Sierra Club, Et Al . v. Federal Energy Regulatory Commission

United States Court of Appeals
FOR THE DISTRICT OF COLUMBIA CIRCUIT
Argued April 7, 2022 Decided May 26, 2023
No. 20-1512
SIERRA CLUB, ET AL .,
PETITIONERS
v.
FEDERAL ENERGY REGULATORY COMMISSION ,
RESPONDENT
EQUITRANS , L.P., ET AL .,
I NTERVENORS
Consolidated with 21-1040
On Petitions for Review of Orders
of the Federal Energy Regulatory Commission
Benjamin A. Luckett argued the cause for petitioners. With
him on the briefs were Elizabeth F. Benson and Julie
Gantenbein.
Matthew W.S. Estes, Attorney, Federal Energy Regulatory
Commission, argued the cause for respondent. With him on
the brief were Matthew R. Christiansen, General Counsel, and

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Robert H. Solomon, Solicitor. Scott R. Ediger, Attorney
Advisor, entered an appearance.
Jeremy C. Marwell argued the cause for respondent-
intervenors Mountain Valley Pipeline, LLC, et al. With him
on the joint brief were Matthew Eggerding, Matthew X.
Etchemendy, James T. Dawson, Jennifer Leigh Flint Brough,
Thomas Knight, Randall S. Rich, Valerie Layne Green,
Charlotte Taylor, and James Olson.
Before: S RINIVASAN , Chief Judge, M ILLETT and W ILKINS ,
Circuit Judges.
Opinion for the Court filed by Chief Judge SRINIVASAN .
SRINIVASAN , Chief Judge: For years, Mountain Valley
Pipeline, LLC has been trying to build its eponymous Mountain
Valley Pipeline through West Virginia and Virginia. In 2017,
the Federal Energy Regulatory Commission first issued a
certificate approving the project. Our court affirmed that order.
But to build an interstate natural gas pipeline, a company often
needs additional federal permits from agencies other than the
Commission. Mountain Valley needed approvals from the
Bureau of Land Management, Forest Service, Army Corps of
Engineers, and Fish and Wildlife Service. While Mountain
Valley initially obtained each of those additional permits, the
United States Court of Appeals for the Fourth Circuit vacated
all of them over time.
The Commission responded with a series of follow-up
orders. As Mountain Valley reacquired permits from the other
agencies, the Commission extended the deadline for
completing construction and authorized work to resume.
Several environmental groups now petition for review of the
Commission’s orders allowing the project to proceed.

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We deny most of their claims and conclude that one is
moot. But we agree with one of the claims: that the
Commission inadequately explained its decision not to prepare
a supplemental environmental impact statement addressing
unexpectedly severe erosion and sedimentation along the
pipeline’s right-of-way. While we grant the petitions for
review in part on that ground, we do not vacate the
Commission’s orders allowing work on the project to resume.
Instead, we remand the orders without vacatur to enable the
Commission either to prepare a supplemental environmental
impact statement or to better explain why one is unnecessary.
I.
A.
The Natural Gas Act authorizes the Federal Energy
Regulatory Commission to regulate the interstate
transportation of natural gas. 15 U.S.C. § 717. A company
desiring to build a natural gas pipeline must first obtain a
certificate of “public convenience and necessity” from the
Commission. Id. § 717f(c).
The Commission’s certificate process incorporates review
of proposed projects under the National Environmental Policy
Act (NEPA), 42 U.S.C. § 4321 et seq. See Food & Water
Watch v. FERC, 28 F.4th 277, 282 (D.C. Cir. 2022). NEPA
“declares a broad national commitment to protecting and
promoting environmental quality, and brings that commitment
to bear on the operations of the federal government.” Sierra
Club v. FERC, 867 F.3d 1357, 1367 (D.C. Cir. 2017)
(quotation marks and citation omitted). To that end, NEPA
requires federal agencies to “identify the reasonable
alternatives to a contemplated action and look hard at the

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environmental effects of their decisions.” City of Bos.
Delegation v. FERC, 897 F.3d 241, 246 (D.C. Cir. 2018)
(alteration, quotation marks, and citation omitted).
Agencies first prepare a draft environmental impact
statement discussing the effects of the proposed action and of
reasonable alternatives. 40 C.F.R. § 1502.9(b). A final
environmental impact statement then accompanies an agency’s
ultimate decision. Id. § 1502.9(c). But an agency’s obligations
under NEPA do not always end there. An agency must
supplement its environmental analysis if “substantial changes
to the proposed action” or “significant new circumstances or
information” raise additional concerns about the action’s
environmental impact. Id. § 1502.9(d)(1)(i)–(ii).
B.
In 2017, the Commission issued a certificate of public
convenience and necessity for the Mountain Valley Pipeline.
Order Issuing Certificates and Granting Abandonment
Authority, Mountain Valley Pipeline, LLC, 161 FERC ¶ 61,043
(Oct. 13, 2017) (Certificate Order), J.A. 86–221. The Pipeline
would carry natural gas 303.5 miles across the Appalachian
Mountains, from Wetzel County, West Virginia, to an
interconnection with a compressor station in Pittsylvania
County, Virginia. The Commission determined that Mountain
Valley had shown market demand for the Pipeline based on
five shipping contracts, known as precedent agreements,
covering the Pipeline’s full capacity.
In its final environmental impact statement, the
Commission recognized that construction of the Pipeline
would cause at least some soil erosion and sedimentation. To
build the Pipeline, Mountain Valley would clear a 125-foot-
wide corridor along the route, which would expose the soil to

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wind and rain. The company would then dig or blast a trench
in which to bury the Pipeline, dislodging more dirt for runoff.
And much of the construction would occur near and across
waterbodies. In those circumstances, sedimentation would be
unavoidable. But the Commission concluded in the
environmental impact statement that control measures such as
silt fences would minimize effects on waterbodies. And in the
end, Mountain Valley planned to return the route to as close to
its original state as practicable. The Certificate Order adopted
the final environmental impact statement and declared the
Pipeline “environmentally acceptable.” Id. ¶ 308.
When approving the project, the Commission also
imposed conditions concerning when construction could begin
and by when it needed to end. At the front end, the Certificate
Order’s Environmental Condition 9 required Mountain Valley,
“before commencing construction of any project facilities,” to
submit “documentation that it has received all applicable
authorizations required under federal law.” Certificate Order,
App. C, Environmental Condition 9. At the back end, the
Commission directed Mountain Valley to complete
construction within three years, by October 13, 2020.
Certificate Order ¶ 310.
Several environmental groups petitioned our court for
review of the Certificate Order. We rejected their challenge.
Appalachian Voices v. FERC, Nos. 17-1271, 18-1002, 18-
1175, 18-1177, 18-1186, 18-1216, 18-1223, 2019 WL 847199
(D.C. Cir. Feb. 19, 2019) (per curiam). We concluded that the
Commission had reasonably found a market need for the
Pipeline based on the “precedent agreements for 100 percent of
the Project’s capacity.” Id. at *1. As for the order’s
environmental analysis, we determined that the Commission
had “adequately considered and disclosed erosion and
sedimentation impacts on aquatic resources.” Id. at *2.

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C.
In addition to obtaining a certificate from the Commission,
a pipeline project must also “comply with all other federal,
state, and local regulations not preempted by the [Natural Gas
Act].” Dominion Transmission, Inc. v. Summers, 723 F.3d 238,
240 (D.C. Cir. 2013). Depending on a pipeline’s proposed
route and potential impacts, permits from various other federal
agencies might be needed.
The Mountain Valley Pipeline would traverse more than
three hundred waterbodies, requiring a permit from the Army
Corps of Engineers. The Pipeline would also cut across
Jefferson National Forest, requiring authorization from the
Department of Interior’s Bureau of Land Management and the
Department of Agriculture’s Forest Service. And the Pipeline
would intersect with the habitats of endangered species,
requiring the approval of the Fish and Wildlife Service.
Mountain Valley obtained all of those necessary permits,
and, pursuant to Environmental Condition 9, received the
Commission’s authorization to break ground, which it did in
February 2018. In the ensuing months, though, the United
States Court of Appeals for the Fourth Circuit vacated each of
the other federal permits.
First, in July 2018, the Fourth Circuit vacated the
authorizations from the Bureau of Land Management and the
Forest Service allowing pipeline construction through
Jefferson National Forest. Sierra Club, Inc. v. U.S. Forest
Serv., 897 F.3d 582 (4th Cir. 2018). The Commission initially
responded with a stop work order due to the possibility that the
Bureau of Land Management and Forest Service might require
the Pipeline to follow a different route through the national

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forest. Within a few weeks, though, the Commission allowed
construction to resume along most of the Pipeline’s route. The
Commission reasoned that completing construction and
restoration work on non-federal lands would best serve the
environment. Still, the Commission continued to prohibit
construction within a 25-mile “exclusion zone” encompassing
the crossing of the national forest and the adjacent watersheds.
The Fourth Circuit subsequently set aside Mountain
Valley’s verification from the Army Corps of Engineers. There
are two ways for Mountain Valley to obtain approval from the
Army Corps of Engineers: it can comply with an existing
nationwide permit, or it can acquire an individual permit
specific to the Pipeline. See Sierra Club v. W. Va. Dep’t of
Env’t Prot., 64 F.4th 487, 495 (4th Cir. 2023). Mountain
Valley chose the first route, and the Huntington District of the
Army Corps of Engineers verified that construction of the
Pipeline could proceed under an existing nationwide permit. In
October 2018, however, the Fourth Circuit vacated that
verification. Sierra Club v. U.S. Army Corps of Eng’rs, 905
F.3d 285 (4th Cir. 2018) (mem.) (order vacating verification);
Sierra Club v. U.S. Army Corps of Eng’rs, 909 F.3d 635 (4th
Cir. 2018) (opinion explaining order). Two other Army Corps
of Engineers districts then also suspended their authorizations
for the Pipeline. Mountain Valley paused work on all stream
crossings in those districts.
Next, Mountain Valley lost its approval from the Fish and
Wildlife Service. In August 2019, in response to new
information about the Pipeline’s potential impact on certain
listed species, Mountain Valley suspended construction in
various watersheds where those species live. The Commission
then asked the Fish and Wildlife Service to reopen consultation
on the Pipeline under the Endangered Species Act. Given those
developments, the Fourth Circuit granted a stay of the Service’s

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prior approval of the Pipeline. See Wild Va. v. U.S. Dep’t of
Interior, No. 19-1866 (4th Cir. Oct. 11, 2019) (order granting
stay).
At that point, Mountain Valley had lost three federal
authorizations it needed for construction: from the Bureau of
Land Management and Forest Service to build in Jefferson
National Forest, from the Army Corps of Engineers to cross
streams, and from the Fish and Wildlife Service to build the
Pipeline despite its impact on listed species. The Commission
again ordered Mountain Valley to stop construction. Letter
from Terry L. Turpin, Dir., Off. of Energy Projects, Fed.
Energy Regul. Comm’n, to Matthew Eggerding, Counsel,
Mountain Valley Pipeline, LLC (Oct. 15, 2019) (Stop Work
Order), J.A. 633–34.
D.
By the time the Commission halted work in response to the
Fourth Circuit’s decisions, Mountain Valley had already built
a substantial portion of the Pipeline. Along the way, state
regulators cited the company for violations related to the
project’s sedimentation impacts.
In 2018, inspections by the Virginia Department of
Environmental Quality of sites along the Pipeline route
revealed repeated violations of state water-quality regulations.
Some control measures intended to mitigate erosion and
sedimentation had been improperly installed, while others had
been inadequately maintained or repaired. Those faulty
controls allowed stormwater to escape the Pipeline right-of-
way, depositing sediment in nearby streams. The Department
sued Mountain Valley in state court, and the parties reached a
settlement requiring the company to pay more than $2 million
in fines. Press Release, Off. of the Virginia Att’y Gen., MVP,

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LLC to Pay More than $2 Million, Submit to Court-Ordered
Compliance and Enhanced, Independent Third-Party
Environmental Monitoring (Oct. 11, 2019).
Similarly, the West Virginia Department of
Environmental Protection issued forty-six violation notices to
Mountain Valley in 2018 and 2019, many of which concerned
sedimentation. The Department attached scores of
photographs showing failed erosion controls along the Pipeline
right-of-way. West Virginia fined Mountain Valley several
hundred thousand dollars for those violations of state water-
quality laws. See Mike Tony, Mountain Valley Pipeline Faces
$303,000 State Fine for Continued Erosion, but Pipeline
Opponents Call for Bigger Penalty, Charleston Gazette-Mail
(Feb. 5, 2021), https://tinyurl.com/yckw3ryn.
E.
In September 2020, Mountain Valley regained two of the
three permits it had lost. First, the Fish and Wildlife Service
issued a revised biological opinion concluding that the Pipeline
would not threaten the existence of listed species or adversely
affect critical habitat. That same month, the relevant districts
of the Army Corps of Engineers reauthorized the Pipeline
under the same national permit they had relied on before.
With those authorizations in hand, Mountain Valley
returned to the Commission. It asked for an extension of the
three-year deadline to complete construction and approval to
resume work outside Jefferson National Forest. (Construction
within the national forest remained on hold pending renewed
approvals from the Bureau of Land Management and the Forest
Service.) The Commission responded to Mountain Valley’s
request in a series of orders, which petitioners challenge here.

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1.
The Commission began with Mountain Valley’s request to
extend the construction deadline. In the initial Certificate
Order, the Commission directed Mountain Valley to finish
building the Pipeline within three years, by October 2020. But
as of September 2020, construction on the Pipeline remained
stalled. Mountain Valley asked for an extension of the deadline
by two years, to October 2022. The Commission granted
Mountain Valley’s request, finding a continued market need
for the Pipeline. Order Granting Requests for Extension of
Time, Mountain Valley Pipeline, LLC, 173 FERC ¶ 61,026
(Oct. 9, 2020) (First Extension Order).
2.
Mountain Valley also asked for the Commission’s
approval to resume work along most of the Pipeline’s route,
except for the 3.5 miles within Jefferson National Forest. By
that time, Mountain Valley had put 256 miles of pipe in the
ground and finished restoring 155 miles of the Pipeline right-
of-way. The company contended that resuming construction
would protect the environment and benefit landowners by
allowing final restoration of additional portions of the route.
In a companion order issued alongside the First Extension
Order, the Commission granted in part Mountain Valley’s
request to resume construction. Order Partially Lifting Stop
Work Order and Allowing Certain Construction to Proceed,
Mountain Valley Pipeline, LLC, 173 FERC ¶ 61,027 (Oct. 9,
2020) (Resume Work Order). The Commission permitted
work to resume, but only outside the same 25-mile exclusion
zone (encompassing the crossing of Jefferson National Forest
and adjacent watersheds) that the Commission had exempted
from its prior order allowing resumed construction. The

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Commission agreed with Mountain Valley that completing
construction and restoration along most of the route—and thus
replacing temporary erosion controls with permanent
measures—would best serve the environment and affected
landowners. Id. ¶¶ 30, 32.
Of relevance here, the Commission concluded that
preparation of a supplemental environmental impact statement
was unnecessary. Although the project’s sedimentation
impacts had been “slightly different” than projected due in part
to “unpredictable rainfall events,” the Commission determined
that any deviation from its initial projections was “not
significant enough to warrant” a supplemental impact
statement. Id. ¶ 39.
The Commission also rejected arguments from petitioners
that allowing construction to resume would violate
Environmental Condition 9 to the original Certificate Order.
That Condition, as noted, required Mountain Valley to obtain
all necessary permits before commencing construction. The
Commission understood that requirement to apply only to the
initial commencement of construction, not to a later resumption
of work.
3.
Less than a week after the Commission issued the Resume
Work Order, Mountain Valley resubmitted its request to
resume construction within the 25-mile exclusion zone (except
for the 3.5 miles within Jefferson National Forest, where the
company still lacked authorization to build). Mountain Valley
presented sedimentation modeling showing that construction in
the exclusion zone would not send sediment into the national
forest. The Commission granted the company’s request to
resume building in the portion of the exclusion zone outside

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Jefferson National Forest. Order Partially Lifting Stop Work
Orders and Allowing Certain Construction to Resume,
Mountain Valley Pipeline, LLC, 173 FERC ¶ 61,252 (Dec. 17,
2020) (Exclusion Zone Order).
4.
Petitioners, who are various environmental groups who
had intervened in the proceedings before the Commission,
sought rehearing of the First Extension, Resume Work, and
Exclusion Zone Orders. Because the Commission failed to act
on those rehearing requests within thirty days, they were
deemed denied as a matter of law for purposes of enabling
judicial review. See 15 U.S.C. § 717r(a); Allegheny Def.
Project v. FERC, 964 F.3d 1, 5 (D.C. Cir. 2020) (en banc). But
the Commission retained power to modify its orders. See 15
U.S.C. § 717r(a). In December 2020, the Commission issued
an order modifying the First Extension and Resume Work
Orders. Order Addressing Arguments Raised on Rehearing,
Mountain Valley Pipeline, LLC, 173 FERC ¶ 61,222 (Dec. 11,
2020) (First Modification Order). In March 2021, the
Commission modified the Exclusion Zone Order. Order
Addressing Arguments Raised on Rehearing and Denying
Stay, Mountain Valley Pipeline, LLC, 174 FERC ¶ 61,192
(Mar. 24, 2021) (Second Modification Order).
F.
Despite getting the green light from the Commission to
resume construction, Mountain Valley ran into further
roadblocks in the Fourth Circuit. In December 2020, that court
stayed decisions from the Huntington and Norfolk districts of
the Army Corps of Engineers reverifying that construction of
the Pipeline could proceed under an existing nationwide
permit. Sierra Club v. U.S. Army Corps of Eng’rs, 981 F.3d

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251 (4th Cir. 2020). Mountain Valley then shifted gears,
ceasing its reliance on a nationwide permit and instead
applying to the Army Corps of Engineers for an individual
permit. Sierra Club, 64 F.4th at 496. In that connection, the
West Virginia Department of Environmental Protection
certified that construction of the Pipeline would not violate the
state’s water quality standards. Id. at 498. Absent that
certification, Mountain Valley could not obtain an individual
permit. See id. at 496 (citing 33 U.S.C. § 1341(a)(1)).
Meanwhile, the Bureau of Land Management and the
Forest Service issued new decisions authorizing construction
in Jefferson National Forest. But in January 2022, after the
close of briefing in this case, the Fourth Circuit vacated those
renewed authorizations. Wild Va. v. U.S. Forest Serv., 24 F.4th
915 (4th Cir. 2022). About a week later, the Fourth Circuit also
vacated the Fish and Wildlife Service’s latest approvals.
Appalachian Voices v. U.S. Dep’t of Interior, 25 F.4th 259 (4th
Cir. 2022). Those decisions again left Mountain Valley
without three federal permits necessary to complete
construction.
G.
In June 2022, Mountain Valley again asked the
Commission to extend the construction deadline, this time by
four years, until October 2026. The Commission granted that
request. Order Granting Request for Extension of Time,
Mountain Valley Pipeline, LLC, 180 FERC ¶ 61,117 (Aug. 23,
2022) (Second Extension Order). With the First Extension
Order having lapsed during the pendency of this case (in
October 2022), the Second Extension Order—and its deadline
of October 2026— now governs the project.

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In February and May 2023, Mountain Valley regained two
federal permits. First, the Fish and Wildlife Service issued a
further revised biological opinion concluding that the Pipeline
would not threaten the existence of listed species or adversely
affect critical habitat. Letter from Cindy Schulz, Field
Supervisor, Va. Ecological Servs., U.S. Fish & Wildlife Serv.,
to Kimberly Bose, Sec’y, Fed. Energy Regul. Comm’n (Feb.
28, 2023), https://tinyurl.com/3ytrnrkr. Second, the Forest
Service and the Bureau of Land Management issued new
decisions authorizing construction in Jefferson National Forest.
Forest Serv., U.S. Dep’t of Agric., Record of Decision,
Mountain Valley Pipeline and Equitrans Expansion Project
(May 2023), https://tinyurl.com/3mrpnubp; Bureau of Land
Mgmt., U.S. Dep’t of Interior, Record of Decision, Mountain
Valley Pipeline and Equitrans Expansion Project Decision to
Grant Right-of-Way and Temporary Use Permit (May 2023),
https://tinyurl.com/2tts6zky.
Meanwhile, in April, Mountain Valley met another,
separate setback in the Fourth Circuit: that court vacated the
West Virginia Department of Environmental Protection’s
certification that the Pipeline’s construction would not violate
the state’s water quality standards. Sierra Club, 64 F.4th 487.
That decision leaves uncertain whether Mountain Valley will
be able to obtain required authorization from the Army Corps
of Engineers through an individual permit.
II.
Petitioners challenge the following Commission orders:
(i) the First Extension Order, which extended the construction
deadline for the Pipeline from October 2020 until October
2022; (ii) the Resume Work Order, which permitted Mountain
Valley to resume work outside the 25-mile exclusion zone
encompassing the crossing of Jefferson National Forest and the

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adjacent watersheds; (iii) the Exclusion Zone Order, which
allowed Mountain Valley to build in the portion of the
exclusion zone outside Jefferson National Forest; (iv) the First
Modification Order, which modified the First Extension and
Resume Work Orders by addressing certain issues raised in
petitioners’ requests for rehearing; and (v) the Second
Modification Order, which modified the Exclusion Zone Order
by elaborating on the Commission’s reasons for allowing
Mountain Valley to move forward with its project in response
to arguments raised in the requests for rehearing.
Before turning to the merits of those challenges, we
consider our jurisdiction to address them. We conclude that we
retain jurisdiction to consider all of petitioners’ claims except
their challenge to the First Extension Order.
A.
Because Article III of the Constitution grants federal
courts power to resolve only “actual, ongoing controversies,”
we lose jurisdiction over a pending claim if it becomes moot.
Planned Parenthood of Wis., Inc. v. Azar, 942 F.3d 512, 516
(D.C. Cir. 2019) (quotation marks and citation omitted). A
claim is moot if intervening events mean the court’s “decision
will neither presently affect the parties’ rights nor have a more-
than-speculative chance of affecting them in the future.”
Clarke v. United States, 915 F.2d 699, 701 (D.C. Cir. 1990)
(quotation marks and citation omitted). The operative question
is whether we can grant “any effectual relief whatever to the
prevailing party.” Campbell-Ewald Co. v. Gomez, 577 U.S.
153, 161 (2016). The “initial heavy burden of establishing
mootness lies with the party asserting” mootness, and “the
opposing party bears the burden of showing an exception
applies.” Honeywell Int’l, Inc. v. Nuclear Regul. Comm’n, 628

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F.3d 568, 576 (D.C. Cir. 2010) (quotation marks and citation
omitted).
1.
We first consider whether the Fourth Circuit’s latest
decisions vacating three agencies’ authorizations for the
Pipeline render this case moot. Although no party so argues,
we also “have an independent obligation to ensure that appeals
before us are not moot.” Planned Parenthood, 942 F.3d at 516
(quotation marks and citation omitted).
Petitioners ask us to redress their asserted injuries by
vacating the Commission’s orders allowing construction of the
Pipeline to continue. If the Fourth Circuit’s decisions
invalidating other agencies’ actions completely foreclosed any
possibility of future construction, then a decision in this case
vacating the Commission’s orders might have no effect on
petitioners’ rights. But none of the Fourth Circuit’s decisions,
whether considered individually or in combination, sweeps so
broadly.
Most obviously, the Fourth Circuit’s decisions vacating
authorizations (or more accurately, reauthorizations) from the
Bureau of Land Management, Forest Service, and Fish and
Wildlife Service do not affect this case. Mountain Valley
subsequently regained those permits, as described above. See
p. 14, supra.
That leaves the Fourth Circuit’s decisions vacating the
Army Corps of Engineers’ approval to build the Pipeline across
waterbodies and the West Virginia Department of
Environmental Protection’s certification pertaining to
obtaining an individual permit from the Army Corps of
Engineers. Mountain Valley represents that it has completed

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some 94 percent of Pipeline construction. And at least some of
the remaining 6 percent entails building across streams,
protected habitats, or both, such that construction in those areas
could not be completed until Mountain Valley regains the
approvals that have been vacated by the Fourth Circuit.
But nothing in the record establishes that the Fourth
Circuit’s decisions entirely preclude Mountain Valley from
engaging in construction on the project. To the contrary,
construction could continue in certain areas adjacent to
wetlands, even while the company awaits permission from the
Army Corps of Engineers to build within wetlands. That
remains true after the Fourth’s Circuit’s recent April 2023
decision, which affects only whether Mountain Valley can
obtain permission from the Army Corps of Engineers to build
within wetlands. Petitioners’ challenge to the Commission’s
orders, by contrast, seeks to halt Pipeline construction
everywhere along the right-of-way, beyond the specific areas
covered by the other federal permits.
There is also a more-than-speculative chance that
Mountain Valley will reacquire the vacated Army Corps of
Engineers’ permit, freeing the company to resume building in
the affected areas. (Indeed, Mountain Valley has already
regained approvals from the Bureau of Land Management,
Forest Service, and Fish and Wildlife Service, as noted above.)
But a decision from this court vacating the Commission’s
approval for the project as a whole would preclude a
resumption of work regardless. For those reasons, the Fourth
Circuit’s decisions do not moot this case.
2.
We next consider whether the expiration of the First
Extension Order during the pendency of this case moots

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petitioners’ challenge to that particular order. Mountain Valley
contends in a post-argument submission that it does. The
company argues that, because the October 2022 deadline set
out in the First Extension Order has passed, and that order has
been superseded by the Second Extension Order’s
establishment of a new deadline of October 2026, petitioners
can no longer “show[] that they have suffered some actual
injury that can be redressed” by our review of the First
Extension Order. Freeport-McMoRan Oil & Gas Co. v. FERC,
962 F.2d 45, 46 (D.C. Cir. 1992) (quotation marks and citation
omitted). We agree.
When a challenged order expires during the pendency of
litigation, the challenge generally becomes moot—at least
when, as here, the challenger seeks only prospective relief. See
id.; Nw. Pipeline Corp. v. FERC, 863 F.2d 73, 75–77 (D.C. Cir.
1988); Md. People’s Counsel v. FERC, 761 F.2d 768, 773
(D.C. Cir. 1985). The First Extension Order has expired and
has been superseded by a subsequent order that now governs.
A decision on the First Extension Order’s validity thus would
“neither presently affect the parties’ rights nor have a more-
than-speculative chance of affecting them in the future.”
Clarke, 915 F.2d at 701.
Petitioners contend that a live controversy remains
because the First Extension Order’s collateral consequences
continue to harm them. They reason that the Commission
could not have issued the Second Extension Order if not for the
First Extension Order, without which the initial Certificate
Order would have already expired. But even so, it does not
follow that petitioners’ challenge to the First Extension Order
remains live. Petitioners could separately seek review of the
Second Extension Order, but their challenge to the First
Extension Order—which no longer has any legal effect—does
not remain justiciable merely because that order’s one-time

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existence enabled the Commission to issue a subsequent
extension order that now governs.
Nor have petitioners carried their burden of showing that
an exception to mootness applies. Petitioners invoke two cases
in which we have applied the “capable of repetition, yet
evading review” exception to mootness. See Montgomery
Env’t Coal. v. Costle, 646 F.2d 568, 578–79 (D.C. Cir. 1980);
Humane Soc’y v. EPA, 790 F.2d 106, 112–14 (D.C. Cir. 1986).
Under that exception, a claim is not moot if “the challenged
action was in its duration too short to be fully litigated prior to
its cessation or expiration” and “there was a reasonable
expectation that the same complaining party would be
subjected to the same action again.” Trump v. Mazars USA,
LLP, 39 F.4th 774, 786 (D.C. Cir. 2022) (quoting Weinstein v.
Bradford, 423 U.S. 147, 149 (1975) (per curiam)).
That exception is inapplicable here. Even if the First
Extension Order was “in its duration too short to be fully
litigated prior to its . . . expiration,” petitioners have not shown
that their challenge to it is “capable of repetition.” Id. A
challenge is “capable of repetition” only if “the legal wrong
complained of by the plaintiff is reasonably likely to recur,”
Ralls Corp. v. Comm. on Foreign Inv. in U.S., 758 F.3d 296,
324 (D.C. Cir. 2014) (quotation marks and citation omitted),
framed “in terms of the legal questions [the challenge] presents
for decision,” J.T. v. Dist. of Columbia, 983 F.3d 516, 524
(D.C. Cir. 2020) (quotation marks and citation omitted). It is
therefore not enough that the Commission can—or did—issue
another order extending the timeline for the Pipeline. It must
also be the case that the Second Extension Order—or any other
orders “reasonably likely to recur” in the future—presents the
same alleged legal wrong and the same legal question as the
First Extension Order.

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20
The “legal wrong” of which petitioners complain in their
challenge to the First Extension Order is the Commission’s
finding of continued market need for the Pipeline. Petitioners
ask us to decide whether that finding was supported by
substantial evidence based on the record before the
Commission at the time it issued the First Extension Order.
That is “not the type of legal question that is capable of
repetition as it is sharply focused on a unique factual context.”
J.T., 983 F.3d at 527–28 (quotation marks and citation
omitted). To be sure, petitioners suggest that the Commission
repeats its legal wrongs from the First Extension Order in the
Second Extension Order. But an analysis of market need
“necessarily varies from one . . . period to the next, depending
upon the circumstances the [Commission] considers,” such that
any challenge to the Second Extension Order would “require
review of a different record from the one on which the [First
Extension Order was] issued.” See Nat’l Ass’n of Home
Builders v. U.S. Army Corps of Eng’rs, 264 F. App’x 10, 13
(D.C. Cir. 2008).
Petitioners thus have not shown that their challenge to the
First Extension Order is “capable of repetition,” or that any
other mootness exception applies. As a result, petitioners’
challenge to that order is moot.
B.
We turn next to statutory jurisdiction. Mountain Valley
contends that we lack jurisdiction under the Natural Gas Act to
consider petitioners’ challenge to the Exclusion Zone and
Second Modification Orders. The problem, according to
Mountain Valley, is that petitioners never filed a separate
petition seeking judicial review of the Second Modification
Order, which amended the Exclusion Zone Order. We are
unpersuaded.

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21
Under the Natural Gas Act, a party aggrieved by an order
of the Commission has thirty days to seek rehearing before the
agency and must do so before coming to court. 15 U.S.C.
§ 717r(a). Petitioners timely sought rehearing of the Exclusion
Zone Order. The Act gives the Commission thirty days to act
on a request for rehearing. Otherwise, the rehearing request is
“deemed to have been denied,” and an aggrieved party is free
to petition for judicial review. Id.
In the past, the Commission frequently issued tolling
orders to extend its deadline for resolving requests for
rehearing. But in Allegheny Defense Project, we held that such
tolling orders “are not the kind of action on a rehearing
application that can fend off a deemed denial and the
opportunity for judicial review.” 964 F.3d at 3–4.
Here, the Commission failed to act on petitioners’ request
for rehearing of the Exclusion Zone Order within thirty days.
The resulting denial of rehearing as a matter of law put both
petitioners and the Commission on the clock. Petitioners had
sixty days to petition for judicial review. 15 U.S.C. § 717r(b).
As for the Commission, although it had missed the deadline for
resolving the rehearing requests on their merits, it retained
authority to “modify or set aside” its original orders in response
to the arguments raised on rehearing, “[u]ntil the record in [the]
proceeding [was] filed in [the] court of appeals.” Id. § 717r(a).
After petitioners’ application for rehearing of the
Exclusion Zone Order was deemed denied as a matter of law,
petitioners sought judicial review of that order. But the
Commission could still modify the order until the record of the
proceeding was filed in our court. The Commission exercised
that authority by issuing the Second Modification Order, in
which it updated its discussion in the Exclusion Zone Order to

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address arguments raised on rehearing. Petitioners did not file
a separate petition for review to challenge the Second
Modification Order.
Mountain Valley contends that we lack jurisdiction to
consider petitioners’ challenges to the Exclusion Zone and
Second Modification Orders. According to Mountain Valley,
the Exclusion Zone Order was not final agency action for
purposes of judicial review, despite the denial of rehearing as a
matter of law, because the Commission later took final action
on the rehearing application in the Second Modification Order.
And we also lack jurisdiction over the Second Modification
Order, Mountain Valley maintains, because petitioners failed
to file a petition for review designating that order as among
those they challenged.
Our decision in Allegheny Defense Project forecloses
Mountain Valley’s arguments. As we explained there, when
the Commission fails to act on a rehearing application within
thirty days, “the applicant may deem its rehearing application
denied and seek judicial review of the now-final agency
action.” Allegheny Def. Project, 964 F.3d at 13. Here,
accordingly, when the Commission failed to act on petitioners’
rehearing request within thirty days, petitioners were free to
deem it denied and seek judicial review, which they did.
To be sure, in its notice that rehearing had been denied by
operation of law, the Commission expressed its intention to
address the arguments raised on rehearing in a future order
modifying the Exclusion Zone Order. But if mere mention of
a desire to amend the original order at some unspecified future
time had the effect of forestalling judicial review, then the
Commission’s notice of denial by operation of law would be
no different from the tolling orders we rejected in Allegheny
Defense Project. As we said there, “the question is not one of

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23
labels, but of signification.” Id. No statement of intent to act
in the future, regardless of what the order containing that
statement may be called, can prevent an action from becoming
final if the Commission fails to decide the merits of a rehearing
application within thirty days. The Exclusion Zone Order thus
became final agency action subject to challenge in court when
the Commission failed to decide petitioners’ rehearing request
within the allotted time.
We also have jurisdiction to consider the Second
Modification Order. A petition for review must “specify the
order or part thereof to be reviewed.” Fed. R. App. P. 15(a)(2).
It is undisputed that petitioners complied with that requirement
when initially seeking review of the Exclusion Zone Order.
After petitioners sought review in our court but before the
record in the proceeding was filed with us, the Commission
exercised its discretion to modify the Exclusion Zone Order by
issuing the Second Modification Order.
Petitioners were under no obligation to file a new petition
for review challenging that additional order. Mountain Valley
portrays the Second Modification Order as a “rehearing order”
requiring a separate petition. But as we have explained, when
the Commission failed to act on petitioners’ rehearing request
within thirty days, rehearing was denied as a matter of law. At
that point, the Commission was limited to updating the
Exclusion Zone Order rather than granting rehearing of it. The
Second Modification Order, then, was not a new order, but was
an amendment to the Exclusion Zone Order. Because the
Exclusion Zone Order, as amended, remains the operative
order that petitioners challenge, their petitions adequately
specify the orders to be reviewed.
In any event, we have held that “inexact specification of
the order to be reviewed will not be fatal to the petition . . . if

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the petitioner’s intent to seek review of a specific order can be
fairly inferred from the petition for review or from other
contemporaneous filings, and the respondent is not misled by
the mistake.” LaRouche’s Comm. for a New Bretton Woods v.
FEC, 439 F.3d 733, 739 (D.C. Cir. 2006) (quotation marks and
citation omitted). We can fairly infer from the petitions for
review that petitioners intended to seek review not only of the
Exclusion Zone Order but also of any amendment to it. And
the Commission could not have been misled, given our
explanation in Allegheny Defense Project of how the statutory
scheme operates, including the Commission’s power to modify
orders up to the time when the record is filed in court. Indeed,
the Commission does not join Mountain Valley in contesting
our jurisdiction over the Second Modification Order.
We therefore have jurisdiction to review the Second
Modification and Exclusion Zone Orders (and also the Resume
Work and First Modification Orders, as to which there is no
challenge to our jurisdiction and over which we undoubtedly
have jurisdiction).
III.
We assess petitioners’ challenges to the Commission’s
orders under the APA’s arbitrary-or-capricious standard of
review. See 5 U.S.C. § 706(2)(A). The Commission’s orders
must be sustained so long as they “examined the relevant
considerations and articulated a satisfactory explanation for its
action, including a rational connection between the facts found
and the choice made.” FERC v. Elec. Power Supply Ass’n, 577
U.S. 260, 292 (2016) (alterations adopted) (quoting Motor
Vehicle Mfrs. Ass’n of the U.S., Inc. v. State Farm Mut. Auto.
Ins. Co., 463 U.S. 29, 43 (1983)).

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A.
We first consider whether the Commission erred in the
Resume Work and Exclusion Zone Orders by allowing
construction to resume before Mountain Valley reacquired all
its other permits. We reject those challenges.
1.
Petitioners contend that the Commission violated
Environmental Condition 9 to the Certificate Order by
permitting construction to resume even though Mountain
Valley was still waiting on reauthorization to build in Jefferson
National Forest. Environment Condition 9 required Mountain
Valley to “receive written authorization” from the Commission
“before commencing construction of any project facilities.”
Certificate Order, App. C, Environmental Condition 9. And to
obtain that authorization from the Commission, Mountain
Valley needed to show “that it ha[d] received all applicable
authorizations required under federal law.” Id.
The Commission interpreted that condition to require
obtaining “all relevant authorizations before the company can
commence construction” at the outset of the project, without
carrying any “ongoing obligation once those authorizations
have been obtained and the Commission has” permitted
construction to begin. Second Modification Order ¶ 16. On
that reading, “Environmental Condition 9 applies to newly-
certificated and unconstructed facilities,” but not in “a scenario
where applicable federal authorizations are vacated after a
company has obtained necessary federal authorizations and
commenced construction.” Id. That is because “the
invalidation of a specific federal authorization does not
necessarily invalidate an authorization to construct generally,

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26
particularly if significant construction is already underway.”
Resume Work Order ¶ 17.
We sustain the Commission’s interpretation of
Environmental Condition 9, particularly in view of the
deference we accord to the Commission’s interpretation of its
own adjudicatory orders. See Cellco P’ship v. FCC, 700 F.3d
534, 544 (D.C. Cir. 2012); Sw. Gas Corp. v. FERC, 145 F.3d
365, 370 (D.C. Cir. 1998). The condition’s use of the word
“commencing” suggests that it applies at the start of
construction. Petitioners argue that the phrase “of any project
facilities” suggests that all authorizations must be in place
before Mountain Valley constructs each successive portion of
the Pipeline. But the word “any” is just as naturally read to
indicate that all necessary authorizations needed to be in place
before Mountain Valley could initially commence construction
on even one—i.e., any—project facility.
As the Commission explained, moreover, if a particular
federal authorization is vacated after construction has begun,
the Commission’s staff “evaluates the circumstances along the
pipeline’s right-of-way as they exist at the time and determines
what course of action would be most protective of the
environment.” Resume Work Order ¶ 19. In some situations,
especially if a substantial portion of construction is already
underway, “it may be most protective of the environment for
additional construction to proceed.” Id. For instance, if
construction is nearly complete on one segment of a pipeline
when a court vacates an authorization affecting a different
segment, it might be prudent to allow construction to continue
along the first segment, hastening final restoration of the right-
of-way for the benefit of the environment and landowners. The
Commission’s interpretation of Environmental Condition 9
enables that choice, whereas petitioners’ competing
interpretation would deny it.

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27
The Commission also adequately explained why resuming
construction was advisable in this case. At the time of the
Resume Work Order, there were about 100 miles of the
Pipeline right-of-way where Mountain Valley had put pipe in
the ground but had yet to complete restoration work. The
Commission explained that leaving temporarily stabilized
areas exposed to the elements can cause “slips, overwhelmed
erosion control devices, and gradual degradation of
annual/seasonal cover crops and/or mulch,” while temporary
controls require regular upkeep. Id. ¶ 30. Moving more of the
Pipeline right-of-way into final restoration would ameliorate
those issues. Replacing temporary erosion and sedimentation
controls with permanent measures “would more effectively
stabilize slip-prone areas, eliminate or significantly reduce
erosion and sedimentation off the right-of-way, and protect
sensitive resources such as waterbodies, wetlands, and habitats
for wildlife and aquatic species.” Id. The Commission
reasonably concluded, then, that allowing construction to
resume would benefit the environment, even without all other
authorizations in place. Id.
Petitioners cite a Fourth Circuit decision addressing a
challenge to a permit issued by the National Park Service for a
different pipeline project. See Sierra Club v. U.S. Dep’t of
Interior, 899 F.3d 260 (4th Cir. 2018). That decision suggests
in a footnote that a condition identical to Environmental
Condition 9 required all federal authorizations to be in place
not only for construction to begin but also for construction to
continue. Id. at 284 n.11. In the Resume Work Order, the
Commission acknowledged that decision but clarified that “the
invalidation of a specific federal authorization does not
necessarily invalidate an authorization to construct generally,
particularly if significant construction is already underway.”
Resume Work Order ¶ 17.

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28
The Fourth Circuit’s brief discussion of the condition in
that decision does not govern here. As the Commission
underscores, the Fourth Circuit’s decision addressed only a
pipeline’s ability to unilaterally proceed to construction after
the invalidation of a federal authorization. See Sierra Club,
899 F.3d at 284 & n.11. It did not contend with a scenario in
which, as here, the Commission expressly authorized
construction to resume following invalidation of a federal
authorization. See Comm’n Br. 37. Moreover, the
Commission was not a party in the Fourth Circuit’s case and so
had no opportunity to present its explanation of the meaning of
the condition to that court. This case afforded the Commission
its first opportunity to explain its interpretation, which we
sustain.
The Resume Work and Exclusion Zone Orders are thus
consistent with Environmental Condition 9, as interpreted by
the Commission.
2.
Petitioners next contend that constructing segments of the
Pipeline up to the border of Jefferson National Forest will
create unwarranted bureaucratic momentum pressuring the
Bureau of Land Management and Forest Service to allow
construction within the national forest. Relying on the Fourth
Circuit’s decision in Maryland Conservation Council v.
Gilchrist, 808 F.2d 1039 (4th Cir. 1986), petitioners imagine
the partially completed segments of the Pipeline “stand[ing]
like gun barrels pointing into the heartland” of the national
forest. Pet’rs’ Br. 51 (quoting Gilchrist, 808 F.2d at 1042).
Our court has rejected the “bureaucratic momentum”
analysis from the Fourth Circuit’s Gilchrist decision, observing

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29
that it “lacks vitality.” Karst Env’t Educ. & Prot., Inc. v. EPA,
475 F.3d 1291, 1297 (D.C. Cir. 2007). In the Exclusion Zone
Order, however, the Commission seemed to acknowledge that,
at least in some situations, one agency’s approval of a project
could create bureaucratic momentum unduly affecting another
agency’s consideration of the project. See Exclusion Zone
Order ¶¶ 12–13. But because the Bureau of Land Management
and Forest Service had already approved the Pipeline’s route
through Jefferson National Forest, the Commission concluded
that its own decision allowing construction to resume would
impose no undue pressure on those agencies.
By their nature, interstate pipeline projects frequently
require multiple federal permits, as this case illustrates. And
no agency could be the first to approve such a project if it were
forbidden from creating any bureaucratic momentum that
might influence other agencies. But even assuming without
deciding that a bureaucratic momentum argument could be
viable in certain situations, we conclude that the Commission
reasonably rejected petitioners’ argument here.
By the time of the Exclusion Zone Order, the Bureau of
Land Management and the Forest Service had twice rejected
all possible alternative routes through Jefferson National
Forest. Id. ¶ 13. In that context, the Commission could allow
construction of the Pipeline up to the border of the national
forest without putting any undue pressure on those other
agencies, which had already decided that the Pipeline’s sole
viable path through the national forest was one corresponding
to the route of Mountain Valley’s construction outside the
forest. In the circumstances of this case, petitioners’
bureaucratic momentum argument thus fails.

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B.
Petitioners’ final two challenges pertain to the
Commission’s decision not to prepare a supplemental
environmental impact statement before permitting construction
to resume. An agency must supplement its environmental
impact statement when “significant new circumstances or
information” raise additional concerns about an action’s
impact. 40 C.F.R. § 1502.9(d)(1)(ii). As we have emphasized,
a supplemental environmental impact statement “must be
prepared only where new information ‘provides a seriously
different picture of the environmental landscape.’” Stand Up
for California! v. U.S. Dep’t of Interior, 994 F.3d 616, 629
(D.C. Cir. 2021) (quoting Friends of Cap. Crescent Trail v.
FTA, 877 F.3d 1051, 1060 (D.C. Cir. 2017)).
1.
Petitioners contend that the Commission should have
prepared a supplemental environmental impact statement to
consider the effects of blasting activity along the Pipeline right-
of-way. They rely on one line in the final environmental
impact statement noting that Mountain Valley had “not
determined whether blasting would be necessary for
construction” of the Pipeline. Final Environmental Impact
Statement 4-203, J.A. 71. In practice, blasting has been
required along much of the right-of-way. Petitioners argue that
the widespread use of blasting constitutes significant new
information warranting a supplemental impact statement. The
Commission reasonably rejected that contention.
The final environmental impact statement included a
thorough discussion of the potential impacts of blasting. The
Commission recognized that blasting likely would be
necessary along much of the Pipeline’s route. The final

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environmental impact statement explained that Pipeline
construction “would cross 216 miles of shallow depth to
bedrock,” id. at 4-44, J.A. 16, and “the potential for blasting
exists at all locations where shallow bedrock may be
encountered,” id. at 4-43, J.A. 15. Given the likelihood of
blasting, the Commission explored in detail the potential
environmental harms that could result, including the impact on
aquifers, fish and other aquatic species, bald and golden eagles,
people and animals who are bothered by loud noises, and so
forth.
Nothing in the record, moreover, suggests that the actual
impacts of blasting to this point have differed in any material
respect from the impacts the Commission anticipated in the
final environmental impact statement. The Commission thus
reasonably determined in the Resume Work Order that
“impacts from blasting and construction [on] steep slopes were
adequately addressed” in the final environmental impact
statement. Resume Work Order ¶ 40.
2.
Petitioners next contend that the Commission’s final
environmental impact statement “vastly overestimated” the
effectiveness of Mountain Valley’s erosion and sedimentation
controls, necessitating a supplemental analysis addressing
sedimentation before construction can resume. Pet’rs’ Br. 41.
We conclude that the Commission failed to provide an
adequate explanation in rejecting that claim. While petitioners
primarily take issue with the Commission’s rejection of that
claim in the Resume Work Order, they frame their challenge as
encompassing all orders on review, see id. at 15–17, 45, and
the Commission does not argue otherwise. We accordingly
treat the challenge as reaching all challenged orders.

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In the final environmental impact statement, the
Commission repeatedly stated that Mountain Valley’s
proposed control measures would “minimize” erosion and
sedimentation associated with Pipeline construction. For
instance, Mountain Valley would “minimize or avoid” any
“minor temporary fluctuations in surface water turbidity”
associated with digging the Pipeline trench by
“implement[ing] . . . the construction practices outlined” in the
company’s erosion and sedimentation control plans. Final
Environmental Impact Statement 4–137, J.A. 53.
Petitioners submit that Mountain Valley’s controls
significantly failed to minimize sedimentation impacts to the
extent the Commission predicted. In supporting that claim,
petitioners rely on information arising from state enforcement
actions brought by Virginia and West Virginia. Virginia, in
suing Mountain Valley for environmental violations,
documented numerous instances in which construction of the
Pipeline resulted in deposits of significant levels of sediment in
streambeds. And West Virginia likewise issued dozens of
violation notices to Mountain Valley associated with failed
sediment controls along the Pipeline right-of-way, leading to
substantial fines. Before the Commission, petitioners invoked
the record underlying those enforcement actions as proof that
the sedimentation impacts of Pipeline construction have been
“seriously different” than originally anticipated. Stand Up for
California!, 994 F.3d at 629 (quotation marks, citation, and
emphasis omitted).
In the face of petitioners’ presentation of that information,
the Commission needed to explain why it was inadequate to
show a substantial deviation from the prior environmental
impact analysis. See Marsh v. Or. Nat. Res. Council, 490 U.S.
360, 374 (1989). But the Commission failed to offer a reasoned

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explanation in that regard. Even under our deferential standard
of review, we cannot sustain its decision.
The Commission “acknowledge[d] that there have been
slightly different outcomes than those projected” in the final
environmental impact statement. Resume Work Order ¶ 39.
The Commission summarily attributed those different
outcomes to “unpredictable rainfall events,” and stated without
elaboration that “the resulting impacts” from erosion and
sedimentation “are not significant enough to warrant a
supplemental [environmental impact statement].” Id. But that
bare conclusion, without any support or explanation, is
insufficient to pass muster. The Commission further noted that
its compliance monitors regularly inspect Pipeline construction
sites to ensure Mountain Valley’s implementation of required
controls. Id. Those controls, though, failed to prevent the
sedimentation documented by state regulators. And the
Commission did not explain why those controls would more
likely be effective going forward (aside from the one passing
reference to unusual rainfall in the past). Nor did the
Commission clarify or update its rationale after petitioners
argued in their request for rehearing that the Commission had
wrongfully dismissed post-certification evidence about
sedimentation. First Modification Order ¶¶ 9–10.
With respect to petitioners’ reliance on the state
enforcement actions, the Commission offered just one sentence
in response: “Mountain Valley reached consent decrees with
both Virginia [] and West Virginia [] to resolve violations of
state environmental standards and regulations and no
additional action by the Commission is necessary at this time.”
First Extension Order ¶ 27. But the mere fact that state
regulators may have settled their actions against Mountain
Valley does not itself afford a basis for declining to prepare a
supplemental environmental impact statement. State

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enforcement of environmental laws in response to worse-than-
anticipated impacts does not absolve the Commission of its
duty to assess the environmental impacts of the project under
federal law.
Those consent decrees require Mountain Valley to
implement additional sedimentation controls. Consent Decree
at 7–9, Paylor v. Mountain Valley Pipeline, LLC, No.
CL18006874-00 (Va. Cir. Ct. Dec. 11, 2019). And perhaps
those additional measures will ensure that the remainder of
construction produces no significant sedimentation impacts
beyond those already anticipated. But the challenged orders do
not offer that or any other explanation for why the consent
decrees eliminate the need for a supplemental environmental
impact statement.
The Commission also points out that the final
environmental impact statement predicted that building the
Pipeline would lead to some sedimentation. Comm’n Br. 60–
61 (citing Certificate Order ¶ 146). But a supplemental
environmental impact statement is necessary not only when the
nature of a project’s environmental impacts is significantly
different than anticipated, but also when the extent of those
impacts is significantly greater than predicted. Marsh, 490
U.S. at 374. The Commission failed to engage with whether
the level of sedimentation observed along the Pipeline right-of-
way was substantially different than expected. For those
reasons, the Commission’s explanation of its decision not to
prepare a supplemental environmental impact statement was
arbitrary and capricious.
C.
Because the Commission inadequately addressed whether
a supplemental environmental impact statement was necessary

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in light of the project’s sedimentation impacts, we must remand
that matter to the Commission. We remand all of the
challenged orders (except the now-moot First Extension Order)
because of that deficiency. We do so, however, without
vacating the challenged orders’ approval of resuming
construction.
“The decision to vacate depends on two factors: the
likelihood that ‘deficiencies’ in an order can be redressed on
remand, even if the agency reaches the same result, and the
‘disruptive consequences’ of vacatur.” Black Oak Energy, LLC
v. FERC, 725 F.3d 230, 244 (D.C. Cir. 2013) (quoting Allied–
Signal v. Nuclear Regul. Comm’n, 988 F.2d 146, 150–51 (D.C.
Cir. 1993)). With regard to the first factor, “[w]hen an agency
bypasses a fundamental procedural step, the vacatur inquiry
asks not whether the ultimate action could be justified, but
whether the agency could, with further explanation, justify its
decision to skip that procedural step.” Standing Rock Sioux
Tribe v. U.S. Army Corps of Eng’rs, 985 F.3d 1032, 1052 (D.C.
Cir. 2021).
Here, the Commission failed to adequately explain its
decision not to prepare a supplemental environmental impact
statement. But after adequately accounting for the evidence of
sedimentation impacts along the Pipeline’s right-of-way, the
Commission could again conclude that a new impact statement
is unnecessary, perhaps in part because of additional control
measures required by the state consent decrees. As for the
second factor, construction of the Pipeline is more than ninety
percent complete, with many portions of the route nearing final
restoration. And in the Commission’s view, the completion of
restoration would help ameliorate the project’s sedimentation
impacts. See pp. 10–11, supra. In those circumstances,
vacating the Commission’s orders would be “quite disruptive.”
Food & Water Watch, 28 F.4th at 292 (quoting City of Oberlin

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v. FERC, 937 F.3d 599, 611 (D.C. Cir. 2019)). We thus
exercise our discretion to remand without vacatur.
* * * * *
For the foregoing reasons, we dismiss in part, grant in part,
and deny in part the petitions for review. We dismiss as moot
the petitions insofar as they challenge the First Extension
Order. We grant the petitions insofar as they challenge the
Commission’s explanation of its decision not to prepare a
supplemental environmental impact statement concerning the
project’s sedimentation impacts, and we deny the petitions with
respect to petitioners’ other arguments. Accordingly, we
remand the Resume Work, Exclusion Zone, First Modification,
and Second Modification Orders to the Commission without
vacatur for further proceedings consistent with this opinion.
So ordered.

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