IN THE UNITED STATES COURT OF APPEALS

FOR THE FIFTH CIRCUIT

No. 18-60116

SIERRA CLUB; NATIONAL PARKS CONSERVATION ASSOCIATION; 

ENTERGY LOUISIANA, L.L.C., 

 Petitioners

v.

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY; ANDREW 

WHEELER, Administrator, United States Environmental Protection Agency, 

 Respondents

On Petitions for Review of Final Administrative Action

of the United States Environmental Protection Agency

Before SMITH, WIENER, and ELROD, Circuit Judges.

WIENER, Circuit Judge:

In a December 21, 2017 Final Rule (“the Final Rule”), the United States 

Environmental Protection Agency (“the EPA”) approved Louisiana’s state 

implementation plan (“SIP”) for controlling regional haze. Louisiana’s regional 

haze SIP had two alleged problems. First, the SIP used an outdated airpollution model called “CALPUFF” to measure the visibility impacts of 

powerplant emissions. Second, the SIP included a sparse explanation for how 

Louisiana weighed five mandatory statutory factors in determining the Best 

Available Retrofit Technology (“BART”) for controlling emissions at Unit 6 of 

the Roy S. Nelson powerplant (“Nelson”). Despite the EPA’s knowledge of these

United States Court of Appeals

Fifth Circuit

FILED

October 3, 2019

Lyle W. Cayce

Clerk

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problems, it determined that Louisiana had fulfilled its obligations under the 

Clean Air Act. 

We consider two petitions for review of the Final Rule. One is from 

Petitioners-Appellants Sierra Club and National Parks Conservation 

Association (collectively, “Environmental Petitioners”). The other is from 

Petitioner-Appellant Entergy Louisiana, L.L.C., the owner of the Nelson 

powerplant, and Cleco Power, L.L.C., an intervenor in this case (collectively, 

“Industry Petitioners”). 

Environmental Petitioners maintain that Louisiana’s SIP does too little 

to curb regional haze at federally protected areas. They contend that (1) 

Louisiana’s determination that “low-sulfur coal” was the BART for the Nelson 

powerplant was deficient in several respects and (2) the EPA acted arbitrarily 

and capriciously in approving Louisiana’s SIP because it knew about those 

deficiencies.

In contrast, Industry Petitioners insist that Louisiana’s SIP 

overestimates the amount of pollution that their powerplants produce. In their 

challenge to the EPA’s approval of Louisiana’s “subject to BART” 

determinations, Industry Petitioners object to Louisiana’s and the EPA’s use 

of the “CALPUFF” model, which they maintain relies on several flawed 

technical assumptions. 

We deny Industry Petitioners’ petition. We afford “significant deference” 

to agency decisions involving analysis of scientific data within the agency’s 

technical expertise. The EPA’s selection of a model to measure air pollution 

levels is precisely that type of decision. The EPA therefore did not act 

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arbitrarily and capriciously in relying on the CALPUFF model to approve 

Louisiana’s “subject to BART” determinations.

Although Environmental Petitioners’ challenge presents a closer 

question, we deny that petition as well. Louisiana’s explanation of its BART 

determination for Nelson omitted two of the five mandatory factors and failed 

to compare—or even set out—the numbers for the costs and benefits of the 

control options Louisiana considered. Louisiana also failed to explain how its 

decision accounted for the EPA-submitted analyses that pointed out 

substantial flaws in other analyses in the administrative record. But applying 

the deferential standards of the Administrative Procedures Act to the facts of 

this case, we hold that the EPA’s approval of Louisiana’s SIP was not arbitrary 

and capricious.

The petitions for review are denied.

I. BACKGROUND

This case addresses the EPA’s approval of Louisiana’s SIP for controlling 

regional haze. The Clean Air Act “requires the states and the federal 

government to set and seek to achieve targets for visibility in protected 

national parks and wildlife areas by modifying regulations that control air 

pollutants in ambient air.”1 Under the Act, the federal government identifies 

air pollutants and sets standards, and the states have “the primary 

responsibility” for implementing those standards through SIPs.2 After a state 

 

1 Texas v. EPA, 829 F.3d 405, 411 (5th Cir. 2016) (citing 42 U.S.C. §§ 71410, 7491, 

7492(e)(2)).

2 Id. (citation omitted).

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submits its SIP, the EPA reviews the SIP for compliance with the Clean Air 

Act.

Powerplants that emit sulfur dioxide (“SO2”) and oxides of nitrogen 

(“NOx”) contribute to regional haze in protected federal areas.3 Louisiana has 

five powerplants that cause or contribute to visibility impairments in such 

areas.4 Since 2008, Louisiana has revised its SIP several times and established 

emission controls at some of those powerplants. In October 2017, Louisiana 

submitted its final SIP revisions, which addressed, inter alia, emission controls 

at Unit 6 of the Nelson powerplant. 

On December 21, 2017, the EPA promulgated a final rule approving

Louisiana’s SIP. 82 Fed. Reg. 60,520 (Dec. 21, 2017) (“the Final Rule”). The two 

petitions for review of the Final Rule address the EPA’s approval of (1) 

Louisiana’s determination that Nelson and two units at the Cleco-owned 

Brame Energy Center (“Brame”) are subject to BART for controlling emissions, 

(2) Louisiana’s selection of low-sulfur coal as BART for controlling SO2

emissions at Nelson, and (3) Louisiana’s reasonable progress goals and longterm strategy. 

Environmental Petitioners first address Louisiana’s BART 

determination for Nelson. They contend that the Louisiana Department of 

 

3 Id. Regional haze is a “visibility impairment that is produced by a multitude of 

sources and activities that are located across a broad geographic area and emit fine 

particulates . . . and their precursors.” 77 Fed. Reg. 42,834, 42,837 (July 20, 2012) (describing 

regional haze and the history of regional haze regulation).

4 See 82 Fed. Reg. 22,936, 22,942 (May 19, 2017).

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Environmental Quality (“LDEQ”) erred in three ways: (1) determining that 

low-sulfur coal was BART for Nelson, despite the EPA-submitted analyses that 

contradicted the analyses in the record, (2) failing to provide a rational basis 

for rejecting a more effective pollution control, and (3) not complying with the 

BART guidelines or considering all the mandatory BART factors.

Environmental Petitioners next object to the Final Rule’s approval of 

Louisiana’s long-term strategy and reasonable progress goals. They maintain 

that Louisiana’s 2017 SIP revisions did not fulfill the state’s obligations to 

revise and resubmit its long-term strategy and reasonable progress goals after 

the EPA disapproved that strategy and those goals in 2012. Louisiana’s 2017 

SIP revisions did not impose additional controls at non-BART “reasonable 

progress” sources and did not address the state’s reasonable progress goals or 

long-term strategy for achieving natural visibility conditions. According to 

Environmental Petitioners, the EPA improperly overlooked these omissions

when it approved Louisiana’s SIP. 

Environmental Petitioners object to the type of BART control Louisiana 

implemented. Industry Petitioners, in contrast, object to Louisiana’s 

determination that Nelson and Brame are subject to BART at all. Industry 

Petitioners challenge the technical assumptions underlying the modeling 

methods on which Louisiana and the EPA relied. Louisiana relied on the 

“CALPUFF” model, and the EPA relied on both the CALPUFF and the “CAMx”

models. According to Industry Petitioners, the CALPUFF model overstates the 

visibility effects of powerplant emissions. They also maintain that the EPA

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exceeded its authority by using its own CAMx modeling to support Louisiana’s 

modeling results. 

Each petitioner in this case is also a respondent-intervenor. The 

Environmental Petitioners, in addition to petitioning for review of some parts 

of the Final Rule, also intervened and filed a responsive brief opposing 

Industry Petitioners’ petition. Likewise, Industry Petitioners, in addition to 

petitioning for review of some parts of the Final Rule, also intervened and filed 

a responsive brief opposing Environmental Petitioners’ petition. 

The EPA responded to both petitions, insisting that the Final Rule 

should be approved in full. The LDEQ filed an amicus brief supporting the 

EPA’s position.

A. Statutory and Regulatory Framework 

This case is governed by the Clean Air Act and the regulations 

implementing it. In 1977, “in response to a growing awareness that visibility 

was rapidly deteriorating in many places, such as wilderness areas and 

national parks,” Congress amended the Act by enacting § 169A.5

That amendment established as a national goal “the prevention of any 

future, and the remedying of any existing, impairment in visibility in 

mandatory class I Federal areas which impairment results from manmade air 

pollution.”6 Protected class I Federal areas include “all (1) international parks, 

(2) national wilderness areas which exceed 5,000 acres in size, (3) national 

 

5 North Dakota v. EPA, 730 F.3d 750, 755 (8th Cir. 2013) (internal quotation omitted). 

6 42 U.S.C. § 7491.

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memorial parks which exceed 5,000 acres in size, and (4) national parks which 

exceed 6,000 acres in size.”7 Louisiana’s Breton National Wildlife Refuge and 

the Caney Creek Wilderness Area in southwest Arkansas are the protected 

Class I Federal areas at issue here.8

The Clean Air Act is “an experiment in cooperative federalism,” in which 

the federal government identifies pollutants and sets visibility targets, and the 

states implement those standards though SIPs.9 The Act directed the EPA to 

issue regulations requiring: (1) that states submit SIPs to the EPA, (2) the 

installation of the “best available retrofit technology, as determined by the 

State . . . for controlling emissions” at specified air-pollution sources, and (3) 

that each state adopt a long-term strategy “for making reasonable progress” 

toward the national visibility goal.10

Based on the Act’s directive, the EPA promulgated the Regional Haze 

Rule in 1999.11 “The Regional Haze Rule established the guidelines for state

compliance with the air visibility requirements of [the Clean Air Act].”12 In 

2005, the EPA revised that Rule and issued the BART guidelines, which set 

out the process for states to establish BART emissions limitations.13

 

7 Id. § 7472(a).

8 77 Fed. Reg. 11,839, 11,845 (Feb. 28, 2012).

9 Texas, 829 F.3d at 411.

10 42 U.S.C. § 7491(b)(2)(A)–(B). The EPA has stated that the national visibility goal 

is “to attain natural visibility conditions by the year 2064.” 40 C.F.R. § 51.308(d)(1)(i)(B).

11 64 Fed. Reg. 35,714 (July 1, 1999); 40 C.F.R. § 51.308 (“Regional Haze Rule”). 12 Texas, 829 F.3d at 412.

13 70 Fed. Reg. 39,104 (July 6, 2005) (“BART Rule”); 40 C.F.R. Part 51, App. Y (“BART 

Guidelines”).

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The Clean Air Act and the Regional Haze Rule impose five requirements 

for SIPs: 

For each affected wilderness and national park, the plan must: (1) 

set “reasonable progress goals” toward achieving natural visibility 

conditions that ensure improvements in visibility on the most 

impaired days over the period of the implementation plan; (2) 

calculate baseline visibility and natural visibility conditions; (3) 

devise a long-term strategy with enforceable emissions limitations,

compliance schedules, and other measures necessary to achieve 

the reasonable progress goals; (4) develop a monitoring strategy 

for measuring and reporting visibility; and (5) list the best 

available retrofit technology . . . that emission sources in the state 

will have to adopt to achieve the visibility goals, along with a 

schedule for implementing BART.14

After a state submits its SIP to the EPA, the agency reviews the SIP for 

compliance with the Clean Air Act. If the EPA determines that a SIP does not 

comply with the Act, it must promulgate a “Federal implementation plan” that 

fixes the SIP’s shortcomings, unless the state corrects the deficiency.15 The 

EPA’s role is confined “to the ministerial function of reviewing SIPs for 

consistency with the Act’s requirements.”16

The parties focus on two of the Clean Air Act’s and Regional Haze Rule’s

requirements: (1) the BART emission limits and (2) the reasonable progress 

goals and long-term strategy that each state must implement.

 

14 Texas, 829 F.3d at 412 (citing 40 C.F.R. § 51.308(d), (e)).

15 42 U.S.C. § 7410(k)(3), (c)(1). Because the EPA approved Louisiana’s SIP, there is 

no Federal implementation plan at issue here. 

16 Texas, 829 F.3d at 411 (quoting Luminant Generation Co. v. EPA, 675 F.3d 917, 921 

(5th Cir. 2012)).

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1. BART Emission Limits

The Regional Haze Rule defines BART as “an emission limitation based 

on the degree of reduction achievable through the application of the best 

system of continuous emission reduction for each pollutant which is emitted by 

an existing stationary facility.”17 The BART process has three steps. First, a 

state must identify all “BART-eligible sources.” Second, it must determine 

which of those BART-eligible sources are “subject to BART.” Third, for each 

source that is “subject to BART,” the state must make a “BART determination” 

by analyzing and selecting the appropriate emission control for that source.18

Step one is identifying all “BART-eligible sources.” That definition 

includes all stationary facilities that (1) were in existence before August 7, 

1977 but were not in operation before August 7, 1962, (2) have “the potential 

to emit 250 tons per year or more of any visibility-impairing air pollutant,” and 

(3) fall within one of 26 listed source categories.19 The parties agree that Nelson 

and Brame satisfy these requirements and are “BART-eligible” sources.

Step two is making “subject to BART” determinations. The state must 

determine which of the BART-eligible sources emit air pollutants that “may 

reasonably be anticipated to cause or contribute to any impairment of 

visibility” in a Class I area.20 The key words are “cause” and “contribute to.” 

 

17 40 C.F.R. § 51.301.

18 BART Guidelines, 40 C.F.R. Part 51, App. Y at I.F; see also Util. Air Regulatory Grp. 

v. EPA, 471 F.3d 1333, 1335–36 (D.C. Cir. 2006) (explaining the process). 

19 40 C.F.R. § 51.301.

20 Id.

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Sources that a state determines may reasonably be anticipated to “cause” or 

“contribute to” visibility impairment at a protected area are “subject to 

BART.”21 Under the BART Guidelines, a 1.0 deciview22 change from an 

individual source “causes” visibility impairment, whereas a 0.5 deciview 

change from an individual source “contributes to” impairment.23 In some 

instances, states may set a lower threshold for sources that “contribute to”

visibility impairment.24

At the “subject to BART” screening step, states have discretion to either 

(a) determine that all BART-eligible sources are “subject to BART” via 

“collective attribution” or (b) conduct individualized testing to determine that 

a source, or a group of sources, is exempt from BART.25 Here, Louisiana opted 

for the second option.

 

21 Id.

22 Visibility impairments are measured in deciviews. A deciview “is the unit of 

measurement on the deciview index scale for quantifying in a standard manner human 

perceptions of visibility.” 40 C.F.R. § 51.301. “A higher deciview measurement indicates more 

haze and less visibility. . . . A single deciview is around the increment that the average person 

can perceive with the naked eye.” Texas, 829 F.3d at 413 n.2.

23 BART Rule, 70 Fed. Reg. at 39,120 (“[W]e are clarifying that for purposes of 

determining which sources are subject to BART, States should consider a 1.0 deciview change 

or more from an individual source to ‘cause’ visibility impairment, and a change of 0.5 

deciviews to ‘contribute’ to impairment.”). For a fuller background on the “cause” or 

“contribute” distinction, see id. at 39,117–39,122. 

24 Id. at 39,120–39,121 (“In a regulatory context, we believe that a State’s decision as 

to an appropriate threshold for contribution could depend upon the number of sources 

affecting a class I area.”).

25 BART Guidelines, 40 C.F.R. Pt. 51, App. Y at III. 

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The third step is the “BART determination,” in which a state must 

identify the appropriate emission control for each “subject to BART” source.26

At each such source, the state must consider five statutory factors: (1) the costs 

of compliance, (2) the energy and nonair quality environmental impacts of 

compliance, (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.27

For powerplants with generating capacities greater than 750 megawatts, 

like those at issue here, a state’s BART determination must comply with the 

BART guidelines,28 which provide step-by-step instructions for making BART 

determinations.29 In contrast, at the BART-eligibility and “subject to BART”

steps, the BART guidelines are advisory only.30

2. Reasonable Progress Goals and Long-Term Strategy

The Regional Haze Rule requires a state to “establish goals (expressed 

in deciviews) that provide for reasonable progress towards achieving natural 

visibility conditions” for each Class I area within that state.31 The process and 

considerations for calculating these goals are as follows:

 

26 Id. at IV.

27 42 U.S.C. § 7491(g)(2); Regional Haze Rule, 40 C.F.R. § 308(e)(1)(ii)(A) .

28 Regional Haze Rule, 40 C.F.R. § 51.308(e)(1)(ii)(B); 42 U.S.C. § 7491(b)(2); see also 

77 Fed. Reg. 11,839, 11,849 (Feb. 28, 2012).

29 See BART Guidelines, 40 C.F.R. Part 51, App. Y § IV.

30 Util. Air Regulatory Grp., 471 F.3d at 1338–39.

31 40 C.F.R. § 51.308(d)(1).

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A state begins by calculating the steady linear rate of decreasing 

emissions that would achieve natural visibility in the covered 

wildernesses and national parks by the year 2064. 40 C.F.R. 

§ 51.308. If a state determines that the linear rate would result in 

unreasonable regulations, it must propose an alternative set of 

reasonable progress goals and demonstrate both that the linear 

rate is unreasonable and that the alternative goals are reasonable. 

Id. § 51.308(d)(1)(ii). The Clean Air Act and the Regional Haze 

Rule require a state to consider four factors when setting 

reasonable progress goals: “the costs of compliance, the time 

necessary for compliance, and the energy and nonair quality 

environmental impacts of compliance, and the remaining useful 

life of any existing source subject to such requirements.” 42 U.S.C. 

§ 7491(g)(1); see also 40 C.F.R. § 51.308(d)(1)(i)(A) (repeating the 

factors listed in § 7491(g)(1)).32

The evaluation of the four statutory factors is often referred to as a “‘four-factor 

analysis’ or ‘reasonable progress analysis.’”33

In addition to setting reasonable progress goals, a state must establish a 

“long-term strategy” to make reasonable progress toward achieving natural 

visibility conditions.34 This strategy must include “enforceable emissions 

limitations, compliance schedules, and other measures necessary to achieve 

the reasonable progress goals.”35 As part of its long-term strategy, a state may 

impose additional emission reduction measures at sources that are not “subject 

to BART.”36 Sources that are regulated through the reasonable progress 

 

32 Texas, 829 F.3d at 412–13.

33 81 Fed. Reg. 66,332, 66,360 (Sept. 27, 2016).

34 40 C.F.R. § 51.308(d)(3).

35 Id.; see 42 U.S.C. § 7491(b)(2)(A).

36 40 C.F.R. § 51.308(d)(3).

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goals—rather than through BART—are referred to as “reasonable progress 

sources.”37

B. Factual Background

The procedural history of this case began when Louisiana submitted its 

regional haze SIP to the EPA in 2008. Since then, Louisiana has revised and 

resubmitted its SIP many times. Louisiana submitted its final SIP revisions in 

October 2017, and the EPA approved Louisiana’s SIP in its December 2017 

Final Rule.38

1. Louisiana’s 2008 Submittal

Louisiana submitted a SIP for addressing regional haze in June 2008. In 

that SIP, Louisiana relied on an emissions-trading program called the Clean 

Air Interstate Rule (“CAIR”) to satisfy its BART, reasonable-progress, and 

long-term strategy obligations. The EPA reviewed that SIP in two separate 

actions in 2012.39

The first such action, a national rulemaking, was based on a D.C. Circuit 

decision that (1) held that states could not rely on CAIR to satisfy their BART 

obligations and (2) remanded CAIR to the EPA.40 In that national rulemaking, 

the EPA finalized a “limited disapproval” of Louisiana’s SIP because it had 

relied on CAIR.41

 

37 Id.

38 See Final Rule, 82 Fed. Reg. at 60,521–60,522 (“Our Previous Actions”). 

39 See 82 Fed. Reg. 32,294, 32,295 (July 13, 2017) (detailing the procedural history).

40 See North Carolina v. EPA, 531 F.3d 896, 930 (D.C. Cir. 2008), reh’g granted in part, 

550 F.3d 1176 (D.C. Cir. 2008).

41 77 Fed. Reg. 33,642, 33,643 (June 7, 2012). 

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The second such action “partially disapproved” Louisiana’s SIP 

submission based on issues other than, and “go[ing beyond],” the SIP’s reliance 

on CAIR. In addition to this “partial disapproval” of particular parts of 

Louisiana’s SIP, that action also included a “partial limited approval” of other 

parts of the SIP.

The “partial limited approval” part of that action was based on the EPA’s 

conclusion that specified parts of the SIP, “as a whole, strengthen[ed] the 

State’s SIP.”42 Although the EPA concluded that some of the SIP provisions—

including Louisiana’s reasonable progress goals and long-term strategy—did 

not comply with the Clean Air Act, those noncompliant provisions were 

included in the partial limited approval.43

In the “partial disapproval” part of that action, the EPA disapproved the 

parts of the SIP related to CAIR, including the BART analyses for non-electric 

generating unit (“EGU”) sources44 and the BART determinations for four

specific non-EGU sources.45 Those deficiencies are not at issue here.

A definitional note: Limited approvals and partial approvals are 

different. If a submittal does not meet all of the Act’s requirements, but a 

“separable” part does meet those requirements, a “partial approval may be 

 

42 77 Fed. Reg. 39,425, 39,426 (July 3, 2012) (“2012 Final Rule”).

43 See id.

44 “[T]he term ‘electric generating unit’ or ‘EGU’ is used to mean a solid fuel-fired 

steam generating unit that serves a generator that produces electricity for sale to the electric 

grid.” EPA Whitepaper on Available and Emerging Technologies for Reducing Greenhouse 

Gas Emissions from Coal-Fired Electric Generating Units (Oct. 2010), 

https://www.epa.gov/sites/production/files/2015-12/documents/electricgeneration.pdf. 45 2012 Final Rule, 77 Fed. Reg. at 39,426.

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used to approve that part of the submittal and disapprove the remainder.”46 In 

contrast, if parts of a submittal do not meet the Clean Air Act’s requirements, 

but “the submittal as a whole” has a “strengthening effect” on the SIP, the EPA

may use a “limited approval” to enact the entire submittal.47 The practical 

difference is

that under a limited approval the EPA’s approval action goes to 

the entire [submittal]. In other words, although portions of a 

[submittal] prevent the EPA from finding that the [submittal]

meets a certain requirement of the Act, the EPA believes that the 

[submittal], as a whole, strengthens the SIP. Therefore, the EPA

approves the entire [submittal]--even those portions that prohibit 

full approval. Likewise, when the EPA issues the limited 

disapproval, the disapproval applies to the entire [submittal] as 

failing to meet a specific requirement of the Act. The [submittal] 

remains a part of the [enforceable] SIP, however, under the limited 

disapproval, because the [submittal] strengthens the SIP. The 

disapproval only applies to whether the submittal meets a specific 

requirement of the Act and does not affect incorporation of the rule 

into the approved, federally enforceable SIP.48

In short, in a partial approval, the approved parts of the submittal go into effect 

and the disapproved parts do not. In a limited approval, the entire part that is 

“limitedly” approved—including the provisions within that part that do not 

 

46 Processing of State Implementation Plan Revisions at 2, the EPA Memorandum 

from John Calcagni (July 9, 1992), https://www.epa.gov/sites/production/files/2015-

07/documents/procsip.pdf. 47 Id. at 2–3.

48 Id. at 3.

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comply with the Clean Air Act—goes into effect and are incorporated into the 

approved SIP.

As a result of the partial disapproval, the EPA was required to 

promulgate a federal implementation plan within two years of that

disapproval, unless it approved a corrected state plan.49 The EPA did not 

promulgate a federal plan or approve a corrected state plan within that 

timeframe. Based on that, the Sierra Club sued the EPA, and a federal district 

court entered a consent decree requiring the EPA to issue a federal plan or 

approve a corrected state plan by December 15, 2017.50

2. Louisiana’s 2017 Revisions and the EPA’s Approval 

To bring its SIP into compliance, Louisiana revised its SIP to, among 

other things, address BART for the Nelson and Brame powerplants. Nelson 

and Brame are two of the largest sources of SO2 and NOx emissions in 

Louisiana, are “BART-eligible,” and have generating capacities greater than 

750 megawatts.51

In August 2016, Louisiana submitted a partial plan addressing BART at 

“non-EGU” sources. The EPA proposed to approve that partial plan in October 

2016 and finalized the approval in the December 2017 Final Rule.52 The 

approval of that partial plan is not at issue here. 

 

49 42 U.S.C. § 7410(c)(1).

50 See Notice of Modification of Consent Decree, Sierra Club v. Pruitt, No. 15-cv-01555-

JEB (D.D.C. Mar. 13, 2017).

51 Final Rule, 82 Fed. Reg. at 60,525–26.

52 81 Fed. Reg. 74,750 (Oct. 27, 2016) (proposed rulemaking); Final Rule, 82 Fed. Reg. 

at 60,522 (“[W]e are finalizing that approval here.”). 

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In February 2017, Louisiana submitted a revised plan addressing BART 

for EGU sources, including Nelson and Brame. In June 2017, Louisiana revised 

its SIP to make a BART determination for Nelson. Louisiana revised its SIP 

again in October 2017. The EPA’s December 2017 Final Rule explains the 

relevant procedural history as follows:

On June 20, 2017, LDEQ submitted a SIP revision for parallel 

processing related to Entergy’s Nelson facility. On July 13, 2017, 

we proposed to approve this SIP revision along with the remaining 

portion of the February 2017 SIP revision that addressed BART 

for the Nelson facility. Specifically, we proposed to approve the 

LDEQ BART determinations for Nelson Units 6 and 4, and the 

Unit 4 auxiliary boiler, and the [administrative order on consent] 

that makes the emission limits that represent BART permanent 

and enforceable for the purposes of regional haze. We also solicited 

comment with respect to any information that would support or 

refute the costs in Entergy’s evaluation of SO2 controls for Unit 6. 

On June 21, 2017, Entergy submitted a comment to LDEQ on its 

proposed SIP revision requesting a three-year compliance deadline 

to achieve the proposed SO2 BART limit for Nelson Unit 6. 

Entergy’s letter explained that the company has coal contracts in 

place for the next three years, so the revised compliance date would 

provide the company sufficient time to transition to new mines 

with lower sulfur coal. Additionally, Entergy stated that it did not 

have the necessary equipment to blend varying fuel supplies. On 

August 24, 2017, we received a letter from LDEQ explaining their 

intent to revise the compliance date in the SIP revision for Nelson 

Unit 6 based on Entergy’s comment letter. On September 26, 2017, 

we supplemented our proposed approval of the SO2 BART 

determination for Nelson by proposing to approve the three-year 

compliance date. On October 26, 2017, we received LDEQ’s final 

SIP revision addressing Nelson, including a final [administrative 

order of consent] with emission limits and a SO2 compliance date 

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three years from the effective date of the EPA’s final approval of 

the SIP revision.53

In the October 2017 SIP revisions, Louisiana (1) determined that Nelson 

and Brame were “subject to BART” and (2) determined that low-sulfur coal was 

BART for controlling SO2 emissions at Nelson. 

In reaching those conclusions, Louisiana considered analyses submitted 

by Entergy, Cleco, and the EPA. The analyses submitted by the parties 

addressed: (1) the modeling methods for making “subject to BART” 

determinations and (2) the potential control options for BART at Nelson. The 

EPA’s analyses contradicted and sharply criticized significant parts of 

Entergy’s and Cleco’s analyses. The LDEQ included all the analyses as 

appendices to its revised SIP. 

i. The “Subject to BART” Determinations

The LDEQ concluded that Nelson and Brame were “subject to BART.”

The department reached that conclusion based on dispersion modeling that 

established that those powerplants produced emissions that surpassed the 0.5 

deciview threshold for “contributing to” visibility impairment at the Breton 

National Wilderness Area and the Caney Creek Wilderness Area. 

The LDEQ relied on the “CALPUFF” model, which “predicts 24-hour 

average pollutant concentrations based on source emissions and how they 

disperse in the atmosphere” and converts those concentrations to daily 

 

53 82 Fed. Reg. at 60,522.

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deciview effects.54 The BART guidelines provide that a state may “use 

CALPUFF or other appropriate model to estimate visibility impacts from a 

single source at a Class I area.”55 When the EPA promulgated those guidelines 

in 2005, CALPUFF was “the best regulatory modeling application currently 

available for predicting a single source’s contribution to visibility impairment 

and [was then] the only EPA-approved model for use in estimating single 

source pollutant concentrations resulting from the long range transport of 

primary pollutants.”56 Although the EPA has recently removed CALPUFF as 

a “preferred” model for other air-quality modeling applications under the Clean 

Air Act, CALPUFF remains a recommended model for making “subject-toBART” and BART emission control determinations.57

Both Entergy’s and the EPA’s CALPUFF modeling showed that Nelson 

and Brame each had a greater than 0.5 deciview impact on visibility 

impairment at Breton and Caney Creek. Entergy, however, submitted reports 

showing that CALPUFF’s reliance on flawed assumptions imposed a too-high 

margin of error.

In addition to conducting CALPUFF modeling, Entergy and the EPA

conducted another type of modeling called “CAMx.” Entergy and the EPA

submitted their CAMx analyses to the LDEQ. 

 

54 See BART Rule, 70 Fed. Reg. at 39,122 (describing the CALPUFF model in detail). 

55 BART Guidelines, 40 C.F.R. Part 51, App. Y, III.A.3.

56 Id.

57 82 Fed. Reg. 5,182, 5,196 (Jan. 17, 2017) (“[T]his final action does not affect the 

EPA’s recommendation that states use CALPUFF to determine the applicability and level of 

best available retrofit technology in regional haze implementation plans.”).

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The EPA’s CAMx modeling showed that Nelson and Brame exceeded the 

0.5 deciview threshold. In contrast, Entergy’s CAMx modeling showed that 

those powerplants’ emissions did not exceed the 0.5 deciview threshold. The 

EPA, however, concluded that Entergy’s CAMx modeling “was not conducted 

in accordance with the BART Guidelines and d[id] not properly assess 

maximum baseline impacts, so [the EPA] consider[ed] this CAMx modeling 

provided by Entergy to be invalid for supporting a determination of minimal 

visibility impacts.”58

When the LDEQ reviewed the models that the parties had submitted, it 

stated that it did “not have the expertise with which to review those [CAMx] 

model runs,” and instead relied only on the CALPUFF modeling. The LDEQ 

did, however, include the CAMx analyses as appendices to its revised SIP.

ii. BART Determinations for Brame and Nelson

Louisiana’s revised SIP also made BART determinations for Brame and 

Nelson. For the two Brame units, the LDEQ determined that “no additional 

controls constitute[d] BART.” The LDEQ reached that determination based on 

those units’ existing controls. At one of those units, BART was satisfied via the 

unit’s earlier conversion from coal to natural gas. The other unit satisfied its

BART obligations based on an earlier dry sorbent injection installation.59

For Nelson, the LDEQ changed its BART determination between the 

February 2017 revision and the June and October 2017 revisions. In the 

 

58 82 Fed. Reg. at 32,299.

59 Cleco does not challenge the LDEQ’s determination about the BART controls at the 

Brame units; it challenges only the determination that the units are “subject to BART.”

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February 2017 SIP revision, the LDEQ concluded that no additional controls 

were necessary for Nelson to satisfy BART. Although the LDEQ stated that 

“low sulfur coal presents the most feasible control based on economics and 

impacts to visibility,” it also stated that it “believe[d] that the visibility 

improvement that would be achieved through the installation and operation of 

controls at each of the Nelson units would be negligible, therefore the facility’s 

existing controls satisfy the BART requirements and no further controls are 

necessary.” 

In its June 2017 SIP revision, however, the LDEQ changed course and 

determined that low-sulfur coal was BART for controlling SO2 at Nelson. The 

October 2017 SIP revision retained that determination and extended the 

compliance date for BART at Nelson by three years. 

In the October 2017 SIP revision, the LDEQ stated that it evaluated four 

different technologies for reducing emissions at Nelson: (1) low-sulfur coal, (2) 

dry sorbent injection (“DSI”), (3) dry flue-gas desulfurization (“FGD”), or a “dry 

scrubber,” and (4) wet FGD, or a “wet scrubber.” The LDEQ stated its

reasoning for selecting low-sulfur coal as BART at Nelson as follows:

In the Entergy BART five-factor SO2 analysis for the Unit 6 

Boiler, a number of emission reduction controls were reviewed. 

The reviewed controls included the use of a lower sulfur coal, DSI, 

enhanced DSI, dry flue-gas desulfurization (FGD) and wet FGD. 

LDEQ has reviewed and weighed the five factors carefully; after a 

review of the information that Entergy and EPA provided, LDEQ 

has concluded that the appropriate BART for this facility is to 

establish an emission limit of .6 lbs/MMBtu based on a 30 day 

rolling average as defined in the AOC (see Appendix D). While 

additional visibility benefits may be available through the use of 

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FGD, the lower sulfur coal option results in visibility benefits at a 

lower annual cost. Along with the extra cost, FGD use results in 

additional waste spent due to spent reagent and has some power 

demands to run the equipment. LDEQ believes, at present, that 

the use of lower sulfur coal presents the appropriate SO2 control 

based on consideration of economics, energy impacts, non-air 

quality environmental impacts, and impacts to visibility.

iii. Long-Term Strategy and Reasonable Progress Goals

Louisiana’s revised SIP did not specifically set out a long-term strategy 

or impose emission controls at additional “reasonable progress sources.” 

Neither did it evaluate the four “reasonable progress factors” for determining 

whether any non-BART reasonable progress sources should be controlled. 

3. The EPA’s Approval of Louisiana’s SIP

The EPA proposed two separate rules to approve Louisiana’s revised 

SIP. In May 2017, the EPA issued a proposed rule to approve the entire 

February 2017 SIP revision except for the part about Nelson, on which the EPA

deferred action.60 This rulemaking included an approval of Louisiana’s “subject 

to BART” determination for Brame.61

In June 2017, Louisiana revised its SIP by changing its previous “no 

further controls” BART determination for Nelson to require the use of lowsulfur coal. In a July 2017 rulemaking (“the Proposed Rule”), the EPA proposed 

to approve the remaining part of Louisiana’s SIP addressing Nelson.62 The 

 

60 82 Fed. Reg. 22,936 (May 19, 2017).

61 Id. at 22,942–22,943. 

62 Proposed Rule, 82 Fed. Reg. 32,294, 32,300 (July 13, 2017).

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Proposed Rule (1) agreed with the LDEQ that Nelson was “subject to BART” 

and (2) stated that the LDEQ had adequately analyzed the five mandatory

BART factors.63 But the Proposed Rule also criticized several aspects of the 

SIP revision, including Entergy’s modeling, cost estimates, and supporting 

documentation. The Proposed Rule stated that the EPA performed its own 

modeling and analyses to correct those errors.64

After the EPA issued the Proposed Rule, Louisiana submitted a letter to 

the EPA explaining the state’s intention to extend the compliance date in its 

draft SIP for Nelson by three years. In response to that letter, the EPA

supplemented the Proposed Rule to reflect such change.65

Louisiana revised its SIP again in October 2017. As discussed above, that 

revision extended the date for Nelson to comply with BART by three years. The 

EPA finalized its proposed approval of all of Louisiana’s SIP revisions when it 

issued the Final Rule on December 21, 2017.66

The Environmental and Industry Petitioners timely petitioned for 

review of the Final Rule. On the same day that this case was filed, the 

Environmental Petitioners also filed an administrative petition for 

reconsideration of the Final Rule. This court stayed the case pending the EPA’s 

 

63 Id. at 32,296–32,297.

64 Id. at 32,297–32,298.

65 82 Fed. Reg. 44,753 (Sept. 26, 2017).

66 Final Rule, 82 Fed. Reg. 60,520 (Dec. 21, 2017).

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decision on the administrative petition, then lifted the stay after the EPA

denied that petition.67 

II. STANDARD OF REVIEW

We review the EPA’s approval of Louisiana’s regional haze SIP under 

the standards set out in the Administrative Procedure Act (“APA”), which 

require us to set aside an agency action that is “arbitrary, capricious, an abuse 

of discretion, or otherwise not in accordance with law.”68 An action is arbitrary 

and capricious “if the agency has relied on factors which Congress has not 

intended it to consider, entirely failed to consider an important aspect of the 

problem, offered an explanation for its decision that runs counter to the 

evidence before the agency, or is so implausible that it could not be ascribed to 

a difference in view or the product of agency expertise.”69

The arbitrary and capricious standard is “narrow,” and we must “be 

mindful not to substitute [our] judgment for that of the agency.”70 We “must 

also ensure that the agency ‘examined the relevant data and articulated a 

satisfactory explanation for its action.’”71 “We consider whether the decision 

 

67 See EPA’s Response to Reconsideration Petition, https://www.regulations.gov/

contentStreamer?documentId=EPA-R06-OAR-2016-0520-0011&contentType=pdf. Although 

we take notice of the administrative petition for reconsideration and the EPA’s response to 

it, our review of the Final Rule “is limited to the record before the agency at the time of its 

decision.” Luminant, 675 F.3d at 925 (quotation omitted). 

68 5 U.S.C. § 706(2)(A).

69 Tex. Oil & Gas Ass’n v. EPA, 161 F.3d 923, 933 (5th Cir. 1998) (quoting Motor 

Vehicle Mfrs. Ass’n v. State Farm Mut. Auto Ins. Co., 463 U.S. 29, 43 (1983)).

70 10 Ring Precision, Inc. v. Jones, 722 F.3d 711, 723 (5th Cir. 2013) (quoting Motor 

Vehicle Mfrs. Ass’n, 463 U.S. at 43).

71 Id. (quoting Motor Vehicle Mfrs. Ass’n, 463 U.S. at 43).

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was based on a consideration of the relevant factors and whether there has 

been a clear error of judgment.”72

Additionally, federal agencies “are required to engage in ‘reasoned 

decisionmaking.’”73 The agency’s process must be “logical and rational,” and its 

decision “is lawful only if it rests ‘on a consideration of the relevant factors.’”74

The agency must “articulate a satisfactory explanation for its action including 

a ‘rational connection between the facts found and the choice made.’”75 Under 

this standard, courts have vacated agency decisions that created “unexplained 

inconsistencies in the rulemaking record.”76

Under the Clean Air Act’s structure of cooperative federalism, Louisiana 

is the entity considering “relevant factors,” and the EPA’s role is confined to 

ensuring that Louisiana’s determinations complied with the Clean Air Act.77

Under this structure, we review whether the EPA was arbitrary and capricious 

in approving Louisiana’s compliance with the Act. 

 

72 Id. (quoting Motor Vehicle Mfrs. Ass’n, 463 U.S. at 43).

73 Michigan v. EPA, 135 S. Ct. 2699, 2706 (2015) (quoting Allentown Mack Sales & 

Serv., Inc. v. NLRB, 622 U.S. 359, 374 (1998)).

74 Id. (quoting Motor Vehicle Mfrs. Ass’n, 463 U.S. at 43).

75 Motor Vehicle Mfrs. Ass’n, 463 U.S. at 43 (quoting Burlington Truck Lines v. United 

States, 371 U.S. 156, 168 (1962)).

76 U.S. Sugar Corp. v. EPA, 830 F.3d 579, 651 (D.C. Cir. 2016); see id. at 650 (collecting 

D.C. Circuit authority and stating “[t]his court has ‘often declined to affirm an agency 

decision if there are unexplained inconsistencies in the final rule’” (citation omitted)); Gulf 

Power Co. v. FERC, 983 F.2d 1095, 1101 (D.C. Cir. 1993) (“[W]hen an agency takes 

inconsistent positions . . . it must explain its reasoning.); Gen. Chem. Corp. v. United States, 

817 F.2d 844, 846 (D.C. Cir. 1987) (holding agency action to be arbitrary because its analysis 

was “internally inconsistent and inadequately explained”). 

77 See Texas, 829 F.3d at 411.

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III. ANALYSIS

As a threshold matter, Industry Petitioners and Environmental 

Petitioners have standing. Industry Petitioners’ standing is based on Entergy’s 

and Cleco’s ownership of the powerplants at issue. Environmental Petitioners 

have standing because one of the Sierra Club’s members submitted a 

declaration adequately asserting that (1) he regularly visits the national parks 

in question, (2) he has concrete plans to return in the future, and (3) regional 

haze affects his visibility. Although the declarations submitted by the National 

Parks Conservation Association do not appear to give it standing in this case, 

“one party with standing is sufficient to satisfy Article III’s case-or-controversy 

requirement.”78

Each petition raises two major issues. Environmental Petitioners 

challenge the EPA’s approval of (1) Louisiana’s selection of low-sulfur coal as 

BART for controlling SO2 emissions at Nelson and (2) Louisiana’s reasonable 

progress goals and long-term strategy. 

Industry Petitioners challenge the EPA’s approval of Louisiana’s 

“subject to BART” determinations at Nelson and Brame. They contend that (1) 

the CALPUFF modeling that Louisiana relied on was technically flawed; (2) 

the CAMx modeling, on which the EPA relied but Louisiana did not, was 

technically flawed; and (3) even if the CAMx modeling were not technically 

 

78 Brackeen v. Bernhardt, 937 F.3d 406, 421 (5th Cir. 2019) (quoting Rumsfeld v. 

Forum for Acad. & Institutional Rights, Inc., 547 U.S. 47, 53 n.2 (2006)).

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flawed, the EPA should not have considered it because Louisiana expressly did 

not consider it.

We address each issue in turn. 

A. The Environmental Petitioners’ Petition

The first part of Environmental Petitioners’ challenge addresses the 

EPA’s approval of Louisiana’s determination that low-sulfur coal was BART 

for Nelson. The second part of their challenge addresses the EPA’s approval of 

Louisiana’s long-term strategy and reasonable progress goals.

We deny Environmental Petitioners’ petition, and we explain our 

reasons below.

1. The EPA’s Approval of the BART Determination for Nelson

In its October 2017 SIP revision, Louisiana selected low-sulfur coal as 

BART for controlling SO2 emissions at Nelson. The LDEQ explained its 

determination as follows:

In the Entergy BART five-factor SO2 analysis for the Unit 6 

Boiler, a number of emission reduction controls were reviewed. 

The reviewed controls included the use of a lower sulfur coal, DSI, 

enhanced DSI, dry flue-gas desulfurization (FGD) and wet FGD. 

LDEQ has reviewed and weighed the five factors carefully; after a 

review of the information that Entergy and EPA provided, LDEQ 

has concluded that the appropriate BART for this facility is to 

establish an emission limit of .6 lbs/MMBtu based on a 30 day 

rolling average as defined in the AOC (see Appendix D). While 

additional visibility benefits may be available through the use of 

FGD, the lower sulfur coal option results in visibility benefits at a 

lower annual cost. Along with the extra cost, FGD use results in 

additional waste spent due to spent reagent and has some power 

demands to run the equipment. LDEQ believes, at present, that 

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the use of lower sulfur coal presents the appropriate SO2 control 

based on consideration of economics, energy impacts, non-air 

quality environmental impacts, and impacts to visibility.

Environmental Petitioners contend that the EPA’s approval of this 

determination was arbitrary and capricious for three reasons. First, 

Louisiana’s selection of low-sulfur coal as BART at Nelson was inconsistent 

with the evidence that the state considered. Second, Louisiana did not provide 

a “rational basis” for rejecting more effective pollution controls. Third, in its 

BART determination, Louisiana did not weigh the Clean Air Act’s factors in 

compliance with the mandatory BART guidelines.

i. The Evidence Louisiana Considered 

According to Environmental Petitioners, Louisiana’s BART 

determination rested solely on analysis by Nelson’s owner, Entergy. 

Environmental Petitioners point out that the EPA was “unable to verify any of 

the company’s costs” because those costs were based on a proprietary database 

to which the EPA was not given access.79 Similarly, the EPA could not verify 

Entergy’s modeling analyses because Entergy did not provide the “inputs” that 

were used in the modeling.

For the parts of Entergy’s analyses that the EPA did review, the EPA

concluded that Entergy’s cost and visibility analyses, on which Louisiana 

relied, had many errors, including: (1) implementing improper costs, (2) 

inflated contingency estimates, and (3) modeling errors. The EPA pointed out 

 

79 Proposed Rule, 82 Fed. Reg. at 39,432.

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these errors in the Proposed Rule: (1) “Entergy’s control cost estimates 

included costs not allowed under our Control Cost Manual (e.g., escalation 

during construction and owner’s costs)”; (2) “Entergy also assumed a 

contingency of 25%, which we note is unusually high”; and (3) “Entergy’s 

CALPUFF modeling included errors in its estimates of sulfuric acid and PM 

emissions.”80

After noting these perceived errors, the EPA submitted its own BART 

analyses that reached markedly different cost-effectiveness estimates for each 

proposed control option at Nelson. The following table compares the EPA’s and 

Entergy’s cost-effectiveness calculations, in cost per ton of pollutant removed,

for each control option.

Cost-Effectiveness Comparison81

Technology Entergy’s Calculation the EPA’s Calculation

Low-sulfur coal $597 $2,957 

DSI $5,611 $3,578 - $4,302

Wet scrubber $4,413 $2,743 

Dry scrubber (SDA) $4,536 $2,706 

Most striking is the difference between the EPA’s and Entergy’s 

calculations for low-sulfur coal. Entergy estimated that low-sulfur coal would 

cost $597 per ton of pollution removed; the EPA estimated that it would cost 

$2,957 per ton. Entergy’s estimate for what the parties agree would be the most 

 

80 Proposed Rule, 82 Fed. Reg. at 32,298–32,299.

81 The Proposed Rule contains a thorough narrative discussion of the EPA’s analyses 

and the problems with Entergy’s analyses. 82 Fed. Reg. at 32,298–32,299.

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effective option—a dry scrubber—was significantly higher than the EPA’s 

estimate. Entergy’s estimate was $4,536 per ton of pollution removed; the 

EPA’s was $2,706 per ton. 

Similarly, the EPA’s conclusions about the visibility improvements for 

each option differed from Entergy’s conclusions. In the Proposed Rule, the EPA

explained that the differences resulted from Entergy’s model’s failure to follow 

the BART guidelines.82 The following chart compares the visibility 

improvement calculations (in deciviews) for each control option.

Expected Visibility Improvement Comparison for Caney Creek

Technology Trinity Consultants’ 

Calculation 

the EPA’s Calculation

Low-sulfur coal 0.164 0.411 

DSI 0.302 0.511 

Dry scrubber (SDA) 0.355 0.831 

According to Environmental Petitioners, Louisiana’s reliance on 

Entergy’s analyses—which the EPA’s analyses concluded overestimated the 

costs and underestimated the benefits of more effective pollution controls—was 

irrational. After the EPA informed Louisiana of those errors, that state 

reached the same BART determination. In its SIP revision, Louisiana did not 

acknowledge the EPA’s criticisms and did not attempt to reconcile the 

 

82 82 Fed. Reg. at 32,299 (“As we discuss above and in the CAMx Modeling TSD, 

Entergy also provided additional screening modeling results using CAMx to support its 

conclusion that visibility impacts from Unit 6 are minimal. However, this modeling was not 

conducted in accordance with the BART Guidelines and does not properly assess maximum 

baseline impacts, so we consider this CAMx modeling provided by Entergy to be invalid for 

supporting a determination of minimal visibility impacts.”).

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conflicting the EPA and Entergy analyses. Environmental Petitioners insist 

that Louisiana’s failure to explain why its decision remained unchanged after 

reviewing the EPA’s contradictory analyses created an “unexplained 

inconsistenc[y] in the rulemaking record” that made the EPA’s approval 

arbitrary and capricious.83

The EPA does not defend these discrepancies. In its brief, it concedes 

that the agency “was aware of these errors when it approved the SIP,” 

acknowledges that the SIP revision contained “a number of errors,” and 

describes Entergy’s submissions as “Entergy’s faulty analyses.”

The EPA contends that, despite these errors, Louisiana “may, to the 

extent supported by the record as a whole, reach the same conclusion both 

before and after reviewing a particular set of information.”84 The EPA points 

to the fact that its own analyses were in the record and that the LDEQ included 

those analyses in an appendix to the revised SIP. The EPA insists that, based 

on the agency’s earlier review of the “entirety of” Louisiana’s SIP submission, 

Louisiana considered all the information in its October 2017 SIP submission, 

weighed that information in arriving at its final BART determination, and 

explained the reasons for its decision.

Industry Respondents defend the analyses they submitted to the LDEQ 

and insist that those analyses adequately supported Louisiana’s BART 

determination. They criticize the analyses that the EPA submitted to the 

 

83 U.S. Sugar Corp, 830 F.3d 579 at 651. 

84 See 42 U.S.C. § 7410(k)(3) (“[the EPA] shall approve such submittal as a whole if it 

meets all of the applicable requirements of [the Act].”).

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LDEQ and challenge the EPA’s earlier determination that their analyses failed 

to comply with the BART guidelines.

Environmental Petitioners have the better arguments on this point. 

Entergy and the EPA reached significantly different conclusions about the 

costs and visibility improvements of each emission control. But after the EPA

submitted analyses pointing out flaws in Entergy’s analysis, the LDEQ did not 

discuss the EPA-identified errors, and it reached the same BART 

determination for Nelson as it did before the EPA identified mistakes. Given 

the EPA’s analysis showing that Entergy significantly underestimated the cost 

of low-sulfur coal and overestimated the cost of a scrubber, Louisiana’s failure 

to address or reconcile the conflicting analyses appears to create an 

“unexplained inconsistenc[y]” in the rulemaking record.85 Although that 

shortcoming in Louisiana’s SIP is worthy of careful scrutiny, it does not fully 

resolve the matter.

ii. Rational Explanation for Rejecting a More Effective 

Control 

Environmental Petitioners next contend that Louisiana did not provide 

a rational explanation for rejecting a more effective pollution control at Nelson. 

They point to the EPA’s past actions that reviewed BART determinations for 

whether the costs and visibility benefits of a determination were within the 

range of the EPA’s prior BART determinations.86 They also cite the BART 

 

85 See U.S. Sugar Corp., 830 F.3d at 651. 

86 See 82 Fed. Reg. 912,938 (Jan. 4, 2017) (“[T]he cost-effectiveness of all of the controls 

that form the basis of our proposed BART determinations are within a range found to be 

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guidelines, which recommend that “[a] reasonable range would be a range that 

is consistent with the range of cost effectiveness values used in other similar 

permit decisions over a period of time.”87

The LDEQ’s SIP revisions did not provide cost-effectiveness numbers for 

any of the control options it considered. Based on the LDEQ’s failure to include 

those numbers in its SIP, the EPA was not able to compare the instant BART 

determination with the EPA’s previously approved BART determinations. 

According to Environmental Petitioners, this lack of a comparison to prior 

EPA-approved BART determinations amounts to an “unexplained deviation 

from past practice.”88

To bolster this argument, Environmental Petitioners compared the 

EPA’s cost-effectiveness numbers for a scrubber with all of the EPA’s prior 

BART determinations. Environmental Petitioners included a graph of those 

results, which shows that the cost-effectiveness numbers for a scrubber align 

with the EPA’s prior BART decisions. 

The EPA responds that, although in other actions it has stated that 

comparisons to prior BART determinations are helpful, the BART guidelines 

do not require such comparisons. The EPA points to the Final Rule’s 

statements explaining that BART determinations depend on the unique 

 

acceptable in other case.”); 80 Fed. Reg. 18,944, 18,952 (Apr. 8, 2015) (“[T]he cost effectiveness 

. . . is within the range of what we consider to be cost-effective for BART.”).

87 BART Guidelines, 40 C.F.R. part 51, App. Y § IV.D.4.f.

88 See Encino Motorcars, LLC v. Navarro, 136 S. Ct. 2117, 2125–26 (2016); WildEarth 

Guardians v. EPA, 770 F.3d 919, 941 (10th Cir. 2014).

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circumstances of each source and that “[s]ome variation is to be expected 

because SIP actions are highly fact-dependent.”89 The EPA also cites several 

cases holding that states have broad authority to weigh the statutory factors 

and to pick appropriate emission controls.90

The EPA has the better argument on this point. Louisiana has the 

authority to select the appropriate BART emission control. The fact that a 

scrubber more closely aligns with the EPA’s prior BART determinations did 

not preclude Louisiana from choosing low-sulfur coal instead. The guideline 

that Environmental Petitioners cite does not require that BART 

determinations align with the EPA’s prior BART determinations:

You should provide documentation of any unusual circumstances 

that exist for the source that would lead to cost-effectiveness 

estimates that would exceed that for recent retrofits. This is 

especially important in cases where recent retrofits have costeffectiveness values that are within what has been considered a 

reasonable range, but your analysis concludes that costs for the 

source being analyzed are not considered reasonable. (A 

reasonable range would be a range that is consistent with the 

range of cost effectiveness values used in other similar permit 

decisions over a period of time.)91

Although the parties do not explain how low-sulfur coal compares to the 

EPA’s prior BART determinations, the record is devoid of any “unusual 

 

89 82 Fed. Reg. at 60,534–60,535. 

90 See Oklahoma v. EPA, 723 F.3d 1201, 1209 (10th Cir. 2013) (“[S]tates ha[ve] broad 

authority to weigh the statutory factors and make BART determinations.”); see also Ariz. ex 

rel. Darwin v. EPA, 852 F.3d 1148, 1161 (9th Cir. 2017).

91 BART Guidelines, 40 C.F.R. part 51, App. Y § IV.D.4.f.

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circumstances” indicating that low-sulfur coal’s cost-effectiveness estimates 

are out of line with prior BART determinations. Therefore, the guideline 

addressing “similar permit decisions over a period of time” does not apply here. 

iii. Weighing the Statutory Factors and Compliance with 

the BART Guidelines

In making a BART determination, a state “shall take into consideration” 

five factors: (1) the costs of compliance, (2) the energy and nonair quality 

environmental impacts of compliance, (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 that may reasonably be anticipated 

to result from the use of such technology.92 States have discretion as to “the 

weight and significance” of each factor, as well as the appropriate emission 

control that qualifies as BART at a given source.93

In addition to considering those statutory factors, for powerplants with 

generating capacities greater than 750 megawatts, like Nelson and Brame, the 

state’s BART determination “shall be determined pursuant to [the BART] 

guidelines.”94 The BART guidelines state: 

From the alternatives you evaluated . . . we recommend you 

develop a chart (or charts) displaying for each of the alternatives:

(1) Expected emission rate . . . ;

 

92 42 U.S.C. § 7491(g)(2).

93 BART Rule, 70 Fed. Reg. at 39,123; see Oklahoma, 723 F.3d at 1209 (“[S]tates ha[ve] 

broad authority to weigh the statutory factors and make BART determinations.”).

94 42 U.S.C. § 7491 (b)(2)(B); see 40 C.F.R. § 51.308(e)(1)(ii)(B). In its brief, the EPA 

concedes that the BART Guidelines are mandatory at this step. 

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(2) Emissions performance level . . . ;

(3) Expected emissions reductions . . . ;

(4) Costs of compliance—total annualized costs ($), cost 

effectiveness ($/ton), and incremental cost effectiveness 

($/ton), and/or any other cost-effectiveness measures (such 

as $/deciview); 

(5) Energy impacts; 

(6) Non-air quality environmental impacts; and 

(7) Modeled visibility impacts.95

. . . . 

You have discretion to determine the order in which you should 

evaluate control options for BART. Whatever the order in which 

you choose to evaluate options, you should always (1) display the 

options evaluated; (2) identify the average and incremental costs 

of each option; (3) consider the energy and non-air quality 

environmental impacts of each option; (4) consider the remaining 

useful life; and (5) consider the modeled visibility impacts. You 

should provide a justification for adopting the technology that you 

select as the “best” level of control, including an explanation of the 

CAA factors that led you to choose that option over other control 

levels.96

The LDEQ’s explanation of its determination that low-sulfur coal was 

BART for Nelson states:

In the Entergy BART five-factor SO2 analysis for the Unit 6 

Boiler, a number of emission reduction controls were reviewed. 

The reviewed controls included the use of a lower sulfur coal, DSI, 

enhanced DSI, dry flue-gas desulfurization (FGD) and wet FGD. 

LDEQ has reviewed and weighed the five factors carefully; after a 

review of the information that Entergy and EPA provided, LDEQ 

 

95 BART Guidelines, 40 C.F.R. part 51, App. Y § IV.E.1 (emphasis added).

96 Id. (emphasis added).

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has concluded that the appropriate BART for this facility is to 

establish an emission limit of .6 lbs/MMBtu based on a 30 day 

rolling average as defined in the AOC (see Appendix D). While 

additional visibility benefits may be available through the use of 

FGD, the lower sulfur coal option results in visibility benefits at a 

lower annual cost. Along with the extra cost, FGD use results in 

additional waste spent due to spent reagent and has some power 

demands to run the equipment. LDEQ believes, at present, that 

the use of lower sulfur coal presents the appropriate SO2 control 

based on consideration of economics, energy impacts, non-air 

quality environmental impacts, and impacts to visibility.

In the 2017 Final Rule, the EPA approved this explanation as compliant 

with the Clean Air Act. The Final Rule relied on the language in the revised 

SIP, which states that “LDEQ has weighed the five factors carefully” and 

reached its decision “after a review of both Entergy’s and the EPA’s 

information.”97 Referring to this statement, the Final Rule concludes: 

This indicates that the State reviewed the information it received 

from both Entergy and the EPA, and thus had adequate 

information upon which to base its determination. After reviewing 

the relevant information contained in LDEQ’s SIP, we determined 

that the State’s SIP meets the requirements of the Act and the 

applicable regulations and guidance.98

Environmental Petitioners challenge the EPA’s approval of the LDEQ’s 

explanation of its BART determination. Those Petitioners contend that, 

because the LDEQ failed to discuss how it weighed each statutory factor, it did 

not comply with the BART guidelines and therefore did not satisfy its 

 

97 Final Rule, 82 Fed. Reg. at 60,532.

98 Id.

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obligations under the Clean Air Act. They point to the LDEQ’s failure to 

evaluate (1) the existing pollution controls at Nelson, (2) the remaining useful 

life of Nelson, (3) the cost-effectiveness of pollution controls, and (4) the 

visibility benefits of pollution controls. 

In response, the EPA concedes that Louisiana “could have expanded its 

discussion of its decisionmaking process.” The EPA nonetheless maintains that 

it “determined that the path Louisiana took in weighing the five factors and 

reaching its BART determination could be reasonably discerned from the 

record before it.” The EPA’s and Industry Respondents’ arguments focus on the 

fact that Entergy’s and the EPA’s analyses—which were included as 

appendices to the SIP revisions—did the appropriate analysis and considered 

all the factors.

Environmental Petitioners are correct that the LDEQ’s explanation did 

not discuss the Clean Air Act’s factors of (1) the existing controls at Nelson, (2) 

Nelson’s remaining useful life, or (3) the BART guidelines factor of “costeffectiveness.”

On the “existing control” factor, the LDEQ’s failure to discuss the 

existing controls at Nelson highlights a factual dispute between the parties. 

Environmental Petitioners maintain that low-sulfur coal is already in use at 

Nelson and has been since 2015. The EPA’s June 2017 technical support 

document states that “beginning in the Spring of 2015, Entergy began 

purchasing coals with lower sulfur contents that occur in a tighter range in 

comparison to those purchased in the past.”

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Regarding the “remaining useful life” factor, the LDEQ’s explanation of 

its BART determination does not mention or address that factor. Neither does 

the LDEQ’s explanation mention “cost-effectiveness.” The BART guidelines 

require states to consider the cost-effectiveness of potential control options.99

Those guidelines define that term as follows: 

Cost-effectiveness, in general, is a criterion used to assess the 

potential for achieving an objective in the most economical way. 

For purposes of air pollutant analysis, “effectiveness” is measured 

in terms of annualized control costs. We recommend two types of 

cost-effectiveness calculations - average cost effectiveness, and 

incremental cost effectiveness.

. . . 

Average cost effectiveness means the total annualized costs of 

control divided by annual emissions reductions (the difference 

between baseline annual emissions and the estimate of emissions 

after controls), using the following formula . . . .100

Louisiana’s explanation mentions “annual cost” but does not mention 

“cost-effectiveness.” As the BART guidelines explain, annual cost and costeffectiveness are different: Annual cost is the annualized capital cost for a 

control; cost-effectiveness is the annual cost of a control divided by the annual 

emissions reductions of that control. In general, the least effective control 

technology will almost always have the lowest absolute (or annual) cost. In 

contrast, the most effective control technology will often have the highest 

 

99 See BART Guidelines, 40 C.F.R. part 51, App. Y § IV.D.4.b; see also id. § IV.E.1.

100 Id. § IV.D.4.(b)–(c).

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absolute (or annual) cost.101 Based on this distinction, the BART guidelines 

impose cost-effectiveness, i.e., the cost per ton of pollution removed—instead of 

annual cost—as the relevant consideration.

* * *

The Clean Air Act requires states to consider five statutory factors when 

making a BART determination. The EPA then must approve or disapprove 

that determination. Our role is to decide whether the EPA was arbitrary and 

capricious in approving Louisiana’s SIP.

The LDEQ’s key statements on this issue are that (1) it “reviewed and 

weighed the five factors carefully,” (2) it reached its decision after “review[ing] 

. . . the information that Entergy and EPA provided,” and (3) the “lower sulfur 

coal option results in visibility benefits at a lower annual cost.” 

The LDEQ’s short explanation is lacking in several respects. It did not 

(1) provide numbers supporting its conclusions, (2) address or reconcile the 

EPA’s criticism of Entergy’s analyses, (3) compare the costs or benefits of each 

control option, or (4) discuss Nelson’s existing controls, remaining useful life, 

or the cost-efficiency of the potential control options. The EPA’s and Industry 

Respondents’ primary contention is that because Entergy and the EPA did the 

appropriate analysis and weighed the statutory factors—and the LDEQ said it 

reviewed those analyses and included them as appendices—the LDEQ 

appropriately weighed the factors. The parties’ briefing on how Louisiana 

weighed the factors focuses almost entirely on the analyses that the EPA and 

 

101 See Proposed Rule, 82 Fed. Reg. at 32,298–32,299.

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Entergy submitted. None of the briefs, however, cite any place in the record in 

which the LDEQ discusses all five statutory factors.

Moreover, the parties rely on the LDEQ’s statement that it considered 

the analyses that Entergy and the EPA provided before making its 

determination, as well as the fact that those analyses were included as 

appendices to the SIP revisions. But the LDEQ expressly disavowed

“agree[ing] with,” “adopt[ing],” or “incorporat[ing]” any of Entergy’s or the 

EPA’s calculations in its revised SIP: 

LDEQ submits these comments in response to certain statements 

in the preamble [of the 2017 Proposed Rule] that matters were 

“adopted and incorporated” into the LDEQ SIP revision. LDEQ 

places all documents and information submitted to it in connection 

with the development of the SIP in an administrative record . . . . 

However, placement in the record does not indicate that LDEQ 

agrees with or has “adopted” positions, conclusions, or decisions, 

nor has “incorporated” them into the SIP revision submitted to the 

EPA. The final SIP document and any enforceable conditions 

included therein encompass the final decision by LDEQ.

Based on this express disavowal, we cannot conclude that the analyses Entergy 

and the EPA submitted to the LDEQ were incorporated into the terms of 

Louisiana’s revised SIP.

And, in contrast to the BART guidelines’ detailed instructions for making 

a BART determination, the LDEQ’s explanation of its BART determination for 

Nelson provides hardly any details. The guidelines recommend “always” 

identifying the average and incremental costs of each option, but the LDEQ 

provided neither specific numbers supporting that decision nor a comparison 

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of the costs and estimated visibility benefits for each control option. Unlike the 

detailed analyses that the EPA and Entergy submitted—which did provide cost 

and pollution-control estimates for each control option—the LDEQ simply 

stated that low-sulfur coal had an unspecified “lower annual cost.” 

Despite these shortcomings, we conclude that the EPA’s approval of 

Louisiana’s BART determination was not arbitrary and capricious.102 The 

standard of review is narrow and highly deferential. Our review is limited to 

“whether the decision was based on a consideration of the relevant factors and 

whether there has been a clear error of judgment.”103

There was a plethora of record evidence—the analyses that Entergy 

submitted to the LDEQ—to support the BART determination. There was also 

considerable record evidence—the analyses that the EPA submitted—

undermining that determination. The LDEQ stated that (1) it considered both 

of these analyses when it made its BART determination and (2) it “reviewed 

and weighed the five factors carefully.” Although the LDEQ could have offered 

a more thorough explanation of its reasoning, its assurance that it weighed the 

five factors carefully indicates that its decision “rest[ed] ‘on a consideration of 

the relevant factors’”104 and that the agency did not “entirely fail[] to consider 

 

102 We note that this would be a much easier case if the LDEQ had (a) explained the 

weight it afforded to any of the five factors, (b) expressly compared the costs of each option, 

or (c) simply reproduced Entergy’s charts and numbers in the revised SIP. 103 10 Ring Precision, Inc., 722 F.3d at 723 (quoting Motor Vehicle Mfrs. Ass’n, 463 

U.S. at 43).

104 Michigan, 135 S. Ct. at 2706 (quoting Motor Vehicle Mfrs. Ass’n, 463 U.S. at 43).

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an important aspect of the problem.”105 The EPA’s approval of that 

determination was not arbitrary and capricious.106

2. Louisiana’s Long-Term Strategy and Reasonable Progress 

Goals

The second part of Environmental Petitioners’ challenge is to the EPA’s

approval of Louisiana’s long-term strategy and reasonable-progress goals. The 

Clean Air Act requires states to adopt long-term strategies “for making 

reasonable progress” toward the national visibility goal.107 Louisiana’s 2008 

SIP included reasonable progress goals and a long-term strategy, but the 2017 

SIP revisions did not. 

Environmental Petitioners contend that the 2017 SIP revisions did not 

comply with the Act because they did not address Louisiana’s long-term 

 

105 Motor Vehicle Mfrs. Ass’n, 463 U.S. at 43.

106 Environmental Petitioners cite no authority, and we are aware of no authority, 

demanding that Louisiana prefer the EPA’s analyses to those provided by industry. Indeed, 

in a highly technical area such as cost-effectiveness of various control options, a private firm 

may well provide more accurate data inputs regarding a specific proposal at the specific plant 

it operates. To take one example, the EPA and Entergy disagreed about the cost-effectiveness 

of low-sulfur coal. Entergy calculated it to cost $597 per ton of pollutant removed while the 

EPA calculated $2,957 per ton. That discrepancy was based on Entergy’s reliance on 

proprietary data, its contingency value, and its consideration of costs that the EPA does not 

allow in its control cost manual. See 82 Fed. Reg. at 32,298. The technical analyses used 

different approaches and presented different strengths and weaknesses. Louisiana 

scrutinized Entergy’s analysis and chose to embrace it. It was free to do so. A state has “wide 

discretion” in formulating its SIP and “may select whatever mix of control devices it desires” 

so long as national standards are met. Union Elec. Co. v. EPA, 427 U.S. 246, 250, 266 (1976). 

That is why Congress tied the EPA’s hands during SIP approval: “the Administrator shall 

approve such submittal as a whole if it meets all of the applicable requirements of this 

chapter.” 42 U.S.C. § 7410(k)(3) (emphasis added). 107 42 U.S.C. § 7491(b)(2)(A)–(B).

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strategy, set out reasonable progress goals, or impose emission controls at any 

additional “reasonable progress sources,” such as the Dolet Hills powerplant. 

Dolet Hills, which is the largest single source of SO2 emissions in Louisiana, is 

a non-BART-eligible EGU powerplant that could be subject to emissions 

controls as a reasonable progress source. 

The EPA points to its actions in 2012 on this issue, including a proposed 

rule and a final rule (“the 2012 Proposed Rule” and “the 2012 Final Rule”), 

which included a “partial disapproval” and “partial limited approval” of 

Louisiana’s 2008 SIP.108 It insists that Louisiana’s reasonable progress goals 

and long-term-strategy obligations were approved as part of the 2012 Final 

Rule’s “partial limited approval.” According to the EPA, the 2012 resolution of 

this issue time-bars the Environmental Petitioners challenge.

The EPA is correct. Louisiana was not required to re-do its reasonable 

progress analysis or re-evaluate the reasonable progress sources because that 

part of its 2008 SIP was approved and made effective by the 2012 Final Rule. 

The 2012 Final Rule “finaliz[ed] a partial limited approval and a partial 

disapproval of a revision to the Louisiana SIP submitted . . . on June 13, 

2008.”109

We resolve this issue based on the distinction between “partial” and 

“limited” approvals. A “limited approval” is used when some parts of a SIP do 

not meet the Clean Air Act’s requirements, but the EPA concludes that “the 

 

108 77 Fed. Reg. 11,839, 11,840 (Feb. 28, 2012) (“2012 Proposed Rule”); 2012 Final 

Rule, 77 Fed. Reg. at 39,425.

109 2012 Final Rule, 77 Fed. Reg. at 39,426. 

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submittal as a whole” has a “strengthening effect” on the SIP.110 In a “limited 

approval,” the provisions of a SIP that are “limitedly approved,” including any

provisions that do not comply with the Act, are incorporated into the SIP and 

go into effect. In contrast, in a “partial approval/disapproval,” the partially 

approved parts of a submittal go into effect, and the disapproved parts do not. 

The 2012 Final Rule contained a “partial limited approval” and a “partial 

disapproval.” This sentence from the Final Rule addresses the parts of the SIP 

that were included in the “limited approval”:

EPA grants a partial limited approval of the LA RH SIP 

submittal for meeting the requirements of: 51.308(d), for the core 

requirements for regional haze SIPs, except for the requirements 

of 51.308(d)(3); 51.308(f), for the commitment to submit 

comprehensive periodic revisions of regional haze SIPs; 51.308(g), 

for the commitment to submit periodic reports describing progress 

towards the reasonable progress goals (RPGs); 51.308(h), for the 

commitment to conduct periodic determinations of the adequacy of 

the existing regional haze SIP; and 51.308(i), for coordination with 

state and Federal Land Managers.111

All provisions of the 2008 SIP referenced in this sentence were “limitedly 

approved,” including the provisions after “except,” which did not meet the Act’s 

requirements. Through this “partial limited approval,” the EPA concluded that 

all of the provisions referenced in that sentence would take effect because the 

submittal “as a whole . . . strengthen[ed] the Louisiana SIP” and the EPA did 

 

110 Processing of State Implementation Plan Revisions at 2–3, the EPA Memorandum 

from John Calcagni (July 9, 1992), https://www.epa.gov/sites/production/files/2015-

07/documents/procsip.pdf. 111 2012 Final Rule, 77 Fed. Reg. at 39,426.

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not specifically “address[] [them in the] partial disapproval.”112 Those

referenced provisions therefore became effective when the EPA issued the 2012 

Final Rule. 

The following sentence in the 2012 Final Rule addresses the provisions 

of the SIP that were “partially disapproved”:

However, . . . the EPA is also partially disapproving the LA 

RH SIP submittal because it does not include fully approvable 

measures for meeting the requirements of 40 CFR 51.308(d)(3), 

long-term strategy for regional haze as it relies on deficient nonEGU BART analyses; and 51.308(e), BART requirements for 

regional haze visibility impairment with respect to emissions of 

visibility impairing pollutants from four non-EGUs.113

Because the provisions referenced in this sentence were “partially 

disapproved,” they did not go into effect when the EPA issued the 2012 Final 

Rule. So, after the EPA issued the 2012 Final Rule, Louisiana was required to 

re-do only the parts of its SIP referenced in that partial disapproval. Those 

were (1) the parts of 2008 SIP’s long-term strategy that “relie[d] on deficient 

non-EGU BART analyses” and (2) the parts of the 2008 SIP’s long-term 

strategy that involved BART requirements “from four non-EGUs.” These were 

the only two provisions that did not go into effect and needed to be remedied 

by Louisiana. 

Other than these two deficiencies, the 2012 Final Rule “result[ed] in 

approval of all of the remaining elements of Louisiana’s [2008 Regional Haze] 

 

112 Id. at 39,425. 

113 Id. at 39,426. 

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SIP.”114 That included Louisiana’s reasonable progress analysis and long-term 

strategy.

Environmental Petitioners focus on one of the EPA’s responses to a 

comment. In the first part of that response, the EPA elaborates on the partial 

disapproval and identifies the two deficiencies that Louisiana needed to 

address in its SIP revisions. 

[1] Louisiana must submit and the EPA must approve a 

revised SIP submittal to address . . . BART for EGUs to cure the 

deficiencies in the SIP resulting from the remand of CAIR. . . . [2] 

Louisiana must also submit revisions sufficient to cure the 

deficiencies in the non-EGU BART determinations.115

Environmental Petitioners rely on a different sentence in that response

to contend that Louisiana was required to re-do its evaluation of the non-BART 

powerplants that qualify as reasonable progress sources. They point to this 

sentence in the EPA’s response: “Louisiana must consider whether EGUs 

previously covered by the CAIR, whether subject to BART or not, should be 

controlled to ensure reasonable progress to meet the State’s long-term 

strategies.”116 However, in context, that sentence simply restates Louisiana’s 

overall obligations under the Clean Air Act. The response reads in full as 

follows:

We have evaluated the LA RH SIP submittal as a whole and 

at this time we are taking final action on all elements of the LA 

RH SIP submittal that were not addressed in the national Better-

 

114 Id. at 39,426.

115 Id. at 39,427.

116 Id.

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than-BART rule. Louisiana must consider whether EGUs 

previously covered by the CAIR, whether subject to BART or not, 

should be controlled to ensure reasonable progress to meet the 

State’s long-term strategies. However, insofar as Louisiana’s LTS 

and RPGs are affected by the remand of CAIR, those issues are 

addressed in the national Better-than-BART rulemaking and are 

outside the scope of this action on the remainder of the LA RH SIP.

Also, the CAA expressly provides authority to the EPA to partially 

approve and partially disapprove a SIP revision. 42 U.S.C. 

7410(k)(3). The EPA has adopted the partial approval approach 

numerous times in SIP actions across the nation over the last 

twenty years. Partial approval and partial disapproval is 

appropriate here because the EPA has determined that a portion 

of Louisiana’s RH SIP meets regional haze requirements and a 

portion of it does not. . . . Therefore, Louisiana must submit and 

the EPA must approve a revised SIP submittal to address both 

NOX and SO2 BART for EGUs to cure the deficiencies in the SIP 

resulting from the remand of CAIR. Louisiana may elect to rely on 

the Transport Rule for NOX BART for EGUs in that 

submittal. However, because Louisiana is not covered under the 

Transport Rule for SO2, the State must submit source-specific 

SO2 BART evaluations for the subject-to-BART EGUs in 

Louisiana. As discussed further in our responses to several 

comments below, Louisiana must also submit revisions sufficient 

to cure the deficiencies in the non-EGU BART determinations.117

This context, including the lack of an express directive to “submit” a new 

long-term strategy or to impose controls at additional reasonable progress 

sources, confirms that the 2012 Final Rule approved Louisiana’s reasonable 

progress goals and selection of reasonable progress sources. Additionally, the 

 

117 2012 Final Rule, 77 Fed. Reg. at 39,427 (emphasis added).

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2012 Final Rule does not mention the single source Louisiana identified as a 

reasonable progress source, Big Cajun II. In three separate parts of the 2012 

Final Rule, the EPA identifies the partially disapproved parts and directs 

Louisiana to address only those provisions.118 If the EPA had intended to 

disapprove Louisiana’s reasonable progress goals, long-term strategy, or 

identification of reasonable progress sources in this response, it would have 

included those provisions of the 2008 SIP in the “partial disapproval” sentence.

Because Louisiana’s reasonable progress goals, long-term strategy, and 

evaluation of reasonable progress sources were included in the 2012 Final 

Rule’s “partial limited approval” of Louisiana’s 2008 SIP, we reject 

Environmental Petitioners’ challenge on this issue.

ii. Notice and Comment

Environmental Petitioners alternatively claim that the EPA violated the 

APA’s notice and comment requirements. 

Under the APA, “notice of proposed rulemaking shall be published in the 

Federal Register,” and “shall be accompanied by a statement of its basis and 

purpose. . . . The statement of basis and purpose shall include a summary of . 

. . the major legal interpretations and policy considerations underlying the 

proposed rule.”119

Environmental Petitioners contend that the EPA did not include its 

reasoning addressing Louisiana’s reasonable progress analysis in the July 

 

118 Id. at 39,426–39,427, 39,435. 

119 42 U.S.C. § 7607(d)(3). 

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2017 Proposed Rule. They assert that the EPA’s inclusion of additional 

reasoning on that issue in the December 2017 Final Rule amounted to a “major 

legal interpretation.”

In the 2017 Proposed Rule, the EPA did not discuss Louisiana’s 

reasonable progress analysis, long-term strategy, or evaluation of reasonable 

progress sources. Environmental Petitioners commented on the 2017 Proposed 

Rule’s failure to address Louisiana’s reasonable progress analysis and longterm strategy, and the EPA responded to that comment in the 2017 Final Rule. 

In its response to Environmental Petitioners’ comments on the 2017 Final 

Rule, the EPA directed Environmental Petitioners to the 2012 Final Rule. The 

agency explained that it had already approved Louisiana’s reasonable progress 

analysis, long-term strategy, and evaluation of reasonable progress sources.120

We conclude that this explanation is not a major legal interpretation or 

policy consideration underlying the 2017 Proposed Rule that required 

additional notice and comment. Rather, it is merely a response to a comment 

that pointed the Environmental Petitioners to the agency’s earlier resolution 

of the issue in the 2012 Final Rule. 

* * *

In short, the EPA’s 2012 Final Rule, which “limitedly approved” most of 

Louisiana’s 2008 SIP, did not require Louisiana to re-do its reasonable 

progress goals or its long-term strategy in its 2017 SIP revisions. Neither did 

 

120 See 82 Fed. Reg. at 60,539–60,540.

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the EPA’s response to Environmental Petitioners’ 2017 comment “reopen” the 

issue121 or violate the APA’s notice and comment provision.

Environmental Petitioners’ petition is denied.

B. The Industry Petitioners’ Petition 

In contrast to Environmental Petitioners’ challenge to Louisiana’s 

selection of emission controls to satisfy BART (step three of the BART 

analysis), Industry Petitioners challenge Louisiana’s determinations that 

Nelson and Brame are “subject to BART” at all (step two of the BART analysis). 

Industry Petitioners object to the EPA’s approval of Louisiana’s “subject to 

BART” determinations, which relied on the “CALPUFF” model. They also 

challenge the EPA’s reliance on its own “CAMx” modeling (on which Louisiana 

did not rely) to approve Louisiana’s SIP. 

The Clean Air Act states that a source is “subject to BART” if it “emits 

any air pollutant which may reasonably be anticipated to cause or contribute 

to any impairment of visibility” in a Class I area.122 Under the BART 

guidelines, a 1.0 deciview change from an individual source “causes” visibility 

impairment, whereas a 0.5 deciview change from an individual source 

“contributes” to visibility impairment.123 Under some circumstances, states 

 

121 See West Virginia v. EPA, 362 F.3d 861, 872 (D.C. Cir. 2004) (“‘[W]hether an agency 

has in fact reopened an issue, explicitly or implicitly,’ depends on the ‘entire context of the 

rulemaking including all relevant proposals and reactions of the agency.’” (citation omitted)). 

122 42 U.S.C. § 7491(b)(2)(A).

123 BART Rule, 70 Fed. Reg. at 39,120. 

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may set a lower threshold for sources that “contribute” to visibility 

impairment.124

In the BART guidelines, the EPA adopted CALPUFF as the preferred 

model for making “subject to BART” determinations.125 The EPA recently 

removed CALPUFF as a “preferred” model for other air-quality modeling 

applications under the Clean Air Act, but retained CALPUFF as a preferred 

model for making “subject-to-BART” determinations.126

The LDEQ reviewed CALPUFF and CAMx modeling results that 

Entergy, Cleco, and the EPA submitted to the department. In the LDEQ’s 

February and June 2017 SIP revisions, it determined that Nelson and two 

units at Brame were “subject to BART.” Louisiana relied on CALPUFF 

modeling to determine that Nelson and Brame exceeded the 0.5 deciview 

threshold. The LDEQ acknowledged, but did not rely on, the CAMx modeling 

that the parties submitted. The LDEQ stated that it did “not have the expertise 

with which to review [the CAMx] model runs.” And, in its amicus brief, the 

LDEQ states that it still does not have the technical expertise to review CAMx

modeling.

 

124 Id. at 39,120–39,121.

125 BART Guidelines, 40 C.F.R. part 51, App. Y, III.A.3. See 69 Fed. Reg. 25,184, 25,194 

(May 5, 2004) (“We are proposing that a CALPUFF assessment of an individual source be 

used as the preferred approach for determining whether a BART-eligible source may be 

exempt from BART.”).

126 82 Fed. Reg. 5,182, 5,196 (Jan. 17, 2017) (“[T]his final action does not affect the 

EPA’s recommendation that states use CALPUFF to determine the applicability and level of 

best available retrofit technology in regional haze implementation plans.”).

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In a May 2017 proposed rule, the EPA proposed to approve the “subject 

to BART” determination for Brame.127 In the July 2017 Proposed Rule, it 

proposed to approve Louisiana’s “subject to BART” and BART 

determinations.128 Industry Petitioners submitted comments on those 

proposed rules (1) objecting to the LDEQ’s reliance on CALPUFF and (2) 

criticizing the EPA’s reliance on its own CAMx modeling. In the instant 2017 

Final Rule, the EPA responded to those comments and approved the LDEQ’s 

determination that Nelson and Brame have visibility effects greater than 0.5 

deciviews at Class I areas and are therefore “subject to BART.”129

Here, Industry Petitioners contend that the EPA’s approval of 

Louisiana’s “subject to BART” determinations at Nelson and Brame was 

arbitrary and capricious. The EPA and Environmental Respondents respond 

that we lack jurisdiction to consider Industry Petitioners’ challenge. They also 

insist that (1) Louisiana permissibly relied on the CALPUFF model in making 

its BART determination and (2) the EPA was not arbitrary and capricious in 

considering its own CAMx modeling.

As we shall explain in greater detail, we conclude that (1) we have 

jurisdiction and (2) the EPA’s approval of Louisiana’s reliance on the 

CALPUFF model was not arbitrary and capricious. 

 

127 82 Fed. Reg. 22,936, 22,941 (May 19, 2017).

128 82 Fed. Reg. 32,294, 32,296 (July 13, 2017).

129 Final Rule, 82 Fed. Reg. at 60,520; id. at 60,525–60,526 (response to comments on 

modeling).

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1. Jurisdiction

a. Environmental Respondents’ Jurisdictional Arguments 

Environmental Respondents contend that parts of Industry Petitioners’ 

challenge address the 2005 BART guidelines rather than the 2017 Final Rule. 

Environmental Respondents assert that this court lacks jurisdiction over the

parts of the Industry Petitioners’ claim that address CALPUFF’s use of 24-

hour actual emissions and natural background conditions. According to 

Environmental Respondents, these are complaints about the policies 

underlying the 2005 BART guidelines, policies to which the EPA responded 

when it promulgated those guidelines. According to Environmental 

Respondents, these concerns should have been raised (1) in the D.C. Circuit 

and (2) within 60 days after those guidelines were published in the Federal 

Register.130

Environmental Respondents liken this case to American Road & 

Transportation Builders Ass’n v. EPA, 705 F.3d 453 (D.C. Cir. 2013), in which 

the D.C. Circuit considered a challenge to the EPA’s approval of a state’s SIP 

in 2011. In that case, the EPA’s approval of a SIP relied on a rule that the 

agency had issued in 1994.131 The petitioner did not claim that the state had 

misapplied the EPA’s rule; rather, it contended that the policies announced in 

the 1994 rule were unlawful.132 Because that challenge was to the 1994 rule—

rather than to the 2011 SIP approval—the D.C. Circuit concluded that it lacked 

 

130 42 U.S.C. § 7607(b)(1).

131 705 F.3d at 454–55.

132 Id. at 456. 

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jurisdiction because the challenge was time-barred under the Clean Air Act’s 

60-day period for filing petitions for review.133

Environmental Respondents maintain that Industry Petitioners’ claims 

objecting to CALPUFF’s assumptions are similarly time-barred. They note 

that Industry Petitioners have an alternative route to recourse under the 

Clean Air Act’s provision that provides for reconsideration of a rule if a 

petitioner can demonstrate that it was impracticable to raise an issue during 

the public comment period.134

The jurisdictional issue here is similar to the one that the D.C. Circuit 

considered in American Road & Transportation Builders. That court held that 

the petitioner’s challenge was to the underlying the EPA rule rather than to 

the EPA’s later approval of a SIP based on the standards set out in that

underlying rule. The D.C. Circuit dismissed that challenge to a SIP approval 

because it was “duplicative of arguments the agency had already rejected” 

many years earlier.135 The court explained that “[t]here would be no pressure 

to challenge regulations within the 60-day period after their promulgation if 

any petitioner could simply wait to test the substance of those regulations once 

the EPA applies them, for example, in an approval of a state SIP revision—as 

[the petitioner] has attempted to do here.”136

 

133 Id. at 458.

134 See 42 U.S.C. § 7607(d)(7)(B).

135 Am. Road & Transportation Builders Ass’n, 705 F.3d at 456.

136 Id. at 458.

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Similarly, in the instant petition for review, Industry Petitioners 

challenge the CALPUFF model based on its use of 24-hour actual emissions

and natural background conditions. The EPA expressly rejected these 

arguments when it adopted CALPUFF as the preferred model at the time in 

2005 that it issued the BART guidelines.137

But, unlike American Road & Transportation Builders, the BART 

guidelines at issue here recommend—but do not require—that states use 

CALPUFF.138 Louisiana could have picked a different model. Because Industry 

Petitioners challenge Louisiana’s choice to use CALPUFF modeling instead of 

a different model, Industry Petitioners’ challenge is properly viewed as a 

challenge to the application of the BART guidelines rather than a challenge to 

the those guidelines themselves. Louisiana had the option to pick a different 

model, so the parts of Industry Petitioners’ challenge addressing CALPUFF’s 

flaws are not barred by the Clean Air Act’s 60-day statute of limitations.

b. The EPA’s Jurisdictional Arguments

The EPA maintains that, after actively participating in Louisiana’s SIPdevelopment process, the Industry Petitioners should have sought judicial 

 

137 BART Guidelines, 40 C.F.R. part 51, App. Y III.A.3 (“We recommend that States 

use the 24 hour average actual emission rate from the highest emitting day of the 

meteorological period modeled.”).

138 BART Rule, 70 Fed. Reg. at 39,123 (“The use of other models and techniques to 

estimate if a source causes or contributes to visibility impairment may be considered by the 

State, and the BART guidelines preserve a State’s ability to use other models.”).

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review of Louisiana’s modeling decisions in state court based on a Louisiana 

statute that allows for review of state rules and regulations.139

This argument is unavailing. Industry Petitioners challenge the EPA’s 

approval of Louisiana’s SIP, not the underlying state action. Although 

Industry Petitioners might also have been able to challenge Louisiana’s 

process for developing its SIP in state court, the Clean Air Act expressly 

provides Industry Petitioners the opportunity to petition this court for review 

of the EPA’s actions.140

2. CALPUFF Modeling

“A reviewing court must be ‘most deferential’ to the agency where, as 

here, its decision is based upon its evaluation of complex scientific data within 

its technical expertise.”141 And “because ‘a model is meant to simplify reality 

in order to make it tractable,’ it is no criticism of a model ‘that it does not fit 

every application perfectly.’”142

 

139 See La. R.S. § 49:963(a)(1)).

140 42 U.S.C. § 7607(b)(1).

141 BCCA Appeal Grp. v. EPA, 355 F.3d 817, 824 (5th Cir. 2003) (quoting Baltimore 

Gas & Elec. Co. v. NRDC, 462 U.S. 87, 103 (1983)). The D.C. Circuit, setting out a similar 

standard, has described this as “extreme deference”:

[W]e will “give an extreme degree of deference to the agency when it is 

evaluating scientific data within its technical expertise.” . . . Furthermore, “we 

must defer to the agency’s decision on how to balance the cost and complexity

of a more elaborate model against the oversimplification of a simpler model.” 

. . . We will “reverse only if the model is so oversimplified that the agency’s 

conclusions from it are unreasonable.”

West Virginia, 362 F.3d at 871 (citations omitted).

142 Ass’n of Battery Recyclers, Inc. v. EPA, 308 F.3d 1047, 1063 (D.C. Cir. 2000) (citation 

omitted).

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Despite the significant deference we afford to decisions involving 

analysis of scientific data within an agency’s technical expertise, Industry 

Petitioners maintain that the EPA’s approval of Louisiana’s CALPUFF 

modeling was arbitrary and capricious. They first point to CALPUFF’s 

shortcomings as a model, including that it (1) is unreliable at predicting 

visibility impacts at locations farther than 300 km from an emission source, (2) 

tends to overestimate visibility impacts, (3) uses “overly simplistic” 

assumptions, and (4) has a high margin of error. They next contend that the 

EPA’s reliance on its own CAMx modeling was improper because the Clean Air 

Act does not give the EPA authority to cure a deficient SIP. Finally, even 

assuming that the EPA could rely on its own CAMx modeling, Industry 

Petitioners take issue with technical flaws in the EPA’s CAMx modeling, 

including that model’s: (1) use of “24-hour maximum emission rates” instead 

of “actual emission rates,” (2) reliance on “absolute maximum modeled 

concentrations” instead of “relative response factors,” and (3) deficient 

performance on a “model performance evaluation.”

i. Distance Limitations

Industry Petitioners contend that the CALPUFF model used at Nelson 

and Brame exceeded that model’s distance limitations and was inconsistent 

with the EPA’s prior determination that CALPUFF is unreliable when 

assessing visibility impacts from sources more than 300 km from a Class I 

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area.143 Nelson is 425 km from Breton and 460 km from Caney Creek; Brame 

is 422 km from Breton and 352 km from Caney Creek. 

Industry Petitioners cite a 1998 statement from the EPA’s Interagency 

Workgroup on Air Quality Modeling (“IWAQM”) that “there are serious 

conceptual concerns with the use of puff dispersion [models like CALPUFF] for 

very long-range transport (300 km and beyond).” In a 2003 final rule, IWAQM 

concluded that the “CALPUFF dispersion model . . . performed in a reasonable 

manner . . . so long as the transport distance was limited to less than 

300km.”144 According to Industry Petitioners, because CALPUFF does not 

perform “in a reasonable manner” at distances greater than 300 km, CALPUFF 

may not be used to determine that sources at such distances may “reasonably

be anticipated” to cause or contribute to visibility impairment. 

Industry Petitioners next point to several regional haze actions in which 

the EPA has stated that it has concerns about using CALPUFF at distances 

greater than 300 km. They rely on the Arkansas Regional Haze Federal 

Implementation Plan, the New Mexico Regional Haze SIP, and the EPA’s 

statement defending its reliance on CAMx for Texas’s and Oklahoma’s regional 

haze SIPs.145

 

143 Industry Petitioners raise the same concerns they raised in their comments on the 

Proposed Rule. 144 68 Fed. Reg. 18,458 (Apr. 15, 2003). 

145 Arkansas Regional Haze Federal Implementation Plan, 81 Fed. Reg. 66,332, 66,394 

(Sept. 27, 2016) (“[T]here are concerns in using CALPUFF for modeling impacts at distances 

much greater than 300 km from the source . . . .”); New Mexico Regional Haze SIP, 79 Fed. 

Reg. 60,978, 60,983 (Oct. 9, 2014) (“CALPUFF results are less reliable at distances greater 

than 300 km.”).

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Industry Petitioners describe these statements and criticisms of 

CALPUFF as indicative of the EPA’s failure to follow its own guidance and 

past practice. They contend that the Final Rule does not provide a rational 

explanation for this departure. And, although the EPA has stated that 

CALPUFF is permissible at sources farther than 300 km “with some additional 

considerations” such as stack height or size of emissions, Industry Petitioners 

maintain that the EPA did not address these “additional considerations” at 

Nelson and Brame.

The EPA responds that Industry Petitioners overstate and oversimplify 

the BART guidelines and the EPA’s prior actions. The EPA insists, contrary to 

Industry Petitioners’ assertions, that it has never stated that: (1) CALPUFF 

should not be used to model visibility impacts more than 300 km from the 

emissions source, (2) CALPUFF is unable to reliably predict visibility impacts 

at distances greater than 300 km, or (3) CALPUFF is “unreliable” and does not 

perform in a reasonable manner. The EPA also contends that Industry 

Petitioners’ reliance on statements from IWAQM is misplaced, arguing that 

IWAQM’s statements (1) set out guidelines for air quality models under the 

Clean Air Act for purposes other than regional haze analyses and (2) were 

issued in 1998 and 2003, before the EPA issued the BART guidelines in 2005.

The EPA explains that CALPUFF has been used at distances greater 

than 300 km, citing South Dakota’s CALPUFF modeling for sources farther 

than 400 km, and Nebraska’s CALPUFF modeling for sources between 300 and 

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600 km.146 In the EPA’s “Modeling Response to Comments” document, it stated 

that “the EPA and [Federal Land Managers] have utilized CALPUFF results 

in a number of different situations when the range was between 300–450 km 

or more.”147

The EPA also points out that historically, “the use of CALPUFF was 

generally acceptable at 300 km or greater for larger emissions sources with 

elevated stacks.” In its Modeling Response to Comments document, the EPA

expressly stated that Nelson and Brame are “larger emissions sources with 

elevated stacks.” Nelson has three BART-eligible electric generating units that 

have a combined 1200 megawatts of production capacity,148 and Brame has two 

BART-eligible electric generating units with a combined output of 963 

megawatts.149 The EPA’s CALPUFF analysis estimated that both Nelson and 

Brame exceeded the 1.0 deciview threshold for “causing” visibility impairment. 

These high visibility numbers for Nelson and Brame align with the EPA’s 

statement in the BART Rule that it anticipated “that most of these plants are 

predicted to have much higher maximum impacts” than 1.0 deciviews.150

Finally, the EPA maintains that its own CAMx modeling provided 

additional support for the CALPUFF model’s results. The EPA’s CAMx 

 

146 Final Rule, 82 Fed. Reg. at 60,525 n.39.

147 See Final Rule, 82 Fed. Reg. at 60,525 (“As discussed in the Modeling RTC 

document, EPA and FLM representatives have utilized CALPUFF results in a number of 

different situations when the range was between 300-450 km or more.”).

148 Final Rule, 82 Fed. Reg. at 60,522, 60,533. 149 82 Fed. Reg. at 22,944.

150 BART Rule, 70 Fed. Reg. at 39,123.

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modeling showed visibility impairments at Caney Creek from Nelson as high 

as 2.22 deciviews and from Brame as high as 2.83 deciviews.151 According to 

the EPA, such large visibility-impact numbers provide additional support for 

the CALPUFF model’s results. 

We conclude that, although the EPA has “a higher confidence level” in 

CALPUFF modeling at distances under than 300 km, the agency did not act 

arbitrarily and capriciously by using that model at Nelson and Brame. Even 

though Nelson and Brame are farther than 300 km from the protected areas 

at issue here, the use of CALPUFF modeling aligns with the EPA’s acceptance 

of CALPUFF at longer distances for powerplants with larger emissions sources 

with elevated stacks like Nelson and Brame.152

ii. The EPA’s January 2017 Action

Industry Petitioners focus on the EPA’s January 2017 action, which 

removed CALPUFF as the preferred model for long-range air quality 

assessments. For those assessments, the EPA concluded that photochemical 

 

151 Final Rule, 82 Fed. Reg. at 60,526 (“Entergy Nelson has a maximum modeled 

impact of 2.22 dv at Caney Creek, with 31 days out of the 365 days modeled exceeding 0.5 dv, 

and 9 days exceeding 1.0 dv. Similarly, Cleco Brame has a maximum modeled impact of 2.833 

dv at Caney Creek, with 30 days out of a maximum 365 days modeled exceeding 0.5 dv and 

10 days exceeding 1.0 dv.”).

152 Our opinion should not be read to countenance the reliability or accuracy of the 

CALPUFF model in general. Although the EPA maintains that it recommends that states 

continue to use CALPUFF modeling for “subject to BART” determinations based on 

“consistency across and within states in the regional haze program” and because most of the 

modeling for this planning period has already been completed, there is reason to question the 

EPA’s recommendation that states continue using a model that it appears to know is not 

reliable when used at distances such as those involved here.

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grid models like CAMx “are generally most appropriate . . . because they 

provide a spatially and temporally dynamic realistic chemical and physical 

environment for plume growth and chemical transformation.”153 Industry 

Petitioners maintain that the EPA’s 2017 action confirms that states should 

rely on CAMx rather than CALPUFF when making BART determinations, 

because it more realistically simulates the processes involved in haze 

formation.

The EPA’s January 2017 action, however, does not support Industry 

Petitioners’ arguments. The EPA removed CALPUFF as a preferred model for 

other types of Clean Air Act analyses, but the agency expressly confirmed that 

CALPUFF remains a recommended option for BART determinations. “[T]his 

final action does not affect the EPA’s recommendation that states use 

CALPUFF to determine the applicability and level of best available retrofit 

technology in regional haze implementation plans.”154

But the EPA retained CALPUFF as a preferred model for BART 

determinations because of concerns about consistency between the states’ 

BART determinations:

The proposed changes to the Guideline do not affect the EPA’s

recommendation in the 2005 BART Guidelines to use CALPUFF 

in the BART determination process. Given that the overwhelming 

majority of BART determinations have been made using 

CALPUFF, we consider it appropriate for states (or the EPA) to 

continue to use this application for the remaining assessments 

 

153 80 Fed. Reg. 45,340, 45,349 (July 29, 2015), finalized at 82 Fed. Reg. 5,182 (Jan. 

17, 2017).

154 82 Fed. Reg. at 5,196.

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under the current Guideline with approved protocols. This 

approach assures consistency across and within states in the 

regional haze program. In addition, in many instances, the 

modeling of visibility impacts has already been completed even 

though the BART determination process is not yet done. Allowing 

states to continue to rely on CALPUFF avoids additional time and 

expense in developing a new assessment of visibility impacts for a 

SIP initially due in 2007.155

Because CALPUFF remains the BART guidelines’ recommended model, 

the January 2017 action does not undermine the use of CALPUFF for BART 

determinations. Rather, the EPA’s explanations about (1) consistency between 

states, (2) that most of the modeling for this planning period has already been 

completed, and (3) avoiding the “additional time and expense in developing a 

new assessment” support the use of that model here.

iii. Overestimation Bias

Industry Petitioners next object to several technical assumptions 

underlying the CALPUFF model. The most significant of these is CALPUFF’s 

simulation of the transformation of SO2 and NOx emissions into visibilityimpairing sulfates and nitrates. CALPUFF’s simplistic handling of chemical 

processes can result in “a systematic bias in the estimated concentrations and 

visibility impacts,” in other words, an “overestimation bias.” When compared 

with “real-world measurements,” CALPUFF overpredicts the contribution of 

nitrates to visibility impairment. According to Industry Petitioners, a 

comparison between the “real-world” impairment data and the CALPUFF 

 

155 80 Fed. Reg. at 45,350.

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modeling results shows that the CALPUFF modeling here overestimated 

nitrate contributions “by nearly 500%.”

Industry Petitioners cite 2005 guidelines from the Central Regional Air 

Planning Association (“CENRAP”) warning that CALPUFF’s overestimation 

bias may lead to “unwarranted and excessive control of emissions from some 

sources.”156 They maintain that the EPA has not articulated a satisfactory 

explanation for ignoring the technical shortcomings in the CALPUFF model.157

In defending its use of CALPUFF here, the EPA emphasizes the policy 

considerations underlying the BART guidelines. When the EPA proposed the 

BART guidelines that recommended CALPUFF as the preferred model, some 

commenters objected on the same grounds raised here: CALPUFF is unreliable

at long distances, relies on simplified assumptions, and overpredicts visibility 

impairment.158 The EPA responded to those criticisms by describing 

CALPUFF as a “conservative” screening model and stating that “conservatism 

is needed because the purpose of the [subject to BART] test [is] solely to 

determine if a closer look is needed.”159 At this “screening” step, the EPA

emphasized that models should capture the “maximum” or “worst case” 

potential impacts of a source.160

 

156 See Alpine Geophysics, LLC, CENRAP BART Modeling Guidelines, at 3–8 (Dec. 

15, 2005). 

157 10 Ring Precision, Inc., 722 F.3d at 723.

158 BART Rule, 70 Fed. Reg. at 39,126.

159 Id. at 39,123 (“[the EPA] understand[s] the concerns of commenters that the 

chemistry modules of the CALPUFF model are less advanced than some of the more recent 

atmospheric chemistry simulations.”).

160 Id. at 39,123, 39,126. 

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We conclude that the BART guidelines accounted for this 

“overestimation” bias. Those guidelines explain the assumptions underlying 

the CALPUFF model, including the use of “the 98th percentile visibility 

impairment rather than the highest daily impact,” which was meant to 

“exclude roughly 7 days per year from consideration” and “minimiz[e] the 

likelihood that the highest modeled visibility impacts might be caused by 

unusual meteorology or conservative assumptions in the model.” As the EPA

explained in the analysis it submitted to the LDEQ, it “made the decision to 

consider the less conservative 98th percentile primarily because the chemistry 

modules in the CALPUFF model are simplified and likely to provide 

conservative (higher) results for peak impacts.” 

iv. Margin of Error 

Entergy submitted analyses to the EPA that purported to demonstrate 

that Nelson’s CALPUFF-predicted visibility impacts at Caney Creek and 

Breton fell within CALPUFF’s margin of error. According to Industry 

Petitioners, its margin of error at Caney Creek is 1.38 deciviews, and its 

margin of error at Breton is 1.25 deciviews. So, based on Entergy’s CALPUFF 

modeling analysis that calculated Nelson’s baseline visibility impact at 0.703 

deciviews at Caney Creek and 0.77 deciviews at Breton, the Entergy-calculated 

margin of error for CALPUFF would put Nelson below the 0.5 deciview “subject 

to BART” threshold. 

Entergy submitted comments on this issue, relying on a Ninth Circuit 

decision, National Parks Conservation Ass’n v. EPA, 788 F.3d 1134, 1146–47 

(9th Cir. 2015), in which the court concluded that the EPA did not 

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“meaningfully address” a comment about model-predicted visibility 

improvements that were within a model’s margin of error.161 There, the federal 

implementation plan for Montana sought to implement a control that 

CALPUFF predicted would improve visibility by only 0.085 deciview.162 A 

commenter maintained that “an improvement of 0.085 deciview [was] ‘beyond 

the CALPUFF model’s ability to predict with any confidence.’”163 The EPA

responded to that comment, but the court concluded that the response did “not 

meaningfully address [the] comment” because it did not “also suffice as a 

reasoned response regarding how CALPUFF could be relied upon to predict an 

improvement of as little as 0.085 deciviews when PPL offered reasons to think 

that doing so was outside the model’s capabilities.”164

Entergy submitted its “margin of error” comments, which compared that 

case to this one. The EPA addressed Entergy’s comments in its November 2017 

Modeling Response to Comments document. 

Industry Petitioners contend that the EPA’s response to Entergy’s 

comments did not adequately respond to the margin of error issue and 

 

161 722 F.3d at 1146–47.

162 Id. Notably, this small number is significantly smaller than the baseline impact 

values at issue here, which are above 1 deciview for both facilities. 

163 Nat’l Parks Conservation Ass’n, 788 F.3d at 1146–47. 

164 Id. One judge on that panel separately concurred to emphasize the procedural focus

of the court’s holding. “I write separately to underline my understanding that . . . we are not 

impugning the EPA’s use of the CALPUFF model generally. Instead we are requiring a 

sufficiently reasoned response to a particular comment regarding CALPUFF’s usefulness in 

these specific circumstances.” Id. at 1149 (Berzon, J., concurring).

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therefore failed to fulfill the agency’s procedural obligation to consider 

significant comments made by the public.

The EPA responded to this “margin of error” comment as follows: 

The commenter mischaracterizes the Ninth Circuit decision 

regarding the “margin of error” of the model. The commenter 

suggests that the Court agreed that the anticipated visibility 

benefits in that case were within the margin of error of the model. 

This is incorrect. The Ninth Circuit decision did not rule on any 

specific issue related to CALPUFF. Rather, the court ruled on a 

procedural error that the EPA did not respond to the comment 

received regarding the CALPUFF margin of error in its 

rulemaking as required under the law. Here and elsewhere in our 

previous response to comments we address a very similar comment 

with respect to CALPUFF modeling for Arkansas sources, as well 

as the commenter’s analysis claiming to estimate the “margin of 

error.”

We responded to comments concerning a very similar “margin of 

error” analysis in our response to comments and final action for 

Regional Haze in Arkansas. The Trinity analysis discussed in the 

comment above purports to calculate a “margin of error” of the 

CALPUFF modeling for Entergy Nelson. In general, the 

commenter’s analysis adds CALPUFF model results for a specific 

source or sources with CAMx model results and compares this 

value to visibility conditions derived from monitored data at each 

Class I area. This analysis is flawed for many reasons as discussed 

in detail in our Arkansas RTC document that discusses a similar 

analysis performed for Entergy Lake Catherine and fails to 

provide any assessment of the ability of the CALPUFF model to 

evaluate visibility impacts or the degree of visibility improvement 

that may be expected from available control technology to inform 

BART and reasonable progress evaluations. Whether or not the 

modeled visibility impacts or benefits lie below this calculated 

“margin of error” is immaterial to any assessment of whether or 

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not the visibility impairment or benefits from controls can 

reasonably be anticipated to occur. We note that the commenter 

did not provide any spreadsheets or detailed calculations to 

support this analysis, therefore we were unable to fully review and 

respond to the individual calculations or specific methodology 

underlying the presented values in the commenter’s summary 

report and comments. 

As discussed elsewhere in this document, we are confident that 

CALPUFF distinguishes, comparatively, the relative contributions 

from sources such that the differences in source configurations, 

sizes, emission rates, and visibility impacts are well-reflected in 

the model results. We agree with LDEQ that the CALPUFF model 

followed the reviewed protocol is an appropriate tool to evaluate 

visibility impacts and benefits to inform a BART determination. 

Furthermore, our CAMx modeling of coal-fired sources included in 

the LA RH SIP (see Appendix F) further supports the conclusion 

that the Entergy Nelson and Cleco Brame sources are subject to 

BART.

This explanation is fulsome. In it, the EPA (1) cited its responses on the 

same issue in the Arkansas and Texas federal implementation plans (which 

are in the administrative record here), (2) disagreed with the commenter’s 

interpretation of National Parks Conservation Ass’n, (3) criticized the 

commenter’s “calculated margin of error” methodology, (4) disagreed with the 

commenter’s method of combining results from two different models, and (5) 

noted the commenter’s failure to provide the underlying data. Although 

Industry Petitioners might not agree with the conclusion that the EPA

reached, the EPA “meaningfully respond[ed]” to the substance of the comment. 

* * *

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In short, Industry Petitioners contend that CALPUFF uses 

oversimplified and unrealistic assumptions. The EPA agrees in part, but 

insists that those assumptions are based on reasoned policy decisions. 

Given the conflicting technical contentions, we defer to the EPA’s 

approval of Louisiana’s reliance on the CALPUFF model. The EPA’s selection 

of modeling methods to measure visibility impacts is exactly the type of 

decision for which “significant deference” is appropriate.165 Although 

CALPUFF has documented flaws, (1) the BART guidelines continue to 

recommend that model for these determinations,166 (2) the EPA has recently 

directed states to use that model,167 and (3) it “has been used for almost every 

single-source BART analysis in the country.” 

We defer to the EPA’s approval of Louisiana’s reliance on the CALPUFF

model. Industry Petitioners have not carried their “considerable burden” to 

overcome the “presumption of regularity” that we afford to “the EPA’s choice 

of analytical methodology.”168 Because a model “is meant to simplify reality in 

order to make it tractable,” and need not “fit every application perfectly,”169 we 

 

165 See Appalachian Power Co. v. EPA, 135 F.3d 791, 802 (D.C. Cir. 1998) (“Statistical 

analysis is perhaps the prime example of those areas of technical wilderness into which 

judicial expeditions are best limited to ascertaining the lay of the land.”). 

166 BART Guidelines, 40 C.F.R. part 51, App. Y, III.A.3.

167 82 Fed. Reg. 5,182, 5,196 (Jan. 17, 2017) (“[T]his final action does not affect the 

EPA’s recommendation that states use CALPUFF to determine the applicability and level of 

best available retrofit technology in regional haze implementation plans.”).

168 BCCA Appeal Grp., 355 F.3d at 832

169 Ass’n of Battery Recyclers, 308 F.3d at 1063.

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hold that the EPA’s reliance on the CALPUFF model was not arbitrary and 

capricious. 

Moreover, the Clean Air Act’s structure gives states the primary 

responsibility for implementing the federal standards. The EPA’s role is to 

review the states’ plans for compliance with the Act’s requirements. Within 

those respective roles, “the States may submit implementation plans more 

stringent than federal law requires,” and the EPA “must approve such plans if 

they meet the minimum requirements” of the Clean Air Act.170 At this “subject 

to BART” stage—the purpose of which is to determine which of the BARTeligible sources warrant a “closer look”171—Louisiana’s reliance on a modeling 

method that tends to be overinclusive would result in a SIP that is more 

stringent than the federal requirements. The EPA’s approval of such a SIP 

would be well within the agency’s role to ensure the SIP “meet[s] the minimum 

requirements” of the Clean Air Act.172

3. Challenge to the EPA’s CAMx Modeling

We have concluded that the EPA’s reliance on the CALPUFF model was 

not arbitrary and capricious, so we need not address Industry Petitioners’ 

contentions about the EPA’s use of CAMx modeling. 

 

170 Union Elec. Co., 427 U.S. at 265; see 42 U.S.C. § 7410(k)(3) (“[the EPA] shall 

approve [a SIP] submittal as a whole if it meets all of the applicable requirements of this 

chapter.”).

171 BART Rule, 70 Fed. Reg. at 39,127.

172 Union Elec. Co., 427 U.S. at 265.

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No. 18-60116

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IV. CONCLUSION

For the foregoing reasons, the petitions for review are DENIED.

 Case: 18-60116 Document: 00515144673 Page: 72 Date Filed: 10/03/2019