Util. Solid Waste Activities Grp. v. Envtl. Prot. Agency ( 2018 )


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  •  United States Court of Appeals
    FOR THE DISTRICT OF COLUMBIA CIRCUIT
    Argued November 20, 2017           Decided August 21, 2018
    No. 15-1219
    UTILITY SOLID WASTE ACTIVITIES GROUP, ET AL.,
    PETITIONERS
    v.
    ENVIRONMENTAL PROTECTION AGENCY,
    RESPONDENT
    WATERKEEPER ALLIANCE, ET AL.,
    INTERVENORS
    Consolidated with 15-1221, 15-1222, 15-1223, 15-1227,
    15-1228, 15-1229
    On Petitions for Review of Administrative Action
    of the United States Environmental Protection Agency
    Douglas H. Green and Paul J. Zidlicky argued the causes
    for Industry petitioners. With them on the joint briefs were
    John F. Cooney, Margaret K. Kuhn, Samuel B. Boxerman, Eric
    Murdock, Makram B. Jaber, Joshua R. More, Raghav Murali,
    Richard G. Stoll, Lori A. Rubin, and Thomas J. Grever.
    Stephen J. Bonebrake, Brian H. Potts, and Aaron J. Wallisch
    entered appearances.
    2
    Thomas Cmar argued the cause for Environmental
    petitioners. With him on the briefs were Matthew E. Gerhart,
    Mary M. Whittle, and Lisa Evans.
    Perry M. Rosen, Attorney, U.S. Department of Justice,
    argued the cause for respondents. With him on the briefs were
    Jeffrey H. Wood, Acting Assistant Attorney General, Jonathan
    Skinner-Thompson, Attorney, and Laurel Celeste, Attorney,
    U.S. Environmental Protection Agency.
    Douglas H. Green, John F. Cooney, and Margaret K.
    Kuhn were on the brief for Industry intervenor-respondents.
    Matthew E. Gerhart, Mary M. Whittle, and Lisa Evans
    were on the brief for Environmental intervenor-respondents.
    Before: HENDERSON, MILLETT and PILLARD, Circuit
    Judges.
    Opinion filed PER CURIAM.
    Opinion concurring in part and concurring in the judgment
    in part filed by Circuit Judge HENDERSON.
    PER CURIAM: These consolidated petitions challenge the
    Environmental Protection Agency’s 2015 Final Rule
    governing the disposal of coal combustion residuals (“Coal
    Residuals”) produced by electric utilities and independent
    power plants. See Hazardous and Solid Waste Management
    System; Disposal of Coal Combustion Residuals from Electric
    Utilities (“Final Rule”), 80 Fed. Reg. 21,302 (April 17, 2015).
    Coal Residuals make up “one of the largest industrial waste
    streams generated in the U.S.” 
    Id. at 21,303.
    Coal-fired
    power plants in the United States burned upwards of 800
    million tons of coal in 2012 alone and produced approximately
    3
    110 million tons of solid waste as Coal Residuals. 
    Id. That waste
    contains myriad carcinogens and neurotoxins. See
    Hazardous and Solid Waste Management System;
    Identification and Listing of Special Wastes; Disposal of Coal
    Combustion Residuals from Electric Utilities (“Proposed
    Rule”), 75 Fed. Reg. 35,128, 35,153, 35,168 (June 21, 2010).
    Power plants generally store it on site in aging piles or pools
    that are at varying degrees of risk of protracted leakage and
    catastrophic structural failure. See 80 Fed. Reg. 21,327–
    21,328. The Final Rule sets criteria designed to ensure that
    human health and the environment face “no reasonable
    probability” of harm from Coal Residuals spilling, leaking, or
    seeping from their storage units and harming humans and the
    environment. 
    Id. at 21,338–21,339;
    42 U.S.C. § 6944(a).
    The statutory framework calling for regulation of solid
    waste generation, storage, and disposal has been in place since
    1976, when Congress enacted the Resource Conservation and
    Recovery Act (“RCRA”), 42 U.S.C. § 6901 et seq., but
    regulations implementing RCRA have been long in the
    making. The EPA has long studied the Coal Residuals
    disposal problem and struggled over how to address its scale,
    complexity, and gravity. The agency has been goaded by
    public outrage over catastrophic failures at sites storing toxic
    Coal Residuals, see 75 Fed. Reg. at 35,132, 35,137, and was
    directed by a federal court to devise a schedule to comply with
    its obligation to regulate under RCRA, see Appalachian Voices
    v. McCarthy, 
    989 F. Supp. 2d 30
    , 56 (D.D.C. 2013). Nearly
    four decades after Congress enacted RCRA, the EPA finally
    promulgated its first Final Rule regulating Coal Residuals in
    2015.
    These consolidated petitions—one on behalf of
    environmental organizations (“Environmental Petitioners”)
    and several others (collectively, “Industry Petition”) for a
    4
    consortium of power companies and their trade associations
    (“Industry Petitioners”)—challenge various provisions of that
    Final Rule under the Administrative Procedure Act and RCRA.
    RCRA Subtitle D calls on the EPA to promulgate criteria
    distinguishing “sanitary landfills,” which are permissible under
    the statute, from “open dumps,” which are prohibited. 42
    U.S.C. § 6944(a); see 
    id. § 6903(14),
    (28). The statutory
    baseline for the EPA’s criteria for sanitary landfills is that, at a
    minimum, they “shall provide that a facility may be classified
    as a sanitary landfill and not an open dump only if there is no
    reasonable probability of adverse effects on health or the
    environment from disposal of solid waste at such facility.” 
    Id. § 6944(a).
    Each claim here relates to what a utility operating
    one or more Coal Residuals disposal site(s) must do to qualify
    such site as a sanitary landfill that may lawfully operate under
    RCRA.
    Shortly before oral argument, the EPA announced its intent
    to reconsider the Final Rule, and moved to hold all proceedings
    in abeyance. We asked for clarification on the exact
    provisions of the Rule that would be subject to reconsideration.
    The EPA then filed a separate motion to remand six specific
    provisions.
    For the reasons that follow, we deny the EPA’s abeyance
    motion, and partially grant its remand motion. We also grant
    in part the Environmental Petition and deny the Industry
    Petition.
    I. Background
    A.
    “Coal Residuals” is a catch-all term for the byproducts of
    coal combustion that occurs at power plants. It includes “fly
    5
    ash,” “bottom ash,” “boiler slag,” and “flue gas desulfurization
    materials.” See 75 Fed. Reg. at 35,137. These residuals vary
    in their size and texture, but all contain “contaminants of * * *
    environmental concern.” 
    Id. at 35,138.
    According to the
    EPA, Coal Residuals contain carcinogens and neurotoxins,
    including arsenic, boron, cadmium, hexavalent chromium,
    lead, lithium, mercury, molybdenum, selenium, and thallium.
    80 Fed. Reg. at 21,449. The risks to humans associated with
    exposure to the identified contaminants include elevated
    probabilities of “cancer in the skin, liver, bladder, and lungs,”
    as well as non-cancer risks such as “neurological and
    psychiatric effects,” “cardiovascular effects,” “damage to
    blood vessels,” and “anemia.” 
    Id. at 21,451.
    Both cancer
    and non-cancer risks to infants “tend[] to be higher than other
    childhood cohorts, and also higher than risks to adults.” 
    Id. at 21,466.
    The risks to plant and animal wildlife include
    “elevated selenium levels in migratory birds, wetland
    vegetative damage, fish kills, amphibian deformities,
    * * * [and] plant toxicity.” 75 Fed. Reg. at 35,172.
    In developing the Final Rule, the EPA collected data on
    coal-fired units and their environs, identified hazards for
    evaluation, and specified benchmarks of toxicity that it
    determined “generally will be considered to pose a substantial
    present or potential hazard to human health and the
    environment and generally will be regulated.” Final Rule, 80
    Fed. Reg. at 21,449, 21,451. The EPA analyzed potential
    pathways of contamination to determine those most likely to
    pose a reasonable probability of adverse effects on humans or
    the environment. 
    Id. at 21,450–21,451.
    The EPA concluded
    that current management practices for Coal Residuals posed
    risks to human health and the environment at levels justifying
    uniform national guidelines. 
    Id. at 21,303.
    The main
    exposure pathways the EPA found were through waste that
    escapes landfills and surface impoundments and then
    6
    contaminates groundwater tapped as drinking water, and
    contaminates surface water that comes in direct contact with
    fish and other ecological receptors. 
    Id. Under most
    circumstances, the operators of coal-fired
    power plants dispose of the waste either by dumping it in dry
    landfills or by mixing it with water to channel it to wet surface
    impoundments. 80 Fed. Reg. at 21,303. These disposal sites
    are massive. On average, landfills span more than 120 acres
    and are more than 40 feet deep. 
    Id. Surface impoundments
    average more than 50 acres in size with an average depth of 20
    feet. 
    Id. As of
    2012, there were at least 310 landfills and 735
    surface impoundments in the United States currently receiving
    coal ash. 
    Id. The EPA
    identified at least 111 surface
    impoundments that are no longer receiving coal ash, but are not
    fully closed. See EPA, Regulatory Impact Analysis: EPA’s
    2015 RCRA Final Rule Regulating Coal Combustion Residual
    (CCR) Landfills and Surface Impoundments at Coal-Fired
    Utility Power Plants, 2–3 (2014), Joint App’x (J.A.) 1096.
    The record does not specify the number of inactive landfills.
    See 
    id. The Rule
    also addresses circumstances under which
    Coal Residuals safely may be “beneficially used”—e.g., to
    make cement—thereby reducing the total volume that must be
    managed as waste. See 75 Fed. Reg. at 35,212.
    Landfills and surface impoundments both pose threats to
    human health and the environment. 80 Fed. Reg. at 21,327–
    21,328.     The risks generally stem from the fact that
    “thousands, if not millions, of tons [of coal ash are] placed in a
    single concentrated location.” 
    Id. These disposal
    sites are at
    risk of structural failure, particularly where they are located in
    unstable areas such as wetlands or seismic impact zones. 
    Id. at 21,304.
    The sheer volume of Coal Residuals at these sites,
    moreover, can force contaminants into the underlying soil and
    groundwater, threatening sources of drinking water. 
    Id. at 7
    21,304–21,305. Surface water bodies—i.e., rivers, lakes, and
    streams, see 75 Fed. Reg. at 35,131—are also at risk of
    contamination through harmful constituents that migrate
    through groundwater, or flow into surface waters as run-off or
    wastewater discharge, any of which can lead to environmental
    harms such as “wetland vegetative damage, fish kills,
    amphibian deformities, * * * [and] plant toxicity.” See 
    id. at 35,172.
    Groundwater contamination is more likely to occur at sites
    that are unlined or lack adequate lining between the coal ash
    and the soil beneath it. See id.; see also Regulatory Impact
    Analysis, 5-22. However, most existing coal ash disposal
    sites—70% of landfills and 65% of surface impoundments—
    have no liner at all. See Regulatory Impact Analysis, 3-4
    nn.104–105, J.A. 1108. And while most new landfills and
    surface impoundments are constructed with liners, see 80 Fed.
    Reg. at 21,324, not all liners are alike. Composite lining,
    which includes a plastic geomembrane and several feet of
    compacted soil to act as a buffer, effectively eliminates the risk
    of groundwater contamination.           See EPA, Human &
    Ecological Risk Assessment of Coal Combustion Residuals
    (Risk Assessment), 4-8 to 4-9, J.A. 1110–1111. But many
    impoundments are lined only with compacted soil and are
    therefore far less protective. See Regulatory Impact Analysis,
    5-22, J.A. 1112. The EPA has acknowledged that it “will not
    always be possible” to restore groundwater or surface water to
    background conditions after a contamination event. See
    Response to Comments 50, J.A. 1301.
    Structural failures of surface impoundments pose
    additional risks that are more episodic but potentially more
    catastrophic than harm from liner leakage. Impoundment dam
    ruptures can result in “significant coal slurry releases, causing
    fish kills and other ecologic damage, and in some instances
    8
    damage to infrastructure.” 80 Fed. Reg. at 21,457 (footnote
    omitted).    The EPA is aware of at least 50 surface
    impoundments that are a “high” hazard, see EPA, Coal
    Combustion Residuals Impoundment Assessment Reports,
    J.A. 446–469, which the Rule defines to mean that “failure or
    mis-operation will probably cause loss of human life” in
    addition to other harms, 40 C.F.R. § 257.53. The EPA has
    tagged another 250 impoundments as posing a “significant”
    hazard, see Impoundment Assessment Reports, J.A. 446–469,
    where failure or mis-operation is unlikely to kill people, but
    would “probably cause economic loss, environmental damage,
    or disruption of lifeline facilities, or impact other concerns.”
    40 C.F.R. § 257.53. Structural risk is exacerbated at sites
    located in geologically unstable areas, such as those with poor
    foundation conditions, areas susceptible to earthquakes or
    other mass movements, or those with karst terrains. See id.;
    80 Fed. Reg. at 21,365–21,367.
    Risks from inactive surface impoundments at inactive
    power plants, which the parties refer to as “legacy ponds,” are
    also apparent in the record. As with surface impoundments at
    active plants, groundwater contamination or catastrophic
    structural failure of a legacy pond threatens human health and
    the environment. But legacy ponds, which by their nature are
    older than most surface impoundments, are “generally unlined”
    and unmonitored, and so are shown to be more likely to leak
    than units at utilities still in operation. 80 Fed. Reg. at 21,343–
    21,344. Without an on-site operator to monitor and maintain
    such a unit, consequences of leakage or structural failure may
    be amplified. Cf. 
    id. at 21,394
    (requiring qualified personnel
    to conduct weekly inspections at active surface
    impoundments).
    The EPA record reports on the many cases in which
    damage has already occurred. “EPA has confirmed a total of
    9
    157 cases * * * in which [Coal Residual] mismanagement has
    caused damage to human health and the environment.” 80
    Fed. Reg. at 21,325. The EPA recounts that public pressure to
    regulate Coal Residuals escalated after an unlined surface
    impoundment in Kingston, Tennessee suffered a
    “catastrophic” structural failure on December 22, 2008. See
    75 Fed. Reg. at 35,132.           The impoundment released
    approximately 5.4 million cubic yards of Coal Residual sludge
    across 300 acres of land and into the nearby Emory River. See
    EPA, Damage Case Compendium:                Technical Support
    Document, Volume I: Proven Damage Cases, 143 (2014), J.A.
    1192. According to the EPA, the spill was one of the “largest
    volume industrial spill[s] in U.S. history.” 
    Id. at 143
    n.612,
    J.A. 1192. The Coal Residual sludge ruptured a natural gas
    line, disrupted power in the area, damaged or destroyed dozens
    of homes, and resulted in elevated levels of arsenic and lead in
    the Emory River. 
    Id. The resulting
    river contamination
    “completely destroyed” more than 80 acres of aquatic
    ecosystems. 
    Id. at 144,
    J.A. 1193. More than a year after the
    spill, the majority of fish collected from the river contained
    toxins that rendered them unsafe for human consumption. 
    Id. The disaster
    forced the closure of the Emory River for almost
    two years. The Tennessee Valley Authority took four years
    and spent more than $1.2 billion to remove Coal Residuals and
    contaminated sediment from the river and adjoining areas, to
    monitor and repair associated damage, and to construct a new
    disposal unit. 
    Id. at 148,
    J.A. 1197.
    10
    B.
    Two years after the Kingston disaster, the EPA
    promulgated the Proposed Rule announcing its intent to
    regulate Coal Residuals under RCRA. See 75 Fed. Reg. at
    35,128.1
    A key question for the EPA had long been whether to
    regulate Coal Residuals as hazardous waste under the cradle-
    to-grave federal hazardous waste management authority
    conferred by RCRA Subtitle C, 42 U.S.C. §§ 6921–6939g, or
    to treat it as nonhazardous solid waste subject to national
    guidelines under Subtitle D, 
    id. §§ 6941–6949a.
    A waste is
    “hazardous” and subject to regulation under Subtitle C only if
    it exhibits one of four hazard characteristics: ignitability,
    corrosivity, reactivity, or toxicity. See 
    id. § 6921;
    40 C.F.R.
    §§ 261.11, 261.20–261.24. Under Subtitle C, the EPA
    directly regulates all stages of production and disposition of
    hazardous wastes, and has administrative enforcement power
    as well as authority to initiate or recommend civil and criminal
    actions in court. See 42 U.S.C. §§ 6922–6928. Subtitle D, in
    contrast, envisions that states are primarily responsible for
    regulating disposal of nonhazardous wastes in landfills and
    dumps. The EPA’s principal role under Subtitle D is to
    announce federal guidelines for state management of
    nonhazardous wastes; Subtitle D leaves it up to the states to
    “use federal financial and technical assistance to develop solid
    waste management plans in accordance with [the] federal
    guidelines.” Environmental Def. Fund v. EPA, 
    852 F.2d 1309
    , 1310 (D.C. Cir. 1988).
    1
    On several previous occasions, the EPA considered, but
    decided against, regulating Coal Residuals under RCRA Subtitle C.
    For background on the EPA’s previous determinations on Coal
    Residuals, see 75 Fed. Reg. at 35,136–35,137.
    11
    Substantively, Subtitle D prohibits the disposal of solid
    waste in “open dumps,” 42 U.S.C. § 6945(a), and calls on the
    EPA to promulgate criteria for determining whether a waste
    facility constitutes an open dump—criteria that, if followed,
    will ensure “no reasonable probability of adverse effects on
    health or the environment from disposal of solid waste at such
    facility,” 
    id. § 6944(a).
    Subtitle D neither grants the EPA
    direct enforcement authority nor requires states to adopt or
    implement its requirements. See 
    id. § 6941.
    Enforcement is
    left to states’ own policy decisions and to the initiative of
    people bringing citizen suits to enforce the federal standards.
    See 
    id. §§ 6946–6947,
    6972. But see infra Part II.A.
    (discussing recent amendments to RCRA).
    The EPA initially published two alternative proposed rules
    to govern Coal Residuals, one under each Subtitle, basing the
    Subtitle C proposal on the toxicity of Coal Residuals. See 75
    Fed. Reg. at 35,146. The proposals drew 450,000 public
    comments, the vast bulk of which spoke to the threshold
    question of which RCRA Subtitle to use, and the majority of
    which supported regulation under Subtitle C. 80 Fed. Reg. at
    21,319. Most of the commenters were individuals and
    environmental groups pressing for stronger regulation
    “because state programs have failed to adequately regulate the
    disposal of [Coal Residuals] and because the risks associated
    with the management of these wastes are significant.” 
    Id. Only a
    handful of states, for example, required any
    groundwater monitoring around units holding Coal Residuals,
    
    id. at 21,323–21,324,
    including only one of the eight states with
    the biggest volumes of Coal Residuals, Regulatory Impact
    Analysis, G-6, J.A. 1121. On the other hand, the enormous
    volume of waste permeated with relatively low concentrations
    of toxins posed practical difficulties for any Subtitle C
    regulation. See 80 Fed. Reg. at 21,321.
    12
    Based on many years of analysis, the EPA found “a
    compelling need for a uniform system of requirements to
    address the[] risks [from Coal Residuals],” and decided to
    move forward with a Final Rule. 80 Fed. Reg. at 21,327.
    The EPA opted to proceed under the less muscular Subtitle D
    even as it continued to study factors potentially supporting
    regulating Coal Residuals as hazardous waste under RCRA
    Subtitle C. See 
    id. at 21,319–21,327.
    The EPA thus formally
    deferred deciding whether Subtitle C regulation is warranted,
    and used its Subtitle D authority to set forth guidelines on
    where and how disposal sites for Coal Residuals are to be built,
    maintained, and monitored. See 80 Fed. Reg. at 21,302.
    The Final Rule sets minimum criteria for the disposal of
    Coal Residuals in landfills and surface impoundments.
    Among the provisions of the Final Rule at issue here are
    location restrictions on landfills and surface impoundments,
    requirements pertaining to lining, structural integrity, and
    groundwater monitoring, and criteria for recycling Coal
    Residuals for beneficial uses, such as substituting for cement
    in road construction, in lieu of keeping it in disposal units. See
    40 C.F.R. §§ 257.60–257.74. The Final Rule also sets
    compliance deadlines, procedures for closing non-complying
    landfills and surface impoundments, and requirements that
    operators of these disposal sites make records of their
    compliance with the Final Rule publicly available. See 
    id. §§ 257.100–257.07.
    We discuss the relevant criteria in more
    detail in addressing the merits of the consolidated petitions.
    13
    C.
    Two groups of petitioners sought review of the Final Rule.
    Environmental Petitioners are an assortment of environmental
    groups that includes the Environmental Integrity Project, Sierra
    Club, and Hoosier Environmental Council. They generally
    claim that EPA did not go far enough to protect the public and
    the environment from the harms of Coal Residual disposal.
    Specifically, they claim that the Final Rule unlawfully
    countenances significant risks of harmful leakage by allowing
    unlined impoundments as well as impoundments lined only
    with a layer of compacted soil to continue receiving Coal
    Residuals. Environmental Petitioners also contend that the
    EPA acted arbitrarily and capriciously by exempting from
    regulation so-called “legacy ponds”—inactive surface
    impoundments at shuttered power plants—given evidence that
    legacy ponds are at risk of unmonitored leaks and catastrophic
    structural failures. They also make a claim, not raised during
    rulemaking, that the EPA violated RCRA’s citizen-suit
    provision by failing to require the operators of Coal Residual
    disposal sites to timely and publicly disclose records reflecting
    their compliance with the Final Rule.
    Industry Petitioners are a collection of industry trade
    associations and utilities including the Utility Solid Waste
    Activities Group, AES Puerto Rico, LP, the Edison Electric
    Institute, the National Rural Electric Cooperative Association,
    and the American Public Power Association. They first assert
    that the EPA exceeded its statutory authority under RCRA to
    set guidelines for facilities where waste “is disposed of,” 42
    U.S.C. § 6903(14), by regulating surface impoundments that
    no longer actively receive Coal Residuals. They further claim
    that the Rule’s restriction on placement of new units and
    expansions of existing units near aquifers, 40 C.F.R. § 257.60
    (aquifer location restriction), was inadequately noticed, and
    14
    that the Rule’s provision for nonconforming units to continue
    in operation if no alternative disposal capacity is available, 
    id. § 257.103
    (alternative closure provision), arbitrarily and
    capriciously excludes cost considerations from its definition of
    “available.” Industry Petitioners also challenge the Rule’s
    location restrictions and structural integrity criteria governing
    units in seismic impact zones. See 
    id. §§ 257.63,
    257.73–
    257.74.      They contend that the deadline for existing
    impoundments’ compliance with those provisions was
    arbitrarily shortened from the timeframe in the Proposed Rule,
    that the Rule arbitrarily applied the location restrictions to new
    but not existing landfills, and that EPA failed to explain the
    strict design criteria it adopted for new landfills and
    impoundments.
    Environmental Petitioners intervened in Industry’s
    petition for review, and vice versa. We consolidated the
    petitions. The case has been pending in this court since 2015,
    but several procedural matters delayed resolution until now.
    In June 2016, we granted the EPA’s unopposed motion to
    remand to itself several provisions of the Final Rule not at issue
    here that the EPA had decided to vacate. See Per Curiam
    Order, Utility Solid Waste Activities Grp. v. EPA, No. 15-1219
    (D.C. Cir. June 14, 2016). In doing so, we held all
    proceedings in abeyance while the EPA revised portions of the
    Rule affected by the vacatur. See 
    id. We then
    set oral
    argument for October 17, 2017.
    Less than a month before oral argument, the EPA
    announced that it had granted the petition of several industry
    groups to reconsider the Final Rule, and moved us to hold all
    proceedings in abeyance. The EPA pointed to Congress’s
    recent enactment of the Water Infrastructure Improvements for
    the Nation Act (“WIIN Act”), Pub. L. No. 114-322, 130 Stat.
    1628 (2016) (codified at 42 U.S.C. § 6945(d)), in December
    15
    2016 that, among other things, amended RCRA Subtitle D to
    allow the EPA to approve State permitting programs “to
    operate in lieu of [EPA] regulation of coal combustion
    residuals units in the State,” provided those programs are at
    least as environmentally protective as the existing (or
    successor) EPA regulations. 42 U.S.C. § 6945(d)(1)(A).
    When we asked EPA to specify which provisions it planned to
    reconsider, the EPA filed another motion. That motion sought
    to remand provisions of the Rule relating to the beneficial use
    of Coal Residuals, alternative compliance provisions, legacy
    ponds, and the EPA’s statutory authority to regulate inactive
    surface impoundments. We deferred a ruling on both motions
    until now.
    On July 30, 2018, the EPA promulgated an amendment to
    the Final Rule (i) allowing a state or the EPA, when acting as
    a permitting authority, to use alternate groundwater
    performance standards, (ii) revising the groundwater
    performance standards for certain constituents, and (iii)
    extending the timeframe for facilities to cease receiving Coal
    Residuals once they are required to close. See Hazardous and
    Solid Waste Management System:              Disposal of Coal
    Combustion Residuals from Electric Utilities; Amendments to
    the National Minimum Criteria, 83 Fed. Reg. 36,435, 36,436
    (July 30, 2018).
    II. Request for Abeyance
    A. WIIN Act
    At the outset, the EPA requests that this case be held in
    abeyance while it considers potential regulatory changes in
    response to Congress’s enactment of the WIIN Act, 42 U.S.C.
    § 6945(d). The WIIN Act amended RCRA’s Subtitle D State
    permitting scheme. As relevant here, Section 6945(d)
    16
    provides that the Administrator may approve qualified State
    “permit program[s] or other system[s] of prior approval and
    conditions under State law for regulation by the State of coal
    combustion residuals units” to “operate in lieu of [EPA]
    regulation of coal combustion residuals units in the
    State * * *.” 42 U.S.C. § 6945(d)(1)(A).
    But the Administrator may only approve a state plan if its
    standards “are at least as protective as the criteria” set by the
    EPA in its corresponding RCRA regulations, specifically
    including Coal Residuals regulation, 40 C.F.R. pt. 257. 42
    U.S.C. § 6945(d)(1)(C); see 
    id. § 6945(d)(1)(B)(i).
    The WIIN
    Act also provides that a Coal Residuals disposal site can only
    qualify as a “sanitary landfill” if it is in full compliance with,
    among other things, the EPA’s extant (or successor)
    regulations governing Coal Residuals waste sites. 42 U.S.C.
    § 6945(d)(6).
    The EPA argues that the WIIN Act has afforded it new
    regulatory options and makes “fundamental changes to RCRA
    Subtitle D as applied specifically to [Coal Residuals].” EPA
    WIIN Br. 4, 6, 8. On that basis, the EPA asks us to hold the
    case in abeyance while it decides whether or not “to alter some
    of its regulatory choices[.]” EPA WIIN Br. at 2, 6.
    We decline to exercise our discretion to hold the case in
    abeyance. We leave it open for the EPA to address on remand
    the relevance of the WIIN Act, the Act’s express incorporation
    of the EPA regulations published at 40 C.F.R. Part 257, and its
    definition of “sanitary landfill.”
    17
    III. Environmental Petitioners’ Challenges
    A. Unlined Surface Impoundments
    Environmental Petitioners challenge the Final Rule’s
    provision that existing, unlined surface impoundments may
    continue to operate until they cause groundwater
    contamination. 40 C.F.R. § 257.101(a)(1). They contend
    that the EPA failed to show how continued operation of unlined
    impoundments meets RCRA’s baseline requirement that any
    solid waste disposal site pose “no reasonable probability of
    adverse effects on health or the environment.” 42 U.S.C.
    § 6944(a).
    The EPA found that unlined impoundments are
    dangerous: It concluded that, among the studied disposal
    methods, putting Coal Residuals “in unlined surface
    impoundments and landfills presents the greatest risks to
    human health and the environment.” 80 Fed. Reg. at 21,451.
    The Rule accordingly requires that all new surface
    impoundments be constructed with composite lining that
    effectively secures against leakage.           See 40 C.F.R.
    § 257.72(a). But it allows existing unlined impoundments to
    continue to receive Coal Residuals indefinitely, until their
    operators detect that they are leaking. 
    Id. § 257.101(a).
    Only
    once a leak is found must the operator of an unlined
    impoundment begin either retrofitting the unit with a
    composite liner, or closing it down—a process that the Rule
    contemplates may take upwards of fifteen years. 
    Id. § 257.102(f).
    In view of the record evidence that led the EPA
    to conclude that composite liners are needed to ensure that new
    impoundments meet RCRA Subtitle D’s “no reasonable
    probability” standard, Environmental Petitioners claim that the
    Rule’s allowance for continued operation of existing, unlined
    18
    surface impoundments is arbitrary and capricious and contrary
    to RCRA.
    The EPA and Industry Intervenors assert that the
    composite lining required for new units is not needed for
    existing units because most unlined impoundments do not leak,
    and an unlined impoundment that is not leaking is not
    dangerous. Industry Intervenors emphasize that the record
    suggests that “almost two-thirds of unlined impoundments do
    not leak,” and they assert that “appropriate controls on
    impoundments that do leak” suffice to meet RCRA’s “no
    reasonable probability” standard. Industry Intervenor Br. 6–
    7. The EPA underscores that it made no finding of any
    “reasonable probability that each and every unlined
    impoundment will, in fact, result in adverse effects on health
    and the environment.” Resp’t Br. 82. It insists that RCRA’s
    “no reasonable probability” standard is met by the Rule’s
    provisions for “extensive monitoring of groundwater to detect
    constituent leaking,” 
    id. at 83,
    and “immediate action to stop
    that leak,” “redress that leak,” and to close the site as soon as a
    harmful leak is detected. Oral Arg. Tr. 100:20–100:25.
    The record shows, however, that the vast majority of
    existing impoundments are unlined, see Regulatory Impact
    Analysis 3-4, J.A. 1108, that unlined impoundments have a
    36.2 to 57 per cent chance of leakage at a harmfully
    contaminating level during their foreseeable use, see 
    id. at 4-9,
    5-22, J.A. 1111–1112, and that the threat of contamination
    from unlined units exceeds the EPA’s cancer risk criteria and
    thus “generally will be considered to pose a substantial present
    or potential hazard to human health and the environment,” 80
    Fed. Reg. at 21,449–21,450; see Risk Assessment 5-5, J.A.
    1041. It is inadequate under RCRA for the EPA to conclude
    that a major category of impoundments that the agency’s own
    data show are prone to leak pose “no reasonable probability of
    19
    adverse effects on health or the environment,” 42 U.S.C.
    § 6944(a), simply because they do not already leak.
    The number of unlined impoundments is large. The EPA
    identified 735 existing active surface impoundments
    throughout the country. Of the 504 sites for which the EPA
    was able to collect liner data, approximately 65 per cent were
    completely unlined, with most of the rest lined only with
    compacted soil or other partial or high-permeability liners.
    See Regulatory Impact Analysis 3-4 n.105, J.A. 1108. Only
    17 per cent of surface impoundments for which the EPA has
    liner data had composite liners—the sole liner type that the
    EPA found to be effective in reducing the risk of toxic chemical
    leakage to the level that the Agency found acceptable.
    Those hundreds of unlined impoundments are at
    significant risk of harmful leakage. Of 157 sites where the
    EPA confirmed that Coal Residuals have already caused
    damage to human health and the environment, the damage
    cases “were primarily associated with unlined units.” 80 Fed.
    Reg. at 21,452.       The record evidence shows that an
    impoundment with composite lining, which the Rule requires
    of all new impoundments, has a 0.1 per cent chance of
    contaminating groundwater at drinking-water wells a mile
    distant from the impoundment perimeter over the course of a
    100-year period. Regulatory Impact Analysis 5-22, J.A. 1112.
    An unlined impoundment, in contrast, has a 36.2 per cent
    chance of contaminating groundwater at such a distance. See
    
    id. And the
    probability of contamination is higher at distances
    closer to the impoundment site, 
    id., J.A. 1112;
    measured one
    meter from the impoundment’s perimeter, the contamination
    risk jumps to 57 per cent, 
    id., J.A. 1111.
    See Risk Assessment
    ES-4, J.A. 1083–1084 (“In many of the potential damages
    cases, groundwater exceedances were discovered near the
    boundary” of the impoundment).              According to the
    20
    administrative record, then, a significant portion of the 575
    identified unlined surface impoundments are likely to
    contaminate groundwater.
    Impoundment leakages pose substantial risks to humans
    and the environment. The EPA studied a wide range of toxins
    present in Coal Residuals, see Risk Assessment ES–4, J.A.
    1010, and considered various forms of potential human and
    environmental exposures. The EPA uses risk benchmarks in
    assessing the propriety of regulatory action. For example, it
    treats a cancer risk in excess of 1 x 104, or 1 in 10,000, as one
    that “generally will be considered to pose a substantial present
    or potential hazard to human health and the environment[.]”
    80 Fed. Reg. at 21,449. For non-cancer risks, the EPA
    determined that a Hazard Quotient—defined as the “ratio of the
    estimated exposure to the exposure at which it is likely that
    there would be no adverse health effects,” 75 Fed. Reg. at
    35,168—gives rise to such a threat when it is greater than or
    equal to 1. See 80 Fed. Reg. at 21,449. Using those
    benchmarks and the data it collected from the Risk
    Assessment, the EPA found that material human exposures
    derive from ingestion of contaminated groundwater or the
    consumption of contaminated fish. 
    Id. at 21,450–21,451.
    2
    The plant and animal exposures the EPA identified as material
    derive from contact with contaminated surface water. See id.;
    Risk Assessment 5-8, J.A. 1044. The EPA also expressed
    concern about the contamination of groundwater that is not
    currently used as a source of drinking water because “[s]ources
    of drinking water are finite, and future users’ interests must
    2
    The EPA’s Risk Assessment found that unlined
    impoundments created an unacceptable human cancer risk as a result
    of exposure to two different arsenics, and an unacceptable non-
    cancer risk as a result of exposure to one type of arsenic, as well as
    lithium, molybdenum, and thallium. See Risk Assessment 5-5, J.A.
    1041.
    21
    also be protected.” 80 Fed. Reg. at 21,452. In view of the
    record’s limitation of the risk calculus associated with leakage
    to the subset of toxins and exposures that the EPA deemed to
    present a substantial risk to human health or the environment,
    the EPA’s assertion in its brief that, even where it occurs,
    leakage “will not necessarily result in contamination of
    groundwater, either above allowable regulatory thresholds, or
    at all,” is at best a red herring. Resp’t Br. at 85. Every
    leakage the EPA record treated as material exceeded regulatory
    thresholds. In defending the Rule here, the EPA looks at too
    narrow a subset of risk information and applies the wrong legal
    test.
    The Final Rule’s approach of relying on leak detection
    followed by closure is arbitrary and contrary to RCRA. This
    approach does not address the identified health and
    environmental harms documented in the record, as RCRA
    requires. Moreover, the EPA has not shown that harmful
    leaks will be promptly detected; that, once detected, they will
    be promptly stopped; or that contamination, once it occurs, can
    be remedied.
    On its own terms, the Rule does not contemplate that
    contamination will be detected as soon as it appears in
    groundwater. The EPA and Industry defend the rule as
    RCRA-compliant principally because, they say, it provides for
    retrofit with a composite liner or closure of an unlined
    impoundment “[o]n the first indication that an unlined unit is
    leaking[.]” Industry Intervenor Br. 6. But the required
    groundwater sampling need only occur “at least
    semiannual[ly],” or perhaps less frequently under certain
    geological conditions.   40 C.F.R. § 257.94(b), (d); 
    id. § 257.95(c).
    The Rule thus contemplates that leaks will often
    go undetected for many months.
    22
    By the time groundwater contamination from an unlined
    impoundment has been detected, more damage will have been
    done than had the impoundment been lined: Leakage from
    unlined impoundments is typically quicker, more pervasive,
    and at larger volumes than from lined impoundments. See 80
    Fed. Reg. at 21,406. Unlike lined impoundments, in which
    leaks are “usually caused by some localized or specific defect
    in the liner system that can more readily be identified and
    corrected,” leakage from unlined impoundments is more
    pervasive and less amenable to any quick, localized fix. 
    Id. at 21,371.
    When an unlined impoundment begins to leak, Coal
    Residual sludge “will flow through the unit and into the
    environment unrestrained,” such that retrofit or closure of the
    unit are typically “the only corrective action strateg[ies] that
    [the] EPA can determine will be effective[.]” See 
    id. Neither retrofitting
    nor closure occurs immediately under
    the Rule; the timeline contemplates a process that takes from
    five to fifteen years. See 40 C.F.R. § 257.102. The EPA
    understates the harm its own record evidences by emphasizing
    that “leaking unlined impoundments must cease receiving
    [Coal Residuals] and initiate closure or retrofit activities within
    six months.” Resp’t Br. at 81; see 40 C.F.R. § 257.101(a)(1).
    What it neglects to account for is that the Rule gives the
    operator a further five years to complete retrofitting or closure
    activities. 
    Id. §§ 257.102(f)(1)(ii),
    257.102(k)(3). The Rule
    also allows the operators of surface impoundments to extend
    that window, by up to two years for smaller units and, for units
    larger than 40 acres—which most are, see 80 Fed. Reg. at
    21,303—for up to ten years, see 40 C.F.R. § 257.102(f)(2)(ii).
    The Rule addresses neither the risks to public health and
    to the environment before leakage is detected, nor the harms
    from continued leakage during the years before leakage is
    ultimately halted by retrofit or closure. See generally 40
    23
    C.F.R. §§ 257.90–257.104.         In defending the Rule as
    compliant with RCRA, the EPA did not even consider harms
    during the retrofit or closure process. See Resp’t Br. 80–86;
    80 Fed. Reg. at 21,403–21,406; cf. Oral Arg. Tr. 102–105 (EPA
    counsel unable to identify record evidence regarding how
    quickly leaks can be detected or how quickly and thoroughly
    responsive action can occur, but referring generally to a
    practice of immediate “pump and treat,” which the Rule does
    not appear to require). An agency’s failure to consider an
    important aspect of the problem is one of the hallmarks of
    arbitrary and capricious reasoning. See United States Sugar
    Corp. v. EPA, 
    830 F.3d 579
    , 606 (D.C. Cir. 2016) (per curiam)
    (citing Motor Vehicle Mfrs. Ass’n v. State Farm Mut. Auto. Ins.
    Co., 
    463 U.S. 29
    , 43 (1983)).
    The EPA’s position suffers additional flaws. The EPA
    determined that contaminated surface waters, such as rivers,
    streams, and lakes, are the principal pathway of harm to
    environmental receptors, but the Final Rule requires only
    monitoring of groundwater, and only for levels of
    contamination that would harm human health. See 40 C.F.R.
    §§ 257.90–257.95 (calling for groundwater monitoring
    systems); 75 Fed. Reg. at 35,130 (defining maximum
    contaminant level in terms of drinking water safety). Surface
    water contamination poses environmental risks from
    “[e]levated selenium levels in migratory birds, wetland
    vegetative damage, fish kills, amphibian deformities,
    * * * [and] plant toxicity,” 75 Fed. Reg. at 35,172, and to
    humans through the possible consumption of contaminated
    fish, 80 Fed. Reg. at 21,444. These risks exceed the EPA’s
    risk criteria for ecological receptors. See Risk Assessment 5–
    8, J.A. 1044. And some contamination levels that do not meet
    the risk threshold for humans may exceed thresholds for
    ecological receptors. See, e.g., 
    id. (noting a
    risk exceedance
    unique to ecological receptors from cadmium). Yet the record
    24
    does not explain how the Rule’s provisions for groundwater
    monitoring, followed by corrective action only when human
    exposure benchmarks are exceeded, will mitigate these risks.
    RCRA requires the EPA to set minimum criteria for sanitary
    landfills that prevent harm to either “health or the
    environment.” 42 U.S.C. § 6944(a) (emphasis added). The
    EPA’s criteria for unlined surface impoundments, limited as
    they are to groundwater monitoring for contaminant levels
    keyed to human health, only partially address the first half of
    the statutory requirement.
    For these reasons, we vacate 40 C.F.R. § 257.101, which
    allows for the continued operation of unlined impoundments,
    and remand for additional consideration consistent with this
    opinion.
    B. Liner Type Criteria
    Environmental Petitioners next challenge the Final Rule’s
    regulation of so-called “clay-lined” surface impoundments. A
    clay liner consists of at least two feet of compacted soil to act
    as a buffer between the Coal Residual sludge and the local soil.
    See Risk Assessment 4-8; J.A. 1024. Even as the Rule
    requires all newly constructed surface impoundments to be
    built with composite lining, disapproving any new
    impoundments lined only with compacted soil, it treats existing
    impoundments constructed with the same compacted soil and
    no geomembrane as if they were “lined.” See 40 C.F.R.
    §§ 257.71(a)(1)(i), 257.96–257.98. The upshot is that such
    clay-lined impoundments may stay open and keep accepting
    Coal Residuals, subject to groundwater monitoring for leakage,
    see 40 C.F.R. § 257.101, but, unlike existing unlined
    impoundments—which must begin closure when they leak, 
    id. § 257.71(a)(1)—clay-lined
    impoundments need not begin
    closure when they are discovered to be leaking. Rather, their
    25
    operators may attempt to repair them first. 
    Id. §§ 257.96–
    257.98. Only if repair is unsuccessful must they then begin
    the protracted process to either retrofit with a composite liner
    or close.
    The EPA contends that, by requiring the operators of clay-
    lined impoundments to fix leaks when they occur, the Rule
    comports with RCRA’s mandate to ensure “no reasonable
    probability of adverse effects on health or the environment.”
    42 U.S.C. § 6944(a); see Resp’t Br. 88–89. For their part,
    Environmental Petitioners point to record evidence that clay-
    lined units are likely to leak, and contend that the EPA’s
    approach “authorizes an endless cycle of spills and clean-ups”
    in violation of RCRA. See Envtl. Pet’r Br. 30.
    Clay-lined units are dangerous: “clay-lined units tended
    to have lower risks than unlined units” but, the record evidence
    showed, they were “still above the criteria” that the EPA set as
    the threshold level requiring regulation. 75 Fed. Reg. at
    35,144. Clay-lined surface impoundments have a 9.1 per cent
    chance of causing groundwater contamination at drinking
    water wells at a one-mile distance from the impoundment
    perimeter. See Regulatory Impact Analysis 5-22, J.A. 1112.
    And, as with unlined impoundments, the EPA acknowledges
    that the risk of contamination from leaking clay-lined
    impoundments is much higher closer to the impoundment
    perimeter. See Risk Assessment 5-39 to 5-40, J.A. 1075–1076
    (“[A]rsenic concentrations fall dramatically as the distance
    from the [waste management units] increases.”); 
    id. at 5-47
    to
    5-48, J.A. 1083–1084 (“In many of the potential damage cases,
    ground water exceedances were discovered near the boundary
    26
    of the W[aste] M[anagement] U[nit].”). 3 Leaks from clay-
    lined units, the EPA found, present cancer and non-cancer risks
    that exceed the EPA’s risk criteria. See Risk Assessment 5-5,
    5-30, J.A 1041, 1066.
    The EPA’s regulation of clay-lined impoundments suffers
    from the same lack of support as its regulation of unlined
    impoundments. 
    See supra
    part III.A. Just as the EPA did not
    explain how the Rule’s contemplated detection and response
    could assure “no reasonable probability of adverse effects to
    health or the environment” at unlined impoundments, it
    likewise failed regarding existing impoundments lined with
    nothing more than compacted soil. The EPA insists that the
    Rule’s criteria ensure that leaks from these clay-lined units will
    be “promptly” addressed, thereby satisfying RCRA. Resp’t
    Br. 91.
    But here, too, the EPA has failed to show how unstaunched
    leakage while a response is pending comports with the “no
    reasonable probability” standard.            The problem is
    compounded by the Rule’s unsupported supposition that
    leaking clay liners, unlike leaking unlined impoundments, can
    be repaired. The Rule thus allows an operator of a leaking
    clay-lined impoundment time to explore repair even before the
    five-to-fifteen year retrofit-or-close clock starts to run. For
    starters, the Rule allows operators of lined impoundments up
    to five months to complete an assessment of possible corrective
    measures, 40 C.F.R. § 257.96(a), and—given the numerous,
    complicated steps involved in doing so—allows an additional,
    indefinite amount of time to actually select a remedy. See 
    id. § 257.97;
    80 Fed. Reg. at 21,407–21,408. Once an operator
    3
    The administrative record does not show the exact probability
    of contamination from clay-lined units at a one-meter distance. See
    Regulatory Impact Analysis, 4-9 to 5-22, J.A. 1111–1112.
    27
    settles on a remedy, it has another three months to initiate
    remedial activities. 
    Id. at §
    257.98(a). If it turns out that no
    effective repair is feasible, or if an attempted repair proves
    unsuccessful, only then does the Rule contemplate the
    impoundment’s operator will begin the protracted process—
    discussed above in connection with the closure of existing,
    unlined impoundments—of retrofitting the site with a
    composite liner or closing it. There is no evidence in the
    record supporting the EPA’s assumption that clay liners are
    reasonably susceptible of repair, nor any explanation or
    account of how the risks of harm during the lengthy response
    periods the Rule allows comport with the “no reasonable
    probability” standard.
    Just as with the EPA’s regulation of unlined
    impoundments, the Rule’s treatment of clay-lined
    impoundments does not capture the full range of health and
    environmental harms they pose, as RCRA requires. By
    responding only to risks from leakage contaminating
    groundwater a mile from the perimeter of the studied
    impoundments, and accordingly setting minimum criteria that
    focus solely on harms to humans through drinking water
    contamination, the EPA has failed to ensure “no reasonable
    probability” of adverse effects to the environment, as RCRA
    requires. 42 U.S.C. § 6944(a).
    For these reasons, we vacate the Rule insofar as it treats
    “clay-lined” units as if they were lined. See 40 C.F.R.
    § 257.71(a)(1)(i).
    C. Legacy Ponds
    The EPA exempted inactive impoundments at inactive
    facilities, which are commonly referred to as “legacy ponds,”
    from the same preventative regulation applied to all other
    28
    inactive impoundments under the Rule.               40 C.F.R.
    § 257.50(e). The EPA considered it sufficient instead just (i)
    to wait to intervene until a substantial environmental or human
    harm is “imminent,” 42 U.S.C. § 6973, or (ii) to attempt to
    remediate the damage after contamination has occurred. 80
    Fed. Reg. at 21,311 n.1; 
    id. at 21,312
    n.2. Environmental
    Petitioners argue that, because legacy ponds pose at least the
    same risks of adverse effects as all other inactive
    impoundments, the EPA failed to articulate a rational
    explanation for their dissimilar treatment.
    The EPA does not dispute the dangers posed by the
    unregulated legacy ponds, but asserts that the difficulties in
    identifying the party responsible for legacy ponds justify its
    reactive approach. Because the EPA’s own record plainly
    contravenes that rationale, and the Rule pays scant attention to
    the substantial risk of harm to human health and the
    environment posed by legacy ponds, we reject the legacy pond
    exemption as arbitrary and capricious.
    1.
    Legacy ponds are a particular subset of inactive
    impoundments. Like all inactive impoundments, they contain
    a toxic “slurry” of Coal Residuals mixed with water, but legacy
    ponds are not receiving new deposits. 80 Fed. Reg. at 21,457
    n.219. What distinguishes legacy ponds from other inactive
    impoundments, then, is their location. Legacy ponds are
    found at power plants that are no longer engaged in energy
    production. In other words, legacy ponds are inactive
    impoundments at inactive facilities.
    As a result, legacy ponds present a unique confluence of
    risks: They pose the same substantial threats to human health
    and the environment as the riskiest Coal Residuals disposal
    29
    methods, compounded by diminished preventative and
    remediation oversight due to the absence of an onsite owner
    and daily monitoring. See 80 Fed. Reg. at 21,343–21,344
    (finding that the greatest disposal risks are “primarily driven
    by the older existing units, which are generally unlined”).
    Notably, this very Rule was prompted by a catastrophic legacy
    pond failure that resulted in a “massive” spill of 39,000 tons of
    coal ash and 27 million gallons of wastewater into North
    Carolina’s Dan River. 
    Id. at 21,394;
    id. at 21,393.
    
    Nevertheless, the EPA chose to leave legacy ponds on the
    regulatory sidelines. 40 C.F.R. § 257.50(e). Unlike all the
    other inactive impoundments, EPA adopted a largely hands-off
    approach, choosing (i) to respond only after “imminent”
    leakage is detected and reported, 42 U.S.C. § 6973(a) (RCRA’s
    “imminent and substantial endangerment” provision), or to (ii)
    attempt an after-the-spill clean up under the Comprehensive
    Environmental Response, Compensation, and Liability Act
    (commonly known as the “Superfund” statute), 42 U.S.C.
    § 9601 et seq. See 80 Fed. Reg. at 21,312 n.2 (citing 42 U.S.C.
    § 9608(b)).
    The EPA’s rationale for allowing legacy ponds, in effect,
    one free leak was its supposed inability to identify the owners
    of legacy ponds. In the absence of an identified owner or
    other responsible party, the EPA reasoned, enforcing the Coal
    Residuals regime would be difficult with no operator onsite to
    generate compliance certifications, conduct inspections, or
    otherwise implement the Rule’s substantive requirements.
    See 80 Fed. Reg. at 21,344.
    The EPA’s decision was arbitrary and capricious. To
    begin with, there is no gainsaying the dangers that unregulated
    legacy ponds present. The EPA itself acknowledges the vital
    importance of regulating inactive impoundments at active
    30
    facilities. That is because, if not properly closed, those
    impoundments will “significant[ly]” threaten “human health
    and the environment through catastrophic failure” for many
    years to come. 75 Fed. Reg. at 35,177; see also 80 Fed. Reg.
    at 21,344 n.40.
    The risks posed by legacy ponds are at least as substantial
    as inactive impoundments at active facilities. See 80 Fed.
    Reg. at 21,342–21,344 (finding “no[] measurabl[e]
    differen[ce]” in risk of catastrophic events between active and
    inactive impoundments). And the threat is very real. Legacy
    ponds caused multiple human-health and environmental
    disasters in the years leading up to the Rule’s promulgation.
    See 75 Fed. Reg. at 35,147 (proposed rule discusses multiple
    serious incidents). For example, a pipe break at a legacy pond
    at the Widows Creek plant in Alabama caused 6.1 million
    gallons of toxic slurry to deluge local waterways. 
    Id. Another legacy
    pond in Gambrills, Maryland caused the heavy
    metal contamination of local drinking water. 
    Id. And the
    preamble to the Rule itself specifically points to the
    catastrophic spill at the Dan River legacy pond in North
    Carolina. 80 Fed. Reg. at 21,393–21,394. Simply hoping
    that somehow there will be last-minute warnings about
    imminent dangers at sites that are not monitored, or relying on
    cleaning up the spills after great damage is done and the harm
    inflicted does not sensibly address those dangers. Certainly it
    does not fulfill the EPA’s statutory duty to ensure “no
    reasonable probability of adverse effects” to environmental
    and human well-being. 42 U.S.C. § 6944(a).
    Confronted by those considerable dangers, the EPA’s
    decision to shrug off preventative regulation makes no sense.
    The asserted difficulty in locating the owners or operators
    responsible for legacy ponds does not hold water. The record
    shows that the EPA knows where existing legacy ponds are
    31
    and, with that and other information, the EPA already is aware
    of or can feasibly identify the responsible parties. After all,
    the owners and operators of the Dan River, Widows Creek, and
    Gambrills, Maryland disasters were all known. See 80 Fed
    Reg. at 21,393–21,394; 75 Fed. Reg. at 35,147.
    Also, the EPA has been compiling and maintaining a
    database for nearly a decade that identifies legacy ponds and
    their owners with specificity. See Regulatory Impact Analysis
    for EPA’s Proposed RCRA Regulation of Coal Combustion
    Residues, Information Request Responses from Electric
    Utilities      (April       30,      2010),     available     at
    https://archive.epa.gov/epawaste/nonhaz/industrial/special/fos
    sil/web/xlsx/survey_database_041212.xlsx. The Final Rule’s
    Regulatory Impact Analysis named more than thirty other
    owners and operators of recently, or soon-to-be, retired power
    plants where more than 100 legacy ponds are located. This
    included a State-by-State list detailing the number of already-
    inactive impoundments, and the utility responsible for each
    one. See id.; see also J.A. 1104, 1119. The database further
    identified 83 power plants that were scheduled to “fully close
    all coal-fired” facilities by the time the Rule went into effect,
    over 75% of which would house a legacy pond upon closure.
    J.A. 1116.
    In sum, the EPA acknowledges that (i) it has the authority
    to regulate inactive units, (ii) it is regulating inactive units at
    active facilities, (iii) the risks posed by legacy ponds are at least
    as severe as the other inactive-impoundment dangers that the
    “[R]ule specifically seeks to address, and [(iv)] there is no
    logical basis for distinguishing between units that present the
    same risks.” 80 Fed. Reg. at 21,343. The EPA also considers
    it “quite clear” that older, unlined impoundments, Oral Arg. Tr.
    at 94:22—which are primarily legacy ponds—pose “the
    greatest risks to human health and the environment,” 80 Fed.
    32
    Reg. at 21,451. Because the administrative record belies the
    EPA’s stated reason for its reactive, rather than preventative,
    approach—the inability to identify the responsible parties—the
    Rule’s legacy ponds exemption is unreasoned, arbitrary, and
    capricious.
    D. Inadequate Notice by Owners and Operators
    Because of RCRA’s reliance on citizen enforcement, the
    statute requires the EPA to “develop and publish minimum
    guidelines for public participation” in the “development,
    revision, implementation, and enforcement” of any RCRA
    regulation. 42 U.S.C. § 6974(b)(1). The EPA implements
    that statutory requirement, as relevant here, by requiring the
    owners of Coal Residuals units to “maintain a publicly
    accessible Internet site” on which they timely disclose
    specified information about their compliance with RCRA
    regulations. 40 C.F.R. § 257.107(a).
    The Environmental Petitioners wage several assaults on
    the Rule’s Internet notice requirements, arguing that they do
    not provide adequate or timely notice to permit the public to
    participate in monitoring compliance with the Rule. For
    example, the Environmental Petitioners object that the Rule
    does not require owners or operators of new Coal Residual
    impoundments to post a design certification—an engineer’s
    certification that the impoundment’s liner meets the EPA’s
    criteria—until sixty days after construction begins. 40 C.F.R.
    § 257.107(f)(1); see 40 C.F.R. § 257.70. That is too late, the
    Environmental Petitioners argue, to put the public on effective
    notice of any potential design problems. They also object that
    the Rule does not require timely public notification about the
    design or liner compliance of impoundment expansions, the
    structural integrity of facilities, protections against airborne
    33
    coal dust, run-off control, hydraulic capacity requirements, or
    the nature of groundwater monitoring efforts.
    The problem for Environmental Petitioners is that,
    although they participated in the notice-and-comment
    rulemaking process, they never voiced objections to the Rule’s
    notice provisions that they now challenge. Having stood
    silent during the rulemaking, the Environmental Petitioners
    may not now raise their complaints for the first time in their
    petition for judicial review. See Military Toxics Project v.
    EPA, 
    146 F.3d 948
    , 956 (D.C. Cir. 1998); see also City of
    Portland v. EPA, 
    507 F.3d 706
    , 710 (D.C. Cir. 2007) (“Because
    [no] party raised this argument before the [EPA] during the
    rulemaking process, however, it is waived, and we will not
    consider it.”). The sanction does not exist as a procedural
    trap; the notice-and-comment process is in place so that the
    agency can consider and—if necessary—revise its proposed
    rule in light of public comments. United States v. L.A. Tucker
    Truck Lines, Inc., 
    344 U.S. 33
    , 37 (1952) (“[O]rderly
    procedure and good administration require that objections to
    the proceedings of an administrative agency be made while it
    has opportunity for correction in order to raise issues
    reviewable by the courts.”). The EPA reasonably focuses its
    resources on consideration and/or modification of challenged
    portions of a proposed rule rather than unchallenged and
    apparently uncontroversial portions thereof. See Interstate
    Nat. Gas Ass’n of Am. v. FERC, 
    494 F.3d 1092
    , 1096 (D.C.
    Cir. 2007) (agency must respond to material comments only).
    Accordingly, we will not address this claim.
    IV. Industry Petitioners’ Challenges
    Industry Petitioners bring a host of their own challenges to
    the Rule. As noted, these claims have dwindled over the
    course of this litigation. At the start, Industry Petitioners
    34
    challenged eighteen provisions of the Final Rule and
    questioned the EPA’s statutory authority to regulate inactive
    surface impoundments. 4 In response, the EPA filed an
    unopposed motion to sever and remand two aspects of the Final
    Rule (regarding five regulatory provisions). On June 14,
    2016, we granted the motion. Industry Petitioners continued
    to challenge the thirteen remaining substantive provisions as
    well as to attack the EPA’s statutory authority. In the parties’
    proposed oral argument structure, however, Industry
    Petitioners moved to dismiss two additional challenges
    (regarding three regulatory provisions). We granted that
    motion as well.
    Accounting for these interim trims, Industry Petitioners
    now assert that the EPA (i) lacks authority to regulate inactive
    impoundments; (ii) failed to provide sufficient notice of its
    intention to apply the aquifer location criteria to existing
    impoundments, to regulate Coal Residual piles of 12,400 or
    more tons, and to regulate the temporary storage of Coal
    4
    Industry Petitioners’ initial brief challenged portions of the
    following regulations: 40 C.F.R. §§ 257.50(c), 257.100 (inactive
    impoundments); 40 C.F.R. § 257.53 (definition of “beneficial use”
    and regulation of CCR “pile”); 40 C.F.R. § 257.60 (aquifer location
    restrictions); 40 C.F.R. §§ 257.73(e), (f)(1), 257.74(e) (minimum
    safety factors); 40 C.F.R. §§ 257.90(d), 257.96(a) (“release”
    response); 40 C.F.R. §§ 257.73(a)(4), 257.74(a)(4) (dike
    requirements); 40 C.F.R. § 257.103(a)(1)(i), (b)(1)(i) (prohibition on
    considering cost and inconvenience); 40 C.F.R. § 257.63(a) (seismic
    impact zone landfill requirements); 40 C.F.R. § 257.63(c)(1)
    (seismic impact zone deadline); 40 C.F.R. § 257.103 (inclusion of
    non-Coal Residuals waste streams in alternative closure provision);
    40 C.F.R. §§ 257.95(h)(2), 257.97 (exclusion of risk-based
    compliance alternatives).
    35
    Residuals destined for beneficial use; and (iii) acted arbitrarily
    in regulating residual piles of 12,400 or more tons, in
    regulating on-site Coal Residuals destined for beneficial use,
    in eliminating the risk-based compliance alternatives, in
    issuing location requirements based on seismic impact zones,
    and in imposing temporary closure procedures.5
    The EPA, now supported in part by Industry Petitioners,
    requests a remand of several of those issues, namely whether
    (i) the EPA has statutory authority to regulate inactive
    impoundments, (ii) the EPA arbitrarily regulated Coal
    Residuals piles of 12,400 or more tons, (iii) the EPA arbitrarily
    regulated on-site Coal Residuals destined for beneficial use,
    and (iv) the EPA arbitrarily eliminated risk-based compliance
    alternatives.
    We grant the request for voluntary remand of the Coal
    Residuals pile-size and beneficial-use issues, and we dismiss
    as moot both the claim regarding risk-based compliance
    alternatives and the accompanying notice challenges. As to
    all remaining issues, we deny remand, and we deny the
    Industry Petitioners’ petition for review.
    A. EPA’s Motion for Voluntary Remand
    We have broad discretion to grant or deny an agency’s
    motion to remand. See Limnia, Inc. v. Department of Energy,
    
    857 F.3d 379
    , 381, 386 (D.C. Cir. 2017). We generally grant
    an agency’s motion to remand so long as “the agency intends
    5
    These challenges encompass the following regulations (or
    portions thereof): 40 C.F.R. §§ 257.50(c), 257.100 (inactive
    impoundments); 40 C.F.R. § 257.103(a)(1)(i), (b)(1)(i) (alternative
    closure requirements); 40 C.F.R. § 257.63(a), (c)(1) (seismic impact
    zone requirements).
    36
    to take further action with respect to the original agency
    decision on review.” 
    Id. (emphasis omitted).
    Remand has
    the benefit of allowing “agencies to cure their own mistakes
    rather than wasting the courts’ and the parties’ resources
    reviewing a record that both sides acknowledge to be incorrect
    or incomplete.” Ethyl Corp. v. Browner, 
    989 F.2d 522
    , 524
    (D.C. Cir. 1993). Remand may also be appropriate if the
    agency’s motion is made in response to “intervening events
    outside of the agency’s control, for example, a new legal
    decision or the passage of new legislation.” SKF USA Inc. v.
    United States, 
    254 F.3d 1022
    , 1028 (Fed. Cir. 2001)
    (discussing National Fuel Gas Supply Corp. v. FERC, 
    899 F.2d 1244
    , 1249 (D.C. Cir. 1990) (per curiam)). Alternatively,
    “even if there are no intervening events, the agency may
    request a remand (without confessing error) in order to
    reconsider its previous position.” 
    Id. at 1029.
    In deciding a motion to remand, we consider whether
    remand would unduly prejudice the non-moving party.         See
    FBME Bank Ltd. v. Lew, 
    142 F. Supp. 3d 70
    , 73 (D.D.C. 2015).
    Additionally, if the agency’s request appears to be frivolous or
    made in bad faith, it is appropriate to deny remand. See SKF
    
    USA, 254 F.3d at 1029
    ; see also Lutheran Church-Missouri
    Synod v. FCC, 
    141 F.3d 344
    , 349 (D.C. Cir. 1998) (denying
    FCC’s “novel, last second motion to remand” because it was
    based on agency’s non-binding prospective policy statement).
    To start, we decline the EPA’s request to remand the
    challenge to the agency’s authority to regulate inactive
    impoundments so that it can reconsider its interpretation of the
    statute, for two reasons. First, the EPA’s statutory authority
    over inactive sites necessarily implicates the Environmental
    Petitioners’ claim regarding legacy ponds. So, even if
    Industry Petitioners are willing to go along with a remand,
    Environmental Petitioners are not and remand would prejudice
    37
    the vindication of their own claim. Second, this claim
    involves a question—the scope of the EPA’s statutory
    authority—that is intertwined with any exercise of agency
    discretion going forward. Given that, the EPA has not met its
    burden of justifying its last-minute request for a remand in this
    case, and we proceed to the merits on this issue.
    The EPA also initially requested a remand of its decision
    to exclude certain risk-based compliance measures. On July
    30, 2018, however, the EPA promulgated amendments to the
    Final Rule. See Hazardous and Solid Waste Management
    System: Disposal of Coal Combustion Residuals From
    Electric Utilities; Amendments to the National Minimum
    Criteria (Phase One, Part One) (“Final Rule Amendments”), 83
    Fed. Reg. 36,435 (July 30, 2018).             The Final Rule
    Amendments provide certain risk-based compliance measures
    and site-specific engineering certifications. Accordingly, we
    dismiss as moot Industry Petitioners’ challenge to 40 C.F.R.
    §§ 257.95(h) and 257.97. See National Min. Ass’n v.
    Department of Interior, 
    251 F.3d 1007
    , 1011 (D.C. Cir. 2001)
    (dismissing challenges as moot due to “substantial changes” in
    regulations and declaring “[a]ny opinion regarding the former
    rules would be merely advisory”).
    For the remaining requests—(i) the regulation of Coal
    Residuals piles; (ii) the Proposed Rule’s notice of the Coal
    Residuals pile regulation; and (iii) the 12,400-ton threshold for
    beneficial use (and notice thereof)—we grant the EPA’s
    motion to remand.6 First and foremost, the EPA has explained
    that it plans to reconsider these provisions and has submitted a
    6
    Specifically, we remand without vacating 40 C.F.R § 257.53
    (definition of “beneficial use” and regulation of Coal Residuals
    “pile”).
    38
    proposed timeline to the court, thereby satisfying the
    requirement for remand that it “take further action with respect
    to the original agency decision on review.” 
    Limnia, 857 F.3d at 386
    (emphasis omitted). Second, although the WIIN Act
    does not affect the validity of the Rule itself, it does provide
    the EPA with new tools to pursue its regulatory goals. See 42
    U.S.C. § 6945(d)(4) (incorporating enforcement provisions of
    Sections 6927 and 6928).7
    The EPA has explained that the Final Rule was
    promulgated with the understanding that there would be no
    regulatory “overseer,” and therefore the Final Rule itself
    should “account for and be protective of all sites, including
    those that are highly vulnerable.” 80 Fed. Reg. at 21,311; 
    id. (explaining how
    “the requirement to establish national criteria
    and the absence of any requirement for direct regulatory
    oversight” influenced the Final Rule). Although a one-size-
    fits-all national standard might have been necessary for the
    self-implementing Final Rule, more precise risk-based
    standards are both feasible and enforceable under the
    individualized permitting programs and direct monitoring
    provisions authorized by the WIIN Act. See Oral Arg. Tr.
    37:12–37:14 (counsel for EPA explaining that certain
    provisions of the Final Rule “cry out for site specific
    enforcement”). Thus, the regulatory tools authorized by the
    WIIN Act support the EPA’s request to reconsider certain
    provisions of the Rule. See SKF 
    USA, 254 F.3d at 1028
    .
    7
    On March 23, 2018, the Consolidated Appropriations Act of
    2018 was signed into law. Pub. L. No. 115-141, 132 Stat. 348. It
    allocates funds to the EPA to “implement[] a coal combustion
    residual permit program under” the WIIN Act. 
    Id. at Division
    G,
    Title II. Accordingly, with its recently acquired funding, the EPA
    is to “implement a permit program” in non-participating states. 42
    U.S.C. § 6945(d)(2)(B).
    39
    Moreover, the provisions we now remand stand
    unchallenged on their merits; accordingly, no party will suffer
    prejudice from remand without vacatur. See FBME 
    Bank, 142 F. Supp. 3d at 73
    . Indeed, at this stage in the litigation, all
    parties agree that the “beneficial use” and “Coal Residuals
    pile” provisions should stay in effect—at least until a new rule
    is promulgated. See EPA Remand Mot. 2 (“EPA seeks
    remand of these provisions without vacatur, and thus they
    remain in place and fully applicable[.]”). Moreover, the only
    parties that object to remand—Environmental Petitioners—did
    not challenge any of the relevant provisions in their petition;
    rather they defended the provisions as Intervenors. See
    generally Envtl. Intervenor-Resp’t Br. 14–22. Accordingly,
    any opinion we issue regarding these provisions would be
    wholly advisory; it would resolve no active case or controversy
    and would award no relief. See Chafin v. Chafin, 
    568 U.S. 165
    , 172 (2013) (case is non-justiciable if court is unable to
    grant concrete relief to any party).
    We conclude that there is no reason to opine on the
    “beneficial use” and “Coal Residuals pile” provisions that the
    EPA wants remanded. At oral argument, the court pressed
    Industry counsel as to why Industry Petitioners did not simply
    dismiss their petition rather than acquiescing in the EPA’s
    motion. Oral Arg. Tr. 49–52. Industry counsel did not
    provide a clear answer. But he did make two concessions:
    First, he declared that Industry does not oppose remand. 
    Id. at 50:16–50:23.
    Second, he acknowledged, “on a remand * * *
    the petition * * * is dismissed as a practical matter.” 
    Id. at 51:6–51:10
    (emphasis added). Counsel is correct in one
    respect.    When combined with the statutory provision
    requiring any challenge to be brought within 90 days of the
    Rule’s promulgation, the legal effect of remand without
    vacatur is simple: The Rule remains in force and Industry
    Petitioners cannot bring another challenge until and unless the
    40
    EPA takes additional regulatory action.            42 U.S.C.
    § 6976(a)(1) (petition for review “shall be filed within ninety
    days from the date of * * * promulgation”). In effect, Industry
    Petitioners have withdrawn their petition with respect to the
    provisions for which it does not oppose remand.
    Accordingly, we deny the EPA’s motion to remand to
    itself Industry Petitioners’ challenge to the EPA’s regulation of
    inactive impoundments and Environmental Petitioner’s
    challenge to the non-regulation of legacy ponds. We
    otherwise grant the motion to remand without vacatur.
    B.   Substantive Challenges
    After deciding the issue of remand, we are left with
    Industry Petitioners’ statutory argument and its three APA
    challenges to the Final Rule.
    1. Authority to Regulate Inactive Impoundments
    Industry Petitioners first challenge the EPA’s regulatory
    authority to set any standards at all for inactive impoundments.
    That claim is without merit. Because those inactive sites
    house waste in “open dumps,” 42 U.S.C. § 6944, RCRA’s
    plain text unambiguously confers regulatory authority on the
    EPA.
    By its terms, RCRA empowers the EPA generally to
    define “which facilities shall be classified as sanitary landfills
    and which shall be classified as open dumps[.]” 42 U.S.C.
    § 6944. Section 6943 of RCRA, in turn, incorporates those
    classification standards into minimum criteria for State
    regulatory plans. 
    Id. § 6943.
    Those statutory minimums
    both require States to “provide for the closing or upgrading of
    all existing open dumps” and prohibit “the establishment of
    41
    new open dumps[.]” 
    Id. § 6943(a)(2),
    (3). The statute also
    provides that, “[a]t a minimum,” the EPA must define sanitary
    landfills to include only facilities where “there is no reasonable
    probability of adverse effects on health or the environment
    from disposal of solid waste[.]” 42 U.S.C. § 6944(a). 8 In
    this way, the statute creates a binary world: A facility is a
    permissible sanitary landfill, or it is an impermissible open
    dump. The EPA regulates both.
    While the statute allows the EPA to establish criteria for
    distinguishing between “open dumps” and “sanitary landfills,”
    it also offers some definitions of its own. RCRA defines
    “open dump” as “any facility or site where solid waste is
    disposed of which is not a sanitary landfill” or a site regulated
    under RCRA Subtitle C’s more rigorous hazardous waste
    provisions. 42 U.S.C. § 6903(14). The statute likewise
    defines “sanitary landfill” as “a facility for the disposal of solid
    waste [that] meets the criteria published under section 6944,”
    
    id. § 6903(26),
    and that operates in accordance with the
    “applicable criteria for coal combustion residuals units under”
    40 C.F.R. Part 257 or its successor regulations, 
    id. § 6945(d)(6).
    Finally, RCRA defines “disposal” as “the discharge,
    deposit, injection, dumping, spilling, leaking, or placing of any
    solid waste or hazardous waste into or on any land or water” in
    a manner by which “such solid waste or hazardous waste or
    any constituent thereof may enter the environment[.]” 42
    U.S.C. § 6903(3).
    8
    As noted earlier, supra, Part II, we leave open on remand the
    definitional and substantive impact on the EPA’s discretion of the
    WIIN Act’s express incorporation of the extant or successor EPA
    regulations under 40 C.F.R. Part 257 into the statutory definition of
    “sanitary landfill.”
    42
    Notwithstanding that broad assignment of regulatory
    authority, see 42 U.S.C. § 6912, Industry Petitioners argue that
    “inactive” impoundments—sites that contain, but no longer
    receive new, solid waste—cannot be “open dumps” within the
    EPA’s regulatory ambit. Seizing on the phrase “is disposed
    of” in the definition of an “open dump,” 
    id. § 6903(14),
    they
    contend that the site must actively receive new waste to come
    within the statutory definition of a regulable waste disposal
    dump. Industry Petitioners also argue that the words used to
    define “disposal”—“discharge, deposit, injection, dumping,
    spilling, leaking, or placing,” 
    id. § 6903(3)—all
    require present
    and ongoing activity.
    RCRA’s reach, however, is not so narrow as Industry
    Petitioners suppose. Rather, a straightforward reading of the
    statute’s language allows for the regulation of inactive sites.
    We start by recognizing that, in RCRA, Congress
    delegated to the EPA “very broad” regulatory authority over
    waste disposal. In re Consolidated Land Disposal Regulation
    Litig., 
    938 F.2d 1386
    , 1388 (D.C. Cir. 1991). We therefore
    review the Industry Petitioners’ challenge under the two-step
    Chevron framework.          Under this rubric, if RCRA is
    unambiguous, its text controls. See Chevron, U.S.A., Inc. v.
    Natural Res. Def. Council, Inc., 
    467 U.S. 837
    , 842–843 (1984);
    see also City of Arlington v. FCC, 
    569 U.S. 290
    , 297 (2013)
    (holding that an agency’s interpretation of the “jurisdictional”
    reach of its governing statute merits Chevron deference). If,
    on the other hand, the statute is silent or equivocal, we ask only
    whether the agency has offered a reasonable interpretation of
    the statute. 
    Chevron, 467 U.S. at 843
    .
    Resolution of this issue begins and ends with RCRA’s
    plain text. The definition of “open dump,” which is the key
    43
    term at issue, does not use the word “disposal.” It uses the
    phrase “is disposed of”: An “open dump” is “any facility or
    site where solid waste is disposed of[.]” 42 U.S.C. § 6903(14)
    (emphasis added). To divine its proper meaning, we must
    interpret the operative phrase “is disposed of” as a whole.
    Importantly, while the “is” retains its active present tense, the
    “disposal” takes the form of a past participle (“disposed”). In
    this way, the disposal itself can exist (it “is”), even if the act of
    disposal took place at some prior time. See Florida Dep’t of
    Revenue v. Piccadilly Cafeterias, Inc., 
    554 U.S. 33
    , 39 (2008)
    (describing a past participle as a “verb form” that reaches “past
    or completed action”) (quoting AMERICAN HERITAGE
    DICTIONARY 1287 (4th ed. 2000)); Sherley v. Sebelius, 
    644 F.3d 388
    , 403 n.4 (D.C. Cir. 2011) (Henderson, J., dissenting)
    (noting that the statute at issue “combine[d] the present tense
    ‘are’ with the past participle ‘destroyed’” to “signify conduct
    that ha[d] already occurred”) (citations omitted).9
    Properly translated then, an open dump includes any
    facility (other than a sanitary landfill or hazardous waste
    disposal facility), where solid waste still “is deposited,” “is
    9
    The concurring opinion notes that Piccadilly Cafeterias was
    ultimately resolved as a Chevron step two case. Concur Op. 4 n.1.
    True enough. But before the Court got to the Chevron step two
    stage of its analysis, it first endorsed, as the “more natural reading”
    of the relevant text, Florida’s construction of the past participle as
    “unambiguously limit[ing]” certain tax exemptions in bankruptcy
    
    proceedings. 554 U.S. at 39
    , 41. Only then did the Court, for
    argument’s sake, “assum[e]” that the relevant text were
    “ambiguous,” and hold that any ambiguity would fall in Florida’s
    favor. 
    Id. at 41.
    The Court, in short, never found any ambiguity in
    the past participle’s coverage of “past or completed action[s],” and
    in fact embraced that more natural meaning. 
    Id. at 39.
    We too give
    Congress’s adjectival past participle “is disposed of” its natural
    meaning.
    44
    dumped,” “is spilled,” “is leaked,” or “is placed,” regardless of
    when it might have originally been dropped off. See 42
    U.S.C. § 6903(3), (14). In other words, the waste in inactive
    impoundments “is disposed of” at a site no longer receiving
    new waste in just the same way that it “is disposed of” in at a
    site that is still operating.
    Tellingly, not even Industry Petitioners embrace the full
    import of their interpretation. They agree that previously
    deposited waste “is disposed of” at an impoundment site, so
    long as the site is actively accepting new waste. But if EPA’s
    authority reaches only active disposal, it stands to reason that
    its authority over the site extends only to that newly deposited
    (or actively leaking) waste. But Industry Petitioners do not
    push this point—probably because, as a practical reality, waste
    is no less “disposed of” at a site the day after operations cease
    than it was the day before. That is, the waste previously
    dumped is still currently “placed” or “deposited” there. 42
    U.S.C. § 6903(3), (14). In other words, the pile of Coal
    Residuals retains its regulated status whether or not anyone
    adds to the pile.
    Think of it this way: If a kindergarten teacher tells her
    students that they must clean up any drink that “is spilled” in
    the room, that would most logically be understood to mean that
    a student must clean up her spilled drink even if the spill is
    already completed and nothing more is leaking out of the
    carton. A student who refused to clean up that completed spill
    (as Industry Petitioners would have it) might well find himself
    on time out.
    What’s more, the Industry Petitioners’ reading butts up
    against the binary world created by the statute. RCRA creates
    two categories for Subtitle D waste: open dumps and sanitary
    landfills. Industry Petitioners offer no explanation of where
    45
    “inactive” sites fit into their understanding of that landscape.
    Nor do they explain why, once the last person turns off the
    lights, Congress’s concern for the substantial health and
    environmental dangers posed by that pile of toxic waste would
    completely evaporate. As our concurring colleague aptly
    notes, “the disposal of [Coal Residuals] in an impoundment is
    not a discrete act. If it were, the EPA would regulate only the
    transfer of [Coal Residuals] from a power facility into an
    impoundment, at which point the ‘disposal’ would end.”
    Concur Op. at 8.
    The concurring opinion spies ambiguity only by splitting
    the operative verb “is disposed” into two distinctly analyzed
    parts: “is” and “disposed.” Concur Op. 2–4. But just as
    courts must not “construe statutory phrases in isolation,” we
    surely must read a single verb “as a whole” and not in pieces.
    United States v. Morton, 
    467 U.S. 822
    , 828 (1984). Even
    more so, we must give effect to the whole adjectival phrase “is
    disposed of.” A site where garbage “is disposed of” is the
    place where garbage is dumped and left. The status of that site
    does not depend on whether or not more garbage is later piled
    on top. A garbage dump is a garbage dump until the deposited
    garbage is gone.
    In short, as facilities “where solid waste is disposed of,”
    42 U.S.C. § 6903(14), inactive impoundments are “open
    dumps,” unless they fall into one of two statutory exceptions—
    neither of which the Industry Petitioners claim applies to their
    inactive impoundments. 10 And no one denies that the EPA
    has authority to regulate (and to prohibit) “open dumps.”
    10
    The two exceptions, which Industry Petitioners do not
    contend apply here, are for “sanitary landfills,” as defined by the
    46
    Instead, the Industry Petitioners point to cases interpreting
    the term “disposal” in the Superfund statute, 42 U.S.C. § 9601
    et seq., to apply only to ongoing disposals. True enough. But
    those cases turned on the Superfund statute’s different
    language, which is “at the time of disposal,” not the RCRA
    phrase “is disposed of.” See 
    id. § 9607(a)
    (responsible
    persons subject to recovery costs under the Superfund statute
    include “any person who at the time of disposal of any
    hazardous substance owned or operated any facility at which
    such hazardous substances were disposed of”). The specific
    signification of that language lies at the heart of those court
    rulings. See Carson Harbor Vill., Ltd. v. Unocal Corp., 
    270 F.3d 863
    , 871 (9th Cir. 2001) (“We must decide in this case
    whether the Partnership Defendants * * * owned the
    contaminated property ‘at the time of disposal of any hazardous
    substance.’”) (citing 42 U.S.C. § 9607(a)(2)).11
    The Superfund statute also contains an “innocent
    landowner” defense by which a person can avoid liability if
    “the disposal or placement of the hazardous substance”
    occurred prior to that party’s acquisition of the property. 42
    U.S.C. § 9601(35)(A). That strengthens the notion that “at the
    time of disposal,” as used in the Superfund statute, is time-
    EPA, 42 U.S.C. § 6944, and sites housing “hazardous” waste
    regulated separately under RCRA Subtitle C, 
    id. § 6921
    et seq.
    11
    See also ABB Indus. Sys., Inc. v. Prime Tech., Inc., 
    120 F.3d 351
    , 356 (2d Cir. 1997) (“Under [the Superfund statute], a prior
    owner or operator is a responsible party if it controlled the site ‘at the
    time of disposal’ of a hazardous substance.”); United States v.
    CDMG Realty Co., 
    96 F.3d 706
    , 712–713 (3d Cir. 1996) (“HMAT
    contends that Dowel is liable as a person who owned or operated the
    facility ‘at the time of disposal’ of a hazardous substance.”); Joslyn
    Mfg. Co. v. Koppers Co., 
    40 F.3d 750
    , 760 (5th Cir. 1994) (similar).
    47
    dependent and refers to the act of placing the waste in the
    holding site. See Carson Harbor 
    Vill., 270 F.3d at 882
    .
    RCRA’s distinct language comes with no such limiting textual
    indicia.
    In short, the fundamental flaw in the Industry Petitioners’
    effort to limit EPA regulation to active impoundments is that
    they focus on the wrong text. For all their efforts to explain
    the meaning of the single word “disposal,” they fail to grapple
    with the full phrase “is disposed of.” RCRA is explicit that
    inactive sites may qualify as open dumps if they are facilities
    where waste “is disposed of,” regardless of whether they are
    also facilities where more “disposal” continues to occur. As
    is often true in statutory interpretation, the words make all the
    difference.
    Even if the text were ambiguous, the EPA’s interpretation
    is eminently reasonable under Chevron step two. First, the
    same reasons supporting our interpretation of the plain
    statutory text demonstrate with even greater force the
    reasonableness of the EPA’s interpretation.
    Second, the EPA’s interpretation directly advances
    RCRA’s stated regulatory purpose. RCRA directs the EPA to
    develop standards that limit permissible waste sites “[a]t a
    minimum” to those with “no reasonable probability of adverse
    effects on health or the environment from disposal of solid
    waste[.]” 42 U.S.C. § 6944(a). No one denies that inactive
    impoundments can have significant adverse environmental and
    health effects. In fact, the EPA persuasively explains that
    inactive sites often pose even greater health risks given their
    age and accompanying deterioration. 80 Fed. Reg. at 21,343
    (indicating that “the risks are primarily driven by the older
    existing units”); see also 
    id. (noting that
    leaks into the Dan
    48
    River from an inactive impoundment occasioned publication of
    this very Rule).
    The EPA’s construction of the text is thus consistent with
    a straightforward reading of statutory text and RCRA’s central
    purpose. See In re Consolidated Consol. Land Disposal
    Regulation 
    Litig., 938 F.2d at 1389
    (EPA’s reading of the term
    “disposal” in RCRA’s Subtitle C, 42 U.S.C. § 6924, to include
    “the continuing presence of waste” was reasonable under
    Chevron step two).
    For all of those reasons, the Industry Petitioners’ attempt
    to confine the EPA’s authority to only active impoundments
    fails.
    2. Notice Challenge to Aquifer Requirements
    Under 5 U.S.C. § 553, an agency is required to give notice
    of a proposed rule and allow interested parties to comment on
    the rule before it is promulgated. Although the final rule need
    not be identical to the proposed rule, it must be the “logical
    outgrowth” thereof. Shell Oil Co. v. EPA, 
    950 F.2d 741
    , 747
    (D.C. Cir. 1991) (per curiam). “A rule is deemed a logical
    outgrowth if interested parties ‘should have anticipated’ that
    the change was possible, and thus reasonably should have filed
    their comments on the subject during the notice-and-comment
    period.” Northeast Md. Waste Disposal Auth. v. EPA, 
    358 F.3d 936
    , 952 (D.C. Cir. 2004) (per curiam) (citing City of
    Waukesha v. EPA, 
    320 F.3d 228
    , 245 (D.C. Cir. 2003)).
    The Final Rule requires that all surface impoundments be
    located no fewer than five feet above the uppermost aquifer or,
    alternatively, that the owner or operator of the impoundment
    demonstrate that the impoundment will not be subject to a
    hydraulic connection with the groundwater supply as
    49
    groundwater levels fluctuate over the course of the year.12 40
    C.F.R. § 257.60(a); see 80 Fed. Reg. at 21,361. Industry
    Petitioners argue that the EPA did not give adequate notice that
    this provision would apply to existing surface impoundments
    because the proposed regulation applied only to “[n]ew [Coal
    Residuals] landfills and new [Coal Residuals] surface
    impoundments[.]” 75 Fed. Reg. at 35,241.13
    The Industry Petitioners’ argument ignores the plain
    language of the preamble to the Proposed Rule, which declares:
    “[b]y contrast [to landfills] * * * the proposed regulations
    would apply all of the location restrictions to existing surface
    impoundments.” 75 Fed. Reg. at 35,198 (emphasis added).
    This is exactly what the Final Rule prescribes. See 40 C.F.R.
    § 257.60. Indeed, the Rule is not only the “logical outgrowth”
    of the Proposed Rule; it faithfully tracks the goals set forth in
    the preamble. See Shell Oil 
    Co., 950 F.2d at 747
    . The
    preamble—and the Proposed Rule as a whole—advised the
    12
    A “hydraulic connection” means a connection between the
    [Coal Residuals] unit and the underground water table. 80 Fed.
    Reg. at 21,362. The EPA received comments explaining that
    “fluctuations in groundwater levels in many geological settings can
    exceed ten feet over the course of the year.” 
    Id. at 21,361.
    To
    account for this change in aquifer levels, the EPA revised its
    definition of “uppermost aquifer” to “specify that the measurement
    of the upper limit of the aquifer must be made at a point nearest to
    the natural ground surface to which the aquifer rises during the wet
    season.” 
    Id. at 21,362.
         13
    In the preamble to the Final Rule, the EPA acknowledged
    that, “[i]n the proposed rule, the regulatory language should have
    included ‘all surface impoundments’ as opposed to only ‘new
    surface impoundments.’” 80 Fed. Reg. at 21,360.
    50
    public that the EPA was at least considering applying the
    aquifer restrictions to existing impoundments, thereby inviting
    Industry’s comments on the topic. Id.14
    3. Seismic Impact Zone Criteria
    The Final Rule contains two seismic impact requirements.
    First, the Rule imposes safety assessment criteria on surface
    impoundments over a specific size. 40 C.F.R. § 257.73(e).
    These criteria had an implementation deadline of October 17,
    2016. 
    Id. § 257.73(f).
    Because the compliance deadline
    lapsed before oral argument, Industry Petitioners voluntarily
    dismissed this challenge. See Sept. 27, 2017 Per Curiam
    Order Granting Motion to Dismiss.
    Second, every new Coal Residual landfill and landfill
    expansion, as well as any new and existing surface
    14
    Although the EPA may not “bootstrap notice from a
    comment,” the sheer volume of Industry Petitioners’ comments on
    this very provision confirms that notice was adequate. Fertilizer
    Inst. v. EPA, 
    935 F.2d 1303
    , 1312 (D.C. Cir. 1991) (internal
    quotation marks omitted). The EPA explains: “Overwhelmingly,
    the issue receiving the most comment was EPA’s intention to subject
    existing [Coal Residuals] surface impoundments to all of the new
    location criteria.” 80 Fed. Reg. at 21,360. Industry Petitioners’
    comments confronted the aquifer location restrictions, including
    their applicability to existing surface impoundments, head-on. See,
    e.g., Comments of the Utility Solid Waste Activities Group on
    Proposal, Nov. 19, 2010, J.A. 775 (“EPA states in the preamble to
    the proposal that it intends to subject existing surface impoundments
    to all of these new location restrictions * * * .”) (emphasis omitted).
    When combined with the clarity of the preamble, Industry
    Petitioners’ comments illustrate that it was both aware of, and
    troubled by, the aquifer restrictions.
    51
    impoundment, is subject to location restrictions that prohibit
    operation in a “seismic impact zone” 15 unless the facility
    demonstrates that it has the appropriate structural components,
    including liners, leachate collection and removal systems and
    surface water control systems. 40 C.F.R. § 257.63(a). For
    existing surface impoundments, the deadline for demonstrating
    compliance with the Rule is October 17, 2018—four and one-
    half years after the Rule was promulgated. 
    Id. § 257.63(c)(1).
    Industry Petitioners attack the seismic impact zone
    requirements on three fronts; they argue that the EPA was
    arbitrary and capricious in: (i) shortening the operating life
    for existing impoundments from five years to four years; (ii)
    applying the seismic impact zone location restriction to new
    Coal Residual landfills and landfill expansions; and (iii)
    regulating the structure of Coal Residual landfills based on a
    2,500-year seismic event. The parties brief these three issues
    separately, and we likewise address—but reject—each of
    Industry Petitioners’ challenges in turn.
    a. Operating Expiration
    Industry Petitioners argue that, although the Proposed
    Rule had a five-year operating expiration for impoundments,
    the Final Rule arbitrarily reduced that window to four years.
    Industry Pet’rs’ Br. 45. As a corollary, Industry Petitioners
    argue that four years is not enough time for impoundment
    owners and operators to switch from wet to dry Coal Residuals
    disposal. Industry Pet’rs’ Reply Br. 21–22.
    15
    “Seismic impact zone means an area having a 2% or greater
    probability that the maximum expected horizontal acceleration,
    expressed as a percentage of the earth’s gravitational pull (g), will
    exceed 0.10 g in 50 years.” 40 C.F.R. § 257.53.
    52
    Industry Petitioners’ arguments misconstrue both the
    Proposed Rule and the Final Rule. The section of the
    Proposed Rule that Industry Petitioners cite for the five-year
    deadline (proposed 40 C.F.R. § 257.65(a)) does not apply to
    the seismic impact zones; instead, it applies to “unstable areas.”
    See 75 Fed. Reg. at 35,242–35,243. Indeed, the Proposed
    Rule does not prescribe an explicit operating deadline for
    seismic impact zones at all.
    Moreover, even assuming the proposed five-year deadline
    for “unstable areas” applies to seismic impact zones, the
    Proposed Rule reads: “Existing [Coal Residuals] landfills and
    surface     impoundments        that    cannot      make       the
    demonstration * * * must close by [date five years after the
    effective date of the final rule].” 75 Fed. Reg. at 35,242
    (brackets in original). The “must close by” language in the
    Proposed Rule is different from the language of the Final Rule,
    which demands only that the regulated facility “complete the
    demonstration [that the site has met the relevant structural
    requirements] no later than October 17, 2018.” 40 C.F.R.
    § 257.63(c)(1).        Contrary to Industry Petitioners’
    representation, then, the Final Rule gives the disposal sites four
    years before they must demonstrate compliance. See 
    id. Only if
    they fail in that demonstration must they begin the
    closure process. 
    Id. And once
    the closure process begins,
    they have at least five years to complete it. See 
    id. § 257.102(f)(1)(ii).16
    16
    Manifesting additional flexibility, the Final Rule’s closure
    timeframe may be extended up to ten years (in consecutive two-year
    periods) “if the owner or operator can demonstrate that it was not
    feasible to complete closure of the [Coal Residuals] unit within the
    required timeframes due to factors beyond the facility’s control.”
    
    Id. § 257.102(f)(2)(i)–(2)(ii)(B).
           Accordingly, in some
    circumstances the impoundment need not complete the closure
    process until 19 years after the Rule’s enactment date.
    53
    Once the Rule’s timeline is correctly understood, there is
    nothing in the record to suggest the Rule’s operating deadline
    is arbitrary and capricious. Indeed, Industry’s comments
    confirm that the Rule’s timeline will provide a sufficient period
    for a non-compliant facility to close (within nine years, and
    more if it meets the extension requirements). See, e.g.,
    Comments of American Elec. Power Co. on Proposal at 5, J.A.
    581 (“[A]t some locations, it will take at least four years from
    the time the new [Coal Residuals] rule becomes effective to
    accomplish the wet-to-dry conversion and to accomplish the
    switch to dry.”); Comments of SCANA Corp. on Proposal at 7,
    J.A. 579 (“The time frame required to site, design, permit, and
    construct a landfill in today’s regulatory environment is at least
    5 to 10 years.”). The EPA’s conclusions are consistent with
    Industry Petitioners’ comments. See 75 Fed. Reg. at 35,202
    (“[Under Subtitle C,] EPA believes that five years will, in most
    cases, be adequate time to complete proper and effective
    facility closure and to arrange for alternative waste
    management * * * . EPA is aware of no reason that the time
    frames would need to differ under subtitle D * * * .”). In sum,
    we conclude that the EPA’s operating timeline is not arbitrary
    and capricious.
    b.    Seismic Restrictions for New Landfills
    The seismic location restrictions apply to impoundments
    as well as new landfills and landfill expansions, but they do not
    apply to existing landfills. 40 C.F.R. § 257.63(a). This
    distinction reflects, inter alia, the EPA’s determination that
    “the risks associated with [Coal Residuals] surface
    impoundments are substantially higher than the risks
    associated with [Coal Residuals] landfills, by approximately an
    order of magnitude.” 80 Fed. Reg. at 21,360. Industry
    Petitioners argue that, if landfills are universally less dangerous
    54
    than surface impoundments, they should not be subject to the
    same seismic standard as surface impoundments. In other
    words, the argument goes, if it is acceptable to exempt existing
    landfills from the seismic location restrictions, it is acceptable
    to exempt new landfills as well. Because Industry Petitioners
    failed to make this argument before the EPA, however, we
    reject it.17
    “Under ordinary principles of administrative law a
    reviewing court will not consider arguments that a party failed
    to raise in timely fashion before an administrative agency.”
    Sims v. Apfel, 
    530 U.S. 103
    , 114 (2000) (Breyer, J., dissenting);
    accord Natural Resource Def. Council, Inc. v. EPA, 
    25 F.3d 1063
    , 1073 (D.C. Cir. 1994) (“We do not reach the merits of
    this challenge because petitioners failed to raise this question
    of statutory and regulatory construction before the agency
    during the notice and comment period. They have therefore
    waived their opportunity to press this argument in court.”); see
    
    discussion, supra, at 33
    .
    This fundamental principle of administrative law applies
    squarely to Industry Petitioners’ challenge. Natural Resource
    Def. 
    Council, 25 F.3d at 1073
    . In the Proposed Rule, the EPA
    explained that, because many Coal Residuals disposal sites are
    within seismic impact zones, it was “concerned that such
    facilities would be unable to meet the requirements, because
    retrofitting would be prohibitively expensive and technically
    very difficult in most cases, and [they] would therefore be
    forced to close.” 75 Fed. Reg. at 35,198. Accordingly, the
    EPA sought comments on “the number of existing [Coal
    Residuals] landfills located in these sensitive areas” and the
    17
    The EPA makes it failure-to-exhaust argument in its opening
    brief. Rep’t Br. 71–72. Industry’s reply brief offers no rebuttal.
    See generally Industry Pet’r’s Reply Br.
    55
    corresponding effect their closure would have on the national
    disposal capacity. 80 Fed. Reg. at 21,360. In spite of the
    invitation to comment, Industry Petitioners cannot point to any
    record evidence that they questioned the application of the Rule
    to new Coal Residuals landfills.18
    Put differently, the EPA did not address the argument that
    new Coal Residuals landfills or landfill expansions should be
    exempted because the public comments gave no reason to
    question the position it announced in the Proposed Rule.
    “Indeed, the notion that a yet-to-be built landfill need not
    comply with basic seismic location restrictions that are
    designed to avoid the potentially catastrophic events identified
    in the record, borders on irrational.” Resp’t Br. 73. In light
    of Industry Petitioners’ failure to alert the EPA to the issue
    while the latter was promulgating the Final Rule, we decline
    reach it.
    c.   The 2,500-Year Standard
    Both the seismic location restrictions and the seismic
    safety assessment criteria incorporate a 2,500-year standard.
    80 Fed. Reg. at 21,384. This means a disposal site in a seismic
    impact area must be designed to withstand the maximum
    expected impact of a 2,500-year earthquake. 
    Id. In establishing
    the 2,500-year standard, the EPA considered
    multiple engineering sources, including (i) Federal Guidelines
    for Dam Safety: Earthquake Analyses and Design of Dams,
    18
    Instead, comments focused on the non-regulation of existing
    landfills, responding to the Proposed Rule’s conclusion that applying
    the seismic location restrictions to existing Coal Residuals landfills
    could cause “disposal capacity shortfalls * * * [that] raise greater
    environmental and public health concerns than the potential failure
    of the [Coal Residuals] landfills in these locales.” 80 Fed. Reg. at
    21,360.
    56
    issued by the Federal Emergency Management Agency
    (FEMA), and (ii) Minimum Design Loads for Buildings and
    Other Structures, International Building Code, a publication of
    the American Society of Civil Engineers (ASCE). 80 Fed.
    Reg. at 21,384; 
    id. at 21,384–21,385
    nn.98–99. The EPA also
    consulted geological sources, including the criteria of the
    National Earthquake Hazards Reduction Program (NEHRP) of
    the U.S. Geological Survey. 75 Fed. Reg. at 35,201. Further,
    the Final Rule’s 2,500-year standard precisely mirrors the
    EPA’s regulations governing municipal solid waste
    management. 75 Fed. Reg. at 35,193 (referencing 40 C.F.R.
    § 258.18).
    In light of the engineering, geological and regulatory
    sources informing and supporting the 2,500-year standard,
    Industry Petitioners face an uphill battle. They nonetheless
    challenge the application of the seismic location restrictions to
    landfills—as opposed to impoundments—because landfills
    pose comparatively fewer risks than impoundments. Thus,
    although FEMA’s dam safety guidelines are applicable to dam-
    like impoundments structures, ASCE’s International Building
    Code is applicable to buildings, and EPA’s municipal landfill
    regulations are applicable to urban landfills, Industry
    Petitioners argue that Coal Residuals landfills are different and
    should be subject to a less demanding standard. In short, it
    asserts that the rule is overprotective and therefore arbitrary
    and capricious. We disagree.
    Industry Petitioners’ argument rests on the assumption that
    the EPA adopted the 2,500-year standard “without
    explanation.” Industry Pet’rs’ Br. 48. To the contrary, the
    EPA first examined the structures of municipal landfills and
    concluded that they were “very similar to those found at [Coal
    Residuals] disposal facilities, and the regulations applicable to
    such units would be expected to address the risks presented by
    57
    the constituents in [Coal Residuals] wastes.” 75 Fed. Reg. at
    35,193 (referencing 40 C.F.R. § 258.18). It then cross-
    referenced the 2,500-year standard with the criteria adopted by
    the U.S. Geological Survey and other engineering experts
    before adopting the Final Rule. 
    Id. at 35,201.
    Indeed, some
    Industry members conceded that “the NEHRP/USGS
    2%PE/50y [2,500-year] standard provides a sufficient margin
    of safety.” Comments of the Southern Company at 34, J.A.
    481. Industry Petitioners may disagree, but the EPA’s
    reasoning was fully explained and is supported by the record.
    Conversely, Industry Petitioners have not cited any record
    evidence that either challenges or provides an alternative to the
    2,500-year standard. The best they can do is highlight
    comments stating generally that the rule is “overly
    protective.”19 Industry Pet’rs’ Br. 47–48. This broad stroke
    19
    Industry Petitioners claim that one commenter suggested a
    250-year standard. See Comments of FirstEnergy Corp. at 11, J.A.
    598.      Again, Industry Petitioners misread the record.
    FirstEnergy’s comment declares:
    EPA intends to incorporate seismic
    performance in section 257.63 of the proposed rule.
    One alternative suggested by EPA is the use of
    seismic impact zones.        A second alternative
    suggests adopting criteria of the National
    Earthquake Hazards Reduction Program (NEHRP)
    of the U.S. Geological Survey, which was used to
    develop national seismic hazard maps. It appears
    the horizontal acceleration expressed as 0.01g in
    250 years in the agency’s first approach closely
    matches the 2% ground motion probability in 50
    years that the seismic maps are based upon.
    58
    does not carry their argument very far. Once the EPA selected
    the Subtitle D rather than the Subtitle C regulatory path, it was
    charged with developing uniform national standards rather
    than implementing a site-specific permit program. See
    generally 42 U.S.C. § 6944(a) (requiring EPA to develop
    minimum criteria for all disposal sites). Consistent with that
    mandate, the EPA developed criteria for all climates and
    conditions within seismic impact zones. Accordingly, it is of
    no moment that the criteria might be “overprotective” for a
    western landfill located miles from any water source. See
    Comments of Electric Power Research Institute on Proposal at
    89, J.A. 596 (explaining that “cap and liners” may not be
    necessary in “western areas where * * * the total rainfall is less
    than 10 inches per year”). Congress demanded national
    minimum standards that ensure “no reasonable probability of
    adverse effects on health or the environment.” 42 U.S.C.
    § 6944(a). The 2,500-year standard does just that.
    4. The Alternative Closure Option
    RCRA states in plain terms that the “open dumping of
    solid waste * * * is prohibited.” 42 U.S.C. § 6945(a). Thus,
    if a disposal site is classified as an open dump, it must either
    retrofit or close. See 
    id. The Final
    Rule stays true to the
    statutory mandate. Under the Final Rule, certain events—
    such as groundwater sampling that reveals an excess of Coal
    Residuals constituents in the water table—establish the
    disposal site as an “open dump,” which triggers the Rule’s
    closure requirements. 40 C.F.R. § 257.101. If the closure
    
    Id. Thus, the
    “250 years” corresponds to the horizontal acceleration
    rate rather than a “ground motion probability” calculation such as the
    one upon which the 2,500-year model is based (2% in 50 years =
    100% in 2,500 years). It is not a free-standing 250-year standard.
    That is, FirstEnergy does not appear to offer an alternative standard.
    59
    requirements are triggered, the surface impoundment or
    landfill ordinarily has six months to either retrofit its facility or
    to stop receiving Coal Residuals and to begin the closure
    process. 
    Id. § 257.101(a)(2),
    (4). In other words, the
    statutory (and regulatory) presumption is that a non-compliant
    disposal site—one that is polluting the groundwater—will
    close. 
    Id. Notwithstanding this
    presumption, the Rule includes an
    “alternative closure” exemption that allows a non-compliant
    Coal Residuals disposal site (an “open dump”) to receive Coal
    Residuals for an additional five years before it ceases
    operations. 40 C.F.R. § 257.103. In order to qualify for the
    alternative closure exception, the owner or operator must
    certify that, inter alia: “No alternative disposal capacity is
    available on-site or off-site.” 
    Id. § 257.103(a)(1)(i).
    In
    making the certification, “[a]n increase in costs or the
    inconvenience of existing capacity is not sufficient to support
    qualification under this section.” 
    Id. Describing the
    rationale for its alternative closure
    exemption, the EPA explained that it did not want to force
    facilities to close and create power shortages “because there is
    no place in which to dispose of the resulting waste.” 80 Fed.
    Reg. at 21,423.         The preamble includes an example:
    “[W]hile it is possible to transport dry ash off-site to [an]
    alternate disposal facility[,] that simply is not feasible for wet-
    generated [Coal Residuals]. Nor can facilities immediately
    convert to dry handling systems. As noted previously, the law
    cannot compel actions that are physically impossible.” 
    Id. Industry Petitioners
    argue that ignoring costs and
    inconvenience in the alternative disposal criteria is arbitrary
    and capricious because it effectively renders the exemption a
    nullity: “If costs or inconvenience cannot be evaluated, off-
    60
    site disposal capacity—no matter where it is located or how
    much it will cost to send [Coal Residuals] there—will always
    be ‘available’ somewhere.” Industry Pet’rs’ Br. 38–39. At
    oral argument, Industry Petitioners lamented that they might be
    required to hire a fleet of 1,000 vacuum trucks in order to
    transfer wet Coal Residuals to an off-site disposal facility.
    Oral Arg. Tr. 23:22–23:23. This result, it argues, would make
    nonsense of the alternative closure requirements.
    Industry Petitioners’ hyperbole faces a roadblock. As the
    United States Supreme Court has explained, if the Congress
    directs the EPA to “regulate on the basis of a factor that on its
    face does not include cost, the Act normally should not be read
    as implicitly allowing the agency to consider cost anyway.”
    Michigan v. EPA, 
    135 S. Ct. 2699
    , 2709 (2015) (citing
    Whitman v. American Trucking Ass’ns, 
    531 U.S. 457
    , 469–472
    (2001)). Applying this rule, the Court held that the EPA is
    prohibited from considering costs when developing its primary
    ambient air quality standards under the Clean Air Act because
    the statute does not mention costs but instead demands
    standards “requisite * * * to protect the public health with an
    adequate margin of safety.” American 
    Trucking, 531 U.S. at 475
    –476 (quoting 42 U.S.C. § 7409(b)(1)). Thus, “public
    health” provided the statutory measuring stick in that instance,
    notwithstanding flexible words such as “requisite” and
    “adequate” that the trucking industry suggested might allow
    the agency to consider costs. 
    Id. at 468.
    Simply put, “to prevail in their present challenge,
    [Industry] must show a textual commitment of authority to the
    EPA to consider costs.” American 
    Trucking, 531 U.S. at 468
    .
    Under any reasonable reading of RCRA, there is no textual
    commitment of authority to the EPA to consider costs in the
    61
    open-dump standards.20 RCRA’s statutory language instructs
    the EPA to classify a disposal site as a sanitary landfill and not
    an open dump only “if there is no reasonable probability of
    adverse effects on health or the environment from disposal of
    solid waste at such facility.” 42 U.S.C. § 6944(a) (emphasis
    added). There is no explicit mention of costs in section 6944;
    nor is there any flexible language such as “appropriate and
    necessary” that might allow the EPA to consider costs in its
    rulemaking. See Michigan v. 
    EPA, 135 S. Ct. at 2709
    . This
    stands in stark contrast with other sections of Title 42—such as
    the Bevill Amendment—where the Congress expressly
    required the EPA to consider, inter alia, “the costs of * * *
    alternatives” in determining whether Coal Residuals should be
    classified as hazardous waste. See 42 U.S.C. § 6982(n)(6).
    With Michigan v. EPA and American Trucking, then, it is
    far from clear that the EPA could consider costs even if it
    wanted to. See Michigan v. 
    EPA, 135 S. Ct. at 2707
    (explaining that “appropriate and necessary” language could
    require consideration of costs in some contexts but not others).
    In any case, there is no statutory support for the assertion that
    EPA was required to consider costs in developing its
    alternative closure plan. Excluding consideration of costs and
    convenience may narrow the alternative closure exemption but
    including cost and convenience would appear to violate
    RCRA’s statutory mandate and run afoul of Supreme Court
    precedent. The EPA was neither arbitrary nor capricious in its
    decision to avoid testing that legal limit.
    20
    At oral argument, neither Industry Petitioners nor the EPA
    could identify a statutory provision that allows the EPA to consider
    costs. Oral Arg. Tr. 83:15–83:23; 116:02–116:10.
    62
    V. Conclusion
    In sum, we deny the EPA’s motion for us to hold these
    petitions in abeyance. We grant in part the EPA’s motion for
    a voluntary remand, remanding to the EPA the provisions in
    the Final Rule pertaining to (i) the definition of “Coal
    Residuals Piles,” see 40 C.F.R. § 257.53; (ii) the 12,400-ton
    beneficial use threshold, see id.; and (iii) the alternative
    groundwater protection standards, see 
    id. § 257.95(h)(2).
    We
    deny the EPA’s motion to remand the provisions in the Final
    Rule pertaining to inactive surface impoundments and landfills
    at active power plants, see 
    id. §§ 257.50(c),
    257.100, and
    inactive surface impoundments at inactive power plants, see 
    id. § 257.50(e).
    On the claims raised by Environmental Petitioners, we
    hold that the EPA acted arbitrarily and capriciously and
    contrary to RCRA in failing to require the closure of unlined
    surface impoundments, in classifying so-called “clay-lined”
    impoundments as lined, and in exempting inactive surface
    impoundments at inactive power plants from regulation. We
    therefore vacate and remand the provisions of the Final Rule
    that permit unlined impoundments to continue receiving coal
    ash unless they leak, see 
    id. § 257.101(a),
    classify “clay-lined”
    impoundments as lined, see 40 C.F.R. § 257.71(a)(1)(i), and
    exempt from regulation inactive impoundments at inactive
    facilities, see 40 C.F.R. § 257.50(e). We reject as forfeited
    Environmental Petitioners’ challenges to the Final Rule’s
    public notice provisions.
    Regarding the Industry Petitioners’ claims, we hold that (i)
    the EPA has statutory authority to regulate inactive
    impoundments; (ii) the EPA provided sufficient notice of its
    intention to apply the aquifer location criteria to existing
    impoundments; (iii) the EPA did not arbitrarily issue location
    63
    requirements based on seismic impact zones; and finally (iv)
    the EPA did not arbitrarily impose temporary closure
    procedures. As to the regulation of Coal Residuals piles of
    12,400 tons or more and the regulation of Coal Residuals
    destined for beneficial use, we remand to the agency as
    requested. We dismiss as moot the two accompanying notice
    challenges and the issue of risk-based compliance alternatives.
    So ordered.
    1
    KAREN LECRAFT HENDERSON, Circuit Judge, concurring
    in part and concurring in the judgment in part: A central
    question before us is whether the EPA exceeded its statutory
    authority under the Resource Conservation and Recovery Act
    (RCRA), 42 U.S.C. §§ 6901 et seq., by applying its Final Rule,
    80 Fed. Reg. 21,302 (Apr. 17, 2015), to an impoundment that
    no longer receives coal combustion residuals (CCR) after the
    effective date of the Rule and thus becomes “inactive.” The
    answer to this question turns on our interpretation of the
    statutory phrase “is disposed of.” My colleagues conclude
    that the verb “to be,” when conjugated in the present tense
    (“is”), unambiguously applies to disposal that occurred entirely
    in the past. I disagree and accordingly concur in the judgment
    with respect to Section IV.B.1 of the opinion. I join all other
    sections of the per curiam opinion in full.
    I.
    I believe there are three tiers to the statutory question.
    First, RCRA directs the EPA to promulgate regulations that
    draw a dividing line between “sanitary landfills” and “open
    dumps.” 42 U.S.C. §§ 6944-45. Generally speaking, a
    sanitary landfill is a disposal site that complies with the EPA’s
    regulations and presents “no reasonable probability of adverse
    effects on health or the environment.” 
    Id. § 6944(a).
    By
    contrast, “any solid waste management practice or disposal of
    solid waste . . . which constitutes the open dumping of solid
    waste or hazardous waste is prohibited.” 
    Id. § 6945(a).
    Second, RCRA defines an “open dump” as “any facility or site
    where solid waste is disposed of which is not a sanitary landfill
    which meets the criteria promulgated under [§ 6944].” 
    Id. § 6903(14)
    (emphasis added).              Third, RCRA defines
    “disposal” as
    the discharge, deposit, injection, dumping,
    spilling, leaking, or placing of any solid waste
    2
    or hazardous waste into or on any land or water
    so that such solid waste or hazardous waste or
    any constituent thereof may enter the
    environment or be emitted into the air or
    discharged into any waters, including ground
    waters.
    
    Id. § 6903(3).
    To interpret RCRA’s text, we turn to the familiar two-step
    framework of Chevron, U.S.A., Inc. v. Natural Resources
    Defense Council, Inc., 
    467 U.S. 837
    (1984). Thus, we begin
    with the statutory language and ask whether the Congress “has
    directly spoken to the precise question at issue.” 
    Id. at 842.
    If the language is plain, our inquiry ends, as we must “give
    effect to the unambiguously expressed intent of Congress.”
    
    Id. at 843.
    If “the statute is silent or ambiguous with respect
    to the specific issue,” however, we defer to the EPA’s
    interpretation so long as it is “based on a permissible
    construction of the statute.” 
    Id. We do
    not alter our analytical framework when the case
    presents a question of an agency’s “jurisdiction” or core
    statutory authority. City of Arlington v. FCC, 
    569 U.S. 290
    ,
    297 (2013) (“[T]he distinction between ‘jurisdictional’ and
    ‘nonjurisdictional’ interpretations is a mirage.”). If “the
    reality is that [the statute] is ambiguous,” it is our duty to
    declare it so and proceed to the second step of the Chevron
    analysis. AT&T Corp. v. Iowa Utils. Bd., 
    525 U.S. 366
    , 395
    (1999).
    II.
    I believe the text—and more precisely, the grammatical
    structure—of RCRA’s definition of “open dump” is temporally
    ambiguous. See United States v. Wilson, 
    503 U.S. 329
    , 333
    3
    (1992) (“Congress’ use of a verb tense is significant in
    construing statutes.”). Under RCRA, an “open dump” is a site
    where solid waste “is disposed of.” 42 U.S.C. § 6903(14).
    The operative verb is the present tense of the infinitive “to be”
    (“is”). The Dictionary Act tells us that “unless the context
    indicates otherwise . . . words used in the present tense include
    the future as well as the present.” 1 U.S.C. § 1. By
    implication, therefore, the Dictionary Act “instructs that the
    present tense generally does not include the past.” Carr v.
    United States, 
    560 U.S. 438
    , 448 (2010). It is plain, therefore,
    that “is” does not mean “was.”
    The verb’s present tense formation takes on additional
    meaning because the “Congress could have phrased its
    requirement in language that looked to the past . . . but it did
    not choose this readily available option.” Gwaltney of
    Smithfield, Ltd. v. Chesapeake Bay Found., Inc., 
    484 U.S. 49
    ,
    57 (1987). It could have conjugated the infinitive “to be” in
    any number of ways to unambiguously include past disposal:
    “is or was disposed of”; “had been disposed of”; or “has been
    disposed of.” See CHICAGO MANUAL OF STYLE ONLINE
    §§ 5.118-35       (17th     ed.    2017),      available      at
    www.chicagomanualofstyle.org//home.html             (explaining
    tenses generally). The Congress could also have included
    unambiguous temporal phrases such as: “ever”; “at any time”;
    “past or present”; or “beginning on a date certain.” It did not
    do so. The present tense of section 6903(14) therefore
    suggests that an “open dump” does not include any
    impoundment where solid waste “was disposed of.”
    Significantly, the Congress used temporally unambiguous
    language in other RCRA provisions. For example, RCRA’s
    “substantial endangerment” provision plainly applies to past
    actions; it allows a state or individual to bring suit against “any
    person . . . who has contributed or who is contributing to the
    4
    past or present . . . disposal of any solid or hazardous waste
    which may present an imminent and substantial endangerment
    to health or the environment.” 42 U.S.C. § 6972(a)(1)(B)
    (emphases added). RCRA Subtitle C provides that the EPA
    must conduct “corrective action for all releases of hazardous
    waste or constituents from any solid waste management
    unit . . . regardless of the time at which waste was placed in
    such unit.” 
    Id. § 6924(u)
    (emphasis added). I believe there
    can be no reasonable dispute that these provisions apply to past
    as well as present and future actions. By itself, therefore, “is”
    at least suggests that the EPA is precluded from including past
    acts of disposal in the definition of an “open dump.”
    The ambiguity comes from the second part of the phrase:
    “disposed of.” A past participle like “disposed” is not singular
    in its purpose; it is defined as “[a] verb form indicating past or
    completed action or time that is used as a verbal adjective in
    phrases such as baked beans and finished work.” Fla. Dep’t
    of Revenue v. Piccadilly Cafeterias, Inc., 
    554 U.S. 33
    , 39
    (2008) (quoting AMERICAN HERITAGE DICTIONARY 1287 (4th
    ed. 2000) (emphasis removed)). In other words, a past
    participle can serve either as a verb (i.e., the pecans were
    covered in chocolate) or as an adjective (i.e., the chocolate-
    covered pecans). Moreover, in verb form, a past participle can
    indicate past (i.e., the pecans were covered in chocolate),
    present (i.e., the pecans are covered in chocolate) or future
    action (i.e., the pecans will be covered in chocolate). In short,
    there is nothing unambiguous about a past participle, at least
    when construed without context.21
    21
    My colleagues cite two authorities for their conclusion that a
    statutory past participle unambiguously signifies retroactive effect.
    Neither authority decides the issue. First, in Florida Department of
    Revenue v. Piccadilly Cafeterias, Inc., 
    554 U.S. 33
    , 41 (2008), the
    5
    I believe “disposed of” must be read in conjunction with
    RCRA’s definition of “disposal,” which includes the
    “discharge, deposit, injection, dumping, spilling, leaking, or
    placing” of solid waste into certain areas. 42 U.S.C. §
    6903(3). Circuit courts disagree about whether “disposal”
    includes the “passive migration” of contaminants, such as a
    slow leak from an inactive CCR impoundment. Compare
    Carson Harbor Vill., Ltd. v. Unocal Corp., 
    270 F.3d 863
    , 867
    (9th Cir. 2001) (en banc) (concluding that “the migration of
    contaminants on the property does not fall within the statutory
    definition of ‘disposal’”), with Nurad, Inc. v. William E.
    Hooper & Sons Co., 
    966 F.2d 837
    , 846 (4th Cir. 1992) (holding
    past owners liable for “disposal” of hazardous wastes that
    Supreme Court assumed the statute at issue was temporally
    ambiguous and resolved the interpretive question at Chevron’s
    second step. Moreover, in Sherley v. Sebelius, the majority found
    ambiguity in a statute that prohibited funding for “research in which
    a human embryo or embryos are destroyed.” 
    644 F.3d 388
    , 390
    (D.C. Cir. 2011) (emphasis added) (internal quotation marks
    omitted). It did so in spite of applicable regulations defining
    research as “a systematic investigation, including research
    development, testing and evaluation, designed to develop or
    contribute to generalizable knowledge.” 
    Id. at 394
    n.* (quoting 45
    C.F.R. § 46.102(d)).       Notwithstanding this temporally broad
    definition, the majority declared that the “definition of research is
    flexible enough to describe either a discrete project or an extended
    process.” 
    Id. at 394
    . I dissented, challenging the majority’s
    interpretive fallacy that “research” can be dissected into “free-
    standing pieces” rather than read as a “systematic [and ongoing]
    investigation.” 
    Id. at 402-04
    (Henderson, J., dissenting). Thus, I
    did not find the phrase “are destroyed” unambiguous standing alone;
    in my view, the explicit connection to research funding—and the
    correct definition of “research”—clarified the temporal scope of the
    statute to include past conduct. 
    Id. 6 leaked
    from underground storage tank notwithstanding they
    were not owners “at the time of disposal”). Because these
    cases arise in a different statutory context, 22 they are not
    precisely on point regarding the question of the EPA’s
    authority to regulate inactive impoundments. Nonetheless,
    they illustrate the ambiguity in the statutory definition of the
    word “disposal”; if courts disagree about the meaning of
    “disposal,” that disagreement strongly suggests there is
    ambiguity in the words “disposed of.” See Final Rule, 80 Fed.
    Reg. at 21,346 (surveying caselaw interpreting “disposal”).
    Although there is some temporal tension between the
    present tense “is” and the past participle “disposed,” it can be
    explained by statutory context. See Brown v. Gardner, 
    513 U.S. 115
    , 118 (1994) (“Ambiguity is a creature not of
    definitional possibilities but of statutory context.”).
    Industry’s entire argument hinges on three words—“is
    disposed of”—in the definition of “open dump.” 42 U.S.C. §
    6903(14). But “open dump” is also defined by what it is not:
    a “sanitary landfill.” 
    Id. The statutory
    categorization is
    binary: a disposal site is either a sanitary landfill or an open
    dump and the EPA is directed to promulgate regulations that
    distinguish between the two. 
    Id. § 6944.
    Thus, as the EPA
    promulgates new regulations that may shift the contours of
    what constitutes a “sanitary landfill,” see 42 U.S.C. § 6912(b)
    (RCRA regulations “shall be reviewed and, where necessary,
    revised not less frequently than every three years”), the
    definition of “open dump” will morph as well, see Appalachian
    Voices v. McCarthy, 
    989 F. Supp. 2d 30
    , 56 (D.D.C. 2013)
    (“requir[ing] the EPA to submit a proposed scheduling order
    setting forth a proposed deadline by which it will comply with
    22
    The cited cases interpret the Comprehensive Environmental
    Response, Compensation, and Liability Act of 1980 (CERCLA),
    which incorporates RCRA’s definition of “disposal.” 42 U.S.C.
    § 9601(29) (incorporating 42 U.S.C. § 6903(14)).
    7
    its statutory obligations” under RCRA). Although not every
    interpretation of “open dump” may be reasonable, see
    Michigan v. EPA, 
    135 S. Ct. 2699
    , 2708 (2015) (“Chevron
    allows agencies to choose among competing reasonable
    interpretations of a statute; it does not license interpretive
    gerrymanders[.]”), RCRA’s mandated flexibility contemplates
    that the regulatory meaning of “open dump” can change over
    time and thus fits the definition of “ambiguity.” See
    Ambiguity, WEBSTER’S THIRD NEW INTERNATIONAL
    DICTIONARY 66 (3d ed. 1993) (“admitting of two or more
    meanings”).
    III.
    Although I believe the statute is temporally ambiguous, I
    nonetheless agree that the EPA reasonably concluded that it has
    the authority to regulate inactive impoundments.             See
    
    Chevron, 467 U.S. at 843
    (deference to agency’s interpretation
    required so long as it is “based on a permissible construction of
    the statute”). In reviewing the reasonableness of an agency’s
    interpretation, we look to the statute’s structure and purpose as
    well as to precedent, Nat’l Ass’n of Home Builders v. Defs. of
    Wildlife, 
    551 U.S. 644
    , 666 (2007), keeping in mind that
    Chevron “does not require the best interpretation [of the
    statute], only a reasonable one,” Van Hollen, Jr. v. FEC, 
    811 F.3d 486
    , 492 (D.C. Cir. 2016) (internal quotation marks
    omitted).
    First, regarding the definition of “disposal,” we have
    rejected a similar “linguistic point that ‘[d]isposal . . . is not a
    continuing activity but occurs anew each time waste is placed
    into or on land.’” In re Consol. Land Disposal Regulation
    Litig., 
    938 F.2d 1386
    , 1389 (D.C. Cir. 1991). In doing so, we
    noted that RCRA’s “equation of ‘disposal’ with ‘leaking,’
    which is a continuous phenomenon rather than a discrete event,
    8
    is enough to blunt the sting of the petitioners’ point.” 
    Id. In that
    case, we concluded that the petitioners’ suggested
    interpretation was, “at most an alternative reading of the
    statute, not an argument as to why the EPA’s reading of the
    statute is unreasonable.” 
    Id. Thus, we
    upheld as reasonable
    the EPA’s interpretation of “disposal” to include “continuous”
    leaking; we can apply a similar reading today. Indeed, the
    record “demonstrates that unlined surface impoundments
    typically operate for 20 years before they begin to leak.” See
    80 Fed. Reg. at 21326-27; see also 40 C.F.R. §§ 257.70-72
    (imposing liner requirements to prevent leaking).            As
    discussed in Section IV.B.1 of the per curiam opinion, the risk
    of leaking does not decrease in an inactive impoundment—
    indeed, it can increase.         Because “disposal” includes
    “leaking”—and because “leaking” does not necessarily cease
    upon an impoundment’s closure—the EPA reasonably
    concluded that CCR continues to be “disposed of” even after
    an impoundment stops receiving CCR. See 75 Fed. Reg.
    35,128, 35,159 (June 21, 2010) (“historical or legacy sites”
    pose leaking risk).
    Second, an impoundment where CCR “is disposed of” is
    different from an impoundment that is actively receiving
    additional CCR. 42 U.S.C. § 6903(14). As the EPA
    suggests, if an individual were to stand on an impoundment
    dam looking out over thousands of tons of wet CCR and ask
    “is this an impoundment where ‘solid waste is disposed of,’”
    the answer would be “yes.” EPA Br. 22. Put differently, the
    disposal of CCR in an impoundment is not a discrete act. If it
    were, the EPA would regulate only the transfer of CCR from a
    power facility into an impoundment, at which point the
    “disposal” would end. Of course, the reality is that CCR
    disposal and its resulting health hazards occur over long
    periods of time. See 80 Fed. Reg. at 21,309 (“estimated time
    to peak potential exposures of CCR through groundwater
    9
    migration to drinking water wells is 75 years” and estimated
    CCR unit lifespan is 40 to 80 years). CCR is not like a bag of
    trash that a homeowner places on the curb to be picked up.
    The homeowner releases control of the bag once he deposits it
    and the garbage truck makes its rounds. In contrast—and by
    definition—an impoundment owner or utility operator does not
    relinquish control of the CCR once it is impounded. See 40
    C.F.R. § 257.53 (defining “owner” and “operator”); see also 
    id. § 257.50(b)
    (Rule applies to “disposal units located off-site of
    the electric utility or independent power producer”).
    Moreover, the impoundment’s purpose is to “dispose of” CCR
    and, accordingly, the disposal process continues so long as the
    CCR remains in the pond. 
    Id. § 257.53
    (“CCR impoundment”
    is a “natural topographic depression, man-made excavation, or
    diked area, which is designed to hold an accumulation of CCR
    and liquids, and the unit treats, stores, or disposes of CCR”
    (emphasis added)).23
    For the foregoing reasons, and regarding Section IV.B.1
    only, I concur in the judgment. Otherwise, I fully concur in
    the per curiam opinion.
    23
    The EPA’s regulatory definition of “impoundment” is
    consistent with the dictionary definition of the verb “impound,”
    which manifests continuing action. See Impound, WEBSTER’S
    THIRD NEW INTERNATIONAL DICTIONARY 1136 (3d ed. 1993)
    (“[T]o confine or store (water)[.]”).
    

Document Info

Docket Number: 15-1219; C-w 15-1221; 15-1222; 15-1223; 15-1227; 15-1228; 15-1229

Judges: Henderson, Millett, Per Curiam, Pillard

Filed Date: 8/21/2018

Precedential Status: Precedential

Modified Date: 10/19/2024

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