The EPA Region IX Acting Regional Administrator, Deborah Jordan, signed the following rule 

on June 30, 2016 and the EPA is submitting it for publication in the Federal Register (FR). While 

we have taken steps to ensure the accuracy of this version of this rule, it is not the official 

version. Please refer to the official version in a forthcoming FR publication appearing on the 

Government Printing Office website, http://fdsys.gpo.gov/fdsys/search/home.action, and on 

www.regulations.gov in Docket Number EPA-R09-OAR-2016-0292.

6560-50-P

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2016-0292, FRL-XXX]

Approval and Revision of Air Plans; Arizona; Regional Haze State and Federal Implementation 

Plans; Reconsideration

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

SUMMARY: The Environmental Protection Agency (EPA) is proposing to approve a sourcespecific revision to the Arizona State Implementation Plan (SIP) that addresses requirements for

best available retrofit technology (BART) at Cholla Generating Station (Cholla). The EPA 

proposes to find that the SIP revision fulfills the requirements of the Clean Air Act (CAA) and the

EPA’s Regional Haze Rule (RHR) for BART at Cholla. In conjunction with this proposed 

approval, we propose to withdraw those portions of the federal implementation plan (FIP) that 

address BART for Cholla. We previously partially granted petitions for reconsideration of that FIP 

from Cholla’s owners, Arizona Public Service Company (APS) and PacifiCorp. We are now 

proposing to find that final withdrawal of the FIP, as it applies to Cholla, would constitute our 

action on APS’s and PacifiCorp’s petitions for reconsideration of the FIP.

DATES: Written comments must be received on or before [Insert date 45 days after the date of 

publication in the Federal Register]. Requests for public hearing must be received on or before 

[Insert date 15 days after the date of publication in the Federal Register].
This document is a prepublication version signed by the EPA Region IX Acting Regional 

Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-OAR-2016-0292

at http://www.regulations.gov, or via email to limaye.vijay@epa.gov. For comments submitted at 

Regulations.gov, follow the online instructions for submitting comments. Once submitted, 

comments cannot be edited or removed from Regulations.gov. For either manner of submission, 

the EPA may publish any comment received to its public docket. Do not submit electronically any 

information you consider to be Confidential Business Information (CBI) or other information 

whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be 

accompanied by a written comment. The written comment is considered the official comment and 

should include discussion of all points you wish to make. The EPA will generally not consider 

comments or comment contents located outside of the primary submission (i.e. on the web, cloud, 

or other file sharing system). For additional submission methods, please contact the person 

identified in the “For Further Information Contact” section. For the full EPA public comment 

policy, information about CBI or multimedia submissions, and general guidance on making 

effective comments, please visit http://www2.epa.gov/dockets/commenting-epa-dockets.

FOR FURTHER INFORMATION CONTACT: Vijay Limaye, U.S. EPA, Region 9, Planning 

Office, Air Division, Air-2, 75 Hawthorne Street, San Francisco, CA 94105. Vijay Limaye can be 

reached at telephone number (415) 972-3086 and via electronic mail at limaye.vijay@epa.gov.

SUPPLEMENTARY INFORMATION: Throughout this document, “we,” “us” and “our” refer 

to the EPA.

Table of Contents

I. General Information

II. Background
This document is a prepublication version signed by the EPA Region IX Acting Regional 

Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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III. Summary of the Cholla SIP Revision

IV. The EPA’s Evaluation of the Cholla SIP Revision

V. Proposed Action

VI. Environmental Justice Considerations

VII. Incorporation by Reference 

VIII. Statutory and Executive Order Reviews

I. General Information

A. Definitions 

For the purpose of this document, we are giving meaning to certain words or initials as 

follows:

 The words or initials Act or CAA mean or refer to the Clean Air Act, unless the context 

indicates otherwise.

 The initials ADEQ mean or refer to the Arizona Department of Environmental Quality.

 The initials AFUDC mean or refer to Allowance for Funds Used During Construction.

 The initials APS mean or refer to Arizona Public Service Company.

 The words Arizona and State mean the State of Arizona.

 The initials BART mean or refer to Best Available Retrofit Technology.

 The term Class I area refers to a mandatory Class I Federal area.1

 The initials CBI mean or refer to Confidential Business Information.

 

1 Although states and tribes may designate as Class I additional areas which they consider to have visibility as an 

important value, the requirements of the visibility program set forth in section 169A of the CAA apply only to 

“mandatory Class I Federal areas.”
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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 The initials CCM mean or refer to the EPA’s Control Cost Manual.

 The words EPA, we, us or our mean or refer to the United States Environmental Protection 

Agency.

 The initials FIP mean or refer to Federal Implementation Plan.

 The initials LNB mean or refer to low-NOX burners.

 The initials MMBtu mean or refer to million British thermal units

 The initials NOX mean or refer to nitrogen oxides.

 The initials OFA mean or refer to over fire air.

 The initials PM10 mean or refer to particulate matter with an aerodynamic diameter of less 

than 10 micrometers. 

 The initials RHR mean or refer to the EPA’s Regional Haze Rule.

 The initials RP mean or refer to Reasonable Progress.

 The initials RPG or RPGs mean or refer to Reasonable Progress Goal(s).

 The initials SCR mean or refer to Selective Catalytic Reduction.

 The initials SIP mean or refer to State Implementation Plan.

 The initials SNCR mean or refer to Selective Non-catalytic Reduction

 The initials SOFA mean or refer to separated over fire air.

 The initials SO2 mean or refer to sulfur dioxide.

B. Docket 

The EPA has established docket number EPA-R09-OAR-2016-0292 for this action. 

Generally, documents in the docket for this action are available electronically at 

http://www.regulations.gov or in hard copy at EPA Region IX, 75 Hawthorne Street, San 
This document is a prepublication version signed by the EPA Region IX Acting Regional 

Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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Francisco, California 94105-3901. While all documents in the docket are listed at 

http://www.regulations.gov, some information may be publicly available only at the hard copy 

location (e.g., copyrighted material, large maps, multi-volume reports), and some may not be 

available in either location (e.g., confidential business information (CBI)). To inspect the hard 

copy materials, please schedule an appointment during normal business hours with the contact 

listed in the FOR FURTHER INFORMATION CONTACT section.

C. Public Hearings 

If anyone contacts the EPA by [Insert date 15 days after publication in the Federal 

Register] requesting to speak at a public hearing, the EPA will schedule a public hearing and 

announce the hearing in the Federal Register. Contact Vijay Limaye at (415) 972-3086 or at 

limaye.vijay@epa.gov to request a hearing or to determine if a hearing will be held. 

II. Background

A. Statutory and Regulatory Background

This section provides a brief overview of the requirements of the CAA and RHR, as they 

apply to this particular action. Please refer to our previous rulemakings on the Arizona Regional 

Haze SIP for additional background regarding the visibility protection provisions of the CAA and 

the RHR.2

In section 169A of the 1977 Amendments to the CAA, Congress created a program for 

protecting visibility in the nation's national parks and wilderness areas. This section of the CAA 

establishes as a national goal the “prevention of any future, and the remedying of any existing, 

 

2 77 FR 42834, 42837-42839 (July 20, 2012), (Arizona Regional Haze “Phase 1” Rule) 77 FR 75704, 75709-75712 

(December 21, 2012), (Arizona Regional Haze “Phase 2” Rule). 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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impairment of visibility in mandatory Class I Federal areas which impairment results from 

manmade air pollution.”3It also directs states to evaluate the use of retrofit controls at certain 

larger, often uncontrolled, older stationary sources in order to address visibility impacts from these 

sources. Specifically, section 169A(b)(2)(A) of the CAA requires states to revise their SIPs to 

contain such measures as may be necessary to make reasonable progress towards the natural 

visibility goal, including a requirement that certain categories of existing major stationary sources 

built between 1962 and 1977 (known as “BART-eligible” sources) procure, install, and operate 

BART. In the 1990 CAA Amendments, Congress amended the visibility provisions in the CAA to 

focus attention on the problem of regional haze, which is visibility impairment produced by a 

multitude of sources and activities located across a broad geographic area.4

In 1999, we promulgated the RHR, which requires states to develop and implement SIPs 

to ensure reasonable progress toward improving visibility in mandatory Class I Federal areas 

(Class I areas)5by reducing emissions that cause or contribute to regional haze.6 Under the RHR, 

states are directed to conduct an analysis and make a BART determination for each BART-eligible 

source that may be anticipated to cause or contribute to any visibility impairment in a Class I area.7

In particular, under CAA section 169A(g)(2) and 40 CFR 51.308(e)(1)(ii)(A), states must analyze 

and consider the following five factors as part of each source-specific BART analysis: (1) the costs 

 

3 42 U.S.C. 7491(a)(1). 

4 See CAA section 169B, 42 U.S.C. 7492.

5 Areas designated as mandatory Class I Federal areas consist of national parks exceeding 6000 acres, wilderness 

areas and national memorial parks exceeding 5000 acres, and all international parks that were in existence on 

August 7, 1977. 42 U.S.C. 7472(a). When we use the term “Class I area” in this action, we mean a “mandatory Class 

I Federal area.”

6 See generally 40 CFR 51.308. 

7 40 CFR 51.308(e). 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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of compliance of each technically feasible control technology, (2) the energy and non-air quality 

environmental impacts of compliance of the control technologies, (3) any existing pollution control 

technology in use at the source, (4) the remaining useful life of the source, and (5) the degree of 

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

technology (collectively known as the “five-factor BART analysis”). 

In 2005, the EPA published the Guidelines for BART Determinations under the Regional 

Haze Rule at Appendix Y to 40 CFR part 51 (“BART Guidelines”) on July 6, 2005. The BART 

Guidelines assist states in determining which of their sources should be subject to the BART 

requirements and in determining appropriate emission limits for each such “subject-to-BART” 

source. In making BART determinations for fossil fuel-fired electric generating plants with a total 

generating capacity in excess of 750 megawatts, states must use the approaches set forth in the 

BART Guidelines. States are encouraged, but not required, to follow the BART Guidelines in 

making BART determinations for other types of sources. In lieu of requiring source-specific 

BART controls, states also have the flexibility to adopt an alternative measure as long as the 

alternative provides greater reasonable progress towards natural visibility conditions than BART

(i.e., the alternative must be “better than BART”).

8

In addition to the visibility protection requirements of the CAA and the RHR, SIP revisions 

concerning regional haze are also subject to the general requirements of CAA section 110. In 

particular, they are subject to the requirement in CAA section 110(l) that SIP revisions must not 

“interfere with any applicable requirement concerning attainment and reasonable further progress 

 

8 40 CFR 51.308(e)(2).
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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(as defined in [CAA § 171]), or any other applicable requirement of [the CAA],” as well as the 

requirement in CAA section 110(a)(2)(A) that SIPs must include enforceable emission limits. 

B. Cholla Generating Station

Cholla Generating Station consists of four primarily coal-fired electricity generating units 

with a total plant-wide generating capacity of 1,150 megawatts. Unit 1 is a 126 MW tangentiallyfired, dry-bottom boiler that is not BART-eligible. Units 2, 3 and 4 have capacities of 272 MW, 

272 MW and 410 MW, respectively, and are tangentially-fired, dry-bottom boilers that are each 

BART-eligible. Units 1, 2, and 3 are owned and operated by APS and Unit 4 is owned by 

PacifiCorp and operated by APS.

C. Summary of State Submittals and EPA Actions 

1. 2011 Arizona Regional Haze SIP 

On February 28, 2011, the Arizona Department of Environmental Quality (ADEQ) 

submitted a Regional Haze SIP under Section 308 of the RHR (“Arizona Regional Haze SIP”) to 

EPA. This submittal included BART analyses and determinations for nitrogen oxides (NOX), 

particulate matter with an aerodynamic diameter of less than 10 micrometers (PM10), and sulfur 

dioxide (SO2) at Cholla Units 2, 3, and 4. ADEQ's BART analyses for Cholla included the 

following seven steps:

• Step 1: Identify the Existing Control Technologies in Use at the Source,

• Step 2: Identify All Available Retrofit Control Options,

• Step 3: Eliminate All Technically Infeasible Control Options,

• Step 4: Evaluate Control Effectiveness of Remaining Technologies,

• Step 5: Evaluate the Energy and Non-Air Quality Environmental Impacts and Document 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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Results,

9

• Step 6: Evaluate Visibility Impacts, and

• Step 7: Select BART.10

2. 2012 EPA Action on Arizona Regional Haze SIP and FIP 

On December 5, 2012, we issued a final rule approving in part and disapproving in part 

ADEQ’s BART determinations for three sources, including Cholla.

11 We found that ADEQ’s 

overall approach to conducting BART analyses and its implementation of the first four steps of its 

approach were generally reasonable and consistent with the RHR and the BART Guidelines. 

However, we found significant flaws in ADEQ’s implementation of the last three steps. In 

particular, under step 5, we found that the costs of compliance were not calculated in accordance 

with the BART Guidelines; under step 6, we found that the visibility benefits were not 

appropriately evaluated and considered; and under step 7, we found that ADEQ did not provide a 

sufficient explanation and rationale for its determinations. 12 As a result of these flaws, we 

disapproved ADEQ’s BART determinations for NOX at Cholla Units 2, 3, and 4. We also found 

that the SIP lacked enforceable emission limits for all units and pollutants. In the same action, we

promulgated a FIP for the disapproved portions of the SIP, including NOX BART determinations 

for Units 2, 3, and 4. We determined that BART for NOX at Units 2, 3, and 4 was an emission limit 

of 0.055 pounds per million British thermal units (lb/MMBtu) determined as an average across the 

 

9 We note that, while ADEQ referred to its Step 5 as an evaluation of energy and non-air quality environmental 

impacts, this step also includes consideration of the costs of compliance and the remaining useful life of the source, 

consistent with the BART Guidelines, 40 CFR part 51, appendix Y, section IV.D.4.

10 Arizona Regional Haze SIP Revision, Appendix D, section XI.

11 77 FR 72511. 

12 See 77 FR 42834, 42840-42941.
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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three units, based on a rolling 30-boiler-operating-day average, which is achievable with the use 

of low-NOX burners (LNB), overfire air (OFA) and selective catalytic reduction (SCR). The 

compliance date for the NOX BART emission limit is December 5, 2017. In addition, we

established an SO2 removal efficiency requirement of 95 percent for the scrubbers on Cholla Units 

2, 3 and 4. Cholla Units 3 and 4 were required to achieve this removal efficiency by December 5, 

2013, and Cholla Unit 2 was required to comply by April 1, 2016. We also established 

requirements for equipment maintenance, monitoring, recordkeeping, and reporting for all units 

and all pollutants.

3. 2015 APS Application for Significant Permit Revision for Cholla Generating Station 

On January 15, 2015, APS and PacifiCorp submitted an “Application for Significant Permit 

Revision and Five-Factor BART Reassessment for Cholla” to ADEQ. APS and PacifiCorp 

requested that ADEQ conduct a revised BART analysis and determination based on new facts 

(“BART Reassessment”) and submit this BART Reassessment to the EPA as a revision to the 

Arizona Regional Haze SIP. Under the Cholla BART Reassessment, APS and PacifiCorp would 

commit to the following measures in lieu of implementing the FIP requirements for the Cholla 

Generating Station:

 Unit 2 would be permanently shut down by April 1, 2016;

 Unit 3 and Unit 4 would continue to operate with currently installed LNB and 

separated over fire air (SOFA). In addition, by April 30, 2025, APS and PacifiCorp 

would permanently cease burning coal at both units with the option to convert to 

pipeline-quality natural gas by July 31, 2025, with a ≤ 20 percent annual average 

capacity factor. 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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4. 2015 Arizona Regional Haze SIP Revision for Cholla Generating Station 

On October 22, 2015, ADEQ submitted a revision to the Arizona Regional Haze SIP that 

incorporates the Cholla BART Reassessment (“Cholla SIP Revision”). The Cholla SIP Revision 

is the subject of this proposal.

III. Summary of the Cholla SIP Revision

The Cholla SIP Revision consists of a revised BART analysis and determination for NOX

at Cholla, an analysis under CAA section 110(l), and a revision to Cholla’s operating permit 

(“Cholla Permit Revision”)13 to implement both the revised BART determination for NOX and 

ADEQ’s prior BART determinations for SO2 and PM10 at Cholla. If fully approved by the EPA, 

the Cholla SIP Revision would fill the gap in the Arizona Regional Haze SIP that resulted from 

the EPA’s disapproval of ADEQ’s BART determinations for NOX at Cholla Units 2, 3, and 4 and 

the lack of enforceable emission limits for all units and pollutants. Accordingly, full approval of 

the Cholla SIP Revision would enable the EPA to withdraw the provisions of the Arizona Regional 

Haze FIP that apply to Cholla.

In the Cholla SIP Revision, ADEQ determined that, if Unit 2 were shut down by April 1, 

2016, no BART determination for Unit 2 would be necessary “because the enforceable shutdown 

date is within the five-year BART window.”

14 For Units 3 and 4, ADEQ performed a revised 

BART analysis, taking into account the new requirements that would be imposed as part of the 

Cholla BART Reassessment. This re-analysis and the resulting BART determinations are 

 

13 Cholla BART SIP Revision, Appendix A Significant Permit Revision No. 61713 to Operating Permit No. 53399 

for Arizona Public Service Company Cholla Generating Station (October 16, 2015).

14 Cholla SIP Revision, section 2.2, page 4. 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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summarized in the following sections. 

A. BART Re-Analysis for Cholla Units 3 and 4

ADEQ’s BART re-analysis for Units 3 and 4 consists of an evaluation of each of the five 

BART factors, effectively replacing step 5 (evaluation of costs of compliance, energy and non-air 

quality environmental impacts, and remaining useful life) and step 6 (evaluation of visibility 

benefits) of ADEQ’s prior BART analysis for Cholla in the Arizona Regional Haze SIP.

1. Cost of Compliance

ADEQ evaluated the costs of compliance for three control options: (1) LNB and SOFA, 

(2) SNCR with LNB and SOFA, and (3) SCR with LNB and SOFA. Two fuel-use scenarios were 

used as a comparison: (1) twenty years of operation on coal and (2) eight years of operation on 

coal followed by twelve years of operation on natural gas (as provided for under the BART 

Reassessment). The cost-effectiveness values for each control option under each of these scenarios 

are shown in Tables 1 and 2. For all options, the costs associated with the BART Reassessment

are due to lower utilization periods (coal firing until 2025 instead of for 20 years) as well as 

significantly lower NOX emissions after conversion to natural gas.

TABLE 1 – COST-EFFECTIVENESS OF NOX CONTROL OPTIONS AT CHOLLA ASSUMING 20 YEARS OF 

OPERATION ON COAL

Average Incremental a

Unit Control option Annual cost 

($/year)

Emission 

reduction 

relative to 

baseline 

(ton/year)

Average 

costeffectiveness 

($/ton)

Incremental 

annual cost 

($/year)

Incremental 

emission 

reduction 

(ton/year)

Incremental 

costeffectivenes

s ($/ton)

3 LNB and SOFA $483,300 1,219 $396 - - -

SNCR with 

LNB and SOFA

$3,070,443 1,911 $1,607 $2,587,143 691 $3,742 

SCR with LNB 

and SOFA

$9,448,912 3,300 $2,838 $8,965,612 2,110 $4,248 

4 LNB and SOFA $673,550 1,756 $384 - - -

SNCR with 

LNB and SOFA

$4,086,366 2,643 $1,546 $3,412,816 887 $3,848 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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SCR with LNB 

and SOFA

$13,590,853 4,408 $3,083 $12,917,303 2,652 $4,871 

a The incremental cost effectiveness results for SNCR and SCR are based on the emission and cost differences

between these technologies and the proposed LNB +SOFA option.

TABLE 2 – COST-EFFECTIVENESS OF NOX CONTROL OPTIONS AT CHOLLA ASSUMING 8 YEARS OF 

OPERATION ON COAL AND 12 YEARS OF OPERATION ON NATURAL GAS

Average Incremental

Unit Control option Annual cost 

($/year)

Emission 

reduction 

relative to 

baseline 

(ton/year)

Average 

costeffectiveness 

($/ton)

Incremental 

annual cost 

($/year)

Incremental 

emission 

reduction 

(ton/year)

Incremental 

costeffectiveness 

($/ton)

3 LNB and SOFA $411,300 488 $843 - - -

SNCR with LNB 

and SOFA

$2,497,743 786 $3,177 $2,086,443 299 $6,989 

SCR with LNB 

and SOFA

$8,716,452 1,387 $6,286 $8,305,152 899 $9,237 

4 LNB and SOFA $571,550 702 $814 - - -

SNCR with LNB 

and SOFA

$3,283,930 1,085 $3,027 $2,712,380 383 $7,091 

SCR with LNB 

and SOFA

$12,480,744 1,833 $6,810 $11,909,194 1,130 $10,539 

2. Energy and Non-Air Environmental Impacts

ADEQ indicated that the energy impacts of LNB, SOFA, and SNCR are minimal and that 

there are no non-air quality environmental impacts associated with LNB and SOFA. ADEQ also

noted that SNCR and SCR would result in ammonia slip and that the transport and handling of 

anhydrous ammonia presents potential safety hazards.

3. Existing Air Pollution Controls

ADEQ noted that, under the Cholla BART Reassessment, use of the existing LNB and 

SOFA would be continued at Units 3 and 4. ADEQ proposed no additional controls for these two 

units. Unit 2 would be shut down in April 2016, while Unit 1 (the non-BART unit) would cease 

burning coal in 2025.

4. Remaining Useful Life

ADEQ used a 20-year amortization period in order to calculate the costs of compliance for 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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Units 3 and 4 because neither unit is subject to an enforceable shutdown date.

5. Degree of Visibility Improvement

ADEQ included the results of modeling conducted by APS and PacifiCorp to predict the 

degree of visibility improvement associated with the three BART scenarios. This modeling 

predicted visibility impacts at the thirteen Class I areas within 300 km of the Cholla facility under 

a baseline scenario (based on 2001-2003 emissions with all four units operating), as well as the 

three BART control scenarios:

 BART Option 1: Unit 1 with 2001-2003 baseline controls (pre-LNB), Unit 2 shut down, 

LNB/SOFA on Units 3 and 4; 

 BART Option 2: Unit 1 with 2001-2003 baseline controls (pre-LNB), Unit 2 shut down, 

LNB/SOFA and SNCR on Units 3 and 4; and 

 BART Option 3: Unit 1 with 2001-2003 baseline controls (pre-LNB), Unit 2 shut down, 

LNB/SOFA and SCR on Units 3 and 4. 

APS and PacifiCorp used CALPUFF version 5.8 and incorporated meteorological data for 2001-

2003, an assumption of 1.0 part per billion background concentration for ammonia, and “Method 

8b” 20 percent best days background conditions for all cases. The results of this modeling are 

shown in Tables 3 and 4.

TABLE 3 - PREDICTED VISIBILITY IMPACTS (22ND HIGHEST DELTA-DV OVER 3-YEAR PERIOD)

Class I Area Baseline BART Option 1 

(LNB/SOFA) 

BART Option 2 

(LNB/SOFA/S

NCR) 

BART Option 3 

(LNB/SOFA/S

CR) 

Petrified Forest NP 5.31 4.33 4.05 3.55 

Grand Canyon NP 3.40 1.79 1.62 1.20 

Capitol Reef NP 2.19 1.04 0.91 0.62 

Mazatzal WA 2.23 0.96 0.87 0.69 
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Sycamore Canyon 

WA 

2.27 1.00 0.88 0.67 

Mount Baldy WA 2.10 0.97 0.85 0.62 

Gila WA 1.53 0.53 0.47 0.39 

Sierra Ancha WA 2.28 1.05 0.97 0.81 

Mesa Verde NP 2.08 0.88 0.78 0.60 

Galiuro WA 0.96 0.34 0.31 0.27 

Superstition WA 2.00 1.00 0.93 0.73 

Saguaro NP 0.70 0.22 0.22 0.20 

Pine Mountain WA 1.64 0.67 0.59 0.48 

TABLE 4 PREDICTED VISIBILITY IMPROVEMENT OVER THE BASELINE VISIBILITY IMPACTS (22ND 

HIGHEST DELTA-DV OVER 3-YEAR PERIOD)

Class I Area BART 

Option 1 

(LNB/SOFA) 

BART 

Option 2 

(LNB/SOFA 

/SNCR) 

BART 

Option 3 

(LNB/SOFA 

/SCR) 

Option 2 

over 

Option 1 

Option 3 

over 

Option 1 

Petrified Forest NP 0.98 1.26 1.77 0.28 0.79 

Grand Canyon NP 1.61 1.78 2.20 0.17 0.59 

Capitol Reef NP 1.15 1.28 1.57 0.13 0.42 

Mazatzal WA 1.27 1.36 1.54 0.09 0.27 

Sycamore Canyon 

WA 

1.27 1.39 1.60 0.12 0.33 

Mount Baldy WA 1.14 1.26 1.48 0.12 0.34 

Gila WA 1.00 1.06 1.14 0.06 0.14 

Sierra Ancha WA 1.22 1.30 1.47 0.08 0.25 

Mesa Verde NP 1.21 1.30 1.49 0.09 0.28 

Galiuro WA 0.62 0.65 0.69 0.03 0.07 

Superstition WA 1.00 1.07 1.28 0.07 0.28 

Saguaro NP 0.48 0.49 0.50 0.01 0.02 

Pine Mountain WA 0.97 1.04 1.16 0.07 0.19 

Cumulative 13.92 15.24 17.89 1.32 3.97 

Average 1.07 1.17 1.38 0.10 0.31 

B. BART Determination for Cholla Units 3 and 4

ADEQ’s BART determination for Cholla Units 3 and 4 in the Cholla SIP Revision

effectively replaces step 7 (select BART) of its prior BART analysis for NOX BART for Cholla in 

the Arizona Regional Haze SIP. In making this determination, ADEQ compared the three emission 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

Page 16 of 46

control options (LNB and SOFA, SNCR with LNB and SOFA, SCR with LNB and SOFA). For 

Option 1, it found that the LNB and SOFA controls could be installed at reasonable costeffectiveness and would deliver visibility improvements ranging from 0.48 to 1.61 dv over baseline 

conditions across thirteen Class I areas. For Option 2, it found the SNCR control option to be too 

costly in comparison to the small additional visibility benefits it would be expected to deliver. For 

Option 3, ADEQ noted that the visibility benefits of SCR (3.97 dv cumulative incremental 

visibility improvement) would only last until 2025 when coal firing would cease, after which the 

incremental benefits of SCR would be “negligible.” Based on its analysis, ADEQ found Option 1

(LNB with SOFA) to be BART for NOX at Cholla Units 3 and 4. The rolling 30-boiler-operatingday NOX emission limits associated with this BART determination are 0.22 lb/MMbtu (effective 

until April 30, 2025), which reflects the use of coal, and 0.080 lb/MMbtu (effective May 1, 2025), 

which reflects the use of natural gas. 

C. 110(l) Analysis 

In addition to the BART re-analysis and determinations, the Cholla SIP Revision also 

includes a demonstration of “noninterference” under CAA section 110(l). In particular, ADEQ 

considered whether the Cholla SIP Revision would interfere with (1) any applicable requirement 

concerning attainment of any National Ambient Air Quality Standards (NAAQS) or (2) any other 

applicable requirement of the CAA.

1. Demonstration of Noninterference with NAAQS Attainment 

ADEQ noted that Cholla is located in Navajo County, Arizona, which is currently 

designated as attainment or unclassifiable for the following NAAQS: carbon monoxide (CO), lead

(Pb), nitrogen dioxide (NO2), ozone (O3) (2008 NAAQS), PM2.5 (1997 and 2006 NAAQS), PM10, 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

Page 17 of 46

and SO2 (1971 NAAQS). ADEQ also noted that it has recommended an attainment/unclassifiable

designation for this area for the 2012 PM2.5 and 2010 SO2 standards. 

ADEQ’s demonstration of noninterference with attainment focused on the NAAQS for 

PM10, SO2, NO2, and O3 because ambient levels of these pollutants are affected by emissions of 

PM10, SO2, and/or NOX. Specifically, ADEQ analyzed emissions of PM10, SO2, and NOX under 

the control strategies in the Cholla BART Reassessment, as compared with the existing control 

requirements in the applicable SIP and FIP. This assessment was conducted by considering revised 

emissions limits included in the Cholla SIP Revision, summarized in Table 5. 

TABLE 5 – EMISSION LIMITS FOR CHOLLA BART REASSESSMENT

Emission Limit (lb/MMbtu)

Unit Dates NOX PM10 SO2

Unit 2 Unit shut down on April 1, 2016

Unit 3 until April 30, 2025 0.22 0.015 0.15

after April 30, 2025 0.08 0.01 0.0006

Unit 4 until April 30, 2025 0.22 0.015 0.15

after April 30, 2025 0.08 0.01 0.0006

For its PM10 analysis, ADEQ found that the emission control strategies in the Cholla BART 

Reassessment will result in greater PM10 reductions than those in the Arizona Regional Haze SIP

beginning in 2016 and continuing into the future, as shown in Table 6. Beginning in 2026, PM10

emissions will be further reduced under the Cholla BART Reassessment, due to the 20 percent 

capacity factor limit and the more stringent emission limits (0.01 lb/MMBtu rather than 0.015 

lb/MMBtu) that will apply after the switch to natural gas at Units 3 and 4. Therefore, ADEQ found 

that the Cholla SIP Revision will not interfere with attainment and maintenance of the PM10

NAAQS.
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TABLE 6 - COMPARISON OF ANNUAL PM10 EMISSIONS FOR 2011 ARIZONA SIP VS. CHOLLA BART

REASSESSMENT

Unit 

Number 

Annual PM10 (tons per year 

(tpy))

Time Period 2011 AZ 

SIP 

Cholla SIP 

Revision 

2016 Unit 1 84 84 

Unit 2 214a78b

Unit 3 197 197 

Unit 4 269 269 

Total 764 628 

2017-2025 Unit 1 84 84 

Unit 2 181 0 

Unit 3 197 197 

Unit 4 269 269 

Total 731 550 

2026 forward Unit 1 84 13 

Unit 2 181 0 

Unit 3 197 30 

Unit 4 269 39 

Total 731 82 

a Based on compliance date of April 1, 2016 for emissions limit of 0.015 lb/MMBtu. 

b Based on operation of Unit 2 until April 1, 2016.

ADEQ also compared SO2 emission control strategies in the 2011 SIP with those in the 

Cholla BART Reassessment. As shown in Table 7, the control strategies in the Cholla BART

Reassessment will result in greater SO2 reductions than those in the 2011 SIP beginning in 2016 

and continuing into the future. Therefore, ADEQ found that the emissions reductions achieved by 

the control strategy outlined in the Cholla SIP Revision will not interfere with attainment and 

maintenance of the SO2 NAAQS.

TABLE 7 - COMPARISON OF ANNUAL SO2 EMISSIONS FOR 2011 ARIZONA SIP VS. CHOLLA BART

REASSESSMENT

Time Period Unit Number Annual SO2 (tpy)

2011 AZ 

SIP 

Cholla SIP 

Revision 

2016 Unit 1 844 844 

Unit 2 1,614 452a
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Unit 3 1,966 1,966 

Unit 4 2,688 2,688 

Total 7,112 5,950 

2017-2025 Unit 1 844 844 

Unit 2 1,614 0 

Unit 3 1,966 1,966 

Unit 4 2,688 2,688 

Total 7,112 5,498 

2026

forward

Unit 1 844 1 

Unit 2 1,614 0 

Unit 3 1,966 2 

Unit 4 2,688 2 

Total 7,112 5 

a Based on operation of Unit 2 until April 1, 2016.

ADEQ also analyzed the emission control strategies for NOX in the Cholla BART 

Reassessment (Unit 2 shutdown and LNB/SOFA controls at Units 3 and 4 until conversion to 

natural gas by 2025 with a ≤ 20 percent annual average capacity factor) in comparison to the FIP, 

which requires the installation of SCR with LNB and SOFA at all units by December 5, 2017. As 

shown in Table 8, while the shutdown of Unit 2 results in lower NOX emissions than the FIP for 

2016, the Reassessment will allow for 4,161 tpy more NOX emissions than the FIP between 2018

and 2025. However, after 2025, due to the conversion to natural gas, the Cholla BART 

Reassessment will result in greater annual NOx emission reductions than the FIP. ADEQ found 

that, because there are no nonattainment or maintenance SIPs that rely on emission reductions at 

Cholla to ensure continued attainment of the NO2 NAAQS and the Cholla BART Reassessment 

will result in NOX emission reductions relative to the existing operating conditions of the facility, 

it will not interfere with attainment or maintenance of the current NO2 NAAQS.

TABLE 8 - COMPARISON OF NOX ANNUAL EMISSIONS FOR FIP VS. CHOLLA BART REASSESSMENT

Unit Annual NOX (tpy)
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Time 

Period 

Number EPA FIP Cholla BART 

Reassessment

Annual Emission Change (Cholla 

BART Reassessment to EPA FIP)

2016 Unit 1 1,131 1,131 0 

Unit 2 3,601 900a-2,701 

Unit 3 2,766 2,766 0 

Unit 4 3,548 3,548 0 

Total 11,046 8,345 -2,701 

2017 Unit 1 1,131 1,131 0 

Unit 2 3,601 0 -3,601 

Unit 3 2,766 2,766 0 

Unit 4 3,548 3,548 0 

Total 11,046 7,445 -3,601 

2018-2025 Unit 1 1,131 1,131 0 

Unit 2 602 0 -602 

Unit 3 655 2,766 2,111 

Unit 4 896 3,548 2,652 

Total 3,284 7,445 4,161 

2026

forward

Unit 1 1,131 105 -1,026 

Unit 2 602 0 -602 

Unit 3 655 244 -411 

Unit 4 896 308 -588 

Total 3,284 657 -2,627 

a Based on operation of Unit 2 until April 1, 2016.

Similarly, with regard to ozone, for which NOX emissions are a precursor, ADEQ noted 

that there are no nonattainment or maintenance SIPs that rely on emission reductions at Cholla to 

ensure continued attainment of the NAAQS and that the Cholla BART Reassessment will result 

in greater long-term NOX emission reductions than the existing FIP. Accordingly, ADEQ 

concluded that the Cholla BART Reassessment will not interfere with the attainment or

maintenance of the 2008 ozone NAAQS.

2. Demonstration of Noninterference with Other CAA Requirements

With regards to the other applicable CAA requirements, ADEQ considered whether the 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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Cholla BART Reassessment would interfere with (1) the requirements of the Regional Haze 

program or (2) the CAA’s air toxics requirements. 

In evaluating potential interference with the RHR, ADEQ relied primarily on the results of 

air quality modeling (using CALPUFF) performed by APS and PacifiCorp to assess the visibility 

impacts of Cholla under the Cholla SIP Revision compared to the existing SIP and FIP 

requirements.

15 These results, summarized in Table 9, show that, compared with the existing SIP 

and FIP requirements, the Cholla SIP Revision would result in less visibility improvement at all 

affected Class I areas between 2018 and 2025, but would result in greater improvement starting in

2026. Based on these results and taking into consideration the long-term goal of the Regional Haze 

Rule to achieve natural visibility conditions, ADEQ found that the BART Reassessment will not 

interfere with the requirements of the regional haze program.

TABLE 9 - MODELED VISIBILITY IMPACTS OF CHOLLA

EPA FIP and 

Existing SIP

SIP Revision BART 

(2018-2025)

SIP Revision BART

(2026 forward)

Class I Area Visibility Impacts 

(dv)

Visibility Impacts

(dv)

Visibility Impacts

(dv)

Petrified Forest NP 2.64 3.75 1.45

Grand Canyon NP 1.11 1.48 0.45

Capitol Reef NP 0.62 0.92 0.29

Mazatzal WA 0.75 0.83 0.30

Sycamore Canyon WA 0.73 0.94 0.29

Mount Baldy WA 0.69 0.87 0.28

Gila WA 0.46 0.47 0.17

Sierra Ancha WA 0.82 0.94 0.36

Mesa Verde NP 0.63 0.84 0.30

Galiuro WA 0.29 0.30 0.09

Superstition WA 0.73 0.88 0.30

 

15 Id.
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Saguaro NP 0.20 0.19 0.05

Pine Mountain WA 0.51 0.58 0.17

Cumulative impacts 10.18 12.99 4.50

Concerning air toxics, ADEQ noted that in addition to ceasing operation of Unit 2, the 

Cholla facility proposes to implement sorbent injection at Units 1, 3, and 4 by March 2016 to 

reduce air toxics and achieve compliance with the EPA’s Mercury and Air Toxics (MATS) rule.

Therefore, ADEQ concluded that the Cholla BART Reassessment will not interfere with any air 

toxics requirements of the CAA.

D. Cholla Permit Revision

The Cholla Permit Revision, which is incorporated as Appendix A to the Cholla SIP 

Revision, was issued by ADEQ on October 16, 2015. The Permit Revision incorporates emission 

limits and compliance dates as well as monitoring, recordkeeping, and reporting requirements to 

implement both the Cholla BART Reassessment and ADEQ’s prior BART determinations for SO2

and PM10 at Cholla.

IV. The EPA’s Evaluation of the Cholla SIP Revision

We have evaluated the Cholla SIP Revision for compliance with the requirements of the 

CAA, the RHR, and the BART Guidelines.16 Our evaluation of each of the major components of 

the Cholla SIP Revision is summarized in the following sections. 

A. The EPA’s Evaluation of the Enforceable Retirement Provision for Cholla Unit 2 

The Cholla Permit Revision requires Unit 2 to be permanently retired by no later than April 

 

16 CAA section 169A(b)(2) and 40 CFR 51.308(e)(1)(ii)(B) require that BART for each fossil-fuel fired generating 

power plant having a total generating capacity in excess of 750 megawatts be determined pursuant to the BART 

Guidelines. Cholla has a total generating capacity in excess of 750 megawatts, so the BART Guidelines are 

mandatory for the Cholla BART analysis and determination.
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1, 2016.17 This date coincides with the compliance deadlines for SO2 and PM10 in the Arizona 

Regional Haze FIP and precedes the deadline for NOX by over a year.18 In fact, the unit was shut 

down on October 1, 2015.19 If Unit 2 were not retired, APS would have been required to install 

additional controls to meet the SO2 and PM10 limits in the SIP, as well as the NOX limit in the FIP, 

which is achievable with SCR. The requirement for permanent retirement will become effective 

and federally enforceable when the Cholla SIP Revision is approved into the SIP and the FIP

provisions applicable to Cholla are withdrawn.20 Accordingly, we agree with ADEQ that no 

further analysis is required for Cholla Unit 2, and we propose to approve the requirement for 

permanent retirement as satisfying the requirements of the CAA and RHR for Cholla Unit 2.

B. The EPA’s Evaluation of ADEQ’s BART Analysis for Cholla Units 3 and 4

We find that ADEQ’s BART analysis for Cholla Units 3 and 4 is consistent with the 

requirements of the CAA, RHR, and the BART Guidelines. In particular, we find that ADEQ’s 

BART re-analysis addresses the flaws that were the basis for our disapproval of ADEQ’s prior 

BART analysis for Cholla.21

With regard to the cost of compliance, in its previous BART analysis for Cholla, ADEQ 

included certain line item costs not allowed by the EPA Control Cost Manual (CCM),22 such as 

owner's costs, surcharge, and Allowance for Funds Used During Construction (AFUDC).23 This 

approach did not comply with BART Guidelines’ direction that cost estimates should be based on 

 

17 Cholla Permit Revision section I.C.1. 

18 See 40 CFR 51.145(f)(4).

19 Letter from Edward Seal, APS, to Kathleen Johnson, EPA, and Eric Massey, ADEQ (October 28, 2015).

20 Cholla Permit Revision section I.A. 

21 See 77 FR 42840-42941 and 42849, 77 FR 72565-72566. 

22 EPA Air Pollution Control Cost Manual, available at https://www3.epa.gov/ttn/ecas/cost_manual.html.

23 See 77 FR 42849.
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the CCM. In the Cholla SIP revision, by contrast, ADEQ used the cost estimates that the EPA 

developed as part of the Regional Haze FIP, 24 which were calculated using the CCM

methodology.

25

We note that in May 2016, EPA revised the CCM chapter that concerns SCR systems.

26

The revised CCM recommends use of a 30-year equipment life for SCR systems,27 whereas the 

previous version recommended a 20-year life.28 As noted above, ADEQ used a 20-year remaining 

useful life in its cost calculations in the Cholla SIP Revision, which was consistent with the current 

CCM recommendation at the time of SIP submittal in October 2015. Given that the majority of 

other BART analyses, including the EPA’s analysis for Cholla in the Arizona Regional Haze FIP,29

have used a 20-year remaining useful life for SCR, we believe that this remains an appropriate 

assumption in this instance in order to ensure a consistent comparison with the cost estimates for 

SCR in other BART determinations. Nonetheless, we have also conducted an additional analysis 

to evaluate how use of a 30-year remaining useful life would affect the cost-effectiveness values 

for SCR at Cholla Units 3 and 4. We found that use of a 30-year remaining useful life would 

increase the average cost-effectiveness of SCR at Unit 3 from $6,286/ton to $7,864/ton and the 

“incremental” cost-effectiveness (as compared with LNB+SOFA) from $9,237/ton to 

 

24 See, e.g., Cholla SIP Revision, Appendix B, Table B-1, footnote (a).

25 See 77 FR 42852.

26 CCM (7th Edition), Section 4, Chapter 2 - Selective Catalytic Reduction (May 2016), available at 

https://www3.epa.gov/ttn/ecas/docs/SCRCostManualchapter7thEdition_2016.pdf. 

27 See id. at 2-78 (“broadly speaking, a representative value of the equipment life for SCR at power plants can be 

considered as 30 years.”) 

28 CCM (6th edition), Section 4.2, Chapter 2 - Selective Catalytic Reduction (October 2000), available at 

https://www3.epa.gov/ttn/ecas/docs/cs4-2ch2.pdf, at 2-48 (“An economic lifetime of 20 years is assumed for the 

SCR system.”)

29 See 77 FR 42854
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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$11,295/ton.30 The average and “incremental” (as compared with LNB+SOFA) cost-effectiveness 

of SCR at Unit 4 would be increased from $6,810/ton to $8,401/ton and from $10,539 to $12,674, 

respectively.31 Thus, if ADEQ had calculated the average and incremental cost-effectiveness of 

SCR based on a 30-year remaining useful life, it would have provided further support for ADEQ’s 

determination that the incremental costs of compliance for SCR are not warranted by the 

incremental benefits.

With regard to visibility modeling, in its previous BART analysis for Cholla, ADEQ 

considered the benefits from controls on only one emitting unit at a time and overlooked significant

benefits at multiple Class I areas, thereby understating the full visibility benefits of the candidate 

controls.

32 By contrast, in the Cholla SIP revision, ADEQ looked at the visibility impacts and 

potential improvements from all three BART-eligible units together and also considered impacts 

and potential improvements at all 13 Class I areas within 300 km of Cholla, based on modeling 

performed by APS and PacifiCorp.

33

In considering the results of this modeling, it should be noted that the baseline scenario 

included emissions from Unit 2, but the control scenarios did not include any emissions from Unit 

2. As a result, the total visibility improvement anticipated under each of the control scenarios 

represents not only the visibility benefits of controls on Units 3 and 4, but also the visibility benefits 

of the closure of Unit 2. We consider this to be a reasonable approach because it is consistent with 

the requirement of the BART Guidelines for states to consider the visibility improvement from 

 

30 See Cholla_SCR_costs (30 yr life).xlsx

31 Id.

32 See 77 FR 42849.

33 See, e.g., Cholla SIP Revision, Table 4 and 5.
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this version, but it is not the official version.

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controls applied to the entire BART-eligible source.34 However, given that ADEQ is not making 

a BART determination for Unit 2 in this instance, we believe it is appropriate to also consider the 

visibility improvement expected to result from controls on Units 3 and 4 only. ADEQ’s evaluation 

of the “incremental" visibility benefits of SNCR (“Option 2 over Option 1” in Table 4) and SCR 

(“Option 3 over Option 1” in Table 4) effectively excludes the benefits of the Unit 2 shutdown 

because Options 1, 2, and 3 all exclude emissions from Unit 2. Given that ADEQ relied heavily

on these “incremental” visibility benefits in reaching its ultimate BART determination,35 we find 

that ADEQ appropriately considered the visibility benefits of controls on Units 3 and 4 only, as 

well as the benefits of the Cholla BART Reassessment as a whole.

We also note that ADEQ did not quantify the expected visibility benefits of SCR and SNCR 

on Units 3 and 4 after these units are converted to gas in 2025, but characterized these benefits as 

“negligible.” In order to evaluate ADEQ’s characterization, we scaled the modeled visibility 

benefits of SCR under the coal-fired scenario to roughly estimate what the benefits would be under 

the gas-fired scenario. The results of this scaling indicate that, under the gas-fired scenario, the 

approximate benefits of SNCR would be 0.07 dv at the most-improved Class I area and 0.31 dv 

cumulatively over all affected Class I areas, while the approximate benefits of SCR would be 0.15

dv at the most-improved Class I area and 0.77 dv cumulatively over all affected Class I areas.36

 

34 In particular, the BART Guidelines explain that, "[i]f the emissions from the list of emissions units at a stationary 

source exceed a potential to emit of 250 tons per year for any visibility-impairing pollutant, then that collection of 

emissions units is a BART-eligible source." 40 CFR part 51, appendix Y, section II.A.4. In other words, the BARTeligible source (the list of BART emissions units at a source) is the collection of units for which one must make a 

BART determination. The BART Guidelines also state "you must conduct a visibility improvement determination 

for the source(s) as part of the BART determination." Id, section IV.D.5. This requires consideration of the visibility 

improvement from BART applied to the BART-eligible source as a whole.

35 See Cholla SIP Revision section 2.3. 

36 See Cholla_SCR_vs_NG rev2.xlsx
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this version, but it is not the official version.

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Thus, the benefits of SNCR or SCR under the gas-fired scenario would be significantly less than 

under the coal-fired scenario, for which the expected “incremental” benefits over LNB+SOFA are

0.28 dv at the most-improved area and 1.32 dv cumulative for SNCR and 0.79 dv at the mostimproved Class I area and 3.97 dv cumulative for SCR.

In the Cholla SIP Revision, ADEQ also appropriately accounted for the requirements that 

will apply to Units 3 and 4 as of 2025, i.e., the permanent cessation of coal burning by April 30, 

2025, with the option to convert to pipeline-quality natural gas and comply with a 20 percent 

annual average capacity factor limit by July 31, 2025. These new requirements significantly

decrease the emission reductions achievable by SCR or SNCR beginning in 2025 and thus increase 

the average $/ton of both SCR and SNCR over the remaining useful life of the units, as shown in 

Tables 1 and 2 above. Similarly, these requirements limit the timeframe in which significant 

visibility benefits would result from either SCR or SNCR to less than eight years.

We note that ADEQ did diverge slightly from the BART Guidelines in its calculation of 

the incremental cost-effectiveness of SCR. In particular, ADEQ calculated the incremental cost, 

as well as incremental visibility benefits, based on a comparison between SCR with LNB+SOFA 

and LNB+SOFA only. This differs from the approach to calculating incremental cost-effectiveness 

that is set forth in the BART Guidelines, under which incremental cost-effectiveness is calculated 

by comparing “the costs and performance level of a control option to those of the next most 

stringent option . . . .”

37 In this case, SNCR with LNB+SOFA is the next most stringent option 

 

37 40 CFR part 51 appendix Y, section IV.D.4.e (emphasis added). The BART Guidelines do not specify a method 

for calculating incremental visibility benefits. We consider it appropriate to calculate these benefits in the same 

manner as incremental costs, i.e. by comparing the expected benefits of a control option to those of the next most 

stringent option.
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compared to SCR with LNB+SOFA. Had ADEQ compared SCR with LNB+SOFA to SNCR with 

LNB+SOFA, the incremental cost-effectiveness using a 20-year remaining useful life would have 

been $10,347/ton for Unit 3 and $12,295/ton for Unit 4,

38 rather than $9,237/ton for Unit 3 and 

$10,539/ton for Unit 4. Similarly, had ADEQ calculated the incremental visibility benefits of SCR 

with LNB+SOFA based on a comparison to SNCR with LNB+SOFA, the per area incremental 

benefits would have ranged from 0.01 dv to 0.51 dv, rather than 0.07 dv to 0.79 dv, and the 

cumulative incremental benefit would have been 2.65 dv rather than 3.97 dv.39 Thus, if ADEQ 

had calculated the incremental costs and benefits of SCR in accordance with the BART Guidelines, 

it would have resulted in higher incremental cost-effectiveness values and lower incremental 

visibility benefits compared with the figures provided in the Cholla SIP Revision, which would 

provide further support for ADEQ’s determination that the incremental costs of compliance for 

SCR are not warranted by the incremental benefits. Accordingly, in reviewing the reasonableness 

of ADEQ’s re-analysis of BART for these units, we find that ADEQ’s diversion from the BART 

Guidelines in this regard was of no consequence.

Based on our findings that the Cholla SIP Revision addresses the flaws that were the basis 

for our disapproval of ADEQ’s prior BART analysis for Cholla and otherwise meets the

requirements of the CAA, RHR, and the BART Guidelines, we propose to approve ADEQ’s BART 

re-analysis for Cholla Units 3 and 4. 

C. The EPA’s Evaluation of ADEQ’s BART Determination for Cholla Units 3 and 4

We also find that ADEQ’s BART determination for NOX at Cholla Units 3 and 4 is 

 

38 Cholla Units 3 and 4 Incremental Costs and Benefits.xlsx

39 Id. 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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consistent with the requirements of the CAA, RHR, and the BART Guidelines. In particular, we 

find that ADEQ appropriately considered and weighed the five BART factors in relation to the 

available control options and reached a reasonable BART determination based on its consideration 

of the factors. 

With regard to SCR, we find that it was reasonable for ADEQ to conclude that the costs of 

SCR were not warranted by the visibility benefits in this instance. In particular, with regard to 

costs, we are not aware of any instance in which the EPA has determined SCR to be BART where 

the average cost-effectiveness of SCR was greater than $6,000/ton and the incremental costeffectiveness (calculated in accordance with the BART Guidelines) was greater than $10,000/ton, 

as is the case with Cholla Units 3 and 4. Similarly, we are not aware of any instance in which the 

EPA has disapproved a state’s BART determination that rejected SCR as BART based on similar 

cost-effectiveness values. Furthermore, while the total visibility benefits of the SCR-based control 

scenario (“BART Option 3”) are large (2.20 dv at the most improved area and 17.89 dv cumulative 

across all affected areas), as noted in the previous section, these benefits include not only the effect 

of SCR installation on Units 3 and 4, but also the retirement of Unit 2. Thus, we believe it was 

appropriate for ADEQ to focus primarily on what it characterized as the “incremental” visibility 

benefits, i.e., the relative degree of visibility improvement expected under Option 3 (Unit 2 retired 

and SCR with LNB+SOFA on Units 3 and 4) compared with Option 1 (Unit 2 retired and 

LNB+SOFA on Units 3 and 4), which were 0.07 dv to 0.79 dv per area and 3.97 dv cumulative.

40

 

40 As described in the previous section, if ADEQ had calculated the incremental benefits of SCR in accordance with 

the BART Guidelines, the per area incremental benefits would have ranged from 0.01 dv to 0.51 dv, and the 

cumulative incremental benefit would have been 2.65 dv.
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this version, but it is not the official version.

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While these benefits are significant, we believe it was reasonable for ADEQ to determine that the 

benefits were not warranted in light of the high costs of SCR and the fact that benefits of this 

magnitude would only last for approximately eight years, after which the benefits of SCR would 

be far less (roughly 0.15 dv at the most-improved Class I area and 0.77 dv cumulatively over all 

affected Class I areas).

With regard to SNCR, we find that it was reasonable for ADEQ to conclude that the costs

of SNCR were not warranted by the visibility benefits. In particular, with regard to costs, we are 

not aware of any instance in which the EPA has determined SNCR to be BART where the average 

cost-effectiveness of SNCR was greater than $3,000/ton and the incremental cost-effectiveness

was roughly $7,000/ton, as is the case with Cholla Units 3 and 4. Similarly, we are not aware of 

any instance in which the EPA has disapproved a state’s BART determination that rejected SNCR 

as BART based on similar cost-effectiveness values. Furthermore, while the total visibility benefits 

of the SNCR-based control scenario (“BART Option 2”) are large (1.78 dv at the most improved 

area and 15.24 dv cumulative across all affected areas), as noted above, these benefits include not 

only the effect of SNCR installation on Units 3 and 4, but also the retirement of Unit 2. Thus, we 

believe it was appropriate for ADEQ to focus primarily on incremental visibility benefits, i.e., the 

relative degree of visibility improvement expected under Option 2 (Unit 2 retired and SNCR with 

LNB+SOFA on Units 3 and 4) compared with Option 1 (Unit 2 retired and LNB+SOFA on Units 

3 and 4), which were 0.01 dv to 0.28 dv per area and 1.32 dv cumulative. While these benefits are 

not insignificant, we believe it was reasonable for ADEQ to determine that the benefits were not 

warranted in light of the relatively high costs of SNCR and the fact that benefits of this magnitude 

would only last for approximately eight years, after which the benefits of SNCR would be far less 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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(roughly 0.07 dv at the most-improved Class I area and 0.31 dv cumulatively over all affected 

Class I areas).

Therefore, we propose to approve ADEQ’s determination that BART for NOX at Cholla 

Units 3 and 4 consists of LNB+SOFA with associated emission limits of 0.22 lb/MMbtu (rolling 

30-boiler-operating-day average) for each unit. As explained above, these emission limits will 

remain in effect until April 30, 2025, at which point both units will be permanently retired or 

converted to natural gas with NOX emission limits of 0.08 lb/MMBtu (rolling 30-boiler-operatingday average).

D. The EPA’s Evaluation Under CAA Section 110(l) 

CAA section 110(l) requires that any revision to an implementation plan shall not be 

approved by the EPA Administrator if the revision would interfere with any applicable requirement 

concerning attainment and reasonable further progress (RFP) or any other applicable requirement 

of the Act.41 In evaluating whether the Cholla SIP Revision would interfere with any CAA 

requirements, we note that overall, the Cholla SIP Revision will result in reduced emissions of

both SO2 and PM10 compared to the existing SIP and FIP requirements beginning in 2016 (see 

Tables 6 and 7 above) due to the retirement of Unit 2. While the Cholla SIP Revision will require

fewer NOX reductions than the FIP between 2018 and 2025, it will ensure that NOX emissions 

remain at or below current levels (i.e., levels consistent with non-operation of Unit 242 and 

operation of LNB and SOFA on Units 1, 3 and 4) until 2025, after which it will require a substantial 

 

41 CAA Section 110(l), 42 U.S.C. 7410(l). 

42 As shown in Table 8, ADEQ projected that total NOX emissions at Cholla Unit 2 would be 900 tpy in 2016, based 

on a Unit 2 shutdown date of April 1, 2016. Because Unit 2 was retired in October 2015, 2016 emissions from Unit 

2 will actually be zero, so we anticipate the total NOX emissions from the facility will be roughly 7,445 tpy for all 

years between 2016 and 2025. 
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reduction in NOX emissions compared to both current levels and the FIP (see Table 8 above). 

With regard to applicable requirements concerning attainment and RFP, as explained by 

ADEQ, Cholla is located in north central Navajo County, Arizona, which is designated as 

unclassifiable/attainment for all of the NAAQS for which the EPA has issued designations.

43

ADEQ also indicated that it has recommended an attainment/unclassifiable designation for this 

area for the 2012 PM2.5 and 2010 SO2 standards. With regard to the 2012 PM2.5 standard, the EPA 

has finalized a designation of unclassifiable/attainment for Navajo County.44 With regard to the 

2010 SO2 standard, we note that, under the EPA’s Data Requirements Rule,

45 ADEQ is required 

to develop and submit air quality data characterizing ambient concentrations of SO2 in the area 

around Cholla.

46 The EPA will take these data into consideration in finalizing a designation for 

the area. Finally, we note that, on October 1, 2015, the EPA promulgated revised primary and 

secondary ozone NAAQS.

47 State designation recommendations for the 2015 ozone NAAQS are 

due to the EPA by October 1, 2016.

48

In summary, Cholla is located in area that is designated unclassifiable/attainment or has 

not yet been designated for each of the current NAAQS. Thus, the Arizona SIP does not currently 

rely on emission limitations at Cholla to satisfy any attainment or RFP requirements. Given that 

the Cholla SIP Revision will result in equivalent or lower emissions of NOX, PM10 and SO2 for all 

future years, compared to current emission levels, in an area that is designated 

 

43 Cholla SIP Revision, pages 12-13, Table 7. 

44 See 40 CFR 81.303. 

45 40 CFR part 51, subpart BB. 

46 See Letter from Eric Massey, ADEQ, to Doris Lo, EPA (January 13, 2016).

47 80 FR 65292 (October 26, 2015).

48 Id. at 65438.
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

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unclassifiable/attainment or has not yet been designated for all NAAQS, we propose to find that 

the Cholla SIP Revision would not interfere with any applicable requirements concerning 

attainment or RFP. 

The other requirements of the CAA that apply to Cholla are:

 Standards of Performance for New Stationary Sources (NSPS), 40 CFR Part 60, 

Subpart D;

 National Emission Standards for Hazardous Air Pollutants (NESHAP), 40 CFR 

Part 63, Subpart UUUUU (also known as MATS); 

 Compliance Assurance Monitoring (CAM), 40 CFR Part 64; and

 BART and other visibility protection requirements under CAA section 169A and 

the RHR.

The Cholla SIP Revision would not affect the applicable NESHAP, NSPS and CAM 

requirements. Therefore, we propose to find that the Cholla SIP Revision would not interfere with 

the applicable NESHAP, NSPS and CAM requirements. 

We also propose to find that Cholla SIP Revision would not interfere with the visibility 

protection requirements of the CAA and the RHR. Our proposed approval of the BART 

Reassessment is based on our determination that, taking into consideration the differences in the

facts underlying the EPA’s prior BART analysis for NOX in Arizona Regional Haze FIP and the 

Cholla BART Reassessment, ADEQ’s revised BART analysis and determination for Cholla meet 

the BART requirements of the CAA and RHR. Furthermore, the Cholla SIP Revision would result 

in greater visibility improvement than the existing SIP and FIP requirements beginning in 2026, 

which is consistent with the long-term national goal of restoring natural visibility conditions at 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

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Class I areas. Thus, we propose to find that the Cholla SIP Revision would not interfere with the 

visibility protection requirements of the CAA. 

E. The EPA’s Evaluation of Enforceable Emission Limits

CAA section 110(a)(2)(A) requires SIPs to include enforceable emission limitations as 

necessary or appropriate to meet the applicable requirements of the Act. In addition, SIPs must 

contain regulatory requirements related to monitoring, recordkeeping, and reporting for applicable 

emission limitations.49 The Cholla Permit Revision includes such enforceable emission limits, as 

well as associated monitoring, recordkeeping, and reporting requirements, for all units and 

pollutants. These requirements will become effective and federally enforceable when the Cholla 

SIP Revision is approved into the SIP and the FIP provisions applicable to Cholla are withdrawn.50

Therefore, we propose to find that the Cholla SIP Revision meets the requirements of the CAA 

and the EPA’s implementing regulations for enforceable emission limitations.

V. Proposed Action

For the reasons described above, the EPA proposes to approve the Cholla SIP Revision. 

Because this approval would fill the gap in the Arizona Regional Haze SIP left by the EPA’s prior 

partial disapproval with respect to Cholla, we propose to withdraw the provisions of the Arizona 

Regional Haze FIP that apply to Cholla. We also propose to find that withdrawal of the FIP would 

constitute our action on APS’s and PacifiCorp’s petitions for reconsideration of the Arizona 

Regional Haze FIP.

VI. Environmental Justice Considerations

 

49 See, e.g., CAA section 110(a)(2)(F) and 40 CFR 51.212(c).

50 Cholla Permit Revision section I.A. 
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As shown in Tables 6 and 7, the Cholla SIP Revision will result in reduced emissions of 

both SO2 and PM10 compared to the existing SIP and FIP requirements beginning in 2016. As 

shown in Table 8, while the Cholla SIP Revision will result in fewer NOX reductions than the FIP 

between 2018 and 2025, it will ensure that NOX emissions remain at or below current levels until 

2025, after which it will require a substantial reduction in NOX emissions compared to both current 

levels and to the existing Arizona Regional Haze FIP. Therefore, the EPA believes that this action 

will not have potential disproportionately high and adverse human health or environmental effects 

on minority, low-income, or indigenous populations.

VII. Incorporation by Reference

In this rule, the EPA is proposing to include in a final EPA rule, regulatory text that includes 

incorporation by reference. In accordance with requirements of 1 CFR 51.5, the EPA is proposing 

to incorporate by reference “Significant Permit Revision No. 61713 to Operating Permit No. 

53399” issued by ADEQ on October 16, 2015. The EPA has made, and will continue to make, this 

document available electronically through www.regulations.gov and in hard copy at U.S. 

Environmental Protection Agency Region IX, Air-2, 75 Hawthorne Street, San Francisco, CA, 

94105-3901. 

VIII. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: 

Improving Regulation and Regulatory Review

This action is not a significant regulatory action and was therefore not submitted to the 

Office of Management and Budget (OMB) for review. This rule applies to only one facility and is 

therefore not a rule of general applicability.
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B. Paperwork Reduction Act (PRA)

This action does not impose an information collection burden under the PRA. This rule 

applies to only one facility. Therefore, its recordkeeping and reporting provisions do not constitute 

a "collection of information" as defined under 44 U.S.C. 3502(3) and 5 CFR 1320.3(c).

C. Regulatory Flexibility Act (RFA)

I certify that this action will not have a significant economic impact on a substantial number 

of small entities. This action will not impose any requirements on small entities. Firms primarily 

engaged in the generation, transmission, and/or distribution of electric energy for sale are small if, 

including affiliates, the total electric output for the preceding fiscal year did not exceed 4 million 

megawatt hours. Both owners of Cholla, APS and PacifiCorp, exceed this threshold.

D. Unfunded Mandates Reform Act (UMRA)

This action does not contain an unfunded mandate of $ 100 million or more as described 

in UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect small governments.

E. Executive Order 13132: Federalism

This action does not have federalism implications. It will not have substantial direct effects 

on the states, on the relationship between the national government and the states, or on the 

distribution of power and responsibilities among the various levels of government.

F. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments

This action does not have tribal implications, as specified in Executive Order 13175. It will 

not have substantial direct effects on any Indian tribes, on the relationship between the Federal 

Government and Indian tribes, or on the distribution of power and responsibilities between the 

Federal Government and Indian tribes. Thus, Executive Order 13175 does not apply to this action.
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

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G. Executive Order 13045: Protection of Children From Environmental Health Risks and Safety 

Risks

The EPA interprets EO 13045 as applying only to those regulatory actions that concern 

health or safety risks that the EPA has reason to believe may disproportionately affect children, 

per the definition of "covered regulatory action" in section 2-202 of the Executive Order. This 

action is not subject to Executive Order 13045 because it does not concern an environmental health

risk or safety risk.

H. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy 

Supply, Distribution, or Use

This action is not subject to Executive Order 13211 because it is not a significant regulatory 

action under Executive Order 12866.

I. National Technology Transfer and Advancement Act

This rulemaking does not involve technical standards. The EPA is not revising any 

technical standards or imposing any new technical standards in this action.

J. Executive Order 12898: Federal Actions To Address Environmental Justice in Minority 

Populations and Low-Income Populations

The EPA believes the human health or environmental risk addressed by this action will not 

have potential disproportionately high and adverse human health or environmental effects on 

minority, low-income, or indigenous populations. The results of this evaluation are contained in 

section VI above.

K. Determination Under Section 307(d)

Pursuant to CAA section 307(d)(1)(B), the EPA proposes to determine that this action is 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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subject to the provisions of section 307(d). Section 307(d) establishes procedural requirements 

specific to certain rulemaking actions under the CAA. Pursuant to CAA section 307(d)(1)(B), the 

withdrawal of the provisions of the Arizona Regional Haze FIP that apply to Cholla is subject to 

the requirements of CAA section 307(d), as it constitutes a revision to a FIP under CAA section 

110(c). Furthermore, CAA section 307(d)(1)(V) provides that the provisions of section 307(d) 

apply to “such other actions as the Administrator may determine.” The EPA proposes that the 

provisions of 307(d) apply to the EPA’s action on the Cholla SIP revision.
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List of Subjects in 40 CFR Part 52

Environmental protection, Air pollution control, Incorporation by reference, 

Intergovernmental relations, Nitrogen dioxide, Particulate matter, Reporting and recordkeeping 

requirements, Sulfur dioxide, Visibility.

AUTHORITY: 42 U.S.C. 7401 et seq.

_______________________________ _____________________________

Dated: Deborah Jordan,

Acting Regional Administrator,

EPA Region IX
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

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PART 52--APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS

1. The authority citation for part 52 continues to read as follows:

Authority: 42 U.S.C. 7401 et seq. 

Subpart D--Arizona

2. In §52.145, revise paragraphs (f)(1), (f)(2), (f)(3), (f)(4), (f)(5), and (f)(10) to read as follows: 

§52.145 Visibility protection.

* * * * *

(f) * * * 

(1) Applicability. This paragraph (f) applies to each owner/operator of the following coal-fired 

electricity generating units (EGUs) in the state of Arizona: Coronado Generating Station, Units 1 

and 2. The provisions of this paragraph (f) are severable, and if any provision of this paragraph 

(f), or the application of any provision of this paragraph (f) to any owner/operator or 

circumstance, is held invalid, the application of such provision to other owner/operators and 

other circumstances, and the remainder of this paragraph (f), shall not be affected thereby.

(2) Definitions. Terms not defined below shall have the meaning given to them in the Clean Air 

Act or EPA's regulations implementing the Clean Air Act. For purposes of this paragraph (f):

ADEQ means the Arizona Department of Environmental Quality.

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 unit.

Coal-fired unit means any of the EGUs identified in paragraph (f)(1) of this section.

Continuous emission monitoring system or CEMS means the equipment required by 40 CFR part 

75 and this paragraph (f).
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

this version, but it is not the official version.

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Emissions limitation or emissions limit means any of the Federal Emission Limitations required 

by this paragraph (f) or any of the applicable PM10 and SO2 emissions limits for Coronado 

Generating Station submitted to EPA as part of the Arizona Regional Haze SIP in a letter dated 

February 28, 2011, and approved into the Arizona State Implementation Plan on December 5, 

2012.

Flue Gas Desulfurization System or FGD means a pollution control device that employs flue gas 

desulfurization technology, including an absorber utilizing lime, fly ash, or limestone slurry, for 

the reduction of sulfur dioxide emissions.

lb means pound(s).

NOX means nitrogen oxides expressed as nitrogen dioxide (NO2).

Owner(s)/operator(s) means any person(s) who own(s) or who operate(s), control(s), or 

supervise(s) one or more of the units identified in paragraph (f)(1) of this section.

MMBtu means million British thermal unit(s).

Operating hour means any hour that fossil fuel is fired in the unit.

PM10 means filterable total particulate matter less than 10 microns and the condensable material 

in the impingers as measured by Methods 201A and 202 in 40 CFR part 51, appendix M.

Regional Administrator means the Regional Administrator of EPA Region IX or his/her 

authorized representative.

SO2 means sulfur dioxide.

SO2 removal efficiency means the quantity of SO2 removed as calculated by the procedure in 

paragraph (f)(5)(iii)(B) of this section.

Unit means any of the EGUs identified in paragraph (f)(1) of this section.
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this version, but it is not the official version.

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Valid data means data recorded when the CEMS is not out-of-control as defined by 40 CFR part 

75.

(3) Federal emission limitations

(i) NOX emission limitations. The owner/operator of each coal-fired unit subject to this paragraph 

(f) shall not emit or cause to be emitted NOX in excess of the following limitations, in pounds per 

million British thermal units (lb/MMBtu) from any coal-fired unit or group of coal-fired units. 

Each emission limit shall be based on a rolling 30-boiler-operating-day average, unless otherwise 

indicated in specific paragraphs.

Coal fired unit or group of coal-fired units

Federal

emission

limitation

Coronado Generating Station Unit 1 0.065

Coronado Generating Station Unit 2 0.080

(4) Compliance dates.

(i) The owners/operators of each unit subject to this paragraph (f) shall comply with the NOX

emissions limitations and other NOX-related requirements of this paragraph (f) no later than 

December 5, 2017.

(ii) The owners/operators of each unit subject to this paragraph (f) shall comply with the 

applicable PM10 and SO2 emissions limits submitted to EPA as part of the Arizona Regional 

Haze SIP in a letter dated February 28, 2011, and approved into the Arizona State 

Implementation Plan on December 5, 2012, as well as the related compliance, recordkeeping and 

reporting of this paragraph (f) no later than June 3, 2013.

(5) Compliance determinations for NOX and SO2

(i) Continuous emission monitoring system.
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(A) At all times after the compliance date specified in paragraph (f)(4) of this section, the 

owner/operator of each coal-fired unit shall maintain, calibrate, and operate a CEMS, in full 

compliance with the requirements found at 40 CFR part 75, to accurately measure SO2, NOX, 

diluent, and stack gas volumetric flow rate from each unit. In addition, the owner/operator of 

Cholla Units 2, 3, and 4 shall calibrate, maintain, and operate a CEMS, in full compliance with 

the requirements found at 40 CFR part 75, to accurately measure SO2 emissions and diluent at 

the inlet of the sulfur dioxide control device. All valid CEMS hourly data shall be used to 

determine compliance with the emission limitations for NOX and SO2 in paragraph (f)(3) of this 

section for each unit. When the CEMS is out-of-control as defined by 40 CFR part 75, that 

CEMs data shall be treated as missing data, and not used to calculate the emission average. Each 

required CEMS must obtain valid data for at least 90 percent of the unit operating hours, on an 

annual basis.

(B) The owner/operator of each unit shall comply with the quality assurance procedures for 

CEMS found in 40 CFR part 75. In addition to these 40 CFR part 75 requirements, relative 

accuracy test audits shall be calculated for both the NOX and SO2 pounds per hour measurement 

and the heat input measurement. The CEMs monitoring data shall not be bias adjusted. The inlet 

SO2 and diluent monitors required by this rule shall also meet the Quality Assurance/Quality 

Control (QA/QC) requirements of 40 CFR part 75. The testing and evaluation of the inlet 

monitors and the calculations of relative accuracy for lb/hr of NOX, SO2 and heat input shall be 

performed each time the 40 CFR part 75 CEMS undergo relative accuracy testing. 

(ii) Compliance determinations for NOX. 

(A) [reserved]
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(B) Coronado Generating Station. Compliance with the NOX emission limits for Coronado Unit 

1 and Coronado Unit 2 in paragraph (f)(3)(i) of this section shall be determined on a rolling 30 

boiler-operating-day basis. The 30-boiler-operating-day rolling NOX emission rate for each unit 

shall be calculated in accordance with the following procedure: Step one, sum the total pounds of 

NOX emitted from the unit during the current boiler operating day and the previous twenty-nine 

(29) boiler operating days; Step two, sum the total heat input to the unit in MMBtu during the 

current boiler operating day and the previous twenty-nine (29) boiler operating days; Step three, 

divide the total number of pounds of NOX emitted from that unit during the thirty (30) boiler 

operating days by the total heat input to the unit during the thirty (30) boiler operating days. A 

new 30-boiler-operating-day rolling average NOX emission rate shall be calculated for each new 

boiler operating day. Each 30-boiler-operating-day average NOX emission rate shall include all 

emissions that occur during all periods within any boiler operating day, including emissions from 

startup, shutdown, and malfunction. 

(C) If a valid NOX pounds per hour or heat input is not available for any hour for a unit, that heat 

input and NOX pounds per hour shall not be used in the calculation of the 30-day rolling average.

(iii) Compliance determinations for SO2. 

(A) The 30-day rolling average SO2 emission rate for each coal-fired unit shall be calculated in 

accordance with the following procedure: Step one, sum the total pounds of SO2 emitted from 

the unit during the current boiler-operating day and the previous twenty-nine (29) boileroperating days; step two, sum the total heat input to the unit in MMBtu during the current boileroperating day and the previous twenty-nine (29) boiler-operating day; and step three, divide the 

total number of pounds of SO2 emitted during the thirty (30) boiler-operating days by the total 
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this version, but it is not the official version.

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heat input during the thirty (30) boiler-operating days. A new 30-day rolling average SO2

emission rate shall be calculated for each new boiler-operating day. Each 30-day rolling average 

SO2 emission rate shall include all emissions and all heat input that occur during all periods 

within any boiler-operating day, including emissions from startup, shutdown, and malfunction.

(B) [reserved]

(C) If a valid SO2 pounds per hour at the outlet of the FGD system or heat input is not available 

for any hour for a unit, that heat input and SO2 pounds per hour shall not be used in the 

calculation of the 30-day rolling average.

(D) If both a valid inlet and outlet SO2 lb/MMBtu and an outlet value of lb/hr of SO2 are not 

available for any hour, that hour shall not be included in the efficiency calculation.

* * * * *

(10) Equipment operations

(i) [reserved]

(ii) Coronado Generating Station. At all times, including periods of startup, shutdown, and 

malfunction, the owner or operator of Coronado Generating Station Unit 1 and Unit 2 shall, to 

the extent practicable, maintain and operate each unit in a manner consistent with good air 

pollution control practices for minimizing emissions. The owner or operator shall continuously 

operate pollution control equipment at all times the unit it serves is in operation, and operate 

pollution control equipment in a manner consistent with technological limitations, manufacturer's 

specifications, and good engineering and good air pollution control practices for minimizing 

emissions. Determination of whether acceptable operating and maintenance procedures are being 

used will be based on information available to the Regional Administrator which may include, 
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Administrator, Deborah Jordan, on June 30, 2016. We have taken steps to ensure the accuracy of 

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but is not limited to, monitoring results, review of operating and maintenance procedures, and 

inspection of each unit.