Court Opinion

ID: 4794740
Source: CourtListenerOpinion
Date Created: 2021-08-20 16:01:16.415955+00
Date Added: 2024-06-11T08:09:54.894992
License: Public Domain

United States Court of Appeals
                         For the Eighth Circuit
                     ___________________________

                             No. 19-3220
                     ___________________________

                          United States of America

                     lllllllllllllllllllllPlaintiff - Appellee

                                  Sierra Club

                   lllllllllllllllllllllIntervenor - Appellee

                                        v.

                              Ameren Missouri

                   lllllllllllllllllllllDefendant - Appellant

                          ------------------------------

Chamber of Commerce of the United States of America; American Chemistry
 Council; America's Power; Missouri Chamber of Commerce and Industry;
   National Association of Manufacturers; National Mining Association

              lllllllllllllllllllllAmici on Behalf of Appellant(s)
                                    ____________

                Appeal from United States District Court
              for the Eastern District of Missouri - St. Louis
                              ____________

                      Submitted: December 16, 2020
                         Filed: August 20, 2021
                             ____________
Before SMITH, Chief Judge, LOKEN and MELLOY, Circuit Judges.
                              ____________

SMITH, Chief Judge.

      Ameren Missouri (“Ameren”) appeals an adverse judgment of the district court
in a Clean Air Act (CAA) enforcement action brought by the United States of
America, acting at the request of the Administrator of the United States
Environmental Protection Agency (EPA) (hereinafter, EPA or “government”).
Ameren argues that the district court erroneously found it liable for not obtaining
permits for projects at its Rush Island Energy Center (“Rush Island”) and, as a result,
assessed liability under the applicable federal regulations. In addition, Ameren
maintains that the district court ordered legally flawed injunctions at both Rush Island
and at a different plant, Labadie Energy Center (“Labadie”). We affirm the district
court’s liability determination, but we reverse in part the remedial portion of its order
concerning the Labadie plant and remand for further proceedings consistent with this
opinion.

                                  I. Background
                A. Statutory and Regulatory Background of the CAA
       “Congress enacted the Clean Air Act Amendments of 1970 seeking to
guarantee the prompt attainment and maintenance of specified air quality standards.”
Sierra Club v. Otter Tail Power Co., 615 F.3d 1008, 1011 (8th Cir. 2010) (quotations
omitted). In enacting the CAA amendments, Congress “directed EPA to devise
National Ambient Air Quality Standards (NAAQS) limiting various pollutants, which
the States were obliged to implement and enforce.” Id. (quotation omitted). The New
Source Performance Standards (NSPS) program was a key part of the CAA’s
regulatory scheme. Id. The NSPS program “required EPA to develop technology-
based performance standards designed to limit emissions from major new sources of

                                          -2-
pollution.” Id. (quotation omitted). Both newly constructed facilities and modified
facilities with increased emissions constitute “[n]ew sources.” Id. “It is ‘unlawful for
any owner or operator of any new source to operate such source in violation of’
applicable performance standards.” Id. (quoting 42 U.S.C. § 7411(e)).

       The NSPS program, however, “did too little to ‘achieve the ambitious goals of
the 1970 amendments.’” Id. (quoting Env’t Def. v. Duke Energy Corp., 549 U.S. 561,
567 (2007)). “Merely setting emissions limits failed to improve air quality in those
areas that had already attained the minimum standards of the NAAQS because
polluters had no incentive to diminish emissions below the established limits.” Id. As
a result, in 1977, Congress amended the CAA “to add the ‘Prevention of Significant
Deterioration’ (PSD) program, which seeks to ensure that the ‘air quality floor’
established by the NAAQS does not ‘in effect become a ceiling.’” Id. (quoting Sierra
Club v. Thomas, 828 F.2d 783, 785 (D.C. Cir. 1987)).

       The PSD program limited construction of major emitting facilities with
specified preconditions. 42 U.S.C. § 7475(a). “The term ‘construction’ when used in
connection with any source or facility, includes the modification . . . of any source or
facility.” Id. § 7479(2)(C) (emphasis added). “The term ‘modification’ means any
physical change in, or change in the method of operation of, a stationary source which
increases the amount of any air pollutant emitted by such source or which results in
the emission of any air pollutant not previously emitted.” Id. § 7411(a)(4).

        The PSD program prohibits the construction of a major emitting facility unless
preconditions are satisfied. One precondition is that the proposed facility obtain a
permit setting forth applicable emission limitations. Id. § 7475(a)(1). Another
precondition is that “the owner or operator of such facility demonstrates . . . that
emissions from construction or operation of such facility will not cause, or contribute
to, air pollution in excess of” prescribed air quality standards. Id. § 7475(a)(3). The
PSD program also requires the owner or operator to install “the best available control

                                          -3-
technology for each pollutant subject to regulation . . . emitted from, or which results
from, [the proposed] facility.” Id. § 7475(a)(4). The “‘best available control
technology’ (BACT) . . . . is not a particular type of technology.” Otter Tail, 615 F.3d
at 1011 (quoting 42 U.S.C. § 7475(a)(4)). Instead, the BACT “is an ‘emission
limitation based on the maximum degree of reduction of each pollutant subject to
regulation . . . which the permitting authority, on a case-by-case basis, taking into
account energy, environmental, and economic impacts and other costs, determines is
achievable’ for the facility in question.” Id. (alteration in original) (quoting 42 U.S.C.
§ 7479(3)).

      Only major modifications to emitting sources are subject to PSD review. Ala.
Power Co. v. Costle, 636 F.2d 323, 399 (D.C. Cir. 1979). “Major modification means
any physical change in or change in the method of operation of a major stationary
source that would result in: a significant emissions increase . . . of a regulated NSR
[New Source Review] pollutant . . . ; and a significant net emissions increase of that
pollutant from the major stationary source.” 40 C.F.R. § 52.21(b)(2)(i).

        For projects that only involve “existing emissions units,” the EPA applies what
it calls the actual-to-projected-actual applicability test. Id. § 52.21(a)(2)(iv)(c).1 To
apply this test, the “baseline actual emissions” must first be calculated. “Baseline
actual emissions means the rate of emissions, in tons per year, of a regulated NSR
pollutant . . . .” Id. § 52.21(b)(48).

      1
       This test provides: “A significant emissions increase of a regulated NSR
pollutant is projected to occur if the sum of the difference between the projected
actual emissions . . . and the baseline actual emissions . . . , for each existing
emissions unit, equals or exceeds the significant amount for that pollutant . . . .” Id.

                                           -4-
      Next, the “projected actual emissions” must be calculated by
      determining the maximum annual rate, in tons per year, at which an
      existing emissions unit is projected to emit a regulated NSR pollutant in
      any one of the 5 years (12–month period) following the date the unit
      resumes regular operation after the project, or in any one of the 10 years
      following that date, if the project involves increasing the emissions
      unit’s design capacity or its potential to emit that regulated NSR
      pollutant and full utilization of the unit would result in a significant
      emissions increase or a significant net emissions increase at the major
      stationary source.

Id. § 52.21(b)(41)(i). An “owner or operator of the major stationary source . . . [must]
consider all relevant information” to calculate “the projected actual emissions.” Id.
§ 52.21(b)(41)(ii)(a). “[A]ll relevant information . . . include[s] . . . historical
operational data, the company’s own representations, the company’s expected
business activity and the company’s highest projections of business activity, the
company’s filings with the State or Federal regulatory authorities, and compliance
plans under the approved State Implementation Plan . . . .” Id. But the owner or
operator “[s]hall exclude” from the projected actual emissions “that portion of the
unit’s emissions following the project that an existing unit could have accommodated
during the consecutive 24-month period used to establish the baseline actual
emissions . . . and that are also unrelated to the particular project, including any
increased utilization due to product demand growth.” Id. § 52.21(b)(41)(ii)(c). The
“exclu[sion] [of] increases stemming from unrelated demand growth” is referred to
as “the ‘demand growth exclusion.’” New York v. EPA, 413 F.3d 3, 16 (D.C. Cir.
2005).

       Finally, the baseline actual emissions calculation is subtracted from the
projected actual emissions calculation to determine if the difference between the
numbers is “significant.” 40 C.F.R. § 52.21(a)(2)(iv)(c). A table in the regulations
sets forth the numeric thresholds that are considered “significant” for each regulated

                                          -5-
pollutant. Id. § 52.21(b)(23)(i). If the difference in the projected actual emissions and
the baseline actual emissions is significant, see id., then a permit is required before
beginning construction on the project. Id. § 52.21(a)(2)(iii).

      The actual-to-projected-actual test is distinguishable from “a potential-to-
potential test,” which “compare[s] past potential emissions with future potential
emissions.” New York, 413 F.3d at 17. “[T]he plain language of the CAA indicates
that Congress intended to apply NSR to changes that increase actual emissions
instead of potential or allowable emissions . . . .” Id. at 40.

                      B. Missouri’s State Implementation Plan
       “The PSD program is primarily implemented by the states through ‘state
implementation plans’ (SIPs).” Otter Tail, 615 F.3d at 1011 (citing 42 U.S.C.
§ 7471). While “[s]tates have broad discretion in designing their SIPs,” their “plans
must include certain federal standards.” Id. The EPA reviews and approves States’
SIPs. Id. at 1011–12.

       Missouri expressly incorporated the EPA’s PSD regulations into its SIP
(“Missouri SIP”). See Mo. Code Regs. Ann. tit. 10, § 6.060(8)(A) (2007) (“All of the
subsections of 40 CFR 52.21, other than [certain subsections], are hereby
incorporated by reference.”). The EPA approved Missouri’s SIP, explaining that “the
provisions of § 52.21 supersede the state provisions for purposes of the PSD
program.” Approval and Promulgation of Implementation Plans; State of Missouri,
71 Fed. Reg. 36,486-02, 36,487 (June 27, 2006); see also id. at 36,489 (“This revision
also incorporates by reference the other provisions of 40 CFR 52.21 as in effect on
July 1, 2003, which supersedes any conflicting provisions in the Missouri rule.
Section 9, pertaining to hazardous air pollutants, is not SIP approved.”).

                                          -6-
                                   C. Title V Program
       In addition to the CAA’s PSD program, “the CAA . . . require[s] each covered
facility to obtain a comprehensive operating permit setting forth all CAA standards
applicable to that facility.” Otter Tail, 615 F.3d at 1012 (citing 42 U.S.C. § 7661a(a)).
The operating permits “incorporate into a single document all of the CAA
requirements governing a facility. Similar to other CAA programs, Title V is
implemented primarily by the states under EPA oversight. In states with EPA
approved programs,” the state permitting authority issues the Title V permits. Id.
(citations omitted). These permits “are subject to EPA review and veto.” Id. The EPA
has approved Missouri’s operating permit program under Title V of the CAA. This
program is incorporated into the Missouri SIP. See Mo. Code. Regs. Ann. tit. 10, §
6.065 (2007).

                   D. Factual Background and Procedural History
       This case involves Ameren’s Rush Island power plant, which includes two
coal-fired electric generating units, Units 1 and 2. These units began service in 1976
and 1977. They were grandfathered into the PSD program. They do not have air
pollution control devices for sulfur dioxide. Rush Island currently emits
approximately 18,000 tons of sulfur dioxide per year. Small performance
improvements or increases in unit availability can result in a 40-ton increase in sulfur
dioxide. For the Rush Island units to emit more than 40 tons of sulfur dioxide, it takes
only an availability of 0.3 percent or an additional 21 hours of operation at full power.

      By 2005, problems with Units 1’s and 2’s major boiler components forced
Ameren to frequently take the units out of service. This made the units underperform
and reduced the amount of electricity Ameren could generate and sell from the units.
Ameren decided to replace the problem components with new, redesigned
components. Ameren, however, did not do any quantitative PSD review for Unit 1’s
project and belatedly performed PSD review for Unit 2’s project. Ameren proceeded
with the projects without reporting its planned modifications to the EPA, obtaining

                                          -7-
the necessary permits, or installing pollution controls. To replace the major boiler
components, Ameren took Unit 1 offline in 2007 and Unit 2 offline in 2010. Each
unit was completely offline for three to four months to complete the projects. Ameren
spent more than $20 million per project.

       By replacing the failing components with new, redesigned components,
Ameren expected unit availability to improve by much more than 0.3 percent,
allowing the units to operate hundreds of hours more per year after the projects.
Ameren expected to use that increased availability (and increased capacity for Unit
2) to burn more coal and generate more electricity. Unavoidably, the units would also
emit more sulfur dioxide pollution.

      As Ameren expected, its replacement of the failing components resulted in
increased availability at Units 1 and 2 by eliminating hundreds of outage hours per
year. And, Unit 2’s capacity increased. The units ran more, burned more coal, and
consequently emitted hundreds of tons more sulfur dioxide per year because of the
operational increases.

       The government filed suit against Ameren in response to the projects. It alleged
that Ameren violated the CAA, the Missouri SIP, and Ameren’s Rush Island Plant
Title V Permit by performing major modifications on Units 1 and 2 without obtaining
the necessary permits, installing pollution control technology, or otherwise complying
with all applicable requirements.

                                   1. Liability Phase
                                a. Summary Judgment
      The district court bifurcated the proceedings into a liability phase and a remedy
phase. During the liability phase, the district court issued two summary-judgment
orders. In the first summary-judgment order, the district court rejected Ameren’s
argument that the major-modification test set forth in the federal regulations did not

                                         -8-
provide the relevant PSD liability test because the Missouri SIP elsewhere separately
defined modification to mean that “the source’s potential emissions would
significantly increase.” United States v. Missouri (Ameren I), 158 F. Supp. 3d 802,
808 (E.D. Mo. 2016) (emphasis added). According to Ameren, the government could
not establish liability because it never alleged that “the [Rush Island] projects
increased the units’ potential emissions.” Id. (emphasis added). In rejecting this
argument, the court first explained that “the PSD rules impose their own independent,
stand-alone applicability provisions in Section (8) of the Missouri SIP (incorporating
EPA’s PSD rules set out at 40 C.F.R. 52.21).” Id. at 809. The court reasoned that “the
PSD-specific applicability language should trump the general applicability language
in Section (1) of the [Missouri] SIP.” Id.

       The court next cited the “well-established” “regulatory and statutory history of
the PSD rules” as leaving “no doubt that the federal PSD rules are focused on ‘major
modifications’ which are based on actual emissions determinations,” not potential
emissions. Id. at 810. The court found “most persuasive[] [that the] EPA’s approval
of the SIP provided that the CAA and the program requirements as set out in 40
C.F.R. § 52.21 would supersede any conflicting provisions in the state SIP.” Id.
(citing Approval and Promulgation of Implementation Plans; State of Missouri, 71
Fed. Reg. at 36,489).

       Finally, the district court concluded that Ameren urged an interpretation of the
SIP that would conflict with the PSD rules and, in the court’s view, “render a portion
of the PSD rules superfluous.” Id.

      In its second summary-judgment order, the district court addressed causation
and “the PSD program’s demand growth exclusion.” United States v. Ameren Mo.
(Ameren II), No. 4:11-cv-77-RWS, 2016 WL 728234, at *9 (E.D. Mo. Feb. 24, 2016).
According to the district court, “two main criteria . . . determine whether a major
source of pollution must obtain a PSD permit. First, there must be a physical change,

                                          -9-
and second, that change would be expected to cause a significant net increase in
actual emissions.” Id. The demand growth exclusion is relevant to the second
criteria—“how to determine whether the physical changes would have caused a
significant net emissions increase, and if so, whether any of the increased emissions
may be excluded from review under the ‘demand growth exclusion.’” Id. The district
court rejected Ameren’s proposed interpretation of the exclusion as applying to “any
emissions increases a unit could have accommodated at baseline.” Id. Instead, the
court held “that the demand growth exclusion requires a showing that the unit ‘could
have accommodated’ the emissions at baseline and that . . . those increases were
unrelated to the project.” Id. at *11. The court also held that “while it remains the
EPA’s burden to prove that Ameren should have expected the projects to cause an
increase in emissions, the burden is Ameren’s to prove that the demand growth
exclusion applies.” Id.

       Also in the second summary-judgment order, the district court addressed
Ameren’s argument that “because EPA brought suit after the challenged projects’
completion,” it was “limited to an ‘actual increase’ theory.” Id. at *13. Under
Ameren’s actual-increase theory, the EPA would have to show that “the Projects
actually caused emissions to increase” to establish Ameren’s liability. Id. By contrast,
under “an ‘expectations’ theory,” the EPA could establish liability by showing “that
Ameren ‘should have expected’ the Projects to increase emissions.” Id. The court held
that the government could proceed on the expectations theory. Id. at *13–16.

      Additionally, the court considered Ameren’s argument that the government had
to “come forward with admissible evidence of what a reasonable power plant operator
or owner would expect, and its failure to do so [was] fatal to EPA’s expectations
theory case.” Id. at *18. But the court agreed with the government “that no special
standard of care evidence is required for the factfinder to be able to determine
whether a reasonable power plant operator or owner would have expected the projects

                                         -10-
to cause a significant emissions increase”; instead, “the PSD regulations themselves
. . . guide the factfinder’s determination.” Id.

      Finally, the court rejected Ameren’s argument that the court “lack[ed] subject
matter jurisdiction to hear EPA’s [Title V] claim that Ameren [was] operating under
an inadequate or deficient permit.” Id. at *24.

                                        b. Trial
       Subsequently, the district court held a trial on the merits. After trial, the district
court entered an order setting forth its factual findings and legal conclusions. See
United States v. Ameren Mo. (Ameren III), 229 F. Supp. 3d 906 (E.D. Mo. 2017). The
court concluded that Ameren’s Rush Island overhauls were major modifications that
triggered PSD pollution-control requirements. The district court found that “[t]he
emissions evidence show[ed] [that] an increase related to the projects should have
been expected and actually occurred.” Id. at 997 (emphasis omitted). The court
identified categories of evidence that “all establish that there is a significant net
[sulfur dioxide] increase of more than 40 tons that was caused by the projects.” Id. at
998.

       First, the court identified “[t]wo key—and undisputed—characteristics of the
Rush Island units.” Id. at 988. The first characteristic was that “the Rush Island units
are big sources of pollution.” Id. The second characteristic was that “the Rush Island
units are ‘baseload’ units” that are “cheap sources of electricity” and “operate as
much as they can.” Id. According to the court, “[t]hese two facts lead to a logical
conclusion [that] if the Rush Island units are upgraded so they can generate more
electricity, they will. Performance improvements have a direct impact on annual
generation and pollution levels.” Id.

      Second, Robert Koppe, a power plant performance expert, opined that the Rush
Island’s plant availability increased because it replaced “these problematic

                                            -11-
components.” Id. at 989. Thereafter, “Dr. Ranajit Sahu, a permitting engineer and
expert for the United States, took Mr. Koppe’s findings on expected improved
availability and used them to calculate the expected additional pollution that would
result from the improvements.” Id. at 990. He “calculated an expected increase in
emissions of 608 tons of [sulfur dioxide] post-project for Unit 1.” Id. And, “[b]ased
on Mr. Koppe’s prediction of regained availability, . . . Dr. Sahu calculated an
expected increase of 415 tons per year of [sulfur dioxide] in Unit 2 that would result
from the availability improvement alone.” Id. at 992.

       Third, Dr. Ezra Hausman, a modeler and market consultant with 20 years’
experience in the electric industry, explained that the “sophisticated computer
modeling program” that Ameren used “to model and predict the Rush Island units’
fuel needs . . . for the years after the 2007 and 2010 major boiler outages” “showed
that both a unit’s capacity level and its availability are linearly related to the unit’s
projected coal consumption.” Id. at 994, 995. Thus, “if Ameren increased the number
of hours its Rush Island units were able to run, or if the company enabled the units
to operate at higher output levels during those hours, then the units would . . . burn[]
more coal and, as a result, emit[] more pollution.” Id. at 994–95. Dr. Hausman’s
“results show[ed] that Ameren’s modeling would predict significant emissions
increases at the Rush Island units as a result of the projects.” Id. at 996.

       Finally, “the actual post-project data” showed “a significant net [sulfur dioxide]
increase of more than 40 tons that was caused by the projects.” Id. at 998. Both units
were available more and operated every hour that they were available. Both units also
increased their maximum generating levels. This resulted in both units increasing
their sulfur dioxide pollution.

     In summary, the court determined that “[b]ased on the known facts that the
Rush Island units are low-cost, baseload units, common sense compels the same

                                          -12-
conclusion: improving availability or capacity at baseload units like Rush Island will
result in additional operations and pollution.” Id.

       Regarding liability, the district court also rejected Ameren’s defenses. First, the
district court concluded that Ameren failed to satisfy “its burden of proving that the
Rush Island projects fall within the narrow routine maintenance exemption.” Id. at
1003. The court characterized “[t]he 2007 and 2010 major boiler outages [as]
unprecedented events for Rush Island Units 1 and 2—they were the centerpieces of
the ‘most significant’ outages in plant history.” Id. (citation omitted).

       Second, the court rejected Ameren’s argument that any increases in production
and pollution were merely the result of demand growth that should be excluded from
the liability assessment. According to the court, the “relevant information” that
Ameren had “showed that the Rush Island units’ performance would improve,
resulting in increased generation and emissions.” Id. at 1010.

       In summary, the district court “enter[ed] a finding of liability against Ameren,”
concluding that the Rush Island Unit 1 and 2 projects described above were major
modifications under the CAA, Ameren violated the PSD program’s requirements “by
failing to obtain a preconstruction permit and install best available pollution control
technology,” and Ameren violated Title V of the CAA. Id. at 1017.

                                     2. Remedy Phase
                                  a. Summary Judgment
       After entering its post-trial order on liability, the district court proceeded to the
remedy phase. The court addressed the parties’ summary-judgment motions. First, the
court rejected Ameren’s argument “that the Clean Air Act does not authorize
injunctions as a remedy for past violations.” United States v. Ameren Mo. (Ameren
IV), 372 F. Supp. 3d 868, 871 (E.D. Mo. 2019). According to the court, “[t]he plain
language of § 7413(b) gives the EPA authority to ‘commence a civil action’ for

                                           -13-
injunctive relief or civil penalties, ‘or both,’ whenever a person ‘has violated or is in
violation of any requirement or prohibition of’ EPA air quality control programs.”
Id. (quoting 42 U.S.C. § 7413(b)). The court reasoned that § 7413(b)’s plain
“language places no restriction on injunctive relief for past violations” and instead
“authorizes the EPA to seek injunctive relief whenever a person has violated the
Clean Air Act.” Id.

       In addition, the district court rejected Ameren’s argument that the court could
not “order injunctive relief that includes emissions reductions or control technology
at the Labadie Energy Center (Labadie) coal-fired power plant.” Id. at 874.

                                         b. Trial
         The district court subsequently held a remedy trial. Following the trial, the
court issued an order imposing a two-pronged remedy with the purpose of “[(1)]
bring[ing] Ameren’s Rush Island facility into compliance with the law and
[(2)] . . . remediat[ing] the harm from the more than 162,000 tons—and counting—in
excess [sulfur dioxide] that Rush Island emitted after Ameren failed to obtain a PSD
permit there.” United States v. Ameren Mo. (Ameren V), 421 F. Supp. 3d 729, 802
(E.D. Mo. 2019).

       As to compliance, the district court concluded that “Ameren must make Rush
Island compliant by obtaining a PSD permit with emissions limitations based on wet
FGD [flue gas desulfurization technology]” used as the BACT. Id. at 806 (emphasis
omitted). The court determined that FGD technology is technically and economically
feasible and “can remove 95% or more of [sulfur dioxide] emissions.” Id. at 812.

       As to remediation, the district court concluded that “Rush Island’s excess
pollution is best remediated by decreasing emissions at the nearby Labadie Energy
Center.” Id. at 789 (emphasis omitted). Labadie consists of four coal-burning units
and is located 35 miles west of St. Louis. Ameren argued that imposition of the

                                          -14-
remedy was “extreme” and “constitute[d] a penalty” “because Labadie is ‘totally
innocent,’ and Ameren has not violated the Clean Air Act there.” Id. at 820. The
district court rejected Ameren’s argument, reasoning that its “remedy is based on
straightforward equitable principles and the authority [it] ha[s] under the Clean Air
Act ‘to restrain’ violations, ‘to require compliance,’ and ‘to award any other
appropriate relief.’” Id. (quoting 42 U.S.C. § 7413(b)). According to the court, its
remedy was “narrowly tailored” because “a tight geographic nexus [exists] between
the harms Rush Island caused and the benefits gained through reducing Labadie’s
emissions. Pollution from Labadie affects the same communities as those affected by
Rush Island, and to the same degree.” Id. at 820–21. The court reasoned that its
remedy “achieve[d] the maximum possible environmental benefit”: “When Ameren
reduces emissions at Labadie commensurate with the excess emissions from Rush
Island, Ameren will have put the public in the place it would have been absent
Ameren’s Clear Air Act violation.” Id. at 821. The court explained that “Ameren’s
ton-for-ton reductions at Labadie will lower the risks of premature mortality and
disease in the same communities impacted by Ameren’s Rush Island violations.” Id.

       The court rejected Ameren’s argument “that any injunction against its Labadie
plant would constitute a penalty.” Id. While the court acknowledged it could not
“issue injunctive relief that would constitute a penalty,” it concluded that “[b]y
ordering emissions reductions up to, but not surpassing, the excess emissions from
Rush Island, [the court was] ordering relief that goes exactly to ‘remedying the
damage caused to the harmed parties by the defendant’s action.’” Id. (quoting United
States v. Ameren Mo., No. 4:11-cv-77-RWS, 2016 WL 468557, at *1 (E.D. Mo. Feb.
8, 2016)). The court “order[ed] Ameren to base its relief at Labadie on DSI [dry
sorbent injection] control technology” “[t]o . . . ensure that any relief at Labadie does
not surpass the damage caused by Rush Island.” Id. Installation of DSI technology on
Labadie’s units would allow Ameren to “operate DSI for as many years as necessary
to remediate Rush Island’s excess emissions[] and terminate its use of DSI without
suffering significant lost capital assets.” Id. The court “order[ed] Ameren to begin

                                          -15-
operating Labadie with DSI, or a more effective pollution control, beginning no later
than three years after [its] order.” Id. at 822.

                                       3. Summary
       In summary, the district court found Ameren in violation of the CAA for
“mak[ing] major modifications to expand Rush Island’s capacity” without “apply[ing]
for a PSD permit and meet[ing] reduced emissions requirements.” Id. at 824. By
failing to “apply for the required PSD permit,” Ameren “skirted PSD’s requirement
to install the best available technology to control the pollution Rush Island emits.” Id.

       “To remedy [Ameren’s] violation of the Clean Air Act,” the district court
ordered Ameren to “apply for a PSD permit for Rush Island within ninety days,
propose wet FGD as BACT in its permit application, and implement BACT no later
than four and one-half years from [the] order.” Id. “In addition to the relief [the court]
order[ed] at Rush Island, [it] also order[ed] Ameren to reduce its pollution at Labadie
in an amount equal to Ameren’s excess emissions at Rush Island.” Id. It left Ameren
the option whether to “install[] DSI or some other more effective pollution control at
Labadie.” Id.

                                     II. Discussion
       Ameren appeals the district court’s orders. It raises five arguments: (1) the
Rush Island projects did not require permits under the Missouri SIP; (2) the Rush
Island projects did not constitute major modifications; (3) the district court lacked
jurisdiction under Article III and statutory authority under the CAA to enter the
injunctions; (4) the injunctive relief ordered at Labadie is punitive, not remedial, and
therefore prohibited; and (5) the district court lacked jurisdiction over the Title V
claims. We address each in turn.

                                          -16-
                                    A. Missouri SIP
       Ameren first argues that “under the plain language of Missouri’s SIP, permits
are required only for increases in potential emissions” and “it [is] undisputed that the
[Rush Island] Projects would not, and did not, increase potential emissions.”
Appellant’s Br. at 30. According to Ameren, the district court erroneously
“substituted the federal regulations’ applicability standard,” which “nullified the SIP
Permit Rule’s Applicability Provision.” Id. at 30–31.

      The Missouri SIP identifies which construction or modification projects at
emission sources require prior construction permits. Mo. Code Regs. Ann. tit. 10,
§ 6.060 (2007). Ameren cites to § 6.060(1) of the Missouri SIP, entitled
“Applicability” (“Applicability Section”). This section governs Missouri’s air quality
construction permit programs. The Applicability Section provides, in relevant part,
that

      [n]o owner or operator shall commence construction[2] or modification
      of any installation subject to this rule, begin operation after that
      construction or modification, or begin operation of any installation
      which has been shut down longer than five (5) years without first
      obtaining a permit from the permitting authority under this rule.

Mo. Code Regs. Ann. tit. 10, § 6.060(1)(C) (2007) (emphases added).

      In turn, the Missouri SIP offers two definitions of modification. First, it
generally defines “[m]odification” as “[a]ny physical change, or change in method of
operation of, a source operation or attendant air pollution control equipment which
would cause an increase in potential emissions of any air pollutant emitted by the
source operation.” Id. § 6.020(2)(M)(10) (emphasis added). “Potential to emit” means

      2
       “It is undisputed that the projects at issue were not ‘construction’ as defined
by the Missouri SIP or the PSD rules.” Ameren I, 158 F. Supp. 3d at 809 n.5.

                                         -17-
the unit’s ability to emit at full design capacity “assuming continuous year-round
operation.” Id. at § 6.020(2)(P)(19).

       Second, the Missouri SIP separately defines “Title I modification.”
Id. § 6.020(2)(M)(11). A “Title I modification” is “[a]ny modification that requires
a permit under 10 CSR 10-6.060 section (7) or (8), or that is subject to any
requirement under 10 CSR 10-6.070 or 10 CSR 10-6.080.” Id. § 6.020(2)(T)(3)
(emphasis added).3

       Ameren maintains that the Missouri SIP limits PSD applicability to only
projects increasing both actual and potential emissions. According to Ameren, the
Missouri SIP’s Applicability Section and definitional sections mean that “[i]f a
project would not increase a unit’s potential emissions, it is not a modification and
does not trigger permitting under the Applicability Provision.” Appellant’s Br. at 35.
Because the government “never alleged that the projects increased the units’ potential
emissions, Ameren argues that it [was] entitled to full summary judgment.” Ameren
I, 158 F. Supp. 3d at 808–09.

       Ameren, however, overlooks that, in contrast to the general definition of
modification in § 6.020(2)(M)(10), § 6.060(8)(A) of the Missouri SIP contains “PSD-
specific applicability language.” Id. at 809 (emphasis added) (citing RadLAX Gateway
Hotel, LLC v. Amalgamated Bank, 566 U.S. 639, 645 (2012)). That
section—expressly referenced in the Missouri SIP’s definition of “Title I
modification”—provides, in relevant part:

      3
       In addition to defining modification, the Missouri SIP independently defines
“[m]ajor modification” as “[a]ny physical change or change in the method of
operation at an installation or in the attendant air pollution control equipment that
would result in a significant net emissions increase of any pollutant.” Id.
§ 6.020(2)(M)(3). The Missouri SIP uses the term major modification in a section
concerning BACT. See id. § 6.020(2)(B)(5).

                                        -18-
      (8) Attainment and Unclassified Area Permits.

      (A) All of the subsections of 40 CFR 52.21 other than (a) Plan
      disapproval, (q) Public participation, (s) Environmental impact
      statements and (u) Delegation of authority are incorporated by
      reference. 40 CFR 52.21 as used in this rule refers to 40 CFR 52.21
      promulgated as of July 1, 2003 as published by the Office of the Federal
      Register, U.S. National Archives and Records, 700 Pennsylvania
      Avenue NW, Washington, D.C. 20408. This rule does not incorporate
      any subsequent amendments or additions.

Mo. Code Regs. Ann. tit. 10, § 6.060(8)(A) (2007) (emphases added).

       In turn, the federal regulation referenced in § 6.060(8)(A) of the Missouri SIP
provides that the PSD’s “[a]pplicability procedures” “apply to the construction of any
new major stationary source or the major modification of any existing major
stationary source” located in a PSD area. 40 C.F.R. § 52.21(a)(2)(ii) (emphasis
added). The regulations explicitly define major modification. “Major modification
means any physical change in or change in the method of operation of a major
stationary source that would result in: a significant emissions increase . . . of a
regulated NSR pollutant . . . ; and a significant net emissions increase of that pollutant
from the major stationary source.” Id. § 52.21(b)(2)(i) (emphasis added). “A . . . major
modification shall meet each applicable emissions limitation under the [SIP] and each
applicable emissions standard and standard of performance under 40 CFR parts 60
and 61.” Id. § 52.21(j)(1).

      The federal regulation establishes that a major modification triggers the PSD
requirements. According to the regulation, “[n]o . . . major modification . . . shall
begin actual construction without a permit that states that the . . . major
modification will meet those requirements.” Id. § 52.21(a)(2)(iii). To assess whether
a major modification occurred, the federal regulation states that an

                                          -19-
“[a]ctual-to-projected-actual applicability test [applies] for projects that only involve
existing emissions units.” Id. § 52.21(a)(2)(iv)(c) (emphasis added). Under that test,

      [a] significant emissions increase of a regulated NSR pollutant is
      projected to occur if the sum of the difference between the projected
      actual emissions . . . and the baseline actual emissions . . . , for each
      existing emissions unit, equals or exceeds the significant amount for that
      pollutant . . . .

Id.

        As the district court observed, “EPA’s approval of the [Missouri] SIP illustrates
why the specific PSD rules control.” Ameren I, 158 F. Supp. 3d at 810. In approving
the Missouri SIP, the EPA stated, “[W]e are approving most of the revisions to the
Construction Permits Required rule because the revisions incorporate, by reference,
the Federal New Source Review reforms . . . . ” Approval and Promulgation of
Implementation Plans; State of Missouri, 71 Fed. Reg. at 36,486. More specifically,
it stated that it was “approving revisions to Missouri rule, 10 CSR 10-6.060,
Construction Permits Required, into the SIP. This rule incorporates by reference the
. . . PSD . . . program in 40 CFR 52.21 . . . .” Id. at 36,487.

       Importantly, the “EPA’s approval of the SIP provided that the CAA and the
program requirements as set out in 40 C.F.R. 52.21 would supersede any conflicting
provisions in the state SIP.” Ameren I, 158 F. Supp. 3d at 810 (quoting 71 Fed. Reg.
at 36,486 (“This revision incorporates by reference the other provisions of 40 C.F.R.
52.21 as in effect on July 1, 2003, which supersedes any conflicting provisions in the
Missouri rule.” (emphasis added in Ameren I))).

       Furthermore, as the district court pointed out, Ameren’s argument that “the
[Missouri] SIP first requires . . . that a threshold determination be made that a project
is a ‘modification’” under § 6.020(2)(M)(1), “would render a portion of the PSD rules

                                          -20-
superfluous.” Id. at 810. The Supreme Court rejected a similar argument in Duke
Energy. In that case, the Court held that the EPA is not required “to conform its PSD
regulations on ‘modification’ to their NSPS counterparts.” 549 U.S. at 565.
According to the Court, aligning the PSD regulations with the NSPS regulations “was
inconsistent with their terms and effectively invalidated them.” Id. Relevant to the
present case, the Court rejected the defendant power company’s argument that,
“before a project can become a ‘major modification’ under the PSD regulations, it
must meet the definition of ‘modification’ under the NSPS regulations.” Id. at 581 n.8
(citations omitted). According to the Court, “the language of the regulations [did] not
support” such a reading because it would render portions of the PSD regulations
superfluous. Id. (“[I]t would be superfluous for PSD regulations to require a ‘major
modification’ to be a ‘physical change in or change in the method of operation,’ if
they presupposed that the NSPS definition of ‘modification,’ which contains the same
prerequisite, had already been satisfied.” (citations omitted)).

      Finally, United States v. Cinergy Corp., 623 F.3d 455 (7th Cir. 2010), upon
which Ameren relies, is distinguishable. There, the EPA brought an enforcement
action against several coal-fired power plants. Id. at 456. As in the present case, the
EPA alleged that the plants’ projects were major modifications requiring a PSD
permit. Id. The plants argued that no permit was required because the projects did not
increase the units’ potential emissions under the Indiana SIP, which based
applicability on increases in potential emissions instead of actual emissions. Id. at
458. On appeal, the Seventh Circuit held that “[t]he Clean Air Act does not authorize
the imposition of sanctions for conduct that complies with a [SIP] that the EPA has
approved.” Id. (citing 42 U.S.C. § 7413(a)(1)).

       Like the power plants in Cinergy, Ameren maintains that it lacked notice “that
EPA would treat its approval of Sections 10–6.060(1)(C) (Applicability) and
10–6.020(2)(M)(10) (definition of ‘modification’) as a rejection of them”;
furthermore, it asserts that “allowing EPA to impose liability when it is undisputed

                                         -21-
no modification has occurred would violate basic principles of due process and fair
notice.” Ameren I, 158 F. Supp. 3d at 812. But Cinergy is distinguishable from the
present case because (1) the Indiana SIP did not incorporate the PSD rules into the
State’s plan; (2) the “EPA’s approval of the Indiana SIP did not expressly provide
that the PSD rules as set out in the Code of Federal Regulations supersede any
conflicting provisions in the state SIP”; and (3) the power plants in Cinergy had
“actual notice” of the Indiana SIP provision, whereas “it is not clear that Ameren had
actual notice of the SIP provision.” Id. Furthermore, Cinergy is merely persuasive
authority and not binding on this court. See Duluth, Winnipeg & Pac. Ry. Co. v. City
of Orr, 529 F.3d 794, 798 (8th Cir. 2008).

       Accordingly, we hold that the district court did not err in holding that the Rush
Island projects required permits through application of the actual-to-projected-actual
applicability test under 40 C.F.R. § 52.21(a)(2)(iv)(c), incorporated by reference in
§ 6.060(8)(A) of the Missouri SIP.

                               B. Major Modification
       Alternatively, Ameren argues that “even if federal regulations governed
applicability, Ameren was held liable under the wrong legal standards, independently
requiring reversal.” Appellant’s Br. at 45. Ameren maintains that the district court
erred in concluding the Rush Island projects constituted major modifications.
Specifically, Ameren contends that the district court erroneously (1) shifted the
burden of proof on causation; (2) “applied new interpretations of the federal
regulations’ causation provision”; and (3) applied a “‘reasonable power plant
operator’ standard the regulations do not require.” Id. at 45–46. In addition, Ameren
asserts that the district court erred by permitting the government to use expert
opinions on actual post-project emissions that were not disclosed. Id. at 56.

      A “[m]ajor modification” at emission sources occurs when a physical change
in the facility would result in “a significant emissions increase.” 40 C.F.R.

                                         -22-
§ 52.21(b)(2)(i). “To satisfy its burden under the [CAA], the government ha[s] to
show that at the time of the projects [Ameren] expected, or should have expected, that
its modifications would result in a ‘significant net emissions increase’ . . . .” United
States v. Ala. Power Co., 730 F.3d 1278, 1282 (11th Cir. 2013).

                                    1. Burden of Proof
       One feature of the federal regulation’s “projected-actual-emissions
methodology [is] the exclusion from the emissions projection of any emissions due
to increased demand.” New York, 413 F.3d at 31. This demand-growth exclusion
functions as a type of defense for the source to avoid triggering PSD requirements.
The federal regulation “allow[s] exclusion of emissions that could have been
accommodated during the baseline period and ‘that are also unrelated to the particular
project.’” Id. at 33 (quoting 40 C.F.R. § 52.21(b)(41)(ii)(c)). Emissions “unrelated to
the particular project . . . include[] any increased utilization due to product demand
growth.” Id. (quoting 40 C.F.R. § 52.21(b)(41)(ii)(c)).

      Thus, under the regulation, “a source must”

      establish[] two criteria . . . before excluding emissions from its
      projection: “(1) [t]he unit could have achieved the necessary level of
      utilization during the consecutive 24-month period [the source] selected
      to establish the baseline actual emissions; and (2) the increase is not
      related to the physical or operational change(s) made to the unit.”

Id. (alterations in original) (emphasis added) (quoting Prevention of Significant
Deterioration (PSD) and Nonattainment New Source Review (NSR): Baseline
Emissions Determination, Actual-to-Future-Actual Methodology, Plantwide
Applicability Limitations, Clean Units, Pollution Control Projects, 67 Fed. Reg.
80,186-01, 80,203 (Dec. 31, 2002)); see also United States v. DTE Energy Co., 845
F.3d 735, 737 (6th Cir. 2017).

                                         -23-
       Ameren argues that “the [d]istrict [c]ourt improperly shifted the burden of
proving causation to Ameren.” Appellant’s Br. at 46. Before the district court, the
parties disputed who bore the burden of proving “that any increases in emissions were
caused by demand growth.” Ameren II, 2016 WL 728234, at *11. Ameren argued that
the EPA bore the burden of proving demand growth “because under the definition of
‘projected actual emissions,’ the regulations require that unrelated emissions be
exempted from the calculation.” Id. By contrast, the EPA maintained that Ameren
bore the burden of proof on demand growth as “the party seeking to benefit from an
exemption.” Id. The district court held that “while it remains EPA’s burden to prove
that Ameren should have expected the projects to cause an increase in emissions, the
burden is Ameren’s to prove that the demand growth exclusion applies.” Id.
(emphasis added).

       The district court is correct. As recognized in New York and DTE Energy, it is
the source’s burden to prove the applicability of the demand-growth exclusion. This
is in accordance with the Supreme Court precedent that the party asserting the
exception bears the burden of proving its applicability. NLRB v. Ky. River Cmty.
Care, Inc., 532 U.S. 706, 711 (2001) (“The burden of proving the applicability of the
supervisory exception . . . should thus fall on the party asserting it.”); FTC v. Morton
Salt Co., 334 U.S. 37, 44–45 (1948) (“[T]he general rule of statutory construction that
the burden of proving justification or exemption under a special exception to the
prohibitions of a statute generally rests on one who claims its benefits . . . .”).

      As a result, we hold that the district court did not impermissibly shift the
burden of proof to Ameren in proving the applicability of the demand-growth
exclusion.

                                   2. Causation
     According to Ameren, in post-trial briefing, the government switched theories
on how the district court should analyze increased demand to satisfy the demand-

                                         -24-
growth exclusion. Ameren also asserts that the government, in effect, promulgated
a new causation standard without following notice-and-comment rulemaking.
Specifically, Ameren contends, the government persuaded the district court that
Ameren had to show “demand growth for a specific unit’s generation.” Appellant’s
Br. at 47. Ameren argues that this causation standard is “the exact opposite of EPA’s
prior statements [that] ‘[d]emand growth refers to what the utility expects to be
required to produce in the way of energy system wide, not for a single unit, but
system wide.’” Id. (citation omitted).

       We hold that the district court did not apply an improper causation standard.
Citing New York, the district court expressly acknowledged that Ameren had to
satisfy “two criteria . . . before excluding emissions from its projection.” Ameren III,
229 F. Supp. 3d at 1003 (quoting New York, 413 F.3d at 33). The first requirement
is that “the unit could have achieved the necessary level of utilization during the
[baseline period].” Id. (emphasis added) (alteration in original) (quoting New York,
413 F.3d at 33). The second requirement is that “the increase is not related to the
physical or operational change(s) made to the unit.” Id. (emphasis added) (quoting
New York, 413 F.3d at 33). This accurately states the appropriate causation standard.
As a result, the district court did not err in holding that to prove the applicability of
the demand-growth exclusion, Ameren had to establish “that demand on the unit
increases.” Id. at 1003.

                         3. Reasonable Power Plant Operator
       “In order to be deemed a major modification, [the government] . . . [must] show
(1) a physical change to the plant; (2) a significant net emissions increase; and (3) a
causal link between the two.” United States v. La. Generating, LLC, 929 F. Supp. 2d
591, 593 (M.D. La. 2012). As explained supra, “the government had to show that at
the time of the projects [Ameren] expected, or should have expected, that its

                                          -25-
modifications would result in a ‘significant net emissions increase’ . . . .” Ala. Power
Co., 730 F.3d at 1282.4

       “[T]he [federal] regulations do not require a utility to be prescient, rather they
require the company to undertake a reasonable estimate of what post-project
emissions would be.” United States v. Duke Energy Corp., No. 1:00-cv-1262, 2010
WL 3023517, at *6 (M.D.N.C. July 28, 2010) (emphasis added) (citing United States
v. Cinergy Corp., 458 F.3d 705, 709 (7th Cir. 2006)). “[T]he question [is] whether the
owner of the facility at the time of the work . . . expected or reasonably should have
expected, the work to increase emissions . . . .” La. Generating, 929 F. Supp. 2d at
593 (emphasis added).

       In its motion for summary judgment at the liability phase, Ameren argued that
“under an expectations theory,” the EPA had to “come forward with admissible
evidence of what a reasonable power plant operator or owner would expect, and its
failure to do so is fatal to EPA’s expectations theory case, warranting a grant of
partial summary judgment.” Ameren II, 2016 WL 728234, at *18. While “Ameren
acknowledge[d] that the determination of whether a party acted reasonably is
generally a question for the factfinder,” it maintained that “when the touchstone for
objective reasonableness requires a technical understanding of the subject matter that
is beyond a layperson’s normal understanding, the factfinder must have guidance to
make that determination.” Id.

      The district court, however, determined “that no special standard of care
evidence is required for the factfinder to be able to determine whether a reasonable
power plant operator or owner would have expected the projects to cause a significant
emissions increase.” Id. The court reasoned that (1) “[t]he legal standards supplied

      4
        Alternatively, the government can prove a project actually resulted in a
significant increase in emissions. See 40 C.F.R. § 52.21(a)(2)(iv)(b).

                                          -26-
by the PSD rules are sufficient to guide the analysis,” and (2) “the parties
. . . submitted mountains of evidence regarding what they believe a reasonable power
plant operator or owner would have concluded.” Id. Specifically, the parties’ experts
would “testify about what Ameren did to make its projections, what information
Ameren considered or did not consider, and why, and what the projections showed.”
Id. The court noted that other “courts that have considered expectations theory
enforcement actions” have applied “[t]his method.” Id. (first citing United States v.
Duke Energy Corp., 981 F. Supp. 2d 435, 439 (M.D.N.C. 2013); then citing Cinergy,
623 F.3d at 459; and then citing La. Generating, 929 F. Supp. 2d at 593).

       On appeal, Ameren now asserts that the district court erroneously denied
“[s]tandard-of-care evidence [in] defining the specific boundaries of reasonableness.”
Appellant’s Br. at 50. According to Ameren, “the written requirements of the
regulations,” as opposed to the “expert witnesses’ subjective views,” “should have
governed liability.” Id. Ameren maintains that “[b]y superimposing a[] [reasonable
power plant operator] standard, the [d]istrict [c]ourt allowed EPA’s experts to second-
guess Ameren’s conclusions even though Ameren followed the regulations’ written
requirements.” Id. at 51.

        We conclude that the district court did not err in holding that “no special
standard of care evidence is required for the factfinder to be able to determine
whether a reasonable power plant operator or owner would have expected the projects
to cause a significant emissions increase.” Ameren II, 2016 WL 728234, at *18.
Instead, the district court, as the factfinder, was entitled to “consider all relevant
information available to [Ameren] at the time of the project, including prior operating
data and [Ameren’s] own statements and documents” in determining whether Ameren
“should have predicted that a project would have caused a [significant] net increase.”
Id. at *19 (quoting Jury Instr. No. 23, United States v. Cinergy, 1:99-cv-1693-LJM-
JMS (S.D. Ind. 2008), ECF No. 1335).

                                         -27-
                               4. Expert Testimony
      Ameren argues that the district court abused its discretion in admitting and
relying on undisclosed expert opinions. See Ryan v. Bd. of Police Comm’rs of St.
Louis, 96 F.3d 1076, 1081 (8th Cir. 1996) (“We review the district court’s decision
to admit evidence over a party’s objection for abuse of discretion.”).

       In two motions filed during the trial on the liability phase and in post-trial
briefs, Ameren moved to exclude the expert testimony of Koppe and Dr. Sahu
“concerning causation of the actual emissions increases.” Ameren III, 229 F. Supp.
3d at 1015. Ameren argued to the district court that “the testimony concerning the
causation of the actual emissions increases are new, undisclosed opinions.” Id.

       The district court denied Ameren’s motions to exclude Koppe’s and Dr. Sahu’s
testimony. First, it rejected Ameren’s argument that the experts’ opinions were “new”
and concluded that Ameren had “sufficient notice of both the United States’ actual
emissions case and of Mr. Koppe and Dr. Sahu’s opinions.” Id. at 1016. The court
highlighted that the experts “(1) analyzed the actual post-project data in their reports,
the attachments, and their work papers, and (2) stated that the projected increases
actually materialized.” Id. at 1015. Additionally, the court noted that the experts
discussed in their reports and depositions “how the projects enable increased
availability and contribute to increases in emissions.” Id. The court explained that the
experts were not required to “state[] their opinions in the precise words that Ameren
thinks they should have used” because the “notice required of expert opinions is not
so formulaic.” Id.; see also Thompson v. Doane Pet Care Co., 470 F.3d 1201,
1202–03 (6th Cir. 2006) (explaining that Federal Rule of Evidence 26(a)(2)(B)
“contemplates that the expert will supplement, elaborate upon, explain and subject
himself to cross-examination upon his report”)).

      Second, the district court concluded that even if it erroneously admitted the
expert testimony, Ameren was unable to “show that it was prejudiced by the

                                          -28-
challenged testimony or the admission of the exhibits.” Ameren III, 229 F. Supp. 3d
at 1016. This was because “[t]he evidence the United States presented to show that
the actual emissions increases were caused by the projects was also presented in the
context of its expectations case regarding the expected causes of projected emissions
increases, so the challenged testimony is in part cumulative evidence.” Id. The court
also noted Ameren’s “opportunity both during pre-trial discovery and during
cross-examination at trial to test those opinions.” Id.

       Here, even assuming that the district court abused its discretion by admitting
the expert testimony, “any error would be harmless.” Smith v. Tenet Healthsystem SL,
Inc., 436 F.3d 879, 889 (8th Cir. 2006). Harmless error applies here because the
district court, as the factfinder, expressly stated that had the expert testimony on
actual emissions not been admitted, the result would not be different.

                                   C. Injunctive Relief
       Ameren argues generally that the district court lacked Article III jurisdiction
and statutory jurisdiction to issue injunctive relief “based on Rush Island’s
operation.” Appellant’s Br. at 66. According to Ameren, the district court found
during the liability phase “that the Rush Island Projects were major modifications
requiring permits before Ameren could commence construction.” Id. at 67. But,
during the remedy phase, the government “did not seek to prove any injury from the
violation it proved” and “[i]nstead . . . sought to obtain relief based on the harm from
Rush Island’s operation without a PSD permit.” Id. Ameren maintains that
“[o]perations do not cause an injury that the PSD program recognizes.” Id. Ameren
further argues that the district court lacked jurisdiction to impose injunctive relief
redressing “excess emissions.” Id. at 69. Ameren asserts that the government waived
“penal relief, including civil penalties; an injunction to prevent construction; an
injunction to obtain information about future planned projects; and declaratory
relief.” Id. at 71 (citations omitted). Finally, Ameren argues that the CAA “does not

                                         -29-
authorize injunctions for wholly past violations” and that “[o]nly past violations are
at issue here.” Id. at 72.

       “We review a district court’s grant of a permanent injunction for abuse of
discretion.” Kittle-Aikeley v. Strong, 844 F.3d 727, 735 (8th Cir. 2016). An abuse of
discretion occurs when a district court “reaches its conclusion by applying erroneous
legal principles or relying on clearly erroneous factual findings.” Id. (citation
omitted). “Where the determinative question is purely legal, our review is more
accurately characterized as de novo.” Id. (quotation omitted).

       “Whenever . . . the [government] finds that any person has violated or is in
violation of any requirement . . . of an applicable implementation plan or permit, [the
government] [must] notify the person . . . of such finding.” 42 U.S.C. § 7413(a)(1)
(emphasis added). Only after the “expiration of 30 days following the date on which
such notice of a violation [was] issued” may the government “bring a civil
[enforcement] action.” Id. § 7413(a)(1)(C). The government is authorized to
“commence a civil action for a permanent or temporary injunction, or to assess and
recover a civil penalty . . . , or both,” “[w]henever such person has violated, or is in
violation of” a requirement of Title I of the CAA. Id. § 7413(b)(1) (emphasis added).
A civil enforcement action

      may be brought in the district court of the United States for the district
      in which the violation is alleged to have occurred, or is occurring, or in
      which the defendant resides, or where the defendant’s principal place of
      business is located, and such court shall have jurisdiction to restrain
      such violation, to require compliance, to assess such civil penalty, to
      collect any fees owed the United States under this chapter (other than
      subchapter II) and any noncompliance assessment and nonpayment
      penalty owed under section 7420 of this title, and to award any other
      appropriate relief.

Id. § 7413(b) (emphases added).

                                         -30-
       In summary,

       [t]he Clean Air Act authorizes the EPA to bring a civil enforcement
       action when any person has violated a permit or SIP, has violated any
       requirement in certain subchapters of the Clean Air Act (including the
       PSD program), or “attempts to construct or modify a major stationary
       source” in any state that the EPA Administrator has found out of
       compliance with the New Source Review program.

United States v. EME Homer City Generation, L.P., 727 F.3d 274, 291–92 (3d Cir.
2013) (emphases added).

       Section 7413(b) “limits a district court’s jurisdiction to awarding certain kinds
of relief.” Id. at 292. “Each type of relief in [§ 7413(b)] (except for civil penalties) is
necessarily forward-looking.” Id. (footnote omitted). The remaining term —“[a]ny
other appropriate relief”—is merely a “catch-all” provision that “follows ‘a list of
specific items separated by commas.’” Id. at 293 (quoting Ali v. Fed. Bureau of
Prisons, 552 U.S. 214, 225 (2008)). “As the word ‘other’ demonstrates, this general
phrase is a residual category of the same type as the preceding items (namely, kinds
of relief).” Id. “[T]he canon of ejusdem generis requires us to interpret this catch-all
as permitting forward-looking relief, consistent with the preceding types of relief in
the list.” Id. at 295.

      In Homer City, the Third Circuit held that “[t]he text of the Clean Air Act does
not authorize an injunction against former owners and operators for a wholly past
PSD violation, even if that violation causes ongoing harm.” Id. at 291 (emphases
added). But the court “express[ed] no opinion” on whether injunctions are “available
in general to remedy ongoing harm from wholly past violations.” Id. at 291 n.19
(emphases added). Indeed, as against the current owners, the court explained that the
government could, after “completion of a facility’s modification, . . . still obtain an
injunction requiring the owner or operator to comply with the PSD requirements.” Id.

                                           -31-
at 289 (emphases added); see also United States v. U.S. Steel Corp., 16 F. Supp. 3d
944, 950 (N.D. Ind. 2014) (“Requiring a company to do ‘a further round of
modifications to get the permit’ could only be done through injunctive relief.”
(quoting United States v. Midwest Generation, LLC, 720 F.3d 644, 646 (7th Cir.
2013)).

      Homer City is distinguishable from the present case because it concerned
injunctive relief against a facility’s former owners. United States v. Luminant
Generation Co., L.L.C., 905 F.3d 874, 888 (5th Cir. 2018), reh’g en banc granted,
929 F.3d 316 (5th Cir. 2019).5 It does not detract from the plain language of
§ 7413(b), which “plainly gives district courts jurisdiction to restrain a violation,
require compliance, and award any other appropriate relief whenever a person has
committed a . . . violation” Id.

      Here, however, Ameren also specifically challenges the district court’s
injunction against its Labadie plant, which committed no violations of the CAA.
According to Ameren, neither the CAA nor the regulations authorize such relief.

      Under § 7413, a district court “has the authority to order [a defendant] to take
appropriate actions that remedy, mitigate and offset harms to the public and the
environment caused by the [defendant’s] proven violations of the CAA.” United
States v. Cinergy Corp., 582 F. Supp. 2d 1055, 1060 (S.D. Ind. 2008) (emphasis
added); see also United States v. Oliver, No. 3:06-CV-196-JWS, 2009 WL 10671371,
at *13 (D. Alaska June 25, 2009) (“Section 113(b) of the Clean Air Act, 42 U.S.C.
§ 7413(b), expressly provides for injunctive relief to redress violations of the Act.”
(emphasis added)), aff’d, 394 F. App’x 376 (9th Cir. 2010).

      5
      The Fifth Circuit ultimately dismissed the appeal in Luminant on the parties’
motion.

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       Here, the government never provided notice of or alleged that the Ameren’s
Labadie plant committed a violation of the CAA. The plain language of § 7413(b) and
caselaw make clear that the injunctive relief a district court may award must redress
a violation of the CAA. See 42 U.S.C. § 7413(b)(1)–(3) (permitting civil enforcement
actions “[w]henever such person has violated, or is in violation of” certain
requirements and noting that the district “court shall have jurisdiction to restrain such
violation”). Because Ameren committed no violation of the CAA at its Labadie plant,
the district court lacked authority to authorize injunctive relief as to it. Cf. United
States v. Cinergy Corp., 618 F. Supp. 2d 942, 967 (S.D. Ind. 2009) (denying
government’s requested relief because the remedy would be punitive as the
government proved no violation at the non-source unit against which it was sought.),
rev’d on other grounds, 623 F.3d 455 (7th Cir. 2010); United States v. Westvaco
Corp., No. MJG-00-2602, 2015 WL 10323214, at *12 & n.27 (D. Md. Feb. 26, 2015)
(rejecting government’s request for the district court to order the defendant “to install
control technology on a totally ‘innocent’ boiler” that the government never alleged
“violated PSD regulations” (footnote omitted)).

      Accordingly, we reverse the Labadie injunction and remand for further
proceedings consistent with this opinion.

                      E. Jurisdiction over Title V Claims
      Finally, Ameren challenges the district court’s jurisdiction over the Title V
claims.

      Ameren operates Rush Island under a Title V permit issued by the Missouri
Department of Natural Resources. This permit “restat[ed] the requirement that
Ameren was prohibited from performing any unpermitted major modifications of
Rush Island Units 1 or 2.” Ameren III, 229 F. Supp. 3d at 985.

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      The government brought Title V claims against Ameren, and Ameren
challenged the district court’s subject matter jurisdiction to hear those claims. It
argued—as it does here—that the Title V violation “is reviewable exclusively by the
courts of appeals, not collaterally in civil . . . enforcement actions in the district
courts.” Appellant’s Br. at 73 (alteration in original) (quoting Homer City, 727 F.3d
at 296–97).

       Ameren’s jurisdictional argument lacks merit. “The EPA has authority to bring
a civil enforcement action against a person who, among other things, ‘has violated,
or is in violation of, any other requirement or prohibition of [various subchapters,
including Title V].’” Homer City, 727 F.3d at 298 (alteration in original) (quoting 42
U.S.C. § 7413(b)(2)). In turn, Title V’s plain text “lists only two ways in which it can
be violated: operating without a Title V permit or violating the terms of a Title V
permit while operating a source.” Id. (emphasis added) (citing 42 U.S.C.§ 7661a(a)).

      The district court expressly found that Ameren violated an express permit term
prohibiting it from performing unpermitted major modifications. Cf. Otter Tail, 615
F.3d at 1020. Under § 7413(b), the district court had jurisdiction to consider whether
Ameren violated the express terms of its Title V permit.

                                    III. Conclusion
       Accordingly, we affirm the judgment of the district court in all respects except
as to the injunctive relief entered against Ameren’s Labadie plant. We remand for
further proceedings consistent with this opinion.
                        ______________________________

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