                FOR PUBLICATION

  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT


CENTER FOR COMMUNITY ACTION              No. 12-56086
AND ENVIRONMENTAL JUSTICE;
EAST YARD COMMUNITIES FOR                   D.C. No.
ENVIRONMENTAL JUSTICE; NATURAL           2:11-cv-08608-
RESOURCES DEFENSE COUNCIL, INC.,             SJO-SS
             Plaintiffs-Appellants,

                 v.                        OPINION

BNSF RAILWAY COMPANY; UNION
PACIFIC RAILROAD COMPANY,
             Defendants-Appellees.


      Appeal from the United States District Court
          for the Central District of California
       S. James Otero, District Judge, Presiding

                 Argued and Submitted
          April 8, 2014—Pasadena, California

                 Filed August 20, 2014

   Before: Ferdinand F. Fernandez, N. Randy Smith,
        and Mary H. Murguia, Circuit Judges.

              Opinion by Judge Murguia
2              CTR. FOR CMTY. ACTION V. BNSF

                           SUMMARY*


                       Environmental Law

    The panel affirmed the district court’s dismissal of an
action filed by environmental organizations under the citizen-
suit provision of the Resource Conservation and Recovery
Act, seeking to enjoin the emission from defendants’
railyards of particulate matter found in diesel exhaust.

    The panel held that defendants’ emission of diesel
particulate matter did not constitute “disposal” of solid waste
within the meaning of RCRA. Accordingly, plaintiffs could
not state a plausible claim for relief under 42 U.S.C.
§ 6972(a)(1)(B).


                            COUNSEL

David Pettit (argued), Melissa Lin Perella, and Morgan
Wyenn, Natural Resources Defense Council, Santa Monica,
California, for Plaintiffs-Appellants.

Mark B. Helm (argued), Henry Weissmann, and Leo
Goldbard, Munger, Tolles & Olson LLP, Los Angeles,
California; Patrick J. Cafferty, Jr., Munger Tolles & Olson
LLP, San Francisco, California; Kevin M. Fong, Pillsbury
Winthrop Shaw Pittman LLP, San Francisco, California;
Mark E. Elliott, Michael R. Barr, Margaret Rosegay, and


  *
    This summary constitutes no part of the opinion of the court. It has
been prepared by court staff for the convenience of the reader.
             CTR. FOR CMTY. ACTION V. BNSF                    3

Amy E. Gaylord, Pillsbury Winthrop Shaw Pittman LLP, Los
Angeles, California, for Defendants-Appellees.


                          OPINION

MURGUIA, Circuit Judge:

    In this case, we must decide whether the citizen-suit
provision of the Solid Waste Disposal Act (Resource
Conservation and Recovery Act (RCRA)), 42 U.S.C.
§§ 6901–6992k, may be used to enjoin the emission from
Defendants’ railyards of particulate matter found in diesel
exhaust. RCRA’s citizen-suit provision permits “any person”
to sue the owner or operator of a solid waste treatment,
storage, or disposal facility if the owner or operator “has
contributed or . . . is contributing to the past or present
handling, storage, treatment, transportation, or 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). We conclude that Defendants’
emission of diesel particulate matter does not constitute
“disposal” of solid waste within the meaning of RCRA, and
that Plaintiffs therefore cannot state a plausible claim for
relief under § 6972(a)(1)(B). We therefore affirm the district
court’s judgment.

                               I.

   Union Pacific Railroad and Burlington Northern Santa Fe
Railway Companies (collectively, “Defendants”) own and
operate sixteen railyards in the State of California. On or
near those railyards, various locomotive, truck, and other
heavy-duty vehicle engines emit tons of diesel particulate
4              CTR. FOR CMTY. ACTION V. BNSF

matter—small, solid particles found in diesel exhaust—into
the air. The California Air Resources Board (CARB) has
identified diesel particulate matter as a toxic air contaminant
with the potential “to cause cancer and other adverse health
problems, including respiratory illnesses and increased risk of
heart disease.” The Environmental Protection Agency (EPA)
has similarly classified diesel exhaust as likely to be
carcinogenic to humans.

    Plaintiffs are environmental organizations whose
members live in the vicinity of Defendants’ railyards.1 They
allege, citing CARB studies, that “over 1.8 million
Californians are at elevated [cancer] risk because of railyard
operations.” Plaintiffs further allege that “people living in
communities close to the source of [diesel particulate]
emissions, such as ports, railyards and intermodal transfer
facilities are likely to suffer greater health impacts and these
impacts will likely add to an existing health burden.” In
2005, according to Plaintiffs, Defendants’ railyards
collectively emitted over 160 tons of diesel particulate matter
into the air.



    1
     Plaintiffs are the Center for Community Action and Environmental
Justice (CCAEJ), East Yard Communities for Environmental Justice
(EYCEJ), and Natural Resources Defense Council (NRDC). CCAEJ
proclaims itself to be “one of the oldest and most accomplished
environmental health and justice organizations in the nation”; its work
focuses on achieving environmental health and justice in Riverside and
San Bernardino Counties, California. Each of those counties is home to
one railyard or intermodal facility owned by Defendants. EYCEJ is
another California environmental health and justice organization. Its
membership base is located in East Los Angeles, where Defendants’
railyards are also located. NRDC is a national organization dedicated to
environmental justice and public health.
              CTR. FOR CMTY. ACTION V. BNSF                      5

     According to Plaintiffs, Defendants “have allowed and are
allowing [diesel particulate matter] to be discharged into the
air, from which it falls onto the ground and water nearby, and
is re-entrained into the atmosphere.” Plaintiffs acknowledge
that diesel particulate matter is initially emitted into the air as
diesel exhaust, but they contend that the solid particles in the
exhaust are “transported by wind and air currents onto the
land and water.” They allege that the particles are “inhaled
by people both directly and after the particles have fallen to
the earth and then have been re-entrained into the air by wind,
air currents and passing vehicles.”

                                II.

    RCRA’s citizen-suit provision authorizes private persons
to sue “any person . . . who has contributed or who is
contributing to the past or present handling, storage,
treatment, transportation, or 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). Invoking that provision, Plaintiffs
sued Defendants in the Central District of California, alleging
that diesel particulates constitute “solid waste and hazardous
waste,” the “handling, storage, treatment, transportation, or
disposal” of which Defendants have contributed or are
contributing to. In their complaint, Plaintiffs sought
injunctive and declaratory relief, asking the district court to
declare Defendants’ activities in violation of RCRA and order
Defendants to take certain control measures to reduce diesel
particulate emissions from their railyards.

   Defendants moved to dismiss Plaintiffs’ complaint,
contending that Plaintiffs failed to state a claim under RCRA.
Specifically, Defendants asserted that the provision of RCRA
6               CTR. FOR CMTY. ACTION V. BNSF

regulating air emissions, 42 U.S.C. § 6924(n), applies to air
pollutants resulting from the burning of fuel “only when the
fuel [itself] consists of or contains ‘solid’ or ‘hazardous’
waste, i.e., a discarded material.”2 All other air emissions,
according to Defendants, fall within the statutory and
regulatory scope of the Clean Air Act, the provisions of
which Plaintiffs do not and cannot invoke.3 Defendants
further argued that, even if Congress had intended RCRA to
apply in this context, Plaintiffs could not prevail because
Defendants did not emit diesel exhaust “into or on any land
or water,” and therefore were not “disposing” of solid waste
within the meaning of RCRA. See 42 U.S.C. § 6903(3)
(defining “disposal” to mean “the discharge, deposit,
injection, dumping, spilling, leaking, or placing of any solid
waste or hazardous waste into or on any land or water so that
[the waste] may enter the environment or be emitted into the
air or discharged into any waters”).

   In response to Defendants’ motion to dismiss, Plaintiffs
argued that failing to apply RCRA to the diesel particulates
emitted at Defendants’ railyards would result in a “gap in the

    2
    Section 6924(n) requires the Administrator of the EPA to promulgate
“regulations for the monitoring and control of air emissions at hazardous
waste treatment, storage, and disposal facilities, including but not limited
to open tanks, surface impoundments, and landfills.” 42 U.S.C. § 6924(n).
    3
      The Clean Air Act’s citizen-suit provision is more limited than
RCRA’s. Under the Clean Air Act, individuals may bring suit only to
enforce the provisions of a permit or rules promulgated by the EPA.
42 U.S.C. § 7604(a)(1). RCRA’s provision, by contrast, authorizes suits
against any person who “has contributed or who is contributing to the 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), whether or not the person sued is complying
with the terms of a permit or regulation.
              CTR. FOR CMTY. ACTION V. BNSF                     7

[Clean Air Act] when it comes to emissions from railyards.”
Because, according to Plaintiffs, both the Clean Air Act and
RCRA are intended to apply to mobile sources of air
pollution—including diesel particulate emissions—the two
laws can and should be “harmonized” to fill the regulatory
gap that Plaintiffs contend otherwise results.

    The district court granted Defendants’ motion and
dismissed Plaintiffs’ complaint with prejudice. In its order,
the court concluded that the Clean Air Act, and not RCRA,
applies to the emissions from Defendants’ railyards and that
any “gap” that might exist between the two statutory schemes
“was created through a series of reasoned and calculated
decisions by Congress and the EPA.” As an “independent
reason” for granting the motion to dismiss, the district court
noted that Plaintiffs failed to state a claim under RCRA
because, even if RCRA does apply, “diesel exhaust is not a
‘solid or hazardous waste.’ ” Plaintiffs timely appealed the
district court’s order.

                               III.

     We review de novo a district court’s order granting a
motion to dismiss under Federal Rule of Civil Procedure
12(b)(6). We accept as true the factual allegations in the
complaint and construe those allegations in the light most
favorable to the nonmoving party. Hinds Invs., L.P. v.
Angioli, 654 F.3d 846, 849–50 (9th Cir. 2011). “To survive
a motion to dismiss, a complaint must contain sufficient
factual matter, accepted as true, to ‘state a claim to relief that
is plausible on its face.’ ” Ashcroft v. Iqbal, 556 U.S. 662, 678
(2009) (quoting Bell Atl. Corp. v. Twombly, 550 U.S. 544,
570 (2007)). We will uphold a district court’s decision to
dismiss “where there is either a lack of a cognizable legal
8            CTR. FOR CMTY. ACTION V. BNSF

theory or the absence of sufficient facts alleged under a
cognizable legal claim.” Hinds Invs., 654 F.3d at 850.

    To survive a motion to dismiss under RCRA’s citizen-suit
provision, Plaintiffs must plausibly allege that Defendants
have contributed or are contributing to “the past or present
handling, storage, treatment, transportation, or 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). In other words, Plaintiffs must
allege, based on a cognizable legal theory, (1) that
Defendants have contributed to the past or are contributing to
the present handling, treatment, transportation, or disposal of
diesel particulate matter; (2) that diesel particulate matter is
a “solid waste”; and (3) that the solid waste that Defendants
emit “may present an imminent and substantial endangerment
to health or the environment.”

    In their complaint, Plaintiffs allege that Defendants
“dispose” of solid waste—specifically, diesel particulate
matter—by allowing the waste to be “transported by wind
and air currents onto the land and water near the railyards.”
According to Plaintiffs’ allegations, the particulates are then
“inhaled by people both directly and after the particles have
fallen to the earth and then have been re-entrained into the air
by wind, air currents, and passing vehicles.” They contend
that Defendants violate RCRA by failing to “limit or control
the amount of [diesel particulate matter] generated on and by
the railyards.” Plaintiffs’ allegations, however, even if true,
do not establish that Defendants “dispose” of solid or
                CTR. FOR CMTY. ACTION V. BNSF                               9

hazardous waste as the term “disposal” is defined under
RCRA.4

     Under RCRA, “disposal” means

         the discharge, deposit, injection, dumping,
         spilling, leaking, or placing of any solid waste
         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.

42 U.S.C. § 6903(3). Although that definition does not
plainly state whether emissions of solid waste into the air fall
within its scope, it does provide sufficient contextual clues
for us to conclude that they do not. See Food & Drug Admin.
v. Brown & Williamson Tobacco Corp., 529 U.S. 120, 132
(2000) (“The meaning—or ambiguity—of certain words or
phrases may only become evident when placed in context.”).

 4
    Plaintiffs do not allege that Defendants contribute or contributed to the
“handling,” “storage,” “treatment,” or “transportation” of solid waste.
Despite Plaintiffs’ contention at oral argument that they had also alleged
that Defendants contributed to the “handling” of solid waste within the
meaning of § 6972(a)(1)(B), we find nothing in the record to support that
assertion. Indeed, in opposing Defendants’ motion to dismiss, Plaintiffs
stated that “[t]he heart of this case is that Defendants’ railyards contribute
to the disposal of a solid hazardous waste—diesel particulate matter—that
may present an imminent and substantial endangerment to the health of
Plaintiffs’ members.” We therefore focus solely on the question whether
the emission of diesel particulate matter by way of diesel exhaust from
Defendants’ railyards constitutes “disposal” within the meaning of RCRA.
See Ravell v. United States, 22 F.3d 960, 962 n.2 (9th Cir. 1994)
(declining to consider a claim raised for the first time at oral argument).
10           CTR. FOR CMTY. ACTION V. BNSF

Our conclusion in that respect is consistent with other
provisions of RCRA, and it does not conflict with the
statute’s purposes or its statutory and legislative histories.
See, e.g., Carson Harbor Vill., Ltd. v. Unocal Corp., 270 F.3d
863, 877 (9th Cir. 2001) (noting that courts resort to
legislative history “even where the plain language is
unambiguous, ‘where the legislative history clearly indicates
that Congress meant something other than what it said’ ”
(quoting Perlman v. Catapult Entm’t, Inc. (In re Catapult
Entm’t, Inc.), 165 F.3d 747, 753 (9th Cir. 1999))).

                              A.

    We begin with RCRA’s text. See Safe Air for Everyone
v. Meyer, 373 F.3d 1035, 1041 (9th Cir. 2004). We note first
that RCRA’s definition of “disposal” does not include the act
of “emitting.” Instead, it includes only the acts of
discharging, depositing, injecting, dumping, spilling, leaking,
and placing. That “emitting” is not included in that list
permits us to assume, at least preliminarily, that “emitting”
solid waste into the air does not constitute “disposal” under
RCRA. See 2A Norman J. Singer & J.D. Shambie Singer,
Sutherland Statutes & Statutory Construction § 47:23 (7th ed.
2012) (noting that expressio unius est exclusio alterius stands
for the proposition that when Congress expresses meaning
through a list, a court may assume that what is not listed is
excluded).

    The text of § 6903(3) is also very specific: it limits the
definition of “disposal” to particular conduct causing a
particular result. By its terms, “disposal” includes only
conduct that results in the placement of solid waste “into or
on any land or water.” 42 U.S.C. § 6903(3). That placement,
in turn, must be “so that such solid waste . . . may enter the
              CTR. FOR CMTY. ACTION V. BNSF                     11

environment or be emitted into the air or discharged into any
waters, including ground waters.” Id. We therefore conclude
that “disposal” occurs where the solid waste is first placed
“into or on any land or water” and is thereafter “emitted into
the air.”

     The solid waste at issue here, however, at least as it is
characterized in Plaintiffs’ complaint, is not first placed “into
or on any land or water”; rather, it is first emitted into the air.
Only after the waste is emitted into the air does it then travel
“onto the land and water.” To adopt Plaintiffs’ interpretation
of § 6903(3), then, would effectively be to rearrange the
wording of the statute—something that we, as a court, cannot
do. Reading § 6903(3) as Congress has drafted it, “disposal”
does not extend to emissions of solid waste directly into the
air.

    Other provisions of RCRA further support that
conclusion. The term “release,” for example, which is
defined in the section of RCRA governing underground
storage tanks, includes “spilling, leaking, emitting,
discharging, escaping, leaching, or disposing . . . into ground
water, surface water or subsurface soils.” 42 U.S.C.
§ 6991(8) (emphasis added). “[W]hen Congress includes
particular language in one section of a statute but omits it in
another section of the same Act, it is generally presumed that
Congress acts intentionally and purposely in the disparate
inclusion or exclusion.” Barnhart v. Sigmon Coal Co., 534
U.S. 438, 452 (2002) (internal quotation marks omitted).
That Congress knew how to define “disposal” to include
emissions, but nonetheless chose not to, counsels against our
reading into the definition of “disposal” conduct that
Congress must have intended to exclude from its reach.
12             CTR. FOR CMTY. ACTION V. BNSF

    United States v. Power Engineering Co., 191 F.3d 1224
(10th Cir. 1999), which Plaintiffs cite for the proposition that
“aerosolized solid waste would not lose its character as solid
waste simply because it was disposed of through the air,” is
not to the contrary. In Power Engineering, the Tenth Circuit
decided the question whether defendant Power Engineering
Company was subject to certain financial assurance
provisions of Colorado’s RCRA State Implementation Plan.
Id. at 1227–28. Power Engineering had been discharging
hexavalent chromium and other hazardous materials into the
soil on its facility’s site, and the materials had then leaked
into the groundwater and made their way into waters of the
Platte River. Id. at 1229, 1231. The court concluded that
disposing of the hazardous mist onto the soil constituted
illegal “disposing of hazardous wastes.” Id. at 1231.
Contrary to Plaintiffs’ contentions, Power Engineering did
not involve disposal of solid waste “through the air,” and so
does not support the proposition that Plaintiffs attribute to it.5

     Plaintiffs additionally contend that, because RCRA has an
“air emissions” provision, see § 6924(n), “emitting” must fall
within the statute’s reach and therefore may form the basis of
a citizen suit under § 6972(a)(1)(B). Plaintiffs read § 6924(n)
as proof that both RCRA and the Clean Air Act extend to air
emissions. Because that is so, Plaintiffs continue, the two


  5
    Plaintiffs cite United States v. Apex Oil Co., No. 05-CV-242-DRH,
2008 WL 2945402 (S.D. Ill. July 28, 2008), for a similar proposition, but
that case is likewise inapposite. In Apex Oil, the vapors were disposed of
onto the land, after which they leaked into groundwater and were released
into the air. Citizens Against Pollution v. Ohio Power Co., No. C2-04-
CV-371, 2006 WL 6870564 (S.D. Ohio July 13, 2006), yet another case
that Plaintiffs cite, is the only case that supports their interpretation.
Because we find the reasoning of Citizens Against Pollution contrary to
RCRA’s text and legislative history, we decline to rely on it.
             CTR. FOR CMTY. ACTION V. BNSF                   13

statutory schemes should be “harmonized” in a way that
“give[s] effect to both.” Plaintiffs suggest that we
“harmonize” the two laws by reading RCRA’s definition of
disposal to include emissions of solid waste from Defendants’
railyards.

    We are not persuaded. Section 6924(n) of RCRA requires
the EPA to promulgate regulations “for the monitoring and
control of air emissions at hazardous waste treatment,
storage, and disposal facilities, including but not limited to
open tanks, surface impoundments, and landfills, as may be
necessary to protect human health and the environment.”
Although that section clearly contemplates that certain air
emissions will fall within RCRA’s regulatory reach, it does
not provide a private right of action. And § 6972(a)(1)(B),
RCRA’s citizen-suit provision, does not permit individuals to
bring suit to enforce § 6924(n). Thus, the fact that RCRA
permits the EPA to regulate air emissions is not to say that it
provides “any person,” by way of its citizen-suit provision, a
private right of action with respect to those emissions.
Indeed, as noted earlier, the very existence of § 6924(n)
suggests that Congress, by not including “emitting” in the
actions prohibited under § 6972(a)(1)(B), intended to exclude
it.

    Thus, we preliminarily conclude—based on the statute’s
wording considered alone and in context—that emitting
diesel particulate matter into the air does not constitute
“disposal” as that term is defined under RCRA. To the extent
that the definition of “disposal” is ambiguous on this point,
see Citizens Against Pollution, 2006 WL 6870564, at *5
(reaching a different conclusion), the statutory and legislative
histories of both RCRA and the Clean Air Act resolve that
ambiguity. We turn to those histories.
14            CTR. FOR CMTY. ACTION V. BNSF

                               B.

    When the Clean Air Act was enacted in 1963, it left the
task of controlling air pollution largely to the states. See
Clean Air Act, Pub. L. No. 88-206, 77 Stat. 392 (1963). It
was not until 1970, after a comprehensive overhaul of the
Act, that Congress adopted a national system of air quality
standards, emission limits, and other requirements seeking to
“preven[t] and control . . . air pollution at its source.” Clean
Air Act Amendments of 1970, Pub. L. No. 91-604,
§ 101(a)(3). The 1970 amendments required the federal
government, by way of the newly created EPA, to establish
National Ambient Air Quality Standards (NAAQS) for
pollutants that adversely affect public health and welfare, as
well as to establish national emission standards for
“hazardous air pollutants.” §§ 108–09, 112, 84 Stat. 1676,
1678–80, 1685–86. The 1970 amendments also required
states to submit “State Implementation Plans” to “provid[e]
for implementation, maintenance, and enforcement” of the
NAAQS. § 110(a)(1), 84 Stat. at 1680.

    Of particular relevance to this case, the legislative history
leading up to the 1970 amendments suggests that Congress
considered, but ultimately did not adopt, a provision that
would have required the EPA to adopt national standards for
emissions from locomotives. See Hearings Before the
Subcommittee on Air and Water Pollution of the Committee
on Public Works, 91st Cong. 139 (1970) (testimony of Robert
H. Finch) (describing the provisions of Senate Bill 3229,
which would have “authorize[d] the Department to establish
national standards for the control of emissions from . . .
locomotives” and noting that although “locomotives . . . are
not major sources of air pollution at this time . . . , we support
the principle of making them subject to emission controls”).
               CTR. FOR CMTY. ACTION V. BNSF                         15

Congress also recognized, but similarly opted not to address,
the environmental problem arising from diesel emissions
from heavy-duty trucks and buses. See, e.g., id. at 65
(testimony of John Middleton) (noting that “beginning
January 1, 1970, . . . all new diesel engines will necessarily
comply with a smoke emission standard” but that “[t]he
serious problem is what do you do with the used diesel
vehicle or the used gasoline-fueled vehicle?”).

    Six years later, Congress enacted RCRA in an effort to
“solv[e] the problems associated with the 3–4 billion tons of
discarded materials generated each year, and the problems
resulting from the anticipated 8% annual increase in the
volume of such waste.” H.R. Rep. No. 94-1491, at 2 (1976)
(Conf. Rep.).6 The law was intended to “eliminat[e] the last
remaining loophole in environmental law, that of unregulated
land disposal of discarded materials and hazardous wastes.”
Id. at 4. As its name suggests, the law was intended to
provide “two possible solutions” to the “discarded materials
problem”: (1) “resource conservation[, achieved] by reducing
the amount of waste generated,” and (2) “resource [recovery],
achieved by reclaiming valuable materials from the waste and
thereby reducing the volume to be disposed of.” Id. at 10.

    By its terms, RCRA thus governs the disposal of
“discarded materials,” including “solid waste.” The law also
governs “hazardous waste,” which is “a solid waste, or
combination of solid wastes, which because of its quantity,
concentration, or physical, chemical, or infectious
characteristics may” cause, contribute to, or “pose a


 6
   RCRA was enacted as an amendment to the Solid Waste Disposal Act,
which was originally enacted in 1965. See Solid Waste Disposal Act, Pub.
L. No. 89-212, 79 Stat. 997 (1965).
16           CTR. FOR CMTY. ACTION V. BNSF

substantial present or potential hazard” to human or
environmental health. 42 U.S.C. § 6903(5). RCRA provides
for solid and hazardous waste management, which are “the
systematic [control or] administration of activities which
provide for the collection, source separation, storage,
transportation, transfer, processing, treatment, and disposal
of” solid and hazardous wastes. 42 U.S.C. § 6903(7), (28).
When RCRA was enacted in 1976, it did not include a
provision regulating air emissions from solid or hazardous
waste disposal facilities.

    In 1977, against the backdrop of RCRA’s enactment the
year before, Congress again significantly overhauled the
Clean Air Act. The 1977 overhaul was made in an effort to
provide additional guidance on matters like best available
control technologies, unregulated pollutants, and other issues
that had gone unaddressed in prior versions of the Act. See
H.R. Rep. No. 95-564 (1977) (Conf. Rep.). As part of the
1977 revision, Congress added two provisions relevant to this
case.

     The first was a provision requiring the EPA to conduct a
railroad emissions study.         In response to industry
recommendations that Congress consider “[f]ederal
regulation of air pollutants emitted from railroad rolling
stock,” Congress requested that the EPA conduct a study to
assess (1) “the extent to which emissions from railroads are
a national problem,” (2) “state of the art of control
technology,” and (3) “the kinds of regulations of emissions
currently imposed on railroads by State and local authorities.”
S. Rep. No. 95-127, at 93 (1977); see also Clean Air Act
Amendments of 1977, Pub. L. No. 95-95, § 404, 91 Stat. 685,
793–94 (calling for a railroad emissions study).
                CTR. FOR CMTY. ACTION V. BNSF                           17

    The second was a series of provisions establishing what
is known as the “indirect source review program.” Those
provisions prohibited the federal government from regulating
any “indirect source,” or any “facility, building, structure,
installation, real property, road, or highway which attracts, or
may attract, mobile sources of pollution,” with the exception
of those that are federally assisted, owned, or operated. Pub.
L. No. 95-95, § 108(e), 91 Stat. at 696. The indirect source
review program permits, but does not require, a state to
regulate indirect sources as part of that state’s Clean Air Act
implementation plan. Id.7 In this case, neither party disputes
that Defendants’ railyards are “indirect sources” within the
meaning of the “indirect source review program” provision.

    So, by 1977, the regulation of emissions from
locomotives and railyards was governed solely by the Clean
Air Act. However, under its indirect source review program,
the Clean Air Act prohibited federal regulation of sources like
Defendants’ railyards, leaving regulation of emissions from
those sources entirely to the states. RCRA, for its part,
included no provision regulating air emissions and, indeed,
did not even contemplate the disposal of material into the air;
according to its stated purpose, RCRA was limited to



 7
   A House Report from 1977 documents a few of the reasons that federal
regulation of indirect sources of pollution was considered so controversial
at that time: (1) indirect sources do not pollute and therefore shouldn’t be
subject to the Clean Air Act; (2) indirect source control should not be
required before automobile pollution is fully controlled; (3) EPA has no
express statutory authority over indirect sources; (4) “[i]ndirect source
controls are veiled land use controls”; (5) indirect source controls will
only delay development and construction, contributing to unemployment,
inflation, and recession; and (6) indirect source controls will promote
urban sprawl. H.R. Rep. No. 95-294, at 220–21 (1977).
18           CTR. FOR CMTY. ACTION V. BNSF

regulating “land disposal.” See H.R. Rep. No. 94-1491, at 4
(1976) (Conf. Rep.).

    That changed in 1984, when Congress amended RCRA to
include a provision regulating air emissions from certain
sources. That provision requires the EPA to “promulgate
such regulations for the monitoring and control of air
emissions at hazardous waste treatment, storage, and disposal
facilities.” Hazardous and Solid Waste Amendments of 1984,
Pub. L. No. 98-616, § 201(n), 98 Stat. 3221, 3233. A Senate
Report summarizing the 1984 amendments sheds some light
on Congress’s intent as to the scope of the emissions
provision:

           There is a considerable body of
       information indicating that emissions into the
       air from hazardous waste facilities pose a
       significant threat to health and the
       environment. Emissions of volatile chemicals
       from treatment, storage and disposal of wastes
       have been estimated to be of a similar
       magnitude as emissions of the same
       compounds from industrial processes. Studies
       of hazardous waste surface impoundments
       and landfills report that significant quantities
       of hazardous constituents in the wastes may
       be emitted into the air. . . .

           Proposals to regulate emissions from
       hazardous waste facilities have been
       published on several occasions since the
       passage of [RCRA] in 1976. Final regulations
       have never been issued. The Agency also has
       authority to regulate emissions of hazardous
                 CTR. FOR CMTY. ACTION V. BNSF                      19

          air pollutants under the Clean Air Act, but its
          performance under that Act has been
          appallingly slow.

S. Rep. No. 98-284, at 63 (1983). Thus, with the 1984
amendments, Congress created the first (and only) overlap
between RCRA and the Clean Air Act: regulation of
emissions of hazardous air pollutants from “hazardous waste
treatment, storage, and disposal facilities.”

    Congress most recently overhauled the Clean Air Act in
1990. See Clean Air Act Amendments of 1990, Pub. L. No.
101-549, 104 Stat. 2399. During that process, Congress
amended the Act to require the EPA to promulgate
regulations “containing standards applicable to emissions
from new locomotives and new engines used in locomotives.”
See § 222(a), 104 Stat. at 2500.8 The amended statute
expressly prohibits the states from doing the same: “No State
or any political subdivision thereof shall adopt or attempt to
enforce any standard or other requirement relating to the
control of emissions from . . . [n]ew locomotives or new


 8
     The provision further states,

          Such standards shall achieve the greatest degree of
          emission reduction achievable through the application
          of technology which the Administrator determines will
          be available for the locomotives or engines to which
          such standards apply, giving appropriate consideration
          to the cost of applying such technology within the
          period of time available to manufacturers and to noise,
          energy, and safety factors associated with the
          application of such technology.

§ 222(a), 104 Stat. at 2500.
20              CTR. FOR CMTY. ACTION V. BNSF

engines used in locomotives.” § 222(b), 104 Stat. at 2502.9
Pursuant to its legislative directive, the EPA promulgated the
“New Locomotive Rule,” 63 Fed. Reg. 18978 (Apr. 16,
1998), and has since promulgated additional rules that apply
to emissions from heavy-duty vehicle engines and nonroad
vehicles. See, e.g., 66 Fed. Reg. 5002 (Jan. 18, 2001)
(Heavy-Duty Highway Rule); 73 Fed. Reg. 37096 (June 30,
2008) (Updated New Locomotive Rule).

    Thus, in 1990, regulation of emissions from locomotives
and railyards, which are indirect sources subject to the
indirect source review program, remained governed by the
provisions of the Clean Air Act. By way of the Act’s 1977
and 1990 amendments, regulation of locomotives and
locomotive engines was left exclusively to the EPA, and
regulation of railyards, as indirect sources of air pollution,
was expressly (although permissively) left to the states.
RCRA applied to neither. The only overlap between the
Clean Air Act and RCRA was in the regulation of emissions
from “hazardous waste treatment, storage, and disposal
facilities.”

                            *    *    *    *   *

    The statutory and legislative histories help to resolve any
textual ambiguities in at least two ways. First, they make
clear that RCRA, in light of its purpose to reduce the volume
of waste that ends up in our nation’s landfills, governs “land
disposal.” The Clean Air Act, by contrast, governs air


 9
   The legislative history suggests that Congress enacted the prohibition
on state regulation in light of the “unconstitutional burdens” that such state
efforts “would impose . . . on interstate commerce.” 136 Cong. Rec. H 12,
848 (daily ed. Oct. 26, 1990) (statement of Rep. Dingell).
             CTR. FOR CMTY. ACTION V. BNSF                    21

pollutants. To that end, the histories confirm our reading of
the RCRA’s text.

    Second, the histories further clarify that Defendants’
railyards, as “indirect sources” of air pollution, are excluded
from regulation under both statutory schemes. As we
explained, when RCRA was amended in 1984 to include the
emissions provision on which Plaintiffs rely here, the Senate
Committee on Environment and Public Works noted that the
EPA “has authority to regulate [these emissions] under the
Clean Air Act, but its performance under that Act has been
appallingly slow.” S. Rep. No. 98-284, at 63 (1983). Thus,
the emissions that Congress intended to be governed by the
newly enacted RCRA provision were also, at that time,
governed by the Clean Air Act. Defendants’ railyards,
however, as indirect sources, fell outside the scope of the
Clean Air Act, and therefore must also be excluded from
RCRA’s regulatory reach.

    The upshot of that conclusion, of course, is that emissions
such as those at issue here—emissions from indirect sources
like railyards—fall entirely outside the ambit of federal
regulation. On one hand, the Clean Air Act’s indirect source
review program prohibits federal regulation of emissions
from indirect sources; on the other, RCRA, as we interpret it,
likewise does not extend to these emissions. Plaintiffs,
relying on the Supreme Court’s decision in Morton v.
Mancari, take issue with the regulatory “gap” that results and
invite us to fill that gap by “harmonizing” the two statutory
schemes. See 417 U.S. 535, 551 (1974) (“When there are two
acts upon the same subject, the rule is to give effect to both if
possible.” (internal quotation marks omitted)). For two
reasons, we decline the invitation.
22           CTR. FOR CMTY. ACTION V. BNSF

    First, the Supreme Court in Morton announced a rule
disfavoring “repeal[s] by implication,” reiterating instead that
the legislature’s intent to repeal must be clear. Id. at 550. “In
the absence of some affirmative showing of an intention to
repeal, the only permissible justification for a repeal by
implication is when the earlier and later statutes are
irreconcilable.” Id. Under Morton, where two laws govern
the same conduct, a court must identify the degree to which
the two laws “irreconcilably conflict”; only where an
irreconcilable conflict occurs will the court consider the later
law to have impliedly repealed the earlier one. But where, as
here, there is no overlap between the two laws, Morton’s rule
simply does not apply.

    But, Morton aside, the second reason we decline to fill the
regulatory “gap” that Plaintiffs contend exists is because we
agree with the district court that any “gap” is the product of
a careful and reasoned decision made by Congress that we are
not at liberty to disturb. The statutory and legislative
histories make clear that Congress, having identified specific
reasons for its decision, intended to exclude indirect sources
from federal regulation. And its reasons for doing so, see
H.R. Rep. No. 95-294, at 220–21, are no less applicable under
RCRA than they are under any other federal law. Congress
was entitled to leave the regulation of indirect sources to the
states, and we defer to its reasoned judgment in doing so.

                              IV.

   We conclude that, by emitting diesel particulate matter
from their railyards and intermodal facilities, Defendants do
               CTR. FOR CMTY. ACTION V. BNSF                         23

not “dispose” of solid waste in violation of RCRA.10 That
conclusion, in our view, follows relatively clearly from
RCRA’s text; however, to the extent that its text is
ambiguous, RCRA’s statutory and legislative histories
resolve that ambiguity. Thus, Plaintiffs fail to state a
plausible claim for relief under § 6972(a)(1)(B). We
therefore AFFIRM the district court’s judgment.




 10
    Because we conclude that Defendants do not “dispose” of solid waste
in violation of RCRA, we need not reach the parties’ arguments about
whether diesel particulate matter is indeed “solid waste” under 42 U.S.C.
§ 6903(27). Likewise, we do not reach the question whether diesel
particulate matter, if it is a solid waste, “present[s] an imminent and
substantial endangerment to health or the environment.” § 6972(a)(1)(B).
