 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 PFOS-
based 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-PFOS-
based 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-air-
pollutants 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 cost-
effectiveness 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 decision-
making 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 non-
PFOS-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-PFOS-
based 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 non-
PFOS-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-PFOS-
based 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.
