Center for Biological Diversity v. U.S. Environmental Protection Agency, et al

FOR PUBLICATION

In the
United States Court of Appeals
For the Eleventh Circuit
____________________
No. 25-10515
____________________

CENTER FOR BIOLOGICAL DIVERSITY,
Petitioner,
versus

U.S. ENVIRONMENTAL PROTECTION AGENCY,
ADMINISTRATOR, U.S. ENVIRONMENTAL
PROTECTION AGENCY,
Respondents,

MOSAIC FERTILIZER, LLC,
Intervenor.

____________________
Petition for Review of a Decision of the
Environmental Protection Agency
Agency No. FRL-12519-01-0A
____________________

Before R
OSENBAUM, LAGOA, and MARCUS, Circuit Judges.
M
ARCUS, Circuit Judge:
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2 Opinion of the Court 25-10515
The Center for Biological Diversity, a nonprofit member-
ship organization, petitions this Court for review of the Environ-
mental Protection Agency’s Notice of Approval for Other Use of
Phosphogypsum. The Notice approved a request submitted by
Mosaic Fertilizer, LLC, a Delaware-based mining and chemical
company, to use a radioactive byproduct of fertilizer production
(phosphogypsum) in a road on the company’s privately owned
New Wales Facility in Polk County, Florida. After a multi-year re-
view of the application, the EPA concluded that Mosaic’s proposed
road was a permissible use of phosphogypsum pursuant to the
EPA’s regulations promulgated under the Clean Air Act.
The Center asks us to vacate or remand the Notice of Ap-
proval because it claims the EPA’s decision violates the controlling
regulatory text or, alternatively, because the decision was arbitrary
and capricious in violation of the Administrative Procedure Act.
The EPA and Mosaic disagree, asserting that this Court is obliged
to dismiss the Center’s petition for want of jurisdiction and that it
also fails on the merits.
After thorough review, and with the benefit of oral argu-
ment, we conclude that the petition must be denied. We are satis-
fied that we have jurisdiction because the Center has associational
standing and the matter has not become moot. However, this ap-
plication fails on the merits. The EPA did not violate the Agency’s
regulations, and its review and technical methodology were well
supported, appropriately tailored, and fully explained. Accord-
ingly, we deny the Center’s petition.
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25-10515 Opinion of the Court 3
I.
At the New Wales Facility (the “Facility”), Intervenor Mo-
saic Fertilizer, LLC, (“Mosaic”) mines and processes phosphate ore
into phosphoric acid, which is subsequently used in the production
of agricultural fertilizer. During this mining and conversion pro-
cess, approximately five tons of phosphogypsum -- a radioactive
solid-waste byproduct -- are produced for each ton of phosphate
fertilizer. Pursuant to federal regulations, Mosaic then stores phos-
phogypsum in large, open-air pyramidic stacks at the Facility.
Even when the byproduct is stored in stacks, phosphogyp-
sum naturally decays and emits dangerous radon gas, which is a
radionuclide long associated with cancer, genetic abnormalities,
and serious illness. On account of these health risks, the EPA has
long regulated the production, disposal, and storage of phos-
phogypsum through federal regulations promulgated under the
Clean Air Act. We recount the winding history of the regulatory
scheme to better understand the nature and resolution of this dis-
pute.
A.
In 1970, Congress enacted the Clean Air Act (the “Act”), 42
U.S.C. §§ 7401–7671q, to “speed up, expand, and intensify the war
against air pollution in the United States with a view to assuring
that the air we breathe throughout the Nation is wholesome once
again.” H.R. Rep. No. 91–1146, 91st Cong., 2d Sess. 1, 1, (1970); see
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4 Opinion of the Court 25-10515
also 42 U.S.C. § 7401(b)(1) (the Act’s purpose is “to protect and en-
hance the quality of the Nation’s air resources so as to promote the
public health and welfare”). Under Section 112 of the Act, Con-
gress authorized the creation of the National Emission Standards
for Hazardous Air Pollutants Program (the “NESHAP” Program).
42 U.S.C. § 7412, Pub. L. No. 91-604, § 112, 84 Stat. 1676, 1685
(1970). The NESHAP Program is twofold; it requires the EPA to
publish “a list which includes each hazardous air pollutant for
which [it] intends to establish an emission standard,” and then re-
quires the EPA to identify sources of the listed pollutants and set
emission standards for each source category at a health threshold
level that “provides an ample margin of safety to protect the public
health[.]” Id. § 112(b)(1)(A)–(B).
As far back as 1979, the EPA listed radionuclides, including
radon, as a Hazardous Air Pollutant (“HAP”). 40 C.F.R. § 61.01(a);
see also Addition of Radionuclides to List of Hazardous Air Pollu-
tants, 44 Fed. Reg. 76738 (Dec. 27, 1979); 42 U.S.C. § 7412(b)(1).
For most Americans, radon is the single greatest source of environ-
mental radiation exposure. The EPA defines radon as a non-thresh-
old pollutant, which means that once radon induces cancer -- typi-
cally lung cancer -- the severity of the disease “is independent of the
dose.” National Emission Standards for Hazardous Air Pollutants;
Radionuclides, 54 Fed. Reg. 51654, 51659 (Dec. 15, 1989) (codified
as amended at 40 C.F.R. pt. 61) [hereinafter “1989 Rule”]. That is,
any non-zero amount of radon exposure can cause cancer of any
severity. Id. Moreover, the EPA estimates that each year, approx-
imately 21,000 lung cancer deaths in the United States are radon-
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25-10515 Opinion of the Court 5
related, making radon the second leading cause of lung cancer after
smoking.
Consistent with the Clean Air Act’s NESHAP Program, the
EPA promulgated emission standards to control radionuclide emis-
sions from various source categories, including from phosphogyp-
sum, in 1989. Id.; 42 U.S.C. § 7412(b)(1) (listing “Radionuclides (in-
cluding radon)” as an HAP). During the 1989 rulemaking process,
the EPA analyzed several sources of radionuclide emissions, includ-
ing from the fertilizer industry’s practice of disposing of phos-
phogypsum in stacks and mines. 1989 Rule, 54 Fed. Reg. at 51675.
The Agency concluded that the maximum lifetime risk associated
with baseline emissions from stack and mine storage -- defined as
the “maximum additional cancer risk of any person due to expo-
sure to an emitted pollutant for a 70-year lifetime” -- was approxi-
mately 9 x 10
-5
(9 in 100,000). Id. at 51655, 51660, 51675. Finding
this risk acceptable and adequately protective of human health, the
1989 Rule (codified, as amended, in Subpart R) required that all
phosphogypsum be disposed of in stacks or old phosphate mines
without exception. Id. at 51675, 51701; see also 42 U.S.C. § 7412.
The 1989 Rule barred all uses of phosphogypsum beyond perma-
nent storage in stacks or mines because the Agency wanted to en-
sure that phosphogypsum could not be “incorporated into other
products or otherwise diffused throughout the country, such that
the Agency will be unable to ensure that the phosphogypsum’s ra-
don emissions do not present an unacceptable risk to public
health.” 1989 Rule, 54 Fed. Reg. at 51675.
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6 Opinion of the Court 25-10515
Less than a year later, the EPA granted limited reconsidera-
tion of Subpart R and commenced an evaluation of the risks asso-
ciated with the use of phosphogypsum in three scenarios: (1) agri-
culture; (2) road construction; and (3) research and development
activities. NESHAPS for Radionuclides Reconsideration; Phos-
phogypsum, 55 Fed. Reg. 13480 (Apr. 10, 1990) (codified as
amended at 40 C.F.R. pt. 61). Consistent with the results of its re-
search, the Agency amended Subpart R in 1992 through the admin-
istrative rulemaking process. See National Emission Standards for
Radon Emissions from Phosphogypsum Stacks, 57 Fed. Reg. 23305,
23312 (June 3, 1992) (codified at 40 C.F.R. pt. 61) [hereinafter “1992
Rule”].
In the preamble to the 1992 Rule (the “Preamble”) the EPA
outlined the results of each of the three scenarios, and explained
how that research informed its amendments to Subpart R. See id.
at 23305–17. As for the use of phosphogypsum in roads, the Pre-
amble explained that the amendments would not create a categor-
ical exception, thereby allowing the distribution and use of phos-
phogypsum in road construction. The EPA’s decision was the
product of an evaluation of modeled risks to road construction
workers, road users, residents near the road, and to future residents
living directly on the phosphogypsum road base, should the road
ever be abandoned (the “reclaimer” scenario). The EPA concluded
that each of the modeled risks exceeded the Agency’s health and
safety thresholds, with the highest lifetime risk applying to reclaim-
ers. Id. at 23310. The 1992 Preamble reads this way:
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25-10515 Opinion of the Court 7
For the road construction scenarios analyzed, the use of
phosphogypsum always resulted in a MIR [Maximum
Individual Risk] greater than the outer bound of the
presumptively safe level of approximately l x 10
-4
[1 in
10,000]. Therefore, EPA has determined that the use
of phosphogypsum in road construction presents an
unacceptable level of risk to public health.
Id. at 23312 (emphasis added).
As for the other use categories -- agricultural and research
purposes -- the Agency concluded that subject to certain re-
strictions, those uses carried estimated maximum individual life-
time cancer risks no higher than 3 x 10
-4
(3 in 10,000). Id. at 23311–
12. The EPA explained that this risk was acceptable for agricultural
and research purposes and thus amended Subpart R to categori-
cally allow for (1) the distribution and use of phosphogypsum for
outdoor agricultural purposes, 40 C.F.R. § 61.204; and (2) the dis-
tribution and use of phosphogypsum for indoor research and de-
velopment, 40 C.F.R. § 61.205. 1992 Rule, 57 Fed. Reg. at 23311–
12, 23315–19.
Finally, the 1992 Rule provided for a process by which enti-
ties could, on a case-by-case basis, request Agency approval for the
use of phosphogypsum for any other purpose. Id. at 23316. The
“other purpose” provision requires that an applicant submit a writ-
ten proposal to the Agency, which must include information about
how the phosphogypsum would be used, in what amounts, the
risks posed by the proposed use, and the intended pollution control
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8 Opinion of the Court 25-10515
measures. 40 C.F.R. § 61.206(a) –(b). An application may be ap-
proved by the EPA if “the proposed distribution and/or use is at
least as protective of public health, in both the short term and the
long term, as disposal of phosphogypsum in a stack or a mine.” Id.
§ 61.206(c). After an application is approved, the applicant still
must prepare and maintain additional records to confirm that the
applicant’s reported radium concentration remains consistent with
previously reported levels. Id. § 61.207.
The next relevant development to the regulatory frame-
work occurred in 2005, when the EPA published a workbook to
“provide information on how to prepare a complete petition to the
U.S. EPA for the distribution and use of phosphogypsum for ‘other
purposes’ that is consistent with the requirement of [the EPA’s]
regulations for radon emissions.” Radiation Prot. Div., Env’t Prot.
Agency, Applying to EPA for Approval of Other Uses of Phos-
phogypsum: Preparing and Submitting a Complete Petition Under
40 C.F.R. § 61.206, at 1 (2005) [hereinafter “2005 Workbook”],
https://www.epa.gov/system/files/documents/2025-
04/wrkbk_sub-r_appl_1105_508-d.pdf. Notably, the 2005 Work-
book discussed the use of phosphogypsum in roads on three occa-
sions, articulating the EPA’s position that an application to use
phosphogypsum in road construction projects may be approved
under Subpart R.
1

1
On page six, the Workbook reads: “[i]f you were proposing to use phos-
phogypsum in a way that would bring it into contact with the surface of the
ground, such as using it for a road base, we might require you to establish a
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25-10515 Opinion of the Court 9
Further, and relevant to the requirements an entity like Mo-
saic must satisfy when applying to use phosphogypsum for an
other purpose, the 2005 Workbook provided guidance on the col-
lection of radium-226 (“Ra-226”)
2
samples under 40 C.F.R.
§ 61.207(a). Section 61.207(a) explains that prior to removing phos-
phogypsum from a stack for use in an other purpose project, the
stack’s average Ra-226 concentration “shall” be measured, and that
the “[m]easurements shall be performed for each [stack] prior to
the initial distribution . . . and at least once during each calendar
year while distribution of phosphogypsum removed from the loca-
tion continues.” Id. The 2005 Workbook explains that consistent
with § 61.207, an application should also include Ra-226 sampling
data collected within the last year. 2005 Workbook at 30. Even so,
the EPA repeatedly said in the Workbook that this does “not re-
place or change the final rule” and this is intended only to “help [an
applicant] submit a complete petition . . . but [the Workbook] is
not intended to be a technical guidance document.” Id. at 1.

ground-water monitoring program.” 2005 Workbook at 6. Two pages later,
the EPA writes: “[s]everal possible ‘other uses’ of phosphogypsum have been
explored over the years. These include . . . [r]oad base material[.]” Id. at 8.
Finally, the Workbook explains again, in near identical language, “if you are
proposing to use phosphogypsum in a way that would bring it into contact
with the surface of the ground, such as using it for a road base, we will proba-
bly require you to establish a ground-water monitoring program.” Id. at 16.
2
Radium-226 is a naturally occurring uranium isotope, which the EPA gener-
ally uses to assess the potential risks associated with proposed projects involv-
ing the use and distribution of phosphogypsum.
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10 Opinion of the Court 25-10515
Finally and most recently, in October 2020 the EPA granted
conditional approval of a 2019 other use application to use phos-
phogypsum in road projects, submitted by The Fertilizer Institute,
an agricultural trade association. Approval of the Request for
Other Use of Phosphogypsum by the Fertilizer Institute, 85 Fed.
Reg. 66550 (Oct. 20, 2020) [hereinafter “Approval of Institute Re-
quest”]. The EPA’s decision marked the first time it had approved
an application to use phosphogypsum in a road project, and the
conditional approval explained the Agency’s position that it “did
not approve road construction as a categorical use of phosphogyp-
sum” in 1992, but rather established “a process to request approval”
for other uses, including in road construction. Id. at 66551.
Several environmental groups, including the Center, peti-
tioned the United States Court of Appeals for the District of Co-
lumbia for direct review of the Agency’s decision and submitted a
request to the EPA asking the Agency to reconsider. See With-
drawal of Approval for Use of Phosphogypsum in Road Construc-
tion, 86 Fed. Reg. 35795 (July 7, 2021). Subsequently, and “[o]n its
own initiative,” the EPA withdrew its approval on procedural
grounds and without prejudice on July 7, 2021, explaining that its
conditional approval was premature because the Institute had not
met the information requirements for an “other purpose applica-
tion” under 40 C.F.R. § 61.206(b). Id.
B.
This decades-long regulatory history provides the backdrop
for this dispute. In March 2022, Mosaic submitted an application
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25-10515 Opinion of the Court 11
to use phosphogypsum -- for what it called a “Small-scale Road Pi-
lot Project on Private Land in Florida” (the “Road Project”) -- to
the EPA pursuant to the other use provision found in § 61.206. Re-
quest For Approval of Additional Uses of Phosphogypsum Pursu-
ant to 40 C.F.R. § 61.206 at 1, Ctr. For Biological Diversity v. EPA, No.
25-10515 (11th Cir. July 7, 2025), Dkt. No. 26-1 [hereinafter “Mosaic
Application”]. Mosaic presented a revised request in August 2023
containing only modest alterations to the original proposal. Re-
quest from The Mosaic Company to Use Phosphogypsum in Road
Construction Pilot (August 2023), Ctr. For Biological Diversity v. EPA,
No. 25-10515 (11th Cir. Aug. 12, 2025), Dkt. No. 30.
Mosaic’s application proposed to construct a pilot road (the
“Road”) comprised of four 500-foot test sections, each containing a
different concentration of phosphogypsum in the road base. Id. at
4. Mosaic estimated that the Project would use 1,200 tons of phos-
phogypsum -- taken from Mosaic’s on-site phosphogypsum stacks
-- across 3,200 feet of roadway. Id. The original application further
explained that the Road would be located on Mosaic’s private Fa-
cility without any public access points. Mosaic Application at 7–8.
Finally, Mosaic reported that it had partnered with the University
of Florida to conduct additional evaluations of the Road, including
laboratory studies, to show that phosphogypsum “when appropri-
ately blended with other aggregate or cementitious materials, can
meet the performance criteria for engineered road base.” Id. at 11.
As part of Mosaic’s proposal, it included summary data from
sampling completed in 2019 -- more than three years before the
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12 Opinion of the Court 25-10515
2023 revisions -- measuring the average concentration of Ra-226 in
the phosphogypsum to be used. Id. at 12. Using those Ra-226 con-
centrations, Mosaic’s application included an analysis of the expo-
sure pathways and risks to road construction workers and truck
drivers transporting the phosphogypsum for the Road Project over
a “period of a few weeks to a month.” Id. at 6–7. Mosaic concluded
that the radioactive exposure to those individuals would be negli-
gible compared to the dose humans are exposed to from naturally
occurring background radiation. Id. However, Mosaic declined to
evaluate the risk the Road Project posed to utility workers, motor-
cycle and bicycle road users, residents living near the road, and po-
tential reclaimers. It offered that these scenarios were inapplicable
because there would be “no public access” to the Road. Id. at 7–8.
More broadly, Mosaic described its Road Project as a logical
outgrowth of the Fertilizer Institute’s 2019 application and it ex-
plained that the additional information and research would demon-
strate that phosphogypsum could be used beneficially and safely in
road construction. Id. at 2, 10. Thus, throughout the Road Project
proposal, Mosaic repeatedly referenced the risks and assumptions
discussed by the Fertilizer Institute in its 2019 proposal and in the
EPA’s conditional approval of that application.
On October 9, 2024, the EPA published its proposed ap-
proval of Mosaic’s Road Project in the Federal Register and solic-
ited public comment. Notice of Pending Approval for Other Use
of Phosphogypsum, 89 Fed. Reg. 81910 (Oct. 9, 2024) [hereinafter
“Pending Approval”]. The Agency also made its technical review
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25-10515 Opinion of the Court 13
of Mosaic’s application available on its website. See id. at 81912;
Radiation Prot. Div., Env’t Prot. Agency, Review of the Small-Scale
Road Pilot Project on Private Land in Florida Submitted by Mosaic
Fertilizer, LLC (2024) [hereinafter “Agency Review”],
https://www.epa.gov/system/files/documents/2024-10/1-mo-
saic_risk_technical_summary_final_508_0.pdf. The Pending Ap-
proval and Agency Review explained that Mosaic’s request in-
cluded all necessary information and was complete under 40 C.F.R.
§ 61.206(b), that Mosaic’s risk assessments were technically ac-
ceptable, and that the potential radiological risks from the pro-
posed Project posed no greater risk than maintaining the phos-
phogypsum in a stack or mine as required under § 61.206(c). Pend-
ing Approval, 89 Fed. Reg. at 81911; Agency Review at 2–3.
The Agency added that Mosaic’s 2019 sampling was accepta-
ble because “the risk assessment scenarios reviewed by [the] EPA
are based on Ra-226 activity concentration values that are roughly
double the average value reported by Mosaic.” Agency Review at
11. The EPA concluded that its “risk assessment [would] remain
valid even if the Ra-226 activity in the phosphogypsum that is used
turns out to be higher.” Id. The Agency nevertheless required that
additional sampling be completed upon final approval of the Pro-
ject and before construction could begin, pursuant to the data col-
lection requirements of § 61.207. Id.
On a more technical level, the EPA analyzed the risks the
Road Project posed to certain individuals and compared those risks
against the individual lifetime cancer risk threshold of 3 in 10,000.
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14 Opinion of the Court 25-10515
For each category of individual the Agency assessed -- construction
workers, truck drivers transporting phosphogypsum, road users,
and nearby residents -- it concluded that the associated risks fell
well below the applicable threshold. Id. at 14, 18–19.
As for the reclaimer scenario, the EPA concluded that the
proposed Project would not alter the site characteristics because
the Facility already included an existing phosphogypsum stack in
the immediate vicinity of the Road. Accordingly, the Agency de-
clined to consider the reclaimer scenario, which it determined to
be inapplicable. Id. at 20–21. Finally, the EPA expressly noted that
its review of Mosaic’s proposal “does not imply any conclusions
about the risks to future reclaimers at other sites which may be fur-
ther from phosphogypsum stacks and may lack the institutional
controls present at the Mosaic facility.” Id. at 21.
The EPA’s review also included an analysis of the water
pathway and the impact the Road Project might have on surface
and groundwater supplies. Id. at 21–22. The Agency concluded
that the potential risk arising from radionuclides leaching into sur-
face or groundwater was low compared to the risks posed by direct
exposure and inhalation of radon gas. Id. Nevertheless, the EPA
required Mosaic to monitor the groundwater following the con-
struction of the Road for a minimum of eighteen months. Id. The
Agency again limited its findings to Mosaic’s Project, explaining
that “the eighteen-month sampling duration proposed by Mosaic
may not necessarily be sufficient to support conclusions about
longer term use in a full-scale project.” Id. at 22.
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25-10515 Opinion of the Court 15
The Center submitted a detailed technical comment on No-
vember 23, 2024, opposing the Agency’s Proposed Approval. See
Comment Submitted by the Center for Biological Diversity, Ctr.
For Biological Diversity v. EPA, No. 25-10515 (11th Cir. Mar. 13,
2025), Dkt. No. 9 Exh. C [hereinafter “Center’s Comment”]. It ar-
gued that: (1) the proposed approval violated Subpart R because
the regulation forbade the use of phosphogypsum in road construc-
tion; (2) the Agency’s decision to apply a 3 in 10,000 safety thresh-
old was violative of the text of Subpart R; and (3) the Agency arbi-
trarily limited the scope of its risk analysis and improperly accepted
Mosaic’s outdated Ra-226 samples. Id. at 1, 4–9.
The EPA responded to public comment on December 11,
2024. Radiation Prot. Div., Env’t Prot. Agency, Request for Ap-
proval of Use of Phosphogypsum in a Small-Scale Road Pilot Pro-
ject on Private Land in Florida Submitted by Mosaic Fertilizer,
LLC: Response to Comments, (2024) [hereinafter “Response to
Comments”], https://www.epa.gov/system/files/docu-
ments/2024-12/response-to-comments_12-12-2024.pdf. As for the
Center’s claims, the Agency explained that road construction was
an appropriate other use for phosphogypsum under Subpart R, that
the 3 in 10,000 safety threshold was the appropriate standard to
evaluate other use applications, and that its risk analysis was sup-
ported and appropriately tailored to Mosaic’s application. Id. at 6–
11. The EPA made no change to its Proposed Approval, and, on
December 23, 2024, the Agency published its Final Approval of Mo-
saic’s application. Agency’s Notice of Approval for Other Use of
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16 Opinion of the Court 25-10515
Phosphogypsum, 89 Fed. Reg. at 104535 (Dec. 23, 2024) [hereinaf-
ter “Notice of Approval”].
The Center timely petitioned this Court for direct review of
the Notice of Approval on February 19, 2025, under § 307(b)(1) of
the Clean Air Act. The Center reprises substantially the same ar-
guments it had raised in its November 2024 comment to the
Agency, asserting that the EPA’s approval violated the plain lan-
guage of Subpart R and that the Agency’s risk assessment was arbi-
trary and capricious. The EPA and Mosaic (collectively, “Respond-
ents”) disagree, claiming that we must dismiss the petition for want
of jurisdiction, and that in any event, the EPA’s action was conso-
nant with the applicable regulations and was neither arbitrary nor
capricious.
II.
Before proceeding to the merits of the Center’s petition, we
consider whether we have jurisdiction. Aguirre v. Seminole County,
158 F.4th 1276, 1291 (11th Cir. 2025) (“Without jurisdiction the
court cannot proceed at all in any cause.” (quoting Ex parte
McCardle, 74 U.S. (7 Wall.) 506, 514, 19 L.Ed. 264 (1868))). The EPA
and Mosaic argue that this Court must dismiss for want of jurisdic-
tion because the Center does not have associational standing; Mo-
saic also claims that the matter has become moot. After thorough
review, however, we are satisfied that we have the power to enter-
tain this petition.
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25-10515 Opinion of the Court 17
A.
We begin with the claim that the Center lacks associational
standing to challenge the EPA’s approval of Mosaic’s Road Project.
Article III of the Constitution limits this Court’s jurisdiction
to “cases” and “controversies.” U.S. Const. art. III, § 2. As part of
Article III’s case-or-controversy requirement, any party seeking re-
lief must have standing to litigate its claim. See Bischoff v. Osceola
County, 222 F.3d 874, 878 (11th Cir. 2000) (“[S]tanding is perhaps
the most important of [the jurisdictional] doctrines.” (quoting
United States v. Hays, 515 U.S. 737, 742 (1995) (alteration added by
Bischoff court)). The central question asked by the standing doc-
trine is “whether [this] litigant is entitled to have the court decide
the merits of the dispute or of particular issues.” Warth v. Seldin,
422 U.S. 490, 498 (1975).
As the party invoking our jurisdiction, the Center bears the
burden of establishing standing. Ga. Republican Party v. SEC, 888
F.3d 1198, 1201–02 (11th Cir. 2018). Under Hunt v. Washington State
Apple Advertising Commission, 432 U.S. 333 (1977), an association like
the Center has standing to challenge an Agency’s action when: “(a)
its members would otherwise have standing to sue in their own
right; (b) the interests it seeks to protect are germane to the organ-
ization’s purpose; and (c) neither the claim asserted nor the relief
requested requires the participation of individual members in the
lawsuit.” Id. at 343; see also Black Warrior Riverkeeper, Inc. v. U.S.
Army Corps of Engineers, 781 F.3d 1271, 1279–80 (11th Cir. 2015).
When associational standing is invoked, the essential question is
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18 Opinion of the Court 25-10515
whether the organization’s members themselves have Article III
standing, Riverkeeper, 781 F.3d at 1279–80, and here the parties dis-
agree only as to that issue.
To establish that at least one of its members has standing to
sue in his own right, the Center filed sworn declarations from two
of its members, Michael Lexner and Elise Pautler Bennett. Lexner
lives a little less than five miles from the Facility and Bennett lives
some fifty miles away. Because the Center need only show that
one of its members would have standing to sue in his individual
capacity, we focus only on Lexner. See Hunt, 432 U.S. at 343.
For just under two decades, Lexner, along with his wife and
children, have lived at their Florida home located less than five
miles “as the crow flies” from Mosaic’s Facility. Lexner attests that
he is a member of the Center for Biological Diversity and that the
Center represents his interest in protecting his health and the envi-
ronment. Specifically, he avers that his family has experienced, and
continues to experience, harm to their recreational interests and
the use and enjoyment of their property because of substantial con-
cerns about radioactive contamination coming from the Facility.
Lexner and his family grew and harvested peas, potatoes and myr-
iad other vegetables at home, but they have ceased gardening on
the property on account of their concern about phosphogypsum
contamination of the groundwater. Lexner likewise stopped rais-
ing horses on the property and no longer drinks the well water
available at his home. To protect his family’s health, Lexner says
that he is forced to purchase jugs of water from local stores and
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25-10515 Opinion of the Court 19
haul the water to his home for drinking and food preparation. He
explains that he first began avoiding drinking and using the well
water on his property in 2016. In that year, a sinkhole opened up
in one of Mosaic’s phosphogypsum stacks, resulting in “hundreds
of millions of gallons of radioactive, toxic waste” collapsing into the
aquifer from whence the Lexner family drew their water. Lexner
also cites and attaches to his declaration a 2018 research study con-
ducted by the University of Central Florida concluding that the
2016 sinkhole carried a potential to contaminate Floridian ground-
water far beyond the Facility.
Lexner further attests that Mosaic’s Road Project will exac-
erbate these harms and injuries. He explains that the EPA’s ap-
proval of the Road Project “once again threatens [his] health” by
constructing still another source of phosphogypsum pollution
which he asserts will “lead to additional radioactive particulate
matter exposure, groundwater contamination, or sinkholes[.]”
This, he says, will “further harm [his] ability to use [his] property,
recreate in ways such as gardening, and protect [his] health and the
health of [his] family.” These injuries, he adds, are likely to affect
the value of his property, causing him additional economic harm.
Finally, Lexner observes that his immediate concerns are based
upon “a long history of pollution events” at the Facility, notably
including the “2016 sinkhole and other pollution events.”
Under the law of this Circuit, to establish that Lexner would
have standing in his own right, his declaration must show that:
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20 Opinion of the Court 25-10515
“(1) [he] has suffered an injury in fact that is (a) concrete and par-
ticularized and (b) actual or imminent, (2) there is a causal connec-
tion between the injury and the conduct complained of, and (3) it
is likely that the injury will be redressed by a favorable decision of
the court.” Sierra Club v. Johnson, 436 F.3d 1269, 1276 (11th Cir.
2006) (citation modified). We address each in turn.
In an environmental case, an injury in fact may be estab-
lished through evidence of concrete and particularized harm to aes-
thetic or recreational interests. Thus, for example, an individual
plaintiff can demonstrate injury by attesting that he uses -- or would
use more often -- an area affected by the alleged violation and that
the challenged conduct harms his aesthetic or recreational enjoy-
ment of that area. See Sierra Club v. Tennessee Valley Auth., 430 F.3d
1337, 1344 (11th Cir. 2005); see also Friends of the Earth, Inc. v. Laidlaw
Env’t Services (TOC), Inc., 528 U.S. 167, 183 (2000). In addition, an
environmental organization may establish standing by showing
that its members use the affected areas and face environmental or
health-related harm resulting from the challenged conduct. See
Riverkeeper, 781 F.3d at 1279–83; see also Parker v. Scrap Metal Proces-
sors, Inc., 386 F.3d 993, 1003–04 (11th Cir. 2004).
The Center says that Lexner’s alleged injuries are concrete
and particularized because they stem from threats of radiation ex-
posure and aquifer contamination, which carry increased individ-
ual health risks. In addition, the Center points out that Lexner has
attested to significant degradation in the enjoyment of his property
and that Mosaic’s Facility has a longstanding and extensive history
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25-10515 Opinion of the Court 21
of creating environmental issues, which will plausibly be exacer-
bated by the Road Project. The Respondents reply that the decla-
ration fails to establish an injury resulting from the Road Project,
because Lexner has asserted only “generalized concerns about liv-
ing near the Mosaic facility, not concerns regarding the Road Pilot
Project at issue here.”
We are satisfied Lexner has presented enough to establish
that he has suffered a concrete and particularized injury in fact.
The harms he describes, including the loss of enjoyment of his own
private property and the manifestation of plausible health risks, are
sufficient. Thus, for example, Lexner attests to the cessation of all
vegetable gardening and the removal of horses from his property.
He adds that he has taken significant steps and continues to act in
a manner designed to avoid using well water otherwise drawn
from the property in order to avoid continued exposure to radio-
active particulate matter.
While these injuries were evident before the Road Project
commenced, the allegations plausibly and concretely assert that
the Road Project exacerbates Lexner’s injuries. Lexner has attested
in no unclear terms -- and has cited to supporting scientific litera-
ture -- that his injuries are plausibly made worse by the Road Pro-
ject, because the Road will create an additional source of radioac-
tive air pollutants, beyond the contaminants emanating from the
phosphogypsum stacks at the Facility.
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22 Opinion of the Court 25-10515
These claims are sufficient for standing purposes to establish
an injury in fact. Time and again, the federal courts have con-
cluded that a concrete and particularized harm arising from a
party’s proximity to radioactive materials constitutes an injury in
fact. See, e.g., Duke Power Co. v. Carolina Environmental Study Group,
Inc., 438 U.S. 59, 74 (1978) (“[T]he emission of non-natural radia-
tion into appellees’ environment would also seem a direct and pre-
sent injury[.]”); Texas v. Nuclear Regul. Comm’n, 78 F.4th 827, 836
(5th Cir. 2023) (owning property within four miles of facility “suf-
ficient to establish injury . . . [i]n the context of radioactive materi-
als” (citation modified)), rev’d on other grounds. by, Nuclear Regul.
Comm’n v. Texas, 605 U.S. 665 (2025); see also Nuclear Energy Inst.,
Inc. v. EPA, 373 F.3d 1251, 1266 (D.C. Cir. 2004) (petitioner living
eighteen miles from facility had standing); Kelley v. Selin, 42 F.3d
1501, 1509 (6th Cir. 1995) (finding injury resulting from storage of
nuclear waste where petitioners asserted “harm to their aesthetic
interests and their physical health” and “that the value of his or her
property will be diminished by the storage of nuclear waste”).
The Supreme Court’s decision in Duke Power is illuminating.
There, the High Court concluded that “the environmental and aes-
thetic consequences of the thermal pollution of the two lakes in the
vicinity of the disputed [nuclear] power plants is the type of harm-
ful effect which has been deemed adequate in prior cases to satisfy
the injury in fact standard.” 438 U.S. 73–74. The Court explained
that “the health and genetic consequences of even small emissions
like those concededly emitted by nuclear power plants” are injuries
in fact. Id. at 74. In this case, as alleged, the emission of additional
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25-10515 Opinion of the Court 23
non-natural radon into Lexner’s environment on account of Mo-
saic’s Road Project -- which Lexner observes will harm his aes-
thetic, recreational, and financial interests -- is enough to assert a
direct and present injury.
Lexner has also met the requirements of causation and re-
dressability. Under the law of this Circuit, “[i]n environmental
suits, the injury-in-fact inquiry tends to be more searching than the
causation or redressability considerations.” Ouachita Watch League
v. Jacobs, 463 F.3d 1163, 1170 (11th Cir. 2006) (citing, inter alia, John-
son, 436 F.3d at 1277–78). Even so, when the alleged injury arises
from the government’s regulation of a third party, as is the case for
the EPA’s regulation of Mosaic, the standing inquiry is more de-
manding: the Center must demonstrate that the decisions of both
the regulator and the regulated party will operate “in such manner
as to produce causation and permit redressability of injury.” Lujan
v. Defs. of Wildlife, 504 U.S. 555, 562 (1992).
As for causation, Mosaic’s ability to complete the Road Pro-
ject is entirely predicated on the EPA’s approval of its application.
Subject to Subpart R, Mosaic is categorically barred from removing
phosphogypsum from its stacks for use in road construction unless
and until it receives authorization from the EPA. See 40
C.F.R. § 61.206. The regulatory scheme thus makes the Agency’s
approval a necessary prerequisite to the Road Project. Absent the
EPA’s express approval, Mosaic could not lawfully proceed with
the Road Project at all. Thus, there is a direct causal connection
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24 Opinion of the Court 25-10515
between the challenged agency action and Mosaic’s completion of
the Road Project.
For similar reasons, the injuries alleged are traceable to the
EPA’s approval of the Project. As we’ve explained, Lexner alleges
that the Road Project will further restrict the use and enjoyment of
his property, diminish its value, and expose him to increased health
risks. These claimed injuries do not arise in a vacuum; they result
from a Project that could not go forward without the EPA’s au-
thorization. The Agency’s decision is therefore not just a back-
ground condition or an attenuated link in the causal chain. Rather,
it is the legal and practical cause that enables Mosaic to undertake
the challenged activity that plausibly gives rise to Lexner’s claimed
injuries.
Finally, Lexner’s injury is redressable by this Court. “Re-
dressability is established . . . when a favorable decision ‘would
amount to a significant increase in the likelihood that the plaintiff
would obtain relief that directly redresses the injury suffered.’”
Harrell v. Fla. Bar, 608 F.3d 1241, 1260 n.7 (11th Cir. 2010) (quoting
Utah v. Evans, 536 U.S. 452, 464 (2002)). The redressability inquiry
“generally assesses whether [a personal] interest exists at the out-
set.” Uzuegbunam v. Preczewski, 592 U.S. 279, 282 (2021). Thus, we
consider whether Lexner had a concrete and particularized injury,
redressable at the time the Center filed its petition in Febru-
ary 2025. See id. We conclude that he did.
If the EPA failed to comply with § 61.206 or the Administra-
tive Procedure Act, we have the authority to vacate or remand the
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25-10515 Opinion of the Court 25
Agency’s Notice. At the time the Center filed its petition -- before
construction of the Road Project had begun -- this relief would have
provided precisely the redress the Center sought. Vacatur would
have invalidated the Notice on which the Project depended, and
remand would have required the EPA to reconsider its action in
compliance with the governing legal requirements before the Pro-
ject could proceed. Either form of relief would have prevented or,
at a minimum, delayed construction of the Road Project until the
EPA could ensure that the Project sufficiently protects the public
health. We are therefore satisfied that Lexner’s injuries were re-
dressable when the action was filed.
The Center has shown that at least one of its members
would have standing in his individual capacity. And because the
environmental interests the Center seeks to protect are also ger-
mane to its purpose and neither the claim asserted nor the relief
sought requires the participation of individual members in the law-
suit, see Johnson, 436 F.3d at 1276, we are satisfied that the Center
has associational standing.
B.
Mosaic, alone, also argues that even if the Center has stand-
ing, we still must dismiss for want of jurisdiction because the mat-
ter has become moot.
3
Mosaic maintains that the matter became

3
At oral argument, counsel for the EPA clarified that while it maintains we
lack jurisdiction because the Center does not have associational standing, the
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26 Opinion of the Court 25-10515
moot in November 2025 when it completed construction on the
test sections of the Road. We are not persuaded.
The standing requirement is only “one strand” of this
Court’s jurisdictional inquiry. United States v. Ross, 963 F.3d 1056,
1062 (11th Cir. 2020) (en banc) (citation modified). Another strand
is mootness, which may offer a separate reason for dismissing the
Center’s petition. A petition becomes moot “when it no longer
presents a live controversy with respect to which the court can give
meaningful relief.” Sheely v. MRI Radiology Network, P.A., 505 F.3d
1173, 1183 (11th Cir. 2007) (quoting Toriano v. Supervisor of Elections,
382 F.3d 1276, 1281–82 (11th Cir. 2004)). While redressability and
mootness are related, mootness “considers whether [a personal in-
terest] exists throughout the proceedings.” Uzuegbunam, 592 U.S.
at 282. “[I]f in the course of litigation a court finds that it can no
longer provide a plaintiff with any effectual relief, the case gener-
ally is moot.” Id. However, unlike the standing inquiry, the “heavy
burden” of proving that a claim is moot falls on the party seeking
dismissal. Norwegian Cruise Line Holdings Ltd. v. State Surgeon Gen.,
Fla. Dep’t of Health, 55 F.4th 1312, 1315 (11th Cir. 2022) (citation
modified). Mosaic has not met its burden.
Mosaic’s application explains that its Road Project has two
phases: first, the company would construct the Road; then, Mosaic
would coordinate with the University of Florida to “test and mon-
itor the road.” Mosaic says that the initial construction phase began

Agency does not agree with Mosaic’s claim that we lack jurisdiction because
the matter is moot.
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25-10515 Opinion of the Court 27
in August 2025
; phosphogypsum was removed from the Facility’s
on-site stacks and applied to the Road beginning on October 7,
2025, and the application of all of the phosphogypsum was com-
plete by November 4, 2025. Although some control sections of the
Road remained under construction at the time of oral argument,
Mosaic represents that the portions of the Project involving phos-
phogypsum are complete and “[n]o additional phosphogypsum
will be removed from any stack in connection with the pilot project
approval.”
Thus, according to Mosaic, its “remaining obligations under
the terms of the approval involve only (1) completing ‘control’ sec-
tions of the road that do not contain any phosphogypsum and
(2) testing and monitoring the already-constructed road and report-
ing the results to EPA, thus providing valuable data on the road’s
environmental performance and suitability.” While Mosaic
acknowledges that the Notice of Approval contains post-construc-
tion monitoring, it says that the Center did not challenge those con-
ditions, that the Court cannot modify these discretionary condi-
tions, and that the Center has not shown how revising monitoring
obligations would redress its alleged injuries. It reasons that be-
cause the Center “has not asserted that testing or monitoring
harm[s] its members,” vacatur or remand of the Agency’s action
can no longer offer the Center redress, rendering the matter moot.
Mosaic cites several cases in support of its claim that the law-
suit has become moot. See, e.g., Nat’l Parks Conservation Ass’n, Inc.
v. U.S. Army Corps of Eng’rs, 574 F. Supp. 2d 1314, 1322 (S.D. Fla.
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28 Opinion of the Court 25-10515
2008) (first citing Save the Bay, Inc. v. U.S. Army, 639 F.2d 1100, 1103
(5th Cir. 1981); then citing Fla.Wildlife Fed’n v. Goldschmidt, 611 F.2d
547, 548 (5th Cir. 1980) (per curiam)).
4
Mosaic also claims that un-
der out-of-circuit precedent, lawsuits seeking to stop an agency-au-
thorized construction project are mooted by the completion of the
project. See, e.g., Knaust v. City of Kingston, 157 F.3d 86, 88 (2d Cir.
1998); Bayou Liberty Ass’n, Inc. v. U.S. Army Corps of Eng’rs, 217 F.3d
393, 398 (5th Cir. 2000); City of Romulus v. Wayne County, 634 F.2d
347, 348 (6th Cir. 1980); One Thousand Friends of Iowa v. Mineta, 364
F.3d 890, 892–94 (8th Cir. 2004); Neighborhood Transp. Network, Inc.
v. Pena, 42 F.3d 1169, 1172 (8th Cir. 1994).
The cases are inapposite. They address claims of mootness
where the petitioner sought only injunctive relief, or declarative
relief in the form of an advisory opinion. See Knaust, 157 F.3d at 88
(“Because this appeal thus seeks to enjoin the future occurrence of
events that are already in the past, we lack appellate jurisdiction.”);
City of Romulus, 634 F.2d at 347 (same); Mineta, 364 F.3d at 892
(same); Pena, 42 F.3d at 1172; Bayou Liberty Ass’n, 217 F.3d at 397–
98 (same for declaratory judgment). Those requests for equitable
relief were rendered moot after construction was completed.
In this case, however, the Center seeks a vacatur or remand
of the Agency decision approving Mosaic’s application, relief that

4
In Bonner v. City of Prichard, 661 F.2d 1206 (11th Cir. 1981) (en banc), the Elev-
enth Circuit adopted as binding precedent all decisions handed down by the
former Fifth Circuit before October 1, 1981. Id. at 1209.
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25-10515 Opinion of the Court 29
could be granted even if the Project has been completed. The Cen-
ter observes that the EPA’s Notice of Approval imposes ongoing
monitoring and testing obligations, which could be altered mark-
edly by a favorable decision from this Court. Thus, in the Center’s
view, a vacatur or remand could still provide meaningful relief; it
would require the EPA to reconsider its approval and the ongoing
monitoring protocols it has imposed.
We agree. A decision in the Center’s favor could still affect
the legal relationship between the parties, notwithstanding Mo-
saic’s progress in building the Road. By way of example, if we were
to conclude that the EPA applied the wrong risk calculus in review-
ing the application, subsequent Agency review could result in
heightened monitoring requirements, capping the road, or indeed,
even tearing the road out. Cf. Airport Neighbors All., Inc. v. United
States, 90 F.3d 426, 427–29 (10th Cir. 1996) (“[W]e could order that
the runway be closed or impose restrictions on its use until Re-
spondents complied with NEPA.”). These remedies remain avail-
able. This matter has not become moot. Thus, we deny Mosaic’s
motion.
III.
We proceed to the merits of the Center’s petition. The Cen-
ter raises two main arguments: first, that the Agency’s approval
misinterprets the demands of Subpart R and violates the text, and,
second, that even if Subpart R was correctly construed, the ap-
proval of the Road Project was arbitrary and capricious. We re-
main unpersuaded.
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30 Opinion of the Court 25-10515
A.
The Administrative Procedure Act (“APA”), 5 U.S.C.
§ 706(2)(A), requires that “courts, not agencies, will decide ‘all rel-
evant questions of law’ arising on review of agency action -- even
those involving ambiguous laws -- and set aside any such action
inconsistent with the law as they interpret it.” Loper Bright Enters.
v. Raimondo, 603 U.S. 369, 392 (2024) (quoting 5 U.S.C. § 706). If an
agency’s final action fails to meet statutory requirements or vio-
lates federal regulations, the court must vacate the challenged ac-
tion. Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402,
413–14 (1971), abrogated on other grounds by, Califano v. Sanders, 430
U.S. 99 (1977).
When we review whether an agency’s action complies with
the applicable text of the agency’s own regulations, we defer to the
agency’s interpretation only if the regulation is “genuinely ambig-
uous.” Kisor v. Wilke, 588 U.S. 558, 563 (2019); see also United States
v. James, 135 F.4th 1329, 1333 (11th Cir. 2025) (“[O]nly if we are left
with real uncertainties about a regulation’s meaning do we [de-
fer].” (citation modified)), cert. denied, No. 25-6267, 2026 WL
922527 (U.S. Apr. 6, 2026); Hayes v. Dir., OWCP, 172 F.4th 1263,
1266 (11th Cir. 2026) (“We review de novo the administrative inter-
pretation of the regulations implementing the Act, but we defer to
agencies’ reasonable readings of genuinely ambiguous regula-
tions.” (citation modified)). To discern whether a regulation is re-
ally ambiguous we “carefully consider the text, structure, history,
and purpose of a regulation, in all the ways [the Court] would if it
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25-10515 Opinion of the Court 31
had no agency to fall back on.” Rafferty v. Denny’s, Inc., 13 F.4th
1166, 1179 (11th Cir. 2021) (citing Kisor, 588 U.S. at 563).
The Center argues that the EPA’s Notice of Approval vio-
lates the unambiguous text of Subpart R in two ways. First, it says
the text categorically prohibits the use of phosphogypsum in road
projects, and so the EPA cannot interpret the other purposes pro-
vision to include road construction without a new rulemaking pro-
cess. Next the Center argues Subpart R requires the Agency to
evaluate other use projects using a maximum risk threshold of 9 in
100,000, and the Agency’s use of a 3 in 10,000 risk threshold was
therefore violative of the regulatory text. We agree that Subpart R
is unambiguous. But the Center’s interpretation of the regulatory
text is wrong.
Again, Subpart R prohibits the distribution and use of phos-
phogypsum for “any purpose not expressly specified in § 61.204 or
§ 61.205 without prior EPA approval.” 40 C.F.R. § 61.206(a). The
regulation provides that the EPA may approve an other use appli-
cation so long as the proposed “use is at least as protective of public
health, in both the short term and the long term, as disposal of
phosphogypsum in a stack or a mine.” Id. § 61.206(c). Subpart R
does not categorically prohibit the use of phosphogypsum in road
construction; in fact, it does not mention road construction at all.
The Center nevertheless argues that Subpart R clearly for-
bids the EPA from approving an other use application to use phos-
phogypsum in road construction. It only relies on language drawn
from the 1992 Rule’s Preamble, not from the regulation itself. The
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32 Opinion of the Court 25-10515
Preamble declared that the EPA’s four modeled road use scenarios
“always” exceeded the presumptively safe level. See 1992 Rule, 57
Fed. Reg. at 23312. Thus, the Center reasons that when Subpart R
is read in concert with the 1992 Preamble, the regulatory text for-
bids the use of phosphogypsum in road construction.
The Respondents agree that the regulatory text is unambig-
uous, but they say that it permits the EPA to review and approve
road projects under the other purposes provision of § 61.206(c).
They assert that under our law we must first look to the text of the
regulation (Subpart R) in order to resolve the dispute, and because
that regulation permits the use of phosphogypsum in road con-
struction (so long as EPA approval is obtained) we have no reason
to consider the 1992 Preamble -- or any other extrinsic evidence --
in interpreting the regulation. Finally, the Respondents contend
that even if we look beyond the text of Subpart R, the Center’s ar-
gument finds no solid footing.
For starters, we agree with the Respondents that regulatory
interpretation begins with, must rely upon, and often ends with the
text of the regulation itself. First, we ask whether the applicable
regulatory language has a “plain and unambiguous meaning.” Gose
v. Native Am. Servs. Corp., 109 F.4th 1297, 1310 (11th Cir. 2024) (ci-
tation modified). We do that by examining “the language itself, the
specific context in which that language is used, and the broader
context of the statute [or regulation] as a whole.” Id. (citation mod-
ified). If the meaning is clear, “there is no need for further inquiry.”
Id. (citation modified). Regulatory preambles may provide context
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25-10515 Opinion of the Court 33
about an agency’s intent, see, e.g., Watkins v. City of Montgomery,
Ala., 775 F.3d 1280, 1284 (11th Cir. 2014) (relying on preamble to
interpret Department of Labor regulations), but preambles “do not
enjoy the force of law” and they cannot override the unambiguous
terms of a regulation itself, Blanco v. Samuel, 91 F.4th 1061, 1076
(11th Cir. 2024) (citing AT&T Corp. v. FCC, 970 F.3d 344, 350 (D.C.
Cir. 2020)).
5

The plain text of Subpart R does not prohibit the use of phos-
phogypsum in road construction. Section 61.206 allows the EPA
to approve an application for the distribution and use of phos-
phogypsum for “any other purpose,” so long as the applicant se-
cures “prior EPA approval.” 40 C.F.R. § 61.206(b). The language
of § 61.206 neither enumerates what other purposes would be per-
missible, nor excludes any particular use; instead, the regulation
only employs the broad term “any.” The Supreme Court has em-
phasized that “the word ‘any’ has an expansive meaning.” Ali v.
Fed. Bureau of Prisons, 552 U.S. 214, 219 (2008) (citation modified);
see also Encino Motorcars, LLC v. Navarro, 584 U.S. 79, 88 (2018) (read-
ing “any” to “bespeak[] breadth”); Harrison v. PPG Indus., Inc., 446
U.S. 578, 589 (1980) (explaining that “any” is “expansive language”
that offers no indication that the text has a “limiting construction”).

5
Our sister Circuits have treated preambles in a similar way, viewing them as
interpretive aids, if necessary, but declining to treat them as operative law.
See, e.g., Saint Francis Med. Ctr. v. Azar, 894 F.3d 290, 297 (D.C. Cir. 2018) (pre-
amble “lacks the force and effect of law”); Peabody Coal Co. v. Dir., Off. of Work-
ers’ Comp. Programs, 746 F.3d 1119, 1125–27 (9th Cir. 2014); Peabody Twentymile
Mining, LLC v. Sec’y of Lab., 931 F.3d 992, 998 (10th Cir. 2019).
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34 Opinion of the Court 25-10515
So have we. See Merritt v. Dillard Paper Co., 120 F.3d 1181, 1186
(11th Cir. 1997) (“[T]he adjective ‘any’ is not ambiguous; it has a
well-established meaning . . . . [A]ny means all.” (citation modi-
fied)); United States v. Castro, 837 F.2d 441, 445 (11th Cir. 1988) (con-
cluding that “any” means “every” or “all”).
Undeniably, road construction falls into the broad any other
purpose category for which the EPA may grant approval. The EPA
did not violate Subpart R when it concluded that Mosaic’s Road
Project was a permissible other purpose use of phosphogypsum.
Since the regulatory text is unambiguous, we need not look
to the 1992 Rule’s Preamble in order to discern its meaning. See,
e.g., Azar, 894 F.3d at 297 (declining to evaluate preamble language
where the regulation itself is clear). But even if we did look beyond
the Rule’s text, the 1992 Preamble offers the Center no support.
The Center primarily relies on a single paragraph from the 1992
Pr eamble which, again, reads this way:
For the road construction scenarios analyzed, the use of
phosphogypsum always resulted in a MIR [Maximum
Individual Risk] greater than the outer bound of the
presumptively safe level of approximately 1 x 10
-
⁴ [1
in 10,000]. Therefore, EPA has determined that the
use of phosphogypsum in road construction presents
an unacceptable level of risk to public health.
1992 Rule, 57 Fed. Reg. at 23312 (emphasis added). This language,
the Center argues, confirms that the EPA intended to “uncondi-
tionally reject[] all road construction as an other purpose.”
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25-10515 Opinion of the Court 35
We are unpersuaded. The 1992 Preamble explained that the
Agency modeled and evaluated only four road construction scenar-
ios. Id. Based on its analysis of those four scenarios, the EPA de-
clined to categorically authorize road construction in the same way
it did for agricultural and research uses. See 40 C.F.R. §§ 61.204–05.
But nowhere in the regulatory text or in the 1992 Preamble can we
discern any indication that the Agency’s decision not to authorize
the use of phosphogypsum in those four road construction scenar-
ios categorically prohibited the use of phosphogypsum in all road
construction scenarios.
The Center also argues that even if the 1992 Rule permits
road construction as an “other purpose,” the EPA violated Sub-
part R when it evaluated Mosaic’s application using a risk threshold
of 3 in 10,000, because the regulation requires an evaluation using
a 9 in 100,000 threshold. The Center says that because the other
use provision requires projects to be “at least as protective of public
health, in both the short term and the long term, as disposal of
phosphogypsum in a stack or a mine,” the EPA could only approve
projects that carry a risk below a 9 in 100,000 threshold, which is
the maximum individual lifetime risk the EPA calculated for phos-
phogypsum stacks and mines in 1989. 1989 Rule, 54 Fed. Reg. at
51654, 51675.
The Respondents observe, however, that the risk threshold
is ultimately irrelevant, because the Road Project’s risks fall well
below both the EPA’s applied risk threshold (3 in 10,000) and the
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36 Opinion of the Court 25-10515
Center’s preferred risk threshold (9 in 100,000).
6
So even if the EPA
incorrectly applied a lower risk threshold -- and we draw no such
conclusion -- that error would be harmless.
We agree with the Respondents. The doctrine of harmless
error applies to administrative agency actions “when a mistake of
the administrative body is one that clearly had no bearing on the
procedure used or the substance of [the] decision reached.” U.S.
Steel Corp. v. EPA, 595 F.2d 207, 215 (5th Cir. 1979) (citation modi-
fied); see also Nat’l Ass’n of Home Builders v. Defs. of Wildlife, 551 U.S.
644, 659–60 (2007). The reviewing court generally conducts a case-
specific inquiry involving “an estimation of the likelihood that the
result would have been different . . . and a hesitancy to generalize
too broadly about particular kinds of errors when the specific fac-
tual circumstances in which the error arises may well make all the
difference.” Shinseki v. Sanders, 556 U.S. 396, 411–12 (2009) (cita-
tion modified).
On this record, we are satisfied that the EPA would have
reached the same result even if it had applied the Center’s preferred
safety threshold of 9 in 100,000. In fact, the Road Project’s risks are
often several orders of magnitude less than the Center’s preferred
threshold: for truck drivers moving phosphogypsum to the site of

6
The Respondents, however, do not concede that the EPA used the incorrect
risk threshold in evaluating Mosaic’s application. Instead, they argue that Sub-
part R requires only that the Project carry a maximum risk below 3 in 10,000,
which is the threshold the Agency used in its 1992 rulemaking process.
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25-10515 Opinion of the Court 37
the test road, the risk is 2.7 x 10
-7
(2.7 in 10,000,000); for construc-
tion workers, the risk is less than 2 x 10
-6
(2 in 1,000,000); for work-
ers at the Facility not directly involved in the Road Project, the risk
is less than 1 x 10
-6
(1 in 1,000,000); and, finally, for nearby residents,
the risk is less than 1 x 10
-6
(1 in 1,000,000). Thus, even for con-
struction workers experiencing the highest risk levels, their risk of
developing fatal cancer is at least 45 times lower than the Center’s
preferred risk threshold of 9 x 10
-5
(9 in 100,000). And for the oth-
ers, the risks are even lower: for truck drivers the risk is approxi-
mately 333 times less than the Center’s preferred threshold, and for
workers at the Facility and nearby residents, the risk is at least 90
times less than that threshold.
The Center argues nevertheless that vacatur or remand is
necessary because the EPA’s application of an incorrect threshold
is a serious procedural error that cannot be excused. Citing United
States Steel Corp. v. EPA, 595 F.2d 207 (5th Cir. 1979), the Center
claims that the EPA’s “error plainly affected the procedure used”
and therefore we “cannot assume that there was no prejudice to
petitioners.” Id. at 215. In that case, the former Fifth Circuit con-
cluded that the EPA’s failure to give notice and comment was not
cured by acceptance of comments after the effective date, and that
the procedural error could not be considered harmless. Id.
Steel Corp. is not analogous. The EPA did not commit a se-
rious procedural error which deprived the Center or its members
of an opportunity to participate in the administrative process, nor
did the EPA’s use of the 3 in 10,000 risk threshold prejudice the
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38 Opinion of the Court 25-10515
Center in any way. The Agency’s approval would be justified even
if it had used the Center’s preferred risk threshold. Here, vacatur
or remand would require the Agency to repeat its Review of the
Road Project only to reach the same result -- a significant and un-
necessary use of administrative resources. The law does not sup-
port ordering so empty an exercise.
B.
Next, the Center argues that regardless of whether the
EPA’s decision violated the text of Subpart R, vacatur or remand is
still required because the Agency’s approval of Mosaic’s application
was arbitrary and capricious. Again, we are unpersuaded.
Under the APA, a reviewing court must set aside an agency
action that is “arbitrary, capricious, an abuse of discretion, or oth-
erwise not in accordance with law[.]” 5 U.S.C. § 706(2)(A); see John-
son, 436 F.3d at 1273. Review under the well-established arbitrary-
and-capricious standard is deferential, but still meaningful. See id.
An agency action would be arbitrary and capricious if the agency
“relied on factors which Congress has not intended it to consider,
entirely failed to consider an important aspect of the problem, of-
fered an explanation for its decision that runs counter to the evi-
dence before the agency, or is so implausible that it could not be
ascribed to a difference in view or the product of agency expertise.”
BBX Capital v. FDIC, 956 F.3d 1304, 1314–15 (11th Cir. 2020) (per
curiam) (quoting Miccosukee Tribe of Indians of Fla. v. United States,
566 F.3d 1257, 1264 (11th Cir. 2009)); Motor Vehicle Mfrs. Ass’n v.
State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43 (1983). Finally, in
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25-10515 Opinion of the Court 39
Clean Air Act cases, where Congress has “delegated to an adminis-
trative agency the critical task of assessing the public health and the
power to make decisions of national import in which individuals’
lives and welfare hang in the balance,” the EPA has the “heaviest
of obligations” to explain its reasoning. Am. Lung Ass’n v. EPA, 134
F.3d 388, 392 (D.C. Cir. 1998).
While the grounds on which the EPA acted must be clearly
disclosed in and sustained by the record, see State Farm, 463 U.S. at
43, the Center bears the burden of proving that the EPA’s action
was arbitrary and capricious. That showing carries a significant
burden here because the Agency made complex scientific and tech-
nical judgments within its area of expertise. See BBX Capital, 956
F.3d at 1314–15. Under our law, the EPA’s risk assessment meth-
odology is a matter of “technical judgment lying fully within the
scope of the EPA’s agency discretion.” Miami-Dade County v. EPA,
529 F.3d 1049, 1070 (11th Cir. 2008) (per curiam). “The law does
not require selection of the single best methodology in any case,
but only a study based on a consideration of the relevant factors
and in the construction of which there has been no clear error of
judgment.” Id. at 1069 (citation modified). “Indeed, courts must
be ‘extremely deferential’ when an agency’s decision rests on the
evaluation of complex scientific data within the agency’s technical
expertise.” Id. at 1065 (quoting New York v. Reilly, 969 F.2d 1147,
1152 (D.C. Cir. 1992)). Ultimately, we may not vacate the Agency’s
decision if in fact the risk assessment methodology “was appropri-
ate for the problem it addressed.” Id. at 1070.
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40 Opinion of the Court 25-10515
The Center makes three claims: first, that the EPA evaluated
the risks of the Project using arbitrarily short exposure durations;
second, that the EPA arbitrarily failed to analyze applicable expo-
sure pathways; and, third, that in assessing exposure pathways, the
Agency accepted deficient and unverifiable sampling data. As a fi-
nal refuge, the Center argues vacatur or remand is necessary be-
cause future road projects may be approved on the results of Mo-
saic’s Project, which have been tainted by the Agency’s deficient
and arbitrary analysis. We are unpersuaded and conclude that we
are obliged to defer to the EPA’s well-supported and appropriately
tailored risk assessment methodology, and the ultimate decision it
yielded.
i.
The Center first says that the EPA’s review arbitrarily lim-
ited the temporal scope of its risk analyses for exposed individuals.
For construction workers and truck drivers transporting phos-
phogypsum, it argues that the EPA arbitrarily limited the analyzed
exposure duration to approximately one month. The Center like-
wise disagrees with the Agency’s decision to assume that a road
user would traverse the Road Project for only 250 hours in a 2,000-
hour work year, as well as its decision to limit the nearest residen-
tial exposure duration to approximately thirty years.
The Respondents counter that each of the Agency’s meth-
odological assumptions were well supported and in large part de-
rived from the EPA’s 1992 analysis and rulemaking process. More-
over, they explain that when evaluating applications for other uses
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25-10515 Opinion of the Court 41
of phosphogypsum, the Agency’s research parameters “should be
commensurate with the level of risk associated with the applica-
tion.” 1992 Rule, 57 Fed. Reg. at 23315. Thus, the Respondents
conclude that the EPA may adjust and evaluate its methodology
based on the actual estimated duration risk from a specific project,
and that it appropriately did so here. The Respondents have the
better of the argument.
Each of the Agency’s assumptions limiting the temporal du-
ration of the likely exposure for individuals was well explained and
fully aligned with the scope of Mosaic’s Road Project. As for the
construction workers and truck drivers transporting phosphogyp-
sum, the Agency’s estimated one-month exposure duration was en-
tirely consistent with Mosaic’s projected construction timeline. In
fact, consistent with Mosaic’s proposal, the construction on the test
sections of the Road -- those sections containing phosphogypsum -
- actually did conclude in less than a month. Phosphogypsum was
applied to the road beginning on October 7, 2025, and the applica-
tion of phosphogypsum was completed by November 4, 2025.
Likewise, the Agency logically explained that because the Road is
located on the Facility with no public access points, its review as-
sumed that any individual user of the Road would be a truck driver
who would have no more than 250 hours of exposure per year.
This assumption was modeled on the methodology the EPA used
in its 1992 rulemaking process to assess the risk to bikers and mo-
torcyclists who each have less protection from the road than a
truck driver. Finally, the EPA explained that its analysis of the risk
to nearby residents of approximately thirty years also was derived
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42 Opinion of the Court 25-10515
from the 1992 rulemaking process, when the EPA used the same
exposure duration to assess the risks to a hypothetical resident liv-
ing only one hundred meters from the road.
The Center still claims that the EPA acted arbitrarily and ca-
priciously by limiting the analyzed duration exposures when the
“actual exposure will likely occur over a much longer duration.”
But the Center’s argument that the EPA must assume a longer ex-
posure period for construction workers, truck drivers transporting
phosphogypsum, road users, and nearby residents is untethered
from the actual parameters of Mosaic’s Road Project. Each of the
EPA’s assumed duration exposures was fully explained and sup-
ported by the actual estimated exposure timelines for at-risk indi-
viduals.
Moreover, and as the Agency points out, even if it had as-
sumed a significantly longer exposure duration for the at-risk indi-
viduals, the calculated risks were so low that even under the Cen-
ter’s preferred exposure durations, the risks still would be negligi-
ble. Assuming a year-long construction period, the highest risk to
construction workers would be 2.4 in 100,000, and assuming a sev-
enty-year exposure for road users and nearby residents, the risks
would be 7.7 in 1,000,000 and, at most, 4.125 in 100,000,000 respec-
tively. Each of these risks fall well below even the Center’s pre-
ferred risk threshold of 9 in 100,000.
In short, the EPA thoroughly explained its decision to limit
its risk assessments to “reflect the actual exposure times that are
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25-10515 Opinion of the Court 43
expected to result from this pilot project,” and its review parame-
ters were fully supported by the record. Agency Review at 15–16.
The EPA’s methodological assumptions reflect a rational attempt
to model real-world exposure, and those methodological decisions
fell well within the EPA’s technical discretion. See Miami-Dade
County, 529 F.3d at 1070 (accepting EPA modeling assumptions
with a “rational relationship to the real world”).
ii.
The Center also argues that the EPA’s methodology was ar-
bitrary and capricious because the Agency failed to analyze the re-
claimer scenario -- where a future resident would build a home on
land where the Road once existed. The Center says this failure was
particularly “glaring” because in the 1992 Preamble, the EPA iden-
tified the reclaimer scenario as posing the highest lifetime risk of all
analyzed phosphogypsum road construction scenarios. 1992 Rule,
57 Fed. Reg. at 23310.
The EPA’s decision to forgo a separate reclaimer analysis
was neither arbitrary nor capricious. The Agency reasonably con-
cluded and thoroughly explained that it excluded the reclaimer sce-
nario in its review because the scenario did not plausibly reflect a
likely exposure pathway posed by Mosaic’s Road Project. The
EPA’s Notice of Approval explained that the Road would be con-
structed on Mosaic’s active industrial Facility, where phosphate ore
mining, phosphoric acid production, and phosphogypsum storage
already occur. Agency Review at 20–21. If the Facility were ever
redeveloped for residential use, the site as a whole -- irrespective of
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44 Opinion of the Court 25-10515
the Road -- would require the developer to undertake substantial
remediation to address the radiological risks associated with the al-
ready existing radioactive residuals. The EPA explained that the
Road Project “would not significantly change the site characteris-
tics or create additional risk” to a future reclaimer and accordingly
determined that a hypothetical scenario in which only the short
road segment was reclaimed for residential use was not a meaning-
ful or plausible basis for evaluating Mosaic’s application. Id.
We find that the Agency’s decision to forgo an analysis of
the reclaimer scenario was well supported and consonant with the
actual parameters of Mosaic’s Road Project and the surrounding
Facility. The EPA offered a thorough account of its decision, and
we can discern nothing arbitrary or capricious in the Agency’s de-
cision to focus only on those exposure scenarios that realistically
corresponded to the Road Project.
iii.
The Center next challenges the EPA’s acceptance of radium
concentration values from samples of Mosaic’s phosphogypsum
stacks that were over three years old when Mosaic revised its ap-
plication.
The Center points to the EPA’s 2005 Workbook, which it
says forbids the EPA from accepting Ra-226 samples that are more
than one year old. The Workbook explains that an application for
the distribution and use of phosphogypsum for other purposes
must include “[t]he average concentration of radium-226 in the
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25-10515 Opinion of the Court 45
phosphogypsum to be used” and that “[t]he sampling must have
been done within the past 12 months.” 2005 Workbook at 30.
The Respondents acknowledge that the Agency accepted
three-year-old data despite the Workbook’s language, but they say
that the Workbook provides only non-binding guidance, and that
the EPA’s decision to accept Mosaic’s Ra-226 sampling was well
reasoned and not arbitrary and capricious. The Agency explains
that it accepted Mosaic’s Ra-226 sampling because those measure-
ments were consistent with the EPA’s own data collected from
other phosphogypsum stacks in central Florida. Agency Review at
16–17. Even so, the EPA then based its analysis of the Road Project
on an assumed Ra-226 concentration of more than two times Mo-
saic’s reported Ra-226 samples -- assuming an Ra-226 concentration
of 35 pCi/g where Mosaic reported a concentration of only 15.1
pCi/g -- to reasonably overestimate the concentration of radium
and arrive at conservative risk estimates. Id. These decisions, it
says, were not arbitrary and capricious, but rather were well-ex-
plained and reasonable methodological assumptions.
We agree. Agency guidance, like the 2005 Workbook, does
not provide binding, operative law. See Lewis v. City of Union City,
Ga., 934 F.3d 1169, 1182 (11th Cir. 2019) (agency guidance is “not
binding”); Nat’l Mining Ass’n v. Sec’y of Lab., 589 F.3d 1368, 1371
(11th Cir. 2009) (a guidance document “leaves the agency free to
exercise its discretion to follow or not to follow that general policy
in an individual case” (quoting Ryder Truck Lines, Inc. v. United
States, 716 F.2d 1369, 1377 (11th Cir. 1983))). Thus, the Center’s
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46 Opinion of the Court 25-10515
argument that the 2005 Workbook created a “regulatory obliga-
tion” that the EPA consider sampling from the past twelve months
is not supported by the law.
The binding and applicable regulatory text in § 61.207(a) ex-
plains that prior to removing phosphogypsum from a stack for use
in an “other purpose” project, the stack’s average Ra-226 concen-
tration “shall” be measured with subsequent measurements per-
formed “each calendar year while distribution of phosphogypsum
removed from the location continues.” Thus, § 61.207 does not
require the EPA to consider Ra-226 sampling from the past twelve
months as part of the initial application.
7
The EPA was free to ac-
cept older Ra-226 sampling in reviewing Mosaic’s application, so
long as it offered a reasonable explanation.
The EPA provided a well-supported explanation of its deci-
sion. It explained that to account for the age of the samples, its
analysis assumed a radium concentration that reflects the mean
concentration of Ra-226 in phosphogypsum stacks in Florida, more
than double the average of Mosaic’s samples. Agency Review at
11, 16. Moreover, the EPA’s approval was conditioned on Mosaic
presenting additional radium sampling before construction began,
in accordance with § 61.207. Id. By requiring further sampling, the

7
The regulatory text required Mosaic to conduct sampling before the Road
Project commenced, and the EPA expressly imposed that requirement in its
Review. See Agency Review at 11 (“Should the project be approved,
§ 61.206(d) requires that sampling that conforms with § 61.207 must be per-
formed on the actual phosphogypsum used for the project, and repeated an-
nually for the duration of phosphogypsum removal from the stack.”).
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25-10515 Opinion of the Court 47
EPA left open the option to rescind or alter its decision upon the
receipt of updated Ra-226 sampling. And as it points out, the EPA
previously rescinded its conditional approval of the Fertilizer Insti-
tute’s other use application for road construction projects based on
information acquired after initial approval. See Withdrawal of Ap-
proval for Use of Phosphogypsum in Road Construction, 86 Fed.
Reg. at 35795.
We are satisfied that the Agency acted within its discretion
when it accepted the three-year-old test samples in its Review of
Mosaic’s Project.
iv.
The Center’s final argument is that vacatur or remand is nec-
essary because the Road Project generally will serve as an “inter-
mediate step between laboratory testing and full-scale” approval of
phosphogypsum in road construction, and these potential future
regulatory amendments will be tainted by the EPA’s arbitrary and
capricious assessment of the Project.
This sweeping argument fails. The EPA’s technical risk as-
sessment methodology was thoroughly explained and well sup-
ported. And to the extent the Center argues that the EPA’s deci-
sion improperly underlies a forthcoming regulatory shift, the argu-
ment is unsupported by the record. The EPA’s Review expressly
and appropriately limited the scope of its decision to Mosaic’s Road
Project, explicitly emphasizing that any future request to construct
phosphogypsum roads anywhere else would require a separate ap-
plication, a separate risk assessment, and separate approval.
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48 Opinion of the Court 25-10515
Agency Review at 3, 21. Because the approval of Mosaic’s Road
Project does not directly bear on potential future projects, which
will be subject to separate Agency action and independent analysis,
we can discern no basis to vacate or remand the Agency’s decision.
* * *
In short, the EPA’s risk assessment articulated a coherent ra-
tionale for its approach. The Agency explained its methodology,
identified the specific exposure pathways it evaluated, described its
reasonable assumptions, and concluded that the Road Project fell
within acceptable risk parameters. The Center may disagree with
the EPA’s methodological choices and its ultimate conclusion, but
disagreement about technical methodology does not render an
agency’s reasoned determination arbitrary and capricious.
PETITION DENIED.

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