for a considerable period of 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

time or risking stranding those investments. According to the commenter, this loss of flexibility would 

hamper the commenter’s ability to respond to the following future scenarios: 

 Changes in the economic viability of coal resources due to the increasing costs of environmental 

regulations, including carbon limits. 

 Changes in 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 use to energy efficiency and demand response programs. 

The commenter (0314) stated that the more likely alternative is that the NGS owners could decide that a 

substantial investment in NGS cannot be justified given current regulatory uncertainties related to the 

lease and rights of way renewals. The commenter noted that NGS is just one of its coal-fired assets that, 

according to the commenter, are currently facing the risk of premature retirement. The commenter 

indicated that it has already proposed to reduce its reliance on coal by over 30 percent and an additional 

30 percent is at risk of premature retirement. The commenter believes that replacing this level of base 

load generation over a relatively short period will require a significant capital investment, with 

correspondingly significant impact on customer rates. 

 The commenter (0314) asserted that this loss of flexibility and associated risk to the commenter 

and its customers is unnecessary given that the regional haze program is intended to make gradual 

reductions in emissions over a decades-long period. The commenter believes that EPA should recognize 

the NOx reductions already made at NGS as BART, then further reductions could be made at the plant 

(including possibly SCR) over subsequent planning periods. The commenter indicated that this approach 

would have the benefits of reducing the immediate financial burden on its customers, allowing time for 

greater certainty in terms of potential carbon limits and customer demand, and retaining greater 

flexibility in future resource decisions. 

Response:

 EPA has provided responses to specific comments on the Affordability Analysis in section 4.1.2 

of this response to comments document. EPA disagrees that we failed to acknowledge and consider the 

complexities in reaching a consensus between the owners in making new capital investments at NGS. In 

our Proposed Rule, EPA outlined the uncertainties that significantly increase the financial risk of nearterm investments in new air pollution controls, including uncertainties in plant ownership and lease 

agreements.85 EPA also highlighted the importance of continued operation of NGS and the Kayenta 

Mine to the Navajo Nation and Hopi Tribe as well as the importance of Reclamation’s share of NGS to 

supply water to many tribes located in Arizona in accordance with several water settlement acts. Based 

on the existing uncertainties and the importance of NGS to tribes, EPA proposed to determine that 

compliance flexibility is necessary or appropriate and put forth a framework for providing additional 

flexibility in the compliance timeframe for alternatives to BART. EPA recognized the NOx reductions 

already made at NGS as a credit for the early and voluntary installation of LNB/SOFA in the framework 

for BART Alternatives. 

Comment: Closure of NGS will raise water costs for all water users, cause economic harm, and 

threaten administration of water rights defined by the AWSA 

85 See Proposed Rule at 78 FR at 8278 (February 5, 2013) and references therein. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

One public sector commenter (0343) stated that the shutdown of NGS, as a result of a 

requirement to install SCR, would more than double the current CAP energy rate, the impact of which 

would fall disproportionately on tribal and non-tribal agricultural users, but also significantly on 

municipal and industrial users. The commenter stated that demand for CAP water is elastic especially 

for Indian and non-Indian agriculture. In response to large increases in water cost, the commenter 

asserted that agricultural users within CAP’s service territory would turn to the less-expensive option of 

pumping groundwater, and that those without sufficient groundwater pumping capacity would be forced 

to take their land out of production. 

Several tribal governments (0039/0317, 0419) similarly expressed in its comments that Indian 

tribes are disproportionately impacted by this regulation due to the social and economic conditions of 

the Indian population. Because Indian tribes receive water from CAP, they are affected by the increase 

in water prices and also affected via the Development Fund. The commenter expressed that EPA does 

not believe power prices will increase above current levels and therefore not impact the Development 

Fund. However, the commenter does not agree with EPA and argued that the Development Fund would 

suffer from the regulation. The commenter asserts that choosing either of the alternatives presented in 

the February 2013 Proposal as BART would restrict or remove the Community’s right to receive and use 

water guaranteed by AWSA, make it difficult or impossible to pay for CAP and interfere with the 

crucial Development Fund revenue stream. One commenter (0419) discussed the history of water 

contracts, details on the entitlement of water from the Colorado River, and other agreements relating to 

tribal water rights. The commenter stated that the U.S. has an obligation to prevent regulatory 

requirements that would interfere with the Tribes’ contractual rights to CAP water, funding for tribal 

infrastructure and water development, and funding assistance from NGS revenue and the Development 

Fund. 

The public sector commenter (0343) also stated that the impact on municipal and industrial 

customers would be significant and, although these users already pay a high cost for CAP water, the 

percentage increase would be less than that experienced by agricultural users. The commenter believes 

that in order to fund the higher power costs that would result if NGS were closed, municipal and 

industrial users would be required to make new capital payments that were previously supported by 

sales of excess NGS power when power market conditions permitted. The commenter referred to the 

NREL study, which the commenter quoted as indicating that a $29 per acre-foot incremental charge for 

CAP repayment would accrue to municipal and industrial users in the event that NGS were to close. 

Response:

In our Proposed Rule, we recognized that the concerns expressed by numerous commenters on 

the ANPR was that a stringent BART determination would force NGS to close. In our Proposed Rule, 

under Factor 2, we included an analysis that showed that the installation of SCR on all three units by 

2018 would not cause the cost of electricity generation at NGS to exceed the cost to purchase wholesale 

power on the open market. In other words, our analysis shows that it would be more economical for 

NGS to install SCR and continue operating than it would be to close and purchase power on the 

wholesale market. As described in responses to other comments on the affordability analysis, EPA has 

updated the analysis and the results still show that our final BART determination requiring compliance 

with an emission limit achievable with SCR in 2019 would not cause the cost of electricity generation at 

NGS to exceed the cost to purchase wholesale power on the open market. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

In our Proposed Rule, EPA also calculated and considered the cost increases associated with 

SCR on SRP electricity rates and CAP water rates. We projected an electricity rate increase to SRP 

customers of 0.66 percent, a water rate increase to CAP municipal and industrial (M&I) customers of 6 

percent, and a water rate increase to tribal and agricultural water users of 14 percent. Although the actual 

amount of the rate increase of $8.40 per acre-foot was projected to be the same for all users (i.e., M&I, 

tribal, and agricultural), the percent increase was higher for tribal and agricultural water users because 

these users pay less for water than M&I users.86

As discussed briefly in our Proposal Rule and in more detail in the TSD to our Proposed Rule, 

EPA recognizes that any electricity owned by Reclamation based on its 24.3 percent participation in 

NGS that is not used by CAP is sold and revenues are deposited into the Development Fund.87 This fund 

is authorized to pay the delivery portion of the cost of CAP water for certain Indian tribes and to pay the 

cost of constructing delivery systems to bring CAP water to certain Indian tribes.88 EPA considers the 

potential economic impacts to the Development Fund, in addition to other potential economic impacts to 

tribes, to argue for thoughtful consideration of how flexibility can be provided consistent with the air 

quality goals of the CAA. 

Comment: EPA should evaluate cumulative economic impact of other rulemakings 

 One commenter (0306) asserted that the BART proposal must take into account the context in 

which the regional haze rules are being implemented. The commenter noted that the two remaining 

copper smelters in Arizona are already subject to BART for SO2 and they also have to make significant 

capital investments to comply with other regulatory programs and initiatives such as the revised SO2

NAAQS. The commenter believes that as part of a proper cumulative impact analysis, EPA should 

consider the existing regulatory cost burden as aggravated by the additional water and electricity costs 

for mining, beneficiation, and mineral processing facilities; that is, the total cost impact of EPA’s 

regulatory initiatives that must be considered. 

Response:

 EPA disagrees with the assertion that we must consider the total cost impact of all EPA 

regulatory requirements in a BART analysis. EPA recognizes that other facilities, whose water and 

electricity rates may be affected by our BART determination for NGS, may also be subject to BART for 

their own emissions of visibility-impairing pollutants. However, we note that BART is a case-by-case 

determination that is based on a source-specific analysis of five factors, as required under the CAA. The 

BART Guidelines do not require consideration of the context in which BART determination is made, 

i.e., it does not require consideration of indirect impacts or cumulative impacts of other rulemakings. 

4.1.2 Comments on the EPA’s Affordability Analysis 

Comment: EPA incorrectly assumes that NGS will not close because power supplies are always 

available from the wholesale power market

86 See Proposed Rule at 78 FR at 8283 and Table 6 (February 5, 2013). 

87 See Proposed Rule at 78 FR at 8282 (February 5, 2013) and TSD at pages 71-72. 

88 See Proposed Rule at 78 FR at 8283 (February 5, 2013). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 The Gila River Indian Community (0039/0317) asserted that EPA made the incorrect assumption 

that wholesale power, sufficient in volume to replace NGS output if NGS were to shut down, will 

always be available. The commenter stated that it would be imprudent for utilities to rely on the 

availability and price of power in the wholesale market for normal base load and even peak energy 

demands. In addition, the commenter believes that electric utilities in Arizona would face significant 

scrutiny by state utility regulators and their ratepayers if such a “risky” supply strategy were employed. 

The commenter added that EPA has not considered a number of factors in assuming that NGS will not 

close. The White Mountain Apache Tribe (0440) also commented that it disputes the reliability of the 

power market pricing projections and recommended a more thorough analysis was needed. 

Response:

EPA disagrees with the assertion that it was inappropriate to assume that sufficient wholesale 

power would be available to replace NGS’s output if NGS were to close. NREL addressed the question 

of sufficiency of wholesale power to replace the power generated at NGS.89 NREL used a production 

cost model to analyze power flows from western generators; the model tested the power supply and 

marginal prices (LMP) in the western system under two scenarios: with NGS operating (the base case) 

and with NGS closed. The modeling results allowed not only insight as to whether there was enough 

surplus power in the western grid to replace NGS power in the event of a closure, but also from where 

such power would be likely obtained. With regard to the availability of excess power, NREL’s analysis 

indicated that there was sufficient excess power in the western grid to adequately replace lost NGS 

production. The base case model indicated that on average, NGS produces approximately 17.5 TWh 

annually. This is the volume of power that would need to be replaced should NGS close. The utilities 

that are participants in NGS (not including the Bureau of Reclamation) all have portfolios of other 

power plants from which they can call upon for the production of the replacement power.90 The NREL 

model results indicated the utilities would need to replace, beyond the new power generated at their 

other power plants, roughly 7.7 TWh of generation. Additionally, the BOR share would need to be 

replaced in whole. Thus, NREL’s analysis indicated that of the 17.5 TWh of total power lost in a closure 

scenario, approximately 12 TWh would need to be replaced, and determined that there was sufficient 

surplus power in the western grid to replace those 12 TWh. 

The NREL model analyzed where this remaining amount of replacement power would be 

obtained. NREL determined that most of this replacement power would originate either in the Desert 

Southwest or California (in most cases, power for the NGS participating utilities was either from 

increased production of their own plants or from redirecting excess power from such plants from 

California to their own southwest load).91 For utilities located in California (and to some extent 

elsewhere where seasonal trades are common), increased production from within each utility’s own 

region (Balancing Authority) was determined as likely. Therefore, the NREL model demonstrated that 

not all generation from NGS would need to be replaced (roughly two-thirds would be) and for the 

amount that would need to be replaced (estimated at 12 TWh), power was available primarily in the 

Desert Southwest and California. 

With regard to the comment (0440) concerning the reliability of power market price projections, 

the EPA study used, as a basis for its long-term (post-2016) forecasted prices, the most current 

projections of the Energy Information Administration (EIA). The EIA forecasts are developed for both a 

national and regional context. In the case of their application in the EPA Affordability Analysis, the 

89 NREL report, p. 32. 

90 See NREL report, Table 2-2, p. 33. 

91 NREL report, pp. 32-35. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

forecast employed was specific to power prices in the southwest region of the nation. For more nearterm prices (current prices out to 2016), we used actual Palo Verde forward index prices. These reflected 

current market conditions at that time and market expectations of the power industry for power priced at 

the Palo Verde Hub, the primary pricing hub for electricity in the southwest region. In order to capture 

any significant change in future price projections, EPA updated both the Palo Verde forward market 

prices and the EIA forecast for long-term southwest power prices on March 7, 2014. The updated Palo 

Verde forward price projection used in the revised Affordability Analysis is shown in the following 

graph (Figure 1). The results of this update, as well as other updates to the Affordability Analysis, are 

discussed elsewhere in this response to comments document. Because our analysis relies on the most 

updated information available, as well as information specific to the southwest region, absent more 

specific comments to dispute our power market pricing projections, EPA disagrees with the assertion 

that a more thorough analysis is needed. 

Figure 1: Projected Palo Verde Forward Prices 

Comment: EPA’s economic analysis relied on invalid assumptions

One industry commenter (0384) submitted a report prepared by Management Information 

Services, Inc. (MISI report) as the basis for many of the following comments. 

This commenter (0384) stated that EPA’s Affordability Analysis shows that under certain low 

market price conditions the cost of SCR retrofit would exceed the cost of replacement power for some 

NGS participants, particularly for SRP and other investor-owned utilities (IOUs) that were NGS 

participants. The commenter concluded that under such scenarios, continued participation by those 

entities facing retrofit costs exceeding replacement power values would withdraw their NGS 

participation. 

The same commenter (0384) asserted that the Affordability Analysis included invalid 

assumptions. First, the commenter asserted the economic analysis assumed that no new capital would be 

$35.00	

$40.00	

$45.00	

$50.00	

$55.00	

$60.00	

$65.00	

$70.00	

$75.00	

$80.00	

20192020202120222023202420252026202720282029203020312032203320342035

ProjectedPalo Verde Forward Prices ($/MWh)

High	Trend Mid	Trend Low	Trend
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

deployed at NGS over the next 25 years but did note that if any new substantial capital cost were to be 

incurred, particularly in the early years of the model timeframe, the resulting impact on the business as 

usual outcome could potentially be reversed, indicating the cost of SCR retrofits exceeding the cost of 

replacement power. The commenter stated multiple new or pending EPA regulations will necessitate 

new capital equipment at the generation station. The commenter asserted that inclusion of these 

incremental capital expenditures will shift the modeling outcome toward a path of closure. 

Regarding the cost of the lease agreement between the NGS participants and the Navajo Nation, 

the commenter (0384) stated the economic model incorporated an estimated value going forward of $15 

million/yr as a likely proxy for a renegotiated value. Instead, the commenter asserted that the parties 

have reached a final solution on the renegotiated lease - $43 million/yr; the economic model’s 

assumption on lease value is undervalued by $25 million/yr. The commenter stated that the incremental 

difference is significant enough to alter the business as usual to show that replacement power is a less 

costly option than SCR retrofits. 

The commenter (0384) further stated that the capital costs as set by the Sargent and Lundy study 

is more inclusive that the cost reflected by the EPA Control Cost Manual; the model’s assumption of the 

SCR capital cost was undervalued by approximately $50 million. The commenter believed the economic 

model failed to address the +/- 30 percent variation in capital cost as described in the EPA Control Cost 

Manual. The commenter stated that adoption of one or both of these changes would again alter the 

business as usual results to show that replacement costs is less expensive and, thus, a shut-down of the 

facility is likely. 

This commenter (0384) stated that, while the NREL report indicated that excess capacity on the 

western grid would likely be adequate to serve as replacement power should NGS close, other items in 

the report suggest more detrimental effects, such as high volatility of gas prices (assumption that 

replacement power would be predominantly gas-fired generation), the larger portion of power currently 

used in Arizona that is coal-fired, that coal-fired power is historically less expensive than gas-fired 

power, and the threat to other Arizona based coal-fired generation as a result of EPA regional haze 

regulations. The commenter believed that a combination of all these suggest that a threat to NGS carries 

a substantial economic impact to the state that must be recognized and accounted for. 

The same commenter (0384) believes the economic threat to the state is particularly true if the 

closure of NGS resulted in increasing the state’s reliance on gas-fired generation; both water and power 

cost would increase significantly. The commenter asserted that the NREL report estimated a likely gas 

cost of $5 to 6 per MCF over the next decade and that replacing the NGS generation with gas-fired, 

assuming those fuel costs, would result in a cost to the state of roughly $3 billion (NPV) over the next 

decade. 

The commenter (0384) disagreed with the forecasted energy prices used in the Affordability 

Analysis and argued the closure of NGS would have price ramifications in the wholesale market, thus 

increasing replacement costs. The commenter added that the model’s forecasted prices failed to capture 

the price volatility of the gas market and the subsequent impact on wholesale power prices. 

Response:

The comments submitted, in part, reflected conclusions drawn from the MISI report. The MISI 

report primarily addressed the macroeconomic links between Arizona and the NGS. These included the 

economic importance of NGS to the Navajo Nation and Hopi Tribe, and the link between the State of 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Arizona’s economic performance, jobs, water/power prices and poverty levels. The report sought to 

quantify potential detrimental effects to the State, Navajo Nation and Hopi Tribe should NGS close 

Additionally, the report addressed the economic impact to parties in the state should NGS close and 

replacement generation be fueled by natural gas. The report cites the volatility of the natural gas market 

to be of particular concern. 

 EPA recognizes the economic importance of NGS to the State of Arizona, the Navajo Nation and 

the Hopi Tribe. Indeed, the premise behind the Affordability Analysis was to determine potential price 

effects from different BART options and whether those effects would have a detrimental impact on 

NGS’s competitiveness within the western power market. The probability of closure was a central focus 

of the Affordability Analysis because a determination that a particular BART option could lead NGS to 

become non-competitive implied that the NGS participating parties would seek to replace the NGS 

generation with less expensive market power. However, the Affordability Analysis indicated that, even 

if BART were determined to be SCR installation on all three units at NGS, power produced at NGS 

remained less expensive than the cost to replace power through wholesale purchases. Because utilities 

will provide power to their customers in a ‘least cost’ manner and because NGS, with the installation 

and operation of SCR, remained the less expensive option, EPA determined that the operation and 

installation of SCR, in and of itself, was not likely to force NGS to close. 

 The commenters state that under certain market conditions (i.e., low power market cost and if the 

LADWP share is absorbed by another IOU) the Affordability Analysis that accompanied the Proposed 

Rule suggested that replacement power for NGS under an assumed closure case would be less expensive 

than the incurred cost of installing SCR on all units. However, in response to multiple comments 

received from various parties that asserted the forecasted values employed in the original model for the 

Proposed Rule are now outdated, EPA updated the Affordability Analysis with the most current EIA 

power market price curves and recent forward power market prices in March 2014.92 The updated model 

results are summarized in Tables 5 and 6 below, and include updates to other modeling variables in 

response to other comments and discussed elsewhere in this response to comments document. 

Table 5: NPV by Case & NPV Incremental to BA Table 6: NPV by Case & NPV Incremental to BAU 

 Assuming Public Utility Takes LADWP Share93 Assuming Investor Utility Takes LADWP Share94

As can be seen, the NPV of SCR investment is less than the cost of wholesale replacement 

power, both under the scenario of the LADWP share of NGS going to a public utility and under the 

92 The updated Affordability Analysis is included in the docket for this rulemaking. See document titled: “Model – 2014 NGS 

BART Affordability Analysis – r0 – 05_08_14”. 

93 See “Model – 2014 NGS BART Affordability Analysis – r0- 04_25_14, Worksheet DASHBOARD” 

94 Id.

SNCR SCR

Low

Market

Mid

Market

High

Market

$						 9,278 8,719 $						 9,395 $							 9,653 $							 9,904 $	

$									 819 260 $									 936 $											 1,194 $							 1,445 $	

NPV by Case: Total Plant with DWP Share to POU

($	million)

Controls & Market NPV Vs. BAU NPV

($	million)

SNCR SCR

Low

Market

Mid

Market

High

Market

$						 9,381 8,761 $						 9,417 $							 9,674 $							 9,924 $	

$									 885 264 $									 921 $											 1,178 $							 1,428 $	

NPV by Case: Total Plant with DWP Share to IOU

($	million)

Controls & Market NPV Vs. BAU NPV

($	million)
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

scenario of the same share going to an investor owned utility (IOU). The updated results support the 

conclusion that closure of NGS is not the ‘least cost’ option. 

With regard to the assertion that EPA used invalid assumptions in the economic model, the initial 

modeling effort was purposefully designed to isolate the effect of an investment due to BART. Thus, 

both SNCR and SCR were modeled separately and under a condition that other investments and input 

costs in the plant were held constant. This allowed the determination of what effect BART would have 

on the cost of electricity generation, and thus, the final value of power produced by the plant. In essence, 

it isolated the cost of compliance of BART. 

 EPA recognizes that the assumption to hold all future capital investments constant was a 

simplification. As mentioned above, the modeling was designed, in part, to isolate just the cost of BART 

as it impacted the final value of power the plant produced. Additionally, however, it was also recognized 

that detailing all future investment costs was not possible. The commenter has highlighted several 

pending or new environmental regulations that in the future may impose additional costs on NGS. The 

compliance investments that would be linked to such regulations are unknown and cannot, at this time, 

be estimated with accuracy. 

 Notwithstanding this inability to accurately estimate future investments at the plant, EPA has 

undertaken revised modeling in the Affordability Analysis which, in part, used proxy values for 

potential future investments. The revision was an attempt to model how the plant’s power cost would be 

affected under both compliance-related investments as well as investments of a different nature such as 

on-going capital expense. We assumed these future investments to be set at a fixed value annually and 

continued over a defined time line. We did not attempt to link the investments to a particular activity the 

plant owners might choose to undertake. However, the proxy values give an indication of whether the 

BART compliance investment, coupled with other estimated capital expense over time, results in NGS 

being non-competitive when compared to the option of acquiring replacement power on the wholesale 

market. Those proxy capital expenses were set at $5 million dollars per year from 2013 through 2038, 

including annual increases for inflation.95 The impact of the additional annual capital expense is 

included in the output tables above. 

 The commenter noted that the lease agreement between the NGS participants and the Navajo 

Nation has now been completed and the resulting new annual lease value is much greater than the 

assumed lease value in the model. During the development of the Affordability Analysis, we understood 

that negotiations were underway on renewing the lease between the NGS participants and the Navajo 

Nation. We correctly assumed that the existing lease value ($3 million per year) would change. We 

assumed a value of $15 million per year that was approximated by taking the amount the lease for the 

Four Corners Power Plant site lease increased following lease renewal and doubling it.96 After the 

original Affordability Analysis was completed, however, the new lease was concluded at a lease value 

95 The modeling estimate for ongoing non-SCR capital expense addresses capital related to replacement of existing facilities. 

A regular annual allocation of new capital expense was utilized rather than projecting capital outlays of smaller or larger 

amounts in conjunction with minor and major maintenance schedules. FERC filings for the regulated utilities and annual 

reports for the public power entities for the period 2003 to 2013 were reviewed. Under the assumption that only some 

fraction of the reported annual capital expense ultimately becomes part of the rate base for electric generation, a modeling 

estimate of $5 million was selected as a reasonable annual average and proxy value for the purpose of accounting for ongoing CAPEX. 

96 Press Release, March 8, 2011, The Navajo Nation, “President Shelly Signs APS Lease Agreement” available at 

http://www.navajo-nsn.gov/News%20Releases/OPVP/Mar11/3811_PresidentShellysignsAPSLeaseAgreement.pdf. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

of $43 million per year.97 Recognizing that the original model had underestimated the actual lease cost, 

EPA has updated the model to incorporate the new value of $43 million per year. The impact of the 

updated lease expense on the modeling economics is included in the tables above. 

 The commenter also expressed concern that EPA underestimated the cost of SCR in the 

Affordability Analysis. EPA’s responses to comments related to the cost of SCR are discussed in 

section 3.1 of this response to comments document. There, we stated that even if EPA used the 2013 

values provided by SRP for the cost of SCR, we would still determine that SCR is cost-effective for 

NGS. Similarly, even if we used the 2013 values provided by SRP for the cost of SCR in the 

Affordability Analysis, the results and conclusions of the analysis would not change. 

 The commenter expressed concern that, if NGS closed and the state became more reliant on 

natural gas-fired generation, the state would face the prospect of higher electricity prices due to the 

volatility of the natural gas market. The commenter noted that historically coal costs have been less than 

the cost of natural gas, thus coal-fired generation has a cost advantage over natural gas-fired generation. 

The commenter asserted that Arizona ratepayers have benefited from the cost differential since the 

majority of electricity generation in Arizona is coal-based. 

 Although the cost differential between coal and natural gas has been evident historically, there is 

uncertainty as to whether such a differential will remain in the future years.98 Given the commenter’s 

own listing of pending or new environmental regulations (e.g., Utility Mercury and Air Toxics Standard, 

Green House Gas Tailoring Rule, Coal Combustion Residuals, and Utility Boiler GHG), the importance 

of these pending regulations is that any and all of these will result in increasing the cost of coal-fired 

generation. Secondly, with the proliferation of hydraulic fracturing and more comprehensive horizontal 

drilling techniques, the nation’s gas supply has greatly increased in just a few years, driving the cost of 

natural gas down.99

 The commenter contends that closure of NGS and increased reliance on gas-fired generation 

could cost the state roughly $3 billion (NPV) over the decade following closure. The values are taken 

from the MISI report (p.67) submitted in support of the comments. The $3 billion value was based upon 

a projected gas price of $5 to $6 per Mcf, as forecast in the NREL report. Depending upon the assumed 

discount rate (which the MISI report did not provide), the assumed gas prices could equal such a NPV 

over a set time (10 years, in this case). The value, however, is misleading in that the cost to Arizona 

ratepayers arising from a switch from coal to gas-fired generation is not the total value of expenditure on 

gas, but instead, the incremental difference between what power would cost when produced by coalbased generation versus the same amount of power produced by gas-fired generation. EPA’s updated 

Affordability Analysis incorporated the latest projected cost values for both coal and natural gas. The 

results of the model shown above reflect the outcomes with these more recent fuel cost values. 

 With regard to comments pertaining to price ramifications in the wholesale market should NGS 

close, the NREL report estimated the price impacts range from 3.2% to 5.3% in the Arizona and 

California (LADWP) Balancing Area Authorities, the pricing areas most impacted by a closure. The 

97 Navajo Nation Council Resolution, Tracking No. 0177-13, June 19, 2013 available at 

http://www.navajonationcouncil.org/Legislations/2013/June/0177-13.pdf. 

98 Gas to Coal Competition in the U.S. Power Sector (http://www.iea.org/publications/insights/CoalvsGas_FINAL_WEB.pdf 99 Manufacturing Energy Consumption Survey (MECS) EIA 

http://www.eia.gov/consumption/manufacturing/reports/2010/ng_cost/
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

overall Western Electricity Coordinating Council (western grid) estimated price impact was 2.6%. Such 

price increases are not seen as being excessive in light of typical increases in utility rates.100

Comment: EPA’s economic analysis was too conservative

One environmental advocacy group (0373) asserted that EPA’s Affordability Analysis concluded 

that the capital cost of SCR installed by 2018 was less than the cost to replace the generation at NGS 

through wholesale market purchases. The commenter, however, stated that this conclusion would have 

provided even stronger conclusions had the model included more accurate assumptions in its 

depreciation and market price analysis (citing a report prepared by David Marcus and submitted with the 

comment). The commenter asserted that there were additional smaller errors in Energy Strategies 

assumptions that, if corrected, would shift the outcome of the model even more favorable for the SCR 

investment as least cost. 

This commenter (0373) also disagreed with a number of assumptions that were adopted by 

NREL in its modeling of the cost of installation of SCR. The commenter believes that the use of a 10-

year amortization schedule for recovery of the retrofit costs was too short a timeframe for amortization 

and skews the modeling results. Additionally, the commenter believed the forecasted price cost of 

energy used by NREL is inaccurate, as is the assumed cost of retiring the NGS facility. The commenter 

concluded that the errors are of such significance that the NREL analysis provides little value in EPA’s 

deliberations and does not support a delay of BART implementation. 

The commenter (0373) also disagreed with how CAP water costs were addressed in the NREL 

model, arguing that NREL adopted some worst-case assumptions in analyzing the impact to CAP water 

cost resulting from SCR installation. The commenter believes that adoption of a more reasonable 

scenario than worst-case could lower the NREL capital cost estimation by as much as a third. 

Additionally, the commenter stated that the actual cost impact to CAP water users is within the range of 

costs adjustment of recent years and the costs are not outside of the expected cost increases in future 

years. Regarding non-Indian agriculture users, the commenter (citing the Marcus Report) concluded 

these users right to CAP water is declining and will be eliminated by 2031 and, thus, any impact to the 

user group is diminished. The commenter believed that such impacts on water users should not be 

reason for a BART implementation delay. 

Commenter (0373) stated that the investment of SCR is the least cost alternative when compared 

to wholesale market purchase of replacement power and benefit the national parks and the health of 

residents of the region. Thus, the commenter concluded that EPA has failed to make a compelling case 

for delaying BART beyond the 2018 timeframe. 

Response:

We address each of the points raised by the commenter below that relate to EPA’s Affordability 

Analysis. EPA is not responding to any comments or concerns raised regarding the NREL analysis 

because EPA was not involved in developing or writing the NREL report. 

The commenter asserted that the Affordability Analysis had employed several assumptions that 

were invalid, and once corrected, would further support the case that investments in SCR for all units 

100 See NREL report, Table 2-6, p.40. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

was the ‘least cost’ option compared to closing NGS and replacing power through purchase on the 

wholesale market. The commenter focused on the comparative economics of the SCR case versus the 

Low Market case. While the original model outcome indicated that the SCR case was less expensive 

than the Low Market case by $25 million, the commenter argued that, based on their calculation, the 

SCR case should be less expensive than the Low Market case by roughly $600 million. The commenter 

asserted that the model contained invalid assumptions in two main areas: treatment of depreciation and 

projected power prices. 

 With regard to the asserted error in depreciation, the commenter suggested that the original 

treatment of undepreciated assets failed to account for the fact that under a closure scenario ratepayers 

would be charged (over a number of years) the cost of such assets. In turn, the value of this “stranded 

investment” would then be added to the cost of procured power, the result of which would be to make 

replacement cost more expensive. 

 As noted in the Marcus Report, the design of the original model was ‘very conservative’ in that it 

did not address the issue of recovery of stranded investment under the market case scenarios which 

assume the closure of NGS. As such, the differential between the SCR case and the Low Market case 

was indeed limited by this simplistic assumption. EPA agrees and has revised the Affordability Analysis 

to reflect the fact that stranded investment would likely be a component of the cost of replacement 

power. The revised model includes the assumption that 100 percent of stranded cost, as defined by the 

undepreciated value of the plant, would be recovered over a 5-year time frame once NGS was closed.101

In addition, and consistent with another assertion that the original model failed to use correct values for 

undepreciated assets of each utility, the value of the net plant in service for each utility was revised to 

reflect actual filed 2012 data by the utilities.102 The impact of changes in both the net plant in service 

and stranded cost recovery are now incorporated in the economic model and their impact is contained in 

the tables above. 

Other commenters asserted that the original model failed to differentiate between nominal and 

real prices with regard to the forecasted power prices. The comments argued that inflation was not 

properly incorporated into the projected prices, thus lowering those projections, resulting in a projected 

replacement cost of power that was artificially low. 

 As a simplifying assumption, the original Affordability Analysis assumed that in an NGS 

shutdown scenario, replacement power would be acquired en masse on a forward basis for the entire 

study term. The forward prices modeled in that case were based on actual executable prices in the 

market at the time, escalated across the study period according to a curve defined by EIA’s nominal 

electricity price escalation values. The concept was to approximate a futures market that went further 

into time than the actual market is traded. Upon further consideration, that specific buying concept does 

not seem likely. EPA acknowledges that the treatment of projected power prices was predicated on 

nominal values and thus did not incorporate an inflation adjustment. Although appropriate for the 

forward power purchase concept, the more likely power replacement scenario would envision both long 

and short term contracting arrangements. For that reason, the model was revised to incorporate recent 

power market pricing and the most current EIA long-term electricity trends. The forward electricity 

101 The period of time over which stranded costs may be recovered is not standardized and it typically set in regulatory 

proceedings before state utility commissions, boards, and city councils. A five-year stranded cost recovery period was 

selected for modeling purposes in recognition of utility rate making practice emphasizing gradualism and generational 

impacts, where excessively short cost recovery periods move utility rates too quickly, and where excessively long recovery 

periods labor ratepayers with cost recovery for costs incurred noticeably before they were served by the utility. 

102 2012 FERC Form 1 filings for APS, TEP, and NV Energy; FY13 Annual Reports for SRP and LADWP. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

price curve utilized in the revised Affordability Analysis also accounts for inflation by using EIA’s real 

rather than nominal dollar prices. 

 In addition to the revisions discussed above, additional enhancements were made to the 

Affordability Analysis model to address commenter feedback and use updated data where available. 

These included: an updated annual lease cost to reflect the final value negotiated with the Navajo Nation 

($43 million per year), updated coal price curves (EIA), an assumed $5 million (escalated) annual 

capital investment in the plant combined across parties, an assumed decommissioning cost if NGS were 

closed, and a higher cost for SCR as reported in the 2013 SRP update.103 The impact of these combined 

changes in assumptions and input values are all contained in the Tables 5 and 6 above and Figure 2 

below. Some of the updated assumptions or inputs caused the cost of SCR to increase. Other updated 

assumptions or inputs caused the cost of replacement power to increase. Overall, the combined changes 

do not change the conclusions from the original Affordability Analysis that installing and operating SCR 

at NGS would be less costly than closing NGS and purchasing replacement power from the wholesale 

market. 

Figure 2: Net Present Value of Control Cases Compared to Market Cases

Comment: Cost of maintaining reliability of electric system if NGS closes 

 A state agency (0017/0289/0320) stated that EPA’s analysis is not based on a comprehensive 

reliability analysis, which would be required to understand the full implications of shutting down NGS. 

According to the commenter, given its size and location and the existing transmission system 

configuration, NGS is a critical resource to the reliable operation of the integrated bulk electric system 

throughout both Arizona and the western interconnection. The commenter indicated that it is highly 

likely that the closure of NGS would result in significant costs associated with transmission system 

103 See “Model – 2014 NGS BART Affordability Analysis – r0- 05_08_14.” 

$8,459	 $8,719	

$9,278	 $9,395	 $9,653	 $9,904	

$8,496	 $8,761	

$9,381	 $9,417	 $9,674	 $9,924	

$‐

$2,000	

$4,000	

$6,000	

$8,000	

$10,000	

$12,000	

BAU SNCR SCR Low	Market Mid	Market High	Market

NPVofTotal Plant Cases

Assuming LADWP Share		is Ownedby POUor IOU($	million)

Total	Plant	w	DWP	Share	to	POU Total	Plant	w	DWP	Share	to	IOU
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

changes to maintain required levels of system reliability. The commenter believes that without having 

performed a comprehensive reliability study, EPA has failed to include all costs that may be associated 

with closure of NGS. 

Response:

The commenter is correct that EPA did not conduct a comprehensive reliability analysis. 

However, EPA disagrees that a more comprehensive analysis of reliability is required to estimate costs 

associated with closure. 

To conduct a reliability study, one would employ a power flow model that would analyze 

detailed flows on the western United States high-voltage grid. The model would test flows under 

different conditions, thus presenting likely outcomes should certain events unfold. Such power flow 

models are often undertaken by the utilities themselves when contemplating new generation or 

transmission asset developments. More often, the power flow models are conducted by WECC to gauge 

system reliability under a variety of circumstances. The NREL study indicated that roughly one-third of 

the required replacement power would be gained by increased production at the NGS participants’ other 

power stations.104 The remaining two-thirds would also be regionally obtained (primarily from the 

Desert Southwest and California), much of which would result from current wholesale sales to 

California being rerouted to the load serving areas of the affected NGS utilities. It would appear, 

therefore, that ‘system impacts’ would be regionalized and, given the ability of the current NGS utilities 

to obtain replacement power from their own facilities (and thus transmit the power over the existing 

lines that serve the utilities today) such impacts would not change the outcome of our Affordability 

Analysis. 

Additionally, under current conditions, it was assumed that reliability would not be adversely 

affected should there be a closure at NGS. This assumption was based upon the recognition that in 

today’s southwest power market, the current reserve margin is approximately 30 percent (compared to 

the target margin of 13.5 percent).105 We assume, therefore, that closure of NGS would not stress the 

regional market to a level where regional reliability would fall below the target margin. In other words, 

even if NGS were to close, the region’s reserve margin should remain well above the target.106 We note 

that the NREL report estimated that the regional target reliability margin would decrease to 

approximately 22 percent without NGS production, assuming no new power plants are built in the 

region.107 With substantial reserve margins in the southwest power market, it was therefore assumed that 

the likelihood of substantial additional costs to be incurred as a function of reduced reliability was small. 

Comment: EPA’s conclusions about Non-Indian Agriculture (NIA) water rights and their ability to 

return to groundwater pumping are erroneous 

104 NREL report, Table 2-2, p. 33. 105 NREL report, p. 27. 106 The 2013 North American Electric Reliability Corporation (NERC) Summer Reliability Assessment, p. 41, reports that the 

southwestern portion of WECC (defined as the Southwest Reserve Sharing Group (SRSG) for purposes of the report) within 

which NGS resides has a planning reserve margin of 33.87% on Net Internal Load of 28,478 MW and Anticipated Resources 

of 38,122 MW. The loss of NGS (2,250 MW) would result in a reduction of the reserve margin from 33.87 percent to 25.96 

percent. See, http://www.nerc.com/pa/RAPA/ra/Reliability%20Assessments%20DL/2013SRA_Final.pdf. 107 NREL report, pp. 27. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 Regarding the Central Arizona Irrigation and Drainage District (CAIDD), Maricopa-Stanfield 

Irrigation and Drainage District (MSIDD), Hohokam Irrigation and Drainage District (HIDD), and New 

Magma Irrigation and Drainage District (NMIDD), one public sector commenter (0347) stated that the 

supposition in the TSD that NIA customers may not be able to return to groundwater pumping if excess 

CAP water becomes unavailable is incorrect. Commenters (0305, 0347) stated that, under state law, the 

districts have the authority to pump groundwater if CAP excess water supplies are not available or if the 

costs of that water become too expensive. The commenter asserted that districts may choose to use their 

groundwater at any time regardless of the availability or price of excess CAP water and they are legally 

entitled under state law to return to groundwater pumping whenever they desire. 

One commenter (0305) stated that agricultural water users will not be forced to cease operations 

if they are unable to continue using CAP water, either due to lack of supply or excessive CAP water 

cost, rather they will convert their supply to groundwater and continue in operation. The commenter 

asserted that the decision by agricultural water users to shift to groundwater sources depends almost 

entirely upon the price difference between CAP water that is available in the future and the cost of 

groundwater. 

One CAP water distributor (0060) stated that EPA’s mention of any potential restriction on NIA 

water users returning to groundwater is a political statement made to undercut the argument that the 

proposed order will force NIA back onto groundwater pumping in direct contradiction of the public 

policy behind the enactment of the CAP-enabling legislation. The commenter asserted this public policy 

goal was to ensure the reduction of groundwater pumping in Arizona, proportionate to the availability of 

CAP water. The commenter stated that they are unaware of any state law prohibiting farmers in CAIDD 

and MSIDD from pumping (through the districts) their full entitlements of groundwater once CAP water 

is no longer available to them. 

Response: 

 EPA disagrees that any statements we made in the TSD to our proposed rulemaking, related to 

the ability of NIA customers to return to groundwater pumping, were political in nature. In our TSD, 

EPA recognized the concerns expressed by NIA users of CAP water, and EPA acknowledged that we 

did not have a clear understanding of several issues related to NIA water use, including how long NIA 

users expected to continue using CAP water, whether any restrictions existed in the ability of NIA water 

users to return to pumping groundwater, and what the expected source of water would be when CAP 

water is no longer available to NIA users. Based on the comments submitted, EPA now understands that 

farmers may return to pumping groundwater anytime now, or when CAP water is no longer available to 

them in 2030 (per the AWSA). EPA recognizes the importance of maintaining, preserving, and 

replenishing groundwater, and that increases in CAP water rates may adversely affect the goal of 

reducing groundwater usage. As stated elsewhere, EPA considers the potential economic impacts to 

tribes to argue for flexibility in the compliance timeframe for NGS. This flexibility also benefits other 

stakeholders, including the NIA users of CAP water. 

Comment: The assumption that NIA CAP water users will not have access to CAP water in the future is 

not accurate

Commenters (0305, 0347) believe that the conclusion reached by EPA that volume of excess 

water for agriculture will be zero by 2024 is erroneous. One commenter (0347) referenced Appendix B 

of the 2012 Annual Report by the Arizona Water Banking Authority (AWBA), a state entity that the 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

commenter stated is responsible for firming municipal and industrial CAP subcontracts, as confirmation 

of the error in EPA’s conclusions that excess CAP water volumes will be zero by 2024. Commenter 

(0060) asserted that EPA’s consultant used the worst-case Colorado Water Supply projections of the 14 

scenarios reviewed in the 2011 Water Resources Development Commission (WRDC) report. The 

commenter suggested that the worst-case scenario was used by EPA to marginalize the impact of the 

resulting high water cost on NIA that would result from BART. 

One commenter (0305) stated that the WRDC report is an imperfect document never intended for 

use as reference material in a regulatory matter. The commenter suggested that EPA should 

acknowledge in its Proposed Rule that the WRDC report is inappropriate for the purposes EPA and its 

contractor used it. The commenter stated that EPA should rely on more informed estimates in the future, 

but believed that if the WRDC continues to be a source that the EPA relies upon, then EPA should select 

the most likely scenarios in the WRDC rather than the worst-case scenario. 

Commenter (0347) stated that the volumes projected in the AWBA’s Annual Report for 2012 

exceed the full agricultural pool of 400,000 acre-feet through 2016 and 300,000 acre-feet through 2022. 

The commenter projected 104,000 acre-feet of excess water to be available through 2030 and concluded 

that the AWBA and ADWR projections do not support EPA’s conclusion that excess water for 

agriculture will be zero by 2024. 

Commenter (0305) stated that, under the Arizona Water Settlement Act (AWSA), agricultural 

water users received a quantity-limited and time-limited pool of CAP water at an affordable price in 

exchange for their long-term entitlements to CAP water. The commenter asserted that those quantities 

and durations are 400,000 acre-feet through 2017, 300,000 acre-feet through 2024, and 225,000 acrefeet through 2030. The commenter asserted that the proposed BART would upset that arrangement since 

the AWSA envisioned a means to provide agricultural water users with an adequate and affordable 

supply of CAP water. 

Response: 

The commenters are correct in noting that the Affordability Analysis report addendum utilized a 

WRDC scenario that assumed declining CAP NIA deliveries starting in 2017. That table was used to 

project cost impacts in Table A-2 of the addendum. The commenters are also correct in noting that the 

ADWR 2012 Annual Report, Appendix B shows a consistent volume of NIA CAP water from 2017 

through 2023, and not a decline. If the volumes stated in the ADWR report are delivered as projected, 

then the volume of CAP water used by NIA customers as a percentage of their total supply would be 

higher than described in the original Affordability Analysis. The addendum to the Affordability Analysis 

also references the same CAP NIA water delivery schedule as indicated in ADWR’s annual report, 

showing a decline from 400,000 acre feet in 2007 to 0 acre feet in 2030. For the period of time from 

2017 to 2030, had the EPA analysis utilized the ADWR projections and not the WRDC projections, the 

percentage of supply from CAP for all NIA users would have been higher. EPA understands that 

increases in CAP water rates are a critical concern to NIA water users of CAP water. As stated 

elsewhere in this response to comments document, EPA considers the potential economic impacts to 

tribes to argue for flexibility in the compliance timeframe for NGS. Because additional flexibility also 

benefits other stakeholders, including the NIA users of CAP water, this comment does not change our 

conclusion related to compliance flexibility. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Comment: EPA’s assumption that NIA CAP water users rely on CAP for only 25 percent of their water 

supply is erroneous and causes EPA’s analysis to reach a faulty conclusion with respect to affordability

Commenter (0347) asserted that EPA’s assumption that the 25 percent of total NIA water users 

water supply comes from the CAP is incorrect. For the four districts (CIDD, MSIDD, HIDD, NMIDD), 

the commenter stated that CAP water as a percentage of total supply ranges from 85-90% when 

agricultural pool water is added to other excess water that is available to the district through partnerships 

they have established with the Arizona Indian CAP contractors and municipal and industrial 

subcontractors of the AWBA. 

Commenter (0060) stated that for the three districts it represents, CAP water is 66-90 percent of 

their annual supply, and between 35-50 percent if only the “Ag Pool” is counted. The commenter 

believed that by using a lower percentage (25 percent) EPA sought to minimize the water cost impact of 

the BART-required emissions controls. 

Another commenter (0305) stated that the erroneous assumption that CAP water use by 

agricultural water users represents only 25 percent of total use is a major assumption resulting in an 

underestimation of the impacts on farmers in districts like New Magma whose CAP supply accounts for 

100 percent of their use, when “in lieu” deliveries are included. The commenter stated that even after 

accounting for only the Ag Pool, its members get 50 percent of their supply from the CAP. The 

commenter asserted that EPA must adjust its analysis by revising the CAP share of total water supply 

for agricultural water users to a realistic level significantly greater than the 25 percent used in the 

Affordability Analysis. The commenter concluded that this erroneous assumption renders EPA’s 

analysis arbitrary. 

Response:

Each of the commenters stated that the volume of CAP water as a percentage of total supply as 

suggested in the Affordability Analysis (25% or lower) is unrealistic and that EPA’s analysis is 

erroneous due to the low assumed value. The comments received indicate that reliance on CAP water for 

NIA users is highly variable between users, with some having substantial if not total reliance on CAP 

water, under certain circumstances. With respect to the calculation of water cost impact in the addendum 

to the Affordability Analysis, NIA CAP customers with higher levels of reliance on CAP water would 

indeed have a higher CAP water cost impact as a result of BART than those with little to no CAP NIA 

water reliance. The impact will be unique for each NIA customer. EPA understands that increases in 

CAP water rates are a critical concern to NIA water users of CAP water. As stated elsewhere, EPA 

considers the potential economic impacts to tribes to argue for flexibility in the compliance timeframe 

for NGS. This additional flexibility also benefits other stakeholders, including the NIA users of CAP 

water, and this comment does not change our conclusion related to compliance flexibility. 

Comment: The CAP NIA water cost increases as a result of SCR costs will cause economic harm to 

CAP farmers

One CAP water distributor (0060) stated that while EPA estimates an increase of $8.40 per acrefoot in CAP water rates for NIA users, CAP estimates an increase of $10.00 per acre-foot. Referencing 

the TSD, the commenter asserted that the EPA estimate of an $8.40 per acre-foot increase in CAP NIA 

water rates would equate to a 14-15 percent increase for both NIA and Indian agriculture. The 

commenter noted that annual increases in NIA water rates have been in the $1-$3 per acre-foot range 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

and that the $8.40 per acre-foot increase estimated by EPA would be unprecedented. The commenter 

further asserted that a $10 per acre-foot rate increase would cost the three districts they represent an 

additional $4.5 million per year, and $9 million if baghouses were required. The commenter believed 

that, as a result of those cost increases, many farmers will be unable to get crop financing. 

One commenter (0305) stated that the cost of water represents the highest operating expense for 

farming (20 percent). The commenter asserted that a major provider of farm credit service in Arizona 

stated that Pinal County water districts have some of the highest water costs in areas financed by Farm 

Credit Services Southwest, and an increase of $16 per acre-foot in water costs could potentially results 

in a negative margin that is not financeable. The commenter stated that CAP NIA water rate increase 

estimates provided by CAP in March 2013 range from 200-300 percent. The commenter believes that 

the EPA’s reliance on the “artificially low estimates” in the Affordability Analysis in the face of CAP’s 

significantly higher estimates to be arbitrary, capricious, and an abuse of discretion. 

Response: 

EPA recognizes that NIA CAP water users are sensitive to water cost increases. As compared to 

business as usual, BART requiring SCR will certainly act to increase NGS costs and therefore increase 

the CAWCD’s Energy 1 rate. Some clarification regarding the cost increase projected by EPA and those 

articulated by the commenters is warranted. EPA’s analysis in the addendum to the Affordability 

Analysis estimates that the increase in the Energy 1 rate in 2018 as a result of SCR would be $8.40 per 

acre foot. That incremental cost represents a 14.5% increase over the estimated 2018 Energy 1 rate of 

$58.00 per acre foot. The commenter’s statement that water costs would increase up to 300% assumes 

that SCR plus baghouses would be required as BART.108 More importantly, the commenter’s 

comparison of SCR-related incremental cost is made against 2013 water rates and not estimated 2018 

water rates.109 Relating the increase in cost against a rate that would not be in place in that year confuses 

the comparison. The source of the commenter’s cost increase estimates is a March 18, 2013 meeting 

between CAWCD and EPA in which the CAWCD presented its estimates of the rate impact of both 

SCR and also SCR plus a baghouse.110 In that presentation, CAWCD discussed other non-BART issues 

that NGS has to resolve in the near term, including coal supply, land lease agreements, and others. 

According to CAWCD, these non-BART issues alone stand to push the CAP rate above $80 per acrefoot in 2018. In contrast, EPA used projections for 2018 CAP water rates of $58 per acre-foot, based on 

CAWCD’s then-current “Advisory” 2016 rate, held constant in the model for 2 years.111 CAWCD’s 

currently published rates indicate a 2014 Energy 1 rate of $67 acre foot, itself $9.00 per acre-foot higher 

than the estimated 2018 rate used in the EPA Affordability Analysis, and a $16 per acre-foot increase 

over the 2014 Energy 1 rate of $51 per acre-foot published in 2011.112 Looking forward just 1 year, 

CAWCD’s published 2015 advisory rate is $74 per acre foot. Therefore, the increases in CAWCD 

Energy 1 rates during the pre-BART determination period (i.e., before 2018) suggest that non-BART 

issues associated with NGS may have a larger impact on water rates than BART. EPA understands that 

increases in CAP water rates are a critical concern to NIA water users of CAP water. As stated 

elsewhere, EPA considers the potential economic impacts to tribes to argue for providing flexibility in 

108 CAP Agricultural Water Users Task Force (0409), pg. 34. 

109 CAP Agricultural Water Users Task Force (0409), pgs. 33-34. For reference, the actual 2013 CAP water rate for 

agricultural users was $53 per acre foot. The April 3, 2014 “Advisory” rate for those users is $81 per acre foot. 

(http://www.cap-az.com/index.php/departments/finance/water-rates). 110 CAP Agricultural Water Users Task Force (0409), pg. 34. 111 CAWCD, “Central Arizona Project Final 2011/2012 Rate Schedule Update”, June 2, 2011, pg. 1 available at 

http://www.cap-az.com/Portals/1/Documents/Teresa's%20Docs/Final%20Updated%20Combined%202012-2016-RateSchedule.pdf. 112 Id. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

the compliance timeframe for NGS. This additional flexibility also benefits other stakeholders, including 

the NIA users of CAP water. 

The revised Affordability Analysis conducted in response to comments of stakeholders and in 

recognition of changes in SCR installation schedules, among others, also changes the impact to 

CAWCD’s Energy 1 rate. Table 7 describes the impact to the CAP rate with implementation of SCR on 

the final unit in 2019. 

Table 7: Increase in CAP Water Rates (Energy 1) from SCR+LNB/SOFA

Comment: EPA’s assumption and description of NIA CAP water rights as being non-secure is not 

correct

Three commenters (0060, 0305, 0347) stated that NIA CAP water rights are more secure than 

represented in EPA’s proposal. Commenter (0060) stated that the NIA excess settlement pool is the 

highest priority of all excess uses (one step down from long term uses) and is expected to be fully 

available unless there are extreme shortage conditions on the river. Commenter (0305) stated that the 

assumption that NIA CAP water users will somehow be without the option of CAP water leads to an 

inaccurate assumption that, in future years, no CAP water will be available for agricultural water users 

and, therefore, no increases in CAP water rates would be passed through to agricultural water users in 

those future years. 

Response:

In the TSD to our Proposed Rule, EPA recognized the concerns expressed by NIA users of CAP 

water, and EPA acknowledged that we did not have a clear understanding of several issues related to 

NIA water use, including how long NIA users expected to continue using CAP water, whether any 

restrictions existed in the ability of NIA water users to return to pumping groundwater, and what the 

expected source of water would be when CAP water is expected to be fully available to NIA water users 

CAP Energy Rate 1:		Impact of Emissions Control Scenarios

Assumptions

Annual	pumping	(AF) 1,550,000

Annual	pumping	energy	(MWh) 2,800,000

2014 2015 2016 2017 2018 2019 2020

$						 74.00 67.00 $			 74.00 $			 74.00 $			 74.00 $			 74.00 $			 74.00 $	

2014 2015 2016 2017 2018 2019 2020

Incremental Power Cost	($/MWh)	 $										 ‐ ‐ $							 ‐ $							 1.61 $					 3.50 $					 5.56 $					 5.43 $	

Incremental	Water	Cost	($/AF) ‐ $										 ‐ $							 ‐ $							 2.92 $					 6.32 $					 10.04 $			 9.82 $	

Resulting	Energy	1	Rate	($/AF) 67.00 $						 74.00 $			 74.00 $			 76.92 $			 80.32 $			 84.04 $			 83.82 $	

0.0% 0.0% 0.0% 3.9% 8.5% 13.6% 13.3%

CAP	Energy	Rate	1:	Advisory	Rates	as	

approved	by	CAWCD	June	2011

Pumping	&	energy	consumption	volumes	as	reported	

by	CAWCD	12/18/2009	Letter	to	EPA

% Increase over Preliminary CAP Rates

SCR	‐	2017/2018/2019 Installation

Energy 1 Rate: ESTIMATED
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

except in the event of an extreme water shortage. EPA understands that increases in CAP water rates are 

a critical concern to NIA water users of CAP water. As stated elsewhere, EPA considers the potential 

economic impacts to tribes to argue for flexibility in the compliance timeframe for NGS. This additional 

flexibility also benefits other stakeholders, including the NIA users of CAP water. 

Comment: EPA’s failure to appropriately consider the impacts to agricultural water users renders its 

Factor 2 analysis arbitrary, capricious, and an abuse of discretion 

One CAP agricultural water users group (0305) stated that, as a result of errors and omissions, 

EPA’s factor 2 analysis is arbitrary, capricious, and an abuse of discretion. The commenter asserted that 

there are a range of problems with EPA’s analysis including erroneous assumptions, insufficient support 

for conclusions, failure to consider decreased farming profitability and increased unemployment, failure 

to acknowledge the inability of NIA water users to pass along cost increases as compared to municipal 

users, and other factors. 

Response:

 EPA recognizes that CAP water is an important resource for NIA and other users of water in 

Arizona. As a result, as one of a number of discretionary analyses EPA conducted on the indirect 

impacts on major stakeholders, EPA calculated water rate increases to NIA users of CAP water and 

municipal and industrial users of CAP water. 

EPA disagrees that our discussion of impacts to NIA users of CAP water renders our Factor 2 

analysis arbitrary, capricious, and an abuse of discretion. Neither the CAA nor the BART Guidelines 

require consideration of indirect costs or indirect impacts of controls in a BART analysis. EPA, 

nevertheless, included an evaluation of impacts to some of the major stakeholders in NGS in our BART 

analysis under Factor 2, including NIA users, as consistent with the statement in the BART Guidelines 

that “the energy impacts analysis may consider . . . whether a given alternative would result in 

significant economic disruption or unemployment” (emphasis added).113

EPA recognizes that the information we had available to us about NIA users of CAP water was 

limited, and we acknowledged in the TSD to our Proposed Rule that we had several questions about 

CAP and groundwater availability to NIA water users. EPA appreciates the clarifications and additional 

information provided by NIA users of CAP water during the comment period for our proposals. The 

additional information provided during the comment period about NIA users of CAP water does not 

change our conclusion under Factor 2, that the potential economic impacts to tribes argue for flexibility 

in the compliance timeframe for NGS, because this compliance flexibility also benefits other 

stakeholders, including the NIA users of CAP water. 

Comment: Available options for financing the cost of SCR are limited

One commenter (0087) stated that EPA, DOI and DOE’s attempts to reassure the public that the 

additional controls being imposed by EPA on NGS was misleading. The commenter does not agree that 

it is appropriate to potentially override deficit control measures to pay for costs imposed by EPA. 

Further, the commenter emphasized its opposition to the proposed regulation arguing that EPA cannot 

113 See BART Guidelines at 70 FR at 39169 (July 6, 2005). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

undermine U.S. obligations to the Native American people, erode sustainable water policy, and subject 

struggling Arizonans to high costs, while at the same time crippling national debt. In the commenter’s 

opinion, when the Administration’s own agencies cannot agree, EPA should not require the most 

expensive technology at this time and unnecessarily impose increased costs on the people who can least 

afford it. 

One commenter (0343) stated that the Bureau of Reclamation (BOR) is highly unlikely to be 

able to obtain Congressional appropriations to fund SCR installation. If NGS were to face closure unless 

SCR were to be installed, the commenter asserted it would be forced to consider sources of funding for 

its share of SCR cost, which the commenter estimated to be $125-$175 million. The commenter stated it 

funded the installation of its share of LNB/SOFA through the Development Fund because the 

investment size was sufficiently modest ($45 million for all NGS participants) that it could be managed 

by cash flows in the fund. The commenter asserted that the cost of SCR, however, would overwhelm the 

fund. The commenter stated that the most recent large capital investment, SO2 scrubbers, was funded by 

appropriations provided by Congress. The commenter asserted that neither Congressional appropriations 

nor low-cost 50-year federal loans are currently in place or available today. 

Regarding the use of general obligation and revenue bonds, the commenter (0343) stated that in 

its experience financing the New Waddell Dam with two bonds issues (1990, 1991) totaling 

approximately $264 million, the last of which was paid off in 2011, the source of debt service for both 

of these bonds was an additional cost recovery charge paid by the Salt River Project (SRP) on the power 

it purchased at the time from BOR’s share of NGS. In those bonding actions, the commenter stated that 

SRP’s credit rating was applied to the bond issues rather than using the commenter’s credit rating. The 

commenter stated that it has never established an independent credit rating. Due to the lack of an 

independent credit rating, the large dollar amount associated with a bonding for SCR, along with the 

uncertainties with respect to ownership, the coal contract, lease approval and other factors, the 

commenter believed that bonding for SCR is an untested hypothesis. 

Response:

 In our Proposed Rule, EPA recognized that the source of funding for Reclamation’s share of 

controls was uncertain. We provided some examples for how air pollution controls at NGS have been 

funded in the past, and discussed the Joint Statement between EPA, DOI, and DOE where the three 

agencies committed to, among other things, seek funding to cover the federal portion of pollution 

controls at NGS. EPA also stated, 

it is not clear at this time whether or what type of mechanisms might be 

available to lessen increased costs. Therefore, as explained further below, 

EPA believes that the potential economic impacts discussed in [Factor 2] 

argue for thoughtful consideration of how flexibility in the compliance 

timeframe can be provided consistent with the air quality goals of the 

Clean Air Act.114

EPA recognizes that funding for Reclamation’s share (approximately $130 million for SCR in 

combination with LNB/SOFA on 3 units) is uncertain. However, we noted in our Proposed Rule that 

114 See Proposed Rule at 78 FR 8284 (February 5, 2013). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

The timeframe for compliance would not, in itself, avoid or mitigate 

increases in water rates for tribes located in Arizona; however, it would 

provide time for collaborating federal agencies to explore options to avoid 

or minimize potential impacts to tribes, including seeking funding to cover 

expenses for the federal portion of pollution controls at NGS. 

Thus, we recognize that funding of Reclamation’s share of controls is a critical issue, and it is one that 

the three agencies have committed to addressing together and in consultation with stakeholders.115

However, we also note that the BART Guidelines do not require EPA or states to consider or determine 

the source of funding or financing options available to utilities as part of the five-factor analysis for 

BART. 

4.2 Comments on Energy and Non-Air Quality Environmental Impacts 

Comment: Health impacts of pollutants 

 Many individuals (0020, 0021, 0025, 0047, 0067, 0091, 0113, 0149, 0181, 0210, 0215, 0216, 

0217, 0221, 0235, 0237, 0238, 0240, 0253, 0264.5, 0264.6, 0264.8, 0283, 0288, 0290, 0327, 0357, 0360, 

0364, 0388, 0396, 0399, 0405, 0414, 0415, 0432) asserted that emissions from NGS harm public health 

and the environment. One commenter (0215) referenced a Phoenix Magazine article that indicated that 

Arizona has not “fully” met air quality standards set by EPA since 1979, and urged EPA to review air 

quality data presented by the ALA. Another commenter (0288) argued that modern pollution controls, 

which are required at more than 250 similar coal plants nationwide, would curb NGS's emissions by 84 

percent, thus reducing public health risks while improving visibility at the region's national parks. The 

commenter stated that, according to the NPS, NGS’s emissions cost Arizonans more than $128 million 

per year in healthcare costs and over $1.08 billion in spending at national parks in the Four Corners 

region, although a new analysis estimates healthcare costs at $13 million annually. 

 One environmental advocacy group (0373) stated the pollutants that cause visibility impairment 

(NOx, SO2, PM, ammonia, and sulfuric acid) are the same pollutants that harm public health. The 

commenter noted that NOx reacts with ammonia, moisture, and other compounds to form particles that 

can cause and worsen respiratory diseases, aggravate heart disease, and lead to premature death, and is 

also is a precursor to ground level ozone, which is associated with respiratory diseases, asthma attacks, 

and decreased lung function. The commenter stated that SO2 increases asthma symptoms, leads to 

increased hospital visits, and can form particles that aggravate respiratory and heart diseases and cause 

premature death, while PM can penetrate deep into the lungs and cause a host of health problems, such 

as aggravated asthma, chronic bronchitis, and heart attacks. 

 The commenter (0373) quoted EPA as estimating that in 2015, full implementation of the RHR 

nationally will prevent 1,600 premature deaths, 2,200 non-fatal heart attacks, 960 hospital admissions, 

and over 1 million lost school and work days, resulting in health benefits valued at $8.4 to $9.8 billion 

annually (citing the Fact Sheet for the final Clean Air Visibility Rule). Citing a report prepared by 

George D. Thurston (Thurston report) submitted with the comments, the commenter stated that 

enforcement of BART requirements at NGS will result in total economic health benefits of $14 to $35 

115 See document titled “2013_0104 Joint Federal Agency Statement on NGS” in document number 0005 in the docket for 

this rule at EPA-R09-OAR-2013-0009. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

million per year. The commenter believes that this is a highly conservative estimate because it includes 

only the adverse effects of PM (and excludes ozone and other pollutants) and it only estimates health 

effects in Arizona (and excludes other downwind states). 

 The commenter (0373) added (citing the Thurston report) that because fine particulates and 

ozone are not threshold pollutants, any reduction in these pollutants improves public health, even in 

areas where the National Ambient Air Quality Standards (NAAQS) are met. The commenter stated that 

these expert findings underscore the need for the EPA to finalize its BART determination for NGS 

promptly, and for EPA to reject alternatives to BART that allow years of delay before SCR is installed. 

A member of the Navajo Nation (0412) who is supportive of the proposed BART determination 

stated that NGS and the FCPP are listed as the worst polluters in the report titled “Coal Blooded. Profits 

Before People,” which the commenter attached to its comments.116 The commenter said that the report 

looks at 378 coal-fired power plants in the United States and how these plants play a significant role in 

contributing to a decline in health disproportionately in low income communities and communities of 

color, and in contributing to GHG emissions. The commenter also referred to the Thurston report, which 

is also attached to its comment, noting that this report studies the health impacts of NOx from NGS. 

One commenter (0529) argued that emissions from NGS cause adverse health effects in the 

surrounding area. The commenter discussed the dangers of particulate matter, and particularly emissions 

from power plants. According to the commenter, the U.S. EPA Environmental Benefits Mapping and 

Analysis Program (BenMAP) air pollution-health effects model shows that each year implementation of 

BART is delayed at NGS will result in an additional two to five deaths, 1,000 additional Restricted 

Activity Days, more than 500 extra Asthma Exacerbation Days, and hundreds more Lost Work Days – 

at an equivalent cost to society of more than $13 million per year. 

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 RHR, which included the requirement for facilities of a certain 

age to install 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 are among the same pollutants that 

affect human and ecosystem health. EPA agrees that human health is an important issue, but specific 

actions based solely on human health are beyond the scope of the BART requirement of the RHR. As 

noted above and elsewhere in this response to comments document, other programs under the CAA 

more directly address the impact of stationary sources on public health. 

Comment: Disparate Water Rates

116 Coal Blooded. Putting Profits Before People. Indigenous Environmental Network. Little Village Environmental Justice 

Organization. National Association for the Advancement of Colored People. Lead Researcher-Author: Adrian Wilson, 

University of Massachusetts at Amherst. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 A public interest advocacy group (0413) said that Navajo water haulers pay substantially more 

for water than customers in southern Arizona. The commenter provided the following comparative rates 

to demonstrate that despite the low economic conditions that many Navajo water haulers come from, the 

price they pay is significantly more than Central Arizona Project users: 

 Kaibeto (Navajo community near Page, AZ): $13,034.04/acre-feet of water 

Glendale, AZ residents: $551.00/acre-feet of water 

Tempe, AZ farmer: $41.00/acre-feet of water 

Response: 

 EPA recognizes that the cost of water can vary significantly. Although EPA acknowledges this 

disparity, EPA also recognizes that the potential impacts to tribes in terms of direct revenues and 

increased water costs are still important issues to tribal governments. 

Comment: GHG Emissions/Climate Impact

One public interest advocacy group (0413), a Navajo grassroots organization, supported EPA’s 

original BART proposal to reduce NOx emissions from NGS by 84 percent within 5 years. The 

commenter expressed concern with adverse effects on health and air quality as a result of coal-fired 

power plants like NGS and said that the BART proposal would improve air quality for nearby residents 

and reduce regional haze. The commenter referred to the Synapse report submitted with the 

comments.117 The commenter stated that climate change is here and that the U.S. is seeing more frequent 

occurrences of extreme and amplified floods, seasons, drought conditions, hurricanes and tornadoes. 

These changes in climate disproportionately impact low-income and indigenous people throughout the 

world. Because NGS emits 19 million tons of CO2 annually, adding to GHG emissions that contribute to 

the warming of the atmosphere, the commenter stressed that the Agency must move quickly towards 

renewable energy in order to minimize CO2 emissions. 

Response:

EPA agrees that electric generating units are large source of greenhouse gas emissions, and 

consistent with President’s Obama, “Blueprint for a Secure Energy Future”, EPA has proposed 

greenhouse gas emission standards for new and existing power plants.118 We note that the purpose of the 

RHR is to reduce emissions of visibility-impairing air pollutants. As such, EPA does not have authority 

under section 169A of the CAA or the RHR to regulate emissions of greenhouse gases. 

Comment: Negative Coal Effects – Indian Tribes Most Heavily Affected

One public interest advocacy group (0413) argued that the Navajo and Hopi people suffer the 

majority of the negative consequences of coal development in Arizona and New Mexico, and that due to 

minimal financial resources, tribes end up in compromising and vulnerable relationships with industries 

117 Sustainable Development for the Navajo Nation. Replacing the Navajo Generating Station with Renewable Energy. 

January 6, 2014. Frank Ackerman, PhD, Sarah Jackson, and Spencer Fields. Synapse Energy Economics, Inc. 485 

Massachusetts Avenue, Suite 2, Cambridge, MA 02139. www.synapse-energy.com. 

118 See http://www2.epa.gov/carbon-pollution-standards/regulatory-actions 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

and the Federal government. The commenter stated that this reliance on coal for economic reasons limits 

the ability for these communities to protect their health and natural environment. The commenter cited 

to EPA’s commitment to Environmental Justice and argued that a process is needed that is adequate and 

culturally sensitive so that Indigenous people can be informed completely in their native language in 

order to give them the ability to provide sufficient input. The commenter indicated that many of their 

people only speak Navajo. The commenter stated that these people make a humble, but proud living as 

ranchers, farmers and healers and deserve the right to be heard. These are the people who live closest to 

the environment, who haul water and are important caretakers of the land. The commenter asserted that 

the Navajo people deserve to know what type of pollution is impacting their way of life. 

One private individual (0025/0267) stated that NGS and FCPP were built away from Phoenix 

and Los Angeles to protect the residents from the dangerous pollution and leave the Navajos with the 

pollution. The commenter claimed the NGS, FCPP, CPP, CGS and SJGS contribute to regional haze and 

bronchiolitis to minority children according to State of Arizona Health Statistics rates for 2010. 

 An environmental advocacy group (0401) indicated that historic injustices and inequities for 

impacted local communities from NGS continue to be unresolved and unevaluated by EPA and other 

agencies responsible for energy decisions in the U.S. Southwest. 

Response:

 EPA agrees that there are consequences for human health and the environment resulting from 

coal mining operations and combustion of coal for electricity. EPA notes that our rulemaking for NGS is 

pursuant to the Regional Haze Rule in order to reduce emissions of visibility-impairing pollutants. 

Although human health was not the impetus for triggering a BART determination for NGS, EPA notes 

that some of the same pollutants that affect visibility also affect human health. EPA recognizes that 

many of the comments submitted to EPA from tribal individuals and community groups are most 

concerned about the environmental and human health costs of delaying controls under our framework 

for BART Alternatives, and that many of the comments submitted to EPA from tribal governments 

focused on the economic costs of setting a stringent emission limit for BART. EPA is finalizing the 

TWG Alternative that establishes a cap in cumulative NOx emissions over 2009-2044 (2009-2044 NOx

Cap) based on our final BART Benchmark for NGS. The BART Benchmark is calculated from our 

proposed determination that compliance with an emission limit of 0.055 lb/MMBtu within five years is 

BART. Our final regulation provides flexibility to NGS to achieve more emission reductions than under 

BART in a step-wise manner, while reducing potential adverse economic impacts to tribes and other 

stakeholders, by implementing the TWG Alternative. 

Comment: Coal combustion by-products 

 A public interest advocacy group (0413) asked that waste generated from the combustion of coal 

be considered an environmental impact under Factor 2 Energy and Non-Air Quality Impacts and for that 

reason be required to be removed and cleaned up from the 800-acre land. According to the commenter, 

the coal ash produced by NGS includes 22,500 lbs of chromium, 27,500 lbs of nickel, and 159,000 lbs 

of manganese, which are all carcinogens causing lung, bladder, kidney and skin cancer, and 26,000 lbs 

of lead, which is a neurotoxin. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Response: 

 EPA recognizes that coal combustion residues are an important concern for human and 

environmental health. However, we note that waste from the combustion of coal is not a non-air quality 

environmental impact of controls, which is the purpose of the analysis of Factor 2. Coal combustion 

residues are not a result of SCR or other air pollution controls, but are a result of continued operation of 

NGS, which is not evaluated under Factor 2 of a BART analysis. We note that EPA, in a separate action, 

has proposed a rulemaking related to CCR.119 The on-going NEPA process provides numerous 

opportunities and the appropriate forum to raise these concerns. 

Comment: No basis for public health claim 

 One of the owners of NGS (0348) stated that EPA has no basis for claiming that the NOx

reductions from NGS that would be achieved by the February 2013 Proposal would lead to a public 

health benefit. The commenter noted that EPA establishes NAAQS at levels that are protective of public 

health and welfare with an adequate margin of safety that accounts for sensitive populations such as 

children and the elderly, and that EPA has never found that any of the areas around NGS fail to attain 

the NAAQS. Accordingly, the commenter believes that there is no reason to believe that a reduction in 

plant emissions to address regional haze would produce a public health benefit. The commenter asserted 

that before it can claim that the proposed rule will result in health benefits, EPA must conduct a health 

risk evaluation that follows the four basic steps of the risk assessment process: hazard identification, 

dose response, exposure assessment, and risk characterization. 

 Three private individuals (0088, 0251, 0358) similarly questioned the extent to which NGS 

emissions are impacting public health. One commenter (0088) stated that EPA has not provided any 

medical data demonstrating the frequency or severity of health risks (e.g., asthma and bronchitis) nor 

have they provided statistical evidence that these health risks would diminish due to NGS installing SCR 

technology. Another commenter (0251) claimed that coal used as household cooking fuel is more 

hazardous to public health than emissions from NGS. 

Response:

Section 169A of the CAA and the RHR focus on reducing emissions of pollutants that affect 

visibility with the ultimate goal of restoring visibility at Class I areas to natural conditions. In this 

rulemaking, EPA is setting a limit to reduce NOx emissions from NGS to reduce the visibility impact 

NGS has on 11 Class I areas. It is undisputed that NOx, which is the sum of nitrogen oxide and nitrogen 

dioxide (NO + NO2) is regulated as a criteria pollutant (NO2) as well as a precursor to the formation of 

ozone and PM2.5, two other criteria pollutants.120 EPA has noted elsewhere in this response to comments 

document that some of the pollutants that affect visibility are also regulated as criteria pollutants that 

affect human and ecosystem health. In our discussion of EO 13045 in our Proposed Rule and 

Supplemental Proposal, EPA has stated “to the extent that the rule will reduce emissions of NOx, which 

contribute to ozone and fine particulate matter formation as well as visibility impairment, the rule will 

have a beneficial effect on children’s health [by] reducing air pollution that causes or exacerbates 

childhood asthma and other respiratory issues.”121 EPA notes that the purpose of this rule is to reduce 

119 http://www.epa.gov/solidwaste/nonhaz/industrial/special/fossil/ccr-rule/index.htm 120 See, for example, http://www.epa.gov/air/urbanair/ 121 See 78 FR at 8292 (February 5, 2013) and 78 FR at 62519 (October 22, 2013). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

visibility impairment caused by emissions of NOx from NGS and involves conducting a five-factor 

analysis as required by the CAA that includes an analysis of the anticipated visibility benefits of 

controls. This process does not involve a health component and therefore, EPA has not conducted a 

health risk evaluation for this rulemaking that attempts to characterize or quantify a public health 

benefit. 

Comment: Impact on ecosystems 

 Six private individuals (0327, 0360, 0393, 0405, 0414, 0415) discussed how the emissions from 

NGS have heavily affected the health of local animals and plant life in the area, which they rely on for 

food. Three commenters (0360, 0405, 0414) specifically stated that fish in local streams are not 

consumable due to high levels of mercury and other toxins, which they believe is a result of NGS 

emissions. Another commenter (0415) agreed that levels of mercury in nearby streams and lakes, 

including Lake Powell are concerning. Similarly, one private individual (0307) noted that forests in 

Arizona and surrounding states are plagued with bark beetles, because the trees are too weak to fight the 

infestation, which the commenter contributes to NGS emissions. 

 One environmental advocacy group (0373) stated the pollutants that cause visibility impairment 

harm terrestrial and aquatic plants and animals, soil health, and moving and stationary water bodies—

entire ecosystems—by contributing to acid rain, ozone formation, and nitrogen deposition. The 

commenter explained that nitrogen deposition, caused by wet and dry deposition of nitrates derived from 

NOx emissions, causes well-known, adverse impacts on ecological systems; in some places saturation of 

the soil already exceeds the “critical load” the ecosystem can tolerate. The commenter added that acid 

rain causes acidification of lakes and streams and can damage certain types of trees and soils; in 

addition, acid rain accelerates the decay of building materials and paints, including irreplaceable 

buildings, statues, and sculptures that are part of the U.S. cultural heritage. 

Response:

 As stated previously, section 169A of the CAA and the RHR focus on reducing emissions of 

pollutants that affect visibility with the ultimate goal of restoring visibility at Class I areas to natural 

conditions. As such, reducing emissions from NGS for the specific purposes of improving human, 

animal, plant, or ecosystem health is beyond the scope of this rulemaking. We note that the joint EIS 

process for the NGS and Kayenta Mine renewals is an appropriate venue for raising concerns related to 

other environmental impacts of NGS and the Kayenta Mine. 

Comment: Water use impacts

 Four individuals (0248, 0240, 0363, 0399) believe that water conservation in the Southwest is 

extremely important because of the dry desert climate. The commenters warned that the Colorado River 

is under enormous stress, partly due to NGS and CAP water demands. 

 One of the commenters (0363) noted that the snowpack feeding the headwaters of the Colorado 

River in the Rocky Mountains have reduced over the years, along with a decrease in the surface areas of 

Lakes Powell and Mead, which the commenter believes is a result of climate change exacerbated by 

NGS emissions. The commenter added that not a single drop of the Colorado River flows to the sea at its 

natural mouth in the Gulf of California, and warned that mega-droughts of historic proportions are 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

projected for the Southwest in the coming decades. Another commenter (0399) demanded that EPA 

maximize Indian water right claims to the Colorado River and the Little Colorado River in order to 

create jobs and improve infrastructure services for residents living without access to water. 

Response: 

 EPA recognizes that water in the Desert Southwest is a critical issue. However, water use and 

changes in water availability as a result of climate change are beyond the scope of this rulemaking. 

Comment: Impact on groundwater 

 Some commenters, including a CAP agricultural water users group (0305), an industry trade 

association (0306), an industry/commerce commenter (0416), and an association of CAP water 

distributors (0398), stated that large increases in the cost of CAP water resulting from installation of 

SCR or closure of NGS could cause the unintended consequence of agricultural and industry users 

shifting back to groundwater supplies. These commenters generally noted that the availability of CAP 

water has been a critical element in arresting the severe groundwater that affects most groundwater 

basins in the state. 

One commenter (0348) stated that as the cost of power increased for delivery of CAP water, an 

unanticipated result would likely materialize – the substitution of more groundwater for CAP water, 

which would risk a shift in the current state’s water portfolio toward more non-renewable supply. The 

commenter suggested that increases in delivered water cost could range between $8-16 per acre-foot 

(depending on whether baghouse technology would also be required) resulting in approximately a 17-33 

percent increase. The commenter noted that such increases were validated by the NREL study. 

 In detailed comments, one CAP agricultural water users group (0305) asserted that EPA failed to 

properly weigh the BART proposal’s impact on Arizona’s already-stressed aquifers in its factor 2 

analysis. The commenter asserts that by raising CAP water costs for agricultural water users to levels 

well beyond those of groundwater pumping costs, a determination that SCR is BART would cause 

many, if not all, agricultural water users to stop taking delivery of CAP water and switch to groundwater 

pumping, a move driven by the commercial realities of the commodity crop marketplace. According to 

the commenter, this would directly contradict a consistent public policy goal of the State of Arizona and 

the federal government to protect and preserve Arizona’s aquifers. 

 This commenter (0305) stated that EPA did not evaluate the impact that selecting SCR as BART 

would have on Arizona groundwater supplies due to an erroneous assumption that agricultural water 

users may not be able to return to groundwater if CAP water is not available. To the contrary, the 

commenter believes that groundwater pumping in Arizona is a matter of state law, and agricultural water 

users generally have continuing rights to pump groundwater from their lands, even if they rely upon 

CAP water. The commenter is not aware of any state law that precludes its members from exercising 

these continuing rights to pump their full entitlements of groundwater once CAP water is no longer 

available to them. The commenter noted that cost of water is already the Central Arizona farmer’s 

highest operating expense, and asserted that farmers will turn to groundwater pumping as the only 

remaining economic source of water if CAP water becomes unavailable. 

 The same commenter (0305) stated that the impact on Arizona’s aquifers of a broad switch to 

groundwater would be swift, devastating, and irreversible, causing water level declines, land subsidence 
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and earth fissuring. According to the commenter, water tables, especially in Arizona’s Active 

Management Areas, would decline and be less able to act as a flexible buffer in times of drought, and 

wells would become less productive and run dry. 

 The commenter (0305) indicated that Arizona groundwater is a scarce, non-renewable, and 

precious resource and that groundwater overdraft has been a concern of the federal government or the 

State of Arizona for at least 75 years. The commenter noted that state law strictly controls the use of 

groundwater, and added that a principle purpose of CAP’s enabling legislation was the protection of 

groundwater. The commenter concluded that to properly consider the non-air environmental impacts of 

SCR as BART in its factor 2 analysis, EPA must consider the impacts that SCR installation, and the 

resulting CAP water rate increases, would have on Arizona groundwater supplies. 

One public/private coalition commenter (0381) also noted significant concern that the increase in 

costs would direct certain industries away from renewable water supplies to more economical, but 

scarce, groundwater. 

Response:

As previously stated in our TSD to our Proposed Rule, EPA recognized increased use of 

groundwater, as expressed by NIA users of CAP water, is a potential indirect effect of our BART 

determination for NGS. EPA recognizes the importance of maintaining, preserving and replenishing 

ground water, and that increases in CAP water rates may adversely affect the goal of reducing 

groundwater usage. As stated elsewhere, EPA considers the potential economic impacts to tribes to 

argue for thoughtful consideration of how flexibility can be provided consistent with the air quality 

goals of the CAA. This consideration of additional flexibility also benefits other stakeholders, including 

the NIA users of CAP water. 

Comment: Impact on Navajo Aquifer

 One public interest advocacy group (0413) stated that Peabody Energy (operator of the Kayenta 

Mine) has been pumping water from the Navajo Aquifer from beneath Black Mesa for industrial 

purposes for over 40 years and must be looked at as an environmental and cultural impact under Factor 2 

Energy and Non-Air Quality Impacts. Further, Peabody Energy uses 1,400 acre-feet per year since 2006 

for its Kayenta Mine operations that provides the coal used at NGS, according to the commenter. Before 

that, the company withdrew on an average of 4,000 acre-feet per year to slurry coal to Nevada, the 

commenter said. The commenter stressed the importance of the Navajo Aquifer as the lifeline to Black 

Mesa and more than 50,000 Navajo and Hopi people. In the commenter’s opinion, the extreme amount 

of water used by Peabody presents a challenge to the natural function of the Navajo Aquifer, which 

jeopardizes the future supply of water supply and the quality of the water. To the Navajo and Hopi, 

Black Mesa and the Navajo Aquifer are also of cultural and spiritual significance, according to the 

commenter. 

One private individual (0261) submitted photos illustrating the effect of pumping water from the 

Navajo Aquifer on land subsidence on Black Mesa. 

Response:
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 EPA recognizes that the Navajo Aquifer is a critical resource to the Navajo and Hopi individuals 

living on Black Mesa. The on-going NEPA process provides numerous opportunities and the appropriate 

forum to raise concerns related to the impacts of mining and use of water from the Navajo Aquifer. We 

further note that representatives of DOI attended all the public hearings on NGS held by EPA and are 

aware of the issues raised by commenters during the BART process regarding mining and the Navajo 

Aquifer. 

Comment: Energy shortage 

 Two individuals (0266, 0292) fear that the closure of coal-power plants, like NGS, may lead to 

an energy shortage in the United States, particularly as the demand for energy grows. One commenter 

(0292) expressed concern that a lack of available energy would result in numerous blackouts and/or 

interruptions of service throughout the United States. Another commenter (0266) explained that 

Arizona's population is expected to double within the next 35 years to well over 13 million people, and 

the power required to meet this demand will be upwards of 100 billion kWh, which is equal to 23 GW or 

10 NGS plants. 

Response:

EPA recognizes that NGS is an integral part of the Western Grid, the interconnected system of 

generation and power transmission lines in the Western United States. While NGS is an important 

contributor to the Western Grid, it is only one of hundreds of power stations that provide power to 

customers in the western states. 

 The NREL study that was conducted to investigate pricing impacts and adequacy of power 

supply should NGS close indicated sufficient power on the Western Grid is available for replacement 

purposes.122 Should NGS close for any reason, the NREL study indicates that multiple options are 

available to replace the NGS power from other generating sources. 

 With regard to the longer term, the Western Grid is monitored and regulated by the WECC, 

whose membership consists of the power generators throughout the western states. WECC’s role is to 

ensure electric reliability at all times throughout the region. WECC planning studies are conducted 

annually and project a 10-year forward market assessment. Growth in power demand throughout the 

region is forecasted and new planned generation and transmission facilities are accounted to ensure that 

the 10-year plan presents adequate growth in generation and transmission to meet the region’s increasing 

need for power. As demand for power grows, as referenced in the comments referring to the projected 

growth in Arizona, there will be new generation developed to keep pace with such growth and to retain 

reliability on the western system. The WECC’s main role is to ensure that such development keeps pace 

with the increasing demand for power. 

122 NREL report, Figure 2-6, p. 34. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

5.0 Comments on Factor Three – Existing Controls at NGS 

Comment: Support for EPA’s consideration of existing controls 

 A CAP agricultural water users group (0305) commented that EPA’s consideration of the 

existing controls at NGS is appropriate and well-supported. The commenter noted that EPA’s 

consideration of the NGS’ voluntary investment in LNB/SOFA takes into account that more than 90,000 

tons of NOx emissions reductions have already been achieved at NGS. The commenter also expressed 

support for the EPA’s recognition of the efficacy of the existing SO2 and PM controls in the context of 

its decision that BART determinations for SO2 and PM are not necessary or appropriate. 

Response:

EPA acknowledges that some commenters support our consideration of existing controls. 

Elsewhere in this response to comments document, we summarize and respond to other comments 

related to our proposed LNB/SOFA credit (section 8.5) and PM and SO2 controls at NGS (sections 8.2 

and 8.3). 

Comment: EPA failed to consider existing controls 

 The operator of the Kayenta Mine (0384) quoted EPA’s Proposed Rule as stating that the early 

installation of LNB/SOFA would not influence EPA’s determination of the proper NOx reduction 

required to achieve BART (citing 78 FR 8284), and added that the Proposed Rule shows that EPA used 

the same approach in modeling (citing 78 FR 8287). Based on this, the commenter concluded that EPA 

failed to consider existing controls, which is impermissible. The commenter stated that EPA cannot 

ignore the previously installed LNB/SOFA and cannot lump the LNB/SOFA with SCR when assessing 

the BART factors. 

Response:

EPA disagrees with the assertion that we failed to consider existing controls. As described in our 

Proposed Rule, our analysis using a 2001 -2003 baseline is consistent with the BART Guidelines and 

agreements between EPA and SRP, as well as SRP and Grand Canyon Trust. Because we used a 2001 – 

2003 baseline in our BART analysis, EPA evaluated LNB/SOFA as a separate control technology, as 

well as a technology that can be used in combination with post-combustion control technologies (i.e., 

SNCR and SCR).123 EPA notes that we also discussed the voluntary installation of LNB/SOFA under 

Factor 3: Existing Controls at NGS.124 The CAA requires consideration of existing controls as one of 

five factors; however, the BART Guidelines provide little guidance on how to consider existing controls, 

except to enumerate the five factors required under the CAA and to direct states (and EPA) to consider 

ways to improve the performance of existing control devices.125 As discussed in section 8.5 of this 

response to comments document, EPA properly considered baseline emissions over the period 2001-

2003 in our analysis of cost effectiveness and anticipated visibility benefits of controls. Therefore, 

although we did not “consider existing controls” in the exact manner preferred by the commenter, we 

did consider the existence of LNB/SOFA in Factor 3 of our BART analysis, and in a manner that is 

123 See Proposed Rule at 78 FR at 8280, 8284 and 8285 (February 5, 2013). 124 Id. at 8284. 125 See Final BART Guidelines at 70 FR at 39163 and 39166 (July 5, 2005). 
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consistent with RHR baseline period and the mutual understandings between EPA, SRP (the operator of 

NGS), and Grand Canyon Trust, developed during the PSD permit process to allow construction of the 

LNB/SOFA on one unit per year over 2009-2011.126

We also note that in our Proposed Rule and Supplemental Proposal, EPA recognized that SRP 

did voluntarily install LNB/SOFA on one unit per year over 2009-2011 and that the early installation of 

modern combustion controls in advance of our proposed BART determination for NGS resulted in early 

and real emission reductions from the facility. As described in our Proposed Rule, EPA also proposed to 

credit NGS for these early reductions in evaluating BART Alternatives. Based on our thorough 

discussion of the early and voluntary installation of LNB/SOFA at NGS in our five-factor BART 

analysis and in our framework for BART Alternatives, EPA disagrees with the assertion that we failed 

to consider existing controls. 

Comment: EPA should determine existing controls to be BART 

 Several private individuals (0046, 0069, 0222, 0233, 0243, 0272, 0392) noted that NGS has 

spent millions of dollars on LNB/SOFA to reduce NOx emissions, improve visibility, and comply with 

existing requirements. One of the commenters (0222) questioned why EPA would propose new haze 

requirements before fully understanding the improvements realized by existing controls. 

One of the owners of NGS (0348) and the operator of the Kayenta Mine (0384) also noted that in 

2009-2011, the NGS voluntarily installed LNB/SOFA on all three units at NGS, reducing NOx

emissions to levels below the presumptive NOx emission levels in the RHR. One of the commenters 

(0348) added that LNB/SOFA eliminated more than 17,000 tons of NOx emissions per year. This 

commenter stated that with LNB/SOFA, the NOx emission rate from all three units at NGS is less than 

the actual NOx emission rates at 236 other coal fired generating stations that are catalogued in EPA’s 

CAMD. 

 According to this commenter (0348), installing LNB/SOFA prior to a requirement to do so under 

the RHR or any other CAA requirement has resulted in greater total NOx emission reductions in the first 

regional haze planning period than would be required by the most stringent EPA BART determination 

(illustrated by a figure in the comments). The commenter stated that EPA should recognize that the 

existing controls at NGS provide a cost-effective means of reducing NOx emissions to a level that is 

lower than more than 200 other coal-fired facilities, and lower than 37 plants operating with SCR. 

The same commenter (0348) stated that EPA supported its proposed BART determination by 

comparing NGS to the NOx emission rates of the 10 largest coal-fired power plants in the nation and 

reporting that NGS has not reduced NOx emissions as much as other large plants despite the installation 

of LNB/SOFA. The commenter asserted that this comparison is inappropriate because the other plants 

were required to install SCR to address issues such as ozone nonattainment, not for regional haze. 

Response: 

 As stated previously, EPA recognizes that the early and voluntary installation of LNB/SOFA on 

one unit per year in 2009-2011 at NGS resulted in significant emission reductions from NGS. However, 

we disagree with statements that LNB/SOFA was installed to comply with existing requirements 

126 See Proposed Rule, 78 FR at 8284 – 8285 (February 5, 2013) and references therein. 
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because no requirements existed in 2009 that required the installation of LNB/SOFA. We also disagree 

that EPA should wait to determine the visibility improvements realized by LNB/SOFA before 

conducting a BART determination for NGS. EPA began evaluating BART for NGS in 2007 and when 

we issued a pre-construction permit in 2009 to NGS to allow SRP to install LNB/SOFA over 2009-

2011. During permitting, SRP and Grand Canyon Trust clearly articulated an understanding that the 

early installation of LNB/SOFA would not prejudice in any way the implementation of more effective 

NOx and particulate matter controls at NGS under the regional haze program.127 EPA understood this 

agreement meant that we would not forgo doing a BART determination for NGS based on SRP’s 

voluntary and early installation of LNS/SOFA. EPA did not interpret this agreement to preclude 

consideration of the installation of controls during our BART determination. 

 EPA agrees that the early installation of LNB/SOFA on one unit per year was voluntary and 

resulted in .NOx reductions. EPA recognizes that LNB/SOFA are cost-effective, however, based on our 

five-factor analysis, we have determined that SCR+LNB/SOFA is also cost-effective and we disagree 

that a limit of 0.24 lb/MMBtu is BART for NGS. Although the commenter asserts that our comparison 

of the NOx emission rates from NGS and the 10 largest coal-fired power plants in the country is 

inappropriate, we note that EPA did not base our proposed BART determination on this comparison. 

Our proposed BART determination is based on our five-factor analysis for NGS. In the introduction 

section of our TSD to the Proposed Rule, EPA included a section titled “A BART Determination for 

NOx is Necessary or Appropriate.”128 Within that section, EPA discussed the numerous Class I areas 

near NGS and the visibility requirements of the CAA and the RHR. EPA also noted that NGS has 

consistently ranked among the twenty highest NOx emitters in the country and in 2011, was the fifth 

largest source of NOx in the United States. However, based on comments on the ANPR, EPA also 

presented ranked data in terms of the amount of NOx emitted per heat input. In terms of this metric, 

NGS ranked number 261 in terms of its lb/MMBtu NOx rate in 2011. Previously, commenters suggested 

that ranking NGS in terms of the NOx rate was more meaningful than reporting only total tons of NOx

emitted and that per unit of energy input, NGS produces fewer NOx emissions than 261 other power 

plants in the United States.129 EPA does not dispute this fact, but notes that this ranking ignores the size 

(in MW) and the capacity factor of the unit, which both affect annual NOx emissions. In the TSD to our 

Proposed Rule, in addition to presenting emissions data as a ranking in terms of total tons of NOx and 

NOx rate (lb/MMBtu), EPA considered the largest coal-fired power plants (NGS tends to rank among 

the largest coal-fired power plants in the country) to assess how NGS compares to the largest coal-fired 

power plants in the country in terms of lb/MMBtu. EPA noted that “although NGS has reduced NOx

emissions in recent years through the installation of new combustion controls, it has still not kept pace 

with the largest coal-fired power plants in terms of reducing emissions of NOx.” While the commenter is 

correct that many of the largest coal-fired power plants in the country reduced emissions of NOx for 

other requirements, that does not negate the fact that, as stated in our TSD, “NGS remains among the 

largest sources of NOx (in terms of total tons of NOx) not only because it is among the largest (heat 

input) power plants, but also because its NOx emission rates is still relatively high compared to other 

large coal-fired power plants.”130 EPA’s presentation of this information was appropriate and 

reasonable, as it was yet another way to understand the same set of emissions data. Although the data 

was used to understand emissions from NGS in the context of other power plants throughout the 

country, it was not used, as the commenter asserts, as support for our proposed BART determination. 

127 See 78 FR at 8284 and 8285 (February 5, 2013) and references therein. 128 See pages 21-24 of the TSD to the Proposed Rule. 

129 See page 24 of SRP comments on the ANPR dated October 2009, submitted by letter dated October 28, 2009 from 

Richard Hayslip. In this letter, SRP cited 2008 data to suggest that NGS produces fewer NOx emissions than 166 other power 

plants in the country. 

130 See page 23 of the TSD to the Proposed Rule. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

6.0 Comments on Factor Four – Remaining Useful Life of NGS 

Comment: Other factors influencing the continuing operation of NGS 

 One of the owners of NGS (0348), a state agency (0017/0289/0320), three CAP water 

distributors (0060, 0194, 0214), two industry/commerce commenters (0052, 0306), and the CAP 

operator (0343) stated that the schedules proposed by EPA for installation of SCR in the proposed 

BART Determination and in Alternative 1 do not provide sufficient time to resolve a number of 

uncertainties facing NGS before the NGS Participants would have to invest significant capital in 

additional controls, with the result that NGS could be forced to shut down. Commenter 0348 submitted 

the most comprehensive comments on this topic and characterized these uncertainties and the related 

concerns as follows: 

 The initial terms of the plant site lease, Rights Of Way (ROWs) for the plant, railroad, and 

transmission lines, and other critical agreements begin to expire in 2019. The renewal or 

extension of these agreements will not be final until comprehensive federal environmental 

reviews are completed. The NGS Participants have reached agreement with the Navajo Nation to 

extend the lease for the plant through 2044 under terms that will increase future operating costs. 

o Those reviews will cover over 20 federal actions and require the complex coordination of at 

least 10 federal agencies and 15 Native American Tribes. Once the reviews are completed, 

the federal agencies will issue a Record of Decision (ROD) and the Secretary of the Interior 

must decide whether to approve or disapprove the extensions. 

o Federal participation in NGS complicates the process because the U.S. Bureau of 

Reclamation (BOR) acts as a project participant on behalf of the United States. Under the 

NGS operative agreements, many decisions, including extending the operating life of the 

plant, require unanimous consent of the participants. The United States may not legally 

authorize, fund, or implement agreements to extend the operations of NGS prior to 

complying with the National Environmental Policy Act (NEPA), the Endangered Species Act 

(ESA) and the National Historic Preservation Act (NHPA), which requires a comprehensive 

multi year federal environmental review process. The Bureau of Indian Affairs (BIA) also 

must approve the new lease. 

o Given the number of stakeholders involved, BOR’s role in the process, the complexity of the 

project, and the extensive public input that is expected, the federal reviews will take several 

years and likely will be subject to litigation. 

o The NGS Participants are concerned that EPA’s proposal will not allow sufficient time to 

complete the federal environmental review processes, resolve anticipated litigation, secure 

the necessary air permits, and complete the design and construction of the additional 

controls. The NGS Participants cannot justify significant capital expenditures on the 

procurement and construction of emissions controls until the lease extension is approved, 

risks of litigation begin to diminish, and they are reasonably certain the plant can continue to 

operate. Additionally, the United States may not be able to authorize or fund the capital 

improvements necessary to comply with the proposed rule until it has complied with NEPA, 

ESA and NHPA, which will take several years. 

 Coal for NGS is supplied by the Kayenta Mine, which is managed by Peabody Western Coal 

Company (Peabody). The coal supply agreement with Peabody needs to be extended beyond 

2019, and is currently being renegotiated. The renegotiated agreements will likely result in 
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higher future operating costs for the NGS Participants, which would affect the overall economics 

of NGS and has not been taken into account in the EPA’s analysis. 

 Two of the current NGS Participants, the Los Angeles Department of Water and Power 

(LADWP) and NV Energy (NVE), have indicated their intent to exit NGS or are required to exit 

NGS, before 2020. LADWP has publically stated its objective of exiting NGS by the end of 

2015. This future ownership uncertainty creates a substantial challenge because all NGS 

Participants may not be able or willing to commit to the significant financial investment. If EPA 

imposes a requirement to install SCRs before the ownership issues are resolved, the remaining 

NGS Participants are not likely to approve the investment. 

According to the commenter (0348), as a result of these uncertainties, the timelines EPA proposed for 

installation of additional controls in its BART Determination (SCR within 5 years) and Alternative 1 

(SCR in 2021 2023) are problematic for the NGS Participants. The commenter added that although the 

commenter is working with the other NGS Participants, various federal agencies, and Native American 

interests to resolve each of these uncertainties, it will be several years before the NGS Participants will 

be reasonably certain that the plant will continue to operate. The commenter asserted that if EPA were to 

issue a final BART rule that includes only its BART Determination and Alternative 1, NGS likely would 

be forced to close. 

 The commenter (0348) submitted a timeline illustrating the alleged timing constraints. According 

to this timeline, the ROD approving the extension of the leases would be expected to be issued in 2018, 

and it would then take until 2026 to plan and design, permit, and construct the controls on the three units 

at NGS. 

 The commenter (0348) noted that while acknowledging that NGS may continue to operate until 

2044 as a potential outcome of the lease renewal negotiations, EPA also recognized that these various 

uncertainties could affect the facility’s ability to operate in the future and proposed a useful life value of 

20 years for NGS and used this value as the default for amortization purposes (citing 78 FR 8285). The 

commenter asserted that if either the proposed BART determination or the proposed Alternative 1 were 

made final, NGS would likely shut down by 2019 because the NGS Participants are not likely to make 

large capital improvements without certainty that the plant could continue to operate beyond 2019. 

Response:

 As discussed in our analysis of Factor 2, EPA conducted an Affordability Analysis to determine 

whether the installation and operation of SCR would make electricity generation at NGS more costly 

than purchasing power on the wholesale market, as a way to evaluate whether SCR would force NGS to 

close. Based on our analysis, the installation and operation of SCR would not make electricity 

generation at NGS more costly than purchasing power on the wholesale market; therefore, EPA 

determined that a useful life of NGS of 20 years as the default value for amortization purposes was 

appropriate. 

EPA recognized that the owners of NGS might express the need for additional flexibility in the 

compliance timeframe. EPA proposed the 2021-2023 timeframe in Alternative 1 because that timeframe 

would allow total emissions under Alternative 1 to be lower than the BART Benchmark when 

accounting for the LNB/SOFA credit. EPA put forth two examples that provided additional time for 

compliance (Alternatives 2 and 3, with compliance in 2023-2025 and 2024-2026, respectively), where 

total emissions were not lower than the BART Benchmark but could be viable if the owners of NGS 
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achieved additional emission reductions to bridge the deficit in NOx emission reductions.131 Based on 

this framework, the Technical Work Group on NGS put forth in Appendix B to the TWG Agreement 

that included the closure of one unit (or equivalent curtailment) by the end of 2019, in addition to the 

LNB/SOFA credit, to allow additional time for compliance with a limit achievable with new postcombustion controls (i.e., SCR). 

Comment: EPA should have accounted for a 30-year life 

 As discussed elsewhere in this response to comments document (section 3.0), one commenter 

(0367) asserted that the lifetime of an SCR system for NGS should be at least 30, not 20 years. The 

commenter argued that even a 30-year lifetime is itself very conservative as many SCRs installed in 

Europe in the 1980s are still in operation today, and an analysis prepared by Black & Veatch for another 

facility assumed a 40-year lifetime for SCR. The lifetime of an SCR retrofit is generally set equal to the 

remaining useful life of the facility – in this case 2044. There is no support in the record for a 20-year 

lifetime and the cost assumptions associated with it. 

Response:

 As discussed in our responses in section 3.0 of this response to comments document, using an 

amortization period of 30 years instead of 20 years would lower the annual cost of controls, making 

SCR appear more cost-effective. EPA has already determined that SCR at NGS is cost-effective, and 

EPA would still determine that SCR at NGS is cost-effective if the annualized cost was lower. This 

would not change our overall determination that an emission limit achievable with SCR is BART for 

NGS. 

131 See 78 FR 8290 (February 5, 2013). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

7.0 Comments on Factor Five – Anticipated Visibility 

Improvements 

Comment: General 

 Numerous individuals (0016, 0026, 0036, 0042, 0044, 0045, 0046, 0048, 0051, 0053, 0054, 

0069, 0070, 0075, 0077, 0078, 0079, 0081, 0086, 0088, 0099, 0106, 0109, 0132, 0145-0148, 0160, 

0161, 0165, 0167, 0168, 0193, 0195, 0200, 0203, 0205, 0212, 0222, 0233, 0251, 0264.1, 0265, 0266, 

0277, 0299, 0329, 0437), government commenters (0287, 0324, 0406), a public/private coalition (0400), 

a chamber of commerce (0140), and industry/commerce trade associations (0084, 0278) questioned the 

extent to which NGS emissions impact visibility at national parks and wilderness areas or disputed 

EPA’s analysis that installation of SCR at NGS would improve visibility. Most of these commenters 

blame the haze on emissions produced from other sources, such as cars, dust storms, forest fires, and 

prescribed burns, as well as pollution produced from nearby cities and states including California. 

Nearly all of the listed commenters, as well as three additional individuals (0056, 0133, 0292) and an 

industry/commerce commenter (0052), encouraged EPA to review existing studies (i.e., an NREL study, 

a study published by the Arizona Republic, and analyses conducted by SRP and done in coordination 

with EPA) that show that NGS does not have a significant impact on regional haze, and that NOx

controls would yield an improvement in visibility at the Grand Canyon. Many commenters also 

suggested that EPA offer more time for people to review the rule and provide comments. 

 Three individuals (0016, 0088, 0233) stated that the wind direction near and around the Grand 

Canyon blow predominantly west to east; thus, emissions from the NGS are pushed away from parks 

(including Zion and Bryce parks) not towards them. One of these commenters (0088) acknowledged that 

parts of Grand Canyon National Park are located within 20 miles of NGS, but emphasized that the most 

visited areas of the park are located more than 70 miles away from the plant. This commenter proposed 

shutting the NGS plant down for a week to see if there are any improvements to visibility at the national 

parks and wilderness areas. 

One commenter (0251) contended that SO2 emissions are a greater contributor to the production 

of haze than NOx emissions, and noted that these emissions at NGS have already been reduced by 95 

percent. Another commenter (0222) mentioned reports that concluded that power plants represent only 

about 5 percent of the emissions that occasionally create haze at the Grand Canyon. 

 One commenter (0358) has not seen evidence of a pollution problem near Lake Powell. In 

contrast, two individuals (0360, 0414) specifically stated that they have experienced haze at Lake 

Powell.

Response:

 We are aware of the studies cited by commenters purporting to show that controls on NGS would 

yield little visibility improvement, and we address them in responses below. We are also aware of work 

performed by the Western Regional Air Partnership showing the relative proportions of sulfate and 

nitrate visibility impacts, and the relative contributions from various types of pollution sources, with 

nitrate from point sources being relatively small.132 We note that the analyses of the most-impaired days 

have a substantial or even dominant contribution from mainly non-anthropogenic wind-blown dust or 

132 See, e.g. WRAP PM Source Apportionment Technology (PSAT) results, available on WRAP Technical Support System, 

Source Apportionment web page at http://vista.cira.colostate.edu/TSS/Results/SA.aspx 
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fires; but that does not mean nitrate contributions from stationary sources are small on other days. In any 

case, a BART determination is required under the Regional Haze Rule because our modeling, conducted 

according to the procedures set out in the BART Guidelines, has shown that NGS causes visibility 

impairment at multiple Class I areas. The RHR requires that the Best Available Retrofit Technology 

(BART) be installed on certain old, large stationary sources as part of the overall approach to improving 

visibility at Class I areas. No one individual control will be sufficient to meet the goal of “remedying of 

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

manmade air pollution”, as set out in Clean Air Act section 169A. Under BART, controls must be 

imposed when a BART-eligible source has the potential to contribute to visibility impairment and costeffective retrofit controls are available, as we have shown for NGS, in accordance with the five factor 

determination set out in the BART Guidelines. 

 On the issue of wind direction, we note that the CALPUFF modeling uses three years of hourly 

meteorological input, which is based on meteorological modeling as well as observational data from 

stations throughout a large area. The input includes wind speed and direction, and would include the 

particular wind direction patterns noted by the commenter. The more sophisticated meteorological 

treatment in CALPUFF enables it to track the pollutant plume from NGS, including its twists and turns 

over multiple days. This is necessary since pollutants do not necessarily follow a straight line single 

wind direction path from NGS to the Grand Canyon. We believe that the approach used in our modeling 

adequately accounts for winds noted by the commenter. 

On the various locations within the Grand Canyon, we note that the CALPUFF modeling carried 

out according the BART Guidelines includes all locations in Grand Canyon National Park, as well as in 

ten other Class I areas. The analysis does not weight particular locations on the basis of visitor 

frequency. Rather, for each modeled day it takes the worst visibility location over the whole area, and 

then finds the 98th percentile among the days (i.e. it excludes the worst seven or so days for each year). 

The underlying visibility goal applies to the entire Class I area, all of which may be visited, and we have 

no basis for excluding particular locations. We also note that vistas seen by visitors necessarily extend 

over many miles, including less-visited areas, so visibility impairment at the latter would be noticed at 

the more-visited areas. 

EPA considers it impractical and unnecessary to shut down NGS to determine its visibility 

impact; that is the purpose of the CALPUFF model as laid out in the BART Guidelines. A temporary 

closure of NGS would result in a substantial impact to the operator of NGS and those that rely on power 

from the facility. In addition, because visibility is the result of the interaction of pollutants from many 

sources, and that interaction varies with meteorology, teasing out the particular effect of NGS would not 

be straightforward. It would require an expensive and time-consuming new study that would be 

impractical and well beyond the level of effort envisaged in the BART Guidelines, which laid out an 

“off-the-shelf” approach applicable to the many sources subject to BART across the country. We believe 

that the CALPUFF approach is adequate for purposes of assessing the visibility impact of NGS. 

Lake Powell is not specifically included in the CALPUFF modeling of NGS, which under the 

RHR and the BART Guidelines focuses on Class I areas, such as national parks. We note that visibility 

impairment close to NGS, such as at Lake Powell, may also be caused by phenomena other than the 

regional-scale haze impairment that occurs as chemical reactions proceed over longer distances. 

Conversely, controls imposed to address visibility impairments at Class I areas are likely to provide 

some benefit in the general area in which Lake Powell is located. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Comment: General support for EPA’s visibility modeling analysis 

 One environmental advocacy group (0373) supported EPA’s modeling results for NGS and 

concluded that NOx emissions from NGS have a substantial impact on visibility in many of the 11 Class 

I areas within 300 kilometers (km) of NGS, with impairment greater than 1 dv at each of the areas. The 

commenter added, based on a report prepared by Victoria Stamper (Stamper report) and submitted with 

the comments, that while EPA limits its BART review to Class I areas within 300 km, there a number of 

other national parks and wilderness areas within 400 km that would likely experience improved air 

quality as a result of BART at NGS. The commenter noted that the RHR establishes a target for 

achieving natural visibility conditions at all Class I areas by 2064, which is within 50 years, and asserted 

that dramatic reductions in visibility impairment attributable to NGS are a prerequisite to meeting this 

goal. The commenter added that it will be nearly impossible to know what other sources in the region 

must do in the first implementation phase (by 2018) absent timely emission reduction at NGS. 

 Another environmental advocacy group (0395) said that it is crucial to apply the most rigorous 

emissions controls available to address NOx emissions at NGS in order to sufficiently protect the 

surrounding Class I areas. The commenter discussed how EPA correctly addressed, via a rigorous 

BART methodology, emissions from NGS under all atmospheric conditions. The commenter pointed out 

that even very small amount of pollution emitted on a clear day degrades visibility dramatically. Also, 

the commenter said that the nitrate impacts associated with large amounts of NOx being emitted from 

NGS will have a greater impact during the winter due to nitrate’s instability at higher temperatures. The 

commenter added that the Agency’s rigorous fact-based BART analysis clearly supports the most 

stringent controls for NOx at NGS. The degree of visibility improvement that will result, which EPA 

thoroughly analyzed, indicates substantial benefit from reducing NOx emissions at NGS. 

Response:

We agree with the commenters that NGS causes haze impairment at multiple Class I areas. More 

distant Class I areas may well also be affected. However, the Federal Land Managers generally 

recommend CALPUFF modeling of areas within 300 km, and we have relatively little experience with 

greater distances. In promulgating CALPUFF as an approved model, we stated: “It was concluded from 

these case studies that the CALPUFF dispersion model had performed in a reasonable manner, and had 

no apparent bias toward over or under prediction, so long as the transport distance was limited to less 

than 300 km.”133 An interagency workgroup (IWAQM) concluded: “With the above thoughts in mind, 

IWAQM recommends use of CALPUFF for transport distances of order 200 km and less. Use of 

CALPUFF for characterizing transport beyond 200 to 300 km should be done cautiously with an 

awareness of the likely problems involved.”134 Finally, given the large number of Class I areas within 

300 km of NGS, and the tendency of facility impacts to decrease with distance, the inclusion of 

additional areas would not have affected the outcome of our BART determination. We believe that the 

300 km radius is appropriate. We also agree that the better the background visibility, the more 

perceptible is a given amount of pollution; this is built into the deciview haze index we use as the 

visibility metric. In other words, a relatively small amount of pollution impairs visibility more in the 

relatively pristine western parts of the U.S. more than it would in the comparatively degraded east. The 

part of the country where NGS is located has historically been known for its excellent visibility, and 

133 “Revision to the Guideline on Air Quality Models: Adoption of a Preferred Long Range Transport Model and Other 

Revisions”; Final Rule, 68 FR 18440, April 15, 2003; at p. 18458. 

134 Interagency Workgroup On Air Quality Modeling (IWAQM) Phase 2 Summary Report And Recommendations For 

Modeling Long Range Transport Impacts (EPA-454/R-98-019), EPA OAQPS, December 1998, p.18. 

http://www.epa.gov/scram001/7thconf/calpuff/phase2.pdf 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

reasonable controls on large sources such as NGS are necessarily part of the overall approach needed to 

restore that visibility. 

Comment: EPA underestimated visibility benefits of SCR 

 One environmental advocacy group (0373) stated that the visibility benefits of SCR are higher 

than modeled by EPA because EPA underestimated SCR performance (see section 8.1) and because 

EPA overestimated the potential increase in sulfate emissions that may come with the addition of SCR 

controls in the following ways: 

 EPA assumed a higher conversion rate across the catalyst than that used by Sargent & Lundy 

(S&L), and the conversion rate used by EPA is high when compared to other examples of SCR 

systems designed for 80 to 90 percent NOx control (citing the Stamper report and the ICAC 

White Paper submitted with the comments). To be consistent with its own modeling for the 

SJGS, EPA should have assumed a conversion rate no higher than 0.5%.

 EPA appears to have erroneously used a higher coal sulfur content than SRP has indicated is 

actually used at NGS. EPA should correct its calculations to reflect a sulfur content of 0.593 

percent, not the 0.772 percent that EPA appears to have used in its calculations.

 The commenter (0373) stated that its modeling shows greater visibility improvement than 

demonstrated by EPA, due in part to the necessary corrections to EPA’s calculations outlined above and 

in the Miller/Sahu report submitted with the comments (citing the Miller/Sahu report). The commenter 

added that SCR produces considerably superior visibility benefits over any other technology or any 

alternative that has been proposed, and concluded that SCR plus LNB/SOFA clearly is BART for NGS 

because SCR plus LNB/SOFA is the best-performing technology for NOx pollutant control, it is cost 

effective, and it achieves significant visibility benefits across all of the Class I areas that are polluted by 

NGS, far more than any other technology or combinations of technologies. 

 The commenter (0373) also noted that EPA’s modeling (with the errors alleged above) showed 

that SCR plus LNB/SOFA at NGS would have the greatest visibility benefits to the affected Class I 

areas, providing at least 1 dv of improvement in all of the Class I areas modeled and far more than 1 dv 

benefit at 75 percent of the 11 affected Class I areas. The commenter indicated that EPA’s modeling 

(even with alleged errors) showed improvements in air quality at Grand Canyon, Capitol Reef, and 

Canyonlands National Parks that are among the single largest improvements in air quality to national 

parks from anywhere within the haze program. The commenter added that, according to EPA’s model, 

cumulatively the air quality in 11 national parks and wilderness areas will improve by 35 deciviews with 

the installation of SCR plus LNB/SOFA at NGS, amounting to a 73 percent improvement in the 

visibility impairment attributable to NGS (citing 78 FR 8287). 

Response:

 EPA agrees that the visibility modeling included in our Proposed Rule for our analysis under 

Factor 5 indicates that SCR+LNB/SOFA results in the largest reduction in the visibility impact of NGS 

at 11 Class I areas. We note that the commenter agrees with EPA’s assessment under Factor 5 and our 

conclusion that BART for NGS represents an emission limit achievable with SCR+LNB/SOFA. In our 

Proposed Rule, we stated “EPA is proposing to determine that the anticipated visibility benefits of NOx

controls at NGS supports SCR+LNB/SOFA as the most stringent technologically feasible and cost 

effective NOx emission control technology for NGS.” The commenter contends that EPA 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

underestimated the visibility benefits of SCR. Thus, the commenter is essentially arguing that the 

anticipated visibility benefits are even more supportive of our proposed BART determination. 

 First, the commenter contends that we underestimated the performance of SCR. EPA addresses 

comments on the performance of SCR (i.e., that SCR can achieve a lower limit than the one proposed by 

EPA as well as comments arguing that EPA’s proposed limit is too high) in section 8.1 of this response 

to comments document. Based on our review and analysis of comments on the BART emission limit, 

EPA is determining that our proposed BART limit of 0.055 lb/MMBtu for each unit at NGS is 

achievable and appropriate. 

 Second, the commenter contends that we overestimated the potential increase in sulfuric acid 

emissions resulting from SCR. In our visibility modeling analysis, we assumed that a 3+1 SCR system 

(composed of a total of four layers of catalyst with initial deployment of three layers, followed by the 

addition of another layer after 16,000 hours of operation) would result in a total SO2 to SO3 conversion 

rate of 0.67 percent.135 As discussed in the TSD to our Proposed Rule, AECOM, the consultant who 

prepared a BART analysis on behalf of SRP, assumed a conversion rate of 1 percent.136 EPA sought 

additional information on lower conversion catalysts and received information from Hitachi Power 

Systems of America (a vendor for low-conversion catalysts), that three layers of the CX series catalyst 

would result in a total conversion rate of 0.5 percent.137 Based on this information, and our 

understanding that an SCR system to meet a limit of 0.05 lb/MMBtu would require a 3+1 system, EPA 

conservatively used the conversion rate when four layers of catalyst are in operation (i.e., 0.5 percent 

from three layers plus 0.17% when the additional layer is deployed).138 Similarly, when considering a 

limit of 0.08 lb/MMBtu (achievable with a 2+1 system), EPA used a conversion rate of 0.5 percent 

based on the period when all three layers are in use. The commenter asserts that this analysis is 

inconsistent with EPA modeling for San Juan Generating Station, where a conversion rate of 0.5 percent 

was used. However, we note that the SCR system at SJGS was intended to be a 2+1 system.139 We also 

note that for Four Corners Power Plant, EPA used a conversion rate of 0.6 percent, based on the average 

of operation with 3 layers (at 0.5 percent) and 4 layers (at 0.7 percent).140 Therefore, although the 

commenter suggests that EPA is being inconsistent with itself, we note that our use of a conversion rate 

of 0.67 percent for NGS is entirely consistent with our use of 0.5 percent for SJGS because NGS is 

intended to be a 3+1 system whereas SJGS was intended to be a 2+1 system. Additionally, our action for 

Four Corners also accounted for higher conversion rates when all layers of catalyst are in use. Although 

we used a higher numerical value for NGS than for Four Corners (i.e., 0.67 percent instead of 0.6 

percent) EPA opted to be more conservative in this case and apply the maximum value rather than an 

135 See document titled “NGS_emissions scenarios for modeling_2012May.xlsx” in document number 0004 in the docket for 

the rule at EPA-R09-OAR-2013-0009. 

136 See page 112 of the TSD for the Proposed Rule, document number 0014 in the docket for the rule at EPA-R09-OAR2013-0009. 

137 Id. and references therein. 138 Although the 2010 Sargent and Lundy SCR Cost study provided a catalyst vendor quote specifying 0.5 percent conversion 

from four layers of catalyst (2+2 system), EPA chose to use the more conservative value and quote we received from Hitachi 

based on 0.5 percent from three layers of catalyst. The 2010 S&L Cost Study, titled “2010-08 

NGS_Report_SCR_and_BH_Cost_Est_Rev_D.pdf” is included in the docket for the rule in document number 0005 in the 

docket for the rule at EPA-R09-OAR-2013-0009. 

139 See page 25 of the document titled “Complete EPA Response to Comments for NM RH SIP final.pdf” in the docket for 

the rule at EPA-R09-OAR-2013-0009. The discussion in this document includes information that lower conversion rates have 

been measured but that vendors will guarantee a total SCR system conversion rate of 0.5 percent for two active and one spare 

layer, and that SJGS will be a 2+1 design. 

140 See tab titled “fc3 SCR”, row 41, in document titled [2-3,95] FCPP_BART_Scenarios_Emissions_EPA_Proposal.xlsx” in 

document number 0017 in the docket for the Four Corners Power Plant rulemaking at EPA-R09-OAR-2010-0683. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

average value. EPA views both methods as reasonable. EPA also notes that the regulatory action on 

SJGS by EPA Region 6 is now proposed to be rescinded and replaced by a SIP revision by the State of 

New Mexico.141

 The commenter states that EPA erroneously used a value for fuel sulfur content of 0.772 percent 

for NGS, and that we should correct our visibility modeling to use a value of 0.593 percent. Although 

we erroneously reported a fuel sulfur content of 0.772 percent in the TSD to our Proposed Rule,142 in the 

emission spreadsheets we developed for our visibility modeling, EPA used the correct value of 0.593 

percent.143 Therefore, although the TSD reported the wrong value, the values used in our visibility 

modeling were correct. 

 Although the commenter contends that EPA underestimated the visibility benefit of SCR, we 

disagree with the assertion that the BART limit for SCR should be lower and that we overestimated the 

increase in sulfuric acid. Although we chose to model sulfuric acid conservatively, even if we had 

chosen the value for SO2 to SO3 conversion recommended by the commenter, the result would be to 

indicate that our analysis of Factor 5 is even more supportive of the conclusion that we already reached 

for Factor 5 based on our more conservative analysis. Therefore, although we disagree with the 

commenters assertions, even if we agreed, the result of our five-factor analysis would not change. 

Comment: Relative visibility impact of NOx from NGS

 One of the owners of NGS (0314) asserted that EPA’s singular focus on NOx emissions from 

stationary sources during the first regional haze planning period is misplaced and will be ineffective 

because nitrate aerosols are a relatively minor contributor to visibility impairment in Class I areas 

located on the Colorado Plateau. 

 A CAP agricultural water users group (0305) stated that EPA’s factor 5 analysis failed to 

appropriately acknowledge that NGS NOx emissions lead to only a very small fraction of total visibility 

impairment in the Grand Canyon and the other Class I areas. As an example, the commenter noted that 

both FCPP and emissions from sources outside the 300 km radius that CALPUFF considers, such as 

mobile sources in California, are contributors. The commenter added that NOx emissions are a very 

small source of visibility impairment in the impacted Class I areas when compared to other pollutants, 

citing a 1996 report by the Grand Canyon Visibility Transport Commission which indicates that nitrate 

is the source of only 4 percent of all visibility impairment in the Grand Canyon. The commenter asserted 

that the factor analysis must take into account the small contribution of NGS NOx to overall visibility 

impairment in the impacted Class I areas because this necessarily impacts the overall cost effectiveness 

of the NGS BART determination. The commenter believes that when properly considered in conjunction 

with the cost of compliance, a proper factor 5 analysis clearly indicates that any marginal visibility 

improvement from SCR at NGS is not worth the cost. 

Response:

As mentioned above, we are aware of studies showing the relative contributions of NOx and 

other pollutants, and the relative contributions of various pollution sources. We also noted that a BART 

141 See 79 FR 26909 (May 12, 2014). 142 See Table 36 in the TSD to the Proposed Rule. 143 See document titled “NGS_emissions scenarios for modeling_2012May.xlsx” in document number 0004 in the docket for 

the rule at EPA-R09-OAR-2013-0009. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

determination is required under the Regional Haze Rule because our modeling, conducted according to 

the procedures set out in the BART Guidelines, has shown that NGS causes visibility impairment at 

multiple Class I areas. Controls on individual large sources are an integral part of the overall effort to 

reduce visibility impairment under the RHR. Our own CALPUFF modeling, conducted in accordance 

with the BART Guidelines, shows that NGS has a substantial nitrate impact at multiple Class I areas, 

and that SCR would give a substantial benefit. The modeling methodology and the deciview thresholds 

used in assessing visibility impacts were set forth in the BART Guidelines. The BART Guidelines were 

subject to public comment and have already been adopted as regulation; they do not accommodate 

consideration of relative contributions as advocated by the commenter. Our analysis of controls has 

shown that SCR controls would be cost-effective at NGS. We disagree that the relative NOx contribution 

cited by the commenters excuses NGS from a BART analysis, or that it may at this late date change the 

visibility assessment methodology used in BART determinations. 

Comment: EPA’s modeling overestimates visibility impact of NGS 

 One of the owners of NGS (0348) and the operator of the Kayenta Mine (0384) contracted with 

consulting firms to review EPA’s visibility modeling for NGS and conduct alternative modeling. The 

commenters submitted the resulting reports with their comments. In each case, the reports indicated that 

EPA’s modeling overestimated the visibility impacts from emissions of NOx at NGS. An overview of 

the reports’ reviews of EPA modeling is presented below; greater detail on some topics is presented in 

subsequent comments. 

 The owners of NGS (0314, 0348) noted that it submitted modeling results (prepared by 

ENSR/now AECOM) in support of its BART analysis in 2007 and then in 2009 after incorporating EPA 

comments. The commenter stated that EPA made a number of changes to the modeling analysis in 

support of its February 2013 Proposal. The commenter retained RTP Environmental Associates (RTP) to 

conduct a sensitivity assessment of the differences in key assumptions between the AECOM and EPA 

BART modeling analyses (report attached to the comments as Appendix V) and reported that according 

to RTP’s analysis, the cumulative effect of EPA’s “conservative assumptions” is a significant overestimation of the visibility improvements likely to be achieved by EPA’s proposed BART controls. One 

commenter (0314) added that its previous modeling submission showed that the incremental visibility 

improvements from the application of SCR at NGS versus LNB/SOFA were well below 1.0 delta dv 

(the level considered by EPA to be humanly perceptible) at all Class I areas, and at most sites the 

difference was less than 0.5 delta dv (EPA’s threshold for “contribution” to visibility impairment). 

 One of the owners of NGS (0348) quoted the RTP report submitted with the comments as 

saying, “EPA has acknowledged that the modeling assumptions affect the modeled visibility benefits, but 

they dismiss this key point by stating that the modeling assumptions do not change the relative ‘ranking 

of controls’. However, an examination of the results shows that the use of AECOM’s assumptions results 

in a model predicted visibility improvement of only 0.27 [deciviews], compared to EPA’s prediction of 

5.34 dv. Clearly, the assumptions do significantly affect the level of BART control beyond which there is 

no benefit (i.e., no perceptible improvement in visibility).” The commenter included the following table 

(Table 8) that purports to show the impact of each of the changes that EPA made to the commenter’s 

initial modeling and the cumulative effect of the changes. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Table 8: Description Provided by Commenters of EPA Changes to AECOM’s Modeling 

Description of Change in Modeling Assumptions 

Modeled 

Visibility at 

Grand 

Canyon (delta 

dv) 

Difference 

ENSR/AECOM 2009 Modeling 0.27 

RTP Replicate of ENSR/AECOM 2009 Modeling 0.26 

Changed Extinction Calculation from Method 6 to Method 8 0.92 0.66 

Changed Ammonia Background Assumptions 3.33 2.41 

Changed SO2 to SO3 Conversion Assumed Across SCR Catalyst 3.79 0.46 

Changed from Annual Average to Best 20% Days Background 

Visibility Conditions 4.57 0.78 

Changed NOx Emission Rate from 0.055 to 0.05 lb/MMBtu 5.31 0.74 

EPA Modeling Result – Scenario N7 in TSD 5.34 0.03 

Cumulative Effect of All Changes (ENSR/AECOM 2009 vs. EPA 2013) 5.08 

 The operator of the Kayenta Mine (0384) retained JBR Environmental Consultants to review 

EPA’s modeling and carry out alternative modeling; the JBR report was submitted as an attachment to 

the comments. As summarized in the comments, the JBR report found the following impact of what it 

identified as errors in EPA modeling approach: 

 Elevated ammonia background concentration assumption – increased modeled visibility 

improvements by 70 to 180 percent. 

 Changed emissions inputs – increased modeled visibility improvements by 50 to 150 percent. 

 Combined impact of ammonia background and emissions – increased modeled visibility 

improvements by 60 to 170 percent. 

 Use of CALPUFF version 5.8 rather than 6.4 – increased modeled visibility improvements by 5 

to 500 percent. 

This commenter (0384) stated that the combination of issues identified with EPA modeling indicates 

that there are serious flaws in that modeling, including the following: 

 The variability of the CALPUFF modeling analysis requires a monitoring-based approach to 

verify the accuracy of the input data and avoid an arbitrary result. This applies to the emissions 

calculations, background ammonia levels, and assumed control efficiencies. 

 EPA modeled improvement from LNB/SOFA (the baseline) to SCR has not been verified in real 

world monitoring, or reviewed or vetted by the modeling community, despite the proposal by 

SRP to EPA to conduct such monitoring. 

 EPA failed to identify which modeled alternative it used for the final determination, while the 

apparent preferred analysis relied upon overly conservative assessments for all variability where 

only limited data existed. 

Response: 

Some of the issues raised in these comments are addressed below in the responses on ammonia 

background concentration, CALPUFF version number, and on validation of visibility improvements via 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

monitoring. Issues about emissions and control efficiencies are addressed elsewhere in this response to 

comments (section 8.0). Aside from these issues, the comments mainly enumerate different modeling 

assumptions and their relative effect on the modeling results, without making the case that our 

assumptions are incorrect. The choices between CALPOST visibility calculation methods 6 vs. 8 (old 

vs. new IMPROVE equation), and between annual average vs. best 20% natural background are 

examples. These commenters favor choices that yield lower estimated visibility impacts and control 

benefits. Our choices reflect our best scientific and technical determinations about what is appropriate 

for BART visibility assessments given the underlying requirements of the regional haze program.144 We 

also note that several of these issues are moot, because even with lower ammonia concentrations “am2”, 

Method 6, and annual average background, the visibility benefits of SCR are substantial, with seven 

Class I areas showing a benefit of 1 dv or more.145

 We disagree that we failed to identify the modeled alternative representing the proposed BART 

determination. We proposed a NOx limit of 0.055 lb/MMBtu based on SCR performance of 0.055 

lb/MMBtu with four layers of catalyst and allowing an adequate compliance margin for normal 

fluctuations;146 thus, there are modeling results for only one EPA SCR control scenario presented in the 

Proposed Rule;147 we stated we relied on 1 ppb ammonia background, visibility Method 8, and 20% best 

days natural background.148 This unambiguously identifies the CALPUFF modeling scenario we relied 

on. Relating that scenario to the specific inputs and CALPUFF file names requires reviewing the TSD 

and our supporting spreadsheets. One spreadsheets showed control scenario N2 with SCR and the four 

catalyst layers (giving an SO2 to SO3 conversion rate of 0.67%), in a specific spreadsheet.149 Another 

spreadsheet identified scenario N2 as the one used in the tables in the Proposed Rule.150 This 

unambiguously identifies the CALPUFF modeling scenario and inputs we relied on; the corresponding 

CALPUFF files all have “n2” in their names. 

 We also disagree with one commenter’s characterization of “no perceptible improvement in 

visibility” as synonymous with “no benefit.” A control that by itself does not provide a perceptible 

improvement may still provide a benefit by combining with other controls to provide a perceptible 

improvement. In any case, human perceptibility is not a requirement for BART controls. As stated in the 

BART Guidelines: 

Even 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 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.151

144 See page 92 in the TSD to the Proposed Rule, document 0014 in the docket for the rule at EPA-R09-OAR-2013-0009. 145 See supporting spreadsheet in docket titled “NGS_RHFIP_TSD_vis_tables_121203.xlsx”, with settings “vm6a” and 

“am2”, in document number 0004 in the docket for the rule at EPA-R09-OAR-2013-0009. 

146 See 78 FR 8280 and 8288 (February 5, 2013). 147 See Table 9, 78 FR 8287 (February 5, 2013). 148 78 FR at 8286 (February 5, 2013). 

149 Cited on page 122 of the TSD, referencing document titled “NGS_BART_Scenarios_Emissions_EPA_proposal.xlsx”, in 

document 0004 in the docket for the rule at EPA-R09-OAR-2013-0009. 

150 Cited on page 35 of the TSD, referencing document titled “NGS_RHFIP_TSD_vis_tables.xlsx” in document 0004 in the 

docket for the rule at EPA-R09-OAR-2013-0009. 

151 BART Guidelines at 70 FR at 39129 (July 6, 2005). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

No one control will be sufficient to achieve the visibility goals of the RHR; the effect of reasonable 

controls on the many contributing sources will cumulatively enable progress toward those goals. In any 

case, our modeling results show that there will be a perceptible visibility benefit. 

Comment: EPA used background ammonia concentrations that were too high 

 Two of the owners of NGS (0314, 0348), an industry trade association (0306), and the operator 

of the Kayenta Mine (0384) indicated that EPA’s assumed ammonia background concentration of 1 part 

per billion (ppb) is unrealistically high compared to measured values in the area, resulting in artificially 

high model projections. 

 One of the owners of NGS (0348) stated that assumptions related to the background 

concentration of ammonia played what the commenter categorized as “the biggest role in overpredicting visibility benefits,” causing a difference of 2.41 dv at the Grand Canyon between EPA’s and 

the commenter’s estimates. The commenter noted that EPA used a default constant of 1.0 parts per 

billion (ppb) for background ammonia concentration, which the commenter believes fails to account for 

known variations in monthly or seasonal ammonia concentration. 

 This commenter (0348) cited the 2012 NREL analysis and an analysis carried out at the 

commenter’s request by AECOM and Dr. Ivar Tombach (which was submitted by the commenter in 

response to the 2009 ANPR and attached to the present comments as Appendix E) as concluding that 

assumed ammonia concentrations are very important in the NGS modeling, particularly in the winter 

months. The commenter also noted that the Tombach study compared modeled predictions of 

ammonium nitrates using both EPA’s and AECOM’s ammonia background concentrations to measured 

ammonia values, with the results demonstrating that the EPA’s assumptions result in over predictions of 

actual measured values by a factor of 10 or more in some cases. The NREL analysis reached a similar 

conclusion, apparently based on review of the Tombach study. The commenter indicated that while 

modeling is supposed to be conservative, such a significant over prediction is well outside the bounds of 

reasonable conservatism, particularly when such a significant financial investment will be made based 

on the results. The commenter asserted that the Tombach study clearly demonstrates that AECOM’s 

ammonia background assumptions are much more appropriate model inputs for the purpose of the 

visibility modeling assessment. 

 The same commenter (0348) stated that EPA essentially ignored this analysis in the February 

2013 Proposal and continued to use a constant ammonia background of 1 ppb, which is the default value 

recommended by the Interagency Workgroup on Air Quality Modeling (IWAQM).152 The commenter 

noted that when this IWAQM guidance was issued 14 years ago, CALPUFF did not have the capability 

of accommodating monthly ammonia background concentrations as it has since been updated to do. The 

commenter asserted that EPA’s reliance on a constant value is an outdated approach that is not 

scientifically credible. The commenter added that EPA has not always relied on a constant value, citing 

EPA’s July 1, 2008, modeling protocol approval letter (attached to the comments as Appendix B) in 

which EPA accepted varying ammonia values proposed by the commenter that had previously been 

accepted by the EPA and the Federal Land Managers in other recently issued permits in the region. 

152 Interagency Workgroup On Air Quality Modeling (IWAQM) Phase 2 Summary Report And Recommendations For 

Modeling Long Range Transport Impacts (EPA-454/R-98-019), EPA OAQPS, December 1998, 

http://www.epa.gov/scram001/7thconf/calpuff/phase2.pdf 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 The commenter (0348) concluded that the use of a higher background ammonia concentration 

results in the prediction of higher visibility impairment by CALPUFF and, all other things being equal, 

has the effect of inflating the estimated benefit of more stringent NOx control options. The commenter 

believes that the use of AECOM’s ammonia background concentrations results in more accurate 

CALPUFF predictions and is the best scientific approach for the visibility modeling conducted in 

support of the BART determination. 

 The operator of the Kayenta Mine (0384) made similar points. The commenter noted that the 

EPA used the IWAQM default background ammonia value of 1 ppb, but quoted the IWAQM as saying 

“[g]iven all the uncertainties in ammonia data, IWAQM recommends use of levels presented above, 

unless specific data are available for the modeling domain that would discredit the value cited.” 

According to the commenter, measurements on the Colorado Plateau submitted by SRP show actual 

ammonia values that are significantly lower than the IWAQM default value.153 The commenter also 

quoted the NREL report’s statement that EPA’s modeling using higher ammonia values resulted in 

modeled ammonia nitrate concentrates an order of magnitude higher than measured values for many 

cases, while the use of the SRP ammonia background values produced a better comparison between 

modeled and measured values. 

 This commenter (0384), citing the JBR report submitted with the comments, criticized the “back 

calculation” method used by EPA to validate the assumed background concentration, stating that this 

method is based on theoretical atmospheric chemistry for which monitoring data is not available and it is 

unclear whether the method reflects the actual atmospheric processes that occur. The commenter also 

stated that the back calculation method has not been vetted by the atmospheric modeling community or 

used in similar BART analysis prior to NGS. 

 The same commenter (0384) stated that EPA’s assumed ammonia levels increased the modeled 

deciview improvements due to installation of SCR by 70 to 180 percent. The commenter gave an 

example from the JBR report where using the SRP ammonia background levels and the same remaining 

inputs as EPA results in a change of 1.3 dv for the Grand Canyon, while using the EPA ammonia 

background levels results in a change of 2.7 dv, which is more than twice the SRP results. 

 The industry trade association (0306) stated that EPA’s refusal to consider the ammonia 

monitoring data, on the basis that the QA/QC was not fully up to EPA’s preferred level, is arbitrary 

because there is even less data to support the regulatory default as applied to NGS than there is to accept 

the monitoring data. Thus, according to the commenter, while it may be appropriate to caveat the 

analysis somewhat – perhaps by using a seasonal average ammonia value – there is no principled 

technical basis for refusing to consider the monitored background ammonia levels altogether as EPA has 

done. The commenter believes that the effect of EPA’s use of cumulative visibility impact values 

(discussed further below) and refusal to use monitored ammonia background values is to overstate the 

benefit of the proposed BART determination, and that if the EPA were to use “actual” values it might 

reach the conclusion that an alternative control strategy best meets the requirements of CAA section 

169A. 

Response:

153 Citing Measurements of Ambient Background Ammonia on the Colorado Plateau and Visibility Modeling 

Implications, I. Tombach and R. Paine, Report by SRP September 2010 submitted to EPA in 2010 and cited by 

West Associates comments on EPA Proposed Rule for Four Comers Plant, EPA-R09-0AR-2013-0498. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

On the issue of CALPUFF ammonia background concentration, we considered the arguments 

and data provided by commenters, who generally advocated lower monthly varying values in place of 

EPA’s constant 1 ppb, the default for arid land from the IWAQM document. These comments are 

largely the same as those provided on EPA’s BART proposal for the Four Corners Power Plant, 

including some of the same attached technical reports. EPA has decided to retain the IWAQM default 

for three main reasons. First, the case for 1 ppb being an overestimate is not as strong as the commenters 

contend, especially for the BART regulatory context, based on both ammonia itself and on ammonium 

nitrate model predictions. Second, the variability of available ammonia monitoring data does not allow 

for a clear alternative to the default. Third, even when the lower ammonia values advocated by some 

commenters are used, the visibility improvements due to SCR on NGS remain substantial, so that the 

particular choice of ammonia background does not change EPA’s determination that SCR is BART for 

NGS.

Before responding to the substantive issue, we note that the July 1, 2008 letter from EPA to SRP 

was not a “BART Modeling Protocol Approval Letter”, as it was characterized in Appendix B to SRP’s 

comments. Rather, the letter was an amendment to an earlier information request, withdrawing the 

specific request that SRP explore alternative ammonia levels. Admittedly, we did refer to the SRP levels 

(0.2 – 1.0 ppb) as “appropriate”. However, the context was not submittal of a modeling protocol for 

EPA approval. This letter was sent before the USDA Forest Service alerted us to higher ammonia values 

measured in the Four Corners Area, as described in the TSD. In any case, we disagree that EPA 

committed to use the same ammonia concentrations used by SRP’s contractor in our own modeling 

analysis for our BART determination. 

Even though the specific ammonia background values used are moot for the NGS BART 

determination, as discussed below, the comments advocating lower values deserve to be addressed. We 

note that we already addressed these issues to varying degrees in the TSD154 for the NGS proposal 

(“NGS TSD”, e.g. section 7.G.3. “Ammonia Background Levels”), the TSD155 for the Four Corners 

Power Plant (FCPP) BART proposal (“FCPP TSD”, section 7.G.1, “Ammonia Background Values”), 

and the Response to Comments156 for the Four Corners Power Plant BART final action (“FCPP RTC”, 

section 7, 2nd comment). 

As mentioned above, our first reason for reason for retaining the 1 ppb IWAQM default 

ammonia concentration is that the case for using lower ammonia background values is not as strong as 

argued by the commenters. This applies both to the measured ammonia data itself, and to CALPUFF 

predictions of nitrate using various ammonia levels as input. Much of the existing measured data cited 

by the commenters157 is from more distant states, and so may not be representative for evaluating 

visibility impacts from NGS. Further, the measurements sometimes comprise only ammonia (NH3) 

itself, and not ammonium (NH4

+

); or if it does include ammonium, that fact is not cited by the 

154 “Technical Support Document, Proposed Rule: Regional Haze Requirements for Navajo Generating Station: Navajo 

Nation”, Docket Number: EPA-R09-OAR-2013-0009. EPA Region 9, rev. February 11, 2013. 

155 “Technical Support Document, Proposed Rule: Source Specific Federal Implementation Plan for Implementing Best 

Available Retrofit Technology for Four Corners Power Plant: Navajo Nation”, Docket Number: EPA-R09-OAR-2010-0683. 

EPA Region 9, October 10, 2010. 

156 “Response to Comments for Proposal and Supplemental Proposal: Source Specific Federal Implementation Plan for 

Implementing Best Available Retrofit Technology for Four Corners Power Plant: Navajo Nation”, Docket Number: EPAR09-OAR-2010-0683. EPA Region 9, August 2012. 

157 E.g. SRP comments appendix G, “Measurements of Ambient Background Ammonia on the Colorado Plateau and 

Visibility Modeling Implications”, Prepared by Salt River Project, Contributors: Ivar Tombach and Robert Paine, September 

2010. Referred to here as “SRP monitoring report”, or Tombach & Paine 2010. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

commenters. Visibility-impairing ammonium sulfate and ammonium nitrate are formed from ammonia, 

SO2, and NOx. Therefore the ammonium represents part of the pool of ammonia that could be available 

to interact with the SO2 and NOx from a facility and contribute to visibility impacts, and should be 

accounted for in estimating ammonia background concentrations. In several of the research papers cited 

by commenters, the amount of measured ammonium is comparable to and at times much greater than the 

amount of ammonia.158 Measurements made by SRP in December 2009 – April 2010 closer to NGS did 

include both NH3 and NH4

+

.

159.Depending on time and location, typical NH3 ranged from 0.2 ppb to 0.8 

ppb. If the measured NH4 is converted to ppb and added to this, then the total is 0.6 – 1.2 ppb, 

considerably higher than the 0.2 ppb winter values used in SRP’s modeling,160 and thus these 

measurements are a weaker argument against EPA’s default than claimed by the commenter. It is true 

that under current conditions, some of the ammonia in the form of NH4 is not available to interact with 

pollutants from NGS, as it has already interacted with pollutants from other sources (this is more true of 

ammonium sulfate than of ammonium nitrate, since the latter can more readily decompose to nitric acid 

and free ammonia). However, it can be argued that for purposes of assessing NGS impacts relative to 

natural background, per the BART Guidelines – that is, without impairment from other anthropogenic 

sources – both ammonia and ammonium should be assumed to be available to interact with emissions 

from NGS. In reality, the proportion of measured ammonia and ammonium that is available for reaction 

is not known. The proportion depends on the key assumption of whether other anthropogenic sources 

should “count”, and also on the location and timing of ammonia emissions, varying temperature and 

humidity, and the particular path of the NGS plume. The sum of ammonia and ammonium provides an 

upper bound estimate of the ammonia background, and a conservative estimate for modeling. Using just 

the ammonia measurements cited by the commenters would neglect this altogether, so their argument for 

lower ammonia values does not persuade us to change our determination to use the 1 ppb IWAQM 

default. 

Even apart from the complications on the availability of ammonium (NH4

+

), there are 

measurements of gaseous ammonia (NH3) that by themselves are close to or greater than 1 ppb, even in 

winter. Winter measurements included in Sather et al.161 (which EPA relied on for modeling of impacts 

at Mesa Verde NP) ranged from 1.1 ppb to 1.8 ppb for a monitor at the Farmington Airport in 

northwestern New Mexico; since these were 3-week averages, the value for individual days would have 

been higher still. Winter 2011-2013 measurements from the AMoN network162 range from 1.1 to 1.3 ppb 

for Farmington, and 0.7 – 0.9 ppb for Chiricahua, in southeastern Arizona. These values are greater than 

158 RoMANS - Rocky Mountain Atmospheric Nitrogen & Sulfur Study, William C. Malm and Jeffrey L. Collett. National Park 

Service, CSU-CIRA, Fort Collins, CO. ISSN 0737-5352-84. October 2009. 

http://www.nature.nps.gov/air/Studies/romans.cfm Table 3.9, p.3-38 shows ammonium comparable to or about half of 

ammonia, depending on measurement method, Table 3.10 p.3-39 shows maximum ammonium to be about 0.57 μg/m3

 or 

0.77 ppb and maximum ammonia to be about 1 μg/m3 or 1.4 ppb; sum of these is about 2.2 ppb. “NH3 Monitoring in the 

Upper Green River Basin, Wyoming”, by John V. Molenar, H. James Newell, Jeffrey Collett, et al. Extended Abstract #70, 

A&WMA Specialty Conference “Aerosol & Atmospheric Optics: Visual Air Quality and Radiation”, Moab, Utah, 28 April - 

2 May 2008, p.3 Figure 1 and p.4 Figure 3 show ammonium comparable to ammonia in summer and far greater in winter. 

“Aerosol Ion Characteristics During the Big Bend Regional Aerosol and Visibility Observational Study,” Taehyoung Lee, 

Sonia M. Kreidenweis & Jeffrey L. Collett Jr. Journal of the Air & Waste Management Assoc. vol.54, issue 5, 2004, pages 

585-592. DOI:10.1080/10473289.2004.10470927, Table 1 p.587 shows ammonium about four times as high as ammonia. 

159 SRP monitoring report, or Tombach & Paine 2010, cited above. 160 SRP comments Appendix C. “Revised BART Analysis for the Navajo Generation Station Units 1-3” (January 2009) and 

Appendix I. “Visibility Modeling Using Upgraded CALPUFF Model” (February 2011) 

161 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. 

162 Atmospheric Ammonia Network, National Atmospheric Deposition Program, http://nadp.sws.uiuc.edu/amon/; data 

available in docket spreadsheet “AMoN_network_AZ_NM_NH3_average.xlsx.” 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

or comparable to the 1 ppb IWAQM default used by EPA, which thus appears to be a reasonable 

intermediate between these measurements and the lower values cited by commenters. In addition, 

regarding the ammonia statements in the NREL study163 cited by some commenters, the National Park 

Service pointed out in a letter164 to EPA that the ammonia concentrations cited are generally seasonal 

averages. The NPS stated that short term (24-hour) ammonia average concentrations in these studies are 

consistent with the values used by EPA, and that the latter were appropriate for 24-hour visibility 

impairment assessments (such as the BART modeling using CALPUFF, which provides 24-hour 

average visibility estimates). 

Turning from measured ammonia data to nitrate (NO3) model predictions based upon them, 

again we disagree with the commenters. Several commenters stated that the EPA default 1 ppb ammonia 

levels lead to overprediction of nitrate concentrations relative to what is observed at monitors; they cite 

work by Scire et al. in 2003165 and 2010166 and the 2009 SRP comments on the ANPR, included as 

appendices D and E of SRP’s comments on the present action. We do not believe the approaches used in 

these studies are appropriate for BART modeling, and we do not believe their results make it appropriate 

to change the ammonia levels used in our BART modeling. The Scire work modeled western Wyoming, 

so its conclusions about ammonia-based overpredictions cannot be directly carried over to locations in 

Arizona and the Four Corners area: ammonia levels that give better model performance in Wyoming 

may not apply to location relevant for NGS. In addition, the CALPUFF modeling in that work was not 

single-source modeling like that done for BART determinations: it involved 1776 sources altogether, 

with many point, area, and mobile sources. In the scenarios cited by the commenters, all of the 

background ammonia appears to have been assumed to be available for nitrate production by all of those 

sources simultaneously, so it is perhaps not surprising that nitrate was overpredicted. A POSTUTIL 

NO3/HNO3 repartitioning step may have been applied, allowing for some competition for ammonia 

between overlapping source plumes, but even then the assumption of 1 ppb everywhere for all source 

plumes would strongly accentuate any CALPUFF tendency toward overprediction. In any case, the 

approach was quite different than BART modeling, where only a single source’s emissions are 

interacting with the ammonia; overpredictions in the multi-source exercise do not directly apply to the 

single source case. So again, this study’s ammonia its conclusions do not carry over to single-source 

CALPUFF modeling for NGS BART. Also, both Scire studies also seem to be based on average nitrate, 

rather than the higher concentrations that would be of more regulatory concern. Further, the objectives 

of the two studies were not evaluation of ammonia levels per se, but rather the showcasing of new 

CALPUFF model changes that could improve performance in some circumstances. The 2003 work 

compared standard CALPUFF using constant ammonia levels against CALPUFF using an Ammonia 

Limiting Method (ALM, a method for accounting for multiple sources’ competing for available 

ammonia) and a Boundary Condition Module (using time-varying inflow boundary concentrations). The 

163 Navajo Generating Station and Air Visibility Regulations: Alternatives and Impacts, David J. Hurlbut, Scott Haase, 

Gregory Brinkman, Kip Funk, Rachel Gelman, Eric Lantz, Christina Larney, David Peterson, Christopher Worley (NREL) 

and Ed Liebsch (HDR Engineering, Inc.), January 2012, NREL/TP-6A20-53024, produced under direction of the U.S. 

Department of the Interior under Interagency Agreement R11PG30024. Report and Compendium available at 

http://www.doi.gov/navajo-gss/index.cfm. In docket as: “2012-03 NREL Report”; also included as Appendix L to SRP 

comments. 

164 Letter from Herbert C. Frost, Ph.D., Associate Director, National Resources Stewardship and Science of the National Park 

Service, to Jared Blumenfeld, April 6, 2012. In docket as: “2012_0406 NPS Letter to EPA” in document number 0004. 

165 Scire et. al. 2003. “Evaluation of the CALPUFF Model in Predicting Concentration, Visibility and Deposition at Class I 

Areas in Wyoming”. Presented at the AWMA Specialty Conference: Guideline on Air Quality Models: The Path Forward. 

Mystic, Connecticut, Oct. 23-24, 2003. 

166 “New Developments and Evaluations of the CALPUFF Model”, Joseph S. Scire, David G. Strimaitis, and Zhong-Xiang 

Wu, March 14-16, 2012, 10th Conference on Air Quality Modeling, RTP, North Carolina. Available at 

http://www.epa.gov/ttn/scram/10thmodconfpres.htm. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

2010 work focused on a new CALPUFF version, 6.42, incorporating a different treatment of 

atmospheric chemistry than the regulatory CALPUFF version, 5.8 (the issue of using an updated version 

of CALPUFF version is discussed below in the response to comments on that specific issue). The two 

studies did show comparisons of monitored nitrate data against CALPUFF predictions using 1 ppb 

ammonia, but were not an exploration of what ammonia value is best to use with the regulatory version 

of CALPUFF in BART assessments. This is not to discount the Scire work, which provided important 

insights and should be examined carefully as we consider changes to the approved version of CALPUFF 

and also the regulatory context in which it is used. However, the different location and different 

methodology used in the studies do not provide a basis for us to change our determination to use the 1 

ppb IWAQM default. 

Appendix E to the SRP comments has a thorough set of comparisons of measured nitrate 

concentrations at the Grand Canyon against modeled predictions using the SRP ammonia levels of 0.2 to 

1.0 ppb, and using the EPA ANPR levels of 0.7 to 1.0 ppb.167 The main comparisons are in that 

appendix’s section 3, “Evaluating the EPA’s Back-Calculation Method”. Three analysis methods are 

used: comparison for particular days (e.g. Figures 3 and 4), comparison of the overall distributions of 

NO3 values (e.g. Figure 5, cumulative percentiles), and ranked comparisons (e.g. Figure 7, plotting the 

highest predicted against the highest measured, the 2nd highest against the 2nd, and so on; also called a 

“Q-Q plot”). For predictions based on EPA ANPRM ammonia levels, the graphics for the three 

respective methods show that various individual days have nitrate higher than observed values, that the 

overall distributions are higher than observed, and likewise for most of the ranked values, again except 

for the very highest ones. Conversely, the graphics also show that predictions based on the SRP 

ammonia levels are lower than the observed. These SRP conclusions are compatible with some nitrate 

comparisons performed by EPA and described in the NGS TSD (p.120ff). We plotted time series of 

daily nitrate concentrations for several modeled receptor locations in the Grand Canyon168, and 

concluded that nitrate predictions were somewhat high in that high values occurred more frequently than 

in the measured IMPROVE data, but that predicted maxima were in the range of maxima seen in the 

measured data. Predictions based on the SRP values appeared to be too low to explain the observed 

maxima. Additional tests were performed for the Four Corners Power Plant nitrate impacts, and found 

that the EPA ANPR values gave fairly good agreement at the highest concentrations, such as the 

maximum and the 98th percentile. The 98th percentile of deciview visibility impacts is the metric used 

for BART assessments under the BART Guideline. Our main conclusion from the various comparisons 

is that at the highest concentrations, which are of most regulatory interest, the ammonia values we used 

are appropriate. 

In sum, commenters presented some evidence that ammonia concentrations at some times and 

places are lower than the 1 ppb default we used for CALPUFF background. However, considering that 

there are also higher measured ammonia concentrations, that some of the nitrate comparisons are not 

directly applicable, and that there is reasonable agreement with nitrate measurements at the levels of 

regulatory interest, we do not find the evidence compelling enough to choose ammonia levels different 

than the IWAQM guidance default values. 

167 The “SRP levels” were developed by AECOM and advocated by SRP; the ANPRM called these scenario “am1”, while the 

present action they are called scenario “am2”. The “EPA ANPRM levels” were ANPRM scenario “am3”, derived using a 

previous version of EPA’s back-calculation approach; they did include a single month with 1.3 ppb. With that one exception, 

these previous values are the same or lower than the present EPA default of 1 ppb, depending on the month. Therefore, SRP 

conclusions that those old levels were too high would also apply to the present action’s 1 ppb levels. 

168 EPA nitrate plots are available in docket spreadsheet titled “NO3_compare_ANPRM.xlsx”, see document number 0004 in 

the docket for this rule at EPA-R09-OAR-2013-0009. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

A second reason for retaining the 1 ppb IWAQM default ammonia concentration is that the 

variety of ammonia concentrations measured at various times and places do not point to a clear 

alternative constant value, nor to an alternative monthly varying scheme. It is not that we are refusing to 

use ammonia measurements (whether for QA/QC or other reason), as claimed by some commenters. 

Rather, our consideration of the available data and other studies leads us to conclude that there is not a 

technically justified alternative to using the IWAQM default. As cited above, there is a variety of 

ammonia values measured at different times and places, and sometimes with different methodologies. 

Even the SRP monitoring report (Tombach & Paine, 2010, cited above) describes a surprisingly high 

spatial variability in ammonia concentrations. The two monitors in the Cameron area south of NGS (and 

east-southeast of the Grand Canyon) showed consistent concentration differences despite being less than 

five miles from each other. This difference may be due to relatively localized ammonia sources, though 

these were not identified. These sites also showed consistently lower measurements than the Hall’s 

crossing site, north of NGS (and southwest of Capitol Reef). Because of the variability and its unknown 

causes, the data collected did not lead to a clear picture of appropriate and representative ammonia 

background concentrations to use with CALPUFF. The variability seen within the SRP study, as well as 

that between the various other studies and sites, underscores the difficulty in choosing representative 

ammonia background concentrations The choice of background ammonia for CALPUFF modeling 

might consider ambient ammonia near NGS and traveling along with its pollutant plume, as well as 

ammonia inflow and ammonia emissions the plume encounters as it travels. Yet measurements of 

ammonia are spatially sparse; the sources of ammonia are not well characterized, and the amount and 

variation of their emissions are not well known. Also relevant for choosing an appropriate background 

are decisions made in the regulatory context on whether to use short-term (24-hour) or monthly 

averages, whether just the maximum or 98th percentile or some other portion of predictions are most 

important, and the degree to which competition for ammonia from other, existing sources should be 

included. In the face of all this uncertainty, it is most supportable to use the default values from the 

IWAQM document, the only guidance available on this issue. 

The third main reason for retaining the 1 ppb IWAQM default is that alternative lower 

assumptions do not change EPA’s BART determination, because CALPUFF modeling169 of SCR shows 

substantial visibility benefits even using the alternative assumptions. For SCR (modeling scenario “f1”, 

with NOx emissions at 0.055 lb/MMBtu), under EPA’s IWAQM 1 ppb ammonia assumption (“am1”), 

the maximum benefit of SCR is 5.4 dv at Capitol Reef NP, and the cumulative benefit over all 11 Class I 

areas is 35.5 dv. Ten areas see a benefit greater than 1 dv, and eight see a benefit greater than 2 dv. By 

contrast, under the ammonia assumption advocated by some commenters (“am2”, ranging from 0.2 ppb 

in winter to 1.0 ppb in summer), the maximum benefit of SCR is 2.3 dv, and the cumulative benefit is 

15.7 dv; these are less than half of the “am1” results. Nine areas see a benefit greater than 1 dv, and one 

sees a benefit greater than 2 dv (two more areas see benefits of 1.9 dv); these are fewer than the areas 

showing such benefits under “am1”. While these “am2” benefits are clearly lower than those using the 

“am1” IWAQM default assumption, they are still quite large. Thus, even if we agreed with all the 

commenters’ objections to the ammonia values we used, the visibility benefits still provide ample 

justification for the EPA determination that SCR is BART for NGS. 

One additional ammonia background issue was raised by commenters, that of EPA’s “backcalculation” method of estimating ammonia concentrations. This issue was addressed in the NGS TSD, 

section E.2 and G.3. and especially in the FCPP RTC, the second comment in section 7. The method 

uses sulfate and nitrate measured at Class I areas, and estimates the amount of ammonia that must have 

been present to neutralize those chemical species (which are in the form of ammonium sulfate and 

169 Full modeling results are available in the docket in the spreadsheet titled “NGS_RHFIP_NFR_vis_tables.xlsx”. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

ammonium nitrate). This method was suggested by the USDA Forest Service, and endorsed by the 

National Park Service. EPA used the method only to help corroborate the results of the 1 ppb default. No 

one has claimed the method is an ideal one, but it is an objective method based on measured data, and 

one that we expect to provide an estimate of the upper bound of available ammonia. In the NGS TSD 

and the FCPP RTC we explain some of the counterbalancing factors affecting the method; we continue 

to believe it provides an estimate worth considering. We believe it corroborates the modeling results 

based on the 1 ppb IWQAM default we are mainly relying upon. Interestingly, despite the strong 

criticism of the method offered by some commenters, especially SRP, the method’s ammonia estimates 

for the Grand Canyon in December - April are fairly close to those seen in the SRP monitoring study at 

its Gray Mountain and Moenkopi Switchyard monitoring sites, around 0.5 to 0.6 ppb. In any case, we 

believe that the modeled visibility benefits from SCR that result from these lower ammonia 

concentrations remain large, and provide justification for the EPA determination that SCR is BART for 

NGS. 

Comment: Invalid definition of “natural visibility” 

 The operator of the Kayenta Mine (0384) stated that the RHR does not define “natural visibility” 

in terms of the best 20 percent days. The commenter quoted the BART Guidelines and additional EPA 

guidance170 to conclude that “natural visibility conditions represent a long term average condition 

analogous to the 5 year average best and worst day conditions that are treated under the regional haze 

program.” The commenter also noted that the BART Guidelines provide that in determining if a control 

results in improved visibility, the implementing agency should use the same approach used to determine 

if the source was subject to a BART analysis. 

 The commenter (0384) contended that EPA based its analysis on only the best 20 percent days 

rather than the average (citing 78 FR 8286), despite what the commenter believes is direction to base the 

analysis on the “5 year average best and worst day condition.” According to the commenter, EPA 

justified this approach based on an internal EPA memo that opined that the EPA can use either the 

annual average background conditions or the average of the best (clearest) 20 percent of days (citing 78 

FR 8286, fn. 56). The commenter noted that this distinction is important because under cleaner visibility 

conditions, relatively less pollution will cause perceptible changes than under more polluted background 

conditions.171 The commenter stated that it is thus possible that NOx emissions from NGS could result in 

perceptible changes under the “best 20 percent days” while under average condition that same level of 

NOx emissions would not. 

 The commenter (0384) opined that EPA cannot modify the approach provided for in the RHR 

and BART Guidelines and equate the best 20 percent of days to “natural visibility,” and that until the 

EPA conducts an appropriate analysis based on the average rather than the best 20 percent of days, it 

cannot conclude that requiring NGS to add SCR to the existing LNB/SOFA controls will result in any 

humanly perceptible improvement in visibility at the Class I areas in question. According to the 

commenter, EPA is in essence changing the requirement to improve the worst 20 percent of days to 

improve the best 20 percent of days, which is not what the RHR requires. The commenter asserted that 

the failure to conduct appropriate modeling is a failure to comply with the mandatory BART factors and 

the RHR and Clean Air Act. 

170 Guidance for Estimating Natural Visibility Conditions under the Regional Haze Program, September 2003 (EPA 454/B03-005). 

171 Citing Interagency Working Group on Air Quality Modeling (IA WBM) Phase 2 Summary Report, December 1998, EPA 

454/R-98-019, p. 23. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Response: 

We disagree with the commenter that our BART modeling used an inappropriate definition of 

natural visibility. We are not aware of any requirement to use average natural conditions in BART 

modeling. The EPA document cited by the commenter, Guidance for Estimating Natural Visibility 

Conditions Under the Regional Haze Program, states “natural visibility conditions represents a longterm average condition analogous to the 5-year average best-and worst-day conditions that are tracked 

under the regional haze program” (sec.1.2, p.1-1). We agree with the commenter that this is consistent 

with RHR requirements. BART is one mechanism that the RHR provides for meeting the RHR goals, 

but it does not follow that the specific metric used to assess progress under the RHR must also be used 

for individual source assessments. The BART Guidelines state “Finally, these final BART guidelines 

use the natural visibility baseline for the 20 percent best visibility days for comparison to the ‘cause or 

contribute’ applicability thresholds. We consider this estimated baseline is likely to be reasonably 

conservative and consistent with the goal of natural conditions.”172 In a subsequent memorandum, EPA 

stated that States could use either the best 20 percent of days or the annual average, but far from 

imposing the average as a requirement, the memo offered it as an optional alternative to the best 20 

percent that is mentioned in the BART Guidelines.173 The BART analyses in many States’ plans used 

the average, which makes the impact of the source appear smaller (the added pollution does not show up 

as much against a dirtier background). While states are free to take this approach, the best 20 percent of 

days is consistent with available guidance and with the goals of the RHR, and we consider it appropriate 

for this action. Finally, however one may interpret the various documents cited by the commenter, we 

note that although the guidance document provides various recommendation, it is not fully prescriptive 

for BART modeling, and indeed does not contain all the natural condition inputs required for BART 

modeling using CALPUFF, as we discuss next. In any case, the natural visibility conditions we used in 

modeling NGS were consistent with the guidance document and the BART Guidelines. 

The Estimating Natural Visibility guidance is aimed at setting natural visibility and reasonable 

progress goals, and is not fully prescriptive for BART modeling. After defining natural conditions, 

under “What is the purpose of the Guidance for Estimating Natural Visibility Conditions Under the 

Regional Haze Rule?” the guidance goes on to say “As part of the program, States will develop goals 

and implement strategies for improving visibility in each mandatory Federal Class I area. Estimates of 

natural visibility conditions are needed by the States for the goal development process.” Its various 

subsections deal with aspects of those goals, and not with modeling. In any case the document does not 

provide the full set of natural concentrations needed to run CALPUFF. The document does not mention 

CALPUFF at all, and its only explicit modeling recommendation is in Appendix A, which covers f(RH) 

relative humidity factors to use in conjunction with the IMPROVE equation for translating pollutant 

concentrations into extinction.174

Apart from the relative humidity factors recommendations, the specific natural concentrations 

that are provided in the document are also not prescriptive or complete because they are not areaspecific. The guidance document describes a “Default Approach to Estimating Natural Visibility 

Conditions”, which includes Table 2-1, “Average Natural Levels of Aerosol Components” (sec.2, p.2-2) 

172 70 FR 39125 (July 6, 2005). 173 “Regional Haze Regulations and Guidelines for Best Available Retrofit Technology (BART) Determinations”, 

memorandum from Joseph W. Paisie, EPA OAQPS, July 19, 2006. In the docket as: 2006_07_19 EPA Memo on RH BART 

Determinations. 

174 The appendix states: “Thus, the 12 monthly-averaged f(RH) values determined in this way for each Class I area should be 

used for all aerosol speciation data or model predictions for that location.” (p.A-3). 
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This table gives default annual average concentrations of several visibility-impairing particulate 

pollutants, with one set for the East and one set for the West. These might be assumed to be default 

concentrations for use in CALPUFF modeling, though that is not explicitly stated. However, as 

suggested by guidance section title’s phrase “default approach”, these natural concentration values are 

better used just as a starting point. It is more appropriate to use area-specific concentrations for 

modeling, because Class I areas do in fact differ from each other. It is also appropriate because only 

area-specific concentration values can be consistent with the area-specific extinction and deciviews 

recommended in Appendix B to the guidance document. 

Finally, the guidance document is not prescriptive or complete because its natural concentrations 

in the guidance document are annual averages. Their use in BART modeling would not be consistent 

with the majority of the guidance text’s focus on 20 percent worst and 20 percent best days, nor with the 

BART Guideline’s recommendation of the best 20 percent natural conditions. As described in the TSD 

(p.93), we used a scaling procedure to adjust the guidance document’s natural concentrations to be 

proportional to the best 20% extinction values it provides. In summary, our procedure resulted in 

concentrations consistent with the multiple aspects of the guidance document, but also usable in 

CALPUFF modeling. We believe that the natural visibility conditions we used in modeling NGS were 

consistent with the guidance document, the BART Guidelines, and the RHR. 

Comment: Other studies indicate there will be no perceptible improvement in visibility 

 The operator of the Kayenta Mine (0384) stated that the addition of SCR will result in no 

perceptible improvement in visibility. The commenter asserted that under the RHR, the degree of 

improvement that must be shown under this BART factor is one of humanly perceptible improvement. 

The commenter indicated that multiple studies and other modeling demonstrate that there will be no 

perceptible improvement in visibility: 

 The NREL report, which stated that it “is inconclusive as to whether removing approximately 

two-thirds of the current NOx emissions from NGS would lead to any perceptible improvement 

in visibility at the Grand Canyon and other areas of concern.” 

 A study on the Mohave Power Project (MPP, also known as the Mohave Generating Station, or 

MGS) closure that found “virtually no evidence that the MPP closure improved visibility in the 

Grand Canyon.” (Additional detail is included in a subsequent comment.) 

 Modeling conducted by the Salt River Project (SRP), a co-owner and the operator of NGS, 

which was submitted with its BART determination. 

 Comments submitted by the Central Arizona Water Control District (CAWCD) on the 2009 

Advanced Notice of Proposed Rulemaking (ANPR) for FCPP and NGS, which indicated that an 

earlier modeling study conducted by ENVIRON found that controlling emissions from FCPP 

would not appreciably improve visibility – a significantly different result than the EPA’s 

CALPUFF modeling. 

A public/private coalition (0381) submitted similar comments arguing that there is no firm 

evidence that addition of SCR would provide NOx reductions that would have an perceivable 

improvement in visibility at the Grand Canyon. Similarly, a CAP agricultural water users group (0305) 

stated that EPA’s analysis of factor 5 does not fully consider the impact (or lack thereof) the control 

options may have on visibility by failing to address and explain contrary evidence and studies in the 
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record (e.g., the NREL report and the study on MPP). In failing to appropriately consider the results of 

these studies, the commenter believes that EPA’s factor 5 analysis is arbitrary, capricious, and not in 

accordance with the law. 

Response: 

 These comments are variations of other comments for which we have provided separate 

responses. We respond to the NREL and MPP closure study below: we believe the conclusions from 

these papers are overstated, and believe we can rely on our CALPUFF results. The different results 

from the other studies mentioned are the result of differing input assumptions, different choices for 

visibility calculation method, and/or different model versions. We responded briefly to the visibility 

calculation method above; we respond to the model version question next. 

Comment: EPA should have used an updated version of CALPUFF 

 Two of the owners of NGS (0314, 0348) and the operator of the Kayenta Mine (0384) indicated 

that EPA erred in using CALPUFF version 5.8 in its modeling rather than the more recent CALPUFF 

version 6.4. 

 One of the owners of NGS (0348) noted that EPA’s BART Guidelines recommend use of the 

CALPUFF model for evaluating visibility impacts, and CALPUFF version 5.8 is the EPA approved 

version for use in BART applications. The commenter cited several studies over the past decade that 

have concluded that CALPUFF version 5.8 over predicts particulate nitrate formation by as much as a 

factor of 3 to 4 during wintertime conditions. The same commenter (0348) stated that model 

development has continued, and TRC (CALPUFF’s developer) released version 6.4 (now 6.42) in 

November 2010 to fix certain coding “bugs” and to improve the chemistry module. The commenter 

cited a number of studies that show that CALPUFF version 6.42 predicts lower nitrate concentrations 

than version 5.8, and gives results that are closer to measured concentrations. 

 This commenter (0348) indicated that while CALPUFF version 6.42 represents a state of the art 

upgrade, EPA continues to use the outdated CALPUFF version 5.8, which results in an over prediction 

in the visibility benefits that can be expected from additional emission controls at NGS. The commenter 

believes that EPA should adopt the most recent, scientifically sound, and accurate version of CALPUFF 

and use that version in assessing BART. The commenter opined that, at the very least, the EPA should 

acknowledge, as it has in the past, that its approved version of CALPUFF significantly over predicts 

visibility impairment and adjust its assessment of the visibility improvement BART factor accordingly. 

 Another co-owner of NGS (0314) likewise stated that EPA continues to conduct its modeling 

using CALPUFF version 5.8 even though it is widely acknowledged (including by EPA, Federal Land 

Managers, and Dr. Joe Scire, the lead developer of the CALPUFF model) to over- predict haze causing 

nitrate formation, even though a newer and more refined model (version 6.42) is available. According to 

this commenter, EPA is obligated to perform its BART analysis using the best application currently 

available for predicting visibility impacts. The commenter asserted that it is extremely concerning that 

EPA would impose a requirement costing a facility hundreds of millions of dollars based on the results 

from the “regulatory version” of a model when a newer, more accurate version of the model is available. 

 The operator of the Kayenta Mine (0384) asserted that use of CALPUFF version 5.8 is not 

consistent with the BART rules. According to the commenter, EPA acknowledged issues with 
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CALPUFF’s chemistry modeling when the 2005 BART rules were finalized (citing 70 FR 39121, 

39122, 39123). The commenter concluded that the BART analysis should be based on the best 

application available with respect to visibility impacts which, when the 2005 BART rules were 

promulgated, was CALPUFF version 5.8. The commenter indicated that use of CALPUFF version 5.8 in 

2005 was consistent with the court’s view that if an agency’s decision does not constitute a “reasonable, 

good-faith presentation of the best information available under the circumstances,” it would be arbitrary 

and capricious (citing Lee v. U.S. Air Force, 220 F.Supp.2nd 1129, 1233-34 (D. N.M. 2002), which cites 

Colorado Environmental Coalition v. Dombeck, 185 F.3rd 1162, 1172 (l0th Cir. 1999). The commenter 

believes that since CALPUFF version 6.4 was the best model for predicting visibility impacts at the time 

SRP submitted its additional modeling results for NGS, the EPA must allow its use even though it has 

not been officially adopted by EPA. The commenter stated that the change from CALPUFF version 5.8 

to 6.4 results in changes to modeled visibility improvements of 5 to 500 percent (citing the JBR report). 

Response: 

The commenters stated that EPA has acknowledged CALPUFF overpredictions of nitrate; no 

citation was provided, but an EPA presentation at the 2012 EPA Regional/State/Local Modelers 

Workshop did include the statement “CALPUFF was known to overestimate nitrates when it was 

promulgated as a regulatory model [68 FR 18440, April 15, 2003] and in the BART Guidelines [70 FR 

39104, July 6, 2005], therefore EPA chose the 98th percentile (8th High) for regulatory evaluations.”175

EPA already considered the limitations of CALPUFF and its included chemistry scheme when selecting 

it for BART modeling; that regulatory action is past, and cannot be revisited in this action. 

We disagree with the commenters that any new CALPUFF version should be used for the BART 

determination. We relied on version 5.8 of CALPUFF because it is the EPA-approved version in 

accordance with the Guideline on Air Quality Models (“GAQM”, 40 CFR 51, Appendix W, section 

6.2.1.e); we 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 070623.176 CALPUFF version 5.8 has been 

thoroughly tested and evaluated, and has been shown to perform consistently with the initial 2003 

version in the analytical situations for which CALPUFF has been approved. 

The latest version of CALPUFF, 6.4, incorporates a more detailed treatment of chemistry, but it 

is not approved by EPA for use in regulatory actions. Given the current regulatory status of CALPUFF, 

the use of version 6.4 would require either a new rulemaking, or an “alternative model” demonstration 

under GAQM 3.2.2. Our 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 5.8 is considered a “screening” 

model, under GAQM section 4.2.1, rather than a “preferred” model; this “screening” status is also 

175“CALPUFF Status and Update”, Tyler J Fox, 2012 EPA Regional/State/Local Modelers Workshop, April 30, 2012. 

Available at http://www.cleanairinfo.com/regionalstatelocalmodelingworkshop/archive/2012/agenda.htm; direct link: 

http://www.cleanairinfo.com/regionalstatelocalmodelingworkshop/archive/2012/presentations/2-

5_2012RSL_CALPUFFstatus_TFox.pdf 

176 A slightly updated version, CALPUFF 5.8.4 (level 130731) was approved by EPA in December 2013, after the modeling 

work for our NPR proposal was completed. We believe it would not be appropriate to redo the modeling in between our 

proposed and final action. Also, the changes were all “bug fixes”, and we do not believe the model results would be 

materially different were the updated version to be used. 
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described in the preamble to the BART Guidelines (70 FR 39123, July 6, 2005).177 A version of 

CALPUFF other than 5.8, and especially one with such fundamental differences in its handling of 

chemistry, would no longer be considered a “screening” model under GAQM section 4.2.1. Instead it 

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, a meteorological preprocessor for CALPUFF, 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.178 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 U.S. Forest Service and EPA review179 of CALPUFF 

version 6.4 results (submitted by certain power plant operators with their BART analyses for their 

facilities) 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. 

Introducing a new regulatory model is a long process. EPA intends to conduct a comprehensive 

evaluation of the latest CALPUFF version along with other “chemistry” air quality models, including a 

full statistical performance evaluation, verification of its scientific basis, and determination of whether 

the underlying science has been incorporated into the modeling system correctly. To accommodate such 

a model, there would have to be an evaluation of the effect on the regulatory framework for its use, 

including in New Source Review permitting, and also changes to the Guideline on Air Quality Models 

and other modeling guidance, in consultation with the FLMs. CALPUFF version 5.8 has already gone 

through this comprehensive evaluation process and remains the EPA-approved version. We believe its 

chemistry algorithms and performance were adequately taken into account in choosing it for BART 

modeling. We believe CALPUFF 5.8 is thus the appropriate version for EPA’s BART determination for 

NGS. 

Comment: Closure of Mohave Project did not improve visibility, shows CALPUFF unreliable 

 One of the owners of NGS (0348) discussed the findings of analysis conducted after the closure 

of the Mohave Power Project (MPP) (a 1,580 MW coal-fired power plant) to evaluate whether the 

closure had resulted in improved visibility in Grand Canyon National Park.180 The commenter indicated 

177 Note that EPA already considered the limitations of CALPUFF and its included chemistry scheme when selecting it 

CALPUFF for BART modeling and EPA is following its own regulations in this rulemaking. 178 “CALPUFF Regulatory Update” Roger W. Brode, Presentation at Regional/State/Local Modelers Workshop, June 10-12, 

2008, available at http://www.cleanairinfo.com/regionalstatelocalmodelingworkshop/archive/2008/agenda.htm. 

179 “CALPUFF Status and Update” Tyler J. Fox, Presentation at Regional/State/Local Modelers Workshop, April 30-May 4, 

2012, available at http://www.cleanairinfo.com/regionalstatelocalmodelingworkshop/archive/2012/agenda.htm. 

180 Jonathan Terhorst and Mark Berkman., Effect of coal-fired power generation on visibility in a nearby national park, 

Atmospheric Environment 44 (2010) 2524-2531. doi:10.1016/j.atmosenv.2010.04.022. (manuscript version also available as 

“Mohave study on visibility” on SRP NGS web page http://www.ngspower.com/reports.aspx ) 
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that although CALPUFF version 5.8 modeling predicted that the plant had a significant impact on 

visibility in the Grand Canyon, this study concluded that there was “virtually no evidence that the MPP 

closure improved visibility in the Grand Canyon; or, equivalently, that the plant’s operation degraded 

it. Mean visibility (deciviews) and light extinction in [the park] did not respond to the closure in a 

statistically significant fashion. Sulfate levels did drop throughout the park, but not by an amount 

sufficient to induce a perceptible improvement in visibility. We are thus unable to conclude that the 

closure improved visibility in the Grand Canyon.” The commenter also quoted report of this study as 

stating that the “results raise questions about the reliability of CALPUFF.” 

 According to the commenter (0348) this analysis demonstrated that, contrary to the predictions 

of the CALPUFF model, a significant reduction in pollutants from a large power plant did not produce a 

perceptible improvement in visibility, providing further evidence that there is substantial over prediction 

bias associated with the CALPUFF model that EPA did not take into account when considering the 

visibility improvement factor in evaluating BART control options for NGS. The commenter believes 

that EPA should utilize more reasonable input assumptions to CALPUFF and avoid layering overly 

conservative inputs, in recognition of the studies such as the MPP study that demonstrate that the model 

is likely to inherently over-predict visibility improvements. 

 Similarly, four individuals (0128, 0233, 0251, 0345) discussed how the MPP was closed because 

it was believed to be a major contributor to haze in the area, and stated that neither the haze conditions 

nor the air quality near Laughlin, NV and Bullhead City, AZ has improve since the plant was 

demolished. Two of the commenters (0233, 0251) referenced the 2010 Terhorst study mentioned above, 

which concluded that the shutdown of the Mohave plant delivered no “statistically significant 

improvement in visibility” at the Grand Canyon, although one of the commenters (0251) recognized that 

a paper published in 2012 disputed this claim.181 This commenter urged EPA to focus on strengthening 

the research on the measurement and cause of haze in parks before taking any action related to the 

operation of NGS. The other commenter (0233) highlighted that the closure of MGS cost the state of 

Arizona nearly 600 jobs and hundreds of millions of dollars in direct economic benefits. 

 In contrast, one individual (0327) applauded the closure of MPP, believing that this plant 

contributed to the production of haze, which negatively impacted visibility at national parks and the 

health of local residents. 

Response: 

We disagree that the Terhorst & Berkman (T&B) study cited by the commenters raises questions 

about CALPUFF’s reliability. The study is worth considering as the Regional Haze program evolves, 

but one study does not invalidate CALPUFF, especially one not designed as a model performance 

evaluation. CALPUFF has had multiple successful performance evaluations, and via the BART 

Guidelines has already gone through public comment and rulemaking to become the recommended 

model for use in BART determinations. We continue to believe that CALPUFF is appropriate for this 

purpose. 

The Terhorst &Berkman conclusion on the effect of MPP closure is actually close to that from 

earlier analyses, which also predicted improvements less than the human perceptibility threshold of 1 dv. 

181 W.H. White, R.J. Farber, W.C. Malm, M. Nuttall, M.L. Pitchford, B.A. Schichtel, Comment on “Effect of coal-fired 

power generation on visibility in a nearby national park (Terhorst and Berkman, 2010)”, Atmospheric Environment 55 

(2012) 173-178. doi:10.1016/j.atmosenv.2012.02.076 (also available on DRI web page: http://www.dri.edu/marcpitchford?showall=&start=2 ) 
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As discussed in the White et al. paper cited by one commenter, the T&B analysis is “misleadingly 

presented as discrediting previous studies and their interpretation by regulators. In reality the T&B 

analysis validates a consensus on MPP’s visibility impact that was established years before its closure.” 

This T&B conclusion is nothing new, despite some commenters’ current focus on the perceptibility of 

the MPP shutdown. In any case, as we note elsewhere in this response to comments, human 

imperceptibility of the effect of a control does not remove the RHR requirement to impose reasonable 

controls on contributing sources, even in the face of uncertainty over the individual source contributions. 

Visibility progress will require emission reductions from many sources on a regional scale. The T&B 

study also did not create any disagreement with earlier work when it stated that other regional sources 

were larger contributors to visibility impairment than MPP was. As White et al. stated, T&B “create 

something of a ‘straw man’ when they rhetorically set their results against an imagined prior belief that 

MPP was the main source of Grand Canyon haze. This was clearly not the assessment of the scientists 

and stakeholders who worked together to estimate MPP’s impact, nor was it the basis for the accord that 

all parties accepted as appropriate for updating MPP’s control technology.” White et al. also noted 

certain discrepancies in the T&B work, such as a 1 dv visibility improvement at two of three monitoring 

sites, yet the result of pooling the three was of a 0.5 dv worsening in visibility; this information calls 

their conclusions into question. 

Finally, White et al. explicitly address the supposed disagreement between the T&B 

methodology and results from CALPUFF, pointing out that the comparison was flawed in several ways. 

For one thing, the ambient data relied upon by T&B is collected only every 3rd day; this results in too 

few days for a statistically valid comparison to the 98th percentile results reported from CALPUFF. 

Another important comparison flaw is that when T&B translated visibility extinction into deciviews, 

they used recent polluted conditions as the background for comparison, whereas the BART Guidelines 

and the CALPUFF results use natural conditions as background.182 When the T&B results are computed 

using natural background, they are substantially larger, and generally in agreement with CALPUFF 

results. 

Specifically, T&B found that MPP closure resulted in a sulfate reduction of 0.20 μg/m3; using 

the IMPROVE equation they computed a corresponding 0.71 Mm-1 improvement in extinction (“bext”) at 

the Meadview monitor in the Grand Canyon. Using the definition of deciviews and a recent measured 

background extinction of 28.22 Mm-1, the extinction improvement was translated into an improvement 

of 0.25 dv. 

The definition of deciview is: 

dv = 10*ln(bext/10). 

The change in deciviews in going from initial conditions to final conditions is: 

dv change = dv final – dv initial 

= 10*ln(final bext/10) - 10*ln(initial bext/10) 

= 10*ln(final bext / initial bext) 

For the MPP closure, with initial = recent measured 28.22, and final = measured minus MPP’s 0.71, the 

T&B calculation was: 

dv change = 10*ln[ (28.22 - 0.71) / 28.22 ] = -0.25 dv (0.25 dv improvement) 

182 EPA considered and rejected comments on the proposed BART Guidelines that visibility impacts should be evaluated to 

relative to current degraded visibility conditions and concluded that “[u]sing existing conditions as the baseline for single 

source visibility impact determinations would create the following paradox: the dirtier the existing air, the less likely it would 

be that any control is required.” (70 FR 39124). 
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However, computing deciviews relative to natural conditions, the visibility benefit from closing MPP is 

considerably larger, 3.3 dv. Using the Grand Canyon’s best 20% of days natural conditions extinction of 

1.83 Mm-1, with initial = natural plus MPP 0.71, and final = natural: 

dv change = 10*ln[ 1.83 / (1.83 + 0.71)] = -3.3 dv 

Even when annual average natural conditions (4.39 Mm-1) are used instead of the best 20%, the closure 

benefit is substantially larger than shown by T&B: 

dv change = 10*ln[ 4.39 / (4.39 + 0.71) ] = -1.5 dv 

Both the best 20% of days and the annual average are consistent with the BART Guidelines; we have 

generally used best 20% for the Regional Haze FIPs. 

The deciview benefits relative to natural conditions are much closer to the -2.0 and -2.4 dv 

CALPUFF results cited by T&B. Thus, their results do not really call the reliability of CALPUFF into 

question, nor show that it has an overprediction bias. 

We agree with commenters’ additional statement that further research on the measurement and 

cause of haze in Class I areas is needed, as the science of regional haze is complex and our 

understanding of it is evolving. But we do not agree that the uncertainty prevents us from implementing 

reasonable controls on contributing sources, nor that it excuses us from carrying out the regulatory 

requirements of the Regional Haze Rule, such as BART. 

Finally, with respect to the assertion that MPP was closed because of its contributions to haze, 

EPA would like to clarify that MPP’s closure was not the result of any EPA rulemaking. Rather, the 

owners of MPP 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 MPP to install pollution controls to reduce emissions of SO2 and PM from the facility. The 

Consent Decree was based on alleged violations by MPP of provisions of the Prevention of Significant 

Deterioration (PSD) program and required installation of the pollution controls by the end of 2005. The 

owners of MPP decided to close the facility rather than install pollution controls. The decision by the 

owners of MPP 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 MPP 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 MPP 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 MPP, 

sought to form a new ownership group to restart MPP, 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 MPP because it could not negotiate its intended purchase of 

Southern California Edison’s share of MPP in time to restart by 2011.183 Therefore, although EPA 

understands that tribes and other communities experienced adverse impacts from the closure of MPP in 

2005, the closure and the failed efforts to restart MPP are not attributable to, or the result of, EPA 

rulemakings related to haze. 

183 See February 6, 2007 Media Advisory from SRP, titled “SRP Press Release on Mohave” in the docket for this rule, and 

article in Power Engineering Magazine: http://www.power-eng.com/articles/print/volume-111/issue3/departments/startup/srp-decision-seen-as-ending-mohave-re-start.html
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Comment: Impact of emission rates and ammonia emission on modeled visibility benefits 

 The operator of the Kayenta Mine (0384) stated that EPA changed the input assumptions for 

emission rates for SO4, PM2.5, and NOx associated with the H2SO4 chemistry. Citing the JBR report, the 

commenter asserted that there is limited, if any, bases in other BART analysis for the proposed 

calculation metrics for H2SO4 chemistry and control effects used by EPA. Also citing the JBR report, the 

commenter indicated that EPA assumed emission changes increased the deciview impacts by 50 to 150 

percent, giving the following example: using the original SRP emissions, the change obtained by 

installing SCR according to SRP would be 0 at the Grand Canyon, while EPA emissions result in a 

0.74 dv change. 

 This commenter (0384) also addressed the cumulative impact of EPA’s assumptions on 

background ammonia concentration and emission rates, based on the JBR report. According to the 

commenter, the combined EPA assumptions increased the modeled deciview improvements due to 

adding SCR to LNB/SOFA by 60 to 170 percent. The commenter gave the example of the combined 

difference between the SRP modeling at the Grand Canyon, 0.86 dv, and EPA modeling, 2.9 dv, which 

is more than three times higher. The commenter stated that with all else being the same except for 

ammonia and emissions, the SRP modeling shows a variance of just over 1 dv for only 2 of the 11 Class 

I areas, while EPA modeling shows an improvement in excess of 1 dv at 8 of the 11 Class I areas. The 

commenter concluded that EPA’s conclusion that there will be a perceptible improvement in visibility is 

premised upon incorrect and unsupported modeling inputs. 

Response:

These comments are mainly the same as those covered in our other responses, especially the one 

above that claims EPA overestimates NGS’s visibility impact. The only additional comment here is the 

challenge to our treatment of H2SO4 chemistry. The commenter does not suggest any alternative and did 

not provide any technical support for their position. Our emissions work was based on similar 

calculations developed by AECOM for SRP, with some alternative assumptions about control 

efficiencies, etc. as documented in our emission calculation spreadsheet in the docket, 

NGS_BART_Scenarios_Emissions_EPA_proposal.xls. In turn, that work relied on work by Electric 

Power Research Institute documents about H2SO4

184 and ammonia,185 as described in the TSD, p.111 

and p.123, respectively. We believe our treatment of H2SO4 and ammonia chemistry is reasonable. 

Comment: Validate modeled predictions of visibility improvement with images/instrumentation

 Two individuals (0049, 0066) questioned the effectiveness of using models to determine 

visibility improvements at national parks and wilderness areas, and recommended that actual imagery be 

used to validate the predicted outcomes and confirm the overall effectiveness of the control measures. 

An industry/commerce commenter (0065) recommended the use of instrumentation to monitor the 

opacity of NGS emissions. 

184 “Estimating Total Sulfuric Acid Emissions from Stationary Power Plants”, Version 2010a, 1020636, Technical Update, 

Electric Power Research Institute, April 2010. Available at 

http://www.epri.com/abstracts/Pages/ProductAbstract.aspx?ProductId=000000000001020636. 

185 “Estimating Ammonia Emissions from Stationary Power Plants”, Electric Power Research Institute (EPRI), Palo Alto, 

CA: 2009, Report No. 1017985. Available at http://my.epri.com/portal/server.pt?Abstract_id=000000000001017985. 
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 One of the individuals (0049) listed the following limitations of climate sensitivity models, citing 

the IPCC: 

1. Observation coverage for initial conditions; 

2. Observation errors for initial conditions; 

3. Errors in quality control; 

4. Equations of motion are incomplete; 

5. Errors in numerical approximations; 

6. Simplified terrain; 

7. Model parameterizations incorrect; and 

8. Missing parameterizations. 

This commenter (0049) added that climate is sensitive to changes in cloud frequency and structure, 

which adds to the complication of modeling. The commenter encouraged the NPS to take part in 

monitoring the impact on visibility through live images or photography, which the commenter believes 

will minimize the possibility of loopholes in implementation. 

 The commenter (0049) discussed visible emissions monitoring methods such as EPA Method 9 

and ALT-082, apparently believing that these methods are suitable for measuring ambient visibility 

conditions. The commenter also cited a 1990 report which, according to the commenter, determined that 

emissions from NGS were the largest contributor to the degradation of visibility at national parks (Haze 

in the Grand Canyon: An Evaluation of WHITEX, 1990). The commenter concluded that it is imperative 

that we do not let this issue escape us for another 25 years and that we actually catch our mistakes with 

live data rather than continue to question the effectiveness of virtual climate models for visibility 

improvement. 

 The industry/commerce commenter (0065) recommended a specific supplier of instruments for 

digitally monitoring the opacity of NGS emissions according to the requirements of the EPA’s ALT-082 

method. 

Response:

We agree with the commenters that additional monitoring on an ongoing basis would help 

evaluate visibility changes over time, including impacts from NGS specifically. We also agree that air 

quality models have some uncertainty and limits to their accuracy, including some of the limitations 

listed by the commenter. We note that the difficulties in assessing the impacts of a particular source 

using imagery and/or actual measurements of pollutants and extinction including the confounding effect 

of pollution from many other sources over a large area; it can be difficult to tease out the effect of the 

one source of interest. In any case, in the BART Guidelines we did not require any new monitoring, 

model validation, or source attribution studies, which would have entailed large expenses and delays for 

the hundreds of sources nationwide for which visibility impacts had to be estimated. In the BART 

Guidelines we also determined that CALPUFF is adequate for the purpose of modeling for BART 

determinations. We also note that previous FIP requirements promulgated for NGS already included an 

opacity requirement, limiting opacity from Units 1, 2, and 3 at NGS to no greater than 20 percent 

opacity, excluding condensed uncombined water droplets, averaged over any six minute period and 40 

percent opacity, averaged over six minutes, during absorber upset transitions.186

186 See 40 CFR 49.5513(d)(4). 
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Comment: Level of human perceptibility 

 One of the owners of NGS (0348) stated that the Fact Sheet accompanying the February 2013 

Proposal rule asserts that “[a] difference of 0.5 deciviews is generally considered a perceptible change.” 

The commenter refuted this assertion, noting that the regional haze rules and BART Guidelines indicate 

that 1.0 dv may generally be considered the threshold for human perceptibility (citing 64 FR 35726-27; 

70 FR 39120) and referring to two studies finding that a change greater than 0.5 dv is required before the 

human eye can detect a shift in conditions. The commenter indicated that one study found 1 to 2 dv 

necessary for human perception, and the second found 1.8 dv necessary. 

Response:

We agree with the commenter that opinions differ on the threshold for human perceptibility. In 

addition to the passage cited by the commenter stating that 1 dv is a correct perceptibility threshold, the 

BART Guidelines also stated: “In the proposal we noted that a 0.5 deciview change in visibility is linked 

to ‘perceptibility,’ or a just noticeable change in most landscapes. .... (changes in light extinction of 5 

percent will evoke a just noticeable change in most landscapes). Converting a 5 percent change in light 

extinction to a change in deciviews yields a change of approximately 0.5 deciviews.”187 In any case, we 

did not rely on this threshold in determining SCR to be BART for NGS. We have referred to visibility 

improvements of 0.5 dv or 1.0 dv in various places as a benchmark, and have stated that the multiple 

Class I areas showing visibility improvements of 1 dv or greater indicate a substantial benefit from SCR. 

Our justification for selecting a SCR level of control as BART is based on our five factor analysis, 

including the substantial visibility improvement that will occur at 11 surrounding Class I areas. We also 

note, as stated in a response above, that human perceptibility is not a requirement for BART. 

Comment: Cumulative dv 

 One of the owners of NGS (0348) and an industry trade association (0306) objected to EPA’s use 

of cumulative impacts in assessing the degree of visibility improvement from emission controls, 

asserting that this approach has no tie to human perception and distorts the BART analysis. One of the 

commenters (0348) referred to a paper authored by Dr. Ivar Tombach (attached to the comments as 

Appendix E) that concludes that this metric is not appropriate because changes cannot be perceived in 

multiple Class I areas by a single observer at a given time; that is, an individual observer cannot 

perceive an additive improvement at multiple Class I areas. The other commenter (0306) stated that the 

cumulative approach distorts the visibility analysis because it sums computer-modeled visibility impacts 

at multiple locations at multiple times, and that this approach is irrational because it treats a single 

source of regional haze differently depending on the number of Class I areas located around the source. 

This commenter believes that the public will be misled by EPA’s “exaggeration” of the benefit of its 

action. 

 The NGS owner (0348) added that the BART Guidelines focus on visibility impacts at individual 

Class I areas and do not recommend or imply that adding the impacts at different sites is appropriate. 

According to the commenter, adding improvements across multiple Class I areas effectively multiplies 

the threshold metric by the number of Class I areas which, the commenter believes, flies in the face of 

the basic science of visibility perception thresholds. The commenter opined that this metric is akin to 

187 70 FR 39119, footnote 28 (July 6, 2005). 
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examining the effects on visibility at several locations within the same Class I area and adding them. 

The commenter believes that a correct modeling result for a given Class I area is determined by finding 

the maximum impact over all receptors, not by adding individual receptors at a Class I area. 

Response:

EPA considers it important to account for visibility impacts at multiple Class I areas. The goal of 

the visibility program is to remedy visibility impairment at all Class I areas.188 One approach to account 

for the benefits to all affected Class I areas is the cumulative “total dv” metric. We disagree with 

commenters that cumulative improvement over multiple areas is an inappropriate metric, or that 

examining a single Class I area is sufficient. The cumulative improvement metric (i.e., the simple sum of 

impacts or improvements over all the Class I areas) is not intended to correspond to a single human’s 

perception at a given time and place, and we did not represent it as such. Indeed, the use of CALPUFF’s 

24-hour average extinction, and the 98th percentile from among daily deciviews that may occur at 

different locations, is already different from what one person would actually observe, however, the 

BART Guidelines consider it adequate for the purpose of modeling in BART determinations. In our 

proposal we stated “In assessing the degree of visibility improvement from controls, we relied heavily 

on the maximum deciview improvement among the Class I areas and the number of areas showing 

improvement (i.e., all 11 Class I areas), with cumulative improvement providing a supplemental 

measure that combines information on the number of areas and on individual area improvement.”189

The approach is simply one way of assessing improvements at multiple areas, for consideration along 

with other visibility metrics. Another approach would be to simply list visibility improvements at the 

various areas, and qualitatively weigh the number of areas and the magnitudes of the improvements. The 

cumulative sum is simply an easily understood and objective way of weighing cumulative visibility 

improvement, as part of the overall BART decision. 

Comment: Lack of information on actual conditions at times of high haze

 One industry trade association (0306) expressed concern at the lack of information related to the 

actual atmospheric conditions that existed at the times that high levels of haze were recorded and the 

degree to which the atmospheric conditions being modeled match those actual conditions. The 

commenter believes that such comparisons are needed to provide reasonable assurance that the approved 

BART limits will actually improve the major haze episodes that are recognized by the public. The 

commenter added that to avoid false expectations, EPA should explain the conditions where visibility 

improvements will be less discernible to the public; for example, the public should know whether the 

BART-imposed emission reductions will produce a noticeable improvement in haze conditions that 

occur as a result of the transport of contaminated air masses from distant population/industrial centers. 

Response:

As stated in or preceding response, under the BART Guidelines we did not require new modeling 

studies or validation, and determined that CALPUFF is appropriate for BART determination modeling. 

Since the modeling was based on three years of meteorological data, we believe that it adequately 

captured the various conditions conducive to high and to low amounts of haze. Somehow using actual 

haze measurements would entail a much larger scale effort of source attribution modeling, such as with 

188 CAA section 169A (a)(1). 

189 78 FR 8286 (February 5, 2013). 
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a photochemical grid model and including the effect of many other sources. This scale of modeling is 

more appropriate for States’ full regional haze plans that assess the progress made by control and other 

source changes over time. It is beyond the scope of what is practical or necessary for BART 

determinations, given that CALPUFF is adequate for this purpose. 

We agree with the commenter that it is important the public not be misled about the visibility 

improvements that will result from BART controls. As noted above, for applications involving chemical 

transformations, the CALPUFF model is considered a “screening” approach. Its treatment of 

atmospheric chemistry is simplified as compared to a photochemical grid model. For CALPUFF BART 

modeling we include only a single source, instead of the hundreds or thousands that affect actual 

visibility. We also use CALPUFF’s 24-hour average estimates, whereas actual visibility seen by a 

national park visitor is instantaneous, not an average over multiple hours. Finally, we use visibility 

estimates at a collection of individual model receptor locations, whereas actual views depend on the 

pollution along a miles-long site path and also on the relative angles of the viewer, the sun, and the 

pollution. In short, CALPUFF is not intended to provide a realistic estimate of what a viewer would 

actually see, but rather an estimate of a source’s approximate average contribution to impairment, if no 

other sources existed. We consider that CALPUFF is adequate and appropriate for that purpose, and for 

use in BART determinations. 
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8.0 Comments on BART Determinations 

8.1 Comments on the Proposed BART Determination for NOx 

Comment: General 

One environmental advocacy group (0373) supported EPA’s proposed finding pursuant to the 

TAR that a BART determination for NGS is “necessary and appropriate” (citing 78 FR 8279 and 40 

CFR 49.11), asserting that NGS is plainly subject to BART under the statutory and regulatory criteria 

Numerous individuals (0067, 0074, 0149, 0162, 0164, 0178, 0218, 0236, 0393, 0240, 0245, 

0264.8, 0283, 0284, 0394, 0399, 0412) and environmental or public interest groups (0395, 0404) 

supported the proposed BART rule requiring NGS to comply with NOx emission limits within 5 years of 

the final rule, while two individuals (0204, 0210) implied that they would support either the proposed 

BART determination rule or the adoption of EPA BART Alternative that would extend the schedule 

requiring the installation of SCR on one unit per year between 2021 and 2023. One public interest 

advocacy group (0015) expressed support for the proposed BART determination and applauded the 

Agency for addressing emissions from NGS despite controversy and resistance. 

One commenter (0420) submitted copies of a number of resolutions enacted by various Navajo 

Nation Chapters in favor of the proposed BART determination to support the position that the most 

stringent pollution controls possible should be applied to NGS, and that there should be a transition to a 

renewable energy plant. The commenter submitted resolutions approved by approximately 30 Chapters 

of the Navajo Nation. A tribal government commenter (0362) similarly urged EPA to hold NGS to the 

highest BART standard and not to let NGS prolong the implementation phase for years. The commenter 

stated that NGS owners are using the Navajo Nation for leverage to continue its operation and use the 

threat of some great economic loss to the Navajo Nation as a strategy to lower the standards to less 

costly requirements regarding BART and strategically delay the retrofit. 

In contrast, a number of individuals (0145, 0146, 0147, 0148, 0161, 0163, 0165, 0167, 0168, 

0193, 0200, 0203, 0205, 0212, 0226), and entities (0024, 0194, 0214, 0252, 0287, 0314, 0324, 0326, 

0343, 0348, 0400, 0406, 0440), opposed EPA’s proposed BART determination for various reasons, 

including the potential adverse impacts if the installation of controls forced NGS to close. Many 

commenters asserted that LNB/SOFA should be determined to be BART at NGS based on the 

“extraordinarily high” incremental cost-effectiveness values in terms of $/ton and $/dv provided in 

submissions by the NGS operator. Other commenters (0175, 0189, 0220, 0293, 0295, 0305, 0317, 0381) 

objected to the BART proposal based on assertions that EPA’s analysis was not based on sound science, 

or that the EPA failed to properly weigh the five BART factors resulting in a proposed BART 

determination that is arbitrary, capricious, and an abuse of discretion. While supporting efforts to ensure 

that the production of power is environmentally responsible, a state agency (0017/0289/0320) asserted 

that the BART proposal does not appropriately balance environmental benefits with the cost to 

consumers. 

Response:

 EPA acknowledges that members of the public and regulated community expressed strong 

support both for and against stringent NOx controls at NGS. The responses to comments related to the 
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compliance timeframe for better than BART alternatives is discussed in section 8.5 and 9.0. Responses 

related to the cost-effectiveness of controls are discussed in section 3.0, and comments related to the 

Affordability Analysis and visibility modeling are discussed in sections 4.0 and 7.0, respectively. 

Comment: BART limit for NGS should be 0.04 lb/MMBtu

An environmental advocacy group (0373) argued that the final BART emission limit should be 

more stringent. The group drew on supporting reports prepared by Victoria Stamper (Stamper report) 

and Nathan Miller and Ranijit Sahu (Miller/Sahu report) (submitted with the comments) to argue that 

SCR typically is designed for and achieves 90 percent NOx removal and that electric generating units 

(EGUs) have been required to achieve lower NOx limits with SCR, therefore, the final BART limit 

should be no higher than 0.04 lb/MMBtu. According to the commenter, this represents 83 percent 

removal which would provide a reasonable margin of operating safety for NGS. The commenter 

indicated that the Stamper report included various SCR-vendor representations to this effect. 

The comment noted that permitting authorities have required lower NOx limits than 0.055 

lb/MMBtu in recent BACT determinations based on SCR in combination with combustion controls, 

including PSD permits for Plant Washington, Desert Rock, Wygen 3, and Dry Fork. The commenter 

also noted that in EPA’s FIP for the San Juan Generating Station (SJGS) in New Mexico, EPA 

determined that SCR was the most cost-effective pollution control for NOx and imposed a NOx BART 

emission limit of 0.05 lb/MMBtu on a 30-BOD average basis. The commenter added that in its response 

to comments on the SJGS BART determination, the EPA confirmed that several EGUs have achieved 

NOx emission rates of 0.05 lb/MMBtu or lower, citing to actual emission rates at Seminole Units 1 and 

2, Morgantown Units 1 and 2, and Cope Generating Station. The commenter also indicated that the Dry 

Fork plant in Wyoming has never emitted NOx higher than 0.04 lb/MMBtu on a 30-BOD average basis. 

Response:

EPA disagrees with the commenter that the BART limit for NGS should be 0.04 lb/MMBtu. As 

discussed below, EPA disagrees with the commenter’s assertion that emission limits associated with 

BART must meet BACT or the lowest emission rate ever achieved with that technology at any coal-fired 

power plant.190

EPA agrees that SCR systems can be designed to achieve higher levels of control. Although the 

commenter provided information to suggest that it is common to design SCR for 90 percent removal, 

exhibit 5 to the Stamper Report did not indicate the extent that combustion controls were used in 

combination with SCR in characterizing the design target. EPA proposed a limit of 0.055 lb/MMBtu 

achievable with SCR+LNB/SOFA, and using a baseline emission rate of 0.35 lb/MMBtu, this represents 

a removal of 84 percent.191 However, as noted in the comment and response related to a higher emission 

limit for NOx, S&L and SRP have indicated they intend to design SCR at NGS to a target of 0.03 

lb/MMBtu. This represents a removal efficiency of 91 percent for SCR+LNB/SOFA (from a baseline of 

0.35 lb/MMBtu), or 88 percent for SCR alone (i.e., from 0.24 lb/MMBtu). Thus, although a SCR system 

190 WildEarth Guardians v. EPA. 9th Circuit slip op. (July 17, 2014) (holding that BART limit should be achievable), in the 

docket for this rulemaking. 

191 In characterizing EPA’s BART determination as 74 to 77 percent removal, the commenter was already accounting for the 

early installation of LNB/SOFA on each unit after the baseline period. After installation of LNB/SOFA over 2009-2011, 

Units 1-3 became subject to a limit of 0.24 lb/MMBtu, and achieved NOx emission rates of approximately 0.21-0.22 

lb/MMBtu on an annual average basis. See page 2 and 3 of the Stamper Report. 
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can be designed to a specific target, the design target is typically not equivalent to the actual applicable 

emission limit. EPA considers a design target of 0.03 lb/MMBtu for NGS to be generally consistent with 

the information provided by the commenter suggesting that SCR is often designed to achieve 90 percent 

control. 

EPA also agrees that PSD permits for new facilities have established BACT limits that are 

numerically lower than 0.055 lb/MMBtu. However, EPA disagrees with the premise that BART limits 

for existing facilities must equal BACT limits for new facilities. The limits of 0.050 lb/MMBtu cited by 

the commenter were set on a 30-day rolling average for two facilities (Plant Washington and Desert 

Rock), and on a 12-month rolling average for other facilities (Wygen 3, Dry Fork, and Spruce 2). EPA 

notes that the two facilities with limits established on a 30-day rolling average basis have not 

demonstrated compliance with those limits in practice. The Plant Washington facility is required in its 

PSD permit to meet a NOx limit of 0.050 lb/MMBtu on a 30-day rolling average basis. EPA notes that 

Plant Washington, a new power plant in Washington County, Georgia, only commenced construction in 

2013.192 Therefore, actual emission data is not yet available to assess SCR performance at Plant 

Washington. The commenter also cites to a PSD permit issued by EPA to Desert Rock, a new facility 

that would have been built on the Navajo Nation Indian Reservation. The PSD permit required a NOx

limit of 0.060 lb/MMBtu over a 24-hour block period, 0.05 lb/MMBtu over a rolling 30-day period, and 

0.0385 lb/MMBtu over a rolling 365-day period. EPA notes that construction of Desert Rock never 

commenced, and the PSD permit issued to this facility is no longer valid.193

As cited by the commenter, Wygen 3, Dry Fork, and Spruce 2 all have permitted emission limits 

for NOx of 0.05 lb/MMBtu on a 12-month rolling average basis. However, as noted elsewhere by the 

commenter, the PSD permit for Spruce 2 sets two NOx limits with different averaging periods.194 Thus, 

Spruce 2 is also subject to a NOx limit of 0.069 lb/MMBtu on a 30-day rolling average basis, which is 

higher than EPA’s proposed BART limit for NGS of 0.055 lb/MMBtu on a 30-BOD basis. 

 The commenter also cites to several EGUs that achieve NOx emission rates of 0.05 lb/MMBtu or 

lower. These EGUs typically represent units that have been retrofit with SCR and participate in emission 

trading programs, such as the Clean Air Interstate Rule (CAIR). As noted by the commenter, numerous 

facilities achieve hourly emission rates less than 0.05 lb/MMBtu, and many facilities also do achieve 30-

BOD averages and annual average emission rates below 0.05 lb/MMBtu as well, e.g., Morgantown 1 

and 2, and WA Parish 7 and 8.195 However, because these facilities operate within an emission trading 

program, they are not bound by a permit condition to consistently meet a specific NOx limit. Therefore, 

although these units provide useful information on the performance capability and variability of units 

that have been retrofit with SCR, they are less relevant, compared to site-specific vendor information or 

the performance of similar units with permit limits, for making a case-by-case determination of BART 

for a specific facility. The commenter also references the source-specific FIP issued by EPA for the San 

Juan Generating Station in New Mexico that set a BART limit for NOx of 0.050 lb /MMBtu on a 30-

BOD basis. However, on May 12, 2014, EPA proposed approval of a New Mexico SIP submittal for 

SJGS to replace EPA’s FIP.196 The New Mexico SIP involves closure of two units at SJGS and sets an 

emission limit of 0.23 lb/MMBtu on the remaining two units, achievable with the installation and 

192 http://power4georgians.com/summary.aspx 

193 See document titled “EPA Letter to Sithe Global Re: Desert Rock” in the docket for this rule. 

194 See Exhibit 72 to Stamper Report (Special Conditions for Spruce 2), document number 0372 in the docket for this rule at 

EPA-R09-OAR-2013-0009. 

195 See Stamper Report at page 7, and references therein, document number 0372 in the docket for this rule at EPA-R09-

OAR-2013-0009. 

196 See 79 FR 26909 (May 12, 2014). 
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operation of SNCR. When EPA takes final action to approve the New Mexico SIP for SJGS, the FIP 

will be withdrawn and SJGS will not be required to meet a limit of 0.050 lb/MMBtu. 

Although BACT limits lower than 0.055 lb/MMBtu have been established and facilities do exist 

that achieve emission rates below 0.055 lb/MMBtu, EPA disagrees with the commenter’s assertion that 

emission limits associated with BART must meet BACT or the lowest emission rate ever 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 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., Plant Washington), or emission rates achieved from the operation of individual facilities 

under an emissions trading program (e.g., Morgantown) may provide important information, but should 

not be construed to represent the most appropriate BART limit representative of a given technology for a 

given facility.197

Accordingly, although EPA acknowledges that BACT determinations for new facilities have 

established slightly lower NOx limits (0.050 lb/MMBtu) than the BART limit EPA proposed for NGS 

(0.055 lb/MMBtu), EPA does not agree that the lower limit recommended by commenters of 0.04 

lb/MMBtu is BART for Units 1-3 at NGS. The commenter has not provided any specific information 

showing that NGS could demonstrate continuous compliance with an emission rate of 0.04 lb/MMBtu. 

Comment: BART limit for NGS should be in the range of 0.07-0.08 lb/MMBtu

Two of the owners of NGS (0314, 0348), a CAP agricultural water users group (0305), and the 

CAP operator (0343) asserted that the BART NOx emission limit proposed for NGS is unachievable. 

The operator of NGS (0348) noted that the proposed limit of 0.055 lb/MMBtu is to be achieved through 

the use of SCR across all three units on a 30 boiler operating day (BOD) basis, which would include 

periods when the SCR is unable to operate such as startup, shutdown, and periods of load cycling. The 

commenter made the following arguments: 

197 EPA’s Environmental Appeals Board has recognized that PSD emission limits must be set to allow fluctuations in 

operations, stating: “To account for these possibilities, a permitting authority must be allowed a certain degree of discretion 

to set the emissions limitation at a level that does not necessarily reflect the highest possible control efficiency, but will allow 

the permittee to achieve compliance consistently.” In Re Masonite Corporation, 5 E.A.D. 551, 560-61 (1994).
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 The information from a catalyst vendor (Hitachi) that the EPA relied on does not support the 

achievability of the proposed emission limit, as later information received from the same vendor 

demonstrates. 

EPA relied on information submitted by Hitachi Power Systems (Hitachi) to support its proposed 

NOx BART limit of 0.055 lb/MMBtu for NGS, noting that the EPA stated that “...for several reasons, 

including information from a catalyst vendor that an SCR system at NGS using ... four layers of catalyst 

can meet a limit of 0.05 lb/MMBtu, EPA is proposing to determine that Units 1-3 can meet an emission 

limit of 0.055 lb/MMBtu using four layers of catalyst” (citing 78 FR 8280). The commenter stated that in 

a subsequent letter submitted to EPA in February 2013, Hitachi (0037) clarified that while it may be 

possible to design an SCR system to achieve 0.05 lb/MMBtu, it would be very difficult for that same 

system to meet a permit limit of 0.055 lb/MMBtu under all potential operating circumstances, and that 

Hitachi further concluded that “the utility and their engineer need to determine what margin needs to be 

applied to insure the unit is capable of achieving less than the permit level on a 30 day rolling 

average.”198

According to the commenter (0348), vendor guarantees for SCR are typically only provided for 

full load operation under a very specific set of conditions, which do not include startup, shutdown, 

equipment malfunction, or load cycling. The commenter noted that vendor guarantees are complex 

business arrangements that balance the needs of the utility and include multiple parameters, including 

NOx performance, operational service life, pressure drop across the SCR during specific conditions, 

SO2 to sulfur trioxide (SO3) conversion, fuel characteristics, and many other elements. The commenter 

stated that guarantees provided by a vendor are typically limited by financial terms within a contract and 

would provide little, if any, assistance to the NGS Participants if the system were to fail to perform as 

guaranteed and they were unable to operate the unit for an extended period of time due to an inability to 

meet the guaranteed emission rate. 

The commenter (0348) also noted that Hitachi acknowledged that it may be possible to design an 

SCR to achieve a lower NOx rate of 0.03 lb/MMBtu but did not conclude that such a design would 

actually be able to achieve the proposed limit of 0.055 lb/MMBtu in all potential operating 

circumstances. 

 The NOx emissions achieved in other SCR retrofit situations do not justify the proposed emission 

limit. 

Although the final NOx BART limit for SJGS was 0.05 lb/MMBtu, one of the plant operator’s 

principal arguments in the Tenth Circuit litigation challenging this NOx BART determination was that 

the EPA had not adequately supported its determination that this limit could be achieved at SJGS. To 

resolve this litigation, the owners of SJGS, the EPA, and the state of New Mexico negotiated a BART 

alternative that imposes a 0.23 lb/MMBtu plantwide NOx emission limit, which will allow for 

installation of Selective Non Catalytic Reduction (SNCR) on two units, and that requires the retirement 

of the other two units. Accordingly, the permit limit for SCR imposed in the final FIP for SJGS does not 

provide any evidence that such a limit is actually achievable in practice or that it is appropriate for NGS. 

While the EPA stated that Parish Units 7 and 8 at have achieved NOx emission rates “consistent 

with the vendor guarantee of 0.03 lb/MMBtu” (citing TSD page 36), the EPA also acknowledged that 

the Parish units can demonstrate compliance using a “cap and trade” approach, which makes them 

198 This letter is in the docket for this rulemaking, Docket No. EPA-R09-OAR-2013-0009-0037. 
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inappropriate to compare to the units at NGS. The EPA further acknowledged that “the Parish units do 

not achieve 0.03 lb/MMBtu on a consistent basis.” The commenter performed a more detailed review of 

the Parish units’ emissions data in the EPA’s Air Program Markets Division (AMPD, formerly known as 

Clean Air Markets Division or CAMD) which, according to the commenter, revealed that NOx

emissions from the units are generally higher than 0.03 lb/MMBtu, and NOx emissions from Parish Unit 

7 have exceeded 0.055 lb/MMBtu during several months since SCR was installed. 

In developing of the Cross State Air Pollution Rule (CSAPR), the EPA concluded that a NOx

limit below 0.06 lb/MMBtu is not achievable through retrofit of SCR on coal fired electric generating 

units (citing 76 FR 1109, 1115). The EPA stated that this “well controlled emission rate of ... 0.06 

lb/MMBtu for NOx represent[s] the lowest annual emission rate assumed achievable when state of the

art pollution control technologies are installed at coal units” (citing 76 FR 1115 and footnote 3). The 

EPA also stated in this rulemaking proceeding that 0.06 lb/MMBtu is unachievable on an annual average 

basis, which means that it also is unachievable on a 30 day rolling average basis. 

In its proposed rule for North Dakota, the EPA based its BART analysis on a 0.05 lb/MMBtu 

emission rate, but then proposed to adopt 0.07 lb/MMBtu as a BART compliance limit in recognition 

that a sufficient margin of compliance must be included (citing 76 FR 58570, 58610). 

In its final rule for South Dakota, the EPA established a NOx limit of 0.10 lb/MMBtu for an 

electric generating unit to allow for an adequate margin of compliance (citing 76 FR 24845, 24848, 

24849). 

 The Sargent & Lundy modeling and analysis show that the proposed emission limit is 

unachievable. 

The operator of NGS (0348) contracted with S&L to conduct a modeling analysis to assess 

whether the NGS units can achieve the proposed 0.055 lb/MMBtu emission limit using SCR control 

technology (attached as an Appendix to the comment). According to the commenter, S&L performed a 

detailed modeling assessment that considered typical historical operating conditions, including periods 

of load cycling and unit startups and shutdowns, using NGS emissions data from EPA’s CAMD to 

develop a model that simulates a variety of operating conditions based on data collected during past 

operation of the units. The commenter noted that the model assumes an SCR design basis of 0.03 

lb/MMBtu, consistent with the Hitachi statement that it might be possible to design an SCR for this 

limit, then the model calculates the emission rates that would actually be achievable by such a system 

when considering transient conditions such as startups, shutdowns, and load cycling. 

 The commenter (0348) explained that load cycling occurs as a result of varying power demand 

from the NGS Participants. According to the commenter, at lower loads, the temperature of the exhaust 

gas decreases, which affects the SCR catalyst performance; specifically, the SCR cannot be operated 

during periods in which the flue gas temperature is below the minimum ammonia injection temperature 

(approximately 600°F) due to concerns over catalyst fouling due to ammonium bisulfate formation, so 

higher emissions would be expected during periods of operation at lower loads. The commenter also 

noted that NOx performance between units varies as a result of the amount of time between maintenance 

intervals, which occur on a staggered schedule every 3 years coinciding with the units’ planned outages 

for major maintenance. The commenter indicated that the LNB/SOFA and SCR equipment also would 

undergo substantial maintenance and inspection during these outage periods, but soon after these 

overhauls NOx performance begins to degrade as a result of routine operations and will continue to 

degrade until the next scheduled overhaul. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 The commenter (0348) indicated that of the eighteen different operating scenarios modeled by 

S&L, seven scenarios exceeded the BART limit proposed by EPA. The commenter stated that during 

periods of low load cycling and startups, the plantwide NOx emission average consistently exceeded the 

EPA’s proposed limit of 0.055 lb/MMBtu, with a plantwide 30 BOD NOx emission average as high as 

0.067 lb/MMBtu in multiple scenarios. (Additional information on the modeling results can be found in 

Table 1 of the comments and in the full S&L analysis attached to the comments.) The commenter added 

that modeled emissions for individual units ranged from 0.047 to 0.077 lb/MMBtu. 

 The commenter (0348) believes that S&L model results clearly demonstrate that a 

0.055 lb/MMBtu NOx emission limit on a 30 BOD basis is unachievable at NGS, adding that S&L’s 

modeling results do not include a compliance margin, which would be necessary to include when setting 

an emission limit. The commenter pointed out that the historical data used in the modeling does not 

account for specific issues that could further increase the number of startups and shutdowns in the 

future, as well as the need for additional low load cycling, such as: 

 Intermittency of operation associated with increasing renewable energy generation. 

 Lower natural gas prices and potential future carbon regulations or policies driving the use of 

natural gas fired generation in place of coal fired generation. 

 Unexpected equipment failure at the plant or offsite (e.g., switchyard and/or substation issues can 

cause additional transmission limitations). 

 Fuel moisture issues (e.g., rain can cause increased moisture content in the fuel, contributing to 

boiler plugging and tube fouling). 

 Events outside of the plant’s control, such as forest fires, which can have direct effects on the 

operation of the units due to transmission impacts. 

For these reasons, the commenter believes that a compliance margin should be added to S&L’s 

calculated highest 30 day averages in order to establish an achievable permit limit for SCR at NGS. 

Based on these considerations, the commenter (0348) drew the following conclusions: 

 The EPA’s proposed plantwide NOx emission limit of 0.055 lb/MMBtu on a 30 BOD rolling 

average basis is unachievable at NGS. 

 Although some equipment vendors may assume a design basis as low as 0.03 lb/MMBtu for SCR 

under steady state conditions, a review of other retrofit SCR operations indicates that actual 

emissions will not achieve this level when factors such as performance degradation between 

planned overhaul intervals and limitations on SCR performance in certain operating conditions 

including startups, shutdowns, and load cycling conditions are taken into consideration. 

 Accordingly, while it may be possible to design an SCR for a basis of 0.03 lb/MMBtu, it is 

critical that sufficient compliance margin be incorporated in establishing an achievable permit 

limit that allows for reasonably expected performance variability. To the commenter’s 

knowledge, there are no retrofit SCRs constructed and operating today – regardless of the NOx

design basis – that demonstrate compliance with a permit limit of 0.055 lb/MMBtu on a 30 BOD 

rolling average basis when startups, shutdowns and load cycling conditions are required to be 

included in the average. 

 Potential future operating conditions that have not been encountered in the past must also be 

considered in establishing an achievable compliance limit. For example, integration of renewable 

resources into a utility’s generation fleet may create situations in which coal fired units such as 

those at NGS are being operated in load cycling modes more frequently. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 S&L’s analysis concludes that a higher emission limit in the range of 0.07 to 0.08 lb/MMBtu 

may be achievable at NGS. However, as demonstrated in S&L’s analysis, a compliance limit 

established at the lower end of this range may require the NGS Participants to limit operation of 

the units in certain modes, unless future technology advances allow the limit to be achievable 

over a broader range of operating conditions. A limit closer to 0.07 lb/MMBtu may also be 

achievable if startup, shutdown or load cycling conditions are excluded from the average. 

Response:

EPA disagrees with the commenter that the BART limit for NGS should be higher than our 

proposed limit of 0.055 lb/MMBtu, in the range of 0.07 to 0.08 lb/MMBtu. 

The commenter (0348) first cites to a comment submitted by Hitachi Power Systems of America 

(0037) that clarifies information Hitachi provided to EPA in 2011 regarding the ability of their SCR 

system to comply with a limit of 0.05 lb/MMBtu on a 30-day rolling average. In 2011, EPA 

corresponded with Hitachi representatives about the design target required for an SCR system to meet a 

limit of 0.05 lb/MMBtu.199 Specifically, EPA asked, “would Hitachi typically design down to 0.03 

lb/MMBtu to meet a 0.05 limit?” In response, Hitachi stated, “All of our designs are based on the 

required NOx at the end of the guarantee period, so I do not think that in order to meet the 0.05 

lb/MMBtu requirement, we would be required to design for a 0.03 lb/MMBtu requirement.” Based, in 

part, on information provided by Hitachi, that an SCR system based on a 3+1 design could meet a limit 

of 0.05 lb/MMBtu, even at the end of the guarantee period (i.e., just prior to catalyst replacement), EPA 

proposed a BART limit of 0.055 lb/MMBtu for Units 1-3 at NGS. 

In 2013, Hitachi submitted a comment to the docket (0037) clarifying that “to set the permit level 

of 0.055 lb/MMBtu on a design of 0.05 lb/MMBtu will be very difficult to achieve. Lowering the design 

to 0.03 lb/MMBtu will increase the volume of catalyst required and could drive the design to a 4 plus 1 

and add significant cost to the project. We agree with the recommendation in the S&L study that a 0.05 

design is more appropriate with a 0.07-0.08 permit level.” 

In EPA’s 2011 direct correspondence with Hitachi representatives, EPA attempted to understand 

Hitachi’s perspective regarding design targets and emission limits by asking whether a design target of 

0.03 lb/MMBtu would be required to meet a limit of 0.05 lb/MMBtu. Hitachi replied that it would not 

need to design to 0.03 lb/MMBtu.200 In 2013, Hitachi reversed its previous statements and implied that it 

would need to design to 0.03 lb/MMBtu in order to meet a limit of 0.05 lb/MMBtu. In its 2013 

comment, Hitachi also noted that, “Hitachi also stated that the utility and their engineer need to 

determine what margin needs to be applied to insure [sic] that the unit is capable of achieving less than 

the permit level on a 30-day rolling average.”201 Consistent with Hitachi’s statement regarding 

coordination between the utility and its engineering firm, SRP submitted a study it commissioned with 

S&L to more closely examine whether the units at NGS would be able to meet an emission limit of 

0.055 lb/MMBtu on a rolling 30-BOD average basis. Therefore, we now focus our response on the S&L 

report commissioned by SRP. 

199 See Email from Stephen Guglielmo, Hitachi, to Anita Lee, EPA, dated March 7, 2011, titled “2011_0307 Email from 

Stephen Guglielmo to Anita Lee”, in the docket for this rulemaking at EPA-R09-OAR-2013-0009-0004. 200 Id. 201 We note that EPA has not been able to locate this statement, or a similar statement, in our 2011 correspondence with 

Hitachi. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

As described in the comment summary above, the S&L report generally argues that because the 

emission limit is established based on a 30-BOD average basis, the proposed emission limit of 0.055 

lb/MMBtu is not consistently achievable at NGS. The S&L report seems to suggest that excluding 

startup, shutdown, and load-cycling emissions from the BART limit might warrant consideration. The 

BART Guidelines require that BART determinations for EGUs 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.202 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. 

The definition of boiler operating day was finalized as proposed.203 Consistent with the BART 

Guidelines, EPA proposed a BART limit for NGS based on the definition of BOD that means the 24-

hour period during which any fuel is combusted at any time in the unit. Based on this definition of BOD, 

the averaging period includes periods of startups, shutdowns, and malfunctions, as well as emissions 

during load-cycling. EPA is not revising the averaging period or the definition of BOD, to exclude 

periods of certain types of operation, for the BART emission limit. 

 The S&L analysis begins by assuming that the SCR system would be designed to a target of 0.03 

lb/MMBtu, and provides results, based on 2012 operations data at NGS, that suggests that even with a 

design target of 0.03 lb/MMBtu, the units at NGS would not be able to consistently meet a limit of 0.055 

lb/MMBtu due to periods of startup, shutdown, and load cycling operation.204 The S&L analysis 

concludes that even with a design target of 0.03 lb/MMBtu, an emission limit in the range of 0.07-0.08 

lb/MMBtu would be required to accommodate the periods of load-cycling operation, startups, and 

shutdowns. This conclusions means that S&L is essentially recommending a limit that is 2.3 to 2.7 times 

higher than the design target, or a compliance margin of 133 to 167 percent. Although, in their 2013 

comment (0037), Hitachi agrees with the 2010 S&L study that a 0.05 design is more appropriate with a 

0.07-0.08 permit level, the S&L analysis submitted by SRP in 2013 (0348) argues that meeting a limit of 

0.07-0.08 lb/MMBtu at NGS requires an even lower design target of 0.03 lb/MMBtu. Because SRP and 

S&L recommend that EPA increase the BART limit to 0.07-0.08 lb/MMBtu (rather than an even higher 

limit), EPA concludes that SRP and S&L intend to design the SCR system with a design target of 0.03 

lb/MMBtu, and that the updated 2013 cost estimates submitted by SRP and S&L are consistent with this 

intended design target.205

202 The BART Guidelines cite to 70 FR 9705, February 28, 2005. 203 See 72 FR 32722 (June 13, 2007). 204 To prevent fouling of the catalyst from the formation of ammonium salts at low exhaust gas temperatures, ammonia 

injection (required for the catalytic reductions) will cease when the exhaust gas falls below a certain temperature. 205 See the 2013 update to the S&L cost estimate report (included as an appendix to SRP’s comment (0348). S&L adjusted 

the initial volume of catalyst deployed in the SCR system to account for the revised design target of 0.03 lb/MMBtu. S&L 

had originally planned for a 2+2 catalyst system (with 2 layers of catalyst for initial deployment) to achieve a design target of 

0.05 lb/MMBtu, and in the 2013 revised cost estimate, revised the design to be a 3+1 system (with 3 layers of catalyst for 

initial deployment). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 The S&L report discusses the temperature limitations associated with SCR, and assumes a 

minimum SCR design temperature of 580 F, which S&L asserts is typical for retrofit SCR control 

systems installed on coal-fired electric generating units with similar coal sulfur content. S&L explains 

that at temperatures below this minimum operating temperature, SCR operation (i.e., ammonia injection) 

must cease to prevent ammonium salt formation on the catalyst. S&L states that this temperature 

corresponds with a gross load of approximately 650 MW (i.e., MWg). S&L further assumes that SRP 

will likely modify the units to increase flue gas temperatures at lower operating loads by installing one 

of several options for low load temperature control. For their analysis, S&L assumes the low load 

temperature control would be achieved with a water-side bypass (to allow water to bypass the 

economizer tube bundles during low-load operation). The S&L report states “[b]ased on a preliminary 

review of the available systems, a water-side bypass system should be capable of increasing the 

temperature of the bulk flue gas by approximately 25 F to 65 F during low-load operation. For this 

evaluation, a low-load temperature control system capable of achieving a temperature increase of 65 F 

during low-load operations was assumed for modeling purposes.” S&L further estimates that this would 

correspond to a minimum gross load of 450 MWg for the SCR to operate. Units 1-3 at NGS are rated at 

a net capacity of 750 MW. For comparison, EPA evaluated AMPD emission data, which includes hourly 

gross load. In 2001, the highest reported hourly gross load was 823 MWg.206 Thus a load of 450 MWg 

roughly corresponds to a requirement that NGS operate at approximately 55% capacity in order to 

operate the SCR system. Using the assumption that the SCR would not operate at loads below 450 

MWg, S&L used 2012 operations data at NGS to estimate emission rates at NGS assuming a design 

target of 0.03 lb/MMBtu with actual steady-state operations achieving 0.04 lb/MMBtu (with periods of 

higher or lower emission rates associated with load increases and decreases). S&L modeled eighteen 

different operating scenarios and identified seven scenarios, which included periods of low load cycling 

along with unit startup and shutdowns, that resulted in the maximum 30-BOD average for each unit and 

facility-wide, that exceeded 0.055 lb/MMBtu. The highest 30-BOD average S&L modeled was 0.077 

lb/MMBtu for Unit 2, achieved under 3 different operating scenarios involving low-load cycling. 

SRP and S&L did not provide the underlying data used in the S&L analysis. Therefore, EPA 

evaluated the S&L report by reviewing AMPD emission data from multiple years at NGS, as well as 

emissions data from other facilities that were constructed or retrofit with SCR.EPA sought to understand 

2012 operations at NGS within the context of longer term operational trends at the facility, as well as 

understand the minimum operating load assumed by S&L for NGS within the context of minimum 

operating loads at other facilities with SCR. 

EPA evaluated the reported hourly gross load operating data for Units 1-3 at NGS for the years 

2001, 2003, 2010, 2011, 2012, and 2013.207 EPA selected these years because they are years that include 

the baseline period for BART (i.e., 2001-2003) as well as recent years of operation. As shown in Table 

9, in terms of the percentage of hours operated below 450 MWg (the assumed minimum operating load 

for SCR), NGS spent a higher percentage of operating hours at gross loads below 450 MWg in 2012 

compared to other years. For Unit 2, the differences between 2012, compared to 2010 and 2013, are also 

shown below in Figures 3-5.208 The horizontal red line indicates a gross load of 450 MW. 

206 See document titled “NGS Hourly Data for 4 years.xlsx” in the docket for this final rulemaking, specifically, tabs titled 

U1_2001, U2_2001, and U3_2001. In the 2010 S&L cost study, S&L reported the gross MW for the boilers at NGS to be 812 

MWg – see Appendix A to the 2010 Cost Study titled Design Basis. 450 MWg also represents roughly 55 percent of 812 

MWg. 

207 Id., specifically the tab titled Summaries. See also document titled “NGS Hourly data for additional years.xlsx”. 208 Graphs of gross load for each unit, for each of the evaluated years, are included in the two documents titled “NGS Hourly 

Data for 4 years.xlsx”, and “NGS Hourly data for additional years.xlsx”. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Table 9: Percentage of Hours NGS Operated Below 450 MWg 

Unit 1 Unit 2 Unit 3 

2001 3.30% 1.02% 1.89% 

2003 2.47% 2.70% 2.99% 

2010 2.79% 5.77% 2.89% 

2011 4.86% 3.87% 1.53% 

2012 8.39% 9.42% 5.56% 

2013 1.27% 2.33% 0.50% 

Figure 3: Gross Load of Unit 2 in 2012 

0

100

200

300

400

500

600

700

800

900

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

NGS Unit 2 Gross Load (MW)  ‐ 2012
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Figure 4: Gross Load of Unit 2 in 2010 

Figure 5: Gross Load of Unit 2 in 2013 

The 2012 gross load profiles for Unit 2 (as well as Units 1 and 3) are characteristic of loadcycling units, with significant periods of time below the SCR minimum operating load assumed by S&L 

of 450 MWg. This low-load cycling was especially pronounced in Spring 2012 (Figure 3). In 2010, as 

indicated in Table 9, Unit 2 also spent a slightly higher percentage of time at loads below 450 MWg. 

However, as shown in Figure 4, the significant periods of loads below 450 MWg occurred following the 

major outage on Unit 2, which was the same year LNB/SOFA was installed on that unit. Thus, the 

periods of low load appear to be associated with adjustments to Unit 2 occurring after a major outage, 

rather than periods of load-cycling. In 2013, the most recent year of data available, Unit 2 did not spend 

a considerable amount of time at loads below 450 MWg. Figure 5 shows that load-cycling was less 

pronounced in 2013 compared to 2012, and the cycling typically remained above 450 MWg. Although 

Units 1-3 at NGS did appear to operate as load-cycling units and operated below 450 MWg for 

significant periods of time in 2012, this type of operation does not appear to be characteristic of typical 

operation at NGS, based on our evaluation of previous years, as well as 2013. 

0

100

200

300

400

500

600

700

800

900

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

NGS Unit 2 Gross Load (MW) ‐ 2010

0

100

200

300

400

500

600

700

800

900

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

NGS Unit 2 Gross Load (MW)  ‐ 2013
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Based on the gross load operating profiles for six years, combined with the S&L assumption that 

the SCR minimum operating load would be 450 MWg, and with the simplifying assumption that the 

units at NGS would achieve an average emission rate of 0.042 lb/MMBtu when the SCR is in operation 

(calculated as the average of S&L’s assumption that steady-state emissions at full load would result in 

0.040 lb/MMBtu, with 0.050 during load increases of 15 MW per hour or more and 0.035 lb/MMBtu 

when load decreases by 15 MW per hour or more),209 EPA estimated the rolling 30-BOD averages for 

each BOD for the six years evaluated to determine whether the operating profiles (which included actual 

startup, shutdown, malfunction, and load-cycling in each year) would result in 30-BOD averages that 

would exceed 0.055 lb/MMBtu. For hours where the gross load was less than 450 MW, EPA used actual 

NOx emitted (in pounds) during that hour, to represent emissions with SCR installed but not operating. 

The results of EPA’s estimates of potential 30-BOD NOx emission rates, using S&L’s assumption of an 

SCR minimum operating load of 450 MWg, and assuming average steady-state NOx emission rates at 

0.042 lb/MMBtu, are shown in Table 10. 

Table 10: EPA’s Evaluation of Potential Maximum 30-BOD Emission Rates for NGS Units 

Operating with SCR for Select Years Using S&L Assumption of SCR Minimum Operation Load 

of 450 MWg

Unit 1 Unit 2 Unit 3 

2001 Number of 30-BODs > 0.055 0 0 0 

Maximum 30-BOD 0.051 0.045 0.045 

2003 Number of 30-BODs > 0.055 0 29 0 

Maximum 30-BOD 0.045 0.066 0.48 

2010 Number of 30-BODs > 0.055 0 29 0 

Maximum 30-BOD 0.051 0.079 0.045 

2011 Number of 30-BODs > 0.055 0 0 0 

Maximum 30-BOD 0.054 0.054 0.049 

2012 Number of 30-BODs > 0.055 75 100 0 

Maximum 30-BOD 0.071 0.075 0.050 

2013 Number of 30-BODs > 0.055 0 0 0 

Maximum 30-BOD 0.047 0.046 0.043 

Because SRP and S&L did not provide the underlying data on which their analysis and results 

were based, EPA was not able to use the S&L scenarios for our analysis and reproduce their results.210

However, for 2012, EPA did find that there were BODs in 2012 where Units 1 and 2 exceeded the 

proposed BART limit of 0.055 lb/MMBtu, and there were also BODs in other years in addition to 2012 

that Unit 2 exceeded the proposed BART limit (in 2003 and 2010). We note that the highest 30-BOD 

averages S&L projected were from Unit 2, at 0.077 lb/MMBtu, under their scenarios 0B (low-load 

cycling for 120 days), 0B.1 (low-load cycling for 120 days with 96 hour shutdown and cold start), and 

4C (60 days of full load cycling followed by 60-days of low load cycling). In EPA’s analysis, in 2012 

209 To be conservative, EPA uses S&L’s assumptions of steady-state NOx emission rates at full load and during changes in 

load that would be achieved if the SCR system was designed to 0.03 lb/MMBtu. However, EPA notes that S&L did not 

provide detailed justification or citations for their assumed values. S&L asserts in Table 2-1 of their analysis, that modeled 

NOx rates are expected to average approximately 30% above the design target rate based on an analysis of other operating 

units. S&L did not provide this analysis. We note that if emission rates at full load average less than 30% above the design 

target, then the projected emission rates at NGS (as shown in Tables B and E) would be lower. 210 S&L modeled Scenarios 0 – 5, that included full-load cycling, low-load cycling, major outages, extended startups, cold 

startups, etc. S&L and SRP did not provide this analysis to EPA, therefore, EPA could not replicate S&L’s various operating 

scenarios. Therefore, EPA examined 6 years of actual hourly NGS data, which included actual startup and shutdown profiles 

in baseline and recent years, load-cycling (i.e., 2012) and major outages (e.g., 2010, and 2011). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

(load-cycling), EPA projected the highest 30-BOD to occur on Unit 2, at 0.075 lb/MMBtu, and for 2010 

(major outage on Unit 2), we projected the maximum 30-BOD to be 0.079 lb/MMBtu on Unit 2. 

Therefore, although the scenarios modeled by S&L and EPA are not identical, the highest 30-BOD 

projected by EPA and S&L, using similar starting assumptions, were comparable. EPA’s analysis, 

which included emission and operating profiles of actual startup and shutdown events, and load-cycling 

in various years, showed that Unit 3 was not projected to exceed 0.055 lb/MMBtu in any of the 

evaluated years, and that there were several years within these six selected years that Units 1 and 2 

would also not exceed 0.055 lb/MMBtu. 

 The analysis of projected 30-BOD emission rates assumes that the S&L assumption, that the 

minimum operating temperature for SCR on Unit 1-3 at NGS would correspond to a load of 450 MWg, 

is correct. As stated previously, this means that each unit must operate at approximately 55% capacity or 

higher in order for the SCR to operate. EPA notes that S&L’s use of 450 MWg was an assumed value 

based on preliminary analysis of available low load temperature control systems. SRP submitted a 

similar S&L analysis for Unit 1 and 3 at Coronado Generating Station (CGS).211 Units 1 and 2 at CGS 

are 430 MW (gross) Riley-Turbo units that typically operate as load-cycling units. CGS burns lowsulfur coal from the Power River Basin (PRB). With the application of low-load temperature controls on 

these units, S&L’s preliminary analysis suggests that the minimum operation load for SCR on Units 1 

and 2 at CGS would be 138 MWg. This means that Units 1 and 2 at CGS could operate at 32 percent 

capacity and still operate SCR. This is in contrast to the minimum operating load capacity in order to 

operate SCR at NGS of approximately 55 percent. NGS does not burn PRB coal; however, NGS does 

burn coal low-sulfur coal from the Kayenta Mine. AECOM, SRP’s consultant for visibility modeling, 

reported the maximum sulfur content of the coal of 0.593 percent based on daily data for the 2001-2003 

period. For comparison, various sources reference PRB coal as generally low-sulfur coal with a sulfur 

content of less than 1 percent, or a mean of 0.5 percent.212 In contrast, high sulfur coal is typically above 

3 percent.213

Information on the minimum operating load for SCR on other units is not readily available, 

however, this information can be approximated by examining AMPD data (graphing hourly NOx rate 

against hourly gross load). Table 11 shows the values for minimum operating load requirements for SCR 

at Coronado Generating Station assumed by S&L, the maximum gross load observed for 2013 for 

several well-performing facilities with SCR, and EPA’s estimates for each unit’s minimum operating 

load for SCR based on observed hourly NOx emission rates and hourly gross load data from 2012 and 

2013.214 Figure 6 is an example showing the hourly NOx rate at Comanche 3 in 2013 plotted against 

hourly gross load. The values in Table 11 for minimum operating load were estimated by visually 

estimating the load where hourly NOx rates begin to increase with decreasing load. The vertical red line 

in Figure 6 shows the minimum operating load EPA estimated for Comanche 3 in 2013. The values in 

Table 11 for estimated capacity required to operate SCR were calculated by dividing the estimated 

minimum operating load by the maximum hourly gross load. These values are not based on information 

provided by SCR vendors for each facility and are simply estimates that are derived empirically by 

evaluating AMPD data for several well-performing facilities in 2012 and 2013. EPA chose to evaluate 

211 See S&L study titled “Salt River Project (SRP) Coronado Generating Station Unit 1 SCR NOx Emissions Modeling” 

dated November 14, 2013, in the docket for this rule. 

212 See, for example, publication from the U.S. Geological Survey, figure PQ-4 and Table PQ-1, available at 

http://pubs.usgs.gov/pp/p1625a/Chapters/PQ.pdf. 213 Id. 214 See documents titled: “Wygen and DryFork 2012.xlsx”, “Wygen and Dry Fork 2013.xlsx”, “TS Power 2012.xlsx”, “TS 

Power 2013.xlsx”, “Comanche 2012.xlsx”, “Comanche 2013.xlsx”, “Parish 2013.xlsx”, “Parish and Spruce 2012.xlsx”, and 

“Spruce 2013.xlsx”. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

well-performing facilities to ensure that the facilities analyzed use low-load temperature controls. 

Facilities that do not use low-load temperature controls would not be comparable for this purpose (to 

understand the potential capabilities of low-load temperature controls at NGS) and would have higher 

estimated capacities required to operate SCR. This methodology may also tend to underestimate a unit’s 

capacity requirement to operate SCR because it relies on the highest gross load observed in the data set, 

rather than the actual value for maximum gross load for that unit. The graphs for all facilities in Table 11 

showed similar profiles as Comanche 3 (Figure 6) except for the graph for TS Power (Figure 7). The 

graph for TS Power does not show a clear point were hourly NOx values increase with decreasing load, 

however, this may be a result of insufficient data points at the very low loads. To be conservative, EPA 

estimated the minimum operating load for TS Power to be at the lowest loads of consistent operation; 

however, data points at lower loads than this level also correspond with low hourly NOx emission rates 

(see Figure 7). Based on the gross load profiles, the facilities discussed in Table 11 represent units that 

operated in 2012 and 2013 as baseload (i.e., Dry Fork, Wygen 2 and 3), and load-cycling (i.e., TS 

Power, Comanche 3, Spruce 2, and WA Parish 7 and 8).215

Table 11: EPA Estimates for Minimum Operating Loads and Capacities Required to Operate 

SCR for Several Well-Performing Facilities in 2012 and 2013 

Facility Coal Source Year 

Maximum 

Gross Load 

(MWg) 

Estimated 

Minimum 

Operating Load 

Estimated 

Capacity Required 

to Operate SCR 

Dry Fork PRB 2012 447 181 40% 

2013 453 208 46% 

Wygen 3 PRB 2012 114 45 39% 

2013 116 49 42% 

Wygen 2 PRB 2012 101 44 44% 

2013 102 45 44% 

TS Power PRB 2012 241 < 94*

 < 39% 

2013 240 < 95* < 40% 

Comanche 3 PRB 2012 827 288 35% 

2013 806 308 38% 

Spruce 2 PRB 2012 826 324 39% 

2013 824 333 40% 

WA Parish 7 PRB 2012 614 220 36% 

2013 614 251 41% 

WA Parish 8 PRB 2012 654 240 37% 

2013 654 254 39% 

Coronado Units 1 

and 2 PRB From S&L 430 138 32% 

* An estimate for minimum operating load for TS Power is more difficult to discern compared to other facilities. To be 

conservative, EPA estimated the minimum operating load for TS Power to be at the lowest loads of consistent operation (see 

Figure E and red vertical line), however, data points at lower loads than this level also correspond with low hourly NOx

emission rates. 

215 Id.
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Figure 6: 2013 Hourly NOx Rate Plotted Against 2013 Hourly Gross Load for Comanche 3 

Figure 7: 2013 Hourly NOx Rate Plotted Against 2013 Hourly Gross Load for TS Power 

The average of the estimated capacities required to operate SCR for the facilities shown in Table 

11 is 39 percent. If we exclude Coronado Units 1 and 2 (the lowest required capacity and the units where 

SCR has not yet been installed), the average capacity is 40 percent. The highest capacity required, from 

the evaluated units, is 46 percent. If we apply the average (40 percent) and maximum (46 percent) 

values for the required capacity to operate SCR at these facilities, to the maximum capacity from 2001 

that EPA estimated for NGS (823 MWg), a reasonable range of possible required capacities to operate 

SCR at NGS could be 330 MWg to 379 MWg. Although these values appear to EPA to be reasonable 

and conservative minimum operating loads compared to existing well-performing facilities, EPA is not 

asserting that these values for minimum operating load will be the values that result after a full 

engineering evaluation is conducted specifically for NGS by S&L. S&L’s estimate of 450 MWg was an 

assumed value based on preliminary review of available low-load temperature control systems, and S&L 

did not provide justification for this value or their assumptions made in selecting this value. EPA’s 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

analysis of other well-performing facilities that burn low-sulfur coal is intended to provide a reasonable 

range of possible capabilities of low-load temperature control systems for SCR at NGS, in order to 

examine the effect of the SCR minimum operating load on the ability of NGS to meet an emission limit 

of 0.055 lb/MMBtu. As shown in Table 10, Unit 2 at NGS is projected to exceed 0.055 lb/MMBtu (30-

BOD average) using operations data from 2003, 2010, 2011, and 2012, and Unit 1 is projected to exceed 

0.055 lb/MMBtu (30-BOD average) using operations data from 2011 and 2012, based on S&L’s 

assumed minimum operating load of 450 MWg and an assumed average steady-state emission rate 0.042 

lb/MMBtu. Unit 3 was not projected to exceed 0.055 lb/MMBtu in any of the years that EPA 

evaluated.216 Table 12 shows EPA’s projections for the 30-BOD averages that would result (for the units 

and years that exceeded 0.055 lb/MMBtu using S&L’s assumed minimum operating load of 450 MWg) 

if the minimum operating load was 379 MWg or 330 MWg (corresponding approximately to a 46 

percent and 40 percent capacity requirement to operate SCR). 

Table 12: EPA Projections for Maximum 30-BOD for Select Units and Years at NGS Using 

Different Minimum Operating Loads for SCR 

450 MWg Minimum 

Operating Load 

(55% capacity) 

379 MWg Minimum 

Operating Load 

(46% capacity) 

330 MWg Minimum 

Operating Load 

(40% capacity) 

Unit 1 in 

2012 

# 30-BOD > 0.055 75 7 0 

Maximum 30-BOD 0.071 0.057 0.043 

Unit 2 in 

2003 

# 30-BOD > 0.055 29 0 0 

Maximum 30-BOD 0.066 0.048 0.045 

Unit 2 in 

2010 

# 30-BOD > 0.055 29 9 0 

Maximum 30-BOD 0.079 0.057 0.055 

Unit 2 in 

2012 

# 30-BOD > 0.055 100 18 0 

Maximum 30-BOD 0.075 0.059 0.046 

Table 12 shows that if the low-load temperature control system at NGS allows NGS to operate 

SCR when running at 46 percent capacity or greater, the highest predicted 30-BOD average was 0.059 

lb/MMBtu for Unit 2 in 2012. If the low-load temperature control system allows operation of SCR when 

running at 40 percent capacity, the highest predicted 30-BOD average was 0.055 lb/MMBtu for Unit 2 

in 2010. As noted above, operation of NGS in 2012 was characterized by extended periods of loadcycling that was not observed to the same extent in 2013 or any of the previous four years that EPA 

examined. Operation of Unit 2 in 2010 was unique compared to previous years and compared to Units 1 

and 3 (none of the 30-BOD averages predicted for Units 1 and 3 exceeded 0.055 lb/MMBtu in 2010). 

Installation of LNB/SOFA on Unit 2 occurred in 2010 during the unit’s scheduled major outage. As 

shown in Figure 4, in the month following the major outage, Unit 2 appeared to be subject to frequent 

cycling down to very low loads in a manner that was not observed in any unit in any other year that EPA 

examined. Although EPA is unaware of the purpose or cause of the extreme low-load cycling observed 

in the month following the major outage on Unit 2, this mode of operation appears to be unique and 

atypical for NGS. 

The S&L report concludes that even with a design target for SCR of 0.03 lb/MMBtu, a limit of 

0.07-0.08 lb/MMBtu is required to accommodate periods of startup, shutdown, and load-cycling 

operation. EPA agrees that load-cycling operation appears to be an important factor, however, EPA 

concludes that the critical S&L assumption, that the units at NGS must operate at approximately 55 

216 See the two documents titled “NGS Hourly Data for 4 years.xlsx”, and “NGS Hourly data for additional years.xlsx”. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

percent capacity in order for the SCR to operate, was not sufficiently supported and was acknowledged 

by S&L to be an assumption based on a preliminary review of available low-load temperature control 

systems. EPA also notes that in the S&L revised 2013 cost analysis, S&L included costs for hot water 

recirculation systems which “maintains SCR in operation at all plant operating loads” (emphasis 

added).217 EPA evaluated emission data of eight well-performing units and generated empirical 

estimates for SCR minimum operating loads and capacity requirements for SCR operation for those 

facilities. This analysis resulted in estimated capacity requirements for SCR operation that ranged from 

35 percent to 46 percent, with an average value of 40 percent. Using the average (40 percent) and the 

maximum (46 percent) capacity requirement to operate SCR, EPA projected that NGS could meet a 

limit of 0.055 lb/MMBtu (on a 30-BOD average) for all but 3 unit-years (i.e., Units 1 and 2 in 2012, and 

Unit 2 in 2010) under the 46 percent capacity requirement. Under the 40 percent capacity requirement to 

run SCR, EPA’s highest projected emission rate was 0.055 lb/MMBtu for Unit 2 in 2010. Operation of 

Unit 2 in 2010 was not typical of normal operation, and operation of NGS in 2012, as a load-cycling 

facility, is also not representative of normal operation. 

The commenter argues that load affects the ability of load-cycling operation to maintain 30-BOD 

emission rates below 0.055 lb/MMBtu is the minimum gross load required to operate SCR. S&L did not 

provide justification for their selected value, and a review of other baseload and load-cycling facilities 

operating with SCR, that also burn low-sulfur coal, suggests that it is reasonable to expect SCR to 

operate at lower loads sufficient to accommodate low-load cycling at NGS. If low-load temperature 

control systems at NGS allow the units to operate SCR while running at 40 percent capacity (i.e., 

equivalent to the average capacity requirement to run a SCR observed at well-performing facilities 

operating SCR that burn low-sulfur coal), then a limit of 0.055 lb/MMBtu would sufficiently 

accommodate emission rates achievable at NGS during the load-cycling operations observed in 2012. 

 The commenter also argues that the BART emission limit must account for unexpected 

malfunctions at the facility, potential events outside of the facility’s control that have direct impacts on 

transmission (e.g., forest fires), and the potential for boiler plugging and tube fouling as a result of fuel 

moisture issues resulting from rain. EPA does not agree that the BART emission limit must account for 

unexpected malfunctions or events outside of the facility’s control. Because EPA evaluated six years of 

actual emissions and operations data from NGS, the potential effects of rain on boiler plugging and tube 

fouling purported by the commenter are likely included in the existing data set. To the extent that the 

commenter is suggesting a potential effect of rain on SCR performance at low loads, the commenter did 

not provide any information to characterize or quantify such effects. Therefore, EPA disagrees that we 

must consider the effects of rain in the BART emission limit. 

The commenter also argues that NOx emissions achieved in other SCR retrofit situations do not 

justify the proposed emission limit of 0.055 lb/MMBtu, citing to the proposed replacement of the FIP’s 

BART determination for San Juan Generating Station (SJGS) with the New Mexico SIP, emission rates 

from WA Parish Units 7 and 8, statements associated with EPA’s national rulemaking for CSAPR, and 

higher BART limits established for North Dakota and South Dakota EGUs. The commenter correctly 

notes that EPA is in the process of replacing the FIP with a SIP from New Mexico at SJGS proposing 

closure of two units and installation of SNCR on the remaining two units. In response to a previous 

comment that BART must be consistent with emission limits established as BACT, EPA stated that 

BACT limits 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. Similarly, 

217 See page 1-2 of the Sargent and Lundy report prepared for SRP, dated January 2, 2014, included as Appendix U to the 

SRP comment letter in the docket for this rulemaking (comment number 0348). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

emission limits established as BART for other facilities (e.g., in North and South Dakota, as cited by the 

commenter, as well as for EGUs in Wyoming and the Four Corners Power Plant on Navajo Nation), 

should not be construed to automatically represent the most appropriate BART limit for NGS. BART is 

a case-by-case determination and appropriate emission limits should be set, not only by considering the 

performance of air pollution technology at similar facilities, but also with consideration of sourcespecific factors.218 In addition, broad statements made in a national rulemaking on the ability of SCR to 

achieve specific emission rates across the national fleet of coal-fired EGUs should also not be construed 

to represent the appropriate limit in a source-specific case-by-case analysis. 

In a response to a previous comment that BART for NGS should be a limit of 0.04 lb/MMBtu, 

EPA stated that units that operate within an emission trading program (e.g., WA Parish 7 and 8) provide 

useful information on the performance capability and variability of units that have been retrofit with 

SCR, but that they are less relevant, compared to site-specific vendor information or the performance of 

similar units with permit limits, for making a case-by-case determination of BART for a specific facility. 

The ability of the WA Parish 7 and 8 to maintain steady-state emission rates below 0.04 lb/MMBtu is 

informative because it indicates that long term steady-state emissions rates can be achieved at that level. 

However, because these units are not subject to an emission limit, these units are not required to 

maintain emission rates below a certain level, and, as noted by the commenter, 30-BOD emission rates 

from these units have exceeded 0.055 lb/MMBtu. 

EPA notes that there are at least six EGUs that operate with SCR that are also required to meet 

permitted emission limits for NOx. These six units were all new units, rather than retrofit units. Although 

SCR performance on new units and retrofit units are generally believed to be less directly comparable, 

finding a unit retrofit with SCR that is currently in operation with a permit limit is difficult.219 Permit 

limits are set when a permit (typically a pre-construction PSD or NSR permit) is required as a result of 

increases in air pollutant emissions that exceed specific thresholds. Pre-construction permits are 

typically triggered for new facilities, or major modifications to existing facilities. New facilities 

typically trigger permit requirements for several pollutants, including NOx, which therefore requires 

limits for each of those triggering pollutants. The installation of SCR at an existing source would 

typically not trigger a PSD permit for NOx emission increases (because SCR should result in a reduction 

of NOx emissions), therefore, SCR retrofits would generally not be subject to a permit limit for NOx, 

even if PSD is triggered for emission increases of other pollutants.220 In addition, permit limits are not 

established under emission trading programs, e.g., CAIR. Therefore, AMPD emissions data appears, at 

this time, to generally be limited to new units that operate under NOx emission limits, and retrofit units 

that operate under a trading program without a NOx emission limit. Therefore, a thorough understanding 

of SCR performance warrants an examination of both new units and retrofit units. 

As stated previously, WA Parish 7 and 8 are units that were retrofit with SCR that achieve 30-

BOD emission rates that, in 2012 and 2013, ranged from 0.043 to 0.051 lb/MMBtu (see Table 13). 

218 For example, the BART emission limit, achievable with SCR, that EPA set for the units at Four Corners Power Plant was 

higher due to site-specific factors, including characteristics of the boilers used FCPP and potential operational issues 

associated with installation of modern LNB to further reduce NOx in upstream of the SCR. See 77 FR 51620 at 51636 

(August 24, 2012). 

219 EPA notes that once BART units that are required to install SCR, and meet BART emission limits, come online, more 

“achieved in practice” data will be available for comparison. 

220 EPA notes that an exception to this is the PSD permit issued to NGS for significant emission increase of carbon monoxide 

(CO) resulting from the installation of LNB/SOFA. Because of the inverse relationship between CO and NOx emissions, 

EPA set a limit for NOx to ensure that attempts to reduce CO emissions during the CO demonstration period would not be at 

the expense of NOx emissions. See page 5 of the document titled “Final NGS PSD Permit AZ 08-01.pdf” located in the 

docket for this rulemaking at EPA-R09-OAR-2013-0009-0005. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Although the commenter noted that NOx emissions from WA Parish 7 exceeded 0.055 lb/MMBtu during 

several months since SCR was installed, the ability of the WA Parish 7 and 8 to sustain emission rates of 

NOx below 0.05 lb/MMBtu indicates that low steady-state emission rates have been achieved in practice 

by units that are retrofit with SCR. Table 13 also shows the six units that were constructed as new units 

designed to operate with SCR and subject to permit limits for NOx. These permits limits were likely 

established as BACT limits. In a previous response to a comment, that BART should be a limit of 0.04 

lb/MMBtu, EPA stated that the 0.05 lb/MMBtu emission limits established for several facilities on a 

rolling 12-month average should not be construed to mean that BART emission limits, established on a 

rolling 30-BOD basis, should be lower than 0.05 lb/MMBtu. Although these limits should not be 

construed to define what BART should be for NGS, the SCR performance at these facilities is still 

instructive. Dry Fork, TS Power, Wygen 3, and Spruce 2 were capable of sustaining, over 2012 and 

2013, rolling 30-BOD emission rates below 0.055 lb/MMBtu. Facilities with higher emission limits, i.e., 

0.07 lb/MMBtu for Wygen 2 and Comanche 3 showed higher 30-BOD emission rates. The emission 

limits for Wygen 2 and Comanche 3 are likely higher because they were established in permits issued 

earlier than the permits for the better-performing facilities.221

Table 13: NOx Emission Rates (lb/MMBtu) of Well-Performing Facilities with SCR 

BACT 

Limit

Averaging 

Period

Year Maximum 

30-BOD 

Achieved

Annual 

Average

Ratio Max 

30-

BOD:Annual 

Avg

Ratio 

Limit:Achieved

WA Parish 

7

N/A N/A 2013 0.043 0.040 1.07 N/A

2012 0.046 0.042 1.09

WA Parish 

8

N/A N/A 2013 0.043 0.040 1.07 N/A

2012 0.051 0.049 1.03

Dry Fork 0.05 

lb/MMBtu

12-month 

rolling

2013 0.040 0.037 1.08 1.35

2012 0.039 0.037 1.07 1.35

TS Power 0.067 

lb/MMBtu

24-hour 

rolling

2013 0.051 0.044 1.15 1.10*

2012 0.050 0.043 1.14 **

Wygen 3 0.05 

lb/MMBtu

12-month 

rolling

2013 0.043 0.042 1.04 1.19

2012 0.047 0.042 1.13 1.19

Wygen 2 0.07 

lb/MMBtu

30-day 

rolling

2013 0.063 0.062 1.02 1.13

2012 0.0632 0.0625 1.01 1.12

Comanche 

3

0.07 

lb/MMBtu

365-day 

rolling

2013 0.068 0.067 1.02 1.04

2012 0.07 0.068 1.03 1.03

Spruce 2 0.069 

lb/MMBtu

30-day 

rolling

2013 0.053 0.045 1.18 1.30

2012 0.044 0.041 1.10 1.57

Spruce 2 0.05 

lb/MMBtu

12-month 

rolling

2013 0.053 0.045 1.18 1.11

2012 0.044 0.041 1.10 1.22 *

For 2013, EPA calculated the maximum daily NOx rate to be 0.061 lb/MMBtu for TS Power. 

** Based on emission data from AMPD, EPA calculated a maximum daily NOx rate of 0.0797 lb/MMBtu for TS Power. This 

maximum daily rate exceeds the permitted emission limit of 0.067 lb/MMBtu (24-hour rolling average). 

For the eight well-performing units operating with SCR shown in Table 13, the ratio of the 

observed maximum 30-BOD average to the observed annual average ranged from 1.01 to 1.18. For these 

221 For example, Comanche Unit 3 was proposed and approved in 2004. See “Plant History” at 

http://www.xcelenergy.com/About_Us/Our_Company/Power_Generation/Comanche_Generating_Station. The permit for 

Wygen 2 was issued in 2003. Permits for Dry Fork, Wygen 3, were issued in 2007 and for TS Power in 2005. See document 

titled “2014_0228 Limited RBLC results.pdf” in the docket for this rulemaking. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

units, the ratio of their permitted emission limits to observed emission rates (i.e., maximum 30-BOD 

achieved for units with permit limits averaged over 30-days, or the annual average for units with permit 

limits averaged over a 12-month period), showed considerable variability and ranged from 1.03 to 1.57. 

The highest value of 1.57 was observed in 2012 for the 30-day rolling average limit for Spruce 2. EPA 

notes that Spruce 2 operates with two different permitted NOx limits over two different averaging 

periods, and that the ratio of the 12-month rolling limit to the annual average in 2012 was 1.22. The 

commenter cites to regional haze actions for North Dakota and South Dakota where the state or EPA 

provided a compliance margin in the BART emission limit. For example, in the North Dakota action 

where EPA concurrently proposed a FIP for portions of the SIP it proposed to disapprove, including 

NOx limits for the Milton R. Young Station, EPA stated “in proposing a BART emission limit of 0.07 

lb/MMBtu, we adjusted the annual design rate of 0.05 lb/MMBtu upwards to allow for sufficient margin 

of compliance for a 30-day rolling average limit that would apply at all times, including startup, 

shutdown, and malfunction.”222

EPA evaluated six years of operations and emissions data from Units 1-3 at NGS, along with 

information supplied by the commenter and S&L, as well as SCR performance information from eight 

well-performing units. The six years of data from NGS includes periods of startup, shutdown, and 

malfunction, as well as load-cycling operations in 2012 that were not characteristic of normal operation 

at NGS, but, as asserted by the commenter, may be more common in the future. Based on these six years 

of data, and EPA’s evaluation of other facilities to understand SCR performance, EPA projected 30-

BOD emission rates that can be reasonably expected from the installation and operation of SCR at NGS. 

As shown in Table 10 and 12, a limit of 0.055 lb/MMBtu for Units 1-3 at NGS is sufficient to 

accommodate normal operation of most units (e.g., 2001, 2003, 2011, and 2013), including periods of 

startup and shutdown. The proposed BART limit is also sufficient to accommodate load-cycling 

operations (based on 2012 load profiles), as well as operations of Unit 2 in 2010, that may have been 

characteristic of boiler tuning or corrections following installation of new combustion controls, provided 

that the load capacity requirement (with low-load temperature controls) to operate SCR at NGS is 

consistent with the average capacity requirements observed at other well-performing facilities. 

 In summary, EPA is determining that a BART Benchmark based on an emission limit for NGS 

of 0.055 lb/MMBtu on a rolling 30-BOD basis is appropriate. In determining the achievability of this 

limit, EPA has conducted an analysis that considers periods of startup, shutdown, malfunction, and lowload cycling. Therefore, this conclusion is consistent with EPA statements elsewhere (e.g., EPA’s 

proposed action for the North Dakota Regional Haze SIP) that BART limits should allow for sufficient 

margins of compliance for startup, shutdown, and malfunction). Based on the understanding that S&L 

would design the SCR system at NGS to a design target of 0.03 lb/MMBtu and achieve average rates at 

full load of roughly 0.042 lb/MMBtu, the BART limit of 0.055 lb/MMBtu represents a 31 percent 

compliance margin to accommodate periods of startup, shutdown, and load-cycling operation. If the 

low-load temperature control systems deployed at NGS are able to allow operation of SCR below 40 

percent load, the operator of NGS will have even more flexibility in the compliance margin for meeting 

the limit of 0.055 lb/MMBtu. 

222 See proposed rule at 76 FR at 58,610 (September 21, 2011). In taking final action, we note that EPA did not finalize the 

proposed emission limit of 0.07 lb/MMBtu for Milton R. Young Station, and instead, approved the state’s BART 

determination for that facility. See final rule at 77 FR at 20897 (April 6, 2012). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Comment: Presumptive BART 

 A CAP agricultural water users group (0305), two of the owners of NGS (0314, 0348), and the 

operator of the Kayenta Mine (0384) noted that with existing LNB/SOFA controls, NGS’s NOx

emission rate is below the presumptive limit of 0.28 lb/MMBtu established by the EPA in the BART 

Guidelines (citing 70 FR 39172, Table 1). The commenters assert that the installation of these advanced 

combustion controls should satisfy the BART requirement for the first planning period. These 

commenters generally indicated that in establishing this presumptive limit EPA stated that it “believe[s] 

that [the presumptive limits] are extremely likely to be appropriate for all greater than 750 MW power 

plants subject to BART” (citing 70 FR 39131) because the EPA concluded that the cost of controls 

required to meet the presumptive limits was reasonable. 

 One of these commenters (0384) included additional citations from the July 2005 final 

rulemaking for the RHR and other rulemakings to stress EPA’s conclusions in those rules that 

combustion controls are presumptive BART for electric generating units (EGUs) because they are cost 

effective and are likely to result in a substantial degree of visibility improvement. The commenter also 

quoted EPA as addressing possible individual cases in which a facility is unable to meet its presumptive 

limit using current combustion control technology with the recommendation to consider of “whether 

advanced combustion control technologies such as rotating opposed fire air should be used to meet these 

limits” (citing 70 FR 39172), with no reference to considering post-combustion controls. The 

commenter noted that BART rules include only two narrow exceptions where post-combustion controls 

should be considered: (1) cyclone units and (2) units that already use post-combustion controls for part 

of the year, for which year-round use of the controls is presumptively BART (citing 70 FR 39171). The 

commenter concluded from these historic citations that NOx BART emission limits are to be based on 

combustion controls, not post-combustion controls such as SCR. 

 Another commenter (0305) acknowledged that the BART Guidelines provide that the reviewing 

agency “may determine that an alternative control level is appropriate based on a careful consideration 

of the [five] statutory factors” (citing 40 CFR part 51, Appendix Y, section IV.E.5), but asserted that 

EPA’s departure from presumptive BART, its conclusion that a 0.055 lb/MMBtu limit is technically 

feasible, and its selective reliance on CAMD data to justify such a conclusion are not adequately 

justified and, furthermore, are arbitrary, capricious, and an abuse of discretion. The commenter also 

stated that to properly justify departure from the presumptive BART limit, EPA must evaluate the 

impacts of the presumptive BART limit in its five-factor analysis, which it did not do. 

Response: 

EPA disagrees with the comment that installation of LNB/SOFA at NGS should satisfy BART 

because it meets the presumptive limit for NOx of 0.28 lb/MMBtu in the BART Guidelines for 

tangential-fired boilers burning bituminous coal. 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, 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 NGS demonstrates that, in considering the expected remaining useful life of NGS and the existing 

controls, SCR is cost effective, results in the most visibility improvement of all feasible control 

technologies, and that the potential energy or non-air quality environmental impacts do not warrant its 

elimination as the top control option. As a result, regardless of the appropriateness of SCR as a control 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

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 performed for NGS 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 the assertion that we did not evaluate the impacts of the presumptive BART limit in 

our five-factor analysis. The presumptive BART limit of 0.28 lb/MMBtu is based on installation and 

operation of modern combustion controls. EPA evaluated LNB/SOFA (at a limit of 0.24 lb/MMBtu, 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

which is each unit’s existing permitted NOx limit for operation with LNB/SOFA) in the five-factor 

analysis on which our proposed rule was based.223

Comment: Install SCR within 3.5 years 

 One environmental advocacy group (0373) stated that the CAA requirement for BART to be 

installed “as expeditiously as practicable” requires installation and full implementation of SCR on all 

three units at NGS within 3.5 years, not later than 2018, rather than allowing the facility 5 years. The 

commenter pointed out that the CAA often mandates compliance “as expeditiously as practicable, but in 

no event later than a set number of years” – as Congress required for BART. 

 According to the commenter, judicial opinions interpreting similar “as expeditiously as 

practicable” compliance deadlines read this language to require compliance as soon as possible, not as 

providing a 5-year default deadline in all instances. The commenter stated that because the “as 

expeditiously as practicable” compliance deadline “appear[s] in several places in [the] statutory text,” it 

is “generally read the same way each time it appears” (Citing Ratzlaf v. United States, 510 U.S. 135, 143 

(1994)). The commenter added that when the CAA requires compliance as expeditiously as practicable 

but not later than a certain date, the date listed in the statute is an “outside date” and does not provide a 

“license” for a state or regulated entity “to take its time in complying with” the Act (citing Am. Lung 

Ass’n v. Kean, 856 F. Supp. 903, 908 (D.N.J. 1994); Individuals for a Better Env‘t v. Wilson, 775 F. 

Supp. 1291, 1298 (N.D. Cal. 1991) (similarly noting that the “as expeditiously as practicable, but in no 

event later than” standard provides an “outside limit” for compliance)). The commenter also indicated 

that compliance before the “outside date” is required whenever earlier compliance is possible (citing 

Union Elec. Co. v. EPA, 427 U.S. 246, 259 (1976)). 

 The commenter then cited several sources as evidence that SCR system can be installed in less 

than 5 years.224 The commenter added that with multiple SCRs for the same plant, there are numerous 

duplicative design, engineering, procurement, fabrication, installation, and commissioning synergies, 

that can speed up the overall timeline. The commenter stated that EPA provided no site-specific factors 

at NGS that would require a longer-than-average installation time for SCR (particularly in light of the 

fact that it appears contractors in the region will not be overwhelmed). The commenter concluded that 

the proposed 5-year compliance deadline fails to meet the requirement that SCR be installed “as 

expeditiously as practicable,” and that EPA should set a 3.5-year compliance deadline for SCR 

installation at NGS. 

223 As noted elsewhere in this document and in our proposed rulemaking, EPA issued a PSD permit to NGS in 2008 for the 

installation of LNB/SOFA on each unit over a three year period (2009-2011). The permit was required for significant 

emission increases of carbon monoxide; however the permit established a NOx limit of 0.24 lb/MMBtu, based on the value 

SRP expected to achieve with LNB/SOFA, because of the relationship in balancing NOx and CO emissions from combustion. 224 The cited sources included: (1) EPA’s Engineering and Economic Factors Affecting The Installation of Control 

Technologies for Multipollutant Strategies, 22 (2002) (it generally takes 21 months to design, install, and test one SCR unit, 

and approximately 35 months for SCR installation at power plants with multiple SCR units); (2) 75 FR 45210, 45273, August 

2, 2010 (proposed Transport Rule) (It takes approximately 21 months to construct a SCR unit to reduce emissions of NOx.); 

(3) ICAC’s Selective Catalytic Reduction (SCR) Control of NOx Emissions From Fossil Fuel-Fired Electric Power Plants

(2009); (4) EPA Region 6, Complete Response to Comments for NM Regional Haze/Visibility Transport FIP, Docket EPAR06-OAR-2010-0846, at 71-72 (August 5, 2011) (in the BART determination for SJGS, the EPA concluded that past SCR

installations have required an average of between 37 and 43 months to design and construct); (5) Supply Chain and Outage 

Analysis of MISO Coal Retrofits for MATS, The Brattle Group, May 2012 (a range of studies and practical experience have 

identified that SCR can typically be installed in less than 5 years). 
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Response: 

 EPA disagrees with the commenter that a 3.5 year compliance deadline is practicable for NGS. 

EPA agrees that there are numerous sources of information, including EPA’s response to comments on 

its BART determination for the San Juan Generating Station, to suggest that on average, installation 

times for SCR can range from 37 to 43 months to design and construct. As with any average value, there 

will be individual cases where installation of controls requires more time than average, and cases where 

installation requires less time than average. The commenter also cites to EPA documents suggesting that 

it generally takes 21 months to design, install, and test one SCR unit, and 35 months for SCR installation 

at power plants with multiple SCR units, and another publication that suggests that SCR can be installed 

in less than 5 years (i.e., document from The Brattle Group). The Brattle Group estimated a duration of 

47 months (nearly 4 years) to complete an SCR retrofit, and stated that “our estimates will tend to be on 

the high end compared to some other sources (including the EPA) because they are compiled to the 

extent possible from industry participants’ experiences on a selection of actual projects, some of which 

experienced various permitting, contracting or installation delays.”225 The Brattle Group does not 

specify whether this duration of 47 months is representative of a single SCR unit, or multiple SCR units 

at a facility. However, given its statements that its estimates are closer to industry estimates than EPA 

estimates, and its previous references to other industry studies suggesting an average duration of 40 

months to retrofit one SCR, EPA interprets the Brattle Group estimate of 47 months (nearly 4 years) to 

represent one unit, not multiple units at one facility.226

The Brattle Group estimate accounts for time required for the pre-construction permitting 

process that is required to be complete before any construction may commence on a project but did not 

specify how much of the 47 months permitting was assumed to require.227 The EPA estimate of 35 

months was one example of the time required for the installation of multiple (seven) SCR units at a 

specific facility. EPA noted that its general timelines for retrofit installations included permitting, and 

assumed the pre-construction permit from the state or local regulatory agency would require nine 

months.228 In addition, although EPA cited to one facility where the retrofit of seven units required 35 

months, EPA also stated “ideally, longer than 35 months would allow for all the retrofits to occur over a 

period of several years so that facility owners can properly plan outages and suppliers can properly plan 

for resource availability.”229

For NGS, EPA notes that three units would be retrofit with SCR, and that there is no state or 

local permitting authority with jurisdiction to issue a pre-construction permit to a facility located on the 

Navajo Nation. As such, EPA would be the permitting authority for a PSD or minor NSR permit for 

NGS. Although a nine-month process may be reasonable for state or local permits, EPA has outlined the 

steps required for PSD permit issuance, and suggests that the preparation of a draft permit, alone, may 

take six months to one year from the time the permit application is determined complete.230 Subsequent 

225 Supply Chain and Outage Analysis of MISO Coal Retrofits for MATS, The Brattle Group, May 2012 (May 2012 Brattle 

Group document), Table 4, page 17, available at 

https://www.misoenergy.org/Library/Repository/Communication%20Material/Key%20Presentations%20and%20Whitepaper

s/Supply%20Chain%20and%20Outage%20Analysis%20of%20MISO%20Coal%20Retrofits%20for%20MATS.pdf, also 

available in the docket for this rule. 

226 The May 2012 Brattle Group document, page 12 and page 17. 227 The May 2012 Brattle Group document, page 17. 228 See EPA’s Engineering and Economic Factors Affecting The Installation of Control Technologies for Multipollutant 

Strategies, 22 (2002), (EPA 2002 Multipollutant Strategies document), page 20, available in the docket for this rule. 

229 See EPA 2002 Multipollutant Strategies document, page 22. 230 http://www.epa.gov/region9/air/permit/psd-issuing.html 
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to the issuance of a draft permit, a public comment period is required, which may include a public 

hearing, and EPA will issue a decision on the final permit after it has considered and responded to all 

comments. The permit usually becomes effective 30 days after EPA issues a final permit, unless the 

final permit is appealed to the Environmental Appeals Board. In addition, PSD permits issued by EPA 

require consultation with other federal agencies (e.g., the U.S. Fish and Wildlife Service related to 

Section 7 of the Endangered Species Act) as well as tribal governments (particularly in cases where the 

facility is located in Indian country). As such, although a nine-month time frame for issuance of preconstruction permits may be appropriate for those issued by state or local permitting authorities; it is our 

experience that PSD permits issued by EPA often require more time.231

The S&L cost study for SCR installation at NGS commissioned by SRP included schedules for 

the design, procurement, installation, and tie-in. The 2013 S&L cost study estimated approximately 41 

months per unit, and 67 months for all three units.232 EPA notes that the 67 month timeframe is beyond 

the 5 year period for BART and does not appear to include time required for pre-construction 

permitting. For our BART determination for Four Corners (for one of two options in our final BART 

determination for this facility), we required compliance with an emission limit achievable with SCR on 

5 units within 5 years of the final rule. Specifically, under BART, EPA required installation and 

operation of SCR controls on one 750 MW unit within four years of the effective date, and the 

remaining 750 MW unit and Units 1 – 3 within five years of the effective date. EPA had proposed 

phased-compliance at Four Corners over years 3, 4, and 5 following the effective date of the final rule. 

However, because the operator of Four Corners was seeking regulatory approval to purchase another 

owner’s share of Four Corners, accounting for the timeframe for final approvals of the transaction would 

have left the operator only 2 years to design, engineer, and construct controls on the first unit (or set of 

units). Therefore, EPA finalized a phase-in schedule over years 4 and 5. Thus, although EPA did not 

require complete installation and operation of SCR on one unit until four years after the effective date of 

the final rule, the purpose of the fourth year (instead of three years) was to accommodate time for 

completion of other regulatory approvals related to ownership changes, to allow, overall, three years for 

complete SCR installation on the first unit following certainty in the plant ownership.233 For San Juan 

Generating Station, EPA had proposed a compliance timeframe of three years and finalized a 

compliance timeframe of five years based on congestion at the facility that would require additional time 

for installation.234 We note that submittals from SRP indicated site congestion around Unit 2 at NGS that 

would affect the cost of compliance for that unit.235 The commenter also states that “it appears 

contractors in the region will not be overwhelmed” to justify why installation time for SCR should not 

be longer than average.236 We note that “installation time” is one part of compliance, and that EPA must 

also consider time for design, procurement, and permitting. We also note that the commenter did not 

231 Although EPA issued a PSD permit to NGS (for significant emission increases of carbon monoxide) over a relatively short 

timeframe, EPA also notes that for the BART Alternative option in the final FIP for the Four Corners Power Plant, which 

was finalized on August 24, 2012 (77 FR 51620) and requires installation of SCR on Units 4 and 5 by mid-2018, the operator 

of FCPP has been actively engaged with EPA in developing its PSD permit application, and as of April 2014, EPA has not 

yet put forth a draft PSD permit for public comment. 

232 See Section 2.0 (Project Schedule) of S&L 2013 Cost Study for NGS in Appendix U-V at document 0354 in the docket 

for this rule at EPA-R09-OAR-2013-0009. 

233 See page 119 of the Four Corners Response to Comments. See document number 0234 in the docket for the Four Corners 

BART Determination at EPA-R09-OAR-2010-0683. 

234 See EPA Response to Comments for San Juan Generating Station, page 75, in the docket for this rule at EPA-R09-OAR2013-0009. 

235 See discussion of higher retrofit cost of SCR on Unit 2 compared to Units 1 and 3 due to physical layout in the ANPR at 

74 FR 44313 at 44321 (August 28, 2009) and references therein at footnote 12.. 

236 See page 17 of the EarthJustice comment letter (0367). 
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provide any support for its statement that contractors in the region will not be overwhelmed. If the 

effective date for the final rule is in mid-2014, 3.5 years from the effective date of a final rule would 

mean compliance with the BART emission limit by the end of 2018. We note that the compliance date 

for the installation of SCR on Units 4 and 5 at the Four Corners Power Plant is mid-2018 and BART 

determinations for several EGUs in Arizona also required NOx emission limits achievable with SCR 

with compliance dates at the end of 2017.237 Therefore, EPA anticipates that leading up to 2018, 

numerous coal-fired EGUs in the region will be retrofit with post-combustion controls. 

EPA continues to find that the five year period for compliance with BART is reasonable. 

Because BART compliance at NGS involves the design, procurement, and installation of SCR on three 

units as well as well as a complex federal permitting process that would require consultation with other 

federal agencies and tribal governments, as well as upcoming ownership changes at NGS as discussed in 

our proposed rule, EPA is determining that a five-year BART compliance timeframe at NGS is as 

expeditious as practicable for purposes of establishing the BART Benchmark. This is within the range 

cited by the commenters and the facility operator (i.e., average of 21 to 47 months per unit, or 35 months 

to 67 months for multiples units at one facility) and is consistent with the CAA that requires BART 

compliance as expeditiously as practicable but no later than five years following the effective date of the 

final rule.238

Comment: Maintain 5 year compliance schedule to install SCR 

A public interest advocacy group (0413) said that EPA must retain the five-year compliance 

schedule for NGS. The commenter stated that other coal fired power plants are complying with BART 

within five years and installing SCR in that timeframe is essential to protect public health, in particular 

for the Navajo and Hopi people whose communities are the closest to the NGS facility and most 

exposed to harmful toxics and particulates emitted. The commenter stressed the importance of a rapid 

timeline as each day makes a difference to peoples’ health, in particular children and the elderly. The 

commenter stated that “lengthening the timeframe suggests that the Federal government can be exempt 

from its own Federal laws, especially when the Federal government is an owner of NGS.”

Response: 

 For calculating the appropriate BART Benchmark, EPA is retaining a NOx emission limit of 

0.055 lb/MMBtu within five years of the effective date of the final rule. However, EPA is finalizing our 

Supplemental Proposal that the TWG Alternative is a better than BART alternative that meets the 

framework we proposed in our February 5, 2013 Proposed Rule. Our final determination for the BART 

limit (0.055 lb/MMBtu) and the BART compliance timeframe (5 years) are used to establish the total 

cap in NOx emissions at NGS over 2009-2044 under the final TWG Alternative. EPA notes that the 

visibility protection provisions, including the BART requirement, under section 169A of the CAA 

relates to visibility protection for Federal class I areas. Although NOx is a visibility-impairing pollutant 

that is also regulated as a criteria pollutant due to its effect on air quality and human health, the statutory 

authority for the Regional Haze Rule is based on visibility protection. Thus, specific issues of public 

health are beyond the scope of this rulemaking. EPA addresses the commenters assertion that using an 

alternative compliance timeframe for the better than BART alternative suggests that the Federal 

237 See Final BART FIP for Four Corners Power Plant an compliance dates under the BART Alternative at 77 FR 51620 at 

51648 (August 24, 2012) and Final Regional Haze FIP for Arizona (phase 1) at 77 FR72512 at 72578 (December 5, 2012). 238 See section 169A of the CAA (§169A(b)(2)(A) and (g)(4)). 
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government can be exempt from its own laws, in Section 8.5 and 9.0 of this response to comments 

document. 

Comment: Allow 6 years to accommodate outage schedule 

 One individual (0091) recommended that EPA require NGS to install BART controls, including 

SCR in combination with LNB, within 6 years. The commenter believes that the extra year would give 

NGS the flexibility to comply without violating CAA or RHR requirements. In addition, the commenter 

stated that any lengthy delays in requiring NGS to install extra pollution controls would undermine 

EPA’s credibility, since neighboring states are undergoing similar requirements. The commenter 

believes that a 6-year compliance date instead of the proposed 5-year timeframe would allow NGS the 

opportunity to keep its current 3-year outage cycle with four layers of catalyst to meet a limit of 0.055 

lb/MMBtu. The commenter (0091) also asserts that because EPA promulgated the Regional Haze Rule 

in 1999, NGS has had ample time to install BART controls. The commenter also asserts that other major 

stationary sources in neighboring states were required to comply with CAA visibility requirements years 

ago; therefore it would be unfair for EPA to approve a more lenient schedule for NGS. 

 One individual (0156) cast doubt that NGS could maintain a 3-year outage cycle with four layers 

of catalyst while achieving a limit of 0.055 lb/MMBtu. 

Response:

 EPA disagrees that requiring NGS to comply with BART within six years is appropriate. We 

note that the compliance timeframe for BART (as expeditiously as practicable but in no event later than 

five years after the effective date of the plan) is a statutory requirement under the CAA. Therefore, EPA 

disagrees that a six-year compliance timeframe for BART is consistent with the CAA. We further note 

that EPA did not propose to extend the compliance timeframe for BART. EPA proposed a BART 

determination that consisted of a NOx limit of 0.055 lb/MMBtu with a five-year compliance time frame. 

Concurrently, EPA also proposed a framework for evaluating better than BART Alternatives, as well as 

two alternatives (Alternative 1 and the TWG Alternative) that both include flexibility in the regulatory 

timeframe for BART Alternatives under the Regional Haze Rule. Our proposed framework established 

the proposed BART determination as a benchmark against which BART Alternatives would be 

compared. Our rationale to provide flexibility in the compliance timeframe for BART Alternatives is 

discussed in our proposed rule and in sections 8.5 and 9.0 of this response to comments document. 

 EPA disagrees that NGS has had since 1999 to install BART controls. See EPA’s response to 

comments in Section 8.5. In addition, BART is a case-by-case analysis that could ultimately require 

installation of one of several different options for air pollution controls. Until a state (or EPA) has 

completed a BART determination, a facility does not know what emission limit it must comply with, 

despite promulgation of the Regional Haze Rule in 1999. We also note that EPA began taking action on 

Regional Haze SIPs, and in some cases, proposing and taking final action on FIPs, over 2011 – 2013. 

Therefore, EPA disagrees with the assertion that major stationary sources were required to comply with 

the CAA visibility requirements “years ago”. EPA also disagrees with the commenter that it is unfair for 

NGS, a facility located in Indian country, to be subject to a longer compliance timeframe than facilities 

located on state land. See Sections 8.5 and 9.0 in this response to comments. 

 Although one commenter (0091) supported the idea that NGS could maintain a 3-year outage 

cycle with four layers of catalyst to meet a limit of 0.055 lb/MMBtu, another commenter (0156) cast 
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doubt based on concerns related to the quality of work from S&L. Because neither commenter provided 

any detail to sufficiently support its assertions as it pertains to catalyst management plans, EPA is not 

responding to these particular statements from the commenter.239 However, we note that the 2013 cost 

analysis from S&L includes updated costs to accommodate a NOx design target of 0.03 lb/MMBtu using 

a 3+1 catalyst system in lieu of a 2+2 system. Although S&L asserts that a design target of 0.03 

lb/MMBtu would be required to meet a limit of 0.07-0.08 lb/MMBtu in order to accommodate loadcycling operation at NGS, S&L do not specifically discuss catalyst management as a potential issue (see 

section 8.1). 

Comment: Proposed BART limit 30-BOD plantwide limit issues 

 One of the owners of NGS (0348) expressed concern that the methodology for assessing 

compliance with the February 2013 proposal’s 30 day rolling average emission limit is impractical and 

produces an average that is meaningless. The commenter noted that the October 2013 Supplemental 

Proposal’s emission rate limits are expressed on a unit by unit basis, which helps to address some of 

these concerns. 

 The commenter (0348) noted that the proposed BART determination would require NGS to 

comply with a plantwide emission limit of 0.055 lb/MMBtu as BART, based on a 30 BOD average 

basis, and to construct the plantwide average, an individual 30 day average must be calculated for each 

unit. According to the commenter, because each unit may have operated on different days, a different 

30 day period might form the average for each unit, which would then be averaged together to form the 

plantwide average. The commenter believes that averaging emissions that occur on different days, at 

different times, and from different units cannot provide the public with a real picture of the plant’s 

emissions, and is therefore meaningless and irrelevant. 

 The commenter (0348) asserted that a plant operator cannot practically manage NOx emissions to 

remain below a permit limit that is structured in the manner that would be required by the proposed rule. 

The commenter stated that the proposed plantwide averaging methodology unnecessarily penalizes NGS 

in the event that a unit is offline because it fails to recognize that there are no emissions from the unit 

during that time. The commenter also is concerned that the proposed averaging methodology creates 

compliance challenges, particularly during times surrounding planned maintenance activities, because 

NOx emissions from coal fired boilers are often at their highest just prior to scheduled maintenance 

outages. Thus, because the proposed BART NOx limit requires NGS to account for the last valid 30

BOD average when a unit is shut down, the commenter believes that NGS will be penalized for an 

extended period of time for performing the necessary maintenance to improve NOx performance. 

 The commenter (0348) added that scheduled maintenance outages at NGS are required to occur 

between October and April, which represents a period of time in which the output from NGS may be 

reduced due to load demand. The commenter asserted that this further exacerbates the issues with the 

averaging provision proposed by EPA, as it is likely that the units will incur more load cycling during 

this time frame with increased NOx emissions as a result (as demonstrated in the S&L modeling 

discussed above). 

239 One commenter (0156) included numerous attachments to its comments as related to S&L’s work on the SanTan 

Generating Station, however, these supporting documents are not directly related to catalyst management plans for NGS. 
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 The commenter (0348) also indicated that the proposed averaging provision does not provide an 

opportunity for NGS to correct any potential exceedances. The commenter noted that an exceedance 

caused by one unit at NGS would result in all three units being out of compliance. The commenter 

added that typically, removing the offending unit from service (and accounting for the zero emissions 

from that unit) while addressing issues would ensure that the remaining units operating within the 

parameters of the permit limit would be able to continue to operate. However, the commenter believes 

that because the CAA prohibits an operator from knowingly violating a permit limit, NGS would be 

forced to remove the remaining units from service. 

 Further, the commenter (0348) believes that NGS would not be able to return any of the units to 

service as a result of counting the last 30 BOD average from each of the units – the emission rate last 

recorded during unit shutdowns would be in effect in perpetuity. According to the commenter, restarting 

the units – and the subsequent emissions penalties for the starts – would potentially constitute a knowing 

violation of a permit limit. 

 The commenter (0348) agreed that, if constructed correctly, averaging provisions can provide 

greater flexibility to the facility operators while achieving desired environmental objectives. However, 

the commenter believes that EPA’s proposed plantwide averaging methodology creates significant 

compliance and enforcement concerns. The commenter added that the EPA has previously 

acknowledged that the use of an offline unit’s preceding 30 BODs’ information in determining 

compliance with a plantwide emission limit is a novel concept.240 The commenter asserted that it has not 

been used in the regional haze context anywhere in the country and that for this reason and the reasons 

noted above, it should not be included in the final rule. 

Response:

 In our Proposed Rule, we determined that a NOx limit was achievable based on a facility-wide, 

rolling average basis of 30 boiler operating days in order to provide additional flexibility to the operator 

of NGS in meeting the proposed limit. In our Supplemental Proposal, EPA proposed emission limits and 

averaging times on a unit-specific basis. The BART Guidelines states that BART limits must “specify an 

averaging time of a 30-day rolling average, and contain a definition of ‘boiler operating day’ that is 

consistent with . . . 40 CFR Part 60, subpart Da.” The BART Guidelines provide that states “should 

consider allowing sources to average emissions across any set of BART-eligible emission units within a 

fenceline,” but does not require that BART limits be established on a facility-wide basis. EPA 

acknowledges the comment from the facility operator that it believes the facility-wide averaging 

methodology is problematic. 

EPA is establishing a BART Benchmark for NGS based on a lifetime cap in NOx emissions 

under the TWG Alternative. Because EPA is taking final action to approve the TWG Alternative, which 

proposed to establish emission limits on a unit-specific basis, this comment is moot. 

Comment: BART in the context of Regional Haze planning 

 Two of the owners of NGS (0314, 0348) stated that EPA’s current process appears to be 

disconnected from all the previous and on going regional haze planning in the Grand Canyon National 

240 The commenter cites to “EPA, Questions for AZ Regional Haze FIP Conference Call, January 2013” but did not provide a 

document to accompany this citation. EPA assumes this was personal communication between EPA staff and SRP staff. 
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Park region. A state agency (0017/0289/0320) noted that EPA stated in the February 2013 Proposal that 

NGS is just one of many contributors to regional haze and indicated that Congress recognized that “all 

sources that emit air pollutants that may reasonably be anticipated to cause or contribute to visibility 

impairment would need to do their part to address the problem” (citing 78 FR 8279). 

 One of the owners of NGS (0348) elaborated that EPA should evaluate the anticipated visibility 

benefits expected from its proposed BART Determination for NGS in combination with the visibility 

improvements expected from the other emission reduction requirements in the Arizona regional haze 

plan and other surrounding states that impact the same Class I areas. The commenter believes that 

failing to do so is at odds with EPA’s own recognition of the value of regional planning efforts, and the 

commenter expressed concern that much of the work of the Grand Canyon Visibility Transport 

Commission (GCVTC) and its successor body, the Western Regional Air Partnership (WRAP), was 

ignored in EPA’s August 2009 Advanced Notice of Proposed Rulemaking as well as in the February 

2013 Proposal. The commenter believes that the EPA’s proposed determination that SCR is BART is 

completely at odds with the goals that EPA itself established for the GCVTC and WRAP efforts. 

 The commenter (0348) indicated that real data measured over time on the Colorado Plateau 

demonstrate that NOx emissions play a small role in visibility impairment in this region, and power plant 

emissions only account for a fraction of that small contribution. The commenter stated that visibility in 

the Colorado Plateau region, as measured by the Interagency Monitoring of Protected Visual 

Environments (IMPROVE) monitoring network, is generally excellent, and the visibility impairment 

that does occur is largely attributable to natural sources, including Rayleigh scattering, wind blown dust, 

and smoke from wildfires, while controlled burns also contribute significantly to visibility impairment. 

The commenter noted that the 1996 technical analyses performed by the GCVTC showed that nitrate 

aerosols account for only 4 percent of light extinction in the Grand Canyon. (Note that this analysis 

ascribed 40 percent of visibility impairment to Rayleigh scattering and divided the remaining 60 percent 

among various types of particles.) The commenter also cited subsequent analyses conducted by WRAP 

which concluded that stationary source emissions of NOx probably cause only about 2 to 5 percent of the 

impairment on the Colorado Plateau. The commenter stated that a more recent review of IMPROVE 

monitoring data at Grand Canyon sites indicates that nitrate aerosols from all sources continue to be a 

relatively small contributor to light extinction within the park and presented data from the 20 percent 

worst visibility days at three sites in the Grand Canyon showing that nitrate aerosols contributed from 

6.1 to 7.3 percent. The commenter added that the NREL report indicated that the body of research is 

inconclusive as to whether removing approximately two-thirds of the current NOx emissions from NGS 

would lead to any perceptible improvement in visibility at the Grand Canyon and other areas of concern. 

 The commenter (0348) stated that EPA directed states in the RHR to consider all sources of man

made haze in developing long term strategies. While conceding that there is a significant focus on 

BART for major stationary sources in the first planning period, the commenter stated that it is clear that 

there are numerous other contributors to regional haze and concluded that EPA’s proposed NOx BART 

determination for NGS fails to take into account this bigger picture. The commenter asserted that the 

proposed BART determination would not achieve any appreciable visibility benefits because NOx from 

power plants – and NGS in particular – is a very small contributor to regional haze. The commenter 

indicated that this is why the commenter’s BART analysis concluded that costly post combustion 

controls for NOx are not justified. 

Response:
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Although EPA agrees that there are numerous contributors to regional haze and that the RHR 

addresses visibility impairment based on multiple sources located across a wide geographic area, those 

considerations are beyond the scope of this rulemaking. This rulemaking is limited to implementing the 

BART requirements in Section 169A of the CAA and the RHR. As discussed elsewhere, the CAA 

requires BART for certain large stationary sources that were put in place between 1962 and 1977.241 For 

any source that is subject to BART, the BART determination is based on five statutory and regulatory 

factors irrespective of the relative measured nitrate contribution. Here, NGS is BART-eligible and 

subject-to-BART because our modeling, conducted according to the procedures set out in the BART 

Guidelines, shows that NGS causes visibility impairment at multiple Class I areas. EPA has authority 

under the TAR to determine what provisions of the CAA and RHR are necessary or appropriate to 

promulgate at this time. The issues cited in the comment are related to whether EPA should require more 

controls for a greater number of sources based on reasonable progress – but this rulemaking is limited to 

implementing BART at NGS. If EPA determines at some point that additional visibility planning efforts 

are necessary or appropriate, we may consider involving surrounding states that impact the same Class I 

areas as suggested by the commenter. 

Regarding the assertion that emissions from power plants represent a small contribution to 

visibility impairment on the Colorado Plateau, EPA notes that 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, impairment due to individual sources are estimated using CALPUFF modeling. 

Estimates of impairment from stationary sources of 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 necessitate controls, 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).242 In particular, EPA modeling of NGS, as 

discussed in the TSD for our proposed rulemaking, showed 98th percentile visibility impacts from NGS 

of 1.3 to 8.4 deciviews, depending on the Class I area (or from 0.8 to 4.3 deciviews if lower ammonia 

background is assumed, as recommended by some commenters).243 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 NGS. The BART analysis is conducted on a source-specific 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. 

Comment: Section 169A is discretionary therefore EPA must balance cost and adverse impacts 

 A CAP agricultural water users group (0305) pointed out that the goal of CAA section 169A is 

an aesthetic goal, and is not a non-discretionary duty of EPA as the NAAQS and MACT standards are 

241 See preamble to the BART Guidelines at 70 FR 39104, at 39105 (July 6, 2005). 242 Id., at 39161. 243 See Tables 43 and 44 in the TSD for the Proposed Rule. 
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(citing CAA section 169A(f)). Instead, according to the commenter, EPA must balance the cost and 

other adverse impacts of BART against the visibility improvements that the BART controls will achieve 

in a five-factor analysis, rather than singularly focusing on maximum emission reductions. For reasons 

detailed elsewhere in this document, the commenter asserts that EPA has improperly used its discretion 

under the RHR because the proposed BART determination would impose substantial costs and other 

adverse impacts, yet would yield what the commenter characterized as de minimis visibility 

improvements. The commenter asserted that a proper cost-effectiveness analysis in the context of a fivefactor analysis would clearly indicate that the high costs of SCR do not justify any minimal visibility 

improvement that would be achieved, and concluded that because EPA’s analysis does not lead to this 

unavoidable conclusion, its determination that SCR is BART is flawed. 

 This commenter (0305) contends that SCR would provide only a marginal visibility benefit over 

SNCR, but at a much greater cost. The commenter quoted the February Proposal as indicating that 

across all 11 impacted Class I areas, SCR would achieve a cumulative visibility improvement of 13 dv 

beyond the improvement through SNCR, with only two Class I areas seeing improvements greater than 

2 dv. According to the commenter, such visibility improvements may not be perceptible to the human 

eye (citing the NREL report) and, therefore, selecting SCR as BART under these circumstances would 

be arbitrary and constitute an abuse of discretion on the part of EPA. 

Response:

The comment states that the goal of CAA section 169A is aesthetic. EPA does not agree with the 

commenter’s characterization of the goal of section 169A. The goal of this statutory provision is stated 

in section 169A(a)(1) of the CAA: “Congress hereby declares 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.” Aesthetics may constitute one benefit of the 

Congressional goal set forth in section 169A(1)(a) but it is not the goal of the statutory provision and is 

only one of many benefits, including the jobs and economic improvement from tourism in the region 

surrounding Class I areas. 

The comment also states that the goal of section 169A is not a non-discretionary duty for EPA in 

contrast to the NAAQS and MACT standards, citing section 169A(f). EPA agrees that the goal 

expressed in section 169A(1)(a) cannot be enforced pursuant to a CAA section 304 citizen suit. Section 

169A(f) provides in full: “For purposes of section 7604(a)(2) of this title, the meeting of the national 

goal specified in subsection (a)(1) of this section by any specific date or dates shall not be considered a 

‘nondiscretionary duty’ of the Administrator.” However, Section 169A(f) by its terms is limited to 

enforcing any dates that may be associated with the Congressional goal to prevent any future, and 

remedy any existing, impairment of visibility in mandatory class I Federal areas if the impairment 

results from manmade air pollution.244

The comment then states that EPA must balance the costs and visibility improvement of BART. 

This portion of the comment does not seem relevant to a discussion about the goal, and citizen suit 

enforceability of the goal, set forth in section 169A. Balancing costs and visibility improvement is 

relevant, inter alia, to a determination of BART. In this FIP, EPA is establishing a BART Benchmark 

and promulgating better than BART regulations that apply to NGS. The requirement for States to 

promulgate implementation plans requiring BART for sources that are subject to BART is set forth in 

244 See CAA section 169A(1)(a). 
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CAA Section 169A(b)(2). The prohibition on citizen suit enforceability in section 169A(f) is not, 

therefore, applicable to the action EPA is taking in this FIP. 

Although section 169A(f) does not apply to a BART determination promulgated pursuant to 

CAA section 169A(b)(2), EPA agrees that our action in promulgating this FIP is discretionary. Our 

action here is discretionary (or “not nondiscretionary”) based not on section 169A(f) but instead based 

on CAA Section 301(d)(4) and 40 CFR 49.11 of EPA’s Tribal Authority Rule.245

The comment does not explain why characterizing EPA’s duty as discretionary or “not 

nondiscretionary” in this action is significant. The comment implies that EPA might weigh the five 

BART factors differently depending on whether its duty is discretionary or mandatory. EPA disagrees 

with the implication that we would exercise discretion to weigh the five factors set forth in CAA Section 

169A(2)(C)(3) differently based on whether we were exercising a mandatory or discretionary duty. 

The commenter claims that EPA must balance the costs and other adverse impacts of BART 

against the visibility improvements that the BART controls will achieve in a five-factor analysis, rather 

than singularly focusing on maximum emission reductions. EPA agrees and has weighed the five BART 

factors in this rulemaking. To the extent the comment contends that EPA has not reasonably weighed the 

BART factors, the commenter has mischaracterized EPA’s action in this FIP. In determining the NOx

emission limit that represents BART, EPA went to considerable lengths to analyze and discuss our 

balancing of the five BART factors, including cost and visibility improvement. EPA’s analysis of the 

five BART factors began with our Advanced Notice of Proposed Rulemaking.246 EPA received 

numerous comments in response to our discussion of the BART factors in the ANPR. EPA considered 

those comments and provided extensive analysis of the five BART factors when we published our 

Notice of Proposed Rulemaking in February 2013.247 EPA’s TSD accompanying the February 2013 

Proposed Rule contains additional detail concerning our analysis of the five BART factors. 

EPA did not “singularly” consider maximum emission reductions. To the contrary, EPA weighed 

the five BART factors to propose finding that an emission limit of 0.055 lb/MMBtu for NOx was BART, 

which is achievable by installing SCRs on all 3 units at NGS.248 After establishing the proposed NOx

BART determination of 0.055 lb/MMBtu, EPA calculated the BART Benchmark, or total NOx

emissions attributable to NGS over long-term operations from 2009 - 2044.249 EPA then proposed to 

find that any alternatives to BART that resulted in lower NOx emissions than the BART Benchmark 

would be better than BART, provided that number was calculated using the same NOx BART emission 

rate (0.055 lb/MMBtu) over the same amount of time (2009-2044).250 Therefore, EPA only considered 

total or cumulative NOx emissions reductions in establishing a framework to evaluate alternatives to the 

BART Benchmark that might be considered better than BART. EPA’s BART proposal was based solely 

on weighing the BART factors and not based on a consideration of maximum emission reductions. 

245 See Dine CARE v. United States Environmental Protection Agency, No. C 12-03987, Order Granting Defendant and 

Intervenor’s Motions for Summary Judgment and Dismissing Action for Lack of Subject Matter Jurisdiction (N.D. CA, Dec. 

03, 2013) (stating: “[T]he provision cited by Plaintiffs requiring the State to submit a determination for each eligible BART 

source does not apply to the Tribe or EPA.” Slip op. at p. 4). 

246 See ANPR at 74 FR 44313, 44320 – 44333 (August 28, 2009). 247 78 FR 8274, 8279 – 8287 (February 5, 2013). 248 See 78 FR at 8288 (February 5, 2013) 

249 Id. at 8289. 250 Id. at 8290. 
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The comment contends that the costs of SCR as BART were much higher than EPA projected 

and that the visibility improvements from SCR would be “minimal.” As discussed elsewhere in this 

document, EPA disagrees with both statements. First, the cost of SCR is reasonable and cost-effective, 

even when we consider the highest cost estimates based on SRP’s 2013 cost analysis (see response to 

comments in section 3.1 of this response to comments document). Second, the commenter relies on a 

report prepared by NREL as the basis for stating the visibility improvements will be minimal. The 

NREL report was not designed to evaluate the magnitude of the visibility improvement from SCR at 

NGS and the statement in the NREL report was conclusory without supporting data. NPS has stated that 

the visibility section of the NREL report was inadequate and that it made a number of inappropriate 

comparisons between models and model results.251 EPA disagrees with the assertion that visibility 

benefits would be minimal and the data in our record for this final rule continue to demonstrate 

substantial visibility improvement from NGS achieving a NOx BART emission rate of 0.055 lb/MMBtu 

on a rolling average of 30 boiler operating days. 

The comment also contends that setting a NOx BART emission rate achievable with SCR would 

only be a nominal improvement over the emission rate achievable with SNCR. Again, citing to the 

NREL report, the commenter states the visibility improvement from SCR over SNCR would not be 

perceptible. We have responded to this comment elsewhere in this document. 

Comment: Support for EPA’s proposed BART determination 

One commenter (0395) supported the finding that SCR is appropriate, citing specifically to the 

incremental cost effectiveness for SCR is less than SNCR ($3,315 versus $4,110 per ton of NOx

removed). The commenter opines that the relative average and incremental cost effectiveness of SCR 

compared to SNCR, in conjunction with the documented key findings in Table 9 of the preamble to the 

proposed rule (showing the improved baseline impairment from NOx emissions by an average of 73 

percent with SCR across 11 Class I areas, as compared to 45 percent associated with SNCR), clearly 

demonstrates the superior visibility benefits can be achieved more cost-effectively by setting a NOx limit 

based on SCR. The commenter added that with LNB/SOFA, NGS has hundreds of modeled impacts 

above a concern threshold of 0.5 dv across 11 federal Class I areas. In the commenter’s opinion, it is 

EPA’s statutory responsibility to set a BART-level of control based on the use of SCR for NOx

reduction, which EPA determined would be double the visibility improvement projected at 11 parks and 

wilderness areas in the region. 

Response:

 EPA agrees with the commenter that our BART determination for NGS, based on our five-factor 

analysis, was appropriate and reasonable. 

8.2 Comments on BART for PM 

Comment: Support/opposition for finding not to establish PM BART 

251 See letter from Herbert Frost, NPS to Jared Blumenfeld, EPA, dated April 6. 2012 (titled “2012_0406 NPS letter to 

EPA”), document number 0004 in the docket for this rule at EPA-R09-OAR-2013-0009. 
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 One of the owners of NGS (0348) and a CAP agricultural water users group (0305) voiced 

support for EPA’s statement that “Because emissions of PM are well controlled at NGS through 

federally enforceable limits, EPA is not proposing that it is “necessary or appropriate” under the TAR to 

determine BART for PM emissions at NGS.” The commenters agree that no additional emission limits 

or controls should be required as a result of BART for PM emissions. 

 The commenters (0305, 0348) also stated that implementation of the Mercury and Air Toxics 

Standards (MATS) in the near future will establish an additional federally enforceable limit for PM 

emissions at NGS. The commenters added that the BART Guidelines provide that one can generally rely 

on MACT standards for purposes of BART (citing 70 FR 39163-34; 40 CFR part 51, Appendix Y, 

section IV.C). One of the commenters (0305) indicated that MATS will reduce the NGS PM limit from 

0.06 lb/MMBtu to 0.03 lb/MMBtu, achieving substantial reductions beyond present levels. Based on 

these arguments, one of the commenters (0348) requested that EPA include the following statement in 

the final rule: 

Because PM emissions at NGS are already well controlled pursuant to 

federally enforceable emission limits and because implementation of 

MATS at NGS would, pursuant to the BART Guidelines, satisfy any PM 

BART requirement that might otherwise be deemed to apply, we need not 

determine that it is necessary or appropriate under the TAR to establish 

PM BART limits for NGS. 

 One of the commenters (0305) added that the EPA appropriately exercised its discretion under 

the RHR, acting on behalf of the Navajo Nation, to consider NGS’s progress on PM (and SO2) to ensure 

that reasonable progress is made toward visibility improvement in the affected Class I areas. The 

commenter believes that the cost of compliance at NGS, the existing pollution controls at NGS, and the 

relatively small degree of additional visibility improvement that would be possible from further PM (or 

SO2) BART controls on already well-controlled units all justify the EPA’s decision not to impose a PM 

(or SO2) BART determination. 

 In contrast, two groups (0373, 0401) asserted that EPA was incorrect in its determination that it 

need not evaluate BART for control of PM at NGS because particulates are well-controlled with a plantwide limit of 0.060 lb/MMBtu (citing 78 FR 8279). According to this commenter, this limit was not 

based on a BART analysis and does not reflect a well-controlled PM emission rate for a coal-fired EGU, 

but is simply a carry-over from what EPA and/or the state has historically applied to NGS under the 

Arizona SIP (citing the Stamper report). The commenter stated that this “historical carry-over approach” 

is not BART and does not meet the requirements of the CAA. 

 This commenter (0373) does not believe that the electrostatic precipitators (ESPs) at NGS 

represent the best system of control for PM. The commenter believes that EPA’s determination is 

inconsistent with its recent determination that the existing PM controls at FCPP (which, according to the 

commenter, currently emits PM at or below 0.03 lb/MMBtu) do not constitute BART (citing the 

Stamper report and 77 FR 51637), and with recent BACT determinations for coal-fired utility boilers 

with PM limits of 0.010 lb/MMBtu based on the use of fabric filter baghouses. The commenter added 

that NGS is allowed to exceed the PM limits during startup and shutdown, while BART requires the best 

system of continuous controls. The commenter asserted that EPA’s “inconsistent” approach to NGS is 

unsupported (citing the Stamper report). 
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 The commenter (0373) believes that fabric filter baghouses should have been evaluated as BART 

at NGS and such evaluation would demonstrate that they are necessary to meet the visibility 

requirements of the CAA. The commenter stated that this technology has been in use since the 1970s 

and is cost effective at $43/ton of PM removed (citing the Stamper report). The commenter added that it 

is likely that baghouses will be required at NGS to meet MATS and that they would save NGS money 

on electricity (citing the Stamper report). In addition, the commenter indicated that it is likely that the 

affected Class I areas would show significant visibility improvements if NGS installed baghouses, and 

cutting PM emissions would have health benefits. The commenter concluded that EPA should revise its 

determination and complete a BART analysis for PM which includes evaluation of fabric filter 

baghouses. 

Response:

EPA agrees with the comment that it is not necessary or appropriate to require BART for PM or 

SO2 emissions from NGS at this time. As we stated in our proposed rule: “Emissions of PM and SO2 are 

controlled by hot-side electrostatic precipitators (HS-ESPs) and wet scrubbers, respectively.”252

With respect to SO2 emissions, EPA made a finding in a 1991 FIP that the wet scrubbers to 

reduce SO2 emissions that would be (and have now been) installed between 1997 – 1999 were better 

than BART with an emission limit of 0.10 lb/MMBtu averaged on an annual basis.253 EPA has not been 

presented with any information in this rulemaking to indicate that our better than BART determination 

in 1991 was insufficient for purposes of regulating regional haze. Therefore, we continue to find that the 

SO2 emissions limit finalized in our 1991 SO2 FIP, and codified in 40 CFR 49.5513(d)(1) continues to 

achieve greater reasonable progress than SO2 BART. 

For PM, EPA’s proposal stated that making a BART determination is not necessary or 

appropriate at this time because the PM emissions are well controlled by HS-ESPs based on federally 

enforceable emissions limits. 254 The PM emission limit of 0.060 lb/MMBtu is codified at 40 CFR 

49.5513(d)(2). In addition, at the time of our BART proposal, the MATS Rule for electric utility steam 

generating units had been finalized.255 The MATS rule sets a limit of 0.03 lb/MMBtu for filterable PM 

that is applicable to the units at NGS. Because NGS will be required to comply with the PM emissions 

limits in the MATS rule, EPA continues to find that it is not necessary or appropriate at this time to 

promulgate a BART emission limit for PM from NGS. EPA’s MATS rule 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.256

One commenter requested that EPA add the following language to the final rule: “Because PM 

emissions at NGS are already well controlled pursuant to federally enforceable emission limits and 

because implementation of MATS at NGS would, pursuant to the BART Guidelines, satisfy any PM 

BART requirement that might otherwise be deemed to apply, we need not determine that it is necessary 

or appropriate under the TAR to establish PM BART limits for NGS.” While EPA agrees with the 

statement, we do not consider it appropriate to include any regulatory text to this effect. EPA expects 

that NGS will continue to comply with the SO2 and PM emissions limit codified at 40 CFR 49.5513(d) 

until the MATS emission limit of 0.03 lb/MMBtu becomes applicable to NGS. 

252 78 FR at 8279 (February 5, 2013). 253 56 FR at 50179 (Oct. 3, 1991, codified originally in 40 CFR 52.145 and re-codified at 40 CFR 49.5513). 254 78 FR at 8279 (February 5, 2013). 255 77 FR 9304 (February 16, 2012) 256 White Stallion Energy Center LLC v. EPA,, in the docket for this rule at EPA-R09-OAR-2013-0009. 
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EPA disagrees with the comments stating that a BART determination for PM is required. One 

commenter stated that EPA’s “historical carry-over approach” for the PM emission limit is not BART 

and does not meet the requirements of the CAA. EPA is not determining that the existing PM emission 

limit for NGS is BART. Instead, it is EPA’s position that it is not necessary or appropriate under our 

discretionary authority promulgated at 40 CFR 49.11 to conduct a BART determination for PM 

emissions because they are currently well controlled and will be further reduced by compliance with the 

MATS rule. 

One commenter asserted that EPA should require fabric filter baghouses as BART for PM, that 

baghouses have been in use since the 1970s and that they are cost effective at $43/ton of PM removed 

(citing the Stamper report). The commenter further added that baghouses may be required at NGS to 

meet MATS, they would save NGS money on electricity, that Class I areas would show significant 

visibility improvements if NGS installed baghouses, and that cutting PM emissions would have health 

benefits. 

EPA cannot agree or disagree that baghouses would be required as BART for PM because we 

have determined that it is not necessary or appropriate at this time to conduct a BART determination for 

PM at NGS. EPA does not consider it necessary or appropriate to conduct a BART determination for 

PM because the PM emissions are currently well controlled and will be subject to a lower emission limit 

pursuant to the MATS rule sooner than BART would have been required. Therefore, EPA has decided to 

use its resources at this time to require only NOx BART for NGS. 

8.3 Comments on BART for SO2

Comment: Support for finding that RP is met for SO2 

 One of the owners of NGS (0348) and a CAP agricultural water users group (0305) noted that 

EPA recognized in the February 2013 Proposal that the emission limits EPA established for SO2 in 1991 

were determined to achieve greater reasonable progress than would BART, therefore the reasonable 

progress goals of CAA section 169A(b)(2) for SO2 at NGS are already satisfied with the installation of 

wet scrubbers (citing 78 FR 8279). The commenters agreed that no additional emission limits or controls 

should be required as a result of BART for SO2 emissions. One of the commenters (0305) noted that the 

existing SO2 limit at NGS is more stringent than the BART Guidelines’ presumptive SO2 limit. 

 One of the commenters (0305) added that EPA appropriately exercised its discretion under the 

RHR, acting on behalf of the Navajo Nation, to consider NGS’s progress on SO2 (and PM) to ensure that 

reasonable progress is made toward visibility improvement in the affected Class I areas. The commenter 

believes that the cost of compliance at NGS, the existing pollution controls at NGS, and the relatively 

small degree of additional visibility improvement that would be possible from further SO2 (or PM) 

BART controls on already well-controlled units all justify EPA’s decision not to impose an SO2 (or PM) 

BART determination. 

Response:

EPA agrees with the comments. As EPA stated in our proposal in February 2013, the SO2

emissions limit established in EPA’s 1991 SO2 FIP was better than BART. Specifically, EPA 

determined that promulgating a SO2 emission limit of 0.10 lb/MMBtu on an annual average basis would 
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result in greater cumulative SO2 emissions over time. Our 1991 SO2 FIP concluded: “After reviewing 

the option recommended by SRP, EDF, and GCT, EPA has determined that such a control strategy will 

provide a substantially greater degree of emissions reduction, and a correspondingly greater degree of 

visibility improvement at a substantially lower cost than the alternative proposed in February 1991. For 

these reasons, EPA also concludes that this option will make additional reasonable progress towards 

attainment of the national visibility goal in comparison to the February 1991 proposal.”257

NGS installed a wet flue gas desulfurization system on each of its boilers in 1997-1999. EPA 

initially codified the requirements for NGS to meet an SO2 emissions limit in an existing FIP for the 

State of Arizona.258 After promulgation of the TAR, EPA moved the NGS SO2 FIP to 40 CFR 49.5513. 

EPA also agrees with the comment implying that it is not necessary or appropriate to conduct a 

BART determination for SO2 or PM at this time, based at least in part on the costs of additional SO2 or 

PM controls. 

8.4 Other Comments on BART 

Comment: SCR is not the best solution for health and the environment 

 One environmental advocacy group (0055) objected to the BART proposal noting concern about 

SCR’s use and generation of hazardous waste. The commenter asserts that it is better to set emission 

limits, monitoring and reporting requirements and deadlines, as opposed to allowing NGS to define their 

own method to meet the emission limits and their own business requirements. The commenter indicated 

substantial concern over the operation of NGS in general and the amount of pollution that it creates, its 

contribution to GHG emissions, and its massive water consumption. The commenter recommended that 

instead of requiring expensive, and in the commenter’s opinion, questionable controls, costs should be 

added to the operation of the plant to develop a fund that compensates communities for the health and 

environmental costs of operating the plant. Also, the commenter urged that for the time being, a deadline 

should be set to transition NGS away from using coal to generate power. 

Response: 

 EPA notes that our BART determination is an emission limit and not a requirement to install a 

specific control technology. The emission limit we proposed as BART is achievable with 

SCR+LNB/SOFA, but the operator of NGS may install any technology that meets the required emission 

limit. The commenter may be confusing our BART determination with the TWG Alternative, which, 

under TWG Alternative B, allows NGS to determine how to meet the 2009-2029 and 2009-2044 NOx

Caps. EPA does not consider SCR to be a questionable control. We note that SCR is a widely-used 

technology on coal-fired and natural-gas fired power plants throughout the country and internationally. 

EPA also notes that general concerns about the environmental impact of NGS can be raised during the 

joint EIS process for NGS and the Kayenta Mine. Finally, as stated previously, EPA does not have 

authority under the RHR to require NGS to transition NGS away from using coal (or otherwise redefine 

the facility). 

257 See 56 FR at 50179 (October 3, 1991). 258 See 40 CFR 52.145. 
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Comment: Downwind monitoring 

 Two industry/commerce commenters (0027, 0076) stated that visible emissions, measured in 

terms of opacity, is the only cost effective and accurate way to control source emissions and should be 

required on the operations to ensure that required controls are controlling the emissions of the source. 

The commenters indicated that control technology performance characteristics are less than perfect and 

suggested that a secondary quality assurance type of measurement be required to achieve desired goals. 

These commenters also suggested that downwind monitoring using actual visibility indicators, such as 

digital imagery, be required to measure the effects of this implementation plan on the visibility levels at 

the North and South Rim centers at the Grand Canyon. 

Response:

 EPA notes that visible emissions, measured in terms of opacity, are an important indicator for 

compliance with emissions limits for particulate matter. We note that previous FIP requirements 

promulgated for NGS already included an opacity requirement, limiting opacity from Units 1, 2, and 3 at 

NGS to no greater than 20 percent opacity, excluding condensed uncombined water droplets, averaged 

over any six minute period and 40 percent opacity, averaged over six minutes, during absorber upset 

transitions.259 Regarding the commenter’s suggestion to use visibility indicators, such as digital imagery, 

at the North and South Rims of the Grand Canyon, to measure the effects of the FIP on visibility, we 

note that while the CALPUFF visibility modeling can estimate the impact of a facility on visibility in a 

Class I area, the modeling cannot predict how all the other sources of air pollution, whether from natural 

or anthropogenic sources, will affect visibility, in combination with NGS, at a given moment. Therefore, 

although visibility indicators are a useful and important measurement for understanding longer-term 

trends in visibility (and the National Park Service does maintain the IMPROVE monitoring network to 

measure visibility impairment), it is inaccurate to suggest that modeling that predicts a reduction in the 

visibility impact of NGS can be easily translated into actual quantification of visibility improvement at a 

Class I area without further understanding of the other sources affecting visibility at any given moment. 

Comment: Other Alternatives to BART 

 One individual (0064) questioned whether imposing a BART rule would be the most effective 

method to meet emission reductions, particularly when the economic impacts to the Navajo Nation are 

largely unknown. Instead, the commenter suggested that NGS be allowed to defer BART requirements 

provided that the Navajo Nation proposes a TIP covering the following: 

1. Emissions standards for NGS. 

2. A plan to coordinate assets and development plans among the owners of NGS. 

3. A plan to transition to cleaner production, the net result of which must be overall emissions 

reductions representing greater or reasonable progress than would result from the installation and 

operation of BART at some clearly defined future time. 

 Two individuals (0237, 0238) requested that NGS comply with EPA’s proposed rule or combine 

retirement and retrofits that would meet the same or greater reductions. One individual (0327) 

259 See 40 CFR 49.5513(d)(4). 
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recommended combining the 2011 Cross-State Air Pollution Rule with one of the proposals to enhance 

the overall effectiveness of the final rule or consider a rule that would require NGS to shut down one 

unit in 2015, another in 2017, and one in 2019. 

 One individual (0345) recommended the OxyFuel alternative as a possible solution to mitigating 

excess NOx emissions from NGS. The commenter explained that the OxyFuel alternative is based the 

principle of treating the cause of excessive NOx emissions by minimizing the presence of nitrogen in the 

combustion systems in the three generating units at NGS, and added that the application of OxyFuel 

technology should offer an ideal tradeoff between minimizing emissions of NOx and minimizing the 

capital cost of doing so. The commenter submitted other technical information and data as an appendix 

to its comment. 

Response: 

 The TWG Alternative, which was developed by a group of diverse stakeholders, includes aspects 

of the suggestions from some commenters that call for a combination of retirements and retrofit of units. 

EPA notes that a rule that requires NGS to shut down one unit in 2015, another in 2017, and one in 2019 

would certainly reduce emissions, but at the expense of the numerous tribes and other stakeholders that 

currently rely on NGS directly for power, or indirectly, to power CAP. Regarding OxyFuel as an 

alternative method for reducing emissions of NOx, as discussed elsewhere in this response to comments 

document, EPA’s BART determination is an emission limit, not a technology requirement. Therefore, 

the operator of NGS may consider and install any technology as long as it complies with the required 

emission limit within the required timeframe. 

8.5 Comments on the EPA’s BART Alternative 

Comment: General comments on EPA BART Alternative 

 Six individuals (0357, 0360, 0366, 0388, 0405, 0414, 043) specifically stated that they support 

Alternative 1. In contrast, one individual (0399) specifically voiced opposition to Alternative 1, stating 

that NGS should not be rewarded for obfuscations and delays, and highlighting that EPA is to 

promulgate such FIP provisions “without unreasonable delay.” One commenter (0025/0071) urged EPA 

to reconsider its decision to give SRP credit for NOx reducing technology and more time, and order SRP 

to install SCR by 2019. 

 One state agency (0017/0289/0320) expressed appreciation for EPA’s recognition of the unique 

circumstances associated with NGS and its desire to provide more flexibility, but opposed Alternative 1 

because the commenter believes that the timing is still unworkable. 

Response: 

 EPA acknowledges the support for Alternative 1. We disagree that the LNB/SOFA credit 

rewards SRP for obfuscations and delays, and we note that although nearly five years has elapsed since 

our ANPR in 2009, EPA has been consistently working to propose and finalize BART determinations 

for Four Corners Power Plant and NGS since then. EPA considers our five-factor analysis and proposal 

to credit NGS with the early and voluntary installation of LNB/SOFA on one unit per year in 2009-2011 

to be reasonable and consistent with the BART Guidelines and the RHR. EPA is exercising our 
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authority and discretion under section 301(d)(4) of the CAA and 40 CFR 49.11(a) to provide flexibility 

with respect to the the compliance timeframe for BART Alternatives. We recognize that continued 

operation of NGS and the Kayenta Mine, as a source of direct revenues through lease payments or coal 

royalties to the Navajo Nation and Hopi Tribe, as well as the importance of Reclamation’s share of NGS 

to supply water to many tribes located in Arizona in accordance with several water settlement acts, is of 

critical importance and we consider that to argue for thoughtful consideration of how flexibility in the 

compliance timeframe can be provided consistent with the air quality goals of the Clean Air Act. 

 As noted elsewhere in this response to comments document, although some commenters 

expressed concern that Alternative 1 was not flexible enough, EPA notes that our framework for BART 

Alternatives provided stakeholders with the ability consider longer timeframes for compliance provided 

the operator of NGS bridged the deficit in emission reductions, as compared to the BART Benchmark, 

by achieving additional emissions reductions. We note that the TWG Alternative was consistent with 

this framework. 

Comment: Support for EPA’s authority for better than BART and delayed implementation 

 Two of the owners of NGS (0314, 0348), a tribal government commenter 

(0024/0098/0316/0326), and a CAP agricultural water users group (0305) expressed support for the 

EPA’s determination in the February 2013 Proposal, as elaborated in the October 2013 Supplemental 

Proposal, that it has discretion to authorize compliance with a BART alternative providing for 

compliance more than 5 years after promulgation of a final FIP for NGS (citing 78 FR 8288-89; 78 FR 

62511-13). The NGS owner (0348) and CAP agricultural water users group (0305) discussed and 

supported EPA’s policy and legal rationale for its discretion to approve “better than BART” alternatives 

and to provide an extended period for implementation of such an alternative at NGS. The NGS owner 

(0348) added additional legal support as follows: 

 The U.S. Courts of Appeals for the D.C. Circuit and the Ninth Circuit have confirmed EPA’s 

broad authority to approve “better than BART” alternatives in lieu of BART (Utility Air 

Regulatory Group v. EPA, 471 F.3d 1333, 1340 41 (D.C. Cir. 2006); Ctr. for Energy & Econ. 

Dev. v. EPA, 398 F.2d 653, 659 60 (D.C. Cir. 2005); Central Ariz. Water Conserv. Dist. v. EPA, 

990 F.2d 1531, 1543 (9th Cir. 1993)). 

 The U.S. Court of Appeals for the Ninth Circuit and the U.S. District Court for the Northern 

District of California have affirmed EPA’s authority and discretion under the Tribal Air Rule 

(TAR) (citing Ariz. Pub. Serv. v. EPA, 562 F3d 1116, 1119, 1123-24, 1125-26 10th Cir. 2009); 

DINÉ CARE v. EPA, 2013 WL 6327530 *4-5 (N.D. Cal.2013)). 

The commenter (0348) believes that establishing an alternative BART deadline will not compromise the 

ultimate goal of the regional haze program, which is to achieve steady progress toward eventually 

eliminating human caused visibility impairment in Class I areas. The commenter added that a modest 

extension of the BART compliance timeframe is reasonable under these circumstances given the long 

time horizon over which the program is to be implemented (i.e., a “goal” of full implementation by 

2064). 

 The commenter (0348) also opined that the 5 year compliance period for BART that is defined 

in section 169A(g)(4) of the CAA applies by its terms only to: (1) SIPs, by providing that the BART 

compliance date shall be no later than “five years after the date of approval of a plan revision under this 
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section”; and (2) FIPs promulgated under CAA section 110(c), by providing that the BART compliance 

date under any such FIP shall be no later than “five years after . . . the date of promulgation of such a 

plan revision in the case of action by the Administrator under section 110(c).” The commenter stated 

that in contrast, the CAA establishes no statutory time limit on the compliance period for any BART 

requirement promulgated pursuant to the EPA’s “necessary or appropriate” authority under the TAR to 

regulate emissions from sources located on tribal lands, including NGS. 

 One tribal government (0024/0098/0316/0326) similarly agreed and supports the EPA’s 

authority for better than BART and delayed implementation. The commenter said that the EPA has 

properly used the CAA section 301(d) treatment as state (TAS) provision, as implemented under the 

Tribal Authority Rule in 40 CFR Part 49, in setting NOx emission limits for NGS. The commenter cited 

the following excerpt from the CAA TAS provision supporting the Agency’s discretion to not treat 

tribes the same as states when such treatment is determined inappropriate or infeasible: 

In any case in which the Administrator determines that the treatment of 

Indian tribes as identical to States is inappropriate or administratively 

infeasible, the Administrator may provide, by regulation, other means by 

which the Administrator will directly administer such provisions so as to 

achieve the appropriate purpose. CAA section 301(d)(4), 40 U.S.C 

§7601(d)(4). 

 The commenter (0316) noted that under the TAS, regulations were adopted that require a FIP 

whenever “necessary or appropriate to protect air quality” in cases where a tribe does not submit or 

submits an inadequate Tribal Implementation Plan (TIP). According to the commenter, the Navajo 

Nation did not submit a TIP for NOx for NGS and subsequently EPA determined that in order to protect 

air quality a Federal regulation was needed. 

 The commenter (0316) added that it supports EPA’s decision that it is justified per TAS to 

include flexibility in terms of the compliance timeframe. While acknowledging that the CAA and the 

RHR require BART within 5 years, the commenter pointed out that the regulations also allow for the 

implementation of rules that will lead to “greater reasonable progress than would be achieved through 

the installation and operation of BART” (citing 40 CFR 51.308(e)(2)). The commenter is of the opinion 

that EPA appropriately followed CAA section 301(d)(4) and 40 CFR 49.11(a) in setting an extended 

timeframe for NGS compliance under the proposed alternative BART NOx emission limit. The 

commenter again reemphasized that EPA has appropriately used its authority and discretion and was 

justified in proposing a delay timeline for compliance using the CAA TAS provision and TAR. 

 The CAP agricultural water users group (0305) expressed strong support for EPA’s consideration 

of better-than-BART alternatives for NGS that extend the deadline for compliance beyond 2018, as 

CAA section 169A would otherwise require. The commenter agreed that because of the unique 

considerations surrounding NGS’s federal ownership and its prominent role in the Arizona and Tribal 

economies, a flexible approach that provides adequate transition time for all NGS stakeholders is 

appropriate. 

Response:

EPA agrees with the comment in support of our action to supplement our proposed BART 

determination with our proposed finding that the TWG Alternative meets the framework established in 
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our February 5, 2013 Proposed Rule. EPA agrees that we have the legal authority under the CAA and 

RHR to implement this better than BART alternative.260

Although the comment refers to EPA’s “TAS” authority, EPA is reading this comment as 

intending to refer to EPA’s “TAR” authority. “TAS” is the acronym the agency uses when it approves a 

tribal entity for “Treatment as State”. Nothing in this rulemaking relates to the Treatment as State 

regulations. Therefore, EPA is reading this comment to refer only to our “TAR” – or Tribal Authority 

Rule – authority. 

EPA agrees that we have the authority under the CAA and the TAR to provide flexibility in the 

compliance date that will apply to the better than BART alternative. Specifically, EPA exercised our 

authority under section 301(d)(4) of the CAA to promulgate the TAR. In doing so, EPA’s regulations 

allowed Tribes (and EPA in a Tribal FIP) to promulgate reasonably severable provisions of the CAA.261

In the TAR, EPA exercised its authority to exempt Tribes from those provisions in the CAA that 

imposed SIP submittal deadlines, stating: “EPA notes at the outset that recurring provisions for which 

EPA is proposing not to treat Tribes in the same manner as States involve certain Clean Air Act 

submittal deadlines.”262 The TAR proposal noted: 

Further, the State program submittal deadlines in the statute are based 

upon a relatively long history of the Clean Air Act planning and 

implementation by States. (footnote omitted) States have assumed an 

active role in Clean Air Act implementation since the 1970 Amendments 

to the Act. By comparison, in substantial part, Tribal authority for Clean 

Air Act programs was expressly addressed in the Act for the first time in 

the 1990 Amendments. Tribes, therefore, are at best in the early stages of 

developing air program expertise and planning efforts. Accordingly, EPA 

believes it would be both infeasible and inappropriate to subject Tribes to 

the State program submittal and related deadlines in the statute as 

explained in more detail below.”263 (emphasis added) 

The TAR listed specific submittal deadlines for which Tribes (and EPA in promulgating a Tribal FIP) 

would be exempt. With respect to submittal deadlines concerning visibility impairment, EPA stated: 

“EPA is not proposing to treat Tribes in the same manner as States for the provisions of section 169A or 

implementing regulations requiring submittal of visibility implementation plans by specific 

deadlines.”264 EPA finalized this approach in the TAR in 1998.265

The TAR as codified at 40 CFR 49.11(a) provides that EPA shall promulgate “such Federal 

implementation plan provisions as are necessary or appropriate to protect air quality” in Indian country 

where a tribe either does not submit a TIP or does not receive approval of a submitted TIP. The United 

260 See 40 CFR 51.308(e)(2); CAWCD v. EPA, 990 F.2d 1531 (9th Cir. 1993); CEED v. EPA, 398 F.3d 653 (D.C. Cir. 

2005); UARG v. EPA, 471 F.3d 1333 (D.C. Cir. 2006). 

261 59 FR 43956 at 43961 col. 3 (“Further, EPA is proposing to accept ‘reasonably severable’ Tribal air program submittals 

that meet the applicable requirements of the CAA.”). (August 25, 1994) 262 See 59 FR at 43964, col. 3. (August 25, 1994) 263 59 FR 43965, col. 1. (August 25, 1994) 264 59 FR 43966, col. 1. (August 25, 1994) 265 63 FR 7254 (February 12, 1998), codified at 40 CFR Part 49.4.
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States Court of Appeals for the District of Columbia Circuit, the only court having jurisdiction over the 

issue, upheld the TAR in 2000.266

EPA’s use of the term “provisions” indicates EPA’s determination that it may only be necessary 

or appropriate to promulgate a FIP of limited scope. The United States Court of Appeals for the Tenth 

Circuit has previously endorsed the application of this approach in a challenge to the federal 

implementation plan for the Four Corners Power Plant. The Court stated: “[49 CFR 49.11(a)] provides 

the EPA discretion to determine what rulemaking is necessary or appropriate to protect air quality and 

requires the EPA to promulgate such rulemaking.”267 The Court continued by observing that “[n]othing 

in 49.11(a) requires EPA . . . to submit a plan meeting the completeness criteria of Appendix V.” Id.

While the Court in the Four Corners case was focused on 40 CFR Part 51, Appendix V, EPA believes 

the same considerations apply to the promulgation of this particular FIP that is being promulgated to 

implement the objectives set forth in 40 CFR 51.308(e) and Part 51, Appendix Y. In particular, EPA has 

discretion to determine if and when a FIP addressing the objectives set forth in Appendix Y should be 

promulgated which necessarily includes discretion to determine the timing for complying with the 

requirements for any such FIP. The same Court recently reiterated that the TAR confers such discretion 

for EPA to act.268

As we have discussed in detail in this RTC, the purpose of this FIP is to protect visibility in Class 

I Federal areas. Congress called for “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.” CAA 169A. In keeping with our commitment to promulgate “such Federal implementation 

plan provisions as are necessary or appropriate to protect air quality” and in furtherance of Congress’s 

stated goal of “the remedying of any existing impairment of visibility in mandatory class I Federal 

areas”, EPA has determined that it is appropriate to promulgate the FIP provisions set forth in this final 

rule at this time. As discussed above, EPA is finalizing its determination that a BART determination for 

NGS is necessary or appropriate because NOx emissions from NGS contribute to visibility impairment at 

11 National Parks and Wilderness Areas (i.e. Class I federal areas). EPA, therefore, believes that it is 

appropriate to require NGS to reduce its NOx emissions in accordance with the BART provisions of the 

Clean Air Act in order to reduce its contribution to visibility impairment in those areas. Thus, absent 

action by EPA, the problem will not be redressed. As a result, it is appropriate for EPA to act at this time 

and EPA is therefore, exercising its “gap-filling” authority in finalizing the FIP provisions set forth in 

this final rule. 

EPA has determined that it is appropriate to limit the scope of the final FIP to the provisions 

specifically identified in this final rule. There are a number of reasons why promulgating this FIP of 

limited scope is appropriate. First, as discussed previously, the owners of NGS are faced with unique 

circumstances. For example, two of the owners of NGS are prohibited from continued long-term 

participation in NGS because of state laws in California and Nevada. Further, because NGS is located on 

the Navajo Nation, upcoming lease and right of way renewals must be approved by the Department of 

Interior, a federal action that triggers a multi-year review under the National Environmental Policy Act. 

Second, as also discussed previously, NGS is of singular importance to numerous Indian tribes located 

in Arizona. For these reasons, EPA has determined that it is appropriate to finalize this FIP to provide 

flexibility to NGS to achieve a greater than 80 percent reduction of current NOx emissions over an 

appropriate timeframe. Our analysis demonstrates that installation of controls to achieve this level of 

266 Arizona Public Service Co. v. EPA, 211 F.3d 1280. 267 Id. 268 WildEarth Guardians v. EPA, No. 1309524, (10th Cir. July 23, 2014) slip op. at p. 25, in the docket for this rulemaking. 
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reduction is cost-effective and would result in significant visibility improvement. We also find that the 

flexible timeframe for installing those controls is appropriate given the unique character of NGS. 

With respect to deadlines in the RHR, it sets forth the requirement for States listed in 40 CFR 

51.300(b)(2) to submit a regional haze SIP by December 17, 2007.269 The regulations also require States 

to submit a long-term strategy for regional haze in 40 CFR 51.308(d)(3). That provision states: “Each 

State listed in 51.300(b)(3) must submit a long-term strategy that addresses regional haze visibility 

impairment for each mandatory Class I Federal area within the State and for each mandatory Class I 

Federal area located outside the State which many be affected by emissions from the State.” The first 

planning period for the long-term strategy is defined based on when States are required to submit 

comprehensive periodic revisions, established in 40 CFR 51.308(f) as July 31, 2018. 40 CFR 51.308(f) 

provides: “Each State identified in § 51.300(b)(3) must revise and submit its regional haze 

implementation plan revision to EPA by July 31, 2018.” However, the Navajo Nation is not a State, does 

not have any mandatory class I Federal areas within its boundaries, is not listed in 40 CFR 51.300(b) and 

based on the TAR is exempt from the SIP submittal deadlines that apply to States. 

EPA, therefore, reasoned in its Supplemental Proposal to approve the TWG Alternative that the 

requirement to submit a long-term strategy does not apply to Navajo Nation or EPA in promulgating a 

Tribal FIP.270 Because the Tribe is not required to submit a long-term strategy for the period December 

2007 to July 2018, the Tribe would not be required to make the showing set forth in 51.308(e)(2)(iii) for 

a better than BART alternative to achieve emissions reductions in 2018. In other words, there is no 

requirement for Tribes to submit a long-term strategy showing that all necessary emission reductions in 

a better than BART alternative took place during the first long-term strategy for regional haze. As 

discussed further in response to comments opposing EPA’s FIP, EPA considers it consistent with the 

TAR and RHR to approve the TWG Alternative with compliance dates in 2019, 2030 and 2044. 

EPA agrees with the comment that approving the TWG Alternative for NGS will not 

compromise the ultimate goal of the CAA regional haze program based on progress toward eliminating 

human caused visibility impairment in Class I areas by 2064.271 Appendix B to the TWG Agreement 

provides that the owner/operator of NGS will be cease conventional coal fired generation in 2044. 

Because the TWG Agreement included the provision for the owner/operator to cease conventional coal 

fired generation in 2044, we are including that provision in the regulatory requirements of the Final 

FIP.272 We anticipate that this means there will little or no visibility-impairing pollutants from 

conventional coal-fired electricity generation emitted from NGS between 2044 and 2064. At its election, 

consistent with the Lease Amendment, the Navajo Nation may continue plant operations at NGS after 

December 22, 2044 consistent with EPA approval. Thus, the Navajo Nation may seek to operate NGS 

after 2044, however, EPA expects that operation of NGS after the owner/operator ceases conventional 

coal-fired generation would involve substantial modification to NGS and NGS would be required to 

meet all applicable regulatory and permitting requirements in existence at that time. Any power 

generating units that may be built to replace NGS will be subject to environmental review, including the 

requirement to comply with the Prevention of Significant Deterioration provisions of the CAA such as 

BACT and a visibility analysis as required by 40 CFR 52.21(p). 

269 40 CFR 51.308(b). 270 See 40 CFR 49.4. 271 See CAA section 169A(1)(a). 272 See 79 FR 12944, 12950 (“While it is true that the Regional Haze Rule and BART Guidelines do not contemplate unit 

retirements as a potential BART option, neither rule prohibits states or EPA from considering a shutdown as part of a BART 

determination if the strategy is proposed by the owner of a BART-eligible source.”) (March 7, 2014). 
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For the period between 2030 and 2044, the TWG Alternative will also have lower emissions than 

NGS would have if it were complying with BART. The effect on visibility at the Class I areas from the 

TWG Alternative’s retirement of the remaining two units in 2044 is discussed in more detail at in 

section 9.0 of this response to comments document.273

EPA agrees with the more detailed comments that EPA has authority under the TAR to 

implement a source-specific FIP requiring BART or a better than BART alternative at NGS, specifically 

pursuant to CAA 301(d)(4) and 40 CFR 49.11. EPA also agrees that our authority to promulgate the FIP 

includes sufficient discretion to approve the TWG Alternative for the reasons discussed in more detail in 

response to comments opposing our legal authority to approve the TWG Alternative EPA agrees that the 

unique considerations that apply to NGS, including but not limited to its partial federal ownership, 

provide in part our justification for allowing the flexible compliance time established in the TWG 

Alternative. 

Comment: General opposition to EPA’s better than BART determinations 

 One environmental advocacy group (0373) stated that EPA may approve an alternative to BART 

only under certain limited circumstances, with the fundamental legal requirement being a demonstration 

that the alternative will “achieve greater reasonable progress toward natural visibility conditions” (citing 

40 CFR 51.308(e)) as supported by the clear weight of evidence (citing 40 CFR 51.308(e)(2)(i)(E)). The 

commenter indicated that there are two ways EPA can make such a demonstration (citing 40 CFR 

51.308(e)(3)): 

 Showing that the distribution of emissions is substantially similar under BART and the 

alternative measure, and that the alternative measure provides greater emissions reductions; or 

 Performing modeling to demonstrate that visibility does not decline in any affected Class I area 

and there is an overall improvement in visibility. 

The commenter added that a BART alternative must ensure that all necessary emission reductions occur 

in the first planning period, which ends in 2018 (citing 40 CFR 51.308(e)(2)(iii)), and that any emission 

reductions resulting from the alternative measure must be surplus to reductions required under other 

provisions of the CAA (citing 40 CFR 51.308(e)(2)(iv)). 

 The commenter (0373) stated that for Alternative 1 (and the TWG Alternative) EPA did not 

demonstrate and cannot demonstrate that the alternatives will achieve greater reasonable progress 

toward natural visibility conditions than BART. The commenter believes that there are multiple flaws 

with EPA’s proposals for each alternative, including improper use of a total NOx cap concept that fails 

to make greater reasonable progress than BART, use of an improper emissions baseline that artificially 

expands the cap for the alternatives only, and a lack of modeling by EPA (or TWG) to demonstrate 

reduced visibility impacts from the alternatives. These objections are discussed further below in 

subsequent comments. The commenter asserted that EPA must reject EPA BART Alternative (and the 

TWG Alternative) as inadequate under the law and not better than BART. 

273 See also 79 FR at 12946 (“Although EPA’s regulations do not require states to consider a fuel switch or a shutdown of an 

existing unit as part of their BART analyses, a state can certainly include such options in its analysis where a company 

voluntarily offers such measures as a strategy for reducing emissions.”) (March 7, 2014). 
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 The commenter (0373) also indicated that EPA’s reliance on the TAR in this instance is 

misplaced. The commenter believes that EPA properly determined under the TAR that BART is 

necessary and appropriate (citing 78 FR 8279) and properly determined that SCR plus LNB/SOFA is 

BART (citing 78 FR 8287-88). According to the commenter, with its BART determination, EPA has set 

the standard against which any alternative must be measured and EPA cannot use the TAR to change 

that. The commenter asserted that with the reasoning presented in the proposal, EPA could use the TAR 

to justify any decision that strays from the law as dictated by Congress, which the commenter 

characterized as “the very definition of arbitrary and capricious.” Further, the commenter contended that 

EPA’s use of the TAR to justify worse air quality for tribes than would otherwise be required is 

particularly dubious, especially in light of EPA’s Environmental Justice obligations under Executive 

Order No. 12,898 (citing 59 FR 7629, February 11, 1994). 

 One individual (0156) asserted that engineering problems at the SRP Santan Generating Station, 

which was reviewed by S&L, cast doubt on the adequacy of TWG Alternative and the work of S&L 

related to NGS. 

Response: 

EPA disagrees with the commenter’s statement that the TWG Alternative fails to demonstrate 

that it will “achieve greater reasonable progress toward natural visibility conditions” as supported by the 

clear weight of evidence. Our terminology that an alternative is “better than BART” is our shorthand 

expression for finding that the TWG Alternative complies with the requirements of 40 CFR 51.308(e)(2) 

and (3), including the requirement that the TWG Alternative will achieve greater reasonable progress 

toward natural visibility conditions.274 EPA has determined that the TWG Alternative complies with this 

requirement because it will result in greater total NOx emissions reductions between 2009 and 2044 than 

the BART Benchmark based on requiring LNB/SOFA and SCR to be installed and operated five years 

after the effective date of a final rule (i.e., 2018 or 2019).275

EPA promulgated its final revisions to 40 CFR 51.308(e) on October 13, 2006. The 2006 final 

rule states: “The regulations finalized today provide that as a general matter, States must undertake 

source specific BART analyses under 51.308(e)(1) for each source subject to BART in order to estimate 

the emissions reductions achievable under the source-by-source BART requirements. The use of such a 

BART benchmark enables a State to design an alternative program that is ‘better than BART’ based on a 

precise estimation of the emissions reductions that could be achieved under BART.”276 In UARG v. 

EPA,277 the D.C. Cir. upheld EPA’s 2005 final rule. Although UARG primarily challenged the second 

prong of the better than BART test promulgated in the 2005 regulations, the court noted: 

“[N]onetheless, the Clean Air Act leaves wide discretion about how the goal [of reasonable progress] is 

to be achieved. Notwithstanding the Act’s discussion of BART in section 169A(b), we have already 

held in CEED that EPA may leave states free to implement BART alternatives so long as those 

alternatives also ensure reasonable progress. 398 F.3d at 660.” 

274 40 CFR 51.308(e)(2) provides: “A State may opt to implement or require participation in an emissions trading program or 

other alternative measure rather than to require sources subject to BART to install, operate, and maintain BART. Such an 

emissions trading program or other alternative measure must achieve greater reasonable progress than would be achieved 

through the installation and operation of BART.” 

275 See 78 FR at 8289-90 (February 5, 2013); 78 FR at 62512-13 (October 22, 2013). 276 71 FR 60612, 60618 (October 13, 2006). 277 UARG v. EPA. 471 F.2d 1333, 
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As discussed above, EPA established a two-prong test for showing the visibility improvement 

factor in a better than BART approach. The first prong of the test in 40 CFR 51.308(e)(3) is: “[i]f the 

distribution of emissions is not substantially different than under BART, and the alternative measure 

results in greater emissions reductions, then the alternative measure may be deemed to achieve greater 

reasonable progress.” Id. The preamble for 40 CFR 51.308(e)(3) specifically refers to the “geographic” 

distribution of emissions. The Preamble stated: “With respect to comments on the degree of difference 

in the geographic distribution of emissions necessary to trigger application of the two prong test, we 

believe it is not necessary for EPA to define that in the rule.”278 The 2005 preamble to finalizing the test 

in 40 CFR 51.308(e)(3) contains two further relevant discussions. First, EPA states: “We also recognize 

that test criteria leave some terms and conditions undefined, and we believe States and Tribes should 

retain the discretion to reasonably interpret and apply these terms as appropriate to the context of the 

particular program.”279 Second, EPA clarified that the test for evaluating ‘reasonable progress’ for a 

better than BART alternative was different than setting reasonable progress goals for Class I areas, 

stating: “The reasonable progress test in the reasonable haze rule remains as a separate test from better 

than BART.”280

Insofar as EPA is promulgating this FIP on behalf of the Tribe, EPA retains discretion to 

interpret and apply ambiguous or undefined terms in 51.308(e). Accordingly, it is appropriate for EPA to 

evaluate the TWG Alternative to determine whether its provisions for retiring capacity and installing 

SCR together achieve a similar geographic distribution of emissions and will result in greater emissions 

reductions than would have occurred if EPA required BART (SCR+LNB/SOFA) at NGS five years 

following the effective date of the final rule 

We interpret the regulations at 40 CFR 51.308(e)(2) and (3) to allow us to approve the TWG 

alternative because it results in greater emissions reductions than the BART Benchmark, with the same 

geographic distribution of emissions because all of the emission reductions for both will be achieved at 

NGS. Nothing more is required. The commenters indicate that the Alternative cannot have a different 

temporal distribution of emissions reductions than the BART Benchmark. However, we have found no 

requirement to have a similar temporal distribution of NOx emissions reductions and the comment has 

not pointed to any such information. Rather, the comment rests on a conclusory statement. 

The comment from EarthJustice, representing Sierra Club among others, appears to argue that 

EPA cannot demonstrate “reasonable progress” by allowing greater emissions reductions at a later date 

than would have occurred under BART.281 Yet, Sierra Club supported a recent Oklahoma SIP BART 

determination, replacing an EPA FIP, which relied on greater yet later emissions reductions.282 There, 

Sierra Club stated: “While benefits to visibility as of January 27, 2017 would be slightly greater under 

the FIP, the advantage is temporary. The FIP scenario may have somewhat greater benefits for several 

years, but the SIP Revision better achieves the overall goals of the Regional Haze program because 

emissions from both units will be completely eliminated by 2026. . . .By 2026 Northeastern’s 

contribution to haze in the regional parks will be zero under the SIP Revision whereas under the FIP 

scenario the plants would continue to contribute to more than 1.5 deciview of impairment (at much 

278 70 FR at 39138 (July 6, 2005). 

279 Id. 280 70 FR at 39138, n . 73. (July 6, 2005) 281 See Comment Letter from EarthJustice, pages 20-21, document number 0367 in the docket for this rule at EPA-R09-

OAR-2013-0009. 

282 See Letter from Elena Saxonhouse, Staff Attorney, Sierra Club, to Guy Donaldson, Chief, Air Planning Section, EPA, 

Region 6 dated September 20, 2013, in the docket for the rule at EPA-R09-OAR-2013-0009. 
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greater cost).”283 Sierra Club also endorsed the SIP revision over the FIP on the basis of emissions alone, 

without requiring or relying on visibility modeling, stating: “Overall the SIP Revision is the less 

polluting option compared to the FIP. DEQ calculates that due to the decreased capacity utilization and 

early shutdown schedule, cumulative SO2 and NOx emissions from Northeastern Units 3 and 4 will 

ultimately amount to only 36% of the emission [sic] that could be emitted under the FIP. See Revised 

BART Determination at 12. This approach is consistent with Congress’s goal of eliminating humancaused haze by 2064, moving Oklahoma toward that goal more quickly than would the FIP.”284

As already discussed in part above, EPA disagrees that the TWG Alternative must ensure that all 

necessary emission reductions occur in the first long-term strategy planning period, which ends in 2018, 

citing 40 CFR 51.308(e)(2)(iii). EPA’s reasoning on this issue is grounded in the TAR. As discussed 

above, the TAR was proposed in 1994 (59 FR 43956) and finalized in 1998 (63 FR 7254, codified at 40 

CFR Part 49). In promulgating the TAR, EPA carried out our authority in CAA sections 301(a) and 

301(d)(4) to allow Tribes to implement reasonably severable provisions of the CAA. The TAR generally 

exempted Tribes from the CAA submittal deadlines that applied to States. EPA interprets the 

requirement in 40 CFR 51.308(e)(2)(iii) to constitute a reasonably severable RHR submittal deadline 

that applies to States but not to Tribes. If the alternative measure is promulgated by the State, it must 

“submit[s] an implementation plan containing the following plan elements and include[s] documentation 

for all required analyses: . . . (iii) A requirement that all necessary emission reductions take place during 

the period of the first long-term strategy for regional haze.” Therefore, it is a required “plan element” for 

a State-only required implementation plan submittal. See 40 CFR 51.308(b)(3)(requirements for States 

to submit long-term strategies). 

EPA’s 1999 RHR included a discussion of the final rule’s implementation in Indian country. 

The Preamble notes: 

Section 301(d)(4) of the CAA confers discretionary authority on EPA to 

provide, through regulation, alternative means to ensure air quality 

protection in cases where it determines that treating tribes as ‘identical’ to 

States would be inappropriate. Accordingly, in promulgating the TAR, 

EPA provided flexibility to tribes seeking to implement the CAA. . . .For 

example, unlike States, tribes are not required by the TAR to adopt and 

implement CAA plans or programs, thus tribes are not subject to 

mandatory deadlines for submittal of implementation plans. As discussed 

in the preamble section identified above, EPA believes that it generally 

would not be reasonable to impose the same types of deadlines on tribes as 

on States.285

Because it is not mandatory for the Tribe to submit a long-term strategy at any particular time, there is 

no mandatory requirement for the Tribe to ensure that all emissions reductions from a better than BART 

alternative occur within some deadline. 

This result is equitable as well as reasonable. As we stated in our Supplemental Proposal: 

The regulations provide that an Alternative to BART must ensure that all 

necessary emission reductions occur within the period of the first long283 Id., p. 4. 284 Id. at p. 5. 285 64 FR at 35758. (July 1, 1999). See also Dine CARE v. EPA, in the docket for this rule at EPA-R09-OAR-2013-0009. 
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term strategy for regional haze (i.e., by 2018) for States that were required 

to submit regional haze SIPs in December 2007. 40 CFR 51.308(e)(2)(iii). 

Thus, if states had submitted timely regional haze SIPs in 2007 with 

BART compliance deadlines in 2012, the RHR would have provided over 

five additional years for the implementation of Alternatives to BART.286

In contrast, the TAR exempted the Tribe from submitting a BART TIP on any mandatory deadline. It 

would be inequitable to penalize the source seeking to comply with a better than BART alternative by 

requiring compliance in 4 years or less. In summary, EPA interprets this provision of the RHR 

regulations, 40 CFR 51.308(e)(2)(iii) to impose a requirement for a submittal deadline that does not 

apply to Tribes.287

EPA’s 2006 final rule also included a consideration of Tribal issues. In response to a comment, 

the 2006 final rule noted: “The EPA agrees that regulatory activities such as BART determinations and 

the development of trading programs are not by any means trivial and would be difficult to perform or 

participate in with the small staffs and limited resources typical of many nascent Tribal air programs.”288

EPA then stated: “Also, EPA is committed to fulfilling its responsibility to implement CAA provisions 

in Indian country as necessary and appropriate, in consultation with any affected Tribes.”289 The 

comments and responses in the 2006 final rule demonstrate that EPA anticipated implementing the RHR 

provisions through the discretion established in the TAR. 

 The commenter also asserted that “EPA claimed that the economic issues justified the delay in 

installation of BART” and that “EPA is incorrect in concluding, in reliance on the NREL report, that the 

installation of SCR at NGS is not economical.”290 We disagree with the commenter’s characterization of 

our proposals. First, we note that in our Proposed Rule, we did not propose a delay in the installation of 

BART. We proposed that BART was an emission limit of 0.055 lb/MMBtu with a compliance date 

within five years of the effective date of the final rule. The additional time for compliance we proposed 

applied to better than BART Alternatives. We also disagree that we stated that SCR at NGS was not 

economical, and that we relied on the NREL report to make that conclusion. In our Proposed Rule, we 

conducted our own Affordability Analysis (distinct from the NREL analysis) and concluded that 

“[b]ased on our analyses, the 25-year NPV of costs to produce power at NGS with SCR installed and 

operated on all units should be below the market prices of wholesale power.”291 In other words, we 

concluded, based on our analyses, that installation and operation of SCR+LNB/SOFA at NGS is more 

economical than closing NGS and purchasing an equivalent amount of power from the wholesale 

market. In our Proposed Rule, we highlighted the critical importance of time and timing and considered 

“the potential economic impacts to argue for thoughtful consideration of how flexibility in the 

compliance timeframe can be provided consistent with the air quality goals of the Clean Air Act.”292

286 78 FR at 62513 (October 22, 2013). 287 See 64 FR at 35758. (July 1, 1999). 288 71 FR at 60627 (October 13, 2006). 

289 Id. 290 See page 23 of the EarthJustice comment letter (0367). 

291 See Proposed Rule at 78 FR at 8284. 

292 Id. We stated “EPA understands the timing of regulatory compliance is an important consideration” and that “EPA in 

conjunction with DOI and DOE, have committed to work together on several short- and long-term goals, including 

innovative clean energy options for electricity generation and seeking funding to cover expenses for the federal portion of 

pollution control at NGS However, it is not clear at this time whether or what type of mechanisms might be available to 

lessen increased costs.” 
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In summary, EPA is determining that the TWG Alternative is better than BART based on 

achieving greater NOx emissions reductions, based on a similar geographic distribution, within the date 

of the goal specified in section 169A of achieving natural conditions in 2064. Given the enforceable 

requirement for the owner/operator to cease conventional coal-fired generation at NGS in 2044, and 

with emissions in 2030 – 2044 being less than the BART Benchmark, the TWG Alternative satisfies the 

requirements of the RHR as applied based on the TAR. 

Comment: BART Alternatives would interfere with 2018 RP in other states 

 One environmental advocacy group (0373) stated delaying the compliance date for BART will 

allow NGS to continue emitting pollutants in excess of the levels modeled by the WRAP. According to 

the commenter, this level of emissions will interfere with the regional haze plans in three states 

(Arizona, Utah, and Colorado), likely negatively affecting their ability to meet their reasonable progress 

goals for 2018. 

Response: 

The issue raised by the commenter is outside the scope of our rulemaking addressing the NOX

BART requirements for NGS. Although 40 CFR 51.308(d)(3) requires states to submit long-term 

strategies that are sufficient to ensure that the state has included all measures needed to achieve its share 

of emission reductions agreed to through the regional planning process, the Navajo Nation has not yet 

submitted a long-term regional haze strategy. In addition, EPA has not yet found it necessary or 

appropriate to address these requirements through a FIP. If EPA determines it is necessary or 

appropriate to do so, we will take appropriate action. 

Meanwhile, we note that for NGS, the WRAP assumed that NOX emissions in 2018 would equal 

10,611 tons per year. NOX emissions under the TWG Alternative, in turn, will range from approximately 

13,000 to 15,000 tons per year following the closure of one unit (or equivalent curtailment) at the end of 

2019. We also note that the closure of one unit (or equivalent curtailment) by the end of 2019 would 

reduce not only NOX, but also emissions of SO2. Given the overall changes in emissions from the 

various regional haze actions since the WRAP made its projections, we will be better able to assess the 

need, if any, for further action once Arizona, Utah, and Colorado have prepared regional haze SIPs for 

the second planning period. 

Comment: EPA’s BART Alternative (Alternative 1) is not flexible enough 

 The operator of the Kayenta Mine (0384), who opposes EPA’s determination that SCR is BART 

for NGS, stated that Alternative 1 to delay installation of SCR on all three units a NGS a few years 

postpones but does not diminish or eliminate the serious risk of closure with all the resulting economic 

problems for Arizona and its residents. The commenter indicated that the problem with this alternative 

remains the conclusion that SCR is BART despite the prior installation of LNB/SOFA. The CAP 

operator (0343) opposed Alternative 1 (and the NOx BART proposal), arguing that the proposed NOx

emission rate cannot be achieved, that timing issues for the NGS owners prevent installation in the 

required timeframes, and that the commenter would face financing challenges. One of the owners of 

NGS (0314) stated that although Alternative 1 provides a measure of compliance flexibility, the 

timelines for installation of additional controls are problematic and could threaten the future viability of 

the plant. 
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Response:

 In our Proposed Rule, EPA proposed Alternative 1 that required compliance with the proposed 

BART limits on one unit per year over 2021 to 2023. EPA also stated in our Proposed Rule that “to the 

extent there may be interest in additional flexibility beyond the 2021-2023 compliance schedule under 

Alternative 1, EPA has evaluated two additional compliance schedules, using the “better than BART” 

analysis framework above, to evaluate additional time for compliance.”293 Generally, EPA stated that 

additional time for compliance beyond 2021-2023 would be viable only if the owners of NGS achieved 

additional reductions to bridge the emission reduction deficit caused by delayed compliance. EPA 

invited suggestions for other alternatives that reduce NOx emissions at NGS and its contribution to 

visibility impairment while providing long-term, sustainable benefits to tribes. As a result of this 

invitation, a group of diverse stakeholders formed the Technical Work Group and submitted the TWG 

Alternative to EPA for consideration. EPA published a Supplemental Proposal based on the TWG 

Alternative and is taking final action to approve the TWG Alternative as better than BART. EPA is not 

taking action to finalize Alternative 1. 

Comment: Opposition to BART benchmark based on total emissions 

 One environmental advocacy group (0373) stated that EPA’s use of total emissions as a 

benchmark to determine whether an alternative is “better than BART” is legally indefensible. The 

commenter indicated that under Alternative 1 (and TWG Alternative) EPA does not assess the actual 

impacts on visibility and the potential for improvement in Class I areas (which are the stated goal and 

obligations of the CAA) but rather projects how much total NOx pollution might be emitted by NGS 

between now and an “arbitrary” date of 2044. The commenter noted that neither EPA nor TWG have 

performed visibility modeling on any proposed alternative, and asserted that the absence of this 

“critical” modeling data makes it challenging or impossible to understand the impact of Alternative 1 

(and TWG Alternative) on affected Class I areas. According to the commenter, EPA failed to 

demonstrate that the distribution of emissions is the same under BART and has not and cannot show that 

either alternative (but especially the TWG Alternative) will result in greater emissions reductions than 

EPA’s BART determination. The commenter also contended that EPA has also made no showing, and 

cannot without modeling, that either alternative will result in greater visibility improvement to the 11 

Class I areas affected by NGS pollution than will BART, either overall, but most particularly by the first 

haze implementation period, 2018 (citing 40 CFR 51.308(d)(1)(i)(B) and 51.308(f); the Stamper report). 

 The commenter (0373) believes that by comparing only the total NOx emissions from over the 

entire 2009-2044 period, EPA is acquiescing to decades of unacceptable and unlawful visibility 

impairment at Class I areas. The commenter stated that nothing in EPA’s NOx cap framework requires 

any meaningful incremental progress during this period, let alone the “reasonable progress” required by 

the CAA and haze regulations. The commenter contended that Alternative 1 clearly defines 3 to 6 years 

of additional pollution and visibility impairment, with the EPA acquiescing to significantly reduced 

visibility between 2018 (which the commenter defines as “as expeditiously as possible” and therefore 

when BART is legally required at NGS) and 2023, when the last of the NGS units is required to install 

SCR. The commenter added that it a “particularly insidious” effect of the NOx cap approach is that the 

longer it takes to develop the final rule, the higher the NOx cap gets, potentially delaying SCR 

installation necessary to meet the expanded cap. 

293 See 78 FR at 8290 (February 5, 2013). 
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 The commenter (0373) stated that this approach is the opposite of reasonable progress and does 

little to ensure that natural visibility will be restored in this century. The commenter asserted that EPA 

cannot and should not allow visibility in our national parks to be impaired by the largest pollution source 

in the West until 2044 because the CAA requires improvement with the first check-in on that progress in 

2018. 

 The commenter (0373) added that the CAA is clear that to make the first big step on the way to 

“reasonable progress,” states (and EPA) must impose BART pollutant controls on the largest, most 

damaging sources of pollutants to Class I areas (citing 42 U.S.C. § 7491(b)(2)). The commenter believes 

that reasonable progress is the overarching obligation of the haze requirements; BART is the required 

large first step in getting there. According to the commenter, the NOx cap approach simply skips the 

BART requirement and makes no showing of how those reductions will otherwise occur. 

Response:

This issue is also discussed elsewhere in this response to comments document. EPA disagrees 

that using a cumulative NOx cap as the benchmark for establishing whether an alternative is better than 

BART is legally indefensible. 

To establish the NGS NOx BART benchmark, EPA undertook a detailed examination of the NOx

emissions level that could be achieved with the best available technology.294 EPA established that NOx

BART would be 0.055 lb/MMBtu.295 Next, EPA considered that it was likely NGS would continue to 

operate until the end of its lease period. 296 NGS and Navajo Nation were negotiating a lease that would 

extend NGS’s operations until 2044.297 Therefore, EPA assumed that NGS would not operate after 2044. 

The assumption was entirely reasonable based on the lease and the age of NGS by 2044. In this FIP, as 

discussed in section 9.0 of this response to comments document, EPA is making that date enforceable 

with respect to ending conventional coal fired generation. To continue to operate after that date, NGS 

will need to undergo PSD permitting review which would require installation of BACT. 

EPA then multiplied the average heat input at NGS by the BART emission limit of 0.055 

lb/MMBtu to calculate cumulative NOx emissions over 2009-2044 if NGS installed SCR in 2018 to 

define the BART Benchmark. EPA began the period in 2009 because that is the date that NGS began 

retrofitting the first of three units with LNB/SOFA. EPA also acknowledged that the installation of 

LNB/SOFA in 2009, 2010, and 2011 was voluntary and early compared to when those controls would 

not have been required (in combination with SCR) under BART, i.e., in 2018.298 For that reason, EPA 

calculated the cumulative NOx emissions that were achieved by installing and operating the LNB/SOFA 

early (97,715 tons) and subtracted that amount from the cumulative total emissions from the BART 

294 78 FR at 8279-8280 (February 5, 2013). 

295 Id. 296 Id. at 8285. EPA assumed the remaining useful life of NGS for purposes of calculating the cost of compliance as 20 years. 

78 FR at 8285. The cost of compliance is directed at the useful life the emissions controls rather than the likelihood the 

facility will continue to operate. Id. For calculating the BART cap, EPA used the more realistic date of 2044 for shutting 

down the facility as opposed to the life of the emissions controls. 

297 Id. 298 In our Proposed Rule, we evaluated emissions assuming five years following the final rule effective date would be January 

1, 2018. In our Supplemental Proposal, we anticipated that five years following the final rule effective date would be July 1, 

2019. 
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Alternatives (EPA referred to these emissions as adjusted emissions for the Alternatives).299 Based on 

this framework, EPA proposed Alternative 1 as resulting in greater emission reductions than BART over 

2009-2044, and thus, achieving greater reasonable progress than BART over time. 

The comment criticizes EPA and the TWG for failing to perform visibility modeling. As 

explained above, there is no regulatory requirement for visibility modeling to demonstrate an alternative 

is better than BART if the geographic distribution of emissions is the same as BART and there are 

greater emission reductions. The commenter (0373) contends that EPA’s analysis of the Alternatives to 

BART was inadequate because we “made no showing that the distribution of emissions under either 

alternative is better or even substantially similar to BART”.300 The TWG Alternative is achieving 

greater NOx emission reductions through retiring capacity at NGS and installing SCR at NGS. The 

reductions will have the same geographic distribution as installing SCR+LNB/SOFA on all 3 units at 

NGS. In fact, the Miller/Sahu Report, submitted by the commenter (0373) concedes that the spatial 

distribution of emissions may be the same (that all emissions and reductions come from NGS) but 

specifically argues that the temporal distribution is not the same.301 As discussed above, EPA interprets 

the requirement in 40 CFR 51.308(e)(3) to require the emissions to be of a similar geographic

distribution. There is no requirement for a similar temporal distribution and the commenter has pointed 

to none. However, as discussed in section 9.0, EPA conducted additional visibility modeling for 

purposes of responding to comments. As discussed in section 9.0, the modeling supports EPA’s 

determination that over time, the TWG Alternative would be better than BART. 

The commenter also fails to provide any factual information to support the conclusory statement 

that the TWG Alternative does not result in greater emission reductions than BART. As discussed in a 

subsequent response in this section, the commenter provided misleading comparisons that purport to 

show that expected emissions under Alternative 1 or the TWG Alternative, even in compliance with the 

2009-2044 NOx Cap, are much higher than BART because the commenter has generated its own target 

for what it believes the BART Benchmark should be. The commenter labeled as “BART-1” or “EPA’s 

BART” a case that is not consistent with BART in EPA’s proposals because it excludes consideration of 

the LNB/SOFA credit, and labeled as “CAP-1”, the value that is consistent with EPA’s proposals.302 The 

commenter then included additional changes to the assumptions used in the calculation to generate a 

cumulative emissions value for “BART” that is significantly lower than EPA’s calculation and calls it 

“BART-9” or “Corrected BART”. As discussed in section 8.0, EPA disagrees with the assumptions used 

by the commenter in calculating its benchmark for BART (e.g., the BART emission limit should be 0.04 

lb/MMBtu and compliance should be required in 3.5 years from the final rule). EPA has calculated the 

NOx emissions from BART based on our determination of BART for NGS, including emission limits 

and the need for flexibility for NGS as outlined in our five-factor analysis for NGS. Based on our 

calculations, the TWG Alternative will result in fewer cumulative NOx emissions than BART over 

2009-2044. The 2009-2044 NOx Cap (and the 2009-2029 NOx Cap) ensures that under each applicable 

sub-option under the TWG Alternative (i.e., TWG Alternative A1, A2, A3, or B), NGS will achieve 

emission reductions sufficient to ensure that the TWG Alternative is better than BART over the life of 

the facility. 

299 See Tables 12 and 13 in 78 FR at 8290 (February 5, 2013). 300 See page 20 of the EarthJustice comment letter, document 0367 in the docket for this rule at EPA-R09-OAR-2013-0009. 301 See Miller and Sahu report, page 4 (document 0370 in the docket for this rule). 302 Id., e.g., page 11. EPA finds the “CAP-1” terminology used by the commenter confusing because the acronym CAP is 

already used in our Proposed Rule to refer to the Central Arizona Project. Therefore, Figure 2 of the Miller/Sahu Report is 

especially confusing because it conflates EPA’s proposal with CAP. 
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The commenter asserts that totaling NOx emissions from 2009-2044 allows decades of 

unacceptable and unlawful visibility impairment at Class I areas and that there is no meaningful progress 

as required by the CAA and haze regulations.303 The commenter contended the BART alternatives allow 

significantly reduced visibility between 2018 and 2023 (Alternative 1) or 2030 (TWG Alternative). We 

note that emission reductions achieved under Alternative 1 would be delayed by five years compared to 

BART (not decades). Under the TWG Alternative, emission reductions would occur in phases, 

accounting first for the voluntary reductions achieved beginning in 2009-2011 at NGS, closure of unit or 

curtailment by the end of 2019, and compliance with a limit of 0.07 lb/MMBtu on two units by the end 

of 2030. Thus, annual emissions under the TWG Alternative would be higher than BART for 

approximately one decade (not decades) over 2019 to 2030 (see response to comments in section 9.0). 

However, EPA has determined that the CAA and RHR do not contain any enforceable deadlines in 

2018, 2023 or 2030 with respect to actions taken on behalf of the Tribe in this FIP. EPA has found no 

deadlines in 2023 or 2030 that are relevant to our FIP implementing NOx BART for NGS. EPA notes 

that the TWG Alternative will result in greater annual emission reductions than BART after 2030, and 

particularly after 2044 when the owner/operator of NGS will cease conventional coal-fired generation 

(see section 9.0). EPA has determined that it is better than BART to require NGS to make a significant 

emission reduction in 2019, followed by additional significant reductions in 2030 and ceasing 

conventional coal fired generation in 2044. 

Comment: EPA overestimated the BART Benchmark 

 Aside from its assertions that an approach using a BART Benchmark based on total emissions is 

not lawful under the CAA (as discussed above), one environmental advocacy group (0373) stated that 

EPA’s assumptions in calculating a numerical value for the BART Benchmark include errors and 

improper credits. 

 EPA’s credit for the early installation of LNB/SOFA runs counter to the Regional Haze Rule, 

EPA’s longstanding policies, and EPA’s specific statements regarding the haze determination for 

NGS (citing the Stamper report; 64 FR 35714, 35728, July 1, 1999; 40 CFR part 51, Appendix 

Y, section IV.D.4.d.). EPA explicitly warned the operator of NGS when it submitted its 

application to install LNB/SOFA that the early installation of this technology would not affect 

EPA’s BART determination, and the operator agreed in a settlement with the Grand Canyon 

Trust that installation of this technology would not prejudice in any way the implementation of 

more effective NOx and PM controls under the reasonable attribution and regional haze programs 

(citing 78 FR 8284-25). Despite these explicit agreements and the need for timely compliance 

with BART, the EPA has shifted course and now proposes to delay additional controls at NGS 

on the basis of the LNB/SOFA credit. EPA’s claimed reliance on “early” LNB/SOFA is 

misplaced and without foundation in the facts or law. 

 EPA’s proposal to delay BART due to the LNB/SOFA credit creates a dangerous precedent that 

threatens to significantly undermine the regional haze program. Although EPA stated that the use 

of a uniform baseline from 2001 to 2003 is important for consistency in the national haze 

program (citing 64 FR 35728 as an example),304 under EPA’s reasoning for NGS, aging facilities 

303 See EarthJustice comment letter at page 20. 304 The commenter added that the Eight Circuit Court of Appeals decision in North Dakota v. EPA, 730 F.3d 750, 62-64 (8th 

Cir. 2013) does not dictate a different result because in that case EPA simply asserted it need not consider existing pollution

controls at all, a proposition the court disagreed with, while here, EPA properly warned the NGS operator that it could not 
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can avoid installing BART controls for many years by installing minimal, inexpensive, and 

plainly inadequate pollution controls as soon as EPA begins its BART determination. 

 EPA made a number of errors in its calculations that all have the effect of artificially inflating the 

BART Benchmark. 

o EPA significantly underestimated how well SCR as BART will perform at NGS (citing 

the comments summarized in section 8.1 and the Stamper report). Because SCR can and 

will achieve greater NOx reductions than estimated by EPA, the total BART Benchmark 

should be corrected downward to reflect the true capabilities of SCR. 

o EPA should use updated emissions data, annual emission rates rather than 30-day rates, 

heat input from the baseline period, and a shortened timeline for the installation of SCR. 

Each of these corrections to EPA’s calculations reduces the total NOx emissions 

associated with the EPA’s SCR as BART calculations, and accordingly reduces the 

BART Benchmark (citing the Miller/Sahu report). 

o All told, assuming rule finalization by July 1, 2014, the corrections above reduce the 

estimated emissions under BART during EPA’s chosen timeframe (2009-2044) by nearly 

100,000 tons, a reduction of approximately 26 percent (citing the Miller/Sahu report). 

o In addition, EPA should use actual, current heat input data and should incorporate a 

shortened timeline for the installation of LNB/SOFA. Incorporating these corrections as 

well serves to lower the BART Benchmark by more than 120,000 tons (citing the 

Miller/Sahu report). 

On this basis, the commenter asserted that if EPA persists in using the emission cap framework (which 

the commenter believes is never appropriate for assessing whether an alternative is better than BART), 

EPA must correct the NOx cap to prevent alternatives from being compared to an artificially inflated 

estimate of total NOx emissions. 

 Another public interest advocacy group (0413) similarly commented that EPA’s credit 

calculations are not clear and are not well justified, which the commenter said will further delay 

cleaning up NGS. The commenter cited the following from the Synapse report: 

EPA justifies this delay as “better than BART” by arbitrarily tilting the 

scales in favor of the new alternative. It does so by double-counting the 

benefits of the installation of low-NOx burners at NGS in 2009-2011. If 

NGS had waited until 2018 to install low-NOx burners, as it perhaps could 

have under prevailing regulations, then cumulative NOx emissions from 

2009 through 2018 would have been about 100,000 tons higher. To 

calculate emissions under its alternative proposal, EPA first calculates 

cumulative emissions under the alternative, including the benefits of early 

installation of low-NOx burners. These emissions are higher than under the 

original BART proposal. EPA then gives NGS roughly 100,000 tons of 

emissions credit for the “early and voluntary” installation of low-NOx

burners, despite the fact that it has already counted this emission reduction 

once. Stripped of double counting, EPA’s own numbers show that, in 

avoid a full BART determination by quickly installing minimal and inadequate pollutant controls and EPA properly included 

existing controls when considering various cost components of BART—a more proper, source-specific place for 

consideration of existing controls. 
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reality, this allegedly “better than BART” alternative will result in an 

increase of more than 50,000 tons in cumulative NOx emissions from NGS 

over the period of 2009-2044. This means more pollution for the 

communities living around the NGS plant, and more haze throughout the 

region. 

Response: 

 EPA disagrees with the assertion that we are delaying BART. As stated elsewhere in this 

response to comments document, as well as in our Proposed Rule and Supplemental Proposal, EPA did 

not propose to “delay BART.”305 EPA proposed to provide additional flexibility in the compliance 

timeframe for Alternatives to BART.306

 The commenter (0373) also asserts that our proposal to credit NGS for the early installation of 

LNB/SOFA runs counter to the Regional Haze Rule, EPA’s long-standing policies, and EPA’s specific 

statements in our BART determination for NGS. The commenter states that “EPA’s claimed reliance on 

“early” LNB/SOFA as an excuse to avoid or delay what is legally required is misplaced and without 

foundation in the facts or law.”307 The commenter cites three sources to support its assertion, (1) page 18 

of the Stamper Report, which was commissioned by the commenter, (2) page 35,728 of the July 1, 1999 

Regional Haze Rule, and (3) section IV.D.4.d of the BART Guidelines.308 EPA disagrees with these 

assertions. 

First, the commenter’s use of quotation marks around the word “early” implies that the 

LNB/SOFA modifications were not, as a factual matter, installed early. However, EPA notes that in 

2008, when the operator of NGS began discussions with EPA regarding the permitting requirements 

associated with the significant increase in CO emissions that would result from the installation of 

LNB/SOFA, EPA had already begun our process for evaluating BART for NGS, but had not yet 

proposed a BART determination or put forth our ANPR. Therefore, no requirement existed that 

mandated the installation of LNB/SOFA at NGS. In addition, the operator of NGS was aware that a 

BART determination, that would likely involve, but may not be limited to LNB/SOFA, was 

forthcoming. As noted in our Proposed Rule, the operator of NGS could have waited until the 

compliance date for BART to initiate reductions in NOx emissions, however, the operator elected in 

2008 to seek the necessary permit to install LNB/SOFA on one unit per year over 2009-2011.309 Thus, 

because the LNB/SOFA modifications were made in 2009-2011, NOx emissions from NGS declined 

from a high of over 35,000 tons in 2002 to less than 20,000 tons after 2011.310 Although some of the 

305 We also note that the commenter (0373) incorrectly summarized our BART determination in their letter dated January 3, 

2014. On page 9 of their comment letter, EarthJustice stated “EPA applied the BART five-factor test set forth in the CAA 

and EPA regulation and as a result, finds that SCR, in combination with Low NOx Burners/Separated Overfire Air 

(“LNB/SOFA”) can achieve 0.05 lb/MMBtu with an emission limit of 0.07-0.08 lb/MMBtu on a 30-day rolling average. 78 

Fed. Reg. at 8280.” We note that this citation actually refers to EPA’s characterization of SRP’s position of what the most 

stringent BART option can achieve (not EPA’s position). On the same page, EPA stated our position, i.e., “EPA is proposing 

to determine that Units 1-3 can meet an emission limit of 0.055 lb/MMBtu.” 

306 See 78 FR at 8288, column 1, describing our proposed BART determination. See also 78 FR at 8289, section titled “Legal 

Rationale for Extending Compliance Schedule for Alternative Measures for NGS.” 307 See page 22 of the EarthJustice letter (0367). 308 See page 21 of the EarthJustice Comment letter, dated January 3, 2104. See document 0367 in the docket for this rule at 

EPA-R09-OAR-2013-0009. 

309 See Proposed Rule at 78 FR at 8289 (February 5, 2013). 310 See summary of annual emission date from AMPD, reproduced in the tab titled “CAMD emissions” in the document titled 

“2014_0311 Better than BART Alternatives for Final Rule.xlsx” in the docket for this rule. In 2011, NGS emitted 19,900 

tons of NOx, in 2012, NGS emitted nearly 16,500 tons of NOx and in 2013, nearly 17,500 tons of NOx. 
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decline in total NOx emissions can be attributed to a decrease in capacity utilization (i.e., decline in heat 

input of approximately 13 percent when comparing 2002 to 2013), the dominant contributor to the 

decline in NOx emissions from NGS was from the installation of LNB/SOFA over 2009-2011. EPA 

considers these emission reductions to be real reductions that were not required (i.e., voluntary and 

surplus) and were achieved in advance of any actual requirement to reduce emissions (i.e., early). 

In addition, each of the three citations provided by the commenter do not support its assertions 

that our proposal to credit NGS for the early installation of LNB/SOFA runs counter to the Regional 

Haze Rule or EPA’s long-standing policies. These three citations merely address the appropriate 

baseline period to use in the five-factor BART analysis. Page 18 of the Stamper Report supports our use 

of 2001-2003 as the baseline period for our BART determination for NGS and cites to 64 FR at 35,728 

of the July 1, 1999 Regional Haze Rule that discusses EPA’s determination that the most appropriate 

baseline period would be over the 2001 to 2004 timeframe. The baseline period is used for evaluating 

the costs and visibility benefits of controls. The Stamper Report also cites to Section IV.D.4.d of the 

BART Guidelines at 40 CFR Part 51 Appendix Y, that states baseline emissions should represent a 

realistic depiction of anticipated emissions for the source, in general, based on actual emissions from a 

baseline period. 

The commenter’s reliance on these citations is misplaced. None of these citations from the 

commenter address or support the commenter’s assertions that our proposed LNB/SOFA credit is 

inconsistent with the RHR or EPA’s long-standing policies. Consistent with the commenter’s citations to 

the RHR and “EPA’s long-standing policies”, EPA used a baseline period of 2001-2003 (prior to the 

installation of LNB/SOFA) in our BART analysis for NGS.311 We used this baseline period for 

determining the cost-effectiveness of controls as well as the anticipated visibility benefits of controls. 

Based on our analysis, using the 2001-2003 baseline period, EPA determined that that an emission limit 

achievable with SCR+LNB/SOFA is BART for NGS. The commenter does not dispute this BART 

determination.312

The commenter also cited to the discussion in our proposed rule under Factor 3, where we 

described, in 2008, how the early installation of LNB/SOFA would not prejudice the implementation of 

more effective controls for BART. As stated previously, we did not apply the LNB/SOFA credit to our 

determination of BART for NGS. The commenter characterizes the credit for early installation of 

LNB/SOFA as a shift in course from the agreements and understandings established in 2008 during the 

PSD permit process for the installation of LNB/SOFA. EPA disagrees with this assertion. As stated in 

our proposed rule, citing to the Ambient Air Quality Impact Report from the 2008 Proposed PSD 

Permit, EPA stated that the early installation of LNB/SOFA systems would not affect the baselines for 

cost or visibility improvements, and therefore will not influence EPA’s determination of the NOx

reductions required for BART.313 EPA’s BART analysis for NGS was consistent with this statement. As 

previously noted, EPA used the 2001-2003 period as the baseline for determining cost-effectiveness and 

311 The commenter even stated earlier in its comment letter that “[i]t should be noted that EPA used a proper NOx emissions 

baseline with determining BART in this case. In accordance with its own regulations and guidelines, EPA properly 

considered NGS NOx emissions from the time period of 2001-2003 for its analysis. (citation omitted) This baseline does not 

include the “voluntary” installation of the LNB/SOFA at a later date.” See footnote 27 on page 11 of the comment letter from 

EarthJustice, dated January 3, 2104. 

312 See page 11 of the comment letter from EarthJustice, dated January 3, 2014, section III., titled “EPA correctly identified 

the installation of SCR plus LNB/SOFA as BART for control of NOx emissions for all NGS units.” 313 See 78 FR at 8284 (February 5, 2013). 
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visibility benefits of controls, and determined, based on our analysis of all five factors, that 

SCR+LNB/SOFA is BART for NGS. 

The commenter relies on EPA’s statements about the appropriate baseline period to support an 

assertion that in a BART analysis, EPA should not give consideration or credit for controls installed 

after the baseline period.314 As stated elsewhere in this response to comments document (section 5.0), 

although we appropriately acknowledged the installation of LNB/SOFA after the baseline period at NGS 

under Factor 3 (existing controls at the facility), our analysis of cost-effectiveness and anticipated 

visibility benefits appropriately compared SCR+LNB/SOFA against the 2001-2003 baseline period.315

We further note that although the CAA requires consideration of existing pollution controls at the 

sources in the five-factor BART analysis, the BART Guidelines provide little guidance on how to 

consider existing controls.316 Thus, the BART Guidelines, like the CAA, are clear that existing controls 

must be considered, but do not specify what or how this consideration must be conducted. 

EPA’s proposed credit for early installation of LNB/SOFA was not associated with our five 

factor analysis or BART determination for NGS. Rather, EPA discussed the LNB/SOFA credit in our 

framework for evaluating alternatives to BART. Specifically, in discussing our framework for BART 

Alternatives, EPA calculated the cumulative NOx reductions achieved early because the operator of 

NGS elected to install LNB/SOFA on one unit per year over 2009-2011, instead of waiting for the 

compliance period for BART. In our Proposed Rule and Supplemental Proposal we used this value, the 

LNB/SOFA credit, when comparing BART Alternatives to BART. As discussed elsewhere in this 

response to comments document, EPA’s proposal to allow BART Alternatives to take credit for the 

early installation of LNB/SOFA at NGS is a reasonable use of our discretion under the TAR.317

EPA disagrees that this credit creates a dangerous precedent that threatens to significantly 

undermine the regional haze program. EPA notes that part of our rationale for the better than BART 

framework for NGS (including the credit for the early installation of LNB/SOFA and the extended 

compliance timeframe for BART Alternatives) was the potential impacts to numerous tribes that rely on 

NGS and/or CAP, as well as the TAR and EPA’s regulations that SIP submittal deadlines that apply to 

states do not apply to Tribes (or to EPA when implementing FIPs in Indian country). EPA notes that the 

only other BART-eligible source in Indian country is the Four Corners Power Plant. EPA has already 

completed the BART determination and FIP for this facility.318

 The commenter (0373) further argues that EPA overestimated the BART Benchmark and NOx

Cap. The commenter asserts that EPA’s BART Benchmark from our Proposed Rule was too high based 

on the following assertions: (1) SCR can achieve greater NOx reductions than assumed by EPA; (2) EPA 

314 Although the commenters assert that EPA should not give credit to NGS for their early reductions, the commenters do not 

hesitate to take credit for those reductions in their calculation of what total emissions under the BART scenario should be 

when they assert that EPA considered a “the made up scenario in which LNB/SOFA have not already been installed at NGS.” 

See page 25 of the EarthJustice comment letter. Thus, on one hand, the commenters argue that EPA cannot consider the early 

emission reductions that occurred after the baseline period, and on the other hand, the commenters count those early emission 

reductions that occurred after the baseline period in their calculation of total emissions under BART. 315 We note that in State of North Dakota v. EPA, the U.S. Court of Appeals for the Eighth Circuit vacated and remanded 

EPA’s promulgation of a FIP for Coal Creek Station because EPA did not consider the existing pollution control technologies 

in use at Coal Creek Station that were voluntarily installed after the baseline period. This document is included in the docket

for this rule. 

316 See Final BART Guidelines at 70 FR at 39163 and 39166 (July 5, 2005). The BART Guidelines includes statements about 

considering ways to improve existing controls. 

317 See 78 FR at 62511. 318 See 77 FR 51620 (August 24, 2012). 
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should have used updated emission data; (3) EPA should have used annual average emission rates rather 

than 30-day average emission rates; (4) EPA should have used heat input values from the baseline 

period; (5) EPA should have set a compliance date within 3.5 years. 

 As discussed in Section 8.1 of this response to comments document, EPA disagrees that BART 

at NGS should be an emission limit of 0.040 lb/MMBtu and that compliance with BART should be 

required in 3.5 years. EPA is setting a BART Benchmark based on our determination that NGS can meet 

a limit of 0.055 lb/MMBtu within five years of the effective date of the final rule. Therefore, EPA is not 

revising the BART Benchmark or NOx Cap to assume a limit of 0.040 lb/MMBtu or a shorter 

compliance time for BART. 

 The commenter also argues that EPA should use updated emission data, noting that the analysis 

of BART and BART Alternatives that EPA included in the docket for the proposed rulemaking cited 

actual emissions and heat input data until 2011, and also noted a minor discrepancy in the values we 

cited for 2011 and the values the commenter pulled from the AMPD. Although EPA’s proposed BART 

determination was signed in January 2013 and published in the FR in February 2013, EPA likely 

developed our analysis at a time when 2011 was the most recent full year of data available. Our revised 

analysis for this final rulemaking includes 2012 and 2013 AMPD data.319 We note that because the 

commenter asserts that NGS should not receive credit for the early installation of LNB/SOFA, the 

commenter represented the emissions associated with “EPA BART” based on actual emissions observed 

over 2009-2012 (and emissions over 2012-2019 assuming an emission rate of 0.24 lb/MMBtu, 

accounting for the early installation of LNB/SOFA) in lieu of EPA’s method of calculating emissions 

over 2009-2019 that would have been emitted if LNB/SOFA and SCR were installed concurrently five 

years following the effective date of our final BART determination. Therefore, although our worksheets 

now include actual data for 2012 and 2013, these values for actual emissions are reflected in our 

emission estimates for the TWG Alternatives, and not for the BART Benchmark or NOx Cap. EPA notes 

that the minor discrepancy found by the commenter in 2011 shows that EPA’s annual NOx emissions 

and heat input in 2011 were lower than those reported by the commenter. EPA reported a value of 

19,837 tons in 2011 with a total heat input of 180,463,627 MMBtu. The commenter reported a value of 

19,840 tons in 2011 and a heat input of 180,490,683 MMBtu. Thus, EPA’s values are approximately 

0.015 percent smaller than those reported by the commenter. EPA is not revising the 2011 values 

because the revision would result in a de minimus change. 

 In addition, the commenter recommends that EPA use average heat input over the baseline 

period (i.e., over 2001-2003) rather than the average over the pre-LNB/SOFA time period (i.e., average 

over 2001-2008) to calculate future emissions. The commenter notes that our calculations for costeffectiveness use baseline heat input over 2001-2003 to calculate pre- and post-control emissions 

(approximately 5,264 tons per year). The commenter asserts that this inconsistency is arbitrary. The 

commenter correctly notes that EPA used the average heat input over 2001-2008 (the pre-LNB/SOFA 

time period) to estimate emissions over 2009-2019 that would have occurred if the operator of NGS had 

not installed LNB/SOFA early, and emissions over 2019 to 2044 under BART (5,345 tons per year). 

The average heat input over the baseline period of 2001-2003 was 191,505,266 MMBtu, while the 

average heat input over 2001-2008 was 194,373,910 MMBtu. This is a difference of about 1.5 percent. 

EPA agrees that use of the same 2001-2003 baseline heat input value for estimating pre- and postcontrol emission rates is appropriate and consistent with the RHR and BART Guidelines, particularly in 

light of the goal of understanding the effect of a given control technology on emissions (i.e., assume 

319 See 2014_0311 Better than BART Alternatives for Final Rule.xlsx in the docket for this rule at EPA-R09-OAR-2013-

0009. 
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identical values for baseline and future heat input to isolate the impact of control technologies). 

However, this approach does not mean that an average from the three-year baseline period (2001-2003) 

is most appropriate for estimating future emissions in determining a benchmark for BART. EPA notes 

that the use of average heat input for 2001-2008 includes the baseline period recommended by the 

commenters and provides a larger data set, and therefore, a more robust average value for estimating 

future emissions. EPA considers the use of an average value based on three years to be less robust than 

an average value based on eight years of data for representing potential future operation, therefore, EPA 

is retaining our use of the average heat input over 2001-2008 for estimating emissions over 2009-2044. 

EPA further notes that emission caps in permit requirements are typically established based on the 

facility’s potential to emit (PTE) and would thus be calculated using maximum heat input values. The 

highest observed annual heat input value was 199,398,687 MMBtu and, if used in the NOx cap, would 

result in a significantly higher BART Benchmark. 

 The commenter also argues that in calculating the NOx cap, EPA should use a value that reflects 

an annual average for post-control emission rates rather than a rate based on a 30-day average limit of 

0.055 lb/MMBtu. The commenter reviewed daily data from 2000 to 2013 and calculated the ratio of the 

maximum 30-day average rate to the annual rate for each year and determined an average ratio of 1.135. 

Based on this ratio, the commenter recommended that the BART emission limit of 0.055 lb/MMBtu (on 

a rolling average of 30 boiler operating days) be reduced by a factor of 1.135 as an estimate of what the 

annual average post-control emission rate would be at NGS (i.e., 0.048 lb/MMBtu). EPA agrees that 

generally, emission rates averaged over an annual basis are lower than emission rates averaged over a 

30-day basis. However, EPA did not propose setting a BART limit for NGS on an annual average basis 

and EPA did not receive any comments suggesting that we do so. Without an enforceable annual limit, 

EPA considers it inappropriate to assume a lower emission rate in our calculation of the NOx Cap. We 

note that the BART Guidelines require that BART limits for EGUs be set on a rolling average of 30 

boiler operating days. Therefore, although the BART Guidelines would not preclude establishing 

multiple emission limits over different averaging periods, the BART Guidelines do not require it. 

 Separately, the commenter also asserts that EPA overestimated the 2009-2044 NOx Cap. The 

commenter represents EPA’s NOx Cap as the scenario it calls “CAP-1” with a value of 494,899 tons. 

This value is consistent with the 2009-2044 NOx Cap EPA proposed in our Supplemental Proposal.320

The commenter asserts that this value is overestimated because (1) actual heat input data should be used 

to calculate the NOx Cap; and (2) the LNB/SOFA could be installed in two years.321 EPA disagrees with 

these assertions. 

 The commenter argues that for the period of 2009-2013, actual heat input data should be used to 

calculate the NOx Cap instead of the average heat input value over 2001-2008. EPA acknowledges that 

actual heat input data is available for the 2009-2013 period, however, EPA considers using the average 

value to be appropriate, recognizing that years of lower than average capacity utilization will be 

balanced with years of higher than average capacity utilization at NGS. The commenter also asserts that 

LNB/SOFA could have been required on a different (earlier) compliance timeframe than installation of 

SCR and that this idea should have been incorporated in our calculation of the NOx Cap. We note that 

we are setting our BART Benchmark as proposed, as a limit of 0.055 lb/MMBtu within five years of the 

effective date of the final rule, achievable with SCR+LNB/SOFA. EPA is not aware of any BART 

determination that required combustion controls on a different schedule than post-combustion controls. 

Although the commenter asserts that LNB/SOFA was installed in under three years (over 2009-2011), 

320 See Table 3 of our Supplemental Proposal at 78 FR at 62516 (October 22, 2013). 321 See Table 3 of the Miller and Sahu Report. 
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EPA notes that the operator began the permitting process in 2008. Based on the permitting requirements 

for both combustion and post-combustion controls, EPA does not consider it practicable to assume the 

LNB/SOFA would or could have been permitted and installed on a separate track from the SCR. 

Although the commenter makes assertions related to purported overestimations of the BART 

Benchmark and the NOx Cap separately (i.e., in sections III and IV of the Miller/Sahu Report), the 

commenter combines all of the assertions together to argue that the 2009-2044 NOx Cap should be 

373,029 tons (121,870 tons, or 25 percent, lower than EPA’s proposed 2009-2044 NOx Cap of 494,899 

tons). As outline above, EPA disagrees than any of the purported corrections suggested by the 

commenter are necessary or appropriate for projecting annual emissions to calculate the 2009-2044 NOx

Cap. 

 Another commenter (0413) asserted that EPA double-counted benefits of the early installation of 

LNB/SOFA, stating that EPA calculates cumulative emissions for the BART alternatives including the 

benefits of early reductions, then subsequently applies a LNB/SOFA credit again to BART alternatives. 

EPA disagrees with the assertion that we double counted emission reductions associated with the early 

installation of LNB/SOFA. 

In our February 5, 2013 Proposed Rule, EPA calculated the value of the LNB/SOFA credit based 

on the difference between total emissions under the BART scenario where LNB/SOFA is installed 

concurrently with SCR and the actual scenario when LNB/SOFA was installed early. The value of this 

credit was then applied to total emissions over 2009-2044 under Alternative 1. 322 Although Alternative 

1 does assume actual emissions with early installation of LNB/SOFA, and thus applying the LNB/SOFA 

credit to the BART Alternative may appear to be double counting, it is not double counting because the 

BART Alternatives were compared against a BART Benchmark that similarly assumed actual emissions 

with early installation of LNB/SOFA. Thus, both the BART Benchmark and Alternative 1 were 

calculated the same way (actual emissions accounting for early LNB/SOFA installation), and the 

LNB/SOFA credit was only applied to Alternative 1. An example of double counting would have been if 

EPA had applied the LNB/SOFA credit to Alternative 1 and then compared that value to total emissions 

under BART assuming LNB/SOFA and SCR were installed concurrently. 

 In our October 22, 2013 Supplemental Proposal, EPA approached the calculation from a 

different, but equivalent perspective. The new calculation approach was used because it was more 

intuitive to apply and understand in the context of an enforceable cap in NOx emissions. In the 

Supplemental Proposal, the BART Benchmark was established as the total emissions over 2009-2044 

that would have occurred if LNB/SOFA and SCR were installed concurrently, five years following the 

effective date of the final rule. Total emissions under BART Alternatives were then calculated using 

actual emissions beginning in 2009 (i.e., accounting for the early installation of LNB/SOFA) and 

projections for future emissions. Thus, in the methodology used in the Supplemental Proposal, the 

LNB/SOFA credit was applied to the BART Benchmark and NOx Cap, rather than to the TWG 

Alternative. This method is equivalent to the one used in the February 5, 2013 proposal but does not 

give the appearance of double counting. In our Supplemental Proposal and supporting documents, EPA 

included calculations to show that these two methods are equivalent.323 The two methods are equivalent 

because what matters in the “better than BART” context is the difference between total emissions under 

BART and total emissions under the BART Alternative. Whether the LNB/SOFA credit is applied to 

322 See document titled “EPA Analysis of BART Alternative.xlsx” in document 0004 in the docket for the rule at EPA-R09-

OAR-2013-0009. 

323 See Table 2 of the Supplemental Proposal (78 FR at 62515, October 22, 2013) and document titled “Supplemental Better 

than BART Alterntives.xlsx” at EPA-R09-OAR-2013-0009-0191. 
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BART or BART Alternatives will affect the absolute value of a total (e.g., using the numbers in Table 2 

of the Supplemental Proposal, the LNB/SOFA credit represents a difference of 377,008 tons or 480,489 

tons), but it does not affect the difference between BART and BART Alternatives. The method used in 

the Supplemental Proposal is more intuitive because BART and the BART Benchmark reflect total 

emissions over 2009-2044 that would have occurred if LNB/SOFA were installed concurrently with 

SCR, and the BART Alternatives reflect actual emissions without further credit or modification. 

Because no credits or modifications are made to actual emissions under the BART Alternatives, this 

method is the more logical accounting methodology for determining compliance with the 2009-2044 

NOx cap. 

 As explained above, EPA disagrees with the assertions that we double-counted or overestimated 

the BART Benchmark and NOx Cap. EPA is taking final action to approve the TWG Alternative with 

the 2009-2044 NOx Cap and 2009-2029 NOx Cap as proposed. 

8.6 Additional Alternatives to BART 

Comment: Alternative Recommendations to Proposal - Solar Power 

One public interest advocacy group (0407) representing the Black Mesa Trust proposed an 

alternative approach to reduce emissions from NGS. The commenter presented an alternative approach 

titled “Crossroad: A Framework to Transition Navajo Generating Station Toward Cleaner Energy 

Generating Station by 2025” that it feels is the best long-term solution for NGS. The commenter 

suggested that alternative power be phased-in at NGS and that one coal generator be decommissioned by 

2019 and replaced with a combined cycle solar/gas unit. This would reduce GHG emissions, coal 

mining and water use from Lake Powell by one-third. Under this alternative approach, the second coal 

generator would be replaced by gas-solar or hydropower by 2024. In the commenter’s opinion, a 

mixture of solar, hydro power and natural or methane gas would be the best option, which would limit 

damages to the environment, cultural resources, health, and global warming. The commenter proposed 

that gas already available from the Southern Ute Indian Tribe could easily be made accessible to NGS 

and natural gas would serve as a bridge until the time when NGS could be powered solely by renewable 

energy. 

 The commenter (0407) proposed that a 1,000 MW solar farm be developed on Hopi and Navajo 

lands; a project that would create 2,500 construction jobs. Further, the commenter proposed that a new 

500 KV transmission line be created, alongside the existing Arizona Public Service 500 KV El Dorado 

Transmission Line, and dedicate the new line to transport solar energy from the proposed solar fields to 

markets in Arizona, California and Nevada, creating additional jobs. In addition, the 100-acre Hopi 

Winslow Industrial facility could be converted into a solar equipment manufacturing and/or storage 

facility, the commenter proposed. This would lead to the development of even more jobs and a 

substantial economic boost to the small community of Winslow. As the last element to the commenter’s 

proposal, it suggested that a Colorado Plateau Clean Energy Initiative be set up to serve as a research 

and development part of Hopi and Navaho, with the goal being a collaborative effort to look at various 

ways energy can be developed using tribal natural resources and training the younger generation how to 

manage resources in the future. 

 The commenter (0407) acknowledged that the proposed objective would represent a substantial 

effort, but that if Hopi and Navajo legislators grant conditional support to move forward, the commenter 

was certain that seed money would be made available from Navajo and Coconino County Board of 
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Supervisors and Southern California Edison (SCE). The commenter noted that SCE has set aside funds 

from the sale of SO2 credit for Hopi and Navajo to develop renewable energy projects on tribal lands. 

With conditional support from Hopi and Navajo legislators, the commenter foresees obtaining long-term 
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funding from DOI, DOE, EPA, the State of Arizona, owners of NGS, Central Arizona Water 

Conservation District, and non-profit foundations. 

 The commenter (0407) stated that this approach would end the destructive strip mining of coal 

on Black Mesa, a sacred homeland of Hopi people, thereby preserving waters stored in ancient aquifers 

for many future generations of Hopi and Navajo children. The commenter asserted that this approach, 

unlike EPA and TWG proposals, is not a piecemeal approach, but will end pollution and save the federal 

government millions of dollars to prepare rules to reduce mercury, carbon dioxide emissions, and other 

pollutants. The commenter added that this approach would guarantee the DOI legal commitment to 

Arizona tribes that are party to the 2004 Arizona Water Settlement and would significantly increase 

employment for Hopi and Navajo people and revenues to continue to support Hopi and Navajo 

governments. The commenter concluded by stating that if the alternative approach it proposed in its 

comments is not accepted by the EPA, that the original requirement, which proposed to require SCR 

within 5 years be finalized. 

One public interest advocacy group (0356) who opposes both BART Alternatives, offered 

another solution involving solar power. The commenter indicated that NRG Energy is able to repower 

NGS with renewable energy and replace fossil fuel dependency. According to the commenter, NRG 

Yield and SunPower recently began operations at California Valley Solar Ranch (CVSR), a 250 MW 

capacity plant, and the plant will sell its electricity to Pacific Gas & Electric under two long-term power 

purchase agreements (PPAs). However, the commenter indicated that PPAs can be modified to 

incentivize utility providers to sell their energy to California, which adopted the California Renewables 

Portfolio Standard (RPS), one of the most ambitious renewable energy standards in the country 

requiring investor-owned utilities, electric service providers, and community choice aggregators to 

increase procurement from eligible renewable energy resources to 33 percent of total procurement by 

2020. The commenter stated that the Navajo Nation, the State of Arizona, and Nevada need to adopt a 

similar Assembly Bill 32: Global Warming Solutions Act. The commenter cited key language from the 

bill describing steps to be taken to achieving reductions in GHG emissions. The commenter stated that 

government and private owned utilities must get out of the business of exploiting people, land, water and 

air for profit, and begin to develop the NRG model in Phoenix and Tucson; including other states like 

Nevada, for everyone who depend on NGS energy and to be weaned from Navajo and Hopi resources. 

The commenter provided further information in its comments with details on NRG Solar implementing 

renewable energy applications as an example that the commenter indicated could be followed to 

transition NGS away from using coal. The information provided by the commenter describes the CVSR 

plant, its capacity and capabilities, jobs created by constructing CVSR, the economic development the 

plant has provided for the local economy, and to whom CVSR currently delivers power. The commenter 

provided additional information describing NRG Energy, NRG Yield, SunPower, and NRG Safe Harbor 

Disclosure, and provided contact information for NRG Energy and SunPower at the conclusion of its 

comments. 

One individual (0025/0156) recommended solar energy to replace NGS. One commenter (420) 

submitted a copy of a recommendation from the Northern Navajo Agency Council for just transition of 

NGS. 

Response: 

 EPA agrees that numerous options exist to produce electricity in a manner that results in lower 

emissions of air pollutants and smaller impacts to the environment and local communities. EPA 

recognizes that numerous stakeholders are interested in the production of cleaner energy and continued 
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development of the economies of the Navajo Nation and Hopi Tribe. However, we note that the purpose 

of the BART requirement under provisions of 169A of the CAA is to protect visibility by requiring 

existing stationary sources of a certain size and age to install the “best available retrofit technology” to 

reduce emissions of visibility-impairing pollutants. This requirement does not require fuel-switching, or 

a redefinition of the source, nor does it give EPA authority to require replacement of existing electric 

generating units with alternative sources of energy generation. We further note that under the TWG 

Agreement, DOI has committed to, among other things, facilitate the development of clean energy 

resources.324

Comment: Invest in Renewable Energy 

One public interest advocacy group (0413) urged Federal agencies to invest in renewable energy 

for CAP power. The commenter referred to the Synapse report and said that if one unit shuts down in 

2019, 1,500 MW of renewable energy can create the same number of jobs and opportunities. Therefore, 

incentives must be provided to tribal nations tied to NGS to encourage renewable energy, in the 

commenter’s opinion. The commenter said that the government must apply the same dedication it did in 

1969 to build and own NGS, to tribal renewable energy projects now. The commenter cited a 2013 

survey conducted by Colorado College, which indicated that 74 percent of Arizona voters chose solar as 

their first or second choice for power while 43 percent of the voters chose wind, 20 percent chose 

natural gas, and 6 percent chose coal as their energy source. 

Response: 

As noted above, EPA recognizes that numerous stakeholders are interested in the production of 

cleaner energy and continued development of the economies of the Navajo Nation and Hopi Tribe. 

However, we note that the purpose of the BART requirement under provisions of 169A of the CAA is to 

protect visibility by requiring stationary sources of a certain size and age to install BART to reduce 

emissions of visibility-impairing pollutants. This requirement does not require fuel-switching, or a 

redefinition of the source, nor does it give EPA authority to require replacement of existing electric 

generating units with alternative sources of energy generation. We further note that under the TWG 

324 See 78 FR 62512 (October 22, 2013) and references therein. 
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Agreement, DOI has committed to, among other things, facilitate the development of clean energy 

resources.325

Comment: Boiler tube cleaning to reduce emissions 

 One industry/commerce commenter (0190) recommended his company’s system to remove slag 

from the boiler tubes during NGS operation and reduce subsequent slag formation on the tubes. The 

commenter believes that this will improve boiler efficiency and reduce the amount of coal that must be 

combusted to produce a given amount of energy, thereby reducing emissions. 

Response:

 EPA notes that a BART determination represents a NOx emission limit with which each unit at 

NGS must comply. EPA does not specify what technology must be used to meet the emission limit. The 

operator has the discretion to implement the most reasonable and cost-effective strategy or strategies 

available to comply with the applicable emission limits under BART. 

Comment: Other emission reduction technologies 

 One commenter (0244) provided information on CEFCO emission reduction technology, which 

the commenter believes provides superior emissions control. Another commenter (0447) provided 

information on a PhotoBioReactor (PBR) technology to reduce emissions while growing algae to 

convert to biofuels. 

Response: 

As noted above, EPA notes that a BART determination represents a NOx emission limit with 

which each unit at NGS must comply. EPA does not specify what technology must be used to meet the 

emission limit. The operator has the discretion to implement the most reasonable and cost-effective 

strategy or strategies available to comply with the applicable emission limits under BART. 

Comment: Convert to natural gas and “condensing flue gas heat recovery” 

 One industry/commerce commenter (0057) noted that the United States is has a great deal of 

natural gas. The commenter stated that EPA is forcing the oldest and dirties power plants to be shut 

down for environmental and health reasons, adding that this would be a perfect time to rebuild these 

power plants to natural gas in these same locations since electricity is still required in America and the 

infrastructure is already in place. The commenter added that the efficiency of natural gas combustion 

can be maximized through “condensing flue gas heat recovery” and suggested that it would be ideal to 

put algae ponds on the land around these power plants where coal dust and ash have been placed for 50 

years or more. The commenter believes that the algae ponds could be kept at optimal warm temperatures 

with the recoverable exhaust heat available from these power plants, and the exhaust gases would 

provide CO2 which would enhance algae grown and be converted to oxygen by the algae. The 

commenter indicated that the water lost to evaporation from the ponds could be made up by condensing 

325 Id. 
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the water vapor from the exhaust stream, and that the algae grown in the ponds could be harvested and 

processed into biofuels and other products. The commenter believes that jobs would be created in every 

step in this process. 

Response:

EPA notes that a BART determination is an emission limit and not a requirement to install a 

specific technology. The facility must comply with the emission limit within the required timeframe, and 

the operator of NGS may consider this, or any other technology, in developing its plan to costeffectively comply with BART. As stated elsewhere in this response to comments document, EPA does 

not have authority through BART to redefine a source to require a coal-fired power plant to convert to 

renewable energy or other fuel sources. 

Comment: Suggested BART Alternative from CAP NIA Users: New controls should not be required 

until after 2030

 One commenter (0305) presented a table purporting to show EPA’s calculations of the NOx caps 

that would apply for a range of potential BART emission limits: 0.055, 0.06, 0.07, and 0.15 lb/MMBtu. 

According to the commenter, the NOx cap that would apply under limits of 0.06 and 0.07 lb/MMBtu 

would exceed the Supplemental Proposal’s NOx CAP by only 2.5 and 7.5 percent, respectively. The 

commenter asserted that these differences would have imperceptible impacts on visibility and that, 

therefore, the use of the NOx cap based on a limit of 0.055 lb/MMBtu unduly constrained TWG’s 

Alternative A and resulted in an unwarranted requirement to install SCR on two NGS units by 2030, 

which would impose inequitable compliance costs on agricultural water users. The commenter stated 

that a NOx cap based on a BART limit of 0.06 or 0.07 lb/MMBtu would be very similar to the proposed 

cap, but would provide enough of an incremental increase to provide a minimum of 3 years of additional 

compliance flexibility for the installation of SCR on two NGS units. 

 The same commenter (0305) also stated that even using a limit of 0.055 lb/MMBtu to establish 

the NOx CAP, with the NOx cap at the level in the Supplemental Proposal, TWG Alternative A contains 

unused “headroom” that renders the operation of SCR by 2030 unnecessary. According to the 

commenter, TWG Alternative A has the effect of forcing NOx emissions to a level that is at least 33,000 

tons below the NOx cap, which the commenter believes makes the requirement to install and operate 

SCR by 2030 is artificially stringent and unnecessary, and therefore arbitrary and capricious. The 

commenter indicated that the headroom under TWG Alternative A1 would yield more than 6 years of 

additional compliance flexibility for the operation of SCR, and TWG Alternatives A2 and A3 would 

yield more than 3 years. The commenter concluded that EPA should revise the TWG Alternatives to 

provide the maximum amount of compliance flexibility for installation of SCR on NGS so as to not 

unnecessarily impose costs on agricultural water users. 

 The commenter (0305) did not address NOx emissions under TWG Alternative B because that 

compliance approach would require the involvement of the new third parties buying into NGS and could 

entail a wide range of possible compliance scenarios. However, the commenter asserted that to the 

extent Alternative A is revised, Alternative B should be revised as well to ensure continued equivalency 

with TWG Alternative A. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

The commenter (0305) presented the following scenarios that it categorized as better-than-BART 

alternatives that would comply with a NOx cap derived from emission limits of 0.055, 0.060, 0.070, and 

0.15 lb/MMBtu. The commenter described the scenarios as follows: 

 Scenario 1, based on a 0.055 lb/MMBtu limit, would have SCR become operational on two NGS 

units by July 2032 and June 2033. 

 Scenarios 2 and 3, based on a 0.06 and 0.07 lb/MMBtu emission limit, respectively, would have 

SCR become operational on two NGS units by 2034 or 2035.

 Scenario 4, based on a 0.15 lb/MMBtu emission limit (consistent with SNCR), would be such 

that shutdown or curtailment of a single unit at NGS would maintain emissions at a level far 

below the NOx cap. NGS’ early and voluntary installation of LNB/SOFA controls, combined 

with either the shutdown or curtailment by 561 MW of a unit by July 2019, would be sufficient 

to control total NOx emissions such that neither SNCR nor SCR controls would be necessary to 

meet the NOx cap.

Without specifically repeating the comments above, an association of CAP water distributors (0398) 

urged EPA to address what the commenter believes are flaws in the EPA’s NOx cap determination. The 

commenter also urged EPA to use the identified headroom to extend the compliance date to 2033 or 

beyond, and to adopt the Supplemental Proposal as modified to account for the delay justified by this 

headroom. 

Response:

 EPA disagrees with the assertion that new controls should not be required until after 2030. As 

stated previously, the TWG Agreement was a negotiated agreement, submitted to EPA, representing 

diverse interests. EPA evaluated Appendix B to the TWG Agreement to determine whether it was 

consistent with our framework for better than BART Alternatives. Thus, although a few commenters 

may believe that the timeframes for compliance in the TWG Alternative are too stringent, the TWG 

Alternative is consistent with our proposed framework and our final BART determination, and it is 

based on a level of control that the operator and owners of NGS, as well as CAP, two tribes and two 

environmental organizations, have determined is acceptable. 

 As stated elsewhere in this response to comments document, we disagree with the assertion that 

BART for NGS is an emission limited associated with SNCR (0.15 lb/MMBtu) or a higher limit 

associated with SCR (0.06 or 0.07 lb/MMBtu). Therefore, the additional time for compliance suggested 

by the commenters using higher BART Benchmarks or NOx Caps are not appropriate. The commenters 

further assert that under their scenario 1, based on a BART limit of 0.055 lb/MMBtu, NGS could 

comply with a limit of 0.07 lb/MMBtu in 2032 and 2033 and still maintain total emissions below the 

2009-2044 NOx Cap. EPA disagrees with commenters that the “unused headroom” warrants additional 

time to comply with the limit of 0.07 lb/MMBtu. The emission estimates that EPA presented in our 

Supplemental Proposal for the TWG Alternative involved projecting future emissions to 2044 based on 

average heat input at NGS over 2001-2008. Heat input in the future is expected to be variable and could 

possibly remain higher than average over an extended period of time, significantly affecting the total 

flexibility or compliance margin. EPA’s analysis was provided simply to assess whether operation 

consistent with requirements under each TWG Alternative (A1-A3) could reasonably be determined to 

maintain emissions below the 2009-2044 NOx Cap and were not intended to represent actual year-byyear emissions in the future. Thus, the “unused headroom” is theoretical and could be smaller or larger 

than cited by the commenters. As stated previously, the TWG Alternative requires a level of control that 

the operator and owners of NGS, CAWCD, as well as two tribes and two environmental organizations, 
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have determined is acceptable EPA has determined that the TWG Alternative is consistent with our 

framework for “better than BART” Alternatives as well as the CAA and RHR. 

Comment: Suggested BART Alternative – Earthjustice 

 One environmental advocacy group (0373) expressed support for examining a BART alternative 

that accounts for the possibility that some of the owners of NGS may choose to sell or retire their 

ownership interest no later than 2019, provided that the alternative produces visibility outcomes that are 

actually and demonstrably better than BART. The commenter (citing the Miller/Sahu report) suggested 

an alternative that includes (1) an enforceable requirement that one NGS unit shut down by 2020 and (2) 

an enforceable requirement that the remaining two units install SCR and meet a NOx emission limit of 

0.065 lb/MMBtu by the beginning of 2020. The commenter recognized that other alternatives may exist, 

but asserted that for any alternative to comply with the minimum legal requirements, it must produce 

better visibility outcomes in Class I areas than BART and demonstrate that it does through the use of 

visibility modeling. 

 The commenter (0373) indicated that its suggested BART alternative is based on the actual 

modeling conducted on the TWG Alternative, and that the suggested modifications to the TWG 

Alternative lead to visibility outcomes that are better than BART. The commenter included a table and 

graph from the Miller/Sahu report that are purported to illustrate this assertion. According to the 

commenter, if the NGS owners elect to retire a single unit, as seems likely, it allows that unit to operate 

through 2019 without additional pollution controls, and the other two units can delay installation of SCR 

until the end of 2019. While 2 additional years is less additional time to install SCR than EPA or TWG 

proposed, the commenter believes that it would allow the current round of lease negotiations to conclude 

before installation is necessary, and the new lease negotiations could take place against the backdrop of 

certainty as to when SCR would be required. The commenter noted that this illustrates one possible 

alternative that is in fact better than BART and welcomed additional creative possibilities. 

Response:

The comment supports a different better than BART alternative which would consist of shutting 

down one unit at NGS by 2020 with installation of SCR on the remaining 2 units also by 2020. The 

commenter also asserts that any better than BART alternative must demonstrate better visibility results 

at Class I areas through modeling. 

EPA disagrees with both of these comments. CAA section 169A and the RHR set out a process 

for EPA to determine BART. EPA is required to consider and balance five factors. BART is not the 

same as BACT, where we are evaluating the lowest emission limit that can be achieved when a new 

source is being constructed. For the statutory and regulatory provisions at issue in this rulemaking, EPA 

is constrained by its consideration of the five BART factors. After we proposed NOx BART for NGS, a 

diverse stakeholder group submitted Appendix B to the TWG Alternative containing recommended 

provisions for a better than BART alternative. Appendix B was not submitted to EPA as a menu of 

options to choose. It was submitted as a complete alternative. EPA does not have the authority to require 

subject to BART units to shutdown. EPA can, however, consider a unit’s closure as part of a BART or a 

better than BART analysis “where a company voluntarily offers such measures as a strategy for 

reducing emissions.”326 Appendix B of the TWG Alternative includes options to voluntarily shutdown or 

326 79 FR 12944 at 12946 (March 7, 2014) 
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curtail operations at one unit at NGS in 2019. The TWG Alternative also included installation of SCR on 

the remaining units in 2030, not 2020. 

EPA does not consider it necessary to require one unit at NGS to shutdown or curtail operations 

by 2020 and also to require installation of SCR at that time. Appendix B to the TWG Agreement as it 

was submitted to EPA results in greater NOx emissions reductions than the BART determination we 

proposed in February 2013. Because the TWG Alternative, which is consistent with Appendix B to the 

TWG Agreement, results in greater NOx emissions reductions from 2009 – 2044, and significantly better 

NOx emissions reductions from 2044 – 2064, EPA is exercising our discretion to finalize our approval of 

it. The commenter relies on the modeling analysis provided in the Miller/Sahu report to support its 

assertion that shutting down one unit by 2020 and installing controls on the remaining units in 2020 will 

provide better visibility improvement. EPA has provided the reasons we disagree with the values used in 

the Miller/Sahu report in responses elsewhere in this document. 
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9.0 Comments on the TWG Alternative and EPA’s Supplemental 

Proposal 

Comment: Support for Supplemental Proposal of TWG Alternative 

 Many individuals (0145, 0146, 0147, 0148, 0161, 0165, 0167, 0168, 0193, 0200, 0203, 0205, 

0206, 0208, 0209, 0211, 0212, 0222, 0224, 0226, 0230, 0231, 0232, 0243, 0247, 0264.4, 0265, 0273, 

0272, 0298, 0307, 0308, 0310, 0329, 0330, 0335, 0382, 0392, 0437), government commenters (0017, 

0159, 0223, 0239, 0258, 0287, 0289, 0297, 0300, 0320, 0324, 0332, 0406, 0411, 0443), tribal 

governments (0316, 0317, 0340, 0387), local government commenters (0176, 0189, 0199, 0201, 0207, 

0213, 0256, 0263, 0280, 0293, 0295, 0296, 0328, 0383), public/private coalitions (0381, 0400), 

chambers of commerce (0188, 0282, 0304), the owners of NGS (0314, 0315, 0348), the operator of CAP 

(0343), the operator of the Kayenta Mine (0384), and industry and industry trade associations (0274, 

0278, 0306, 0338) urged EPA to approve the TWG Alternative. Most of these commenters specifically 

stated that the TWG Alternative is a fair compromise created by a diverse group of stakeholders that 

achieves greater NOx reductions than EPA’s proposed rule. These commenters believe that the 

Supplemental Proposal will provide a path for future operation at NGS and serves the interest of CAP 

water users by reducing and delaying SCR installation and operation expenditures. Furthermore, many 

of these commenters opined that the TWG Alternative is consistent with the TWG Agreement, which 

will allow for further economic development and the development of renewable energy projects that 

could benefit Native American tribes and the people of Arizona. Two CAP water distributors (0194, 

0214) an association of CAP water distributors (0252), and an industry/commerce commenter (0416) 

made many of the same points. Although supporting the TWG Alternative, one commenter (0264.4) 

encouraged Arizona to incorporate alternative energy sources, which the commenter believes is essential 

to ensuring reliable and affordable water and power in the future, as well as being in the best interest of 

our national security. Some commenters also noted that the TWG Alternative was consistent with the 

federal trust responsibility to Indian tribes, would honor existing water settlement agreements, and 

mitigate economic harm to Indian and non-Indian communities without adding to the federal deficit by 

imposing additional costs on taxpayers. 

 Two commenters (0395, 0411) also noted that the TWG Alternative would reduce an array of 

pollutants from NGS by one-third, including GHG, toxic metals, and other pollutants that are 

detrimental to human health such as PM and SO2. The commenter (0411) also noted that if 

implemented, the TWG Alternative would decrease the amount of water needed at NGS and the Kayenta 

coal mine. One commenter (0395) noted that it is supportive of the TWG Alternative because, over its 

life, it is projected to achieve greater overall visibility improvement because one generating unit at NGS 

is expected to be retired or curtailed by the end of 2019. The commenter opined that these multipollutant reductions would not occur under EPA’s BART proposal. The commenter stated that it 

strongly supports TWG Alternative A, which in total reduces NOx emissions by 16,000 tons more than 

the proposed BART or Alternative 1, will reduce SO2 emissions by 1,600 tpy, or as much as 33,000 tons 

on a cumulative basis, and direct PM by 1,000 tpy, or 24,000 tons cumulatively. The commenter 

emphasized the importance of considering the benefits in protecting public health from emissions of 

direct particulates and SO2, as well as protecting visibility by reducing emissions of these pollutants, in 

EPA’s decision-making process. The commenter lastly noted that TWG Alternative A would also 

achieve a direct reduction in CO2 emissions by about 7 million tpy or cumulatively 166 million tons. 

Further commitments made by the DOI as part of the TWG Agreement will lead to additional CO2

reductions by 11 million metric tons between 2015 and 2035, the commenter said. In the commenter’s 

opinion, these measures will provide human health, welfare and environmental benefits beyond those of 
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the proposed BART or Alternative 1. The commenter said that EPA should conduct a comparative 

emission reduction benefit analysis and present the findings of that analysis in the final rule. 

The Navajo Nation (0316) opined that the TWG Agreement is very important to the Navajo 

Nation because it provides significant benefits from the Federal government in assisting with future lowemitting energy projects on the Navajo Nation and is least likely to result in adverse impacts on the 

Navajo Nation. The Ak-Chin Indian Community (0387) noted that it receives it entire water supply 

through the CAP system and holds a substantial stake in ensuring that the impact of the regulation will 

maintain the viability of CAP. The Ak-Chin opined on the federal trust responsibility to Indian Tribes 

and noted that the federal government is therefore responsible for guaranteeing tribal water entitlement. 

The commenter further noted that the Ak-Chin Indian Community was also excluded from participation 

in the development of the TWG Agreement, and indicated that it understands the concerns expressed by 

the Hopi Tribe and other tribes that were excluded, about conditions related to the proposed better than 

BART Alternative. However, the commenter supports the TWG Alternative and urged EPA to finalize 

the rule as soon as possible. 

The Gila River Indian Community (0317) recommended that EPA finalize the TWG Alternative 

because it is best available option that will allow NGS to continue to produce power and ensure the 

rights of CAP water recipients. The commenter disagreed with EPA’s statements in the Supplemental 

Proposal that EPA would not respond to comments received on other elements of the TWG Agreement 

other than the Appendix B to the TWG Agreement. The commenter stated that the Agency must take 

into account the other elements of the TWG Agreement required by Federal regulations when 

determining BART. For example, the commenter indicated that the TWG Agreement contains several 

elements related to clean energy commitments by the United States that is a positive impact on the 

environment and of economic benefit to Indian Tribes and the area around NGS. The commenter asserts 

that these benefits would only occur if the TWG Alternative is finalized. The commenter specified the 

following positive environmental impacts: 

 The DOI will commit to reduce the CO2 associated with the energy used to pump CAP water by 

3 percent annually for a total of 11.3 million metric tons to be achieved at NGS or through 

qualifying low-emitting clean energy projects no later than December 31, 2035. 

 To advance clean energy economic development that benefits the Indian tribes affected by NGS, 

DOI will facilitate the development of Clean Energy Projects at a pace and scope to achieve 80 

percent Clean Energy by 2035 for the U.S. share in NGS by securing approximately 26,975,000 

MWh of Clean Energy Projects. 

 DOI will identify, prioritize, and further low emitting energy projects to benefit affected tribes, 

such as a 33 MW solar facility proposed by the Gila River Indian Community and local, 

community based and large-scale renewable energy projects within the Navajo Nation and the 

Hopi Tribe. 

 DOI will commit to carry out the NREL Phase 2 Study to analyze options for the future of NGS, 

including identifying options for replacing the federal share of energy from NGS with low

emitting energy resources. 

Although the Tohono O’odham Nation (0340) indicated that it supports the TWG Alternative, it 

strenuously objects to how the working group was formed and operated. The commenter’s concerns are 

discussed in more detail in section 10.0. In addition, the commenter expressed concerns over the lack of 

specificity around the number of commitments by the DOI under the TWG Agreement. The commenter 

opined that there are areas of the TWG Agreement that are unknown, specifically how the DOI 

commitments will be funded and what the impact of these commitments will be on the LCRBDF and on 
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the Tohono O’odham Nation’s Cooperative Fund, and if expenditure of funds from the Reclamation 

Water Settlement Fund, as proposed, is consistent with the authorization in that statute. 

Response: 

 EPA recognizes that numerous commenters supported the Appendix B to the TWG Agreement 

and EPA’s proposal of the TWG Alternative in our Supplemental Proposal. Specific comments on the 

exclusion of numerous stakeholders from participating in the TWG were included in more detail 

elsewhere in sections 9 and 10 of the response to comments document. EPA agrees with commenters 

that the closure or curtailment of one unit, associated with the TWG Alternative, will result in other 

environmental benefits than just NOx reductions. As noted by commenters, emissions of other 

pollutants, including SO2, PM, CO2, and hazardous air pollutants would be reduced by approximately 

one-third. EPA recognizes that under the TWG Agreement, DOI made several additional commitments, 

not directly related to BART, that benefit tribes and the environment. Although EPA recognizes these 

benefits, because EPA was not party to the TWG Agreement, not a signatory of the TWG Agreement, 

and not directly involved in DOI’s commitments under the TWG Agreement, EPA is not the appropriate 

agency to address comments or other concerns related to aspects of the DOI’s commitments that are not 

contained within Appendix B of the TWG Agreement. 

Comment: Opposition to TWG Alternative because it is premised on SCR as BART 

A CAP agricultural water users group (0305) argued that the NOx emission cap used for the 

TWG Alternative is unduly and arbitrarily stringent because it is based on a BART limit of 0.055 

lb/MMBtu, which the commenter believes is too stringent (as discussed elsewhere in this document) 

because (1) EPA should not have determined that SCR is BART and (2) even if SCR were the 

appropriate basis for BART, 0.055 lb/MMBtu is not achievable. According to the commenter, the TWG 

Alternative would unnecessarily and unfairly impose high costs on agricultural water users to pay for 

SCR technology that will not be required to be in service until after the agricultural water users are no 

longer getting the benefit of NGS power. The commenter stated that because Arizona agricultural users 

will phase out their use of CAP Ag Pool water by December 2030 pursuant to the Arizona Water 

Settlements Act (AWSA), capital costs that are collected in advance of SCR operation will be imposed 

on Arizona agricultural water users in exchange for no benefit. The commenter asserted that if EPA 

finalizes either of the “better than BART” Alternatives without modification, it would be arbitrarily and 

capriciously apportioning compliance costs to agricultural water users for which they are not 

responsible. Given EPA's acknowledgment of the compliance flexibility that exists with respect to FIPs 

under the TAR, and with respect to the NGS specifically, the commenter believes that the failure to 

consider potential “better than BART” Alternatives that would afford compliance flexibility to all NGS 

stakeholders on an evenhanded basis constitutes an abuse of discretion on the part of EPA. 

Response: 

 EPA disagrees with the assertion that the TWG Alternative is unduly and arbitrarily stringent 

because it is based on a BART limit of 0.055 lb/MMBtu. EPA addressed comments related to the BART 

limit in section 8.1 of this response to comments document. We note that the TWG Alternative is 

consistent with Appendix B to the TWG Agreement, which was developed among six diverse 

stakeholders, including SRP, the operator of NGS on behalf of itself and other co-owners, and the 

Central Arizona Water Conservation District. Although both entities submitted comments in opposition 

to the proposed BART limit of 0.055 lb/MMBtu, both parties signed the TWG Agreement that 
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establishes the NOx Cap based on compliance with the proposed BART limit of 0.055 lb/MMBtu within 

five years. This underscores the fact that Appendix B to the TWG Agreement was a negotiated 

agreement, submitted to EPA, representing diverse interests. EPA evaluated Appendix B to the TWG 

Agreement to determine whether it was consistent with our framework for “better than BART” 

Alternatives. Thus, although a few commenters may believe that the TWG Alternative is too stringent, it 

is consistent with our proposed framework and consistent with a level of control that the operator and 

owners find acceptable. 

The commenters indicate that their access to CAP Ag Pool water is expected to end in 2030, and 

assert that the timeframes for compliance with the limit of 0.07 lb/MMBtu in 2030 would necessitate 

water rate increases prior to 2030. The commenter asserts that it is arbitrary and capricious for NIA 

water users to pay a few years of higher CAP water rates for controls that will not be operational until 

after their access to the CAP Ag Pool expires. EPA notes that the direct impact of compliance with the 

limit of 0.07 lb/MMBtu in 2030 under the TWG Agreement, presumably with installation and operation 

of SCR, would be on the cost of electricity generation. Increasing water rates are indirect impacts that 

result from the relationship between NGS and CAP. EPA does not set or determine water rates charged 

by CAWCD to the CAP Ag Pool or any other classes of CAP customers. EPA’s proposed and final 

approval of the TWG Alternative as a better than BART Alternative is based on our review of the 

anticipated emission reductions associated with the TWG Alternative compared to BART. Although 

EPA, DOI, and DOE have committed to work together on many issues related to NGS, including 

funding for the federal portion of capital improvements at NGS, EPA does not determine how controls 

would be financed and how and when electricity or water rates would be adjusted to recover costs. 

Finally, EPA also notes, as stated previously, that the timeframes for compliance with the limit of 0.07 

lb/MMBtu were not established by EPA and were determined by the TWG as a negotiated compromise 

between diverse stakeholders. 

Comment: Request public comment on better-than-BART alternatives at higher level of NOx cap

 A CAP agricultural water users group (0305), while disagreeing with the methodology used by 

EPA to calculated the NOx cap (as discussed elsewhere in this document), supported EPA’s subsequent 

upward adjustments to the cap. However, the commenter stated that EPA should solicit comment from 

the public on whether there are other better-than-BART alternatives that stakeholders might propose that 

would comply with the revised NOx cap and provide greater flexibility. The commenter asserted that 

EPA’s failure to request that the public submit such alternatives would be arbitrary and capricious given 

that the EPA has now stated that the NOx cap is 494,899 tons but has only requested better-than-BART 

proposals that comply with the previously-proposed NOx cap of 451,149 tons. 

Response: 

 EPA disagrees with the comment that we must solicit public comment on other “better than 

BART” Alternatives to comply with the 2009-2044 NOx Cap of 494,899 tons in the Supplemental 

Proposal. Although the commenter refers to the value 451,149 as the “previously-proposed NOx cap”, 

EPA notes that in our February 5, 2013 Proposed Rule, we did not propose any NOx emission caps and 

used the total emissions over 2009-2044 simply as the BART benchmark against which BART 

Alternatives should be compared. The value of 451,149 represents the sum of two values from our 

Proposed Rule: the total emissions over 2009-2044 under BART (i.e., the BART threshold or 

benchmark at 358,974 tons) and the LNB/SOFA credit (92,175 tons). Thus, contrary to the assertion of 

the commenters, EPA did not “change the NOx cap” because EPA did not specifically propose an actual 
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emission cap over 2009-2044 in our Proposed Rule. However, to the extent that the commenter is 

concerned that the public was not invited to submit additional alternatives to comply with the 2009-2044 

NOx Cap of 494,899 tons in the Supplemental Proposal, EPA notes that we accepted comment on all 

aspects of our proposals, irrespective of whether EPA highlights a particular question or aspect of our 

analysis for public comment. At any time during the public comment period for our proposals, any 

group or member of the public could have provided comments on the absolute value of the BART 

Benchmark, the NOx Caps under the TWG Alternative, or a “better than BART” Alternative that meets 

any benchmark or cap value that the commenter determines is appropriate. For example, one commenter 

(0367/0370) submitted comments asserting that the absolute value of the 2009-2044 NOx Cap, as 

proposed, was too high, submitted a revised value for the NOx Cap, and an additional BART Alternative 

to EPA for consideration (closure of one unit in 2020 and an emission limit consistent with SCR on the 

remaining two units in 2020, as discussed above).327

 EPA stated in our Proposed Rule that “EPA seeks comment on the analysis and conclusions 

presented in this proposal and invites suggestions for other alternatives that reduce NOx emissions at 

NGS and its contribution to visibility impairment while providing long-term sustainable benefits to 

tribes.”328 In our Supplemental Proposal, we stated that “EPA is accepting public comment concurrently 

on our February 5, 2013 proposed BART determination and proposed Alternative 1 and the TWG 

Alternative put forth in today’s Supplemental Proposal.”329 EPA further stated that “after considering 

public comments, EPA may finalize provisions from either or both proposal, i.e., our proposed BART 

determination, proposed Alternative 1, or the TWG Alternative.”330 Although EPA did not explicitly 

request comment on additional BART Alternatives in the context of the 2009-2044 NOx Cap of 494,899 

tons, we note that our statements are clear that EPA is accepting comment on all aspects of the analysis 

and conclusions and that the final rule may include provisions from either or both proposals, after 

consideration of public comments.331 Thus, it is implicit that the public may submit general or specific 

comments on any aspect of both proposals, including additional alternatives, BART benchmarks, or NOx

emission caps as described in the Proposed Rule or the Supplemental Proposal. 

Comment: TWG Alternative does not fully meet EPA’s obligations to the Gila River Indian Community 

 One tribal government commenter (0039/0317) said that even though it is in full support of the 

TWG Alternative, it raised concerns that even under this alternative EPA has not met its obligations to 

the Gila River Indian Community because of the significant costs BART will have to NGS and impact 

the Community. Rather, the commenter views the TWG Alternative as the first step in a process that 

will limit the impacts on the Community because only if the TWG Alternative is finalized will key U.S. 

commitments contained in the TWG Agreement be realized. Specifically, under the TWG Agreement, 

and as outlined by the commenter in comments above, the DOI will work with the Gila Indian River 

Community and other tribes in the area around NGS, to evaluate the actual impacts the regulatory 

requirements will have on NGS over time. The commenter specifically referred to the U.S. commitment 

327 See comment letter from EarthJustice, document number 0367 in the docket for the rule at EPA-R09-OAR-2013-0009. 328 See 78 FR at 8291 (February 5, 2013). 

329 78 FR at 62518 (October 22, 2013) 330 Id.. 331 We further note that in our Proposed Rule and Supplemental Proposal, EPA explicitly requests public comment on very 

few specific aspects of our analysis, but that does not preclude the public from submitting comments any and all aspects of 

any document in our docket for the rulemaking, as well as documents or ideas that are not included in our analysis and 

docket. 
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to allocate $10 million annually for 10 years starting in 2020, from the Reclamation Water Settlements 

Fund to reduce impacts to the LCRBDF. 

Response: 

EPA acknowledges the comment and is aware that costs associated with implementing the TWG 

Alternative will have implications for numerous Tribes, including the Gila River Indian Community. 

EPA is committed to continuing to work with the Department of the Interior and the Department of 

Energy in the Interagency Working Group on NGS, as laid out in the Joint Statement signed in January 

2013 by the heads of the three agencies, to work with tribes to address long-term issues related to NGS. 

The provisions in the TWG Agreement that are not related to EPA’s authority to evaluate BART or a 

“better than BART” alternative, however, are beyond the scope of this rulemaking. 

Comment: Preference for TWG Alternative A 

 One individual (0221) acknowledged that EPA’s proposed BART rule for NGS would 

effectively reduce the emissions produce by the plant, but asserted that the cost of doing so would be 

drastic. Therefore, the commenter believes that the proposed TWG Alternative A would be a better 

option, because it would help ease the financial burden of installing three SCR units while still reducing 

emissions to a lower level than the EPA’s proposed rule, and by allowing NGS to temporarily shut down 

one unit or reduce the generation of all three units, the plant would still stay under the required level of 

0.055 lb/MMBtu. The commenter further noted that although the TWG Alternative B also requires the 

reduction of NOx emissions it does not outline how this reduction would be completed, and the 

requirement of annual Emission Reduction Plans would require owners to continuously monitor 

emission rates which can be burdensome. 

Response: 

 EPA agrees that TWG Alternative A is simpler and provides more specificity than TWG 

Alternative B. However, contrary to the commenter’s statement, EPA notes that the closure 

requirements under TWG Alternative A1 and A2 represent permanent closure of one unit. 

Comment: Objection to NOx cap 

 As discussed in greater detail above in section 8.5, one environmental advocacy group (0373) 

stated that EPA’s use of total emissions as a benchmark to determine whether an alternative is “better 

than BART” is legally indefensible. The commenter indicated that under the TWG Alternative (and 

Alternative 1) EPA does not assess the actual impacts on visibility and the potential for improvement in 

Class I areas (which are the stated goal and obligations of the CAA) but rather projects how much total 

NOx pollution might be emitted by NGS between now and an “arbitrary” date of 2044. 

 The commenter (0373) believes that by comparing only the total NOx emissions from over the 

entire 2009-2044 period, EPA is acquiescing to decades of unacceptable and unlawful visibility 

impairment at Class I areas. The commenter stated that nothing in EPA’s NOx cap framework requires 

any meaningful incremental progress during this period, let alone the “reasonable progress” required by 

the CAA and haze regulations. The commenter asserted that for the TWG Alternative, it appears NGS 
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owners could avoid NOx emissions reductions for decades, and then retire capacity at the last minute as 

needed to just barely stay under the cap by 2044. 

Response:

This issue is also discussed elsewhere in this document. See responses and comments in section 

8.5. 

Comment: Errors in calculations and assumptions in the NOx Cap 

 Notwithstanding its assertions that a NOx Cap is unlawful under the CAA (as discussed 

elsewhere), one environmental advocacy group (0373) stated that EPA’s calculations and assumptions 

for the NOx cap include errors and improper credits (these points are summarized in detail in section 8.5 

of this response to comments document). The commenter concluded that if EPA continues to use the 

NOx cap framework (which the commenter believes is never appropriate for assessing whether an 

alternative is “better than BART”), EPA must correct the NOx cap to prevent alternatives from being 

compared to an artificially inflated estimate of total NOx emissions. 

 The commenter (0373) stated that the graphs used by EPA in its discussion of the TWG 

Alternative are misleading because they label as BART a line that the commenter believes is clearly not 

BART but “a made up scenario in which LNB/SOFA have not already been installed at NGS (in other 

words, the NOx cap).” The commenter attached a graph from the Miller/Sahu report which, according to 

the commenter, includes an additional line that represents the “actual BART” as calculated by EPA and 

shows that the TWG Alternative and the NOx cap are substantially worse than BART. 

Response:

 Regarding the concerns raised about EPA’s calculations and assumptions in calculating the NOx

Cap, see EPA’s response to a similar comment in section 8.5 regarding EPA’s calculations and 

assumptions for the BART Benchmark, which formed the basis for the NOx Cap in the Supplemental 

Proposal. As discussed in our response in section 8.5, EPA disagrees that the BART Benchmark and 

NOx Cap were inflated. EPA is taking final action to approve the TWG Alternative with the 2009-2044 

NOx Cap and 2009-2029 NOx Cap as proposed. 

 EPA disagrees with the comment that our graphs in the discussion of the TWG Alternative were 

misleading. In our Proposed Rule and our Supplemental Proposal, EPA clearly stated that for NGS, we 

were proposing to give credit for the early and voluntary installation of LNB/SOFA on one unit per year 

in 2009, 2010, and 2011. The difference between the two lines the commenter asserts to be “made up 

BART” and “actual BART” is the LNB/SOFA credit. In addition, the underlying worksheet for EPA’s 

graph depicting BART and the TWG Alternative indicates that BART is “5-year BART as if LNB was 

not yet installed” and we calculated this value to be 494,899 tons. This value was reported in our 

Supplemental Proposal, where we describe our application of the LNB/SOFA credit to the BART 

Benchmark from our February 5, 2013 Proposed Rule. EPA recognizes that some individuals may 

interpret this idea as a “made up scenario” and we also recognize that if not for the LNB/SOFA credit 

the alternatives to BART considered in our proposals (Alternative 1 and the TWG Alternative) would 

not be “better than BART.” Fundamentally, this comment addresses the fact that the commenter 

disagrees with the early installation credit for LNB/SOFA. 
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As stated in our proposed rules, EPA is exercising our discretion and authority under the 

Regional Haze Rule and the TAR to propose a flexible timeframe for an alternative measure under the 

RHR for NGS and a key part of the flexible timeframe is our recognition that the owners of NGS elected 

to install LNB/SOFA early and voluntarily, and that our BART Benchmark requiring a limit of 0.055 

lb/MMBtu represents the level that would be achieved with SCR in combination with LNB/SOFA. 

Thus, the owners of NGS could have waited until five years after the effective date of our final BART 

determination (i.e., 2019) to install LNB/SOFA. However, because the owners installed LNB/SOFA on 

one unit per year in 2009, 2010, and 2011, the environment realized actual NOx reductions 

approximately 10 years earlier than would have been achieved under BART. These early emission 

reductions are real and EPA proposed the LNB/SOFA credit supporting a flexible timeframe for NGS 

based on the discretion provided under section 301(d)(4) of the CAA and 40 CFR 49.11(a).332

Comment: TWG Alternative is vague and unenforceable 

 One environmental advocacy group (0373) stated that a BART determination must include clear 

requirements for emissions reductions and a clear timeline for those reductions, to ensure continuing 

visibility improvements in Class I areas. According to the commenter, the future ownership scenarios 

and associated emission control possibilities included in the TWG Alternative are at best vaguely 

defined and at worst entirely open-ended and unenforceable. The commenter indicated that without 

specific emission limits and/or commitments to retire specific amounts of capacity from specific units, 

as of a date certain, it is impossible to calculate the visibility improvements that will result from the 

TWG Alternative, and it will be impossible for individuals or EPA to assess whether NGS is on track to 

meet the emission reductions necessary to ensure reasonable progress toward natural visibility affected 

Class I areas. The commenter asserted that such an undefined and unenforceable plan to reduce 

emissions at some point in the future is not adequate to substitute for a date-certain and emission ratespecific BART requirement. The commenter added that the proposed requirement for NGS to submit 

annual Emission Reduction Plans (citing the Supplemental Proposal at 78 FR at 62518) is not adequate 

because the plans are not enforceable, as FIP requirements must be, and because the EPA does not state 

what percentage of total NOx reductions NGS must achieve annually. The commenter contended that the 

TWG Alternative is nothing more than illegal self-regulation (citing Envtl. Def. Ctr. v. EPA, 344 F.3d 

832, 855-56 (9th Cir. 2003)). 

 The commenter (0373) stated that TWG Alternative A is built around the premise that some 

amount of capacity at NGS will be retired in 2019. According to the commenter, EPA assumed in its 

analysis that if all three units continued to operate, with a reduction in total combined capacity, that two 

units would install SCR and that those two units would operate at full capacity, with a third unit 

operating at partial capacity with only LNB/SOFA. The commenter believes that while that is one 

possibility, nothing guarantees or requires the owners of NGS to choose that outcome, and the owners of 

NGS could shift capacity among the three units as they see fit under the terms of the alternative. The 

commenter contended that this substantial uncertainty means that it is impossible to know precisely 

when and by how much emissions will be reduced at any of the three NGS units under Alternative A. 

 The commenter (0373) asserted that TWG Alternative B is more open-ended than Alternative A 

in that it only requires that the three units meet a 2009-2029 NOx emissions sub-cap, along with the 

overall 2009-2044 NOx Cap. According to the commenter, EPA proposed two scenarios to consider 

under Alternative B; in one scenario the units all install SCR earlier, and thereafter meet a NOx emission 

332 See 78 FR 62513 (October 22, 2013) and references therein. 
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limit of 0.07 lb/MMBtu, and in the other, the units all install SCR later and thereafter meet a NOx limit 

of 0.055 lb/MMBtu. The commenter stated that these two options are by no means the only possible or 

even likely outcomes under the open-ended Alternative B, asserting that there are an infinite number of 

ways the NGS owners could choose to meet these limits, involving some combination of reduced 

capacity and/or pollution controls at various different dates (citing the Miller/Sahu report). 

The Hopi Tribe (0134) indicated that it has serious concerns with the proposed TWG Alternative 

for several reasons, including because the TWG Alternative does not specify the technology, i.e., either 

SCR or an equivalent that will be used to achieve the same level of NOx reductions as the BART 

proposal. In the commenter’s opinion, the TWG Alternative is ambiguous because both scenarios are 

vague and do not include the same level of assurance that the NOx reductions will be the same as under 

the BART proposal. Also, because under the proposed TWG Alternative the extended time NGS would 

be permitted to operate without SCR (or equivalent alternative) the commenter believes the TWG 

alternative jeopardizes the goal of the CAA and the purpose of this regulation. 

Response:

 EPA disagrees with the assertions that the TWG Alternative is vague and unenforceable. EPA 

acknowledges that the TWG Alternative is complex. This complexity is a result of the role future 

ownership outcomes and regulatory requirements stemming from lease and coal contract negotiations 

will have in determining the most reasonable compliance options in the future. For example, LADWP 

and NV Energy, who together own nearly one-third of the generating capacity at NGS, intend to divest 

their ownership share of NGS prior to the end of the current lease term. If LADWP and NV Energy 

divest by retiring their interests in NGS, the most logical operational outcome would be closure of one 

of the three units at NGS. If, instead, LADWP and NV Energy choose to divest by selling to an outside 

party (i.e., a party that is not currently an owner of NGS), then the most logical business outcome is no 

longer closure of one unit. Instead, the operator of NGS must take steps to ensure the necessary emission 

reductions to maintain compliance with the applicable NOx emission caps over 2009-2029 and 2009-

2044. In addition to future decisions that are yet to be made by LADWP and NV Energy, under the 

terms of the renewed site lease for NGS, the Navajo Nation has the option to purchase up to a 170 MW 

ownership interest in NGS. This represents another future ownership possibility that will affect the 

determination of the most reasonable compliance option. 

 Contrary to the assertions by the commenter, EPA included proposed regulatory language in our 

Supplemental Proposal that provided specific and enforceable timelines for achieving emission 

reductions under the TWG Alternative. The proposed language under 40 CFR §49.5513(j)(3)(i), 

“Operating Scenarios to Comply with 2009-2044 NOx Cap,” defines the timeframes and requirements 

under TWG Alternatives A1, A2, A3, and B, all of which must be implemented in a manner that ensures 

total NOx emissions over 2009-2044 remain below the 2009-2044 NOx Cap. Specifically, 

§49.5513(j)(3)(i)(A) defines Alternative A1, that specifies the following requirements: (1) by December 

31, 2019, the owner/operator shall permanently cease operation of one coal-fired unit and (2) by 

December 31, 2030, the owner/operator shall comply with a NOx emission limit of 0.07 lb/MMBtu on 

each of the two remaining coal-fired units. Alternative A1 is the simplest of the possible operating 

scenarios under the TWG Alternative and §49.5513(j)(3)(ii)(A) specifies that Alternative A1 applies 

under three potential future ownership possibilities. 

 TWG Alternative A2 is defined in §49.5513(j)(3)(i)(B), requiring (1) by December 31, 2019, the 

owner/operator shall permanently cease operation of one coal-fired unit, and (2) by December 31, 2019, 

the owner/operator may elect to increase net generating capacity of the remaining two coal-fired units by 
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a combined total of no more than 189 MW. The actual increase in net generating capacity shall be 

limited to the sum of 19 MW and the ownership interest, in net MW capacity of up to 170 MW, 

purchased by the Navajo Nation by December 31, 2019. The owner/operator shall ensure that any 

increase in the net generating capacity is in compliance with all pre-construction permitting 

requirements, as applicable, and (3) by December 31, 2030, the owner/operator shall comply with a NOx

emission limit of 0.07 lb/MMBtu on each of the two remaining coal-fired units. The future ownership 

possibilities that would trigger Alternative A2 are defined in §49.5513(j)(3)(ii)(B). 

 TWG Alternative A3 is defined in §49.5513(j)(3)(i)(C), requiring (1) by December 31, 2019, the 

owner/operator shall reduce net generating capacity of NGS by no less than 561 MW. The actual 

reduction in net generating capacity of NGS shall be determined by the difference between 731 MW and 

the ownership interest, in net MW capacity of up to 170 MW, purchased by the Navajo Nation by 

December 31, 2019, and (2) by December 31, 2030, the owner/operator shall comply with a NOx

emission limit of 0.07 lb/MMBtu on two units. The future ownership possibilities that would trigger 

Alternative A2 are defined in §49.5513(j)(3)(ii)(C). 

 TWG Alternative B is defined in §49.5513(j)(3)(i)(D), requiring that in addition to the 2009-

2044 NOx Cap, the owner/operator shall ensure compliance with the 2009-2029 NOx Cap. The 2009-

2044 NOx Cap is defined in §49.5513(j)(2)(ii) as no more than 494,899 tons of NOx, and the 2009-2029 

NOx Cap is defined in §49.5513(j)(2)(i) as no more than 416,865 tons of NOx. The 2009-2029 NOx Cap 

is based on closure of one unit by December 31, 2019 and the 2009-2044 NOx Cap is based on 

compliance with the BART emission limit of 0.055 lb/MMBtu within five years of the final rule. The 

future ownership possibilities that would trigger Alternative B are defined in §49.5513(j)(3)(ii)(D). As 

described in §49.5513(j)(4)(iv), if TWG Alternative B is triggered, the owner/operator must submit 

annual Emission Reduction Plans that contains the anticipated year-by-year emissions to ensure 

compliance with the 2009-2029 and 2009-2044 NOx Caps. 

The commenter asserts that under the scenario of reduced capacity (three units remain open, i.e., 

TWG Alternative A3), EPA ignored other possible outcomes and simplistically assumed that two units 

would continue to operate at full capacity with SCR and the unit whose operation is curtailed would 

operate only with LNB/SOFA. The commenter asserts that there is no guarantee that the operator will 

choose to comply with TWG Alternative A3 in this manner. Although this specific arrangement under 

TWG Alternative A3 is not required, EPA disagrees that nothing compels the operator to comply with 

this operating scenario in a manner that reduces emissions comparably with the assumption that two 

units would operate at full capacity with SCR and the unit that is curtailed would operate with 

LNB/SOFA. EPA notes that under TWG Alternative A3, as well as all other TWG Alternatives, the 

owner/operator must operate the units at NGS so that total emissions remain below the 2009-2044 NOx

Cap (as well as the 2009-2029 NOx Cap under Alternative B). Thus, although flexibility exists for the 

owner/operator to shift capacity between the three units in different ways, under §49.5513(j)(3)(i)(C), 

the actual strategy the owner/operator uses under TWG Alternative A3 must still comply with the 2009-

2044 NOx Cap and the timeframes required for reducing capacity and meeting the 0.07 lb/MMBtu 

emission limit on two units. EPA notes that if the operator, for example, chose to curtail all three units 

by a total of 561 MW equally, and comply with a limit of 0.07 lb/MMBtu on two units and 0.24 

lb/MMBtu on one unit, total emissions over 2009-2044 would not comply with the 2009-2044 NOx

Cap.333 Thus, the operator would be prohibited from operating in this manner and would need to, for 

333 See tab titled “TWG A3” in the document titled “2014_0311 Better than BART Alternatives for Final Rule.xlsx” in the 

docket for the rule at EPA-R09-OAR-2013-0009. We also note that in our Supplemental Proposal, EPA mistakenly expected 

emissions under TWG A2 to be identical to TWG A3. This scenario would be possible if, under TWG A3, the operator of 
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example, significantly curtail operations to reduce emissions further, or risk violating the FIP. As noted 

in our Supplemental Proposal, EPA estimated total NOx emissions over 2009-2044 for TWG 

Alternatives A1, A2, and A3 to provide assurance that the owner/operator could reasonably meet the 

2009-2044 NOx Cap under the specific terms of those alternatives. EPA does not need to determine that 

all operating possibilities that are consistent with the requirements of TWG Alternative A1, A2, and A3 

would also meet the 2009-2044 NOx Cap. The regulatory requirements EPA proposed for the TWG 

Alternatives provide specific dates on which the owner/operator must close a unit, curtail operations, 

and meet emission limits. While there is some flexibility in how emissions might be curtailed under 

TWG Alternative A3, the 2009-2044 NOx Cap ensures that the operator does not implement a strategy 

that results in substantially more emissions than would be achieved by installing SCR on the two units 

that are operated at full capacity and curtailing operations on the unit that was not retrofit with SCR. 

 The commenter asserts that TWG Alternative B is more open-ended than TWG Alternative A 

and that there are an infinite number of ways the operator could comply with the 2009-2029 and 2009-

2044 NOx Caps. The commenter further states that the two possibilities EPA considered in our 

Supplemental Proposal are not likely to be the outcomes under TWG Alternative B. EPA agrees that 

TWG Alternative B is more open-ended than TWG Alternative A. However, EPA disagrees with the 

sentiment that TWG Alternative B is so open-ended that it would not be enforceable or that it would not 

result in emission reductions at NGS. We note that the 2009-2029 NOx Cap was calculated based on the 

closure of one unit with no additional increase in capacity (i.e., equivalent to emissions under TWG 

Alternative A1). Thus, the operator cannot maintain the status quo (operation of all three units at full 

capacity at a limit of 0.24 lb/MMBtu) and meet the 2009-2029 NOx Cap. We also note that the 2009-

2044 NOx Cap was calculated based on compliance with 0.055 lb/MMBtu within five years of the final 

rule. The difference between the 2009-2044 NOx Cap and the 2009-2029 NOx Cap is small (494,899 

tons – 416,865 tons =78,034 tons), and when distributed over the fifteen year period (2030-2044), 

requires significant emission reductions that would come in the form of new NOx controls, significant 

curtailment, or earlier retirement than 2044. While installation of new NOx controls would reduce NOx, 

possibilities that involve earlier retirement or significant curtailment would also reduce emissions of 

other pollutants emitted at NGS. Although TWG Alternative B is not specific in how the emission 

reductions must be achieved, the range of possible operating choices are substantially constrained by the 

requirement to comply with the 2009-2029 and 2009-2044 NOx Caps. The commenter further notes that 

the Emission Reductions Plans required under TWG Alternative B are not, but must be, enforceable. 

EPA agrees with the commenter that the anticipated measures and year-by-year emissions outlined in 

the Emission Reduction Plans are not enforceable. However, we note that the requirement to submit the 

Emission Reduction Plans, and the 2009-2029 and 2009-2044 NOx Caps are all enforceable under the 

FIP. Thus, while we will not require the operator to operate in the exact manner it outlines in an annual 

Emission Reduction Plan, the operator must comply with the 2009-2029 and 2009-2044 NOx Caps that 

are consistent with meeting a limit of 0.055 lb/MMBtu at all three units in 2019 or closing a unit in 2019 

and meeting a limit of 0.07 lb/MMBtu on two units in 2030. 

One commenter (0367), in a footnote in its comment letter, asserted that EPA was incorrect to 

claim that the TWG Alternative would absolve NGS of obligations related to a Reasonably Attributable 

NGS elected to close a unit to achieve a reduction of 561 MW capacity, rather than achieving the reduction through 

curtailment. In the curtailment scenario, emissions under TWG A3 would be higher than TWG A2. EPA evaluated potential 

emissions under TWG A3 in the updated spreadsheet (tab “TWG A3”) under three possible scenarios, and determined that 

only one of the three scenarios would maintain emissions below the 2009-2044 NOx Cap. Therefore, although options under 

TWG A3 may seem broad, the operator of NGS must still operate in a manner to ensure compliance with the 2009-2044 NOx

Cap. EPA did not receive comments specifically noting that emissions under TWG A3 would likely not equal TWG A2. 
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Visibility Impairment (RAVI) finding that may be made for NGS.334 EPA disagrees that we claimed that 

the TWG Alternative would absolve NGS of obligations related to RAVI. The commenter cited to 

footnote 21 in our Supplemental Proposal.335 In that footnote, we acknowledged that the TWG had 

intended their alternative to satisfy both the better than BART requirements of the RHR as well as any 

requirements of the RAVI program. However, in our Supplemental Proposal, EPA did not propose any 

action related to RAVI. In our footnote, we noted that there was no outstanding petition to certify 

impairment from NGS at any Class I area and outlined the process and requirements for triggering a 

BART determination under RAVI. Specifically, we noted: 

If NPS were to certify RAVI at Grand Canyon from NGS, EPA must 

determine whether visibility impairment at Grand Canyon is indeed 

attributable to NGS. If EPA were to make a positive attribution 

determination, then EPA would be required to conduct a BART 

determination for NGS. We note, however, that while the process for 

determining whether a given stationary source causes or contributes to 

RAVI or regional haze are different, the process for determining BART 

under both programs is essentially the same. In other words, a BART 

determination for RAVI would likely be the same as a BART 

determination for regional haze. 

Although we stated that a BART determination under RAVI would likely be the same as a 

BART determination under regional haze (i.e., an analysis of the five factors listed in the CAA), EPA 

did not make any conclusions or absolve NGS of any obligations related to RAVI because there is 

currently no action before EPA to make an attribution finding related to NGS. 

As discussed in our Supplemental Proposal, the National Parks Conservation Association 

(NPCA) petitioned the Department of the Interior on May 5, 2009, to certify that emissions of NOx and 

particulate matter cause visibility impairment at the Grand Canyon National Park. This type of visibility 

impairment, reasonably attributable from a single stationary source, is known as Reasonably 

Attributable Visibility Impairment (RAVI). On January 20, 2011, NPCA filed a complaint in the United 

States District Court for the District of Columbia contending that the Department of the Interior was 

unreasonably delaying making a finding of reasonable attribution from NGS. In a letter dated March 8, 

2011 to NPCA, the National Park Service (NPS) declined to make such a finding based on EPA’s ongoing work related to a BART determination for NGS. On June 30, 2011, the Court dismissed the 

complaint holding the NPS letter refusing to make the finding of reasonable attribution constituted 

denying the Petitioner’s request for a RAVI finding.336 If NPS were to certify RAVI at Grand Canyon 

from NGS, EPA must determine whether visibility impairment at Grand Canyon is indeed reasonably 

attributable to NGS. If EPA were to make a positive attribution determination, then EPA would be 

required to conduct a BART determination for NGS. 

Although there are no such petitions, EPA also notes that the action we are taking in this 

rulemaking is consistent with responding to a petition for reasonable attribution. In other words, EPA’s 

BART determination for purposes of 40 CFR 51.308(e) for regional haze visibility impairment requires 

the same analysis that we would undertake for a BART determination for reasonable attribution. The 

BART determinations under both provisions are the same. 

334 See EarthJustice letter, page 10, footnote 25. 335 See Supplemental Proposal, 78 FR at 62513, footnote 21 (October 22, 2013). 336 The documents dated May 5, 2009, January 20, 2011, March 8, 2011, and June 30, 2011 are all available in the docket for 

the rule in document number 0184 at EPA-R09-OAR-2013-0009. 
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One commenter raised concerns with the TWG Alternative because it does not specify the 

technology that must be installed. EPA notes that our proposed BART determination also does not 

specify what technology must be used. Our proposed BART determination and the regulatory 

requirements of the TWG Alternative all impose emission limits for NOx. The limits for the BART 

Benchmark (0.055 lb/MMBtu) and the TWG Alternative (0.07 lb/MMBtu) are based on what is 

achievable using a specific technology. Currently, both limits are achievable with SCR, but the operator 

may consider using newer technologies, if available, as long as each unit complies with its applicable 

emission limit by its compliance date. The commenter also noted that the flexible period for compliance 

under the TWG Alternative also jeopardizes the goal of the CAA and the purpose of the Regional Haze 

Rule. EPA notes that the under section 169A of the CAA, Congress established the goal of restoring 

visibility in Class I areas to natural conditions and EPA’s RHR established a target for achieving natural 

conditions by 2064.337 EPA is finalizing the requirements of the TWG Alternative, which require, 

among other things, emission reductions in 2019 and in 2030. EPA is also adding as an enforceable 

requirement, the commitment from the Appendix B of the TWG Agreement for the owner/operator to 

cease conventional coal-fired electricity generation at NGS by 2044. EPA considers these time frames to 

be consistent with the stated goal of section 169A of the CAA. EPA has addressed comments regarding 

consistency with EPA’s regulations, including the Regional Haze Rule and the Tribal Authority Rule, 

elsewhere in this response to comments document (see section 8.5). 

Comment: “Arbitrary” 2044 end date 

 One environmental advocacy group (0373) stated that the 2009-2044 period analyzed for the 

TWG Alternative is arbitrary because it is quite likely that one or more NGS units will operate beyond 

that time frame. According to the commenter, if they do so, the TWG Alternative, especially Alternative 

B, does not guarantee any emissions reductions beyond 2044. The commenter asserted that if NGS units 

continue to operate for even 3 additional years, until 2047, the TWG Alternative permits outcomes that 

will result in greater total NOx emissions than EPA’s NOx cap (citing the Miller/Sahu report). The 

commenter contended that the TWG Alternative does not require all units to retire in 2044, and limiting 

analysis to this period is unsupported. 

Response:

 EPA disagrees with the comment that the 2044 end date for the NOx Cap is arbitrary. EPA used 

2044 as the end date in our February 5, 2014 Proposed Rule in our calculations of the BART 

Benchmark. EPA noted that we selected 2009-2044 as most appropriate because it includes the early 

installation dates for LNB/SOFA and extends until the anticipated 2044 termination date of the new site 

lease that was approved by the Navajo Nation.338 The TWG Agreement provides further support for the 

end date of 2044 because, under the TWG Agreement signed by six entities including the Navajo Nation 

and SRP, the operator of NGS, the NGS Co-Tenants shall cease their operation of conventional coalfired generating at NGS no later than December 22, 2044. At its election, consistent with the Lease 

Amendment, the Navajo Nation may continue plant operations at NGS after December 22, 2044 

consistent with EPA approval.339 EPA interprets this to mean that following the cessation of 

conventional coal-fired electricity generation at NGS in late 2044, the Navajo Nation may seek to 

operate NGS after 2044 as a new source that would be subject to pre-construction permitting 

337 40 CFR 51.308(d). 338 See Footnote 60 in the Proposed Rule, 78 FR at 8290 (February 5, 2013). 

339 See Section VII.F of the TWG Agreement (page 14). 
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requirements (including BACT and associated emission limits). However, EPA agrees that the 2044 end 

date, as included in the TWG Agreement, is not enforceable by EPA. Therefore, to make this end date 

federally-enforceable, EPA is adding it as a requirement to the regulatory language in today’s final 

action. EPA is adding the following requirement to the regulatory language in the final rule: 

By December 22, 2044, the owner/operator shall permanently cease 

operation of all coal-fired units at NGS. At its election, the Navajo Nation 

may continue plant operator at NGS after December 22, 2044, consistent 

with EPA approval under the New Source Review program. 

EPA is adding the forgoing paragraph to the following sections of the regulatory language: 40 CFR § 

49.5513(j)(3)(i)(A), (B), (C), and (D). 

Comment: Emissions under TWG Alternative 

 One environmental advocacy group (0373) stated that neither EPA nor TWG have provided a 

comprehensive technical analysis of the emissions and visibility outcomes that are possible under the 

TWG Alternative. The commenter asserted that it is EPA’s responsibility to provide an administrative 

record that contains comprehensive modeling and analysis for any BART proposal, but EPA left this 

critical component of the alternatives analysis undone. 

 The commenter (0373) indicated that it looked at a number of different permissible outcomes 

under TWG Alternative A and B, analyzed the resulting emission reductions, and conducted 

independent analyses to assess the visibility outcomes of these possible scenarios. For Alternative A, the 

commenter analyzed the scenarios that EPA chose (with “corrections” as discussed elsewhere in this 

document) and three additional options that would be permissible under the third scenario in Alternative 

A. According to the commenter (citing the Miller/Sahu report), these three additional outcomes would 

all result in emissions that are greater than the emissions for the scenarios EPA considered under TWG 

Alternative A – while emissions would be less than or equal to the NOx cap as calculated by EPA, 

emissions would not stay under the commenter’s corrected NOx cap and would not be close to BART 

levels. 

 The commenter (0373) also analyzed and modeled four options that would be permissible under 

Alternative B in addition to the two scenarios addressed by EPA. According to the commenter, these 

additional outcomes all lead to cumulative emissions that are no greater than the NOx cap as calculated 

by EPA, but emissions do not stay under the commenter’s corrected NOx cap and are not close to BART 

levels. 

Response: 

 EPA disagrees with the comment that we have failed to provide a comprehensive technical 

analysis of the emissions and visibility outcomes that are possible under the TWG Alternative. We also 

disagree with the assertion that our administrative record for this rulemaking is incomplete. EPA 

provided extensive analysis of the potential BART scenarios, beginning with our ANPR in August 2009. 

After considering the numerous comments on the ANPR and taking into account the unique and varied 

interests affecting NGS, EPA proposed to find that NOx BART for NGS is an emission limit of 0.055 
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lb/MMBtu which can be achieved by installation of SCR+LNB/SOFA on Units 1 – 3.340 Our proposed 

BART determination included one “better than BART” Alternative and a framework for evaluating 

other “better than BART” Alternatives. The TWG submitted the TWG Agreement. EPA evaluated 

Appendix B of the TWG Agreement and published a Supplemental Proposal that put forth our analysis 

of the alternative and proposed approval of requirements consistent with the TWG Agreement based on 

our analysis that it is “better than BART”.341 The comment does not provide any facts or information to 

support the conclusory statements that our analysis was not “comprehensive” or that our administrative 

record is incomplete. 

Instead, the comment relies on a report prepared by Miller and Sahu submitted with the 

comment. The Miller/Sahu Report contends that EPA’s evaluation of the TWG Alternative is incorrect 

based on changing the central inputs underlying our calculations for the BART Benchmark and the 

TWG Alternative. The specific technical reasons that we disagree with the inputs that the Miller/Sahu 

report changed (e.g. NOx emissions limit achievable with SCR, heat input values from baseline period, 

annual vs. 30-day emission rates) are explained in detail in section 8.5 of this response to comments 

document. EPA notes that if we have provided a reasoned explanation for selecting the technical inputs 

for our decision, our decision is entitled to deference despite the commenter’s preference for some other 

set of inputs. As the 9th Circuit stated in CACWD v. EPA: 

The administrative record reveals that EPA adequately considered the 

relevant factors in promulgating the Final Rule. [footnote omitted] 

Petitioners’ essential argument does not claim that EPA failed to consider 

the relevant factors, but instead contends that EPA erred in its 

consideration of those factors. This court is not to substitute Petitioners’ 

judgment, or its own, for that of EPA, as long as the agency’s 

interpretation is reasonable. In fact, this is just the type of case in which 

the Supreme Court has stated that judicial review should ‘be at its most 

deferential’ because the agency is ‘making predictions, within its area of 

special expertise, at the frontiers of science.’ [citation omitted]. 342

EPA provided a reasonable interpretation of its calculation of a cumulative NOx BART cap, and of the 

emissions that will result from the TWG Alternative. Because the TWG Alternative will result in greater 

NOx emissions reductions than BART, with the same geographic distribution, EPA is properly 

approving the TWG Alternative as “better than BART.” 

Table 2 in the Miller/Sahu report lists BART-1 as “EPA BART (No Corrections)”, showing a 

value of 379,152 tons of NOx emissions, 2009-2044 Cumulative.343 The value that Miller/Sahu attributes 

as EPA’s value with “no corrections”, however, is nowhere traceable to EPA’s documents. EPA’s 

Proposed Rule calculates the NOx BART Benchmark to equal 358,974 tons of NOx emissions, plus the 

LNB/SOFA credit of 92,715 tons of NOx emissions. EPA made some corrections to that value in its 

Supplemental Proposal, which increased the 2009-2044 cumulative NOx emissions cap to 377,015 tons 

before the LNB/SOFA Credit. The Miller/Sahu report provides no explanation for the value of 379,152 

tons that they nonetheless attribute to EPA with “no corrections.” The Miller/Sahu report then makes 

several “corrections” to reach a value of 280,554 tons of cumulative NOx emissions over 2009-2044. 

EPA has explained in detail why we disagree with each of the Miller/Sahu “corrections” in section 8.5 

340 78 FR 8274 (February 5, 2013). 341 78 FR 62509 (October 22, 2013). 342 990 F.2d 1531, 1543 (9th Cir. 1993) 343 Miller/Sahu Report, Table 2 at p. 7. 
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of this response to comments document and references therein. None of the “corrections” is changing 

an input to EPA’s calculation that is incorrect. EPA was correct in determining that SCR+LNB/SOFA 

operating at NGS could achieve a NOx emission rate of 0.055 lb/MMBtu. The operator of NGS, SRP, 

submitted comments contending that with LNB/SOFA and SCR, it could only achieve at a NOx

emission rate of 0.070 to 0.080 lb/MMBtu. EPA disagrees with both commenters and continues to find 

that a NOx emission rate of 0.055 lb/MMBtu is BART. For the reasons set forth in section 8.5, we also 

continue to disagree that our calculation of the BART Benchmark or the NOx Cap has relied on any 

incorrect inputs. 

Because we disagree with the “corrections” and the values presented in the Miller/Sahu report, 

we also disagree with the conclusions of Miller/Sahu that the TWG Alternative fails to satisfy our 

requirements for demonstrating an alternative is “better than BART.” The commenter cannot change the 

fact that its alternative preferences on the inputs for calculating BART are just preferences by calling 

them “corrections.” 

Finally, the commenter presented the results of modeling. However, the conclusions the 

commenters draw from the modeling are based on the values that the commenter has selected (i.e. 

calculated with its preferred inputs) – not the values determined by EPA as a scientific and technical 

matter to be appropriate. For all of the reasons that we disagree with the values calculated by the 

commenter for the NOx BART Benchmark and the NOx Cap, we also disagree with the results of the 

modeling derived from those values. 

Comment: Visibility modeling under the TWG Alternative 

 One environmental advocacy group (0373) pointed out that EPA did not conduct visibility 

modeling on any of the TWG Alternatives. According to the commenter, visibility modeling is required 

unless the distribution of emissions for a BART alternative is the same as it would be under BART, and 

here that is not the case. The commenter stated that the TWG Alternative distributes emissions over time 

very differently than BART: while BART would require real and measurable reductions in NOx within 5 

years due to the installation of SCR, the bulk of the reductions in the TWG Alternative might not come 

until the end of the 2009-2044 period analyzed by EPA (as demonstrated by the additional scenarios 

analyzed by the commenter), resulting in decades of lost visibility at many of our most iconic national 

parks. The commenter added that the pollutants reduced are also distributed differently. According to the 

commenter, EPA indicated that if one or more units retire or reduce their capacity, emissions of SO2 and 

PM will also be reduced, contributing to visibility improvements; the commenter believes that without 

modeling there is no way to know whether these reductions are significant. 

 The commenter (0373) stated that the additional analysis and modeling conducted by the 

commenter reveal that the TWG Alternative is likely substantially worse than BART, depending on 

which of the nearly limitless options the owners elect to pursue (citing the Miller/Sahu report). 

According to the commenter, the results of the visibility modeling show that many of the possible 

outcomes under the TWG Alternative produce substantially worse visibility outcomes than EPA’s NOx

cap, even where the total emissions from an outcome remain below the NOx cap. The commenter further 

asserted that all of the outcomes for the TWG Alternatives produce substantially worse visibility 

outcomes than the commenter’s corrected BART. The commenter reproduced a table and graphs from 

the Miller/Sahu report that compare outcomes under BART, the NOx cap, and a variety of scenarios 

under the TWG Alternative. According to the commenter, the table and graphs show that while 

cumulative emissions of these scenarios remain below EPA’s calculated NOx cap (but not the 
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commenter’s “corrected” NOx cap or the BART emissions calculated by the EPA or the commenter), 

visibility impacts measured in cumulative dv for many of the scenarios are worse than under EPA’s NOx

cap and significantly worse than the commenter’s corrected BART. 

 The commenter (0373) believes that these results illustrate the inadequacy of comparing 

cumulative total emissions to assess whether an alternative is better than BART, and demonstrate that 

comprehensive visibility modeling is necessary before EPA may approve any BART alternative at NGS. 

The commenter asserted that these results also clearly show that strict controls on NOx emissions (i.e., 

SCR) are necessary because the reductions in SO2 and PM from reduced capacity or retirement have 

little impact on visibility. The commenter stated that its modeling and analysis show that the TWG 

Alternative allows for many decades of visibility impairment before any improvements are made, 

contrary to the requirements of the CAA. 

Response:

EPA did not conduct visibility modeling as a basis for proposing to approve the TWG 

Alternative because EPA’s regulations provide that an alternative that results in the same distribution of 

emissions and greater emissions reductions is “better than BART” and that no additional modeling is 

required. 40 CFR 51.308(e)(3). The comment states that the TWG Alternative does not comply with the 

regulations because it will result in different temporal distribution of emissions. In fact, the comment 

admits that the “spatial” distribution of the emissions from BART and the TWG Alternative will be the 

same. 

EPA interprets the requirement of 40 CFR 51.308(e)(3) to require the same geographic 

distribution of emissions. There is no requirement in EPA’s regulations for a similar temporal 

distribution of emissions. See responses in section 8.5 of this document. EPA notes that Sierra Club 

endorsed the substitution of an Oklahoma SIP revision for EPA’s FIP despite the SIP revision having a 

different temporal distribution of emissions than the FIP it was replacing. The Sierra Club comment 

letter in that instance stated: “The FIP scenario may have somewhat greater benefits for several years, 

but the SIP Revision better achieves the overall goals of the Regional Haze program because emissions 

from both units will be completely eliminated by 2016.”344

In summary, there is no requirement in 40 CFR 51.308(e)(3) for EPA to demonstrate that the 

NOx emissions reductions from the TWG Alternative have a similar temporal distribution as BART. 

EPA interpreted this requirement to require a similar geographic distribution when we promulgated the 

rule in 2005, 70 FR at 39136-38. The requirements for visibility impairing pollutants to be reduced over 

time are contained in 40 CFR 51.308(d). EPA notes also that the regional haze program has a long time 

horizon and is a long term program with a horizon in 2064. 

Although visibility modeling is not required for the TWG Alternative because it has the same 

geographic distribution of emission reductions as BART and because EPA disagrees with the way the 

visibility analyses were presented in the Miller/Sahu Report, EPA conducted our own analysis of the 

anticipated visibility impacts of the TWG Alternative. The Miller/Sahu Report compared anticipated 

visibility impacts in 2020 and the sum of all visibility impacts over 2009-2044 (cumulative visibility 

impacts), for the Class I areas that EPA properly modeled that are within 300 km of NGS, as well as 

Class I areas within 520 km. The Miller/Sahu Report labeled as “BART-1” a scenario that is not 

consistent with EPA’s proposals and labeled as “CAP-1” the scenario that is consistent with EPA’s 

344 Letter from Elena Saxonhouse, Sierra Club to Guy Donaldson, EPA, Region 6, dated September 20, 2013. 
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proposals. Thus, the logical comparison between the commenter’s BART-1 and the TWG Alternative 

scenarios when viewing graphics in the report is misleading because BART-1 does not represent EPA’s 

position on BART for NGS.345 The proper comparison, which was not intuitive, would have been 

between the TWG Alternatives and the commenter’s CAP-1 scenario. Exhibit 2 to the Miller/Sahu 

Report shows that the TWG Alternative scenarios considered by the commenters, that meet the 2009-

2044 and 2009-2029 NOx Caps (as applicable) generally result in lower or comparable visibility impacts 

as EPA’s proposals for NGS (i.e., commenter’s depiction of CAP-1).346

In addition, the commenters opine that EPA’s graphs, included as supporting information for our 

Supplemental Proposal, were misleading because we labeled a line as “BART” that was actually the 

NOx Cap (i.e., it incorporated the LNB/SOFA credit). As discussed elsewhere in this response to 

comments document, EPA was clear in our Supplemental Proposal and supporting documentation, that 

the BART Benchmark, as computed in the Supplemental Proposal, included the LNB/SOFA credit, or in 

other words, it represented “5-year BART as if LNB not yet installed.”347 EPA also explained and 

provided supporting calculations to show that the two methods used to compare BART and BART 

Alternatives in the Proposed Rule and the Supplemental Proposal were equivalent (see Supplemental 

Proposal and section 8.5 of this response to comments document). Figure 3 of the Miller/Sahu Report 

reproduces EPA’s graph along with the line that the commenter asserts is more appropriate (i.e., BART 

accounting for the early and voluntary installation of LNB/SOFA in 2009-2011). The commenter opines 

that the difference between their BART line and EPA’s BART line is dramatic.348 Because the 

difference between the two lines represents whether or not the LNB/SOFA credit is included, the 

dramatic difference cited by the commenter actually illustrates the dramatic effect on cumulative 

emissions of the early and voluntary installation of LNB/SOFA in 2009-2011. Although the commenter 

(0367) attempts to portray the installation of LNB/SOFA as not truly “early” or truly “voluntary” or an 

attempt to “game the system,”349 Figure 3 of the Miller/Sahu Report illustrates that the decision by the 

operator of NGS to install LNB/SOFA on one unit per year over 2009-2011 did result in a dramatic 

change in the overall cumulative emissions profile for NGS. As stated elsewhere in this response to 

comments document, these emission reductions, as a factual matter, were early, real, and voluntary. 

Although some commenters opine that NGS should not be rewarded for “obfuscation and delay,” we 

note that Figure 3 of the Miller/Sahu Report graphically shows the benefit in emission reductions 

achieved by the operator’s decision to install LNB/SOFA early. Although EPA does not consider our 

Proposed Rule and Supplemental Proposal to be a “reward” (as NGS will still be required to close one 

unit or curtail operations by an equivalent amount and comply with emission limits achievable with 

SCR+LNB/SOFA), we also do not consider it appropriate to penalize NGS for their early and voluntary 

345 See Exhibit 2 to Miller/Sahu Report, titled “ex. 2 Visib and Emis for NGS.xlsx” in the docket for the rulemaking at EPAR09-OAR-2013-0009-0370. Because the commenters degreed with our proposal to give credit to NGS for the early and 

voluntary installation of LNB/SOFA, the scenario labeled “BART-1” excludes that credit and is therefore not consistent with 

EPA’s proposals. The Miller/Sahu Report also included a scenario labeled “BART-9” that applies additional corrections as 

recommended by the commenter. 

346 Id. See “dV profiles” tab. The commenter depicted TWG-1, 2, 12, 13, and 14 with cumulative visibility impacts over 

2009-2044 that are clearly lower than CAP-1. The commenter’s depictions of TWG-8, 9, and 11 with cumulative visibility 

impacts that appear to be slightly higher than CAP-1. Further inspection of the tab indicates that the difference between CAP1 and TWG-8, 9, and 11 is less than 5 percent, or a cumulative difference of 30 deciviews, distributed over 11 Class I areas 

over 35 years. The commenters did not show visibility results for scenarios that did not meet the 2009-2044 NOx Cap. 347 See, e.g., tab titled “TWG A1” in the document titled “Supplemental Better than BART Alternatives.xlsx” in document 

number 0191 in the docket for this rule at EPA-R09-OAR-2013-0009. 

348 See pages 14 and 15 of the Miller/Sahu Report. 

349 See, e.g., footnote 27 on pages 11-12 and page 22 of the EarthJustice Letter 
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reductions by setting an emissions cap that takes credit for those emission reductions (i.e., includes those 

reductions in the pre-BART period). 

EPA conducted visibility modeling to compare TWG Alternatives A1, A2, and A3 in 2019 and 

2030 against our proposed BART determination.350 As indicated by commenters, other possibilities exist 

beyond the scenarios for the TWG Alternatives we considered explicitly in our Supplemental Proposal. 

EPA has stated elsewhere that we need not consider potential emissions under all possible scenarios in 

setting the NOx Cap, but must verify that NGS can reasonably be expected to comply with 2009-2044 

NOx Cap under the various constraints imposed under the TWG Alternatives (i.e., closure, curtailment, 

and a secondary 2009-2029 NOx cap). However, EPA explored two other possibilities under TWG 

Alternative A3 beyond the one shown in Table 14 below. Those two possibilities included reducing 

capacity on all three units equally or reducing capacity on two units and installing SCR on the two units 

that operate at reduced capacity.351 EPA did not include those two additional possibilities under TWG 

Alternative A3 in our visibility modeling analysis because those scenarios do not reduce emissions 

sufficiently to meet the 2009-2044 NOx Cap. 

Table 14: EPA’s Additional Modeling for Final Rule to Compare TWG Alternatives with BART 

Scenario Year Description NOx Emission 

Rate (lb/hour) 

SO2 Emission 

Rate (lb/hour) 

TWG A1 in 2019 Close one unit. LNB/SOFA on two units. 4,309 1,064 

TWG A1 in 2030 Close one unit. SCR+LNB/SOFA on two 

units (0.07 lb/MMBtu). 1,257 1,064 

TWG A2 in 2019 

Close one unit. Increase capacity on two 

remaining units by 189 MW total. 

LNB/SOFA on those two units. 

4,851 1,198 

TWG A2 in 2030 

Close one unit. Increase capacity on two 

remaining units by 189 MW total. 

SCR+LNB/SOFA on those two units (0.07 

lb/MMBtu). 

1,415 1,198 

TWG A3 in 2019 Reduce capacity on Unit 2 by 561 MW. 

LNB/SOFA on three units. 4,878 1,197 

TWG A3 in 2030 

Reduce capacity on Unit 2 by 561 MW. 

SCR+LNB/SOFA on Units 1 and 3 (0.07 

lb/MMBtu). 

1,827 1,197 

BART 2019 + SCR+LNB/SOFA on three units (0.055 

lb/MMBtu). 1,506 1,591 

 Our visibility modeling of the TWG Alternatives compared to our proposed BART 

determination shows that, as expected, during the approximate 10-year period between 2019 and 2030, 

the visibility impacts of NGS under the TWG Alternatives are higher than the visibility impacts of NGS 

under BART (see Figure 8). Specifically, our modeling results indicate an anticipated cumulative 

visibility impact of NGS at all 11 Class I areas as a result of the TWG Alternatives A1-A3 ranging from 

350 See document titled “2014_0307 Emission Spreadsheets for NGS modeling for Final Rule.xlsx” in the docket for this 

rulemaking. EPA also remodeled the BART scenario using a rate when operating with SCR of 0.055 lb/MMBtu. The 

modeling EPA included with our proposed rule had modeled SCR at 0.05 lb/MMBtu. 

351 Id. See tab labeled “Read Me”. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

23 to 26 deciviews and a cumulative visibility impact of NGS as a result of BART of 13 deciviews.352

The commenter’s depictions of BART and the TWG Alternatives are generally consistent with our 

modeling. The commenters results show cumulative visibility impacts, at all 11 Class I areas (i.e., their 

depictions of areas within 300 km), in 2020 from the TWG Alternatives to range from 20 to 28 

deciviews and from BART to be 12 deciviews.353

After 2030, when NGS achieves additional emission reductions through compliance with a limit 

of 0.07 lb/MMBtu on two units, our modeling indicates that the visibility impacts under the TWG 

Alternatives are comparable to or lower than visibility impacts under BART (see Figure 8). Specifically, 

our results indicate an anticipated cumulative visibility impact of NGS at all 11 Class I areas as a result 

of the TWG Alternatives A1-A3 ranging from 10 to 13 deciviews and a cumulative visibility impact of 

NGS as a result of BART of 13 deciviews.354 The commenter’s depictions of the TWG Alternatives are 

generally consistent with our modeling, showing cumulative visibility impacts at all 11 Class I areas, 

that range from 9 to 14 deciviews.355 The commenter included other possible TWG scenarios that result 

in higher visibility impacts of NGS in 2030 and beyond, e.g., the TWG-11, representing two SCR and 

no unit curtailment or closure, at 17 deciviews; TWG-12 and TWG-13, representing closure of more 

than one unit with no installation of controls. However, despite the commenter’s depictions of visibility 

impacts in any given year, the commenter also showed that the cumulative visibility impacts across all 

11 Class I areas over 2009-2044 under their TWG scenarios (e.g., TWG-11 through TWG-14) were 

comparable to BART (i.e., the case the commenter labeled as CAP-1) 356. 

As stated previously, although the commenter also included emission and visibility scenarios for 

what they believe should be BART (i.e., depicted as BART-1 and BART-9), EPA disagrees that our 

proposed rules, including a credit for the early and voluntary installation of LNB/SOFA and emission 

limits and timing of compliance are not appropriate for NGS. Therefore, although the commenter 

compares the TWG Alternatives against depictions of its preferred BART determination to suggest that 

the TWG Alternative is not better than BART, EPA disagrees that those comparisons are appropriate. 

 Figure 8 below also shows anticipated visibility impacts of NGS after 2044. As noted elsewhere 

in this response to comments document, EPA is including as part of the TWG Alternative, in the 

regulatory language in the final rule, a provision consistent with the TWG Agreement that the 

owner/operator of NGS permanently cease conventional coal-fired generation by the end of 2044. Thus, 

under the TWG Alternative, the visibility impact of NGS is expected to be reduced or close to zero in 

2045 and thereafter. At its election, consistent with the Lease Amendment, the Navajo Nation may 

continue plant operations at NGS after December 22, 2044 consistent with EPA approval.357 Thus, the 

Navajo Nation may seek to operate NGS after 2044, however, EPA expects that operation of NGS after 

the owner/operator ceases conventional coal-fired generation would involve substantial modification to 

NGS and NGS would be required to meet all applicable regulatory and permitting requirements in 

existence at that time. Under BART, there would be no commitment or enforceable requirement for the 

352 See tab titled “Visibility Summary”, row 26, columns AT to AW, in the document titled “2014_0311 Better than BART 

Alternatives_Revised for Final Rule.xlsx” in the docket for this rulemaking. 

353 See tab titled “dV Profiles”, cells, e.g., Y15, BA15, BH15, BO15, and CC15 in Exhibit 2 to the Miller/Sahu report titled 

“ex. 2 Visib and Emis for NGS.xlsx” at EPA-R09-OAR-2013-0009-0370. 

354 See tab titled “Visibility Summary”, row 37, columns AT to AW in document titled “2014_0311 Better than BART 

Alternatives_Revised for Final Rule.xlsx” in the docket for this rulemaking. 

355 See tab titled “dV Profiles”, e.g., row 26, columns BA BH, BO, and BV in Exhibit 2 to the Miller/Sahu report titled “ex. 2 

Visib and Emis for NGS.xlsx” at EPA-R09-OAR-2013-0009-0370. 

356 See tab titled “TWG Emissions Graphs”, two graphs titled “Cumulative NOx Emissions, Tons, 2009-2044” in Exhibit 2 to 

the Miller/Sahu report titled “ex. 2 Visib and Emis for NGS.xlsx” at EPA-R09-OAR-2013-0009-0370. 

357 See Section VII.F of the TWG Agreement (page 14). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

owner/operator to cease conventional coal fired generation after 2044, therefore, visibility impacts of 

NGS at all 11 Class I areas would be expected to continue in 2045 and thereafter. We note that under the 

TWG Agreement, although the Navajo Nation has the option to continue operation of NGS after 2044, 

the Navajo Nation would be required to undergo New Source Review and control technology 

requirements as they exist in the future. Thirty years from now, as technologies advance, BACT for NOx

(and other criteria pollutants and greenhouse gas emissions) would likely require an emissions profile at 

NGS that is even more stringent than BART levels established in the present day. 

 Although visibility modeling of the TWG Alternative was not required under the RHR, EPA 

conducted visibility modeling in response to results submitted by the commenter in the Miller/Sahu 

Report. Our results indicate, as expected, that there is a period of time (over 2019 to 2030) when BART 

is better than the TWG Alternative, but after 2030, and especially after 2044, the TWG Alternative 

reduces the visibility impact of NGS on 11 Class I areas to a greater extent than BART. We also note 

that Sierra Club recently endorsed the substitution of an Oklahoma SIP revision for EPA’s FIP despite 

the SIP revision having a period of higher emissions than the FIP it was replacing. The Sierra Club 

comment letter in that instance stated: “The FIP scenario may have somewhat greater benefits for 

several years, but the SIP Revision better achieves the overall goals of the Regional Haze program 

because emissions from both units will be completely eliminated by 2026.”358 Therefore, although not 

required, EPA conducted additional visibility modeling and the results rebut the commenter’s assertions 

that the TWG Alternative is not “better than BART.” 

358 Letter from Elena Saxonhouse, Sierra Club to Guy Donaldson, EPA, Region 6, dated September 20, 2013. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 Figure 8: Comparison of Anticipated Visibility Impact over 2001-2044 under BART Benchmark and TWG A

0

102030405060

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

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2014

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Cumulative decivew impact of NGS on 11 ClassI Areas

Year

BARTTWG ATWG ATWG A

TWG is better than BART

BART is better than TWG

TWG is better than B

LNB/SOFA

Credit

TWG Step 3: Two

units meet 0.07

lb/MMBtu limit

TWG Step 2: Closure or

Curtailment

TWG Step 1: Early

install of

LNB/SOFA

BART: Three

units meet 0.055

lb/MMBtu limit
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Comment: TWG Alternative is not “better than BART” 

 One environmental advocacy group (0373) stated that EPA has not demonstrated and cannot 

demonstrate that the BART alternatives will achieve greater reasonable progress toward natural 

visibility conditions than BART. The commenter believes that there are multiple flaws with EPA’s 

proposals for each alternative, including improper use of a total NOx cap concept that fails to make 

greater reasonable progress than BART, use of an improper emissions baseline that artificially expands 

the cap for the alternatives only, and a lack of modeling by EPA (or TWG) to demonstrate reduced 

visibility impacts from the alternatives (see section 8.5 and in preceding comments in this section). The 

commenter asserted that EPA must reject the TWG Alternative (and Alternative 1) as inadequate as it is 

not “better than BART.” 

 One environmental group (0254) expressed skepticism regarding the timeframe for the TWG 

Alternative, which the commenter believes is too long, and the uncertainty provided by Alternative B. 

The commenter asserted that NGS should be cleaned up much sooner than 2030, regardless of the 

plant’s ownership arrangements. The commenter added that it is encouraging to see DOI’s commitment 

to a clean energy transition in the TWG Agreement, but the commenter contended that greater and more 

enforceable commitments should be made in order to transition our energy usage toward clean energy 

projects like wind and solar. 

 A public interest advocacy group (0356) also strongly objected to the TWG Alternative based on 

assertions that it does not benefit the environment, cultural resources and public health; it only bails out 

SRP, BOR, and Arizona utilities from having to find investors to take over California and Nevada’s 

share of NGS. In addition, the commenter does not support the TWG Alternative because the Hopi Tribe 

was not part of the TWG. The commenter does not support the EPA’s BART Alternative, which would 

allow early installation credit for low-NOx burners and SCR to be installed per unit between 2021 and 

2023. The commenter opined that that the owners of NGS should not be rewarded for obfuscation and 

delay, and pointed to EPA’s task to promulgate without unreasonable delay FIP provisions needed to 

protect air quality. The commenter added that the USBOR has several hydro-electric power projects in 

the West that can be used to produce power for CAP and tribes with water settlement agreements. 

A public interest advocacy group (0413) also objected to the TWG Alternative, which it believes 

is missing the economic and environmental justice interest of tribal communities that are affected by 

pollution caused by coal burning at NGS. The commenter said that the TWG appears to be a standard 

that is “better than BART,” but it cannot compete with the original BART standard proposed by EPA 

that will achieve a NOx reduction of 84 percent immediately after installing SCR within 5 years of the 

rule. One individual (0025/0130) asserted the TWG Alternative will have a disproportionately high and 

adverse human health or environmental effects on minority or low-income populations because it 

decreases the level of environmental protection. The commenter urged EPA to reject the TWG 

Alternative as it will create more bronchiolitis, which harms small children and minorities, and retain the 

NOx limit of 0.055 lb/MMBtu. 

The Hopi Tribe (0134) also expressed concern that EPA did not assess the potential economic 

impacts of the TWG Alternative to the Hopi Tribe. The commenter opined that EPA recognized the 

significance of NGS to the Hopi Tribe in its analysis under Factor 2 concluding EPA did not anticipate 

adverse impacts on the Navajo Nation and Hopi Tribe based on the analysis that SCR would not force 

NGS to close. Because the TWG Alternative includes closure of at least one unit in 2019, and EPA did 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

not address the potential economic impacts of partial closure of NGS on the Hopi Tribe, the Agency has 

not complied with its own BART regulations and guidance. The commenter noted the trust 

responsibility of the United States to the Hopi Tribe. The Hopi Tribe further noted that in the event 

capacity is reduced at NGS under the Supplemental Proposal, the amount of coal and water purchases 

would decrease leading to a decrease in income to the tribe from the sale of these. Also, the commenter 

stated that the Supplemental Proposal is not as effective in improving air quality and visibility for the 

Hopi reservation. Extending the timeframe during which NGS can continue to operate without SCR or 

an equivalent technology would cause a continued air quality burden on the Hopi Tribe. 

One commenter (0420) submitted copies of a petition signed by more than 70 members of the 

Navajo Nation favoring implementation of NOx controls at NGS within 5 years and opposing the TWG 

Alternative. 

Response: 

 EPA recognizes that numerous commenters do not support the TWG Alternative. EPA disagrees 

with the assertion that the TWG Alternative is not “better than BART.” EPA has responded elsewhere in 

this document to comments related to the NOx Cap, the BART Benchmark, the credit for the early and 

voluntary installation of LNB/SOFA, the flexible timeframe for compliance, the enforceability of the 

TWG Alternatives, and whether visibility modeling is required for BART Alternatives in cases where 

the geographic distribution of emissions under BART and the Alternative are the same (see section 8.5). 

To the extent that royalties paid to the Hopi Tribe depend on the amount of coal mined at the 

Kayenta Mine, and to the extent that the amount of water purchased depends on the amount of coal 

mined, EPA recognizes that the TWG Alternative, which includes closure of one unit at NGS or 

equivalent curtailment of operation, may change the royalties and other payments related to coal and 

water that are paid to the Hopi Tribe. Although EPA evaluated potential economic impacts of the BART 

options in our five-factor analysis, we disagree that we must also conduct similar analyses for 

Alternatives to BART. The BART Guidelines do not provide any guidance on the evaluation of BART 

Alternatives beyond the discussion in the Preambles for the 1999 and 2005 rules, and the Regional Haze 

Rule does not require an analysis of economic impacts of BART Alternatives. EPA’s evaluation of 

potential impacts to tribes in our five-factor analysis under BART is consistent with the BART 

Guidelines and was also used to inform our government-to-government consultation with tribes. 

EPA disagrees with the assertion that the TWG Alternative decreases the level of environmental 

protection and will have disproportionately high and adverse human health or environmental effects on 

minority or low-income populations. EPA notes that the BART determination requires emission 

reductions of NOx and does not permit or authorize new or greater pollutant emissions. Thus, if EPA 

took no action to finalize a BART determination, emissions from NGS would remain at current levels. 

In EPA’s final action, EPA is setting a BART Benchmark for NOx emissions over 2009-2044 based on 

an emission limit of 0.055 lb/MMBtu and requiring the operator of NGS to implement the TWG 

Alternative and reduce emissions in a phased manner to ensure total emission reductions remain below 

the BART Benchmark. Although the timeframe for the TWG Alternative (new reductions in 2019 and 

2030) is longer than the timeframe for BART (in 2019), we note that BART would only reduce 

emissions of NOx, whereas the TWG Alternative, in 2019, would also reduce emissions of SO2, PM, 

CO2, and hazardous air pollutants as a result of the closure of one unit (or equivalent curtailment). In 

addition, the regional haze program as envisioned by Congress and implemented in regulations by EPA 

is a long-term program spanning until 2064. Retirement of NGS as a conventional coal fired power plant 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

in 2044 will eliminate the visibility impairing pollutants 20 years before 2064. This result will also 

eliminate pollutants that affect human health and have other environmental effects. For the reasons 

described above, and elsewhere in this response to comments document, EPA disagrees that the TWG 

Alternative is not better than BART. 

Comment: Support for some changes EPA made to the TWG Alternative in the Supplemental Proposal 

 The TWG (0313) and one of the owners of NGS (0348) noted that there were several differences 

between Appendix B of the TWG Agreement and EPA’s Supplemental Proposal. The commenters 

expressed support for some of these as discussed below. Differences with which the commenters 

expressed concern are discussed later in this section. 

 The commenters (0313, 0348) agreed with the methodology that EPA used to calculate the 2009-

2044 NOx cap of 494,899 tons. The commenters noted that EPA adjusted this cap to provide credit for 

the early installation of LNB/SOFA up until the summer of 2014 based on the expectation that the 

BART FIP for NGS will not be final and effective until then. 

 The commenters (0313, 0348) noted that in the Supplemental Proposal, EPA proposed to require 

the NGS operator to notify EPA by December 1, 2019, of “the final ownership outcome and the 

resulting applicable operating scenario that it will implement” (citing 78 FR 62518). The commenters 

presume that EPA intended to require a notification of which TWG Alternative (A or B) applies based 

on the ownership of the plant at that time, and the commenter supports this requirement. However, the 

commenters requested that EPA not refer to the “operating scenario” in this context because the same 

term is used in the description of the Emission Reduction Plan required under Alternative B, and the 

NGS operator would not be in a position in 2019 to identify the operating scenario within the Emission 

Reduction Plan that it will implement if Alternative B applies. The commenters therefore requested that 

the same language be used in the preamble as in 40 CFR 49.5513(j)(4)(i) to clarify this requirement: “No 

later than December 1, 2019, the owner/operator must notify EPA of the applicable Alternative for 

ensuring compliance with the 2009–2044 NOx Cap.” 

 The commenters (0313, 0348) support the additional requirement to report annual heat input, 

although this information is already reported through the Acid Rain Program. However, the commenters 

requested that additional time be provided to ensure that the data submitted in the annual report is 

consistent with the data that the NGS operator submits to the Clean Air Markets Database (CAMD), in 

the annual emission inventory, and in the greenhouse gas (GHG) report required by 40 CFR part 98, 

which are not due until March 31st. To address this issue, the commenters suggested the following 

changes to 40 CFR 49.5513(j)(4)(ii): 

Beginning January 31, in 2015 and annually thereafter until the earlier of December 22, 

2044 or the date on which the owner/operator ceases conventional coal fired generation 

at NGS, the owner/operator shall submit to the Regional Administrator, a report 

summarizing the annual heat input, the annual emissions of sulfur dioxide, carbon 

dioxide, and annual and cumulative emissions of NOx from NGS for the previous full 

calendar year. The owner/operator shall make this report available to the public, either 

through a link on its Web site or directly on its Web site. The report shall be made 

available within 30 days of the submittal deadline associated with the annual 

emissions inventory required by the NGS Title V Operating Permit. 
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Response:

 EPA recognizes that the TWG supports some of the differences between EPA’s Supplemental 

Proposal of the TWG Alternative and the Appendix B to the TWG Agreement, including EPA’s 

revisions to the 2009-2044 NOx Cap and the requirement to report annual heat input. EPA agrees that it 

is reasonable to require the timeframe for the reporting requirements under BART to generally be more 

consistent with reporting requirements under the Part 71 operating permit. Therefore, EPA is making the 

change to the regulatory language recommended by the commenter. The commenter also noted that 

language in the preamble to our Supplemental Proposal related to notification to EPA by December 1, 

2019 was inconsistent with the language in the proposed regulatory requirements in our Supplemental 

Proposal. The commenter recommended that the preamble language match the language in the 

regulatory requirements. EPA agrees this is appropriate and will make efforts to ensure that the language 

in the preamble to the final rule is consistent with the actual language in the regulatory requirements of 

the final rule. 

Comment: Suggested addition to §§49.5513(j)(4)(iv)(A) and (B) 

 The TWG (0313) and one of the owners of NGS (0348) requested that EPA clarify the scope and 

content of the title V permit revision that is necessary to incorporate elements of the BART alternative 

by adding the language below from the TWG Alternative to the end of proposed §49.5513(j)(4)(iv)(B), 

and similar language to proposed §49.5513(j)(4)(iv)(A): 

The requirement to establish the Implementation Plan [Emission 

Reduction Plan] by December 31, 2029, and annually thereafter, and the 

requirement to operate in accordance with one of the operating scenarios 

outlined in the plan, shall be incorporated into the NGS Title V Operating 

Permit as federally enforceable permit conditions. In addition, the NGS 

Title V Operating Permit shall incorporate practically enforceable limits of 

0.24 lb/MMBtu, on a 30 Day Rolling Average basis, for each Unit 

equipped with LNB/SOFA, or 0.07 lb/MMBtu, on a 30 Day Rolling 

Average basis, for each Unit equipped with SCR, as federally enforceable 

permit conditions to achieve the emission reductions required under the 

Implementation Plan [Emission Reduction Plan]. The Implementation 

Plan [Emission Reduction Plan] will ensure that the Reasonable Progress 

Alternative to BART achieves greater reasonable progress than the 

Proposed BART Rule by providing a plan for managing NOx emissions to 

less than the 2009 2044 NOx Cap.

The CAP operator (0250/0343) noted only that the Supplemental Proposal is unclear with regard to 

which compliance requirements are needed in the title V permit revisions, without suggesting specific 

rule language. 

Response: 

EPA did not include the language from Appendix B to the TWG Agreement related to the title V 

(part 71) operating permit in the regulatory language in our Supplemental Proposal because the title V 
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(part 71) regulations require that the operating permits include all applicable requirements, which, for 

NGS, would include the permit limits that exist in its PSD permit (i.e., the limit of 0.24 lb/MMBtu when 

operating with LNB/SOFA) as well as the final requirements in this FIP (e.g., the limit of 0.07 

lb/MMBtu on two units in 2030). Therefore, a specific requirement in the FIP that directs the operating 

permit to incorporate applicable requirements is not necessary. However, to the extent the TWG requests 

consistency with the language in the TWG Alternative, although EPA considers it unnecessary, EPA 

will amend §49.5513(j)(4)(iii) to read: 

No later than December 31, 2020, the owner/operator shall submit an 

application to revise its existing Part 71 Operating Permit to incorporate 

the requirements and emission limits of the applicable Alternative to 

BART under paragraph (j)(3). The Part 71 Operating Permit for NGS shall 

incorporate practically enforceable limits for NOx of 0.24 lb/MMBtu, on a 

30 day rolling average basis, for each Unit equipped with LNB/SOFA, 

and 0.07 lb/MMBtu, on a rolling average basis of 30 boiler operating days, 

for each Unit equipped with SCR, as federally enforceable permit 

conditions. 

EPA will also add in the following provision as §49.5513(j)(4)(iv)(C): 

The requirement to establish annual Emission Reduction Plans by 

December 31, 2019 shall be incorporated into the Part 71 Operating 

Permit for NGS as federally enforceable permit conditions. In addition, the 

Part 71 Operating Permit for NGS shall incorporate practically 

enforceable limits for NOx of 0.24 lb/MMBtu, on a 30 Day Rolling 

Average basis, for each Unit equipped with LNB/SOFA, or 0.07 

lb/MMBtu, on a rolling average basis of 30 boiler operating days, for each 

Unit equipped with SCR, as federally enforceable permit conditions to 

achieve the emission reductions required under the Emission Reduction 

Plan. The Emission Reduction Plan will ensure that the Alternative to 

BART achieves greater reasonable progress than the Proposed BART 

Rule by providing a plan for managing NOx emissions to less than the 

2009 2044 NOx Cap.

We further note that in the proposed regulatory language in our Supplemental Proposal, EPA 

inadvertently did not specify an averaging period for the emission limits under the TWG Alternative 

Operating Scenarios (§49.5513(j)(3)). Therefore, EPA is adding to the regulatory language that emission 

limits apply over a rolling average of 30 boiler operating days, to 40 CFR §49.5513(j)(3), (j)(3)(i)(A)(2), 

(j)(3)(i)(B)(3), and (j)(3)(i)(C)(2). 

Comment: Another suggested addition to §§49.5513(j)(4)(iv)(A) and (B) 

 The TWG (0313), the CAP operator (0250/0343), and one of the owners of NGS (0348) stated 

that the EPA Supplemental Proposal specified a short term NOx limit of 0.07 lb/MMBtu on a 30 day 

rolling average basis for TWG Alternative A, but did not specify a limit for Alternative B as was 

included in the TWG Agreement. Two of the commenters (0313, 0348) requested that EPA add the 
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following language, which is taken from the TWG Agreement, to proposed §§49.5513(j)(4)(iv)(B) and 

49.5513(j)(4)(iv)(A) to address this issue: 

The NGS Title V Operating Permit shall incorporate practically 

enforceable limits of 0.24 lb/MMBtu, on a 30 Day Rolling Average basis, 

for each Unit equipped with LNB/SOFA, or 0.07 lb/MMBtu, on a 30 Day 

Rolling Average basis, for each Unit equipped with SCR, as federally 

enforceable permit conditions to achieve the emission reductions required 

under the Implementation Plan. 

Without suggesting specific language, the other commenter (0250/0343) anticipated that this 

discrepancy is an oversight that can be reconciled in the final rule. 

Response: 

EPA agrees that if the owners of NGS elect to install SCR in order to comply with the applicable 

NOx Caps under TWG Alternative B, then it is useful to specify the emission limit that would apply. 

Although the limit of 0.07 lb/MMBtu (on a rolling average basis of 30 boiler operating days) would 

apply under TWG Alternatives A1, A2, A3, or B, EPA notes that the operator of NGS may need to 

operate SCR at an emission rate that is lower than 0.07 lb/MMBtu depending on their compliance with 

the NOx Cap, but the addition of this provision would prohibit emissions of NOx, when operating with 

SCR, to exceed 0.07 lb/MMBtu (on a rolling average basis of 30 boiler operating days). EPA will amend 

§49.5513(j)(4)(iii) to read: 

No later than December 31, 2020, the owner/operator shall submit an 

application to revise its existing Part 71 Operating Permit to incorporate 

the requirements and emission limits of the applicable Alternative to 

BART under paragraph (j)(3). The Part 71 Operating Permit for NGS shall 

incorporate practically enforceable limits for NOx of 0.24 lb/MMBtu, on a 

30 day rolling average basis, for each Unit equipped with LNB/SOFA, 

and 0.07 lb/MMBtu, on a rolling average basis of 30 boiler operating days, 

for each Unit equipped with SCR, as federally enforceable permit 

conditions. 

EPA will also add in the following provision as §49.5513(j)(4)(iv)(C): 

The requirement to establish annual Emission Reduction Plan by 

December 31, 2019 shall be incorporated into the Part 71 Operating 

Permit for NGS as federally enforceable permit conditions. In addition, the 

Part 71 Operating Permit for NGS shall incorporate practically 

enforceable limits for NOx of 0.24 lb/MMBtu, on a 30 Day Rolling 

Average basis, for each Unit equipped with LNB/SOFA, or 0.07 

lb/MMBtu, on a rolling average basis of 30 boiler operating days, for each 

Unit equipped with SCR, as federally enforceable permit conditions to 

achieve the emission reductions required under the Emission Reduction 

Plan. The Emission Reduction Plan will ensure that the Alternative to 

BART achieves greater reasonable progress than the Proposed BART 
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Rule by providing a plan for managing NOx emissions to less than the 

2009 2044 NOx Cap.

Comment: Omitted ownership outcome 

 The TWG (0313) and one of the owners of NGS (0348) stated that EPA described the NGS 

ownership outcomes in a manner that is different from the scenarios outlined in the TWG Agreement. 

The commenters indicated that the ownership outcomes appear to be consistent, except that one 

potential outcome was omitted the scenario in which one or more of the existing NGS Participants 

(LADWP or NV Energy) remain in NGS, which would trigger Alternative B. To address this issue, the 

commenters suggested the addition of the following language to proposed §49.5513(j)(3)(ii)(D): 

Alternative B shall apply if, by December 31, 2019, either of the Departing Participants 

sells its ownership interests to a Party that is not an Existing Participant, or if either of 

the Departing Participants remains in NGS. 

Response: 

 EPA agrees that we inadvertently omitted, from §49.5513(j)(3)(ii)(D), the potential scenario 

where one or both of the Departing Participants (i.e., LADWP or NV Energy) do not exit NGS as 

expected. EPA is updating the language to incorporate the additional omitted ownership possibility. 

Comment: Describe details of TWG Agreement more fully in the preamble to the final rule 

The TWG (0313) and one environmental advocacy group (0395) said that EPA only briefly 

described the elements of the TWG Agreement in the October 2013 Supplemental Proposal (citing to a 

paragraph at 78 FR 62512 of the proposed rule). The environmental advocacy group (0395) asserted that 

this limited paragraph does not accurately present the provisions of the Agreement as it relates to clean 

energy economic development for affected Tribes, the rigorous development and consideration of clean 

energy alternatives to NGS, mitigation of CO2 emissions, and local Benefit Fund to address concerns of 

the public in the vicinity of NGS and the Kayenta-Black Mesa Mine Complex. Should EPA proceed 

with this alternative in the final rule, the commenter requested that the Agency fully describe the key 

elements in the preamble to the final rule by including the following and by elaborating on these 

elements and pulling text from the Agreement itself: 

EPA recognizes that the TWG Agreement has significant environmental, 

clean energy and economic benefits beyond those provisions included in 

Appendix B. These benefits include commitments for clean energy 

economic development for the affected Tribes, a Local Benefit Fund for 

community improvement projects within 100 miles of NGS or the Kayenta 

Mine, provisions for potential carbon dioxide emission reductions at NGS, 

a commitment to identify funding for and ensure completion of the Phase 

2 study by the National Renewable Energy Laboratory to analyze a full 

range of clean energy options for NGS, and commitments by the 

Department of the Interior to reduce or offset the carbon dioxide emissions 

associated with its Central Arizona Project pumping loads by 3 percent per 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

year, pursuant to a specifically described carbon dioxide emission 

accounting mechanism, and to facilitate the development of 26,975,000 

MWh of clean energy. 

The TWG (0313) requested that the same language be included in the preamble to the final rule, with the 

addition of an additional sentence: 

Nothing in this final rule shall preclude the NGS Participants from seeking 

to obtain greenhouse gas emission reduction credits, or similar 

commodities associated with activities committed to in the TWG 

Agreement, under any Federal or State law or policy to the extent 

permitted under such applicable law or policy. 

One of the owners of NGS (0348) also requested that this statement regarding the ability of NGS 

Participants to seek GHG emission reduction credits, which based on the language in the TWG 

Agreement, be included in the preamble to the final rule. The commenter stated that this provision is 

very important to the NGS Participants. Without suggesting specific language, the CAP operator 

(0250/0343) similarly noted that this aspect of the TWG Agreement was not incorporated or recognized 

in the Supplemental Proposal. This commenter anticipates that this discrepancy is an oversight that can 

be reconciled in the final rule. 

Response:

EPA acknowledged that the TWG Agreement contains additional provisions that will be 

beneficial to the tribes in the area and to the environment. However, EPA does not consider it 

appropriate to provide a detailed discussion of these additional provisions of the TWG Agreement in our 

final rule. EPA was not a signatory to the TWG Agreement and did not participate in the TWG 

Stakeholder group. The TWG Agreement speaks for itself and the participants and signatories are the 

appropriate entities to interpret the provisions of the TWG Agreement. EPA is acting as a regulatory 

agency because we are finding that it is necessary or appropriate to regulate NOx emissions from NGS to 

improve visibility at the GCNP and 10 other Class I areas. EPA is not exercising authority other than 

that set forth in CAA section 169A. Therefore, EPA is declining to provide any further discussion of the 

non-regional haze provisions of the TWG Agreement. 

The comment also requests EPA to add certain language to the final rule. Specifically, the 

comment asks EPA to add: “Nothing in this final rule shall preclude the NGS Participants from 

seeking to obtain greenhouse gas emission reduction credits, or similar commodities associated 

with activities committed to in the TWG Agreement, under any Federal or State law or policy to 

the extent permitted under such applicable law or policy.” 

EPA is also declining to add the requested language to our final rule. EPA is not 

exercising any authority in this action other than implementing CAA section 169A, through our 

discretion in the TAR. It would be inappropriate in this action to take any position on the future 

use or regulation of GHG emission reductions or “similar commodities.” 

Comment: TWG Alternative should satisfy Reasonable Progress requirements 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 One of the owners of NGS (0348) stated that Appendix B to the TWG Agreement was designed 

to meet not only BART requirements, but also reasonable progress requirements applicable to NGS 

through 2044. The commenter believes that because of the importance of NGS to the owners, tribal 

entities, and the State of Arizona, it is important to have as much regulatory certainty as possible. 

Accordingly, the commenter requested that EPA determine that the TWG Alternative satisfies both the 

BART and reasonable progress requirements of the CAA through 2044. Specifically, the commenter 

requested that EPA add the following language to the preamble in the final rule: 

Given that the TWG Alternative contains NOx reduction measures that 

will be implemented over a long term period through 2044, and the factors 

that will be considered in a future reasonable progress determination, as 

prescribed in section 169A(g)(1) of the Clean Air Act (CAA), are similar 

to the BART factors in section 169A(g)(2) of the CAA, the outcome of a 

future review under the reasonable progress requirements of the CAA is 

expected to conclude that the TWG Alternative satisfies both BART and 

the reasonable progress requirements of the CAA with respect to NGS 

through 2044. 

 The CAP operator (0250/0343) similarly noted that the Supplemental Proposal does not specify 

that the TWG Alternative satisfies reasonable progress requirement, as was intended by the TWG. 

Without suggesting specific language, the commenter anticipated that this discrepancy is an oversight 

that can be reconciled in the final rule. 

Response: 

EPA has not made any finding pursuant to 40 CFR 49.11(a) that it is necessary or appropriate at 

this time to promulgate a FIP to meet the reasonable progress requirements for States under the RHR. 

The requirement for States to develop reasonable progress goals are established in 40 CFR 51.308(d)(1). 

But there is no requirement for that provision of the RHR to apply to the Navajo Nation until EPA 

makes a determination that it is necessary or appropriate for EPA to promulgate a FIP for that provision. 

In any event, the reasonable progress goals would not be directly applicable to NGS without substantial 

further analysis. Because it is premature to determine that it is necessary or appropriate to promulgate 

such a FIP, it is also premature to determine that it is not necessary or appropriate. Therefore, EPA is 

declining to take the action requested in the comments. 

Comment: Delete requirement to keep records of maintenance 

 One of the owners of NGS (0348) requested that EPA delete the requirement in proposed 

§49.5513(j)(7)(vi) that the NGS operator keep records of all major maintenance activities that occur at 

NGS. According to the commenter, the existing title V permit requirement that the NGS operator 

operate and maintain emission control equipment in a manner that is consistent with good engineering 

practices to keep emissions at or below applicable emissions limitations provides sufficient assurance 

that emission control equipment will be operated and maintained in accordance with best practices. 

Response: 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 EPA is deleting the requirement proposed under §49.5513(j)(7)(vi) to require the operator of 

NGS to keep records of all major maintenance activities at NGS because records of major maintenance 

activities are not needed for demonstrating compliance with the 2009-2044 or 2009-2029 NOx Caps or 

other provisions of the TWG Alternative. 

Comment: 0.07 lb/MMBtu limit 

 One of the owners of NGS (0348) noted that the TWG Agreement would establish a NOx

emission limit of 0.07 lb/MMBtu for any unit equipped with SCR. The commenter pointed out that this 

proposed emission limit is at the lower end of the range recommended in S&L’s analysis of achievable 

emission limits at NGS (discussed in section 8.1 of this document), which could require the NGS 

Participants to limit operation of the units in certain modes, unless future technology advances allow the 

limit to be achievable over a broader range of operating conditions. The commenter views the 0.07 

lb/MMBtu limit not as BART but as a “better than BART” limit in that it would result in greater NOx

emission reductions than the February 2013 Proposal. 

Response: 

 EPA agrees that the commenter correctly noted that 0.07 lb/MMBtu is the lower end of the range 

recommended by S&L in their analysis. EPA also agrees that 0.07 lb/MMBtu is not BART (as discussed 

in section 8.1, EPA is determining that BART for NGS is a limit of 0.055 lb/MMBtu). However, EPA 

disagrees with the commenter that 0.07 lb/MMBtu, by itself, is better than BART. Although the TWG 

Alternative results in more emission reductions than would have been achieved under BART, we note 

that 0.07 lb/MMBtu is not, in itself, a better than BART limit because the TWG Alternative includes two 

other components besides compliance with a limit of 0.07 lb/MMBtu in 2030, namely, closure of one 

unit (or equivalent curtailment) in 2019, and a credit for the early and voluntary installation of 

LNB/SOFA over 2009-2011. 

Comment: Update past agreements

 One individual (0415) recommended that past agreements cited in the TWG proposal, including 

the Navajo-Hopi Rehabilitation Act of 1950, the Colorado River Basin Project Act of 1968, Central 

Arizona Project, and the federal government’s “unique and continuing trust relationship with and 

responsibility to Indian tribes,” be revisited and revised to reflect current knowledge and data on fossil 

fuels. 

Response: 

 EPA included a summary of this comment in this response to comments document, however, we 

note that this comment is not directly related to our Proposed Rule or our Supplemental Proposal and is 

beyond the scope of our rulemaking; therefore, we are not providing a response to this comment. 

Comment: Concern that the Hopi Tribe and other affected parties were excluded from TWG
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 Five individuals (0240, 0245, 0281, 0394, 0399) were frustrated that all affected parties, 

particularly the Hopi Tribe, were not included in the development of the TWG Alternative. One 

commenter (0281) noted that the Hopi Tribe has a Generating Performance Agreement with SRP that 

should have mandated their involvement. The White Mountain Apache Tribe (0440) also notes that it 

was not party to the TWG Agreement. Another commenter (0394) noted that a presidential Executive 

Order, initially issued by President Clinton and then reissued by President Obama, requires that all tribal 

nations be consulted on these types of regulations, and asserted that EPA and DOI violated this order. In 

addition, this commenter noted that several letters by then-Chairman of the Hopi Tribe Leroy 

Shingoitewa were sent to DOI complaining about the lack of consultation. Another commenter (0399) 

argued that the TWG proposal did not consider grassroots statements, including comments from Black 

Mesa, and discouraged their participation in TWG public forums, instead conducting meetings with only 

industry stakeholders who had financial interests. 

 One of the individuals (0281) stated that EPA did not give the public enough time to comment 

on the TWG Agreement before issuing a Supplemental Proposal and, on that basis, demanded that EPA 

withdraw its approval of the TWG Alternative. The commenter added that the TWG Agreement is based 

on the assumption that the Hopi will support the Kayenta Mine Lease extension when it expires in 2025, 

but the Hopi have yet to discuss the extension with the 12 Hopi independent villages, which is a 

requirement in the Hopi Constitution. Furthermore, the commenter noted that the TWG Agreement 

ignores the requirement of completing an EIS and ROD before the NGS site lease with the Navajo 

Nation expires in 2019. The commenter argued that the DOI-BOR’s approval of the TWG Agreement 

without the fulfillment of these requirements violates the NEPA process. The commenter added that in 

1989, the Hopi Tribe rejected the Draft Kayenta Mine-Black Mesa Mine EIS in its entirety, and implied 

that the decision to accept the TWG proposal could compromise EPA’s final decision. 

Response:

 EPA recognizes that there are affected tribes and other stakeholders that were not included in the 

Technical Work Group. We note that EPA was not involved in the formation of the TWG and not 

involved in any meetings or discussions of the TWG.359 As discussed in section 10.0 of this response to 

comments document, consistent with Executive Order 13175: Consultation and Coordination with 

Indian Tribal Governments, EPA consulted with tribes early and regularly during the development of 

this rulemaking for NGS. We note that the Regional Administrator for Region 9 spoke with thenChairman LeRoy Shingoitewa on September 13, 2013 about the TWG Agreement and notified elected 

leaders or legal counsel for five tribes when EPA signed the Supplemental Proposal. EPA also held 

individual and joint consultation meetings with tribal leaders in Phoenix, Arizona on December 9-10, 

2013. 

EPA disagrees that we did not provide the public enough time to review the TWG Agreement. 

EPA posted the TWG Agreement to the public docket on July 26, 2013, the same day it was submitted 

to EPA.360 EPA reviewed the TWG Agreement and on September 25, 2013, signed a Supplemental 

Proposal that put forth the TWG Alternative, consistent with Appendix B of the TWG Agreement, as an 

additional “better than BART” Alternative for public comment, and on October 22, 2013, the 

359 At the request of the TWG, at their kick-off meeting, EPA presented a summary of our Proposed Rule and framework for 

BART Alternatives. The presentation at the TWG kick-off meeting was generally the same presentation EPA provided to 

other stakeholders. See document 0033 in the docket for the rule at EPA-R09-OAR-2013-0009. 

360 See document number 0122 in the docket for this rulemaking, at EPA-R09-OAR-2013-0009-0122. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Supplemental Proposal published in the Federal Register.

361 The public had nearly six months to review 

the TWG Agreement as submitted to EPA and approximately three months to review EPA’s 

Supplemental Proposal. EPA also notes that EPA’s rulemaking is not subject to NEPA. 

Comment: EPA’s relationship to the TWG is confusing 

 The White Mountain Apache Tribe (0440) opined that although EPA stated it was not involved 

in the TWG, EPA was a signatory of the “Joint Federal Agency Statement Regarding Navajo Generating 

Station”, the scope of which includes numerous elements that reference EPA’s commitments, along with 

the Departments of the Interior and Energy in relation to NGS. The commenter suggests that EPA was 

involved in a legal triangulation with the TWG signatories and that such action is an extra-jurisdictional 

exercise by EPA, to which the Tribe does not consent. The commenter concludes that the Tribe cannot 

consider the TWG Alternative unless its published form is changed by EPA to fully disentangle the 

proposal from the signatory group and all non-BART terms of the TWG Agreement, and additional 

public comment is thereafter allowed. 

Response:

The Joint Federal Agency Statement Regarding Navajo Generating Station is a document that is 

completely separate from the TWG. The Joint Federal Agency Statement was signed by the 

Administrator of EPA and the Secretaries of the Interior and Energy on January 4, 2013. That document 

acknowledged that each of the three federal agencies have an interest in the operation of NGS. In 

contrast, EPA was not part of the TWG. EPA did not participate in any of the substantive discussions 

and negotiations of the TWG. Two representatives of EPA attended the beginning of the first meeting of 

the TWG but only to present an summary of EPA’s February 5, 2013 Proposed Rule.362 After the initial 

meeting, EPA was not involved with the TWG until the TWG Alternative was completed. 

The TWG was not primarily composed of federal agencies. The TWG had two environmental 

organizations (Environmental Defense Fund and Western Resource Advocates), two Tribes (Gila River 

Indian Community and the Navajo Nation), two Arizona utilities (Central Arizona Water Conservation 

District and Salt River Project) and the Department of the Interior. Appendix B of the TWG Agreement 

contains provisions relating to BART but there were several other provisions of the TWG Agreement 

that are beyond the scope of BART and are not part of EPA’s rulemaking in this action. 

EPA disagrees with the commenter that EPA is “entangled” with the TWG. As stated previously, 

EPA did not participate in the TWG and was not involved in the TWG Agreement. EPA does not 

understand what the commenter means in stating that the White Mountain Apache Tribe “cannot 

consider the TWG Alternative unless its published form is changed by EPA to fully disentangle the 

proposal from the signatory group and all non-BART Agreement terms.” EPA does not agree that any 

further public comment is warranted.

361 See document number 0182 and 0186 in the docket for this rulemaking, at EPA-R09-OAR-2013-0009-0182 and EPAR09-OAR-2013-0009-0186. 

362 At the request of the TWG, at their kick-off meeting, EPA presented a summary of our Proposed Rule and framework for 

BART Alternatives. The presentation at the TWG kick-off meeting was generally the same presentation EPA provided to 

other stakeholders. See document 0033 in the docket for the rule at EPA-R09-OAR-2013-0009. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

10.0 Other Comments 

Comment: General Support 

 In general, many individuals (0020, 0021, 0038, 0040, 0047, 0064, 0067, 0083, 0091, 0112, 

0113, 0123, 0248, 0177, 0179, 0180, 0181, 0197, 0202, 0215, 0216, 0217, 0235, 0241, 0242, 0261, 

0264.3, 0264.5, 0264.6, 0275, 0281, 0290, 0327, 0331, 0344, 0361, 0364, 0396, 0415), support EPA’s 

effort to reduce emissions from NGS. Many of these commenters asked for the most stringent 

regulations and urged EPA not to delay BART control requirements. Two commenters (0047, 0064) 

applauded EPA’s effort to fully engage the stakeholders in the rulemaking process, which they believe 

shows a willingness to work together on the part of Agency. Another commenter (0112) compared 

EPA’s efforts to John F. Kennedy’s determination to send a man to the moon, and believes that regional 

haze regulations will force the energy industry to invest in better technology more quickly than if they 

were not asked to do so. Similarly, one commenter (0264.3) quoted President Roosevelt who stated 

“Leave it as it is,” referring to the Grand Canyon. 

 Four individuals (0164, 0179, 0344, 0415) asserted that opponents to the proposal take advantage 

of Arizona’s air quality for their own personal gains (e.g., maximum bonuses and salaries). One of these 

commenters (0415) stated that Peabody’s September 2013 quarterly report references 3rd quarter 

revenues of $1.80 billion and a new $2.85 billion credit facility, and argued that this report proves that 

Peabody can make the financial investments needed to NGS to reduce emissions. Two other individuals 

(0204, 0331) stated that facility owners can afford propaganda to promote their views and tribal 

communities cannot. Another individual (0215) urged EPA to mount its own campaign addressing the 

health and environmental risks to Arizonans if the state of Arizona does not address air pollution. 

 Six individuals (0177, 0197, 0235, 0264.6, 0327, 0341) would prefer that NGS be shut down 

completely. One individual (0149) argued that soot from coal-fired power plants like NGS contribute 

twice as much to global warming as non-soot forming power sources, and claimed that if these plants 

were located closer to major cities, like Phoenix or Tucson, they would have retrofitted or shut down 

already. 

Response: 

 EPA recognizes that numerous individuals supported our proposed BART determination for 

NGS and several individuals expressed their preference that NGS close immediately or in the near 

future. EPA does not have authority under the RHR and the BART requirements of the CAA to require a 

facility to close. In recognition of the role NGS plays in the economies of the Navajo Nation and the 

Hopi Tribe, and in providing power to CAP, which serves numerous tribes located in Arizona, EPA is 

finalizing the TWG Alternative that requires greater NOx reductions than what would have been 

otherwise achieved under BART in exchange for additional flexibility in the compliance timeframe to 

ensure continued operation of NGS and reduced impacts to tribes. 

EPA recognizes that certain stakeholders may have greater resources than others to prepare 

comments. However, EPA provided a lengthy comment period and numerous opportunities to talk with 

representatives from EPA and submit comments orally or in writing. EPA notes that Peabody Energy 

operates the Kayenta Mine, but is not the operator of NGS. Therefore, statements made about the ability 

of Peabody Energy to make financial investments in NGS are not germane. 
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Comment: Disproportionate impacts to tribes 

The Tonto Apache Tribe and the San Carlos Apache Tribe (0419) believe that both the original 

BART proposal and the proposed TWG Alternative are contrary to U.S. obligations and trust 

responsibilities to Indian Tribes under CAP and have disproportionate impacts on tribes with CAP 

contracts. The commenter expressed that environmental quality is of upmost importance to the tribes, 

but clean air is the responsibility of all citizens. Therefore, the commenters assert that because the 

United States owns 24.3 percent of NGS, the costs of compliance for that 24.3 percent share should be 

shared among all American people, who will benefit from cleaner air. The commenters urged EPA to 

develop an alternative regulation that does not place additional burden on Indian Tribes. 

Response: 

 EPA agrees that our proposed BART determination and the TWG Alternative will impact tribes 

with CAP water contracts. We note that the Joint Federal Agency Statement on NGS reflects the U.S. 

Government’s recognition of its responsibilities related to NGS and trust responsibility to Indian tribes 

affected by NGS. 

Although EPA is finalizing a BART Benchmark for NGS, the regulatory requirements will 

include only the requirements and compliance timeframes under the TWG Alternative as proposed in 

our Supplemental Proposal. As defined in our Supplemental Proposal, emission reductions at NGS 

would be achieved in phases, including closure of one unit or the equivalent in 2019, and compliance 

with an emission limit achievable with SCR in 2030. We note that the closure of one unit was possible 

because of the planned divestment of LADWP and NV Energy from NGS by 2019. Because LADWP 

and NV Energy are unrelated to CAP, EPA does not expect substantial compliance costs to be borne by 

Reclamation (and thus, tribes or other CAP water users) due to the first phase of emission reductions at 

NGS in 2019. EPA further notes that the 2030 compliance date for meeting an emission limit achievable 

with SCR on two units at NGS is approximately 16 years from the present day. As stated elsewhere in 

this response to comments document, the requirements under BART and the TWG Alternative are for 

meeting emission limits, rather than installing a particular technology. Thus, 16 years from now, 

although SCR will be capable of meeting the emission limit, other technologies or options may become 

available for the operator of NGS to more cost-effectively meet the NOx emission limit of 0.07 

lb/MMBtu. 

EPA agrees with the commenter’s statement that the Department of the Interior, Department of 

Energy, and EPA, in the 2013 Joint Statement on NGS, committed to work together with stakeholders to 

support implementation of BART requirements at NGS in a manner that reduces emissions while 

supporting longer-term goals that include, among other things, minimizing impacts to tribal nations that 

benefit from NGS, and that this commitment included, as an example action, seeking funding for the 

federal portion of air pollution upgrades at NGS.363 However, EPA notes that the commenter 

mischaracterized the commitment made in the TWG Agreement (in which EPA and DOE did not 

participate) related to the Reclamation Water Settlements Fund. The commenter stated that BOR would 

deposit $10 million into the Fund to assist tribes in transitioning away from reliance on NGS. The TWG 

363 See document titled “2013_0104 Joint Federal Agency Statement on NGS” in document number 0005 in the docket for 

this rule at EPA-R09-OAR-2013-0009. 
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Agreement actually states that the Department of the Interior commitment to expend at least $10 million 

over 2020-2029 (a total of $100 million) for the purpose of providing financial assistance for the fixed 

OM&R costs. 

EPA recognized the potential impacts to tribes of our proposed BART determination and sought 

ways to provide flexibility and a framework for affected stakeholders to develop alternative approaches 

to BART. EPA has determined that the TWG Alternative achieves greater emission reductions than 

would otherwise be achieved under our proposed BART determination, while providing additional time 

for compliance. This additional time allows the DOI, DOE, and EPA time to work with tribal 

stakeholders to identify and implement strategies for achieving the goals outlined in the Joint Federal 

Agency Statement on NGS. 

Comment: Conduct Impact Assessments 

An environmental advocacy group (0395) said that one of the main concerns raised at the public 

hearings was the importance of addressing public health concerns related to the collection of industrial 

activities at NGS and Kayenta-Black Mesa Mine Complex and protection of water resources. The 

commenter urged EPA to collaborate with other experts and expert agencies to address these concerns, 

conduct a rigorous impact assessment, and take corrective action. The commenter stressed the 

importance of the Navajo aquifer and other water resources of the Colorado Plateau. For example, under 

TWG Alternative A, one-third the capacity at NGS would close in 2019. The commenter stressed that a 

transparent and inclusive process is essential for determining solutions for wise stewardship of the water 

that would continue to be used by the remaining coal units at NGS. 

A public interest advocacy group (0413) also asked that a health assessment be conducted to 

study the impacts of NGS pollution on the Navajo Nation. The plant has been releasing large quantities 

of pollution and toxic metals since 1974, putting the health and lives of Navajo and Hopi people in 

danger. The facility emits more than 16,000 tons per year of NOx according to EPA Air Markets 

Program Data, 13,000 pounds per year of hydrochloric acid (HCl), more than 19,000 pounds per year of 

hydrogen fluoride (HF) and more than 580 pounds of mercury, according to the EPA Toxic Release 

Inventory, and is one of the top 10 worst-emitting coal plants in the country. 

Response: 

 EPA recognizes that NGS, together with the Kayenta Mine, have environmental impacts that 

extend beyond regional haze and visibility impairment at Class I areas. EPA notes that the NGS site 

lease and other grants of rights-of-way associated with NGS and the Kayenta Mine are subject to NEPA. 

The Department of the Interior, with Bureau of Reclamation as lead Federal agency, is initiating the 

preparation of an Environmental Impact Statement (EIS) to cover these actions. EPA will have a role in 

reviewing the EIS for NEPA compliance and may become a cooperating agency. 

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 

people with asthma, children, and the elderly. At this time the Navajo Nation is not identified as out of 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

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. 

Comment: Require recordkeeping for the life of the plant 

One environmental advocacy group (0395) indicated that the current requirement to maintain 

records for 5 years is insufficient and inappropriate for the compliance schedule associated with NGS 

and recommended that records be maintained from 2009 through the remaining operating life of the 

plant. It is essential to maintain transparency and enforceability for the final rule and requirements for 

NGS. The commenter urged the Agency to finalize a requirement that will provide the public the ability 

to participate and evaluate in real time the emissions performance and compliance activity of this major 

emitting facility.

Response: 

 EPA agrees that because the operator of NGS must ensure compliance with the 2009-2044 NOx

Cap, the operator of NGS should also maintain records for the life of the facility to demonstrate 

compliance with the TWG Alternative. In the regulatory language in our Final Rule, EPA is amending 

§49.5513(j)(7) to require the owner or operator of each unit to maintain records, as required under 

§49.5513(j)(7)(i) to (vi), until the earlier of December 22, 2044 or the date that conventional coal-fired 

operation of all units at NGS permanently ceases. As discussed elsewhere in this response to comments 

document, EPA is adding to the final rule the provision of the TWG Agreement that prohibits continued 

operation of conventional coal-fired generation at NGS beyond December 22, 2044. If the Navajo 

Nation elects to continue plant operations at NGS, the Navajo Nation must obtain permits under the 

New Source Review or PSD programs. 

Comment: Oppose Operation of NGS 

One public interest advocacy group (0403) indicated that it is opposed to the current and 

proposed operation at NGS and associated activities because it violates the SMCRA, CAA, Clean Water 

Act, UN Declaration of the Rights of Man, and customary law. 

One individual (0025/0139) submitted legal opinions to support their position that NGS does not 

have a Certificate of Environment Compatibility (CEC) from the Arizona Corporation Commission. See 

685, State of Arizona ex rel. Merrill v. Turtle, 413 F. 2d 683 - Court of Appeals, 9th Circuit 1969. 

Response: 

EPA is taking a limited action in this rulemaking with clearly defined boundaries. We are finding 

under 40 CFR 49.11 that it is necessary or appropriate to promulgate a FIP to implement the 

requirements in CAA section 169A and 40 CFR 51.308(e) to implement BART or a better than BART 

alternative for NOx emissions at NGS.364 The allegations of violations of other provisions of the CAA 

and of other statutes, treaties or laws are not within the scope of this action. EPA’s action in 

364 EPA’s authority to act in this manner has been upheld in Arizona Public Service Co. v. EPA, 562 F.3d 1116, 1131 (10th

Cir. 2009); see also WildEarth Guardians v. EPA, No. 13-9524, (10th Cir. July 23, 2014) slip op. at 24-26, in the docket for 

this rulemaking. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

promulgating this FIP is also separate and independent of any alleged violations of Arizona state law 

based on potential requirements of the Arizona Corporations Commission. 

Comment: EPA lacks authority to regulate NGS

 Three individuals (0043, 0137, 0346) indicated that EPA overstepped its authority, and five other 

individuals (0081, 0090, 0230, 0231, 0312) stated that EPA’s proposal hinders the state’s ability to deal 

with environmental issues on a local level. Two commenters (0230, 0231) stated that SIPs are the best 

method for achieving a long-term transition to less carbon, and that the 10th Amendment requires EPA to 

use the SIP when implementing these regulations. 

 One individual (0292) claimed that EPA does not have the authority to proceed with the 

proposed regulations because it failed to consider indirect and direct costs of compliance, as outlined in 

the CAA. 

One individual (0127) stated that EPA’s regulations are an attack on free enterprise, and believes 

that Obama’s agenda to ban all coal-fired power plants regardless of the economic effect is no different 

from the agenda of a communist dictator. 

Response: 

EPA disagrees that it has overstepped its regulatory authority and disagrees that any State has 

authority to regulate air pollution from sources located on the Navajo Nation. EPA’s authority to 

regulate NGS is derived from section 301(a) and 301(d)(4) of the CAA. Section 301(d)(4) directs EPA 

to directly administer provisions of the CAA on Tribal land under certain circumstances. The State of 

Arizona has no jurisdiction to regulate air pollution on Tribal lands. The D.C. Circuit upheld EPA’s 

promulgation of the TAR in Arizona Public Service v. EPA. The court characterized Congress’s addition 

of CAA section 301(d) in the 1990 Amendments, stating: “The Act establishes a framework for a 

federal-state partnership to regulate air quality. The provisions of the 1990 amendments under review, 

fairly read, constitute an attempt by Congress to increase the role of Native America nations in this 

partnership.”365 EPA is the proper governmental entity to regulate visibility impairment associated with 

NGS at this time. 

EPA disagrees that the 10th Amendment requires EPA to use a State Implementation Plan to 

implement the BART provision of the RHR. The comment provides no support for the statement. 

EPA disagrees that the regulations promulgated in this action, which is approval of the TWG 

Alternative, consistent with the Appendix B of the TWG Agreement, constitutes an attack on free 

enterprise. The TWG Alternative authorizes NGS to continue to operate until 2044. The TWG 

Agreement was submitted to EPA by a stakeholder group that had determined it was a more costeffective approach to continuing to operate NGS than a prior proposal by EPA. EPA considered the 

direct costs of compliance in our five-factor BART analysis, and considered numerous indirect impacts 

and costs specifically in our analysis of Factor 2. The comment provides no information other than 

conclusory statements that EPA failed to adequately consider the cost of compliance. Far from banning 

365 211 F.3d 1280, in the docket for this rulemaking. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

coal burning, this rule allows NGS to continue to operate until 2044 when its lease with the Navajo 

Nation expires. 

Comment: The Federal Government should set an example

One individual (0067) believes that the U.S. government, as a major owner of NGS, is 

responsible for setting a good example by requiring the plant to run more efficiently. 

Response: 

 EPA agrees that the Bureau of Reclamation, under the U.S. Department of the Interior, is a 

participant in NGS with a 24.3 percent share. As discussed in our Proposed Rule, Reclamation 

participates in NGS for the benefit of the Central Arizona Project, and this relationship benefits 

numerous tribes in Arizona, as well as other water users, including municipal, industrial, and agricultural 

users of CAP water. EPA notes that we are establishing a BART Benchmark based on compliance with 

an emission limit of 0.055 lb/MMBtu within five years of the effective date of the final rule. The 

emission limit associated with the BART Benchmark for NGS is among the lowest NOx limits required 

under BART.366 We note that the 2009-2044 NOx Cap under the TWG Alternative is calculated based 

on the BART Benchmark, and that our final action on NGS will result in step-wise emission reductions 

to reduce the impact of NGS on visibility at eleven Class I areas. 

Comment: Political considerations 

 One individual (0080) stated that EPA’s proposal creates a foundation for political opposition to 

existing and future environmental policies because it is too costly and will achieve little to no benefits. 

One individual (0116) claimed that EPA’s regulation has nothing to do with haze, but rather 

political gains, and asserted that the federal government has a vendetta against Arizona, as evidenced by 

federal law suits. Similarly, one individual (0128) believes that EPA has lost sight of its mission and is 

being used to carry out a political agenda. 

One individual (0327) stated that EPA catered to local politicians that attend the public hearings, 

particularly the hearing held in Phoenix. The commenter claimed that these representatives, along with 

representatives from industry, provided no usable comments on haze. 

Response: 

 EPA disagrees that this rulemaking is too costly and will achieve little to no benefits. We also 

disagree that this rule is for political gain and has nothing to do with haze. Our five-factor analysis 

shows that our BART determination is cost-effective and will significantly reduce the impact that NOx

emissions from NGS have on visibility impairment at 11 Class I areas. In addition, our Supplemental 

Proposal is consistent with Appendix B of the TWG Agreement, which was developed by a group of 

diverse stakeholders, including the facility operator, two tribal nations, CAP water interests in Arizona, 

and two environmental organizations, and represents a compromise among the various interests to 

366 See spreadsheet titled “Western Coal EGU BART Summary.xlsx” in the docket for this rule. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

achieve greater emission reductions than our proposed BART determination in exchange for greater 

flexibility in the compliance timeframe. In 1993, the 9th Circuit Court of Appeals upheld the rule 

finalizing the alternative to SO2 BART for NGS. In concluding remarks, the Court stated: “Even if this 

case highlights how hard it is to engage in ‘reasoned decisionmaking’ in cases involving scientific 

uncertainty, EPA’s actions in promulgating the Final Rule were reasonable and within the bounds of its 

statutory authority, and not arbitrary and capricious.”367 EPA notes that Congress, under section 169A 

of the CAA, established as a national goal, the prevention and restoration of visibility to natural 

conditions at our nation’s national parks and wilderness areas and mandated EPA to develop a program 

that, among other things, required major stationary sources of a certain age to install Best Available 

Retrofit Technology (BART) to reduce emissions of visibility-impairing pollution. 

 EPA recognizes the frustration expressed by one commenter regarding the public hearing in 

Phoenix, Arizona. The commenter asserts that EPA catered to local politicians at that hearing. EPA 

notes that more individuals signed up to speak in Phoenix than at any other hearing and that EPA staff 

worked to ensure that all individuals who wished to provide oral comments had an opportunity to do so. 

EPA recognizes that some individuals endured a lengthy wait to speak and EPA appreciates the time 

everyone who attended took to participate in the public comment and hearing process. In some cases, at 

the request of individuals, EPA did attempt to accommodate the schedules of local elected officials. 

However, EPA gives equal weight and consideration to all written and oral comments submitted to EPA 

on our proposed rulemakings. 

Comment: War on coal 

 One commenter (0258) stated that if EPA moves forward with the BART proposal, it can only 

mean that the agency, and the administration it serves, is determined to wage a war on coal regardless of 

the cost to the country’s economy and its citizens. According to the commenter, EPA’s radical and 

unprecedented agenda will increase costs for Arizona businesses and residents, endanger the long-term 

viability of Arizona’s agriculture industry, and deal a severe blow to the state’s economic recovery, as 

well as ignore the customs, cultures, and well-being of Arizona's communities. 

Response: 

 EPA disagrees that our action in this rulemaking for NGS represents a war on coal. Under 

section 169A of the CAA, Congress required major stationary sources of a certain age that cause or 

contribute to visibility impairment at Class I areas to install BART. NGS is subject to the BART 

requirement of the CAA and is among the largest sources of NOx in the country and impacts visibility at 

11 Class I areas, including the Grand Canyon and other National Parks and Wilderness Areas where 

visibility is an important value. Our five-factor analysis shows that our proposed BART determination is 

cost-effective and will significantly reduce the impact NGS has on the surrounding Class I areas. 

However, in our proposed BART determination, EPA also recognized the important relationship NGS 

has with tribes, as a source of revenue to two tribal governments and as the source of power to deliver 

CAP water to numerous tribes throughout Arizona. Based on the unique role of NGS, EPA put forth a 

framework for BART Alternatives that credited NGS with early and voluntary emission reductions and 

provided additional compliance flexibility in exchange for greater emission reductions. EPA proposed 

an Alternative to BART that extended the compliance timeframe to 2021-2023 (Alternative 1) and 

367 CAWCD v. EPA, 990 F.2nd 1531 (9th Cir. 1993). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

invited stakeholders to submit additional alternatives to BART. Following our proposed rule, a group of 

diverse stakeholders, known as the Technical Work Group (TWG) developed an agreement that 

included a BART Alternative that results in greater emission reductions than our proposed BART 

determination in exchange for a longer compliance timeframe to install air pollution controls. This 

compromise balances the interests of numerous stakeholders in NGS, including the owners of NGS, the 

operator of the CAP, two tribal nations, and two environmental groups. EPA put forth a Supplemental 

Proposal based on our evaluation of Appendix B to the TWG Agreement and is finalizing regulatory 

requirements for NGS that we put forth in the Supplemental Proposal. 

Comment: State regulators/politicians 

One individual (0248) asserted that local regulators have become too familiar with those they 

regulate. The commenter advocated for a change from the current rate structure (present Cost [base rate] 

plus profit [ROR]) to a structure that recovers costs but pays profit based on sharing of cost reductions 

with ratepayers and facilitating the development of local solar electric generation and storage solutions. 

Another individual (0281) noted that state representatives have long received significant 

campaign contributions from utility companies, which likely influence their decision-making process. A 

third individual (0284) similarly pointed out that his Congressman receives contributions from power 

companies and mining interests, and is a champion of their causes in the name of jobs. While 

acknowledging that jobs are important, the commenter stressed the importance of a livable environment 

in which to work. 

Response: 

Although EPA has included a summary of this comment in this response to comment document, 

this comment is not related to our BART determination for NGS. Therefore, EPA is not providing a 

response to this comment. 

Comment: Tribal assistance 

One individual (0415) questioned what the federal government is doing to help tribal 

communities in their effort to develop alternatives to coal power. The commenter stated that without the 

EPA’s assistance, national energy policies like President’s Obama, “Blueprint for a Secure Energy 

Future” will have no hope in being implemented, particularly if congressional power shifts during the 

2014 and 2016 elections. 

Response: 

 In addition to the commitments made by DOI, DOE, and EPA in the 2013 Joint Statement on 

NGS to collaborate on several short- and long-term goals, including completion of the NREL Phase 2 

study to analyze a full range of clean energy options for NGS, and the commitments made by DOI in the 

TWG Agreement related to low-emitting energy projects to benefit affected tribes, DOE and DOI also 

have programs related to renewable energy on tribal land. DOE runs the Tribal Energy Program within 

the Office of Energy Efficiency and Renewable Energy to provide financial and technical assistance to 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

enable tribes to evaluate and develop renewable energy resources.368 DOI, through the Bureau of Indian 

Affairs, runs the Office of Indian Energy and Economic Development to assist tribes in the exploration 

and development of energy resources.369

Comment: Alternative energy sources 

 Several individuals (0025/0156, 0040, 0113, 0123, 0248, 0149, 0235, 0253, 0264.6, 0341) 

argued that NGS and other coal-fired power plants should be phased out and replaced with renewable 

and sustainable energy sources (e.g., solar, nuclear, and natural gas). Most of these commenters noted 

that Arizona’s climate is ideally suited for solar technology, and believe that the use of alternative 

energy sources would reduce emissions of harmful pollutants. One commenter (0113) contended that the 

coal and power industry should be required to implement best practices, since they are heavily 

subsidized by U.S. taxpayers. Another commenter (0149) noted that existing power plants that have 

switched from coal to alternative power sources (e.g., wind and solar power) have already begun to reap 

the economic benefits of switching (e.g., lower operating costs). 

 Four individuals (0248, 0240, 0394, 0399) indicated that an economy built on renewable energy 

sources would create job opportunities and generate revenue just as much as, if not more than, a coalpowered economy. One of these commenters (0399) stated that he has been working with the 

community of Cameron, Arizona, to establish a 500 MW wind farm on top of Gray Mountain, since 

2007, but the project has been highly discouraged by the Navajo Nation and industry representatives. 

 Another commenter (0248) believes that utility leaders and the Arizona Corporation 

Commission, not rate or tax payers, should be responsible for the true cost associated with fossil-fueled 

generation, such as the annual loss of billions of gallons of water due to evaporation, reduced annual 

rainfall due to climate change, and what the commenter termed the “billions of dollars in annual costs 

charged to ratepayers to mitigate the shortcomings of fossil-fueled generation,” which the commenter 

listed as follows: 

 Fuel surcharges. 

 Time-of-use/demand charges. 

 Transmission infrastructure and related significant energy losses, which result in more 

generation/emissions. 

 The selling of surplus electricity at less than cost to a few customers at night, shifting of the 

unrecovered costs to other ratepayers, because baseload plants are not dispatchable. 

 The location of baseload plants in remote regions because they are noxious to humans. 

The commenter (0248) stated that although the circumstances are difficult and complicated, these 

costs/revenues can be reallocated to establish local solar (photovoltaic) electric generation, 

within/adjacent to distribution infrastructure, closer to load centers. The commenter added that bids for 

those facilities should include local manufacturing of components, where feasible, and require the 

market to partner and provide economical storage technology, which the commenter believes is a true 

“game changer.” The commenter believes that this approach would generate enormous trade and 

revenue throughout America, Mexico, and the rest of world, and that renewable energy credits could be 

368 http://apps1.eere.energy.gov/tribalenergy/ 

369 http://www.bia.gov/WhoWeAre/AS-IA/IEED/index.htm 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

sold on the developing national carbon market to generate revenues and facilitate the development of 

new jobs and the retraining required to re-employ those impacted by the closing what the commenter 

considers to be an obsolete technology. The commenter suggested that Cleantech Federal Grants could 

be acquired to promote the development of this generation model. 

 The commenter (0248) also stated that at less than $2 per watt, solar electric generating facilities 

(250 MW to 500 MW) can be established at load points and lift stations, along the CAP aqueduct at less 

cost than the emissions scrubbing equipment. The commenter added that these facilities can also provide 

fixed-price electricity for 25 to 30 years in a manner that could reduce the loss of billions of gallons of 

potable water each year to evaporation. The commenter cited the EIA which stated that a hydroelectric 

dam loses 6.5 gallon per kWh of water to surface evaporation, and noted that the CAP aqueduct is 

hundreds of miles in length with substantial surface area and motion which promotes evaporation. The 

commenter further noted that electricity generation loses 3/4 gallon per kWh of water to evaporation via 

steam, which is a combined loss of billions of gallons of precious potable CAP water each year. 

On the other hand, three individuals (0064, 0266, 0392) questioned whether there are any viable 

alternative energy sources readily available that could easily replace coal. One commenter (0266) 

highlighted that in 2012, partly due to an increase in population, coal accounts for nearly 41 percent of 

Arizona’s power. The commenter continued that the contribution of coal in Arizona is so great that 

replacing it would require the state to construct 6 nuclear power plants, build the equivalent of 11 

Hoover Dams, or install over 12,500 wind turbines stretching more than 2,500 miles. Additionally, the 

commenter noted that over the last 10 years, the price of coal to produce electricity in Arizona averaged 

only $1.95 per unit, while the price of natural gas averaged over $5.75 per unit. The commenter added 

that the price of natural gas is extremely volatile compared to coal; thus, making it difficult to predict 

overall costs, which will only worsen as the demand for gas increases domestically and internationally. 

The commenter reference EIA data that indicated new gas production by 2025 will equal almost 5 

trillion cubic feet, far less than the estimated demand. 

Response: 

Although EPA has included a summary of this comment in this response to comment document, 

this comment is not related to our BART determination for NGS. Therefore, EPA is not providing a 

response to this comment. As stated elsewhere in this response to comments document, EPA does not 

have authority through BART to redefine a source to require a coal-fired power plant to convert to 

renewable energy or other fuel sources. 

Comment: CO2 emissions 

 A few individuals (0040, 0230, 0231, 0240, 0312, 0345, 0363, 0431, 0437) commented on CO2

emissions. One commenter (0040) supports any effort to control CO2 emissions and asked whether 

carbon dioxide capture and sequestration technology has been researched as a possible control. 

Similarly, another commenter (0240) stated that NGS is Arizona’s single largest individual source of 

carbon pollution and one of the largest sources of carbon pollution in the country, and claimed that NGS 

emits more carbon into the atmosphere than 3 million cars. 

 Four commenters (0230, 0231, 0312, 0431) oppose carbon regulations for existing coal-fired 

power plants (e.g., carbon cap and tax), including NGS, because most believe that such regulations do 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

not take into account variation in costs depending on an area’s topography. Three commenters (0230, 

0231, 0437) noted that Arizona does not have oil wells into which CO2 can be pumped nor does the state 

have natural gas supplies. 

 Another individual (0345) recommended the installation of OxyFuel Technology, which the 

commenter believes can be used to capture CO2 emissions in the combustion gases. The commenter 

explained that this technology, on a moisture free basis, concentrates the carbon dioxide in the 

combustion gases from the conventional ±20 percent by volume to ±80 percent by volume, almost 

complete carbon capture. The commenter submitted more technical information and data as an appendix 

to the comment. 

Response:

Although EPA has included a summary of these comments in this response to comment 

document, these comments are not related to this rulemaking to reduce emissions of visibility-impairing 

pollutants from NGS. EPA has clearly defined the boundaries of this action. Therefore, EPA is not 

providing a response to this comment. As stated elsewhere in this response to comments document, EPA 

does not have authority through BART to regulate CO2 emissions and that the BART determination is 

an emission limit for NOx, rather than a requirement to install a specific technology. Therefore, the 

operator of NGS has flexibility install a different control technology that has co-benefits for other 

pollutants, as long as the technology meets the BART emission limit for NOx. 

Comment: Lack of Consultation with Tribes 

The Navajo Nation (0024/0098/0316/0326) commented that EPA should improve 

communication at the start of any rulemakings to ensure that the Navajo Nation can provide meaningful 

information. The commenter said that even when the Agency develops supporting rule information like 

the RIA the Navajo Nation would like to be involved as it could impact the Nation. The commenter 

pointed out that EPA has known for decades that NGS and FCPP located on the Navajo Nation and that 

the Nation would be impacted by regulation of those facilities. The commenter quoted excerpts from 

Executive Order 13175 - Consultation and Coordination with Indian Tribal Governments and said that 

the standard for determining if a regulation has tribal implication is not whether it “impose[s] substantial 

direct compliance costs on tribal governments,” but rather a regulation has “substantial direct effects on 

one or more Indian tribes.” The commenter said that it has on numerous occasions indicated this concern 

to the Agency, but felt compelled to reemphasize this. 

The commenter (0024/0098/0316/0326) indicated that in August of 2009, one day prior to the 

ANPR for NGS and FCPP, EPA made a courtesy call to the President of the Navajo Nation. The 

commenter said that it was not consulted during the development of the ANPR. The commenter 

indicated that in the end, the two facilities were addressed and regulated separately. But, the BART 

process should have been properly analyzed and proposed separately because each facility is unique and 

has distinctive features affecting the Nation and the area it is located on. The Navajo Nation believes 

that if early and meaningful consultation with the Nation had occurred this could have led to an adequate 

5-factor analysis and careful examination of non-air quality impacts. 

The commenter (0024/0098/0316/0326) submitted comments on the ANPR on March 1, 2010, 

where it addressed concerns about the compliance schedule and other non-air quality impacts that the 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

commenter believes were not adequately considered in the ANPR. In the comments, concerns about 

tribal consultation with EPA, the economic interests of the Navajo Nation, inconsistencies between the 

anticipated compliance costs presented by NGS, FCPP, and the NPS, plus concerns with visibility 

improvement, were voiced. The commenter reiterated that moving forward, there are many actions that 

may have the potential to negatively impact the Navajo Nation and other tribes, and it is essential for 

EPA to consult with the Navajo Nation to be its statutory obligations prior to issuing a final rule. 

In a separate letter, the commenter (0024/0098/0316/0326) asked that additional discussions 

between the Navajo Nation and EPA take place to comply with the requirements of Executive Order 

13175, Consultation and Coordination with Tribal Governments. The commenter has previously 

indicated its objection to the proposed BART for NGS, which would have drastic effects on the Navajo 

Nation’s economy. The commenter requested to discuss these issues with EPA, plus new and relevant 

information including the Navajo Nation and NGS owners’ 2013 lease amendments and the 2013 ASU 

Economic Impacts to the Navajo Nation Report. The commenter said that the EPA needs to consider this 

new information as the Agency moves forward with the regulation and take into account the impact 

regulatory requirements would have on the Navajo Nation’s major source of revenue. 

The Gila River Indian Community (0039/0317) expressed similar concerns regarding the lack of 

consultation. The commenter said that the last time EPA consulted with the Community was August 7, 

2012. During this consultation, the commenter said that it was with the understanding that EPA would 

describe to the Community the proposed regulation prior to the rulemaking being issued. Instead, the 

commenter said, EPA called the night before issuing the rule, which the commenter said was inadequate 

and inconsistent with the expectations regarding consultation. The commenter also understood that the 

rule was to be proposed in September 2012, however, it was not proposed until January 2013 and in 

meantime several stakeholders provided additional input to the Agency. However, the Community was 

not consulted during this time. According to EPA, it will be 2 years between proposal and promulgation 

of the rule, the commenter said and indicated that it expects at least two more substantive consultation 

sessions. In addition, the Community expects an explanation of the final rule after it is issued by EPA. 

 Another tribal government (0134) (The Hopi Tribe) also commented on the lack of consultation 

and involvement of tribes in developing the regulation. The commenter submitted multiple letters to 

EPA indicating its concern about not being involved in the development of the rule and consulted and 

not having access to pertinent information. In one of the letters, the commenter said that the government 

acknowledged the Hopi Tribe as a stakeholder and the intention to work with the Tribe, however, this is 

contrary to the following excerpt from the Joint Federal Statement, the commenter said: 

The NGS Working Group intends to work with stakeholders, including 

NGS plant owners, Navajo Nation, Hopi Tribe, CAP, Gila River Indian 

Community and other Arizona Indian tribes who receive water from 

CAP...It should be consistent with Federal trust responsibilities to 

federally recognized Indian tribes in the region. 

 The commenter (0134) specifically indicated that it was denied information regarding the TWG 

Alternative and the development of the alternative, something the commenter pointed out is essential in 

order to provide relevant and useful comments to EPA. The commenter said that it has submitted two 

Freedom of Information Act requests to the DOI, which included all of NGS’ construction and operating 

permits issued since 1990, and any documentation of NGS’ capital expenditures and service, 

maintenance, and repair since 2000. Also, the commenter requested paperwork on the three units at NGS 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

related to the repair, retrofit and modification of the units since 2000, information on when the units 

were installed, their capacity, operating hours, the type and amount of fuel used, the electricity generated 

since 2000, and details on the emissions from the units since 2000. 

 The commenter (0134) also indicated that in its request under FOIA to the DOI, the commenter 

asked for information documenting the DOI’s representation of the Hopi Tribe during the negotiation of 

the BART Alternative, supporting information used by the DOI during this process, and various other 

information evidencing DOI’s actions during the negotiation. The commenter said that until it has the 

information requested via FOIA, it is not able to provide written comments on the TWG Alternative. 

The commenter (0134) added that the Non-Disclosure Agreement has prohibited the Hopi Tribe from 

obtaining necessary information. 

The commenter asserted that it is has been treated differently than other tribal stakeholders in the 

TWG Agreement. For example, the TWG Agreement states that SRP will advocate to EPA the Navajo 

Nation’s treatment as state status (TAS). The Hopi Tribe indicated that the SRP would likely oppose the 

Hopi Tribe being treated as a state and given TAS status due to the adversarial positions taken by SRP 

opposing the Hopi Tribe in the LCR adjudication that is currently ongoing and in failed attempts to 

settle the LCR adjudication. In addition, according to the commenter, SRP demanded that the Hopi 

Tribe be excluded from the TWG, which in the commenter’s opinion would suggest that SRP would be 

against the Hopi Tribe obtaining TAS status. 

The commenter (0134) indicated that the TWG Agreement protects the economic interests of the 

Navajo Nation and the Gila River Indian Community; two stakeholders who were involved in the TWG, 

but compromises the coal revenues of the Hopi Tribe and contains no mitigation measures for this 

significant and adverse economic impact. The Hopi Tribe indicated that it will be disproportionately 

adversely impacted by the reduced capacity at NGS. The commenter additionally said that the 

stakeholders who were part of the development of the TWG Agreement have taken opposite positions of 

the Hopi Tribe in terms of water rights to the Colorado River and Little Colorado River. Both water 

sources affect NGS operations, the commenter said. SRP, the Navajo Nation, and the Gila River 

Community are all competing claimants to the Hopi Tribe for water from the LCR and the mainstem 

Colorado River and so therefore the commenter said that these claimants have an unfair advantage over 

the Hopi Tribe since they were involved in the TWG. The commenter strongly opposes how the impacts 

were assessed for NGS affected tribes and the outcome of the rule should not economically reward one 

tribe at the expense of another tribe. 

The commenter (0134) asserted that EPA is required to consider tribal impacts and fulfill its trust 

obligations and said that the U.S. President has directed the Agency to consider tribal impacts. Another 

tribal government (0039/0317) also expressed these concerns. The commenter referred to the Ninth 

Circuit, which has recognized EPA’s trust obligations to Tribes affected by a rulemaking. The 

commenter believes that the DOI has a conflict of interest due to its dual roles as part owner of NGS via 

BOR and as owing trust responsibilities to the Hopi Tribe. 

The Kaibab Band of Paiute Indians (0421) expressed similar concerns regarding the lack of 

involvement of Indian Tribes and demanded that EPA consider the requests of the Kaibab Paiute. The 

commenter referred to the TWG Agreement and requested that the Kaibab Paiute Indian Reservation 

receive $2.5 million of the $5 million Local Benefit Fund designated for community projects within 100 

mile of NGS (the reservation is 60 miles from NGS). Also, the commenter said that the TWG 

Agreement promotes the development of clean energy, and based on that provision of the agreement, the 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

commenter requested a 250 MW solar farm for economic reasons. The commenter indicated that the 

Navajo McCullough 500 kV transmission line crosses the reservation in two locations and therefore said 

that the infrastructure is already in place. Related to that, the commenter wished to renegotiate the lease 

on this transmission line that runs through the commenter’s reservation. The commenter believes that 

the provisions of the TWG Agreement will help the Kaibab Paiute see through its commitments to tribal 

communities and stressed that it wishes to protect its water rights with Arizona and Utah. 

The Tohono O’odham Nation (0340) objected strongly to the TWG working group, specifically 

the fact that a number of Indian nations that would be substantially affected by the rule were excluded 

from the working group. These affected stakeholders should have been part of the TWG. The 

commenter noted that it is particularly concerned with maintaining CAP water delivery under whatever 

rule is finalized by EPA. 

Response:

EPA understands that NGS is important to numerous tribes located in Arizona and we take 

seriously our trust responsibility to Indian tribes affected by NGS. As a result, we have attempted to 

ensure that these tribes were consulted throughout the rulemaking process. We respectfully disagree that 

there was a lack of consultation with tribes. 

EPA agrees with the commenter that Executive Order 13175 defines “policies that have tribal 

implications” to refer to regulations or other actions that have substantial direct effects on one or more 

Indian tribes.370 In our discussion of EO 13175, we included consideration of substantial direct 

compliance costs to tribal governments, as well as the broader consideration of substantial direct effects 

on one or more Indian tribes. We concluded that our proposed action on NGS will have tribal 

implications, noting that indirect effects may result from the TWG Alternative and Reclamation’s 

ownership interest in NGS, including decreased revenues to the Hopi Tribe and Navajo Nation in 2019 

as well as increased water costs to tribes receiving CAP water in 2030. However, EPA also notes that 

this Final Rule will not impose substantial direct compliance costs on Indian tribal governments because 

no tribal government is an owner or participant in NGS and therefore no tribal government will be 

required to pay direct costs of compliance.371 We also conclude that this rule is required under the CAA 

because NGS is a facility that is subject to BART. 

In our proposed rule, EPA provided a document that listed all written or telephone 

correspondence as well as consultation meetings between EPA and Tribes on NGS. The list that was 

included in the docket for the proposed rule was current as of January 9, 2013.372 The commenter asserts 

that EPA did not consult with the Navajo Nation during the development of the ANPR and implies that 

EPA’s telephone call to the President of the Navajo Nation one day prior to the signature of the ANPR 

in August 2009 was our first communication with the Navajo Nation on the subject. EPA notes that our 

timeline of correspondence and consultation first lists written and telephone correspondence (pages 1-3 

of the January 9, 2013 document) and then lists consultation meetings (pages 4 and 5 of the January 9, 

370 http://www.gpo.gov/fdsys/pkg/WCPD-2000-11-13/pdf/WCPD-2000-11-13-Pg2806-2.pdf 371 We also note that the Navajo Nation has the option to purchase up to a 170 MW share of NGS in 2019. EPA understands 

that the Navajo Nation has not yet made its decision and therefore, currently, no tribal government is a Participant in NGS. 

372 See document titled “2013_0109 Timeline of all tribal consultations on NGS.docx” in the docket at EPA-R09-OAR-2013-

0009-0005. For our final rule, EPA has updated this timeline. See document titled “Updated Timeline of all tribal 

consultations on BART for final rule.docx” in the docket for this rulemaking. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

2013 document). Although the August 19, 2009 telephone call between EPA and President Shirley was 

the first item listed in our timeline, we noted that a meeting between EPA and the Navajo Nation 

occurred two months prior to the ANPR, during the development of the ANPR, to discuss EPA’s plans 

to move forward on an ANPR related to our on-going BART analyses for FCPP and NGS (see listed 

item indicating consultation meeting on June 10, 2009 between Laura Yoshii, Acting Regional 

Administrator of EPA Region 9, and President Joe Shirley, Jr., of the Navajo Nation, to discuss moving 

forward on the ANPR for Four Corners Power Plant and NGS).373 EPA further notes that the ANPR was 

not a proposed rule. The ANPR was an Advanced Notice of Proposed Rulemaking where we provided 

the public advance notice of our intention to develop rulemakings for FCPP and NGS. EPA included 

some initial analysis of the two BART factors and stated that the “specific purpose of this ANPR is for 

EPA to collect additional information.”374 Subsequent to the publication of the ANPR in the Federal 

Register on August 28, 2009, and prior to our proposed rule on NGS, EPA held four consultation 

meetings with tribes in 2009, eight consultation meetings with tribes in 2010, eight consultation 

meetings in 2011, and ten consultation meetings with tribes in 2012.375 Of these meetings, at least eight 

were held as group consultation sessions where all tribes in Arizona were invited to participate and were 

provided the opportunity to request individual consultation meetings as well.376

The Navajo Nation, the Hopi Tribe, the Gila River Indian Community, the Tohono O’odham 

Nation, the Ak-Chin Indian Community, the Pascua Yaqui Tribe, the Fort McDowell Yavapai Nation, 

and the Yavapai-Apache Nation, and the Inter Tribal Council of Arizona submitted comments to EPA 

on the ANPR. EPA summarized and provided responses to comments received from tribal governments 

in the TSD for our proposed rule on NGS.377 The primary concerns expressed by the tribal governments 

related to the economic importance of NGS and the relationship of NGS with CAP and Indian Water 

Settlement Agreements. The Navajo Nation also commented on specific aspects of the five-factor 

analysis for BART, and the Hopi Tribe submitted an economic study it had commissioned that expresses 

concern that regulatory actions would force NGS to close. In our proposed rule and in the development 

of our proposed framework for BART Alternatives, including the credit for early installation of 

LNB/SOFA, EPA recognized the importance of NGS to tribes in Arizona, both in contributing to the 

economies of the Navajo Nation and Hopi Tribe, and in serving as a source of electrical power for CAP 

and a source of revenue to the Lower Colorado River Basin Development Fund, as related to water 

settlement agreements with numerous tribes in Arizona. Based on this recognition, EPA put forth 

additional options for greater flexibility in the compliance timeframe and invited stakeholders to develop 

and submit additional BART Alternatives to EPA for consideration. 

Following the publication of our proposed rule on February 5, 2013, EPA engaged in 17 

consultation meetings with tribes prior to the January 2014 close of the public comment period.378 Of 

these meetings, at least two were held as group consultation sessions where all tribes in Arizona were 

373 See document titled “Updated Timeline of all tribal consultations on BART_for final rule.docx” in the docket for this 

rulemaking, page 4. 

374 See 74 FR 44313 at 44314 (August 28, 2009). 375 See document titled “2013_0109 Timeline of all tribal consultation on NGS.pdf” in document number 0005 in the docket 

for the rule at EPA-R09-OAR-2013-0009 and document titled “Updated Timeline of all Tribal Consultation on NGS_for 

Final Rule.pdf” in the docket for the rule at EPA-R09-OAR-2013-0009. 

376 Id., and See, e.g., document 0008 in the docket for the rule at EPA-R09-OAR-2013-0009. 377 See TSD to the Proposed Rule, document 0014 in the docket for the rule at EPA-R09-OAR-2013-0009. See e.g., pages 25 

and 56. 

378 See document titled “Updated Timeline of all Tribal Consultation on NGS_for Final Rule.pdf” in the docket for the rule at 

EPA-R09-OAR-2013-0009. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

invited to participate and were provided the opportunity to request individual consultation meetings as 

well.379 EPA received comment letters on our proposal and Supplemental Proposal from the Navajo 

Nation, the Gila River Indian Community, the Tohono O’odham Nation, the Ak-Chin Indian 

Community, the Tonto Apache Tribe, the San Carlos Apache Tribe, and the Kaibab Band of Paiute 

Indians.380 At the request of two tribes for additional time beyond January 6, 2014 to submit comments, 

EPA exercised our discretion to accept comments from tribal governments after the close of the 

comment period. The White Mountain Apache Tribe submitted comments on February 5, 2014.381 In 

addition, in response to their request to EPA for information related to NGS, we provided responsive 

documents to the Hopi Tribe on January 7, 2014.382 As shown in additional correspondence, the Hopi 

Tribe requested additional time to submit comments, and EPA continued to exercise our discretion to 

accept late comments from the Hopi Tribe.383

Several tribes also expressed concern that the TWG included only two tribes, the Navajo Nation 

and the Gila River Indian Community, and excluded numerous other tribes that also have a significant 

economic interest in NGS. EPA recognizes that many tribes were excluded from the development of the 

TWG Agreement. EPA was not involved in the formation of the TWG or any of the negotiations 

between the members of the TWG in developing the TWG Agreement. In addition, our evaluation of the 

TWG Agreement was for the sole purpose of determining whether the Appendix B to the TWG 

Agreement meets our framework for a “better than BART” Alternative. Therefore, although EPA agrees 

that many tribes have economic interest in NGS and CAP, EPA does not have any role in the 

distribution of funds described in the TWG Agreement. We understand that DOI provided its response 

to the FOIA submitted by the Hopi Tribe.384

Based on numerous consultation meetings between high-level officials from EPA and elected 

tribal leaders, beginning in 2009 and extending into 2013, and our development of flexible options for 

BART Alternatives in response to comments from tribes, EPA considers our consultation on NGS to be 

consistent with EO 13175 and EPA’s policy to engage in early and meaningful consultation with 

tribes.385 EPA will provide notification of our final rule, in writing, to all tribal governments that 

submitted comments to EPA on our Proposed Rule or Supplemental Proposal and will provide our 

written responses to their specific comments. All written correspondence from tribal governments to 

EPA regarding NGS and our proposed BART determination is available in the docket for this 

rulemaking.386

Comment: Communication within the Navajo Nation 

379 Id. 380 See comment numbers 0340, 0317, 0387, 0402, 0419, and 0421 in the docket for the rule at EPA-R09-OAR-2013-0009. 381 See comment number 0440 in the docket for the rule at EPA-R09-OAR-2013-0009. 382 See document titled “2014_0107 EPA Letter to Chairman Honanie with Enclosure 1.pdf” in the docket for this rule at 

EPA-R09-OAR-2013-0009. 

383 See document titled “2014_0131 Letter from Chairman Honanie.pdf” and document titled “2014_0206 EPA Response to 

Chairman Honanie_Hopi Tribe.pdf” in the docket for this rule at EPA-R09-OAR-2013-0009. 384 See document titled “DOI FOIA response to Hopi Tribe” in the docket for this rulemaking. 385 EPA’s policy on Consultation and Coordination with Indian Tribes is posted on the following website: 

http://www.epa.gov/tribal/consultation/consult-policy.htm 386 See Appendix A (List of Written Comments) to this response to comments document and the docket for this rulemaking at 

EPA-R09-OAR-2013-0009. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

 One individual (0025/0135) stated that he did not receive 0177-13 until 2 hours before the final 

vote, that all meetings were held in secret from the Navajo Nation public, and only certain portions of 

0177-13 were made available to the Navajo Nation public. 

 One individual (0025) stated this NGS lease is very important to the Navajo people and should 

not be kept in secret. Commenter asserted the Navajo Nation says loss of the NGS will have devastating 

impacts on the Navajo people, but yet the Navajo Nation keeps the NGS lease secret from its own 

people. 

Response: 

 EPA included this comment in our response to comments document because it relates to the 

NGS lease renewal. However, we note that this comment does not relate to a specific aspect of our 

BART determination for NGS, nor does it related specifically to EPA, therefore, EPA is not responding 

to this comment. 

Comment: Additional Public Hearings Needed 

A few government commenters (0082, 0095, 0097, 0104) requested that in order for meaningful 

comments to be developed and submitted on this rule, EPA should hold additional public hearings to 

hear from affected stakeholders. Some of the commenters, including commenters 0104 and 0082 

suggested a number of hearings in the Phoenix area and in Arizona in an effort to obtain a complete 

picture of the direct and indirect impacts of the rule. According to several of the commenters, hearing 

directly from all affected stakeholders would lead to sound policy decisions. 

Response:

The public comment period for EPA’s proposed rule was open for nearly one year and the public 

comment period for EPA’s Supplemental Proposal extended for over two months.387 In addition to the 

lengthy public comment period, EPA held five public hearings in combination with open house events, 

at locations that extended from northern Arizona, to central and southern Arizona, and included 

locations on the Navajo Nation and the Hopi Tribe. Many of the tribes receiving CAP water are located 

in central and southern Arizona. EPA considers our public outreach and public comment process to have 

been extensive and allowed EPA to hear and receive comments from any affected stakeholder that 

wished to submit comments on our proposed rulemakings. As noted elsewhere, EPA received over 

77,000 comments on our proposed rulemakings on NGS. 

Comment: NGS importance to public policy goals

 A CAP agricultural water users group (0305) stated that NGS and CAP are key components of a 

comprehensive resolution of a number of contentious, long-standing public policy disputes in Arizona. 

387 We note that the public comment period for the Supplemental Proposal should have extended longer, i.e., EPA signed the 

Supplemental Proposal on September 25, 2013. On the same day, EPA made the pre-publication version available online in 

the docket and on our website. However, publication of the Supplemental Proposal in the Federal Register was delayed due 

to the shutdown of the federal government that extended from October 1 – 16, 2013. The Supplemental Proposal published in 

the Federal Register on October 22, 2013. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

The commenter indicated that finalizing the proposed rule would upset those public policy goals in the 

following ways: 

 Federal and state legislation related to CAP were both put in place with the idea that CAP water, 

made available and affordable by NGS-generated power, would be a replacement for Arizona’s 

non-renewable groundwater. If the proposed rule is adopted in its current form, much of Central 

Arizona farming will return to groundwater pumping because the installation of SCR would lead 

to significant increases in CAP water rates, making it relatively less attractive than groundwater 

pumping. 

 The NGS and CAP facilitated resolution of water rights disputes between tribes and other 

Arizona water users. The 2004 Arizona Water Settlements Act resolved disputes about the longterm water rights of the Gila River Indian Community. Agricultural water users provided a 

substantial supply of long-term CAP water to the Gila River Indian Community in return for 

rights to affordable CAP water through the year 2030. If the proposed rule is adopted in its 

current form, this compromise will be nullified, because agricultural water users will be forced 

off of CAP water because it will become too expensive. 

 The ready supply of power generated by the NGS eliminated pressure to generate hydropower in 

the Grand Canyon. The EPA noted in the preamble to the proposed rule that “Federal 

participation in NGS was authorized in the Colorado River Basin Project Act of 1968 as a 

preferred alternative to building hydroelectric dams in the Grand Canyon for providing power to 

the Central Arizona Project. 

The CAP operator (0343) similarly stated that one of Congress’ primary objectives in authorizing the 

CAP was to provide a renewable water supply to reduce the overdraft of groundwater in central and 

southern Arizona, and it has achieved that aim. The commenter indicated that for CAP water to be a 

viable alternative to groundwater, its cost must be competitive with groundwater pumping, and that 

competitively priced CAP water is inherently linked to the affordable power that NGS provides because 

that power is a significant component of CAP water rates, particularly for Arizona’s tribes and 

agricultural interests. 

 This commenter (0343) indicated that affordable CAP water has been a crucial component in the 

successful negotiation of multiple Native American water rights settlements in Arizona, adding that 

today 46 percent of CAP water is dedicated to Indian use, with nine tribes holding contracts for CAP 

water. An industry/commerce commenter (0416) also made this point. The CAP agricultural water users 

group (0305) also pointed out that NGS power available to CAP but not needed for CAP pumping 

(“Navajo Surplus”) is sold pursuant to federal law and policy to help repay the construction costs of the 

CAP and fund the costs of Indian water rights settlements in Arizona, as specifically authorized by 

Congress. Thus, according to the commenter, NGS is critical not only to CAP operations and the ability 

of CAP to meet its statutory purposes, but also in the creation of Navajo Surplus that is available to 

bolster CAWCD finances and help fulfill commitments made in numerous Indian water rights 

settlements. 

Response:

 EPA recognizes that NGS is a critical component of CAP. We also appreciate the importance of 

policies to reduce groundwater use in the state of Arizona and support water settlement agreements with 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

tribes in Arizona. EPA discussed the history and importance of NGS in our proposed rulemaking.388 We 

note that the potential impacts of our proposed BART determination for NGS on tribes in Arizona, was 

the impetus for the development of a framework for better than BART Alternatives that provided 

additional flexibility to NGS for the timeframe for achieving emission reductions at NGS. Although we 

are establishing a BART Benchmark based on our proposed BART determination, the regulatory 

requirements that we are finalizing in today’s action are the requirements and compliance timeframes 

based the TWG Alternative as published in our Supplemental Proposal. Therefore, EPA is taking action 

to require emission reductions at NGS to reduce impact on visibility impairment at 11 Class I areas, in a 

manner that provides the necessary flexibility to reduce adverse impacts to tribes in Arizona. 

Comment: Maintain cooperation among stakeholders in implementing future regulations 

 One state agency (0017/0289/0320) noted that EPA is continuing to implement a number of new 

environmental initiatives targeted at power plant emissions and stated that any such initiatives at NGS 

should be undertaken in a spirit of cooperation between interested stakeholders and EPA. The 

commenter reiterated the importance of NGS to the State of Arizona, including tribal and local 

communities, and stated that because the plant owners and the state have gone through considerable 

effort to preserve this unique plant, it deserves some amount of regulatory certainty. The commenter 

asked that EPA consider all of the benefits afforded under the current proposal as it looks to implement 

future regulations. 

Response:

As stated previously, EPA recognizes that NGS is a critical component of CAP, policies to 

reduce groundwater use in the state of Arizona, and water settlement agreements with tribes in Arizona. 

EPA discussed the history and importance of NGS in our proposed rulemaking. EPA acknowledges the 

sentiment expressed by this commenter regarding the importance of regulatory certainty and the request 

that EPA consider the benefits of the TWG Agreement in the implementation of future regulations. 

Comment: Sound science

 Without being more specific, an association of CAP water distributors (0398) urged the EPA to 

address the “significant challenge [Commenter 0305] has made to EPA’s obligation to support its 

decision making with sound science.” 

Response:

 This comment urges EPA to address the issues raised by another commenter (0305). The various 

comments from this commenter (0305) are summarized throughout this document. EPA has responded 

to all comments in this document. Our final determination is based on the analyses presented in this 

response to comment document and supporting information, as well as our Proposed Rule and 

Supplemental Proposal. 

388 See Proposed Rule at 78 FR 8275 (February 5, 2013). 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Comment: Bituminous coal at FCPP 

 One individual (0157) stated that BHP coal has always been thought of as sub-bituminous, but it 

is actually bituminous. Citing “Determination of Four Corners Coal Ranking, March 11, 2008, Alan 

Papp, (Borrowing Heavily from the work of Dave Biser; and attached to the docket), the commenter 

asserted that the report details the misuse of a formula where the formula requires percent to be entered, 

but instead decimals were entered resulting in a lower Btu/lb for Four Corners Coal. Commenter stated 

that this report says the FCPP has been burning bituminous coal instead of sub-bituminous and only 

paying for sub-bituminous prices. Commenter believed the Navajo Nation has been cheated of $1 billion 

of coal royalties since the creation of Navajo Mine and that the State of Arizona has been missing out on 

taxes from the extra energy created all these years. 

Response:

 Although EPA has included a summary of this comment in this response to comment document, 

this comment is not related to NGS, the Kayenta Mine, which supplies coal to NGS, or our proposed 

BART determination for NGS. Therefore, EPA is not providing a response to this comment. 

Comment: No 111(d) authority to regulate CO2 at existing power plants 

 One industry/commerce commenter (0325) presented arguments that EPA does not have 

authority under CAA section 111(d) to adopt CO2 performance standards for existing coal-fired EGUs 

that are so stringent as to force plant retirements or curtailments. 

Response:

This comment is beyond the scope of this rulemaking. EPA has a separate, national rulemaking 

process for implementing regulation of greenhouse gases, including CO2 from coal-fired EGUs. The 

action EPA is taking here has a narrow scope and does not impose any regulation on CO2 or any 

greenhouse gases from NGS. 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0015 Comment on FR Doc # 2013-01858: Arizona Interfaith Power and Light Environmental/Public Interest Advocacy Group 0016 Comment from webmail dated 1-26-2013 from Patrick Mattingly Private Individual 0017 Comment letter dated 1-30-2013 from Bob Stump, Chairman, Arizona Corporation Commission (ACC) State/Local Government S

0

0018 Comment letter dated 2-13-2013 from David Mallavia, President of Canyonlands Health Care Industry/Commerce 0019 

Comment letter dated 2-13-2013 from Grant R. Ward, Maricopa-Stanfield Irrigation and Drainage District 

CAP Water Interest Group 

S

0020 Comment letter dated 2-13-2013 from Sylvia Colton Private Individual 0021 Comment submitted through webforms, dated 2-14-2013, from W.B. "Tug" Kangus Private Individual 0022 

Comment letter dated 2-14-2013 from Kelly Barr, Salt River Project 

Industry/Commerce S

040

0023 

Comment letter dated 2-21-2013 from Central Arizona Water Conservation District (CAWCD), David Modeer 

CAP Operator S

0r

0024 

2013_0301 Navajo Nation Request for 90-day Extension of Comment Period 

Tribal Government S

0r

389 Appendix A: List of Comments represents all documents that are labeled as “Comments” in the docket (at EPA-R09-OAR-2013-000

Appendix A, not all documents are comments (e.g., in some cases documents generated by EPA, such as memos to file, were inadverte“comments”), not all comments included attachments, and some comments are duplicated. EPA has included a separate column, titled “clarification, as needed. 
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Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0025 

Comment Letter Dated March 4, 2013 from Vincent Yazzie 

(commenter submitted multiple further comments and/or attachments to the docket under document IDs 0041, 0071, 0072, 0124, 0125, 0126, 0130, 0131, 0135, 0136, 0139, 0153, 0154, 0155, 0156, 0157, 0158, 0171, 0267, 0269, 0355; for clarity, all comments are identified in the RTC as: 0025/0***) 

Private Individual 

0026 Comment submitted through Regulations.gov on 3-9-13 from Andrew Key Private Individual 0027 Comment submitted through Regulations.gov on 3-9-13 from Shawn Dolan Industry/Commerce0036 Comment from Dave Crawford on FR Doc # 2013-01858 Private Individual0037 Comment from Hitachi Power Systems America on FR Doc # 2013-01858 Industry/Commerce C0038 Comment from Jean Miyake received March 10, 2013 Private Individual 0039 Comment from Governor Gregory Mendoza, Gila River Indian Community, received March 11, 2013 Tribal Government 0040 Comment from Keith Woodward received Marcy 13, 2013 Private Individual 0041 Comment from Vincent H. Yazzie received March 12, 2013 Private Individual 0042 Comment from James Drake received March 14, 2013 Private Individual 0043 Comment from Duncan Harvey received March 15, 2013 Private Individual 0044 Comment from David Becker received March 16, 2013 Private Individual 0045 Comment from Paula Smith received March 16, 2013 Private Individual 0046 Comment from Barbara J. Sattler received March 25, 2013 (dated March 19, 2013) Private Individual 0047 Comment on FR Doc # 2013-01858 Private Individual 0048 Comment on FR Doc # 2013-06196 Private Individual 0049 Comment on FR Doc # 2013-01858 Private Individual 0050 Comment on FR Doc # 2013-06196 Private Individual 0051 Comment from Cindy Siepel dated April 5, 2013 via email. Private Individual 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0052 Comment letter from Sundt Construction Inc. David S. Crawford, P.E. dated April 8, 2013. Industry/Commerce 0053 Comment from Brian D. Gary, BS Geological Engineering Student, dated April 9, 2013 via email. Private Individual 0054 Comment from Jon Borges, L.M.P. dated April 9, 2013 via email. Private Individual 0055 Comment from John Neville, LEED-AP, President of Sustainable Arizona, dated April 12, 2013. Environmental/Public Interest Advocacy Group0056 Comment from Janice Berger, dated April 14, 2013, via email. Private Individual 0057 Comment from Sid Abma, Sidel Systems, dated April 15, 2013, via email. Industry/Commerce 0058 

Comments (4) from WildEarth Guardians (WEG), dated April 15, 2013, via emails. 

Environmental/Public Interest Advocacy Group 

MCW

0059 

Comment (1) from WildEarth Guardians (WEG), dated April 16, 2013, via email. 

Environmental/Public Interest Advocacy Group 

MCW

0060 

2013_0311 Meeting materials from Maricopa Stanfield Irrigation District 

CAP Water Interest Group 

TSR

0064 Comment on FR Doc # 2013-01858 Private Individual 0065 Comment from Scott Hicks, dated May 5, 2013, on FR Doc # 2013-01858 Industry/Commerce 0066 Comment from Concerned Individual on FR Doc # 2013-01858 Private Individual 0067 

Comment from Christopher Lish, May 6, 2013, on FR Doc # 2013-01858 

Private Individual I

s0
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Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0068 

Comment (1), April 17, 2013, from Malcolm Brown, via WildEarth Guardians. 

Private Individual M

CW

0069 Comment from Dennis Lemon, May 2, 2013. Private Individual 0070 Comment from Patricia Alvarez, May 2, 2013, on FR Doc # 2013-06196 Private Individual 0071 Comment from Vincent Yazzi, May 6, 2013 letter with 13 files attached Private Individual 0072 Comment from Vincent Yazzi, May 9, 2013 letter with 2 files Private Individual 0074 Comment, 2013-0430 from Kenneth Kovovich Private Individual 0075 Comment, 2013-05-02 from Patricia Alvarez Private Individual 0076 Comment, 2013-05-06 from Steve Rasmussen Industry/Commerce I0077 Comment, 2013-05-08 from Joseph Roundtree Private Individual 0078 Comment, 2013-05-08 from Thomas Pyzdek Private Individual 0079 Comment, 2013-05-09 from Ann McMullen Private Individual 0080 Comment, 2013-05-09 R Wade Private Individual 0081 Comment, 2013-05-10 from Lee Calamaio Private Individual 0082 Comment from AZ House of Representatives on 5/29/13 on FR Doc # 2013-06196 Elected Officials 0083 

Comment from Roger Moder on 5/31/2013 on FR Doc # 2013-06196 

Private Individual S

00

0084 Comment from Rick Murray, AZ Small Business Association, June 4, 2013, on FR Doc # 2013-06196 Industry/Commerce 0085 Comment from Senator Steve Pierce, AZ State Senate, June 4, 2013, on FR Doc # 2013-06196 Elected Official 0086 Comment from Concerned Individual, June 4, 3013, on FR Doc # 2013-06196 Private Individual 0087 2013_0307 Letter from Senators Flake and McCain on NGS Elected Officials 
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Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0088 2013_0508 Comment from Wayne Collins Private Individual 0089 2013_0515 Letter from Members of the AZ House of Representatives Elected Officials D0090 2013_0524 Comment from Frank Jones Private Individual 0091 2013_0604 Comment from Roger Turner Private Individual 0095 2013_0528 Letter from Tom Horne, AZ Attorney Gen. AND EPA Response to letter dated June 6, 2013 State/Local Government 0097 2013_0606 Letter from NV State Senator Kelvin Atkinson Elected Official 0098 

2013_0611 Letter from President Shelly, Navajo Nation requesting consultation meeting 

Tribal Government S

0r

0099 2013_0616 Email comment from Susan and John Private Individual 0102 

2013_0620 Stakeholder Request for Additional Extension of Comment Period 

Technical Work Group S

0t

0104 2013_0612 Letter from AZ State Senate President Biggs Elected Official 0105 2013_0613 Letter from AZ State Rep. Kavanagh Elected Official 0106 2013_0625 Comment from Verna Stoddard Private Individual 0109 2013_0702 Email Comment from John Yoder Private Individual 0112 Comment from Member of Navajo Tribe on FR Doc # 2013- 14630 dated 7/7/13 Private Individual 0113 Comment from Rick Spilsbury on FR Doc # 2013-14630 dated 7/10/13 Private Individual 0114 

Anonymous Comment on FR Doc # 2013-14630 dated 7/12/13 Private Individual M

CS

0115 Anonymous Comment on FR Doc # 2013-06196 dated 7/2/13 Private Individual 0116 Anonymous #2 Comment on FR Doc # 2013-06196 dated 7/2/13 Private Individual 
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Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0117 Anonymous #3 Comment on FR Doc # 2013-06196 dated 7/2/13 Private Individual 0119 2013_0717 Comment from Alvern Woods Private Individual 0120 

2013_0713 Example Take Action Email from Sierra Club (over 36,000 received as of 7/26/13) 

Environmental/Public Interest Advocacy Group 

MCS

0121 

2013_0724 Example Take Action Email from Care2 (over 5,900 received as of 7/26/13) 

Environmental/Public Interest Advocacy Group 

MCCteS

0123 COMMENT from Fred Bauder, 7-29-13, via email Private Individual 0124 COMMENT from Vincent Yazzie, 7-29-13, via email Private Individual 0125 COMMENT #2 from Vincent Yazzie, 7-29-13, via email Private Individual 0126 COMMENT #3 from Vincent Yazzie, 7-29-13, via email Private Individual 0127 COMMENT from Val Summers, 8-03-12, via email Private Individual 0128 COMMENT from Terry L. O'Neal, letter dated August 6, 2013 Private Individual 0129 COMMENT from Terry Finefrock, 8-07-13, via email Private Individual I0130 COMMENT from Vincent Yazzie, 8-09-13, via email Private Individual 0131 COMMENT from Vincent Yazzie, 8-10-13, via email Private Individual 0132 COMMENT from L.S. Willingyrme, M.D., 8-12-13, via email Private Individual 0133 COMMENT from Paul Mitchell, 8-16-13, via email Private Individual 0134 

COMMENT from LeRoy Shingoitewa, Chairman, The Hopi Tribe, letter dated August 19, 2013 

Tribal Government S

0r

0135 COMMENT from Vincent Yazzie, dated August 4, 2013, received in email August 5, 2013, with attachments Private Individual 
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Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0136 COMMENT from Vincent Yazzie, dated August 14, 2013, received in email August 14, 2013, with attachments Private Individual 0137 Comment on EPA-R09-OAR-2013-0009-0029 Private Individual 0138 Comment on EPA-R09-OAR-2013-0009-0029 Private Individual 0139 Comment from Vincent Yazzie, August 26, 2013, via email Private Individual 0140 Comment from Joe Galli with Scottsdale Chamber of Commerce, dated August 27, 2013 Industry/Commerce 0141 Comment from Joe Galli, Scottsdale Chamber of Commerce on EPA-R09-OAR-2013-0009-0111 Industry/Commerce D0142 

COMMENT from Dave Hummer, Mining Engineer, 

Department of the Interior, Office of Indian Energy and Economic Development, August 22, 2013, via email. 

Federal Agency 

0145 Comment from Carrie Wilkinson, 9-11-13, on EPA-R09-OAR- 2013-0009-0111 Private Individual 0146 Comment from Kathy Jirschele, 9-11-13, on EPA-R09-OAR- 2013-0009-0111 Private Individual I0147 Comment from Malcolm Cox, 9-11-13, on EPA-R09-OAR- 2013-0009-0111 Private Individual I0148 Comment from Lindsey Normoyle, 9-11-13, on EPA-R09- OAR-2013-0009-0111 Private Individual I0149 Comment from Tracy Scheinkman, 9-11-13, on EPA-R09- OAR-2013-0009-0111 Private Individual 0153 2013_0829 Comment from Vincent Yazzie, dated August 29, 2013 via email Private Individual 0154 2013_0830 Comment from Vincent Yazzie, dated August 30, 2013, via email Private Individual 0155 2013_0831 Comment from Vincent Yazzie, dated August 31, 2013, via email Private Individual 
Page 253

EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0156 2013_0902 Comment from Vincent Yazzie, dated September 2, 2013 Private Individual 0157 2013_0906 Comment from Vincent Yazzie, dated September 6, 2013 Private Individual 0158 2013_0909 Comment from Vincent Yazzie, dated September 9, 2013 Private Individual 0159 2013_0826 Comment Letter from Arizona Power Authority State/Local Government 0160 2013_0910 Comment from Craig Weatherford via email Private Individual 0161 2013_0910 Comment from Justin Elder via email Private Individual I0162 2013_0910 Comment from Rob Rauh via email Private Individual 0163 2013_0910 Comment from Ted Falkowski via email Private Individual S

i

0164 2013_0910 Comment from Mark Shaw via email Private Individual 0165 2013_0914 Comment from Mike Fisher on EPA-R09-OAR- 2013-0009-0111 Private Individual E

i

0167 2013_0912 Comment from Rebecca Schlofner Private Individual I0168 2013_0912 Comment from George Duffield Private Individual E

i

0169 2013_0913 Comment from Bill Ahlbrandt Private Individual 0170 2013_0913 Comment from Su Story Private Individual 0171 2013_0916 Comment Vincent Yazzie Private Individual 0175 Comment from Linda Kavanagh, Mayor of Fountain Hills, AZ State/Local Government 0176 2013_0903 Comment from Bruce Hamblin, Mayor of Eagar, and other elected officials State/Local Government 0177 2013_0912 Comment from Christopher Thunberg Private Individual 0178 2013_0918 Comment from Aaron Lenzing Private Individual 0179 2013_0918 Comment from R. Grim Private Individual 0180 2013_0920 Comment from Julia Larrabee Private Individual 
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Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0181 2013_0923 Comment from Nikolai Messner Private Individual 0187 Comment from Christopher Lish Private Individual D0188 Comment from Todd Sanders, Greater Phoenix Chamber of Commerce Industry/Commerce 0189 Comment from Sal deCiccio, Phoenix City Council State/Local Government 0190 Comment from BinnurGunesin via regulations.gov Industry/Commerce 0192 Comment from Mayor of Oro Valley Arizona, Satish I. Hiremath, September 18, 2013. State/Local Government N

r

0193 Comment from Harrison and Mary Johnson, September 23, 2013. Private Individual I0194 Comment from Flowing Wells Irrigation District, David Crockett, September 23, 2013. CAP Water Interest Group S

i

0195 Comment from Anita Christy, Arizona for Water, September 25, 2013. Private Individual 0196 Comment from BinnurGunesin, Dutoit/Gunesin CS, September 25, 2013. Industry/Commerce D0197 Comment from JojeanDikeman, September 26, 2013. Private Individual 0198 

Comment EXAMPLE of 11 form letters received September 27, 2013. 

Private Individual M

Cd

0199 Comment from City of Chandler Arizona, Mayor Jay Tibshraeny, September 26, 2013. State/Local Government 0200 Comment from Richard B. and Kathleen H. Coolidge, October 2, 2013. Private Individual I0201 Comment from City of Goodyear Arizona, Mayor Georgia Lord, October 3, 2013. State/Local Government 0202 Comment from Mark Shaw, October 7, 2013. Private Individual 0203 Comment from Rod and Rhonda Lucas, October 3, 2013. Private Individual E

0
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Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0204 Comment from James Orcutt, October 7, 2013. Private Individual S

i

0205 Comment from Don Blume, October 4, 2013. Private Individual I0206 Comment from Karen Lowe, October 9, 2013. Private Individual 0207 Comment from City of El Mirage Arizona, Mayor Lana Mook, October 10, 2013. State/Local Government S

i

0208 Comment from Lisa A. Atkins, October 10, 2013. Private Individual S

i

0209 Comment from Thomas J. Lowe, Chairman of Univest, October 10, 2013. Private Individual 0210 Comment from Jeff Strang, October 11, 2013. Private Individual S

i

0211 Comment #1 from Arlene Alder, October 12, 2013. Private Individual 0212 Comment #2 from Arlene Alder, October 12, 2013. Private Individual E

i

0213 Comment from City of Litchfield Park Arizona, Mayor Thomas Schoaf, October 15, 2013. State/Local Government 0214 Comment from Metro Water District, Tucson Arizona, Chairwoman, Judy Scrivener, October 16, 2013. CAP Water Interest Group S

i

0215 Comment from Terry Carleton, October 16, 2013. Private Individual 0216 Comment from Maria Randklev, October 17, 2013. Private Individual 0217 Comment from Shaina Shay, October 17, 2013. Private Individual 0218 Comment from Chuck Gordon, October 23, 2013. Private Individual 0220 

Comment thru Regulations.gov from Councilman Jim Waring, 

City of Phoenix, October 4, 2013, on EPA-R09-OAR-2013-0009-0186 

State/Local Government 

0221 Comment thru Regulations.gov on EPA-R09-OAR-2013-0009- 0186 Private Individual 
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0222 Comment thru Regulations.gov on EPA-R09-OAR-2013-0009- 0186 Private Individual 0223 Comment from Andy Tobin, Speaker of the House, thru Regulations.gov on EPA-R09-OAR-2013-0009-0186 Elected Official D0224 Comment thru Regulations.gov on EPA-R09-OAR-2013-0009- 0186 Private Individual 0225 Comment thru Regulation.gov from Joe Galli, North Scottsdale Chamber of Commerce, August 28, 2013 Industry/Commerce D0226 Comment thru Regulation.gov from Carrie Wilkinson, September 11, 2013. Private Individual I0227 Comment thru Regulation.gov from Tracy Scheinkman Private Individual D0228 

Comment in letter/email from taxpayers from Arizona, Thomas and Anita Christy, November 11, 2013. 

Private Individual N

ad0

0229 Comment from Kimberli Lee via email, November 4, 2013. Private Individual 0230 Comment from Sandi Bartlett via email, November 6, 2013. Private Individual 0231 Comment from Merrianne Geisdorf via email, November 7, 2013. Private Individual I0232 Comment from John Brakeman via email, November 8, 2013. Private Individual S

i

0233 Comment from Joy Staveley via email November 13, 2013. Private Individual 0234 Comment from Julie Pastrick, Flagstaff Chamber of Commerce, sent by Mike Sistak via email, November 13, 2013. Industry/Commerce 0235 Comment from Mike Campbell via email, November 13, 2013. Private Individual 0236 Comment from Charles Parke via email, November 14, 2013. Private Individual 0237 Comment from Dr. Kenneth Langton via email, November 14, 2013. Private Individual 0238 Comment from Lori Girshick via email, November 14, 2013. Private Individual 
Page 257

EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0239 Comment from Senator Bob Worsley via email, November 14, 2013. Elected Official 0240 Comment from Cathy Della Penta via email, November 15, 2013. Private Individual 0241 Comment from SPierce via email, November 16, 2013. Private Individual 0242 Comment from Will Hodges via email, November 16, 2013. Private Individual 0243 Comment from William Erb via email, November 17, 2013. Private Individual 0244 Comment from Robert Tang via email, November 18, 2013. Industry/Commerce 0245 Comment from Jack Utter via email, November 19, 2013. Private Individual 0246 Comment from Kendall Stephenson received via email, 2013_1108 Private Individual 0247 Comment from Stacy Brimhall received via email, 2013_1108 Private Individual 0248 Comment from Terry Finefrock received via email, 2013_1111 Private Individual I0249 

Comment from G. Brad Brown, Peabody Energy, at Tucson Hearing 

Industry/Commerce S

0t

0250 

Comment from David Modeer, General Manager, Central Arizona Conservation Water District, Central Arizona Project, 

November 15, 2013 at Tucson Hearing. 

CAP Operator S

0r

0251 Comment from J. J. Riley at Tucson Hearing Private Individual 0252 Comment from Chris E. Ward, President, Southern Arizona Water Users Association at Tucson Hearing CAP Water Interest Group S

i

0253 Comments from Tucson Hearing: 2 single page comments, from Melissa Donovan and Lea Marquez Peterson Private Individual 0254 Comment from Bret Fanshaw, Environment Arizona, at Phoenix Hearing, November 14, 2013 Environmental/Public Interest Advocacy Group 0255 

Comment from G. Brad Brown, Peabody Energy at Phoenix 

Hearing 

Industry/Commerce S

0t
Page 258

EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0256 Comment from the Town of Cave Creek, Arizona, at the Phoenix Hearing State/Local Government R0257 

Comment from David Modeer, General Manager, Central Arizona Water Conservation District at Phoenix Hearing 

CAP Operator S

0r

0258 Comment from Gail Griffin, State Senator, representing Southeast Arizona, at Phoenix Hearing Elected Official 0259 

Comment from Dr. George D. Thurston, Professor of Environmental Medicine at the New York School of Medicine at 

the Phoenix Hearing, November 14, 2013 

Private Individual A

sE

0260 

Comment from Mark Hajduk, Environmental Consultant, Arizona Public Service Company at the Phoenix Hearing 

Industry/Commerce S

00

0261 Comment from Marshal Johnson, Photos, at the Phoenix Hearing Private Individual 0262 

Comment from Dr. Roger H. Bezdek, President of MISI, at the 

Phoenix Hearing November 14, 2013 

Private Individual A

sP

0263 Comment from William Mattingly, Utilities Director, City of Peoria AZ, at the Phoenix Hearing, November 14, 2013 State/Local Government 

0264b Comments-8 single pages from various speakers at the Phoenix Hearing 

0264.1 Comment from Ed S. at the Phoenix Hearing Private Individual0264.2 

Comment from Kelly Barr at the Phoenix Hearing Industry/Commerce S

0r

0264.3 Comment from Jack Hamblet at the Phoenix Hearing Private Individual0264.4 Comment from Gregory O’Reilly at the Phoenix Hearing Private Individual0264.5 Comment from Liz Hourican at the Phoenix Hearing Private Individual
Page 259

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Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0264.6 Comment from Liz Hourican at the Phoenix Hearing Private Individual0264.7 Comment from Paul Bott at the Phoenix Hearing Private Individual0264.8 Comment from Kathy Walsh at the Phoenix Hearing Private Individual

0265 Comment from Eugene T. Begay at the Page Hearing Private Individual 0266 Comment from Professor Frank Clemente, Penn State University, at the Page Hearing, November 12, 2013 Private Individual 0267 Comment from Vincent Yazzie, Photos, at the Page Hearing Private Individual 0268 

Comment from Mike Hummel, SRP Associate General Manager, at the LeChee Hearing 

Industry/Commerce S

040

0269 Comment from Vincent Yazzie - Photos at the LeChee Hearing Private Individual 0270 Comment from Frank Clemente, Professor Emeritus at Penn State University, at the Kykotsmovi Hearing Private Individual D0271 Comment from Vernon Masayesva, Black Mesa Trust, at the Kykotsmovi Hearing Environmental/Public Interest Advocacy Group D0272 Comment from Chet Haryasz Private Individual 0273 Comment from Jim Newton Private Individual 0274 Comment from Ralph Marra, BKW Farms Industry/Commerce 0275 Comment from John Morgan Private Individual 0276 

Comment from Roger Moder Private Individual S

00

0277 Comment from Karen Johnson Private Individual F

S

0278 Jeff Jensen, Golf Course Superintendents Association of America, letter dated November 15, 2013 Industry/Commerce E

i
Page 260

EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0279 

Comment from Zak Draskovich, dated November 21, 2013 Private Individual M

CLf

0280 Comment from Christian Prive, Mayor of Maricopa, letter dated November 21, 2013 State/Local Government 0281 Comment from Vernon Masayesva from Kykotsmovi Hearing, November 13, 2013 Private Individual 0282 Comment from Peoria Chamber of Commerce, Bobbi Magdaleno, Chair Industry/Commerce 0283 Comment from Peggie Jo Vincent, November 15, 2013 Private Individual 0284 Comment from Dennis DuVall, November 14, 2013 Private Individual 0285 Comment from Andy M. Tobin, Speaker, AZ House of Representative, letter dated November 13, 2013 Elected Official N

a

0286 

Comment from William A. Rigsby, letter dated November 12, 2013 

Private Individual M

CLf

0287 Comment from Judy Burges, AZ State Senate, November 12, 2013 Elected Official S

i

0288 Comment Robert E. Rutkowski, dated November 12, 2013 Private Individual 0289 Comment from Arizona Corporation Commission, Bob Stump, Chairman, November 5, 2013 State/Local Government S

0

0290 Comment from Art Felsinger and Paul Bott Private Individual 0291 

Comment from Marcus D. Martin, October 25, 2013 Private Individual M

CLf

0292 Comment from James Shlenvogt, October 24, 2013 Private Individual 
Page 261

EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0293 Comment from City of Gilbert, John W. Lewis, Mayor, October 24, 2013 State/Local Government 0294 Comment EXAMPLE of 82 comment cards from Black Mesa Water Coalition, October 2013 Environmental/Public Interest Advocacy Group M

C

0295 Comment from City of Scottsdale Arizona, W.J. "Jim" Lane, Mayor, October 23, 2013 State/Local Government 0296 Comment from City of Glendale Arizona, Brenda S. Fishcer, City Manager, October 23, 2013 State/Local Government 0297 Comment from State of Arizona, Janice K. Brewer, Governor, October 21, 2013 State/Local Government 0298 Comment from Dan Spacek, December 14, 2013 Private Individual 0299 Comment on EPA-R09-OAR-2013-0009-0186 Private Individual 0300 Comment on EPA-R09-OAR-2013-0009-0186; AZ House of Representatives Majority Leader Elected Official 0304 Comment on EPA-R09-OAR-2013-0009-0186, Dave Perry, President, Greater Oro Valley Chamber of Commerce Industry/Commerce 0305 Comment on EPA-R09-OAR-2013-0009-0186 Task Force 01- 06-2014, Grant Ward and Paul Orme Submitters CAP Water Interest Group 0306 

Comment letter dated January 6, 2014 from AZ Mining 

Association, Kelly Norton, President, with attachment, "The 

NGS Battle" dated October 2013, 

Industry/Commerce S

0307 Comment from Carol W. West, November 26, 2013 Private Individual 0308 Comment from Rory Van Poucke, December 4, 2013 Private Individual 0309 

Comment from Daryl P. Rachey, December 6, 2013 Private Individual M

CLf

0310 Comment from Brian Stevens, December 8, 2013 Private Individual 
Page 262

EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0311 

Comment from Eric Hayes, December 8, 2013 Private Individual M

CLf

0312 Comment from Steven and Joan Harris, December 8, 2013 Private Individual 0313 

Comment from TWG to Jared Blumenfeld, RA, USEPA R9, dated January 6, 2014 

Technical Work Group S

0t

0314 Comment from Tucson Electric Power (TEP), Mark Mansfield, Vice President, Generation, dated January 6, 2014 Industry/Commerce C0315 

Comment from Arizona Public Service (APS), Chas Spell, Director of Environmental Policy Program, dated January 6, 2014 

Industry/Commerce C

0316 

Comment from Navajo Nation, Ben Shelly, President, January 6, 2014 

Tribal Government I

S0r

0317 Comment from Gila River Indian Community (GRIC), Linus Everling, dated January 2, 2014 Tribal Government 00318 Comment from David M. Gowan, Sr., House Majority Leader, Arizona House of Representatives, December 9, 2013 Elected Officials D0319 

Comment from Deborah Maust, December 9, 2013 Private Individual M

CLf

0320 

Comment from Arizona Corporation Commission (ACC), January 6, 2014 

State/Local Government S

rS0
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Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0321 Comment from Jeff McIntyre, Special Education Counselor, Page High School, December 9, 2013 Private Individual 0322 

Comment from Monica Kloskowski, December 9, 2013 Private Individual M

CLf

0323 

Comment from Herman G. Honarie, Chairman, The Hopi Tribe, December 9, 2013 

Tribal Government S

0r

0324 Comment from Duane Blumberg, Ph.D., Mayor, Town of Sahuarita, December 10, 2013 State/Local Government E

i

0325 Comment from Arizona Coalition for Water, Energy, Jobs Tom Dorn, dated January 6, 2014 Industry/Commerce P

C

0326 

Comment from 22nd Navajo Nation, Honorable Johnny Naize, January 6, 2014 

Tribal Government I

S0r

0327 Comment from Donald Begalke, December 12, 2013 Private Individual 0328 Comment from Mark Mitchell, Mayor, City of Tempe, December 13, 2013 State/Local Government 0329 Comment from Mary Worman, December 13, 2013 Private Individual 0330 Comment from Mike Dvorak, December 13, 2013 Private Individual 0331 Comment from James Terwilliger, December 14, 2013 Private Individual 0332 Comment from Arizona Congressional Delegation, submitted by Kris Kiefer (Flake), December 16, 2013 Elected Officials 0333 

Comment from Herman Honanie, Chairman of The Hopi Tribe, December 16, 2013 

Tribal Government S

ar
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EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0334 Comment from Ronnie Lupe, Chairman, White Mountain Apache Tribe, December 17, 2013 Tribal Government N

d

0335 Comment from Charles Spitzer, December 21, 2013 Private Individual 0336 

Response letter from Jared Blumenfeld, EPAR9, RA, to Herman G. Honanie, Chairman of the Hopi Tribe, December 24, 2013, resulting from government-to-government consultation of December 9, 2013 

Federal Agency N

0337 

Letter from Jared Blumenfeld, RA, USEPA R9, to Ronnie Lupe, Chairman, White Mountain Apache Tribe, December 24, 2013, regarding the December 10, 2013 consultation meeting and the duration of the comment period 

Federal Agency N

0338 

Comment from Virgil W. Davis, Chairman of the Board, Community Water Company of Green Valley, December 27, 2013 

CAP Water Interest Group 

0339 Comment from Dave Perry, President/CEO, Greater Oro Valley Chamber of Commerce, December 27, 2013 Industry Commerce D0340 

Comment from Tohono O'odham Nation, submitted by Jonathan L. Jantzen, Office of Attorney General of the Tohono O'odham Nation, December 27, 2013 

Tribal Government 

0341 Comment from Glenn Martin, December 30, 2013 Private Individual 0342 Comment from Lee Beam, re PhotoBioReactor, December 30, 2013 Private Individual N

a

0343 

Comment from Central Arizona Water Conservation District (CAWCD), David Modeer, General Manager, dated January 6, 2014 

CAP Operator S

0r

0344 Comment from Mary Ann Osterbrink, December 30, 2013 Private Individual 0345 Comment from Charles Bliss, ChE, Oxyfuel Alternative, January 2, 2014 Private Individual 0346 Comment from Dominic Bailin, January 3, 2014 Private Individual 
Page 265

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Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0347 Comment from Arizona Department of Water Resources, Thomas Buschatzke, dated January 6, 2014 State/Local Government 0348 Comment letter from SRP, Kelly J. Barr, with enclosures separately posted Industry/Commerce C

o

0349 Comment from SRP, Appendices A-C Industry/Commerce 00350 Comment from SRP, Appendices D-F Industry/Commerce 00351 Comment from SRP, Appendices G-K Industry/Commerce 00352 Comment from SRP, Appendices L-O Industry/Commerce 00353 Comment from SRP, Appendices P-T Industry/Commerce 00354 Comment from SRP, Appendices U-V Industry/Commerce 00355 Comment from Vincent Yazzie, January 6, 2014 Private Individual 0356 Comment from Don Yellowman, President, Forgotten People CDC, January 3, 2014 Environmental/Public Interest Advocacy Group 0357 Comment from Douglas Dewitz, January 3, 2014 Private Individual 0358 Comment from Nance Harris, January 3, 2014 Private Individual 0359 

Comment from Herman Honanie, Chairman, The Hopi Tribe, January 3, 2014 

Tribal Government S

0r

0360 Comment from James and Carolyn Shelton, January 4, 2014 Private Individual 0361 Comment from Sarah Carignan, January 4, 2014 Private Individual 0362 

Comment from Dwight Witherspoon, Council Delegate for: Black Mesa Chapter, Forest Lake Chapter, Hardrock Chapter, Pinon Chapter, Wippoorwill Chapter, January 5, 2014 

State/Local Government 

0363 Comment from Michael L. Weiss, January 6, 2014 Private Individual 0364 Comment from Tracy Hiscock, January 5, 2014 Private Individual 0365 Letter Response to Governor Janice Brewer, from Administrator Gina McCarthy, January 6, 2014 Federal Agency N0366 Comment from Bob and Karen LeCour, January 5, 2014 Private Individual 
Page 266

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Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0367 

Comments and Exhibits submitted by Earth Justice on behalf of "Conservations Organizations": National Parks Conservation Association, Sierra Club, Grand Canyon Trust and National Resources Defense Council 

Environmental/Public Interest Advocacy Group 

0

0368 

Comments and Exhibits submitted by Earth Justice on behalf of "Conservations Organizations": National Parks Conservation Association, Sierra Club, Grand Canyon Trust and National Resources Defense Council: David Marcus, December 31, 2013 

Environmental/Public Interest Advocacy Group 

0

0369 

Comments and Exhibits submitted by Earth Justice on behalf of "Conservations Organizations": National Parks Conservation Association, Sierra Club, Grand Canyon Trust and National Resources Defense Council: George D. Thurston's Report, December 12, 2013 

Environmental/Public Interest Advocacy Group 

0

0370 

Comments and Exhibits submitted by Earth Justice on behalf of "Conservations Organizations": National Parks Conservation Association, Sierra Club, Grand Canyon Trust and National Resources Defense Council: Nathan Miller and Ranijit Sahu , December 31, 2013 

Environmental/Public Interest Advocacy Group 

0

0373 

Letter, January 3, 2014: Comments and Exhibits submitted by Earth Justice on behalf of "Conservations Organizations": National Parks Conservation Association, Sierra Club, Grand Canyon Trust and National Resources Defense Council 

Environmental/Public Interest Advocacy Group 

0374 

Comments: Example of 728 emails from Environment Arizona Campaign received 1-3-14 

Environmental/Public Interest Advocacy Group 

MCE
Page 267

EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0375 

Comments: Example of 1, 111 emails received by EPA from Care2 Take Action Campaign, 1-6-14 

Environmental/Public Interest Advocacy Group 

MCTdc

0376 

Comments: Example of 1,226 emails from Wild Earth Guardians received by EPA as of 1/6/14 

Environmental/Public Interest Advocacy Group 

MCW

0377 

Comments: Example of 26 Similar Emails all containing "Taxpayer from AZ" in signature line received by EPA as of 1-6-14 

Private Individual M

C"A

0378 

Comment from Dan Spacek, December 14, 2013 Private Individual M

C"A

0379 

Comment from Jim Staude, December 16, 2013 Private Individual M

C"A

0380 Comments: Example of 114 Emails All With Identical Subject Line received by 1-6-14 Private Individual M

C

0381 Comment from Pinal Partnership Board, Sandie Smith, CEO, dated 12-20-13 Industry/Commerce 0382 Comment from Everett Rhodes, 12-23-13 Private Individual 0383 Comment from City of Phoenix, Water Services Department, Clifford A. Neal, P.E., Advisor, December 30, 2013 State/Local Government 0384 Comment from Peabody Energy, Mary L. Frontezak, Senior Vice President and General Counsel Peabody, January 2, 2014 Industry/Commerce S

0
Page 268

EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0385 

Comments: Example of 35,293 letters from National Parks Conservation Association Campaign 

Environmental/Public Interest Advocacy Group 

MCv

0386 

Comments: Example 38,365 emails from Sierra Club received by EPA as of 1-6-14 

Environmental/Public Interest Advocacy Group 

MCeod

0387 Comment from Ak-Chin Indian Community, Louis J. Manuel, Jr., Chairman, 1-6-14 Tribal Government 0388 Comment from Allen Gilberg, January 6, 2014 Private Individual 0389 

Comment from Arizona Public Services (APS), Chas Spell, Director of Environmental Policies and Programs, January 6, 

2014 

Industry/Commerce S

0n

0390 Memo to File, 1-8-14, Anita Lee, re Comment attachments for V. Yazzie, January 6, 2014 submitted thru regulations.gov Federal Agency N0391 Comment from Arizona Corporation Commission submitted by Michele Finical, January 6, 2014 Industry/Commerce D0392 Comment from Craig J. Sanderson, January 6, 2014 Private Individual 0393 Comment from Dorothy Rl Yazzie, January 6, 2014 Private Individual 0394 Comment from Ed Becenti, January 6, 2014 Private Individual 0395 Comments from Western Resource Advocates and Environmental Defense Fund, January 6, 2014 Environmental/Public Interest Advocacy Group 0396 Comment from Frank Bain, January 6, 2014 Private Individual 0397 Comment from Gila River Indian Community, letter dated January 2, 2014, submitted by Linus Everling, January 6, 2014 Tribal Government D0398 

Comments from Irrigation and Electrical Districts Association of Arizona, Robert S. Lynch, January 6, 2014 

CAP Water Interest Group 

Ic& 
Page 269

EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0399 Comments from Leonard Gilmore, January 6, 2014 Private Individual 0400 Comment from West Maricopa Coalition, WESTMARC, Michelle Rider, January 6, 2014 Industry/Commerce I0401 Comment from San Juan Individuals Alliance, Mike Eisenfeld, January 6, 2014 Environmental/Public Interest Advocacy Group S

c

0402 Comments from Navajo Nation, Ben Shelly, President, January 6, 2014 Tribal Government D0403 

Comment from Forgotten People, Fern, Mabelle and Norman Benally, Pauline Whitesinger, Vincent Yazzie, Bessie Wilson, Marsha Monestersky and Danny Blackgoat, submitted by S.D. Smith, January 6, 2014 

Environmental/Public Interest Advocacy Group 

0404 Comment from The Tax Payer Association of Kane County, submitted by Dr. Sky Chaney, January 6, 2014 Environmental/Public Interest Advocacy Group0405 Comment from Susan Hand, January 6, 2014 Private Individual 0406 Comment from Town of Marana AZ, John P. Kmiec, Utilities Director, January 6, 2014 State/Local Government E

i

0407 

Comment from Black Mesa Trust, Vernon Masayesva, Founder and Director of Black Mesa Trust, January 6, 2014 

Environmental/Public Interest Advocacy Group 

Iwc

0408 Comment from Arizona Department of Water Resources, submitted by Theresa Johnson, January 6, 2014 State/Local Government D0409 

Comment from Central Arizona Project Agricultural Water Users Navajo Generating Station Task Force, Van Smith, January 6, 2014 

Industry/Commerce D

0410 Comment from Central Arizona Water Conservation District, Jay M. Johnson, January 6, 2014 Industry/Commerce D0411 Comment from United States Department of the Interior, Alletta Belin, January 6, 2014 Federal Agency 
Page 270

EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0412 Comment from Donna House, Member of Oak Springs Chapter of Navajo Nation, January 6, 2014 Private Individual 0413 Comment from Black Mesa Water Coalition, Jihan Gearon, January 6, 2014 Environmental/Public Interest Advocacy Group 0414 Comment from Jim and Lora Gale, January 5, 2014 Private Individual 0415 Comment from Lisa Rutherford, January 6, 20144 Private Individual 0416 Comment from Water Resource Institute, L.L.C., Mark Lewis, January 6, 2014 Industry/Commerce 0417 Comment from Salt River Project Agricultural Improvement and Power District (SRP), Kelly J. Barr, January 6, 2014 Industry/Commerce D0418 Comments from Technical Work Group (TWG), submitted by Kelly J. Barr, January 6, 2014 Technical Work Group D0419 Comment from Tonto Apache Tribe and San Carlos Apache Tribe, submitted by Julia Rowen Kolsrud, January 6, 2014 Tribal Government S

c

0420 Comment of Navajo Nation Resolutions submitted by Marshall Johnson, January 6, 2014 Tribal Government 0421 Comment from Kaibab Band of Paiute Indians, submitted by Chairman Manuel M. Savala, January 6, 2014 Tribal Government 0422 

Comment from Lois McConville, December 16, 2013 Private Individual M

CLf

0423 

Comment from Mike McConville, December 13, 2013 Private Individual M

CLf
Page 271

EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0424 

Comment example of 51 post cards received January 6, 2014 Environmental/Public 

Interest Advocacy Group 

Ca csMC2

0431 Comment from Steven and Joan Harris, December 8, 2013 Private Individual 0432 Comment from Bob and Karen LeCour, January 5, 2014 Private Individual 0433 

Memo to File, January 28, 2014: Re: Electronic Mass Mail Comments Received, by Anita Lee 

Federal Agency T

oM

0434 

Comments, Unique Emails, Do Not Delay NGS Cleanup 

Campaign, example dated December 19, 2013, from Caroline Johnson 

Private Individual M

CDC

0435 

Comments, Unique Emails, Clean Air for the Grand Canyon, 

Environment Arizona, example dated December 25, 2013, from Jane Beattie 

Private Individual M

CEA

0436 Comments, Unique Emails from Sierra Club Campaign, example dated December 10, 2013, from John Browne Private Individual 40437 

Comments, Unique Emails from Taxpayers from AZ Campaign, 

example dated November 6, 2013, Alma Engel 

Private Individual M

C"A

0438 

Comments, Unique Emails from Wild Earth Guardians Campaign, example dated May 16, 2013, Mr. AJ Averett 

Private Individual M

CW
Page 272

EPA Responses to Comments: Navajo Generating Station Final Rule | July 28, 2014 

Appendix A: List of Written Comments389

Document ID a

Title Type of Commenter N

0439 

Comment, Unique Letters from NPCA Campaign, example 

dated June 11, 2013, Mr. Thomas French 

Private Individual 2

MC

0440 Comment from the White Mountain Apache Tribe, submitted by Chairman Ronnie Lupe dated February 5, 2014 Tribal Government 0441 

Postcard Comments from 48 Individuals postmarked January 6, 2014 

Private Individuals M

ct

0442 

Late Postcard Comments from 58 Individuals postmarked January 7, 2014 

Private Individuals M

ct

0443 

Re-Posting to Add Missing Attachment from Document Number 

0192: Comment from Mayor of Oro Valley, AZ, Satish I. Hiremath dated September 18, 2013 

Government – Local O

wa

0446 

Re-posting to attach missing file for comment number 0285: Comment from Andy Tobin, Speaker, AZ House of Representatives dated November 13, 2013 

Government – State O

wa

0447 

Re-posting to attach missing file for comment number 0342: Comment from Lee Beam, re: PhotoBioReactor, December 30, 2013 

Individual O

wa

a Document ID identifies written comments found in Docket No. EPA-R09-OAR-2013-0009 by document numbb Document No. 0264 was uploaded on the Docket as one comment, although it is a compilation of eight differen

represent different interests. We have assigned individual numbers to each commenter to avoid confusion.