Daikin Applied Americas Inc. v. EPA

United States Court of Appeals

FOR THE DISTRICT OF COLUMBIA CIRCUIT

Argued April 28, 2022 Decided July 8, 2022
No. 20-1479
DAIKIN APPLIED AMERICAS INC. AND SUPER RADIATOR COILS
LP,
PETITIONERS

Vv.

ENVIRONMENTAL PROTECTION AGENCY,
RESPONDENT

On Petition for Review of a Final Rule
of the Environmental Protection Agency

Charles B. Rogers argued the cause for petitioners. With
him on the briefs were M. Annie Santos, Harvey M. Sheldon,
and Nancy Q. Burke.

Martin F. McDermott, Attorney, U.S. Department of
Justice, argued the cause for respondent. With him on the brief
were Todd Kim, Assistant Attorney General, and Erik Swenson,
Attorney, U.S. Environmental Protection Agency.

Before: SRINIVASAN, Chief Judge, HENDERSON and
PILLARD, Circuit Judges.

Opinion for the Court filed by Circuit Judge HENDERSON.
2

KAREN LECRAFT HENDERSON, Circuit Judge: Pursuant to
the Comprehensive Environmental Response, Compensation,
and Liability Act of 1980 (CERCLA), 42 U.S.C. §$§ 9601-
9675, the Environmental Protection Agency (EPA) maintains
the National Priorities List (NPL), a list of hazardous waste
sites that are high priorities for long-term federal remedial
evaluation and response. See id. § 9605(a)(8)(B); 40 C.F.R.
§ 300.5. To determine whether to list a given site, the EPA
primarily uses the Hazard Ranking System (HRS), a set of
comprehensive scoring points for evaluating the potential
damage from hazardous waste releases. See 40 C.F.R. pt. 300,
App. A (HRS). If a release exceeds a certain threshold score,
the EPA is authorized to include the site on the NPL, beginning
a process that may include Superfund-financed remedial
action. Id. § 300.425(c)(1).

After performing an HRS analysis of a site of groundwater
contamination southwest of Minneapolis, Minnesota, the EPA
determined that the HRS site score exceeded the required
threshold for NPL listing. In its analysis, the EPA found
observed releases of the same contaminants across a series of
overlapping underground aquifers, the deepest of which is a
drinking water aquifer used by residents in two cities. Two
parts of the HRS analysis are particularly relevant to the
petitioners’ claims. First, because several possible sources of
contamination existed, the EPA scored the site as a “ground
water plume with no identified source,” enabling the EPA to
treat the plume, rather than a particular facility, as the source.
HRS § 1.1. Second, the EPA concluded that adequate evidence
of “aquifer interconnections” existed, allowing it to evaluate
the aquifers as one unit. See id. §§ 3.0.1.2, 3.0.1.2.1. After
considering and responding to comments on the HRS analysis,
the EPA listed the site as the Highway 100 and County Road 3
Groundwater Plume (Site). National Priorities List, 85 Fed.
3

Reg. 54,931, 51,934 (Sept. 3, 2020) (Site Listing Rule),
reprinted in Joint Appendix (J.A.) 1-6.

Petitioners Daikin Applied Americas Inc. and Super
Radiator Coils LP, former owners of a metal fabricating facility
that is a possible source of the contaminants, challenge the
listing as arbitrary and capricious and unsupported by
substantial evidence. The petitioners contend that the EPA
arbitrarily ignored other possible sources of contamination in
determining the site and that the EPA both ignored evidence
disproving, and failed to provide adequate evidence of, aquifer
interconnectivity. Because the EPA was not required to
attribute the contamination to a specific source and adequately
supported aquifer interconnectivity, we reject the petitioners’
claims and deny the petition for review. They also move to
supplement the record with evidence the EPA allegedly failed
to consider, which motion we deny.

I. BACKGROUND
A. STATUTORY AND REGULATORY BACKGROUND
1. CERCLA and the National Priorities List

Enacted by the Congress to address the “growing problem
of inactive hazardous waste sites throughout the United
States,” Eagle-Picher Indus., Inc. v. EPA (Eagle-Picher IT),
759 F.2d 922, 925 (D.C. Cir. 1985), CERCLA authorizes the
EPA “to establish and revise annually a National Priorities List
of known hazardous waste sites considered high priorities for
environmental remediation,” Genuine Parts Co. v. EPA, 890
F.3d 304, 308 (D.C. Cir. 2018) (citing 42 U.S.C.
§ 9605(a)(8)(A)). Once a site is listed on the NPL, the EPA
4

may use Superfund! moneys to fund remedial? actions. 40
C.F.R. § 300.425(b)(1).

“The EPA’s listing a site on the NPL, however, does not
necessarily mean it will order remedial action at that site;
rather, it guarantees only more detailed study.” Carus Chem.
Co. v. EPA, 395 F.3d 434, 437 (D.C. Cir. 2005) (internal
citations omitted). Listing can “have significant adverse
consequences for the owner of a listed property,” id.
(consequences may include damage to business reputation or

' CERCLA is “also known as the Superfund statute,” Add.
Richfield Co. v. Christian, 140 S. Ct. 1335, 1345 (2020), because “it
establishes a fund, the ‘Superfund’, to finance EPA remedial action
on contaminated sites,” Apache Powder Co. v. United States, 968
F.2d 66, 68 (D.C. Cir. 1992) (citing 42 U.S.C. § 9611). Initially
financed through excise taxes on the chemical and petroleum
industries, the Superfund is now financed by, inter alia, transfers
from the U.S. Treasury’s General Fund and cost recovery actions
against potentially responsible parties. Anthony A. Cilluffo and
David M. Bearden, Cong. Rsch. Serv., IF11982, Superfund Tax
Legislation in the 117th Congress 1 (Nov. 29, 2021). Because
inclusion on the NPL establishes eligibility for Superfund-financed
remedial action, 40 C.F.R. § 300.425(b)(1), NPL sites are
“commonly known as Superfund sites.” Atl. Richfield, 140 S. Ct. at
1346.

2 CERCLA provides for removal actions and remedial actions.
See 42 U.S.C. §§ 9601(23), 9601024). Removal actions are generally
interim measures involving the “cleanup or removal of released
hazardous substances from the environment.” See id. § 9601(23).
“Remedial action” is a “permanent remedy” and is employed “‘in the
event of a release or threatened release of a hazardous substance into
the environment, to prevent or minimize the release of hazardous
substances so that they do not migrate to cause substantial danger to
present or future public health or welfare or the environment.” Id.
§ 9601(24).
5

lower property values), and it can take decades for a site to be
removed from the NPL. Indeed, it has been almost forty years
since the EPA first listed the Reilly Tar & Chemical Site
(Reilly Tar Site), an NPL site largely northwest of the plume at
issue. See Amendment to National Oil and Hazardous
Substance Contingency Plan; National Priorities List, 48 Fed.
Reg. 40,658, 40,670 (Sept. 8, 1983). In essence, “the NPL is
simply the first step in a process—nothing more, nothing less.”
Eagle-Picher II, 759 F.2d at 932. Listing serves as “a tool for
identifying quickly and inexpensively those sites meriting
closer environmental scrutiny,” Wash. State Dep’t of Transp.
v. EPA, 917 F.2d 1309, 1310 (D.C. Cir. 1990), and “does not
determine any party’s liability for the cost of cleanup at the
site,” Kent County v. EPA, 963 F.2d 391, 394 (D.C. Cir. 1992).

2. The Hazard Ranking System

CERCLA required the EPA to develop “criteria for
determining priorities among releases or threatened releases [of
hazardous substances] throughout the United States for the
purpose of taking remedial action.” 42 U.S.C. § 9605(a)(8)(A).
Pursuant to that mandate, the EPA promulgated the HRS
regulation to screen the sites that make the NPL. See 40 C.F.R.
§ 300.425(c)(1); see also HRS § 1.0 (“The [HRS] is the
principal mechanism the [EPA] uses to place sites on the
[NPL].”). The HRS lays out a “comprehensive methodology
and mathematical model” that “quantif[ies] the environmental
risks a site poses.” Carus Chem., 395 F.3d at 437 (quoting in
second quotation Tex Tin Corp. v. EPA, 992 F.2d 353, 353
(D.C. Cir. 1993)).

Because the HRS scoring procedures are central to the
petitioners’ claims, it is necessary to march through important
6

aspects of the HRS analysis regarding a groundwater®
contamination site. The first is the relevance of classifying the
site as a groundwater plume with no identified source.

a. Observed Release, Site and Source

According to the HRS, a “[s]ite” is an “[a]rea[] where a
hazardous substance has been deposited, stored, disposed, or
placed, or has otherwise come to be located. Such areas may
include multiple sources and may include the area between
sources.” HRS § 1.1. The scope of the site may expand or
contract after listing if additional study reveals more (or less)
expansive contamination, see Wash. State Dep’t of Transp.,
917 F.2d at 1310 n.1, and as the EPA explained in the listing at
issue, “[t]he NPL does not describe releases in precise
geographical terms. . . . Indeed, the precise nature and extent of
the site are typically not known at the time of listing.” Site
Listing Rule, 85 Fed. Reg. at 54,932.

For each site, the HRS allows the EPA to assess a site’s
“relative degree of risk to human health and the environment,”
42 U.S.C. § 9605(c)(1), by examining possible migration
pathways of hazardous substances, see HRS § 2.1 (listing air,
soil, surface water and groundwater as pathways). The EPA
calculates a numerical score for each potentially affected
pathway based on three factors: the (1) “likelihood of release,”
meaning the risk that a hazardous substance “has been or will
be released,” id. § 2.3; (2) “waste characteristics,” including

3 “Ground water’ and ‘groundwater’ are synonymous; the

spelling is...due to “ground water’ being codified as part of the
HRS, while ‘groundwater’ is the modern spelling.” HRS Revised
Documentation Record, Highway 100 and County Road 3
Groundwater Plume, at 1 n.1 (Sept. 2020) (Revised Documentation
Record), reprinted in J.A. 296-356.
7

the substance’s mobility and toxicity, id. § 2.4; and (3)
“targets” (e.g., humans or environments) of the contamination
associated with that pathway, id. § 2.5. Based on the evidence
for each pathway, the EPA then “plug[s] the resulting
individual pathway scores into a formula to obtain the site
score.” US Magnesium, LLC v. EPA, 630 F.3d 188, 189-90
(D.C. Cir. 2011). The site score ranges from 0 to 100, HRS
§ 2.1.1, and a site is eligible for NPL listing if the score is over
28.50, National Priorities List, Final Rule No. 53, 77 Fed. Reg.
15,276, 15,278 (Mar. 15, 2012).

When analyzing a groundwater pathway, the EPA assesses
various factors for each aquifer. See HRS § 3.0 (Table 3-1).
The likelihood of release factor for an individual aquifer” “is
assigned the maximum value... whenever the criteria for an
observed release are met.” Id. § 2.3 (emphasis added). The
EPA assigns an observed release to an aquifer “by
demonstrating that the site has released a hazardous substance
to the aquifer,” based on either “[d]irect observation” or
“Tc]hemical analysis.” /d. § 3.1.1. The EPA shows an observed
release through chemical analysis by comparing groundwater
samples. If a sample has a hazardous substance concentration
that is “significantly above” that of a background sample, the
EPA has established an observed release. See id.

Similar to a “site,” a “[s]ource” is “[a]ny area where a
hazardous substance has been deposited, stored, disposed, or
placed, plus those soils that have become contaminated from
migration of a hazardous substance.” /d. § 1.1. With one
exception, a source does not “include those volumes

4 An aquifer is a layer “of rock or sediment that is saturated and
sufficiently permeable to yield economically significant quantities of
water to wells or springs.” EPA, HRS Guidance Manual 116 (1992)
(ARS Manual), reprinted in J.A. 546-92.
8

of... ground water...that have become contaminated by
migration.” /d. The exception is crucial to this case: “In the case
of ...a ground water plume with no identified source . . . , the
plume ...may be considered a source.” Jd. According to
longstanding EPA guidance, “a contaminated ground water
plume can only be evaluated as a source for HRS scoring
purposes when the original source of hazardous substances
contributing to the plume cannot be reasonably identified.”
EPA, Publication 9320.8-O1FS, Evaluating Ground Water
Plumes Under the Hazard Ranking System 1 (1998).

Connecting a “source” to an observed release that was
established using chemical analysis, the EPA typically must
show attribution—that the “significant increase” of
contaminants comes from the site—to establish an observed
release through chemical analysis. HRS § 3.1.1. But “when the
source itself consists of a ground water plume with no
identified source, no separate attribution is required.” /d.
Accordingly, if the EPA cannot reasonably identify an original
source of contamination, the observed releases—not a specific
source or boundaries—define the site.

b, Aquifer Interconnections

The second relevant aspect of the HRS analysis is aquifer
interconnections. Jd. § 3.0.1.2.1. An individual aquifer is
ordinarily scored by treating it as separate from surrounding
aquifers. See id. The EPA may, however, “[c]ombine multiple
aquifers into a single hydrologic unit for scoring purposes if
aquifer interconnections can be established for these aquifers.”
Id. § 3.0.1.2. To assess interconnection, the HRS directs as
follows:

Evaluate whether aquifer interconnections
occur within 2 miles of the sources at the site. If
they occur within this 2-mile distance, combine
9

the aquifers having interconnections in scoring
the site. In addition, if observed ground water
contamination attributable to the sources at the
site extends beyond 2 miles from the sources,
use any locations within the limits of this
observed ground water contamination in
evaluating aquifer interconnections.

Id. § 3.0.1.2.1. The EPA’s guidance manual for HRS scoring
provides examples of evidence that usually establish
interconnectivity. See generally EPA, HRS Guidance Manual
(1992) (HRS Manual), reprinted in J.A. 546-92. Relevant
examples include: well logs> showing there is “no continuous,
significantly lower hydraulic conductivity layer” separating the
aquifers; pump tests showing that withdrawing water from one
aquifer affects water levels in another; and observed
contamination across an aquifer boundary separating the
aquifers within the two-mile radius. Jd. at 127. Importantly, for
the last example, “the mechanism of vertical migration does not
have to be defined, and the [contaminants] do not have to be
attributable to the site being evaluated.” Hazard Ranking
System, 55 Fed. Reg. 51,532, 51,553 (Dec. 14, 1990).

After the EPA has adequate evidence of aquifer
interconnections, it then must consider whether there are
aquifer discontinuities. “An aquifer discontinuity occurs for
scoring purposes only when a geologic, topographic, or other
structure or feature entirely transects an aquifer within the

> A well log is a “record of geologic materials with depth based
on data obtained beneath a point on the land surface and
representative of types, depths, and thicknesses of materials beneath
that point. The data may represent visual observations,
physical/chemical characterizations, and/or geophysical properties.”
ARS Manual, supra, at 117.
10

4-mile target distance limit, thereby creating a continuous
boundary to ground water flow within this limit.” HRS
§ 3.0.1.2.2 (emphasis added). A boundary preventing the
migration of groundwater is also known as an “aquitard” or
“confining layer.” And the “target distance limit” for a
groundwater plume with no identified source is measured from
the center of the plume. Jd. § 3.0.1.1. The HRS directs,
however, that “if hazardous substances have migrated across
an apparent discontinuity within the 4-mile target distance
limit, do not consider this to be a discontinuity in scoring the
site.” Id. § 3.0.1.2.2.

In sum, “[a]quifer interconnections cannot be assumed, but
must be supported by evidence.” HRS Manual, supra, at 135.
And if the EPA shows observed releases of hazardous
substances on both sides of an apparent aquifer boundary,
sufficient evidence for aquifer interconnection exists
notwithstanding the boundary is an “apparent discontinuity,”
HRS § 3.0.1.2.2, or the lack of an established migration
mechanism between the aquifers, Hazard Ranking System, 55
Fed. Reg. at 51,553.

B. FACTUAL AND PROCEDURAL BACKGROUND
1. History of the Site

The Site covers two Minnesota cities, St. Louis Park and
Edina, both cities with a history of groundwater contamination.
In 1983, the EPA added the previously mentioned Reilly Tar
Site in St. Louis Park to the NPL because it was a documented
source of a hazardous chemical, namely, polynuclear aromatic
hydrocarbon (PAH). J.A. 94. Through well samples, the
Minnesota Department of Health later detected other hazardous
chemicals, chlorinated volatile organic compounds (CVOCs),
in Edina’s groundwater as early as 1993 and St. Louis Park’s
groundwater as early as 1994. See HRS Revised
11

Documentation Record, Highway 100 and County Road 3
Groundwater Plume, at 13-14 (Sept. 2020) (Revised
Documentation Record), reprinted in J.A. 296-356. The
relevant CVOCs are 1,1-dichloroethene (DCE); cis-1,2-DCE;
trans-1,2-DCE; trichloroethene (TCE); and vinyl chloride—all
of which are breakdown products of tetrachloroethene (PCE),
a chemical used in certain industrial and cleaning processes.
Revised Documentation Record at 14, 33. The Minnesota
Pollution Control Agency (MPCA) became involved in 2004
when Edina requested assistance to determine the source of
CVOCs in one of its municipal drinking water wells, E7. Jd. As
the investigation expanded farther north, CVOCs were detected
in four aquifers: the Quaternary Drift Aquifer (Drift Aquifer),
which is generally 0 to 90 feet below ground surface (bgs); the
Platteville-Glenwood Aquifer, which is generally 90 to 122
feet bgs; the St. Peter Aquifer, which is generally 135 to 290
feet bgs; and the Prairie du Chien-Jordan Aquifer, which is
generally 290 to 417 feet bgs. Revised Documentation Record
at 15; see also J.A. 361 (cross-section and geological
descriptions), 368-69 (cross-sectional maps).

In 2007, the MPCA sought the EPA’s assistance in testing
soil in the area for CVOCs. Revised Documentation Record at
15. In 2016, the MPCA prepared a preliminary assessment of
the Site. Jd. Subsequently, under a cooperation agreement with
the EPA, the MPCA conducted a site inspection, which
included extensive data from groundwater samples collected
from monitoring and municipal wells intersecting the four
aquifers at varying depths. Jd. at 15, 18. The data showed
CVOC contamination in all of the aquifers. /d. at 15. The
inspection focused on evaluating contamination of the Prairie
du Chien-Jordan Aquifer because Edina and St. Louis Park
12

municipal drinking water wells draw from that aquifer.® Jd. at
16.

The site inspection recommended further investigation to
establish whether a contaminant pathway interconnected the
aquifers. Id. at 18. Accordingly, the MPCA conducted an
Expanded Site Inspection Report (ESI), which included a
hydrogeologic investigation. /d.; see generally J.A. 357-97
(relevant portions of the ESI). The ESI concluded that the four
aquifers were “laterally continuous and... hydraulically
interconnected between St. Louis Park and Edina” based on
“aquifer pump tests that showed drawdown in the test wells,
and analytical results that document[ed] the migration of
[CVOCs] from the Quaternary Drift, Platteville-Glenwood, St.
Peter, and Prairie du Chien-Jordan aquifers.” Revised
Documentation Record at 18.

2. NPL Listing

Following the ESI, the EPA issued a proposed rule listing
the Site as a groundwater plume contaminating multiple
aquifers. See National Priorities List, 84 Fed. Reg. 60,357,
60,358 (Nov. 8, 2019), reprinted in J.A. 7-13. To explain its
HRS analysis, the EPA provided a lengthy HRS
Documentation Record, in which the EPA defined the
groundwater plume “by documented observed releases [of
CVOCs] in groundwater monitoring and municipal water wells
in Edina and St. Louis Park.” Revised Documentation Record

© Due to treatment systems set up by city and state authorities
after discovering the CVOCs, “drinking water provided by both the
cities of Edina and St. Louis Park currently [is] in compliance
with...the Safe Drnking Water Act.” Narrative Summary,
Highway 100 and County Road 3 Groundwater Plume (Nov. 2019),
reprinted in J.A. 14.
13

at 13. The wells with observed releases thus defined the
amorphous boundaries of the plume.’ The EPA explained that
the observed releases “cannot reasonably be attributed to one
or more specific sources” because of “the comingled [sic.]
nature of the releases” from multiple sources, “including dry
cleaners, print shops, metals fabricators,...heat treating
operations, [and] other commercial and industrial facilities.”
Id. at 19. The EPA then scored the Site as a “groundwater
plume with no identified source.” Jd. at 20.

The EPA evaluated the Site using the standard three
factors. See id. at 3 (likelihood of release, waste characteristics
and targets). For the likelihood of release factor, the EPA relied
on groundwater samples from release and background wells in
all four aquifers to establish observed releases of CVOCs
through chemical analysis. See id. at 33-54. The EPA then
concluded that the aquifers were interconnected based on (1)
pump tests of wells showing “no significant difference in
hydraulic conductivity” across all aquifers, (2) well log data
from “municipal wells indicat[ing] the same stratigraphic
units” and (3) “groundwater contamination ...in St. Louis
Park and Edina municipal wells, as well as monitoring wells
that withdraw water from” all the aquifers. /d. at 55. Given the
interconnectivity and observed, not potential, releases, the
likelihood of release factor for the interconnected aquifers
received the maximum score. See id. After calculating the
scores for waste characteristics and targets, the EPA calculated
a site score of 50, id. at 2-3, well above the 28.5 threshold for
NPL designation.

The petitioners submitted extensive comments on the HRS
analysis, primarily challenging aquifer interconnectivity. See

’ For a map of the relevant wells, see attached Appendix A,
which can be found at Revised Documentation Record at 6.
14

generally J.A. 17—295. First, they took particular issue with the
EPA’s purported use of a “natural migration pathway” between
the Drift Aquifer and the Prairie du Chien-Jordan Aquifer. J.A.
24. Drawing on the placement of the wells used to define the
plume, they argued that the EPA’s asserted pathway was
scientifically impossible because it required assuming that
CVOCs migrated upgradient—against the general, east-
southeast flow of the groundwater. J.A. 266-67. Next, they
contended that the EPA omitted evidence of a confining layer,
the St. Peter confining layer, that would prevent permeation to
the Prairie du Chien-Jordan Aquifer. J.A. 266-67, 269. In a
final interconnectivity challenge, they argued that the pump
tests were inadequate because they covered only the Prairie du
Chien-Jordan Aquifer. J.A. 268-69.°

The EPA responded at length to the petitioners’ comments.
See Support Document for the Revised National Priorities List
Final Rule, Highway 100 and County Road 3 Groundwater
Plume (Sept. 2020) (Support Document), reprinted in J.A.
398-545. Acknowledging the interconnectivity challenges and
standing by its interconnectivity findings, the EPA “identified

* The petitioners also made two other challenges of note. Again
assuming that the EPA had to show attribution through a “plausible
migration pathway,” J.A. 266, and maintaining that the EPA had
identified a “source area,” J.A. 265, they asserted that the EPA erred
by ignoring possible migration pathways and sources of the CVOCs
in the Prairie du Chien-Jordan Aquifer, including the Reilly Tar Site
and multi-aquifer wells, J.A. 270, 275. As the name suggests, multi-
aquifer wells are wells that go deep enough to intersect multiple
aquifers, thus providing possible paths for contaminants to migrate
between aquifers. See Support Document for the Revised National
Priorities List Final Rule, Highway 100 and County Road 3
Groundwater Plume, at 52 (Sept. 2020) (Support Document). In
addition, they argued that the EPA improperly excluded certain
documents from the administrative record. J.A. 279-80.
15

multiple lines of evidence documenting aquifer
interconnections.” Jd. at 48. Responding to the natural
migration pathway argument, the EPA noted that “the
mechanism of vertical migration does not have to be defined”
because it had documented observed releases in both the
shallower aquifers and the Prairie du Chien-Jordan Aquifer. Jd.
at 48, 50. It explained that it did “not identify specific migration
paths through the aquifer layers as [the petitioners] suggest[;]
rather,...the EPA evaluated each aquifer layer and all
plausible mechanisms and evidence (natural migration in some
aquifers, joints, fractures, solution channels, multi-aquifer
wells, and observed contamination migration) to determine that
the aquifers are interconnected for HRS purposes.” /d. at 50.

Next, the EPA noted that, although it had inadvertently
excluded a portion of a confining layer from one of the figures
demonstrating interconnectivity, there were no continuously
present confining layers because the St. Peter confining layer
“is locally absent due to erosion.” /d. at 45. It also noted that
the St. Peter confining layer is “[a]bsent in well HS-1 about
1.55 miles east of municipal well SLP4.” Jd. at 46.
Accordingly, the EPA asserted there were no aquifer
discontinuities at the site. Jd. at 49. It responded to the pump
test challenge by disclaiming reliance on the pump test data to
show interconnectivity. /d. at 51.

In response to the petitioners’ arguments involving
allegedly ignored possible sources, the EPA iterated that
consistent with the classification of the Site as a groundwater
plume with no identified source, it need not and did not
“attribute the release to a specific source or sources.” /d. at 83.
It then affirmed its definition of the Site as consistent with the
HRS procedures, which permit the plume to be defined by
observed releases from wells. /d. at 88. It emphasized that
16

[t]he HRS is a screening model that uses limited
resources to determine whether a site should be
placed on the NPL for possible Superfund
response. AS necessary, additional
investigations to determine definitive sources at
a particular site are performed at the [Remedial
Investigation/Feasibility Study] stage of the
Superfund process at which time site conditions
and hazards are characterized more
comprehensively.

Id. at 87. The EPA also iterated that “the fact that [it] initially
identifies and lists the [site] based on areview of contamination
at a certain location—in this case a contaminated groundwater
plume with no identified source—does not necessarily mean
that the site boundaries are limited to that location.” /d. at 11.
In response to the petitioners’ contention that it had ignored
multi-aquifer wells as a contributor to contaminant migration,
the EPA pointed out that multi-aquifer wells do “influence
... contaminant migration” and therefore “[t]he presence of
multi-aquifer wells at this Site only provides additional
documentation of hydrological interconnections between the
aquifer layers at the Site.” Jd. at 52.

Replying to the petitioners’ claim that it had improperly
excluded from the administrative record adverse evidence
provided by them, the EPA acknowledged that it “must include
all pertinent information in the administrative record, both
favorable and unfavorable to [its] final decision.” /d. at 14. It
then stated it had “included all the relevant information it
considered to support the HRS score in this case and all such
information has been placed in the listing docket that makes up
the administrative record.” /d. It also noted that the petitioners
“ha[d] not explained how the submitted documents impact the
HRS score.” Id.
17

The EPA issued the final rule adding the Site to the NPL
on September 3, 2020. Site Listing Rule, 85 Fed. Reg. at
54,933. The petitioners filed a timely petition for review. On
May 4, 2021, they filed a Motion for the Court to Review and
Consider Extra-Record Evidence.

Under CERCLA, we have jurisdiction to review the
petition. See 42 U.S.C. § 9613(a).

Il. ANALYSIS

Echoing their comments to the agency, the petitioners
mount two challenges to the NPL listing. We begin with their
claim that the EPA arbitrarily and capriciously defined the site
by ignoring possible sources of contamination. We then
address their substantial-evidence and arbitrary-and-capricious
aquifer interconnectivity challenges. Because the EPA
properly followed the HRS scoring procedures, supported its
conclusions with substantial evidence and adequately
addressed the petitioners’ comments, we conclude that their
claims are without merit. Finally, we deny their motion to
supplement the record with extra-record evidence.

A. STANDARD OF REVIEW

We review the EPA’s NPL listing decisions under the
Administrative Procedure Act’s (APA) arbitrary and
capricious and substantial evidence standards. See Genuine
Parts, 890 F.3d at 311 (citations omitted). Given “the ‘highly
technical issues involved’ [in an NPL listing] and because the
NPL serves merely as a ‘rough list of priorities, assembled
quickly and inexpensively,’” we afford the EPA “significant
deference” in NPL listing decisions. Carus Chem., 395 F.3d at
441 (quoting Bradley Mining Co. v. EPA, 972 F.2d 1356, 1359
(D.C. Cir. 1992)).
18

If an agency has “entirely failed to consider an important
aspect of the problem [or] offered an explanation for its
decision that runs counter to the evidence before the agency,”
Motor Vehicle Mfrs. Ass’n of U.S., Inc. v. State Farm Mut.
Auto. Ins. Co., 463 U.S. 29, 43 (1983), we will vacate its
decision as arbitrary and capricious. We will, however,
“uphold a decision of less than ideal clarity if the agency’s path
may reasonably be discerned.” Bowman Transp., Inc. v.
Arkansas-Best Freight Sys., Inc., 419 U.S. 281, 286 (1974).
Substantial evidence review requires that we “consider the
whole record upon which an agency’s factual findings are
based,” Genuine Parts, 890 F.3d at 312, to determine if the
agency “ignore[d] evidence contradicting its position,” Butte
County v. Hogen, 613 F.3d 190, 194 (D.C. Cir. 2010), or
“minimize[d] such evidence without adequate explanation,”
Genuine Parts, 890 F.3d at 312 (citation omitted). “[I]n their
application to the requirement of factual support[,] the
substantial evidence test and the arbitrary or capricious test are
one and the same.” Butte County, 613 F.3d at 194 (citation
omitted).

B. SITE DEFINITION CHALLENGES

We first address the petitioners’ claim that the “EPA
arbitrarily included the Drift Aquifer Area in the Site definition
while ignoring relevant evidence of other known areas of
contamination.” Pet’rs Br. 59. As a preliminary matter, the
petitioners coin the term “Drift Aquifer Area” and employ it to
refer to a triangular area surrounding the three release wells in
the Drift Aquifer.’ See id. at 6-8. They contend that the EPA

’ For a depiction of the general area of the petitioners’ Drift
Aquifer Area, see Appendix B, which is available at Petitioners
Brief 8. This map also includes the layout of the release wells but
19

did not “holistically evaluate[]” the Site and should “eliminate
the arbitrarily exclusive Drift Aquifer Area from the Site
definition.” /d. at 12. The Site definition is arbitrarily
exclusive, they argue, because even after determining the
aquifers were interconnected, the EPA “failed to include
additional, contaminated Drift [Aquifer] wells or locations in
the Site definition.” Jd. at 60. They point out that their
comments directed the EPA toward a number of possible
sources of the contaminants—including the Reilly Tar Site,
other industrial facilities and multi-aquifer wells—but that the
EPA nevertheless arbitrarily excluded these other
contaminated areas from the Drift Aquifer Area. See id. at 59-
63.

The petitioners are mistaken for three reasons. First, and
most fundamentally, the EPA did not arbitrarily exclude any
sources because it properly defined the Site as a groundwater
plume with no identified source. See Revised Documentation
Record at 20; see also HRS 8§ 1.1, 3.1.1. Pursuant to the HRS
procedures, see supra, at 6-8, the EPA defined the site by using
chemical analysis to show that observed releases had occurred
across the four aquifers. Revised Documentation Record at 33—
53. Then, after considering “several likely sources and/or
potential contributors,” the EPA reasonably determined that
because of the “comingled [sic.] nature of the releases” likely
resulting from one or more sources, it could not attribute the
observed releases to a specific source.!° Id. at 19; see also id.
at 54-55; Support Document at 26, 84.

was created for this litigation and may not depict precise boundaries
of the groundwater plume.

10 As the petitioners note, the HRS Manual states that “efforts
should be undertaken to identify the original source(s) of
contamination” prior to scoring a site as a groundwater plume
20

Second, to define a site under the HRS procedures, the
EPA need not “evaluate all known releases,” Pet’rs Br. 12, or
“include additional, contaminated Drift [Aquifer] wells,” id. at
60. The petitioners point to no HRS requirement that the EPA
must sample every well with a potential release. Such a
requirement would be inconsistent with the “narrowly focused”
purpose of the NPL and the HRS: “identify[ing], quickly and
inexpensively, sites that may warrant further action under
CERCLA.” Eagle-Picher Indus., Inc. v. EPA (Eagle-Picher 1),
759 F.2d 905, 911 (D.C. Cir. 1985). Listing does not set the
Site boundaries in stone. As more information becomes
available in the remedial investigation/feasibility study stage,
the EPA may expand (or contract) the Site. See Revised
Documentation Record at 1; Wash. State Dep ’t of Transp., 917
F.2d at 1310 n.1.

Third, the EPA did not arbitrarily ignore the petitioners’
comments on other plausible sources of contamination,
including the Reilly Tar Site and multi-aquifer wells.'! Indeed,
the EPA acknowledged their comments regarding the
possibility that other sources may contribute to contamination,

without an identifiable source. HRS Manual, supra, at 46. But those
efforts need only be “equivalent to those of an expanded [site
inspection].” Jd. The EPA met that standard by relying on the
MPCA’s Expanded Site Inspection Report, which documented the
latter’s efforts to identify a single source of the groundwater
contamination. See Revised Documentation Record at 13-14.

‘| The petitioners assert that other possible sources are: a
previous Schloff Chemical release of PCE, a former Flame Metals
facility, a former Control Data Corporation site, a Lindberg Heat
Treating Facility, a former Reynolds Welding site, Pet’rs Br. 60-62;
see also J.A. 274—76, and “the area near the intersection of Highway
7 and Louisiana Avenue,” Pet’rs Br. 42 (quoting J.A. 387). See also
id. at 66 (map of petitioners’ asserted possible sources).
21

Support Document at 27, 31-33, and noted that “additional
characterization is necessary to delineate the plume and
attribute the release to a facility,” id. at 31. “Moreover,” the
EPA explained, CVOC contamination associated with other
facilities like the Reilly Tar Site “supports the evaluation of the
site as a contaminated groundwater plume without an identified
source because the significant increase in the plume could not
be attributed to a specific source.” Id. (emphasis added). The
EPA also acknowledged and even agreed that contamination
can migrate through multi-aquifer wells.'? Jd. at 51-52.

C. INTERCONNECTIVITY CHALLENGES

Largely renewing arguments included in their comments,
the petitioners argue that the aquifer interconnections in the
HRS analysis were not supported by substantial evidence and
that the EPA acted arbitrarily and capriciously by concluding
that the aquifers were interconnected. Pet’rs Br. 17-48. Their
arguments founder because the EPA properly established

To support their multi-aquifer-well pathway argument, the
petitioners point to radioisotope studies showing “that the
groundwater in the contaminated portion of the Prairie du Chien-
Jordan Aquifer is ‘newer’ than the contaminated groundwater in the
St. Peter Aquifer above it,” Pet’rs Br. 46, and to evidence that the St.
Peter Aquifer is “cleane[r]” than the Prairie du Chien-Jordan
Aquifer, id. at 43-44. They claim that these data suggest a
contaminated groundwater is migrating not through descending
aquifers but through multi-aquifer wells. fd. at 44, 46-47. But the
EPA reasonably established interconnectivity without relying on any
specific migration mechanism. See Hazard Ranking System, 55 Fed.
Reg. at 51,553. Moreover, the EPA recognizes that multi-aquifer
wells may be contributing to contaminant migration, see Revised
Documentation Record at 14, 31; Support Document at 52, and that
subsequent investigations may reveal more information regarding
specific contaminant sources, see Support Document at 41.
22

aquifer interconnectivity by showing observed contaminant
migration through observed releases in each of the aquifers. See
Support Document at 48; HRS Manual, supra, at 127.

As already described, the HRS regulations and
accompanying guidance provide the structure for establishing
aquifer interconnections. See supra, at 8-10. And one method
to establish interconnectivity is by observed contamination
across aquifers. See Hazard Ranking System, 55 Fed. Reg. at
51,553; HRS Manual, supra, at 127, 131. Here, the EPA
provided copious documentation of observed releases across
all four aquifers through chemical analysis. See Revised
Documentation Record at 33-53. Relying on the HRS
procedures and the observed releases within two miles of the
Site, the EPA reasonably concluded that “contamination has
migrated through the aquifer layers into the Prairie du Chien
[A]quifer.” Support Document at 48. The EPA then considered
whether there were any qualifying aquifer discontinuities and
concluded that although confining layers existed in portions of
the Platteville-Glenwood formation and the St. Peter
formation, these layers were “documented to either not be
present at locations in the [target distance limit] or are
documented to allow contamination to migrate through” the
formations. /d. at 49 (emphasis added). Because the “apparent
discontinuit[ies]” allowed hazardous substances to migrate, the
EPA properly found that there were no _ qualifying
discontinuities, HRS § 3.0.1.2.2, and reasonably concluded
that the aquifers were interconnected based on observed
contamination, see id. § 3.0.1.2.1.

Challenging the EPA’s use of the observed-contamination
method of proving interconnectivity, the petitioners argue that
the EPA did not adequately establish observed releases. Pet’rs
Br. 35-39. In particular, they contend that the EPA’s chemical
analysis was flawed. 7d. at 35-36. Recall that showing an
23

observed release by chemical analysis requires comparing a
sample from a background well to a sample from a release well
and determining whether the concentration in the release well
is “significantly above the background concentration.” See
HRS § 3.1.1. The petitioners first argue that the EPA
improperly listed five Prairie du Chien-Jordan wells as “release
wells” because they failed to exceed the requisite threshold of
one contaminant, TCE, to qualify as an observed release
relative to the background concentration. Pet’rs Br. 36. They
then briefly argue that EPA “cherry-picked” well data and
background wells, specifically asserting that the EPA should
have picked more wells farther north and west to better capture
its theory of contamination migration. /d. at 38.

None of these arguments is persuasive. First, the EPA did
not improperly list five wells as “release wells.” The petitioners
misread the chart listing the wells and the hazardous substances
exceeding the release threshold. See Revised Documentation
Record at 39. The EPA lists six wells that qualified as “release
wells” based on releases of different hazardous substances but,
as the petitioners point out, only one exceeded the threshold
limit for TCE. See id. The EPA accordingly did not include
TCE in the list of qualifying releases for all six release wells
and instead listed five of the wells as release wells for other
CVOCs detected in the aquifers. Jd. Second, the EPA did not
arbitrarily select well data. “The HRS does not identify
requirements or define conditions for establishing background
levels,” nor for selecting background wells. Support Document
at 62. Here, the EPA provided adequate evidence of observed
releases across numerous wells and over four years, see
Revised Documentation Record at 33-53, and sufficiently
responded to comments about the selection of well data, see
Support Document at 11—12, 66-68. In any listing decision, the
EPA balances “the need for certainty before action with the
need for inexpensive, expeditious procedures to identify
24

potentially hazardous sites.” Eagle-Picher I, 759 F.2d at 921.
Its reliance on previously compiled well data that
comprehensively demonstrated observed releases was anything
but arbitrary and capricious.

The petitioners next challenge the EPA’s purported
“natural migration pathway” theory of interconnectivity.'
Pet’rs Br. 17, 43. They first argue that the EPA’s conclusion on
the lack of continuous confining layers was not supported by
substantial evidence. /d. at 18-32. In particular, they point to
errors in one figure that the EPA used to illustrate that the St.
Peter confining layer was not continuous. See id. at 23. In this
figure, the EPA allegedly inaccurately depicted the continuity
of the St. Peter confining layer at certain wells. See id. The
petitioners reproduced maps and geological figures from the
U.S. Geological Survey (USGS) to show the presence of the
same confining layer. Jd. at 26-27. Although one of the figures
shows that the confining layer is absent east of the Site—as
shown in well log data for well HS-1, see Support Document
at 45— they contend that absence is “almost two miles outside
of EPA’s alleged plume area” and that “interconnectedness at
HS-1 has no bearing on [the] EPA’s allegation that a ‘plume’
is migrating from the Drift Aquifer Area to the Prairie du
Chien-Jordan Aquifer.” Pet’rs Br. 40.

For its part, the EPA indeed maintained that the St. Peter
confining layer is “locally absent due to erosion,” relying on
the same USGS study. See Revised Documentation Record at
27. It also noted that well HS-1 is located about 1.55 miles east
of municipal well SLP4, an observed-release well. Jd. Citing

'3 The petitioners also challenge the use of pump test data to
establish interconnectivity. Pet’rs Br. 33-34. That challenge is
meritless because the EPA disclaimed reliance on the pump tests to
establish interconnectivity. See Support Document at 51.
25

the HRS regulation that identifies “well logs indicating that
a... confining layer separating the aquifers is not continuous
through the two-mile radius” as one “of the types of
information useful in identifying aquifer interconnections,”
Hazard Ranking System, 55 Fed. Reg. at 51,553, the EPA
concluded that in addition to the observed-contamination
method of proving interconnectivity, the lack of a continuous
confining layer also supported interconnectivity. Support
Document at 48.

We need not resolve this conflict because the petitioners’
migration-pathway argument is not responsive to the observed-
release method of establishing interconnectivity. See Hazard
Ranking System, 55 Fed. Reg. at 51,553 (“For [the observed-
contamination method], the mechanism of vertical migration
does not have to be defined.”); accord Genuine Parts, 890 F.3d
at 316 (noting irrelevance of groundwater flow to HRS analysis
when assessing targets). Further, the EPA correctly noted that
“at this stage of the listing, groundwater modeling, 3D or
otherwise, to predict migration pathways [is] not required as
part of an HRS evaluation.” Revised Documentation Record at
40. Accordingly, even if they are correct about the continuity
of the St. Peter confining layer, the EPA’s error was harmless
because it established interconnectivity via observed releases
across the aquifers and did not rely on a specific migration
pathway. See Jicarilla Apache Nation v. U.S. Dep’t of Interior,
613 F.3d 1112, 1121 (D.C. Cir. 2010) (harmless error applies
to agency action because “if the agency’s mistake did not affect
the outcome, if it did not prejudice the petitioner, it would be
senseless to vacate and remand for reconsideration.” (alteration
omitted) (quoting PDK Laby’s., Inc. v. DEA, 362 F.3d 786, 799
(D.C. Cir. 2004)).!4

'* Tex Tin and Genuine Parts do not help the petitioners. Pet’rs
Br. 30-31 (citing Genuine Parts, 890 F.3d at 307, 310-11, 315), 48
26

D. EXTRA-RECORD EVIDENCE

The petitioners ask us to review and consider extra-record
evidence and to supplement the administrative record with
numerous documents, including a (1) post-final rule
declaration by Melinda Hahn (Hahn Declaration), J.A. 593-

(citing Tex Tin, 992 F.2d at 356). In Tex Tin, we vacated the NPL
listing of a tin manufacturing facility because the EPA had failed to
comply with our remand directing the agency to explain how a tin-
production byproduct deposited arsenic in soil adjacent to the
facility. 992 F.2d at 356. We concluded that the agency’s explanation
was arbitrary because the facility’s smokestack, which annually
emitted large quantities of arsenic, was a more likely source of the
arsenic in the soil “in the absence of any chemical analysis linking
the arsenic found in the soil to the tin [byproduct].” Jd. The
petitioners argue that here the EPA failed to explain its “natural
migration pathway|[]” and arbitrarily ignored more likely pathways
of contaminants into the Prairie du Chien-Jordan Aquifer. Pet’rs Br.
48. But Tex Tin is inapposite because here the EPA established a
chemical connection between numerous potential sources and the
contaminants defining the observed releases. See Revised
Documentation Record at 54. More broadly, the petitioners’
argument again incorrectly assumes the EPA attributed the release to
a specific source or pathway. See Support Document at 85.

The petitioners assert that, as in Genuine Parts, the EPA was
arbitrary and capricious in failing to consider credible evidence of a
confining layer. See 890 F.3d at 315. Genuine Parts, however, is
distinguishable as there the EPA did not rely on evidence of observed
contamination in the deeper aquifer to establish interconnection. /d.
at 309. Rather than showing interconnectivity through observed
releases, the EPA relied on a migration-pathway theory. See id. at
309-10. Accordingly, the EPA had to show that a confining layer
was not continuous within two miles of the site, see id. at 313, and
could not disregard an apparent discontinuity, see HRS § 3.0.1.2.2.
Not so here.
27

626; (2) sources that the petitioners relied on at the agency level
and that the EPA allegedly ignored, see J.A. 641-45 (listing
sources); and (3) two documents that existed before the Site’s
NPL listing: the Record of Decision for the Reilly Tar
Superfund Site, J.A. 646-676, and a 2009 groundwater study
by AECOM, a firm retained by the MPCA, J.A. 677-95. We
deny the motion.

“TWle do not allow parties to supplement the record
‘unless they can demonstrate the unusual circumstances
justifying departure from this general rule.’” City of Dania
Beach v. FAA, 628 F.3d 581, 590 (D.C. Cir. 2010) (quoting
Texas Rural Legal Aid, Inc. v. Legal Servs. Corp., 940 F.2d
685, 698 (D.C. Cir. 1991)). “Exceptions to that rule are quite
narrow and rarely invoked. They are primarily limited to cases
where the procedural validity of the agency’s action remains in
serious question, or the agency affirmatively excluded relevant
evidence.” CTS Corp. v. EPA, 759 F.3d 52, 64 (D.C. Cir. 2014)
(internal quotation marks and citations omitted). The
petitioners rely on two exceptions to the general rule: we have
supplemented the record if “background information [is]
needed ‘to determine whether the agency considered all the
relevant factors,” City of Dania Beach, 628 F.3d at 590
(quoting Am. Wildlands v. Kempthorne, 530 F.3d 991, 1002
(D.C. Cir. 2008)), or if “the agency affirmatively exclude[s]
relevant evidence,” CTS Corp., 759 F.3d at 64.

We easily deny the motion with respect to the Hahn
Declaration. Although it provides background, the petitioners
make the same arguments in their briefs to us and previously
made them at the agency level. Compare Hahn Decl. { 19
(arguing it is “not hydraulically possible” that W23
contamination originates from downgradient), with Pet’rs Br.
43 (arguing that EPA’s asserted migration pathway is
“scientifically unsupportable”), and J.A. 266 (same).
28

Moreover, Hahn had an opportunity to comment at the agency
level, including a meeting at the EPA. We decline to make an
exception for a declaration that could have been included in the
record earlier. See Kent County, 963 F.2d at 396 (declining to
supplement record with document created after EPA decision
at issue).

As to the sources the petitioners relied on before the
agency, J.A. 641-45, they argue we should consider these
allegedly adverse sources because the EPA improperly
excluded them from the record. Pet’rs Br. 58. (citing Kent
County, 963 F.2d at 395-96). As in City of Dania Beach,
however, Hahn’s general explanations of the source documents
“hardly suppl[y] the requisite ‘unusual circumstances’ to
justify” our consideration of the thousands of pages of expert
reports and their relation to the NPL listing. See 628 F.3d at
590 (quoting Texas Rural Legal Aid, 940 F.2d at 698).

Finally, the petitioners cite extra-record evidence to
buttress their migration-pathway argument that there exist
more plausible sources of contamination than the Drift Aquifer
Area. Pet’rs Br. 52-56, 60. In particular, they urge us to
consider the EPA Record of Decision on Remedial Action
Alternative Selection for the Reilly Tar Site, J.A. 646-76, and
a 2009 report by AECOM, a firm retained by the MPCA, J.A.
677-95. The petitioners contend that these documents show
that multi-aquifer wells and coal tar from the Reilly Tar Site
are the “primary pathways of contamination of the Prairie du
Chien-Jordan aquifer,” J.A. 665, and that the source of the
“bulk of ... contamination” of St. Louis Park and Edina is
upgradient of the Drift Aquifer Area and “near the intersection
of Highway 7 and Louisiana Ave,” J.A. 684.

Granted, the EPA did not include the AECOM report or
the Reilly Tar Record of Decision in the administrative record.
29

But exclusion was harmless error, if error at all, because the
EPA’s arguments on source attribution still apply: concerns
about the most plausible pathways and sources are inapplicable
because “no separate attribution is necessary when the source
at the site is a groundwater plume.” Support Document at 83.
Accordingly, we see no “unusual circumstances” to warrant
supplementing the record with these two sources. See City of
Dania Beach, 628 F.3d at 590 (citation omitted).

For the foregoing reasons, we deny both the petition for
review and the motion to consider extra-record evidence.

So ordered.
30

Legend

Background Groundwater Samples Observed Release Groundwater Samples
AX Quaternary Dnt Aquiter @ Quaternary Dnt Aquifer
AX Plattovitio-Gienwood Aquiter ~~ @ _ Piatteville.Glenwood Aquifer
A. St. Peter Aquitor @® st Potor Aguiter

AX Prairie du Chion Jordan Aquifor © Prairie du ChienJordan Aquiter

Source: The source of his map is ERSI, used by EPA with ESAs permission.
Refs. 6, pp. 33 Bough 41.73, pp 5.6; 75, pp 6,7, 52,53, 54, 58, 05, 64,

Highway 100 and County
Road 3 Groundwater Plume
‘St Louis Park and Edina
Hennepin County, Minnesota

Figure 3
Groundwater Observed Release

(7) TETRA TECH

31

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