United States Court of Appeals 

FOR THE DISTRICT OF COLUMBIA CIRCUIT

Argued December 3, 2014 Decided July 21, 2015 

No. 12-1459 

NATIONAL ASSOCIATION FOR SURFACE FINISHING, 

PETITIONER

v. 

ENVIRONMENTAL PROTECTION AGENCY AND GINA 

MCCARTHY, 

RESPONDENTS

CALIFORNIA COMMUNITIES AGAINST TOXICS, ET AL., 

INTERVENORS

Consolidated with 12-1460, 13-1147 

On Petitions for Review of Final Agency Action of 

the United States Environmental Protection Agency 

Jerry Stouck argued the cause for petitioner National 

Association for Surface Finishing. With him on the briefs 

was Christopher L. Bell. Joel F. Visser and Roger R. 

Martella Jr. entered appearances. 

Emma C. Cheuse argued the cause for petitioners Clean 

Air Council et al. With her on the briefs was James S. Pew. 

Khushi K. Desai entered an appearance. 
2 

Jonathan A. Wiener, Deputy Attorney General, Office of 

the Attorney General for the State of California, argued the 

cause for amici curiae California Air Resources Board, et al. 

With him on the brief were Kamala D. Harris, Attorney 

General, Robert W. Byrne, Senior Assistant Attorney General, 

Gavin G. McCabe, Supervising Deputy Attorney General, 

Ross H. Hirsch, Deputy Attorney General, Eric T. 

Schneidermann, Attorney General, Office of the Attorney 

General for the State of New York, Michael J. Myers, 

Assistant Attorney General, Kurt R. Wiese, and Barbara B. 

Baird. 

William L. Wehrum, Elizabeth L. Horner, Leslie A. 

Hulse, and Quentin Riegel were on the brief for amicus curiae

Chromium RTR Coalition in support of petitioner National 

Association for Surface Finishing. 

John T. Suttles, Myra D. Blake, and Patrice L. Simms

were on the brief for American Lung Association, et al. as 

amici curiae in support of environmental petitioners. 

Scott L. Nelson and Allison M. Zieve were on the brief for 

amicus curiae United States Representative Henry A. 

Waxman in support of environmental petitioners. 

T. Monique Peoples, Attorney, U.S. Department of 

Justice, argued the cause for respondents. With her on the 

brief were Sam Hirsch, Acting Assistant Attorney General, 

Stephanie J. Talbert, Attorney, and Jan M. Tierney, Attorney, 

U.S. Environmental Protection Agency. 

Robert G. Dreher and Jon M. Lipshultz, Attorneys, U.S. 

Department of Justice, entered appearances. 
3 

Jerry Stouck and Christopher L. Bell were on the brief for 

intervenor-respondent National Association of Surface 

Finishing. 

Emma C. Cheuse and James S. Pew were on the brief for 

environmental respondents-intervenors Clean Air Act 

Council, et al. 

Before: GRIFFITH and PILLARD, Circuit Judges, and 

WILLIAMS, Senior Circuit Judge. 

Opinion for the Court filed by Circuit Judge PILLARD. 

PILLARD, Circuit Judge: In this case we consider a pair 

of challenges to a 2012 regulation promulgated by the U.S. 

Environmental Protection Agency (EPA), revising Clean Air 

Act standards for emissions of hexavalent chromium. 

Hexavalent chromium is a carcinogenic compound emitted 

into the air during various chrome-finishing processes at more 

than a thousand facilities across the country. The facilities 

regulated under the challenged rule provide final, shiny, 

corrosion-resistant coatings on the surfaces of products 

ranging from plumbing fixtures to airplane wings. The 

various finishing processes used at those facilities all have the 

unfortunate side effect of generating misty chromium 

emissions that, if not properly controlled, can cause cancer. 

Facilities limit those emissions through the use of devices that 

capture emissions from the finishing tanks, or with fume 

suppressants that inhibit chromium droplets from bursting 

from the tank surface into the air in the first place. The new 

rule imposes more stringent emissions limitations than its 

predecessor and mandates the phase-out of a category of fume 

suppressants containing the toxic compound perfluorooctyl 

sulfonate (PFOS). 
4 

Various environmental organizations and an industry 

association have filed petitions challenging EPA’s revised 

rule. The environmental petitioners—the Clean Air Council, 

California Communities Against Toxics, and the Sierra 

Club—argue that the rule is too lax because EPA ignored 

relevant information and impermissibly considered costs in 

calculating revised emissions standards. The industry 

petitioner—the National Association for Surface Finishing 

(the Association)—argues that the rule is too stringent. The 

Association contends that EPA failed to make a determination 

of developments in practices, processes, or control 

technologies that the Association claims is a statutorily 

required precondition to rule revision, that the agency lacked 

adequate support in the record for phasing out the PFOSbased fume suppressants, and that EPA unreasonably assessed 

public health risk. The environmental petitioners and the 

Association intervened in each other’s cases, and we 

consolidated the cases for review. We deny the petitions. 

I. 

Section 112 of the Clean Air Act requires EPA to 

promulgate, and periodically revise as appropriate, national 

emissions standards for hazardous air pollutants. See 42 

U.S.C. § 7412(d). When Congress enacted that emissions 

standards program in 1970, it directed EPA to identify and 

regulate hazardous air pollutants. Dissatisfied with EPA’s 

progress in identifying hazardous air pollutants, Congress 

amended the Act in 1990 to name nearly 200 such pollutants, 

including chromium compounds, and charged EPA with 

identifying sources of those pollutants and setting emissions 

standards for them. See 42 U.S.C. § 7412(b)(1), (c), (d); see 

also, e.g., Mexichem Specialty Resins, Inc. v. EPA, 787 F.3d 

544, 549-50 (D.C. Cir. 2015); Natural Res. Def. Council v. 

EPA (“NRDC”), 529 F.3d 1077, 1079 (D.C. Cir. 2008). EPA 
5 

undertakes two basic regulatory tasks under section 112 that 

are relevant to this case: initial promulgation, followed by 

periodic review and potential revision, of emissions standards. 

EPA promulgates an emissions standard for a given 

pollutant by first determining the average emissions already 

achieved by the top tier of least polluting emitters, then 

considering whether a more demanding standard might be 

practicable and cost effective, and, if so, setting a standard 

that pushes beyond current practice. For starters, the agency 

identifies the 12% of facilities that emit the pollutant at the 

lowest levels, and then calculates the average level of 

emissions achieved by those facilities. 42 U.S.C. 

§ 7412(d)(3). That calculation is dubbed the “MACT floor” 

because it is based on “maximum achievable control 

technology,” and the standard EPA promulgates must not be 

less stringent than that performance “floor.” See Mexichem, 

787 F.3d at 549-50 & n.2; Nat’l Lime Ass’n v. EPA, 233 F.3d 

625, 629 (D.C. Cir. 2000). EPA then considers whether, 

taking into account costs, certain health and environmental 

effects, and energy requirements, a standard might be 

practicable that would go beyond the emissions reductions 

those existing facilities already achieve. See 42 U.S.C.

§ 7412(d)(2); Nat’l Lime, 233 F.3d at 629. If a more stringent 

standard is practicable in view of those factors, EPA 

promulgates a “beyond-the-floor” standard at that more 

stringent level; otherwise the agency sets the standard at the 

performance-based MACT floor. See Mexichem, 787 F.3d at 

549-50. 

EPA then periodically reviews and, if appropriate, revises 

the promulgated emissions standard, starting within eight 

years of the initial promulgation. That entails two distinct, 

parallel analyses: a recurring “technology review” under 

section 112(d)(6) and a one-time “risk review” under section 
6 

112(f)(2). In the technology review, EPA periodically 

assesses, no less often than every eight years, whether 

standards should be tightened in view of developments in 

technologies and practices since the standard’s promulgation 

or last revision, and, in particular, the cost and feasibility of 

developments and corresponding emissions savings. See 42 

U.S.C. § 7412(d)(6); see also Ass’n of Battery Recyclers, Inc. 

v. EPA (“ABR”), 716 F.3d 667, 673-74 (D.C. Cir. 2013). 

Separately, in the one-time risk review, EPA addresses, 

within eight years of a standard’s promulgation, lingering 

public health risk that the initial standard did not eliminate. 

See 42 U.S.C. § 7412(f)(2). To that end, EPA first considers 

whether the residual health risk is “acceptable,” a threshold 

EPA generally interprets as carrying cancer incidence no 

greater than 100 in one million. 75 Fed. Reg. 65,068, 65,071-

72 (Oct. 21, 2010); see NRDC, 529 F.3d at 1082. If the risk is 

not acceptable, EPA sets a more stringent standard regardless 

of cost to bring the risk down to an acceptable level. Even if 

a risk would be deemed acceptable because it is under that 

threshold, however, EPA considers whether a more stringent 

standard is “required in order to provide an ample margin of 

safety to public health.” 42 U.S.C. § 7412(f)(2)(A). What 

determines whether a more stringent standard providing an 

ample margin of safety is statutorily required is the agency’s 

consideration of health information as well as costs, economic 

impact, feasibility, and other relevant factors. See id.; see 

also NRDC, 529 F.3d at 1083; 75 Fed. Reg. at 65,072. If, 

taking those relevant considerations into account, further risk 

reductions are attainable beyond the “acceptable” threshold, 

they are required. 
7 

II. 

Two decades ago, EPA promulgated standards restricting 

emissions of hexavalent chromium from the types of 

chromium electroplating and anodizing facilities regulated 

under the rule challenged in this case.1

 60 Fed. Reg. 4,948 

(Jan. 25, 1995). The agency has reviewed and revised those 

standards over the years. At issue here is the 2012 Final Rule 

that most recently updated them. See Final Rule, National 

Emissions Standards for Hazardous Air Pollutant Emissions: 

Hard and Decorative Chromium Electroplating and 

Chromium Anodizing Tanks; and Steel Pickling—HCl 

Process Facilities and Hydrochloric Acid Regeneration Plants, 

77 Fed. Reg. 58,220 (Sept. 19, 2012). 

The initial, 1995 rule set emissions limits and allowed 

facilities to demonstrate compliance with them either by 

directly measuring chromium emissions or by gauging the 

surface tension of the chemical baths in their finishing tanks. 

60 Fed. Reg. at 4,953-54, 4,956, 4,959. The latter compliance 

option worked because of the “direct link between surface 

tension and emissions.” Id. at 4,959. As we explain below, 

surface tension describes how strongly a fluid sticks together 

where it meets the air. The surface tension of the chromium 

solution in which products are submerged during the finishing 

 

1

 Electroplating facilities finish products by dipping them in a salty 

chemical solution containing chromium and passing an electrical 

current through the solution. That causes chromium particles to 

deposit onto the products’ submerged surfaces, forming a protective 

seal. Anodizing facilities use a distinct but similar process to create 

a protective oxidation film over products’ surfaces. The challenged 

rule also regulates steel pickling facilities, but those facilities were 

not part of the earlier rulemakings recounted herein and are not 

directly implicated by the challenges in this case. 
8 

process determines the force with which non-chromium gas 

bubbles generated in the process burst out of the solution in 

the finishing tanks. Reducing surface tension makes it easier 

for bubbles to pass through the solution into the air, which 

diminishes the force of bubble-bursting at the surface. That, 

in turn, reduces the amount of harmful chromium droplets that 

pop into the air and create misty toxic emissions. In a 2004 

rulemaking, EPA reaffirmed and modified the option of 

compliance by controlling surface tension. 69 Fed. Reg. 

42,885, 42,886-88 (July 19, 2004).2

Before issuing the Final Rule petitioners challenge, EPA 

published a 2010 notice of proposed rulemaking (Notice) and 

a 2012 supplemental notice of proposed rulemaking 

(Supplemental Notice). In the initial Notice, EPA proposed to 

determine that the data before the agency did not warrant 

tightening the existing emissions standards. 75 Fed. Reg. at 

65,093-94. EPA nonetheless solicited additional data and 

comments. Id. at 65,125. Meanwhile, EPA proposed to 

phase out surfactant-based chemical fume suppressants 

containing the hazardous chemical PFOS. Id. at 65,094. 

Surfactants reduce the surface tension of solutions to which 

they are added. EPA concluded that less toxic, non-PFOSbased fume suppressants had proven effective at controlling 

surface tensions, even though they were not yet used 

extensively in the industry. The agency saw no reason why 

non-PFOS-based suppressants could not cost-effectively 

replace their toxic PFOS-containing counterparts, so the 

agency solicited input on its proposal to prohibit PFOS. Id. 

 

2

 EPA did not timely conduct the full technology and risk reviews 

required by the statute, see 69 Fed. Reg. at 42,888-89—a timing 

failure not at issue in this case. 
9 

Nearly a year and a half later, after having received more 

accurate and comprehensive data in response to the Notice, 

EPA in the Supplemental Notice proposed to reverse its prior 

tentative determinations that more stringent emissions 

standards were unnecessary. 77 Fed. Reg. 6,628 (Feb. 8, 

2012). EPA suggested that revised standards were warranted 

based on both its technology review and its risk review. Id. at 

6,631-52. In its technology review, EPA noted its additional 

analyses based on new data and explained its proposed 

selection of feasible, cost-effective options to further limit 

emissions. Id. at 6,632, 6,638-45. EPA solicited information 

regarding whether the surface tension limits proposed in the 

Supplemental Notice were achievable using non-PFOS-based 

suppressants. Id. at 6,645. In its risk review, EPA proposed 

to conclude that cancer risk was well below the “acceptable” 

100-in-one-million level, and that the same standards the 

agency was proposing as a result of the technology review 

would likewise provide the requisite “ample margin of safety” 

for purposes of its risk review. Id. at 6,648-49. 

EPA issued the Final Rule in September 2012, adopting 

the emissions standards proposed in the Supplemental Notice. 

77 Fed. Reg. at 58,225. EPA explained that additional 

information submitted during the interim period and 

additional analyses the agency had performed bolstered the 

determinations proposed in the Supplemental Notice. Id. at 

58,225-26. EPA also finalized the phase-out of PFOS-based 

fume suppressants, emphasizing data the agency collected 

from Minnesota facilities that had been controlling surface 

tensions effectively using non-PFOS-based suppressants. Id. 

at 58,230, 58,236-37. 
10 

III. 

This court applies the familiar, deferential standard 

announced in Chevron, U.S.A., Inc. v. Natural Resources 

Defense Council, Inc., to sustain any reasonable agency 

interpretation of ambiguity in the Clean Air Act. 467 U.S. 

837, 842-44 (1984). We reverse EPA’s determinations under 

the Act when they are “arbitrary, capricious, an abuse of 

discretion, or otherwise not in accordance with law.” 42 

U.S.C. § 7607(d)(9)(A). Under arbitrary-and-capricious 

review, EPA’s determinations are “presumptively valid 

provided [they] meet[] a minimum rationality standard.” 

Natural Res. Def. Council, Inc. v. EPA, 194 F.3d 130, 136 

(D.C. Cir. 1999). We uphold EPA’s determinations so long 

as “EPA acted within its delegated statutory authority, 

considered all of the relevant factors, and demonstrated a 

reasonable connection between the facts on the record and its 

decision.” Ethyl Corp. v. EPA, 51 F.3d 1053, 1064 (D.C. Cir. 

1995). We afford special deference “where the agency’s 

decision rests on an evaluation of complex scientific data 

within the agency’s technical expertise.” Troy Corp. v. 

Browner, 120 F.3d 277, 283 (D.C. Cir. 1997). 

The environmental petitioners challenge the Final Rule as 

too lax on the grounds that EPA unreasonably (1) declined to 

recalculate a technology-based emissions stringency floor that 

is independent of cost considerations, and (2) ignored 

emissions data from California in calculating revised 

standards. The Association challenges the rules as 

unauthorized and overly stringent on the grounds that EPA 

(1) did not adequately tie its revision of standards to 

technological “developments” that had occurred since the 

initial standard-promulgation, (2) concluded without 

sufficient evidentiary support that non-PFOS-based fume 

suppressants are capable of achieving the rule’s emissions 
11 

limits, and (3) in its risk review, unreasonably failed to 

determine whether existing emissions limits provided the 

requisite margin of safety, deviated from the agency’s prior 

determination that the requisite margin of safety had been 

attained, and relied on inaccurate data. 

A. 

The environmental petitioners contend that EPA was 

required to calculate a new MACT floor when it revised 

emissions standards pursuant to its technology review under 

section 112(d)(6). Subparagraph (d)(6) requires EPA, no less 

often than every eight years, to “review, and revise as 

necessary (taking into account developments in practices, 

processes, and control technologies) emission standards 

promulgated under” that section. 42 U.S.C. § 7412(d)(6). 

The environmental petitioners assert that EPA’s revision of 

standards in its technology review must be treated as a 

“promulgation” of an emissions standard, such that it triggers 

the Clean Air Act’s requirement that any promulgation must 

begin with EPA setting a MACT floor. They argue, in effect, 

that EPA must calculate a new MACT floor whenever the 

agency revises an existing emissions standard based on its 

periodic technology review under section 112(d)(6). A new 

MACT floor, if EPA set one, would be based purely on the 

achievements of the best-performing facilities in the industry 

after initial emissions standards had been operative for several 

years, and thus presumably would be more stringent than the 

existing MACT floor, and likely also more stringent than 

technology or risk-based revisions that take costs and other 

potentially constraining factors into account. 
12 

EPA itself has not so read the statute, and our precedent 

binds us to reject the environmental petitioners’ argument that 

it must so read it.3 We initially confronted a version of this 

question in NRDC, a case in which EPA had conducted a 

technology review but determined that revision was not 

warranted. 529 F.3d at 1080. The parties in NRDC briefed 

the argument the environmental petitioners press here. We 

concluded that the agency was not required to recalculate the 

MACT floor at the outset of its technology review, at least 

where EPA had decided not to revise emissions standards as a 

result of that review. Id. at 1084. 

We had occasion to address the issue more squarely in 

ABR, a case in which EPA had not only reviewed, but also 

revised, standards after a technology review. 716 F.3d at 670. 

The court in ABR was not persuaded by petitioners’ 

contention—pressed again by the environmental petitioners 

here—that our decision in NRDC was inapposite on the 

ground that it dealt with an EPA review that yielded no 

revision of any standard. ABR emphasized that NRDC rested 

“on two independent conclusions,” and that in such a case, 

“the ruling on neither is obiter [dictum], but each is the 

judgment of the court, and of equal validity with the other.” 

Id. at 673 (internal quotation marks omitted). We held in 

ABR that the petitioners’ argument that the agency must 

recalculate the MACT floor, “although far better developed 

 

3

 Neither this case nor any of our precedents addresses the distinct 

question whether, had EPA itself adopted the environmental 

petitioners’ reading, its interpretation would be valid under 

Chevron. 
13 

than the identical claim in [NRDC], [was] barred by that 

decision.” Id.4

The environmental petitioners incorrectly suggest that 

our decisions on this point in ABR and NRDC were abrogated 

by our later decision in White Stallion Energy Ctr., LLC v. 

EPA, 748 F.3d 1222 (D.C. Cir. 2014), which the Supreme 

Court recently partially reversed in Michigan v. EPA, No. 14-

46, 2015 WL 2473453, 576 U.S. __ (June 29, 2015).5

 In 

 

4

 The environmental petitioners argue that this court “has never 

addressed or decided the statutory issue presented here: that 

revised standards promulgated following a § 112(d)(6) review are 

‘emissions standards promulgated under this subsection’ and, 

therefore, subject to the stringency requirements in § 112(d)(2) and 

(d)(3).” Envtl. Pet. Br. 35. As they see it, NRDC addressed a 

different question, and ABR then erroneously treated the scant 

reasoning in NRDC as binding. See id. at 32-37. “Because ABR is 

directly at odds with clear statutory text that neither ABR nor NRDC

addresses,” they request en banc action via an Irons footnote. Id. at 

33, 37; see Irons v. Diamond, 670 F.2d 265, 267-68 & n.11 (D.C. 

Cir. 1981); Policy Statement on En Banc Endorsement of Panel 

Decisions (January 17, 1996). This is not, however, the kind of 

minor or marginal issue, nor one on which our precedents have 

been shown by intervening decisions to be clearly incorrect, such as 

might call for reversal in an Irons footnote. 

5

 The Supreme Court held in Michigan that EPA may not decline to 

consider cost as part of a required threshold inquiry under Clean 

Air Act section 112(n)(1)(A) into whether it is “appropriate and 

necessary” to regulate power plants. Michigan, supra, slip op. at 6-

14; see 42 U.S.C. § 7412(n)(1)(A). The “unique” section 

112(n)(1)(A) precondition to power-plant regulation that the Court 

reviewed in Michigan is “[q]uite apart from the hazardous-airpollutants program” at issue here. See Michigan, supra, slip op. at 

2. The “appropriate and necessary” provision that the Court held 

EPA unlawfully interpreted does not apply to the program that 
14 

White Stallion, we addressed EPA’s interpretation of Clean 

Air Act section 112(n)(1)(A), and its relationship to section 

112(d). 748 F.3d at 1242-44. Section 112(n)(1)(A) provides 

for EPA regulation of fossil-fuel-fired power plants when 

“appropriate and necessary.” 42 U.S.C. § 7412(n)(1)(A). We 

sustained as reasonable EPA’s interpretation of “under this 

section,” as used in that provision, to refer to the entirety of 

section 112, such that the regulation required whenever 

section 112(n)(1)(A)’s “appropriate and necessary” criteria 

are met must comport with the procedures of the rest of 

section 112, including those of section 112(d), addressing 

emissions standards generally. 748 F.3d at 1243-44; see 42 

U.S.C. § 7412(d). The environmental petitioners assert that 

the relationship between section 112(n)(1)(A), with its 

“regulate” as “appropriate and necessary” trigger, and section 

112, governing hazardous air pollution regulation generally 

(including the setting of MACT floors under section 

112(d)(2)-(3)), is the same as the relationship between section 

112(d)(6), with its “review, and revise as necessary” 

language, and section 112(d)(2)-(3). However, White Stallion 

did not tie section 112(n)(1)(A) to section 112(d)(2)-(3) 

specifically, as the petitioners’ analogy assumes. Nor did that 

decision address the distinction EPA makes here between 

initial promulgation under section 112(d)(2)-(3) and 

promulgation of revised standards as necessary under section 

112(d)(6). We simply deferred to EPA’s view that regulation 

triggered under section 112(n)(1)(A) must follow the 

procedures of section 112(d). 

 

regulates hexavalent chromium emissions from chrome-plating 

facilities. 
15 

B. 

The environmental petitioners also contend that EPA 

unreasonably disregarded, in both its technology and risk 

reviews, the emissions reductions and technological 

advancements achieved in California, where that state’s more 

stringent emissions standards require facilities to employ 

more ambitious controls. 

EPA took account of the California emissions data. In its 

technology and risk reviews, EPA estimates actual nationwide 

emissions and costs by extrapolating data collected from a 

sample of facilities across the country in order to establish 

baselines against which the agency can assess emissions 

decreases, health risk, and cost effectiveness associated with 

different practices, technologies, and emissions limitations. 

See, e.g., 77 Fed. Reg. at 6,631-34. EPA did not ignore 

California’s emissions data; it omitted it only from the dataset 

from which the agency extrapolated other states’ emissions. 

Id. at 6,633-34. That was prudent as a matter of statistical 

accuracy because “California plants are not representative of 

emissions for non-California plants.” Id. at 6,634; see also 

J.A. 531 (same in response to comments). EPA used 

California data, meanwhile, to estimate emissions for other 

plants in that state. 77 Fed. Reg. at 6,634. The agency thus 

“did not exclude the California [emissions] data from the 

overall analysis,” but rather “treated the data from plants in 

California differently” so as to achieve a statistically accurate 

portrait of nationwide emissions. Id. EPA’s approach was 

reasonable because extrapolating California’s nationally 

unrepresentative data to the rest of the country would have 

distorted the emissions figures that EPA uses in its costeffectiveness and risk analyses, whereas reliance on that data 

for California-specific estimates had no such distorting effect. 
16 

EPA also did not ignore California’s technological 

advances in assessing the cost effectiveness of applying 

nationally the standards in effect in California. The agency 

acknowledged that California emissions standards require 

controls that are more stringent than those required elsewhere, 

and that they had been feasibly implemented in California. 

The agency weighed the costs and benefits of requiring those 

controls nationally, and concluded that the relatively minimal 

reductions in emissions and risk that could be expected from 

extending California-like controls across the country would 

not warrant the associated expense. EPA “considered the 

option of requiring controls similar to standards adopted in 

California, which would essentially require facilities to install 

high efficiency particulate air (HEPA) filters,” but found that 

“overall costs for that option were significantly higher than 

. . . other options” EPA had examined, “and would have 

resulted in much greater economic impacts to small 

businesses.” 77 Fed. Reg. at 58,227. 

The agency further explained that “requirements similar 

to the California standards” were “not appropriate . . . to 

provide an ample margin of safety to protect public health” in 

light of “the high overall costs and economic impacts.” Id. 

Responding to a comment that EPA had “failed to provide 

any explanation for not considering the California 

reductions,” the agency explained that it had “evaluated . . . 

the controls used to comply with the standards in California” 

and concluded “that requiring these controls throughout the 

industry was not appropriate under either section 112(d)(6) 

[technology review] or section 112(f)(2) [risk review].” Id. at 

58,231-32; see also 75 Fed. Reg. at 65,092-94 (assessing risk 

level and cost associated with HEPA filters). The 

environmental petitioners suggest that EPA should have 

performed additional analyses beyond that related to HEPA 

filters but, as the agency reasonably explained, EPA lacked 
17 

the necessary information to do so: EPA was not provided 

with, and was otherwise unaware of, the detailed explanations 

of the assumptions and methodology behind California cost 

analyses that the agency would have needed to parse 

California’s data and accurately assess its applicability to the 

national regulatory context. See, e.g., J.A. 543. 

EPA took into account the statutorily required 

considerations of, inter alia, cost, emissions reductions, and 

health risk. The agency then provided a transparent, reasoned 

explanation of its decisions, considering all relevant 

information in the record. The statute does not mandate a 

particular method of cost-benefit analysis. Therefore, we 

defer to EPA’s methodology as well as its ultimate balancing 

decisions. See Husqvarna AB v. EPA, 254 F.3d 195, 200 

(D.C. Cir. 2001); cf. Brown v. United States, 327 F.3d 1198, 

1205-06 (D.C. Cir. 2003) (deferring to an agency’s reasoned 

methodology even under the less deferential Skidmore 

standard of review).6

C. 

The Association, in the first of its three challenges, 

asserts that EPA unreasonably determined in its technology 

review that “developments” had occurred after the original 

rulemaking that required revision of the existing emissions 

standards. The statute calls on EPA to revise promulgated 

standards “as necessary (taking into account developments in 

 

6

 The environmental petitioners’ related challenges to EPA’s 

treatment of the California data—that the agency’s disregard of that 

data derogated from its duty to consider all significant aspects of 

the statutory problem, and contravened the purpose of the Clean Air 

Act—also fail because they rest on the same false premise, 

addressed above, that EPA unreasonably disregarded the data. 
18 

practices, processes, and control technologies).” 42 U.S.C. 

§ 7412(d)(6). EPA and the Association agree that the agency 

could not revise standards in its technology review unless 

such pertinent “developments” occurred after the 1995 rule. 

The Association argues, however, that EPA failed to identify 

the requisite “developments” and failed to specify how its 

revised standards were tied to them. The Association also 

suggests EPA was arbitrary and capricious in changing 

course: in 2010 its proposed determination was that 

“developments” did not warrant revision, but in 2012 EPA 

concluded that revision was warranted after all. The 

Association further argues that EPA’s statistical analysis of 

emissions data was unreasonably flawed. 

EPA permissibly identified and took into account 

cognizable developments in practices, processes and control 

technologies. The agency interprets “developments” to 

encompass not only wholly new methods, but also 

technological “improvements . . . that could result in 

significant additional emission reduction.” 75 Fed. Reg. at 

65,083. “Developments” thus include “improvements in 

efficiency, reduced costs or other changes that indicate that a 

previously considered option for reducing emissions may now 

be cost effective or technologically feasible.” 77 Fed. Reg. at 

58,231. 

The Association does not directly challenge those 

interpretations, but maintains that EPA failed to identify what 

specific “developments,” including technological 

“improvements,” occurred in this case that warranted 

revision. EPA identified several technologies, such as 

emissions elimination devices, HEPA filters, enclosing tank 

hoods, and fume suppressants. 77 Fed. Reg. at 6,632 (2012 

Supplemental Notice referencing developments identified in 

2010 Notice); 75 Fed. Reg. at 65,083, 65,093-94 (Notice 
19 

identifying the aforementioned developments); J.A. 152-54 

(2010 technology review memorandum discussing the same). 

EPA further explained that, although the technologies were 

not brand new, improvements in the performance of some of 

them had resulted in emissions reductions. J.A. 516 (2012 

response to comments); see also 77 Fed. Reg. at 6,631-32 

(acknowledging data showing improved facility 

performance). 

It suffices for EPA to assess and discuss the collective 

impact of the developments it has identified, and to revise 

standards appropriately in light thereof. Section 112(d)(6) 

simply requires that EPA “take[] into account developments 

in practices, processes, and control technologies” when 

considering whether to revise standards. The agency 

explained that it had examined what emissions levels could be 

achieved using various add-on control devises and fume 

suppressants, including developments the agency had 

previously identified. See, e.g., 77 Fed. Reg. at 6,632. EPA 

went on to provide details regarding the costs and emissions 

reductions identified, and evaluated in the course of arriving 

at its conclusion that specified, best-available control 

technologies could cost-effectively meet more stringent 

emissions standards. See, e.g., id. at 6,640. The statute does 

not require EPA to identify a nexus between each distinct 

development and the revised standards. EPA’s decisionmaking was sufficiently clear and rational. See Int’l 

Fabricare Inst. v. EPA, 972 F.2d 384, 389 (D.C. Cir. 1992). 

Moreover, the shift in EPA’s position from 2010 to 2012 

was reasonable because the agency received intervening 

information relevant to its decision. See, e.g., Sierra Club v. 

EPA, 353 F.3d 976, 986-87 (D.C. Cir. 2004) (“[T]he 

adequacy of the underlying justification offered by the agency 

is the pertinent factor—not what the agency did on a different 
20 

record . . . .”). In 2010, EPA proposed to leave the existing 

emissions standards in place, not because no technological 

developments had occurred, but because the agency 

determined based on the data before it that requiring 

nationwide implementation of those technologies was not 

feasible, cost effective, and otherwise warranted. 75 Fed. 

Reg. at 65,093-95. EPA’s Notices solicited comments, 

however, and EPA contacted pollution control authorities to 

gain fuller, more accurate data. New data showed that 

facilities were performing better with respect to emissions 

than previously thought. 77 Fed. Reg. at 58,225-26, 58,231; 

77 Fed. Reg. at 6,631-32. Reductions in emissions are, of 

course, relevant to the cost effectiveness of emissions-control 

technologies in controlling emissions. See, e.g., J.A. 483-89 

(2012 memorandum). The agency thus concluded, based on 

the improved data, that more stringent technology-based 

standards were cost effective and otherwise appropriate. See 

77 Fed. Reg. at 58,225-26; 77 Fed. Reg. at 6,632-33, 6,638-

45. EPA’s change in position therefore was not arbitrary and 

capricious. 

Finally, the dataset EPA used to estimate facilities’ 

compliance rates—a component of the agency’s technology 

review—was not impermissibly small or inaccurate. The 

Association charges that EPA’s analysis was not designed to 

provide an accurate cross-section of the industry. It asserts 

that EPA did not sample facilities “on any statistical or 

representative basis,” and faults the agency for not requesting 

“all emissions data the states had in their files.” Ass’n Br. 30. 

EPA responds that it relied on data from a statistically 

significant number of facilities and a range that reflected 

“current, available information from facilities across all major 

regions of the country.” EPA Br. 50. Reacting to concerns 

raised after the 2010 Notice that the agency’s dataset was too 

small and unrepresentative, EPA sought detailed information 
21 

about emissions associated with various facility types. 77 

Fed. Reg. at 6,631. EPA explained that emissions data 

available for collection is limited because many smaller 

facilities are not required to submit annual emissions 

inventories—an informational dearth in light of which EPA 

gathered what it concluded was the “best information 

available to the Agency” and “minimized the [statistical] 

uncertainties to the extent feasible.” J.A. 535-36. In the face 

of those challenges, the agency obtained information from 24 

state and local agencies, as well as some information from the 

Association itself, to achieve a sample that included data from 

301 operational plants. 77 Fed. Reg. at 6,631. EPA 

determined that conducting a more in-depth industry-wide 

survey, requiring more facilities to collect and submit 

additional data, would have been statistically unnecessary and 

would not have warranted the substantial burden on smaller 

facilities. J.A. 537. 

Tellingly, the Association does not identify any specific, 

superior statistical threshold of data-gathering 

comprehensiveness that, in its view, would have been 

reasonable. Rather, acknowledging that a limited amount of 

emissions data is available to EPA, the Association simply 

criticizes the agency for not obtaining and evaluating more 

data. But “[w]e generally defer to an agency’s decision to 

proceed on the basis of imperfect scientific information, 

rather than to invest the resources to conduct the perfect 

study.” NRDC, 529 F.3d at 1086 (quoting Sierra Club v. 

EPA, 167 F.3d 658, 662 (D.C. Cir. 1999)). We recognize that 

EPA conceivably “could have used better data in conducting 

its risk analysis,” but that “misstates [our] inquiry under the 

arbitrary and capricious standard,” which is “whether EPA 

has acted reasonably, not whether it has acted flawlessly.” Id. 

(emphasis omitted). We cannot say that the size and 

representativeness of the dataset EPA used to estimate 
22 

compliance rates was statistically unreasonable, nor can we 

characterize as arbitrary EPA’s considered judgment that 

collecting additional data was unnecessary and not worth the 

cost, keeping in mind the “wide latitude” we afford the 

agency in its data-gathering decisions. Id. (quoting Sierra 

Club, 167 F.3d at 662); see also White Stallion, 748 F.3d at 

1247-48 (“EPA’s data-collection process was reasonable, 

even if it may not have resulted in a perfect dataset.”), rev’d 

in part on other grounds, Michigan, supra. We are satisfied 

that EPA’s data-gathering and analysis was adequate. 

D. 

The Association further argues that EPA’s decision to 

phase out PFOS-based fume suppressants was arbitrary and 

capricious. As we explain below, fume suppressants reduce 

finishing baths’ surface tension and, consequently, their 

chromium emissions. The Association’s claim hinges on its 

contention that there is inadequate support in the record 

showing that non-PFOS-based substitutes can effectively 

achieve the emissions limits required by the Final Rule. The 

Association does not challenge the compliance option that 

facilities have enjoyed since the original 1995 rule to measure 

the surface tension of their finishing baths rather than the 

emissions therefrom. See 60 Fed. Reg. at 4,953-54, 4,956. 

Nor does it seriously question that the administrative record 

shows that non-PFOS-based suppressants are capable of 

meeting the Final Rule’s surface tension limits. Rather, the 

Association contends that EPA failed empirically to support 

the conclusion that the same emissions control will result 

from equal surface tension reductions, whether those 

reductions are achieved with non-PFOS-based suppressants or 

PFOS-based suppressants. To that end, the Association points 

to what it perceives as an absence of reliable studies that 
23 

measure the emissions from baths whose surface tension is 

controlled by non-PFOS-based suppressants. 

The Association’s challenge fails to appreciate the 

finding, documented in the record, that the relationship 

between surface tension and emissions does not depend on the 

identity of the suppressant used to achieve that surface 

tension. Reducing a finishing bath’s surface tension reduces 

emissions from that bath. Surface tension describes a liquid’s 

cohesive strength where the liquid meets the air. The higher 

the surface tension, the more the liquid will bulge when its 

surface is pressured and the more resistant it will be to 

allowing bubbles to break through. E.g., J.A. 349. That is 

significant in the context of surface finishing because the 

electrolysis-induced finishing process generates bubbles of 

gas within the finishing solution. When those bubbles fizz up 

through the chromium-solution bath and pop upon hitting the 

surface, the bursting action sends tiny droplets of the solution 

into the air as mist. J.A. 440. Adding a surfactant-based 

fume suppressant to the finishing solution reduces its surface 

tension, which allows gases generated within the bath to pass 

through the surface of the solution more easily. That results 

in less forceful bubble-popping at the surface, which in turn 

diminishes the amount of chromium mist emitted. E.g., 77 

Fed. Reg. at 58,236-37; J.A. 349, 440-43. Because the 

physical relationship between surface tension and emissions 

exists independent of the specific tension-controlling agent, it 

is sufficient for EPA to rely on the evidence in the record 

establishing the relationship between non-PFOS-based 

suppressants and surface tension; EPA need not identify 

studies directly confirming the relationship between the 

specific surface tension controlling agent and the emission 

reduction. 
24 

That physical relationship between surface tension and 

emissions level is the basis of EPA’s long-standing rule 

allowing facilities to demonstrate compliance with emissions 

standards by measuring finishing baths’ surface tension rather 

than directly measuring their emissions. It is the established 

“direct link between surface tension and emissions” that has 

supported EPA’s acceptance of surface tension control as a 

proxy for emissions control. 60 Fed. Reg. at 4,959 (1995 

rule). 

The 1995 rulemaking in which EPA determined to rely 

on the relationship between surface tension and emissions 

never suggested that the type of fume suppressant used to 

control surface tension matters to emissions level. See id.

(“Based on data collected by the EPA, the [emissions] 

performance of an electroplating bath controlled with a 

wetting agent-type [i.e. chemical surfactant] fume suppressant 

can be determined by the surface tension of the bath.”); see 

also 58 Fed. Reg. 65,768, 65,795 (Dec. 16, 1993) (original 

proposed rule) (“[M]easurement of the surface tension of the 

bath . . . at least once every 4 hours during operation of the 

tank would be sufficient to ensure continuous compliance 

with the emission limit.”). 

EPA explicitly confirmed in the 2004 rulemaking that the 

tension/emissions relationship does not depend on suppressant 

type when it recognized that “[s]ources will be in compliance 

with the emission limits provided the surface tension is 

maintained at or below the proposed limits, regardless of the 

type of fume suppressant used”; the data before the agency 

did not “indicate that emission control levels are a function of 

the type of fume suppressant used in the tank solution.” 69 

Fed. Reg. at 42,888. 
25 

EPA reiterated in 2012 that “emissions are a function of 

the surface tension” and that lower surface tension results in 

lower emissions “regardless of the specific chemicals used.” 

J.A. 479 (EPA memorandum cited in Final Rule); see also 77 

Fed. Reg. at 58,237 (“It is our understanding that this 

relationship between surface tension and chromium emissions 

is dependent primarily on the surface tension of the tank and 

not on the product used to reduce surface tension.”). It is the 

property of surface tension on the bath, not some other 

reaction unique to the particular surfactant employed, that 

affects the force with which bubbles in the chromium bath 

burst and send droplets into the air. See, e.g., J.A. 349, 440-

43. 

Neither logic nor the record supports the Association’s 

conclusory suggestion that emissions will vary, given a 

constant surface tension, depending on whether PFOS- or 

non-PFOS-based fume suppressants are used to achieve that 

surface tension. The Association points out that EPA’s 

statements in earlier rulemakings were made in the context of 

considering only various PFOS-based suppressants. That 

ignores the fact that EPA restated in 2012, in a memorandum 

in which it was also considering the effectiveness of nonPFOS-based suppressants, that the suppressant’s chemical 

identity is irrelevant. See J.A. 479, 482. Moreover, the 

Association provides no explanation and points to no 

evidence supporting its suggestion that the principle EPA 

earlier recognized does not apply to non-PFOS-based 

suppressants. If EPA had established, in a rulemaking 

involving various kitchen stoves, that water boils when it 

reaches 212°F regardless of the type of stove used, and later 

took that boiling point as a given in a rulemaking involving 

campfires, we would not require EPA to document the same 

scientific phenomenon of water boiling at 212°F in the new, 

campfire context—at least not where a petitioner proffered 
26 

nothing suggesting why the heat-source difference might 

matter. The Association’s bare assertion that EPA needed to 

provide fresh empirical support for the applicability of the 

tension/emissions relationship in the context of non-PFOSbased suppressants is insufficient to undermine the 

documentation already in the record. “Agencies do not need 

to conduct experiments in order to rely on the prediction that 

an unsupported stone will fall.” Assoc’d Gas Distribs. v. 

FERC, 824 F.2d 981, 1008-09 (D.C. Cir. 1987); cf. Chamber 

of Commerce of U.S. v. SEC, 412 F.3d 133, 142 (D.C. Cir. 

2005) (“[W]e are acutely aware that an agency need not—

indeed cannot—base its every action upon empirical 

data . . . .”). 

The studies in the administrative record are consistent 

with EPA’s understanding that surface tension is a reliable 

proxy for emissions regardless of the fume suppressant 

employed. A 2011 study expressly contemplates the 

PFOS/non-PFOS dichotomy and treats that difference as 

immaterial to the tension-emissions relationship. See J.A. 

439-49 (Neil Patton & Gene Barlowe, Atotech, Non-PFOS, 

Permanent Mist Suppressants for Hard Chromium Plating, 

Decorative Chromium Plating and Chromic Etch 

Applications (2011)). The study identifies “mist 

suppressants” as a general category of surfactants, noting they 

all “work by reducing the surface tension of the solution.” 

J.A. 442; see id. (stating without reference to the surfactant’s 

chemical composition that reducing surface tension lowers 

mist generation). The study then identifies several 

characteristics of effective suppressants—including the ability 

to control surface tension and emissions, as well as unrelated 

criteria such as effect on plating quality—without suggesting 

that ability to meet those criteria depends on PFOS 

composition. J.A. 444. The study explains that earlier 

generations of non-PFOS-based suppressants were disfavored 
27 

not because of non-correlation between surface tension and 

emissions, but rather because they were less stable and tended 

chemically to foment a scum that degraded plating quality. 

J.A. 445. The authors go on to recognize that newer nonPFOS-based suppressants for years have been performing 

“just as well” as PFOS-based suppressants. J.A. 444-47. 

Other studies in the record, which measured only emissions 

directly and did not document emissions’ relationship to 

surface tension, are consistent with that understanding.7

 

Therefore, it suffices for EPA to show that non-PFOSbased suppressants are as effective at controlling surface 

tension as PFOS-based suppressants (which the Association 

does not contend are incapable of achieving the Final Rule’s 

surface tension limits). We conclude that the data from 

Minnesota facilities emphasized in the Final Rule shows that 

effectiveness. See 77 Fed. Reg. at 58,236-37. The Minnesota 

data show that non-PFOS-based suppressants perform, in the 

facilities’ experience, “pretty similarly” and pose “no 

noticeable differences” in comparison to PFOS-based 

suppressants. J.A. 415-16; see J.A. 417-21 (raw data 

 

7

 A 2011 Danish study and a 2012 German study directly compared 

emissions from PFOS and non-PFOS tanks without clearly 

recording surface tensions. See J.A. 410-13, 423-25. EPA 

interprets those studies as showing that non-PFOS-based 

suppressants are comparably effective at reducing emissions. See

77 Fed. Reg. at 58,237; J.A. 507-512. The Association responds 

that the studies failed to demonstrate that non-PFOS-based 

suppressants can meet the Final Rule’s emissions limitations. We 

need not opine on that question because, as discussed above, the 

established relationship between surface tension and emissions 

means that it suffices for EPA to rely on data demonstrating that 

non-PFOS-based suppressants meet the Final Rule’s surface tension 

limits. 
28 

supporting those observations); J.A. 482 (additional data 

analysis). The Association does not meaningfully argue 

otherwise, conceding that the Minnesota data “indicate that 

non-PFOS fume suppressants might be used to meet the new 

surface tension standards.” Ass’n Br. 41. 

E. 

The Association argues that EPA’s risk review under 

section 112(f)(2) was unreasonable, for three reasons.8

First, the Association asserts that EPA failed to make a 

finding in the Final Rule that a revised standard was “required 

in order to provide an ample margin of safety to public 

health.” 42 U.S.C. § 7412(f)(2). However, EPA did not skip 

the step of determining in the Final Rule that revised 

standards were required to provide an ample margin of safety. 

The agency expressly stated that it was “promulgating 

standards under Section 112(f) to provide an ample margin of 

safety.” 77 Fed. Reg. at 58,226; see also id. at 58,229 

(“[A]fter considering all the health and cost factors . . . , the 

agency has determined that . . . [the revised standard] will 

provide an ample margin of safety . . . .”). 

The Association argues that EPA’s determinations that 

revised standards would provide an ample margin of safety 

did not contain a determination that they were required to 

 

8

 While we affirm EPA’s determinations under section 112(f)(2), 

we note that even if we disapproved of them, the same emissions 

standards would survive because EPA determined that they were 

independently warranted by its technology review under section 

112(d)(6). See 77 Fed. Reg. at 58,224-25; 77 Fed. Reg. at 6,648. 

The Association’s counsel acknowledged as much at argument. 

Oral Arg. Tr. at 16:20-17:8. 
29 

provide that margin. That is simply not the case. In response 

to comments, for instance, the agency reiterated its 

understanding that section 112(f)(2) mandates revision when, 

“required to provide an ample margin of safety.” J.A. 527. 

The agency has consistently viewed itself as “required to 

propose emissions standards . . . that reduce risk to a level that 

is acceptable and provides an ample margin of safety.” 75 

Fed. Reg. at 65,091. It is precisely as a result of the further 

consideration and context-based determination that additional 

risk reductions can be achieved cost effectively and in light of 

other statutorily relevant factors that the agency’s obligation 

arises to tighten standards to provide an “ample margin of 

safety.” EPA’s determination that revision was required was 

therefore at least implicit. 

Second, the Association argues that any finding EPA may 

have made in 2012 that the revised standards were required to 

protect the public health was an arbitrary and capricious 

reversal of its earlier 2010 determination. The Association 

contends, more specifically, that it was unreasonable for EPA 

to conclude in 2010 that the requisite “ample margin of 

safety” was in place, but to conclude in 2012 that revised 

standards were necessary to achieve such a margin of 

safety—and to do so at the same time that EPA acknowledged 

that health risks were equal to or lower than it had thought 

they were in 2010. EPA’s “ample margin of safety” 

determination does not hinge solely on public health risk, 

however; it may also take into account “costs and economic 

impacts, technological feasibility, and other [non-health] 

factors.” NRDC, 529 F.3d at 1083 (internal quotation marks 

omitted). That being the case, the fact that EPA considered a 

prior standard to provide an ample margin of safety under 

older data does not prevent EPA from determining that new 

data on cost and feasibility require a more stringent standard. 

In this case, EPA gained significant new data between 2010 
30 

and 2012 that changed its calculus about cost effectiveness 

and feasibility. 77 Fed. Reg. at 58,225-26; J.A. 521-22 

(response to comments). EPA’s change in position was 

therefore reasonable. See Sierra Club, 353 F.3d 986-87; cf. 

Nat’l Ass’n of Mfrs. v. EPA, 750 F.3d 921, 925 (D.C. Cir. 

2014) (“[W]e do not assign ‘presumptive validity’ to the prior 

[standards]; the question is whether EPA reasonably explains 

the current standards.”).

Lastly, the Association characterizes EPA’s statistical 

methodology for estimating emissions (and, consequently, 

cancer risk) as unreasonably flawed. It asserts that the sample 

of facilities on which EPA based its emissions estimates in the 

Supplemental Notice included many facilities that were either 

closed or not subject to regulation, or that emissions estimates 

from those facilities were inaccurately high. 

The Association identified inaccuracies in the sample 

EPA had used by contacting facilities in that sample and 

comparing the information they provided against EPA’s 

assumptions. It also reported that those inaccuracies were 

corroborated by a supplemental sample it generated to check 

the accuracy of EPA’s model. J.A. 284-305, 312-27 (March 

2012 submission in response to Supplemental Notice). The 

Association claims that its supplemental data show that EPA’s 

initial sample was unacceptably unrepresentative of the larger 

population of facilities. 

EPA responded by adjusting its data inputs, removing all 

the data that the Association had identified as coming from 

closed facilities or those that did not emit hexavalent 

chromium, and added the more specific, verifiable data that 

the Association had provided. 77 Fed. Reg. at 58,235; J.A. 

546-47 (response to comment); see also J.A. 637-38 (EPA 

correspondence to the Association further explaining the 
31 

adjustments). EPA declined, however, to incorporate any of 

the Association’s data that the agency determined was too 

vague or lacking in detail to be reliable and susceptible of 

incorporation into its predictive model. J.A. 638. EPA also 

declined to adopt the Association’s extrapolations from its 

supplemental data sample because, the agency explained, the 

Association did not provide sufficient information about its 

sampling methodology for EPA to discern whether the 

supplemental data sample was collected in a statistically 

representative, reliable fashion. J.A. 647. 

The Association has never challenged EPA’s predictive 

model, as distinct from the data inputs into that model. EPA 

thus retained the “Monte Carlo” statistical technique of 

extrapolating an estimate of emissions from all facilities from 

actual emissions data from a smaller sample of facilities. 

EPA re-ran its model based on a dataset adjusted as just 

described, and determined that the resulting emissions 

estimates supported its risk conclusions. 77 Fed. Reg. at 

58,225-30, 58,235-36. 

We conclude that EPA’s methodology passes muster. 

Keeping in mind the “wide latitude” we afford EPA’s 

expertise-informed choice of data-gathering methodology, we 

find that EPA’s data-collection process was reasonable. See 

NRDC, 529 F.3d at 1086 (quoting Sierra Club, 167 F.3d at 

662); see also White Stallion, 748 F.3d at 1247-48. The 

Association contends that EPA’s response to its submission—

adjusting the inputs of its dataset—was insufficient. But we 

must bear in mind that “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.” Appalachian Power Co. v. EPA, 135 F.3d 

791, 802 (D.C. Cir. 1998). We uphold EPA’s model as long 

as the agency “explain[s] the assumptions and methodology 
32 

used in preparing the model” and “provide[s] a complete 

analytic defense” should the model be challenged. Small 

Refiner Lead Phase-Down Task Force v. EPA, 705 F.2d 506, 

535 (D.C. Cir. 1983) (internal quotation marks omitted). As 

outlined above, EPA provided such an explanation and 

defense of how and why it formulated the sample and 

conducted the analysis that it did. See, e.g., 77 Fed. Reg. at 

58,235; see also J.A. 467-472 (memorandum specifically 

explaining and defending EPA’s revised emissions 

simulation). Moreover, the Association does not explain why 

the level of uncertainty resulting from EPA’s ultimate sample 

and analysis was statistically unacceptable, nor does it offer 

any superior method that it contends EPA should have used 

instead. 

* * * 

For the reasons above, we deny the petitions for review 

and uphold the Final Rule. 

So ordered.