(Slip Opinion)              OCTOBER TERM, 2008                                       1

                                       Syllabus

         NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
       being done in connection with this case, at the time the opinion is issued.
       The syllabus constitutes no part of the opinion of the Court but has been
       prepared by the Reporter of Decisions for the convenience of the reader.
       See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337.


SUPREME COURT OF THE UNITED STATES

                                       Syllabus

      COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

          CONSERVATION COUNCIL ET AL. 


CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR
                  THE NINTH CIRCUIT

    No. 07–984.      Argued January 12, 2009—Decided June 22, 2009*
In reviving a closed Alaska gold mine using a “froth flotation” tech
  nique, petitioner Coeur Alaska, Inc., plans to dispose of the resulting
  waste material, a rock and water mixture called “slurry,” by pumping
  it into a nearby lake and then discharging purified lake water into a
  downstream creek. The Clean Water Act (CWA), inter alia, classifies
  crushed rock as a “pollutant,” §352(6); forbids its discharge “[e]xcept
  as in compliance” with the Act, §301(a); empowers the Army Corps of
  Engineers (Corps) to “issue permits . . . for the discharge of . . . fill
  material,” §404(a); and authorizes the Environmental Protection
  Agency (EPA) to “issue a permit for the discharge of any pollutant,”
  “[e]xcept as provided in [§404],” §402(a). The Corps and the EPA to
  gether define “fill material” as any “material [that] has the effect of
  . . . [c]hanging the bottom elevation” of water, including “slurry . . . or
  similar mining-related materials.” 40 CFR §232.2. Coeur Alaska ob
  tained a §404 permit for the slurry discharge from the Corps and a
  §402 permit for the lake water discharge from the EPA.
      Respondent environmental groups (collectively, SEACC) sued the
  Corps and several of its officials under the Administrative Procedure
  Act, arguing that the CWA §404 permit was not “in accordance with
  law,” 5 U. S. C. §706(2)(A), because (1) Coeur Alaska should have
  sought a CWA §402 permit from the EPA instead, just as it did for
  the lake water discharge; and (2) the slurry discharge would violate
  the “new source performance standard” the EPA had promulgated
  under CWA §306(b), forbidding froth-flotation gold mines to dis
——————
  * Together with No. 07–990, Alaska v. Southeast Alaska Conservation
Council et al., also on certiorari to the same court.
2           COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

                   CONSERVATION COUNCIL

                            Syllabus 


    charge “process wastewater,” which includes solid wastes, 40 CFR
    §440.104(b)(1). Coeur Alaska and petitioner Alaska intervened as de
    fendants. The District Court granted the defendants summary
    judgment, but the Ninth Circuit reversed, holding that the proposed
    slurry discharge would violate the EPA’s performance standard and
    §306(e).
Held:
    1. The Corps, not the EPA, has authority to permit the slurry dis
 charge. Pp. 9–13.
       (a) By specifying that, “[e]xcept as provided in . . . [§404,]” the
 EPA “may . . . issue permit[s] for the discharge of any pollutant,”
 §402(a) forbids the EPA to issue permits for fill materials falling un
 der the Corps’ §404 authority. Even if there were ambiguity on this
 point, it would be resolved by the EPA’s own regulation providing
 that “[d]ischarges of . . . fill material . . . which are regulated under
 section 404” “do not require [EPA §402] permits.” 40 CFR §122.3.
 The agencies have interpreted this regulation to essentially restate
 §402’s text, ibid., and the EPA has confirmed that reading before this
 Court. Because it is not “plainly erroneous or inconsistent with the
 regulation,” the Court accepts the EPA’s interpretation as correct.
 Auer v. Robbins, 519 U. S. 452, 461. Thus, the question whether the
 EPA is the proper agency to regulate the slurry discharge depends on
 whether the Corps has authority to do so. If so, the EPA may not
 regulate. Pp. 9–11.
       (b) Because §404(a) empowers the Corps to “issue permits . . . for
 the discharge of . . . fill material,” and the agencies’ joint regulation
 defines “fill material” to include “slurry . . . or similar mining-related
 materials” having the “effect of . . . [c]hanging the bottom elevation”
 of water, 40 CFR §232.2, the slurry Coeur Alaska wishes to discharge
 into the lake falls well within the Corps’ §404 permitting authority,
 rather than the EPA’s §402 authority. The CWA gives no indication
 that Congress intended to burden industry with the confusing divi
 sion of permitting authority that SEACC’s contrary reading would
 create. Pp. 11–13.
    2. The Corps acted in accordance with law in issuing the slurry dis
 charge permit to Coeur Alaska. Pp. 13–28.
       (a) The CWA alone does not resolve these cases. Pp. 14–18.
         (i) SEACC contends that because the EPA’s performance stan
 dard forbids even minute solid waste discharges, 40 CFR
 §440.104(b)(1), it also forbids Coeur Alaska’s slurry discharge, 30% of
 which is solid waste, into the lake. Thus, says SEACC, the slurry
 discharge is “unlawful” under CWA §306(e), which prohibits “any
 owner . . . of any new source to operate such source in violation of any
 standard of performance applicable to such source.” Pp. 14–16.
                    Cite as: 557 U. S. ____ (2009)                       3

                               Syllabus

        (ii) Petitioners and the federal agencies counter that CWA
§404 grants the Corps authority to determine whether to issue a
permit allowing the slurry discharge without regard to the EPA’s
new source performance standard or §306(e)’s prohibition. Pp. 16–18.
        (iii) The CWA is ambiguous on the question whether §306 ap
plies to discharges of fill material regulated under §404. On the one
hand, §306 provides that a discharge that violates an EPA new
source performance standard is “unlawful”—without an exception for
fill material. On the other hand, §404 grants the Corps blanket au
thority to permit the discharge of fill material—without mentioning
§306. This tension indicates that Congress has not “directly spoken”
to the “precise question” at issue. Chevron U. S. A. Inc. v. Natural
Resources Defense Council, Inc., 467 U. S. 837, 842. P. 18.
     (b) Although the agencies’ regulations construing the CWA are
entitled to deference if they resolve the statutory ambiguity in a rea
sonable manner, see Chevron, supra, at 842, the regulations bearing
on §§306 and 404, like the CWA itself, do not do so. For example,
each of the two principal regulations seems to stand on its own with
out reference to the other. The EPA’s performance standard contains
no exception for fill material, and it forbids any discharge of “process
wastewater,” including solid wastes. 40 CFR §440.104(b)(1). The
agencies’ joint regulation defining fill material includes “slurry or . . .
similar mining-related materials,” §232.2, but contains no exception
for slurry regulated by an EPA performance standard. Additional
regulations noted by the parties offer no basis for reconciliation.
Pp. 18–20.
     (c) In light of the ambiguities in the CWA and the pertinent regu
lations, the Court turns to the agencies’ subsequent interpretation of
those regulations. Auer, supra, at 461. The question at issue is ad
dressed and resolved in a reasonable and coherent way by the two
agencies’ practice and policy, as recited in the EPA’s internal “Regas
Memorandum” (Memorandum), which explains that the performance
standard applies only to the discharge of water from the lake into the
downstream creek, and not to the initial discharge of slurry into the
lake. Though the Memorandum is not subject to sufficiently formal
procedures to merit full Chevron deference, the Court defers to it be
cause it is not “plainly erroneous or inconsistent with the regula
tion[s],” Auer, supra, at 461. Five factors inform that conclusion: The
Memorandum (1) confines its own scope to closed bodies of water like
the lake here, thereby preserving a role for the performance stan
dards; (2) guards against the possibility of evasion of those standards;
(3) employs the Corps’ expertise in evaluating the effects of fill mate
rial on the aquatic environment; (4) does not allow toxic compounds
to be discharged into navigable waters; and (5) reconciles §§306, 402,
4           COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

                   CONSERVATION COUNCIL

                            Syllabus 


    and 404, and the regulations implementing them, better than any of
    the parties’ alternatives. The Court agrees with the parties that a
    two-permit regime is contrary to the statute and regulations. Pp. 20–
    23.
          (d) The Court rejects SEACC’s contention that the Regas Memo
    randum is not entitled to deference because it contradicts the agen
    cies’ published statements and prior practice. Though SEACC cites
    three such statements, its arguments are not convincing. Pp. 23–28.
            (i) Although a 1986 memorandum of agreement (MOA) be
    tween the EPA and the Corps seeking to reconcile their then-differing
    “fill material” definitions suggests, as SEACC asserts, that §402 will
    “normally” apply to discharges of “suspended”—i.e., solid—pollutants,
    that statement is not contrary to the Regas Memorandum, which ac
    knowledges that the EPA retains authority under §402 to regulate
    the discharge of suspended solids from the lake into downstream wa
    ters. The MOA does not address the question presented by these
    cases, and answered by the Regas Memorandum, and is, in fact, con
    sistent with the agencies’ determination that the Corps regulates all
    discharges of fill material and that §306 does not apply to these dis
    charges. Pp. 23–25.
            (ii) Despite SEACC’s assertion that the fill regulation’s pream
    ble demonstrates that the fill rule was not intended to displace the
    pre-existing froth-flotation gold mine performance standard, the pre
    amble is consistent with the Regas Memorandum when it explicitly
    notes that the EPA has “never sought to regulate fill material under
    effluent guidelines,” 67 Fed. Reg. 31135. If a discharge does not qual
    ify as fill, the EPA’s new source performance standard applies. If the
    discharge qualifies as fill, the performance standard does not apply;
    and there was no earlier agency practice or policy to the contrary.
    Pp. 25–26.
            (iii) Remarks made by the two agencies in promulgating the fill
    regulation, which pledge that the EPA’s “previou[s] . . . determina
    tion[s]” with regard to the application of performance standards “re
    main vali[d],” are not conclusive of the question at issue. The Regas
    Memorandum has followed this policy by applying the performance
    standard to the discharge of water from the lake into the creek. The
    remarks do not state that the EPA will apply such standards to dis
    charges of fill material. Pp. 26–27.
            (iv) While SEACC cites no instance in which the EPA has ap
    plied a performance standard to a discharge of fill material, Coeur
    Alaska cites two instances in which the Corps issued a §404 permit
    authorizing a mine to discharge solid waste as fill material. These
    permits illustrate that the agencies did not have a prior practice of
    applying EPA performance standards to discharges of mining wastes
                     Cite as: 557 U. S. ____ (2009)                  5

                                Syllabus

  that qualify as fill material. Pp. 27–28.
486 F. 3d 638, reversed and remanded.

   KENNEDY, J., delivered the opinion of the Court, in which ROBERTS,
C. J., and THOMAS, BREYER, and ALITO, JJ., joined, and in which SCALIA,
J., joined in part. BREYER, J., filed a concurring opinion. SCALIA, J.,
filed an opinion concurring in part and concurring in the judgment.
GINSBURG, J., filed a dissenting opinion, in which STEVENS and SOUTER,
JJ., joined.
                       Cite as: 557 U. S. ____ (2009)                              1

                            Opinion of the Court

    NOTICE: This opinion is subject to formal revision before publication in the
    preliminary print of the United States Reports. Readers are requested to
    notify the Reporter of Decisions, Supreme Court of the United States, Wash
    ington, D. C. 20543, of any typographical or other formal errors, in order
    that corrections may be made before the preliminary print goes to press.


SUPREME COURT OF THE UNITED STATES
                                  _________________

                          Nos. 07–984 and 07–990
                                  _________________


       COEUR ALASKA, INC., PETITIONER
07–984              v.
  SOUTHEAST ALASKA CONSERVATION COUNCIL
                  ET AL.


            ALASKA, PETITIONER
07–990               v.
  SOUTHEAST ALASKA CONSERVATION COUNCIL
                  ET AL.

ON WRITS OF CERTIORARI TO THE UNITED STATES COURT OF
            APPEALS FOR THE NINTH CIRCUIT
                                [June 22, 2009]

  JUSTICE KENNEDY delivered the opinion of the Court.
  These cases require us to address two questions under
the Clean Water Act (CWA or Act). The first is whether
the Act gives authority to the United States Army Corps of
Engineers, or instead to the Environmental Protection
Agency (EPA), to issue a permit for the discharge of min
ing waste, called slurry. The Corps of Engineers has
issued a permit to petitioner Coeur Alaska, Inc. (Coeur
Alaska), for a discharge of slurry into a lake in Southeast
Alaska. The second question is whether, when the Corps
issued that permit, the agency acted in accordance with
law. We conclude that the Corps was the appropriate
agency to issue the permit and that the permit is lawful.
  With regard to the first question, §404(a) of the CWA
2       COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

               CONSERVATION COUNCIL

                  Opinion of the Court 


grants the Corps the power to “issue permits . . . for the
discharge of . . . fill material.” 86 Stat. 884; 33 U. S. C.
§1344(a). But the EPA also has authority to issue permits
for the discharge of pollutants. Section 402 of the Act
grants the EPA authority to “issue a permit for the dis
charge of any pollutant” “[e]xcept as provided in” §404. 33
U. S. C. §1342(a). We conclude that because the slurry
Coeur Alaska wishes to discharge is defined by regulation
as “fill material,” 40 CFR §232.2 (2008), Coeur Alaska
properly obtained its permit from the Corps of Engineers,
under §404, rather than from the EPA, under §402.
   The second question is whether the Corps permit is
lawful. Three environmental groups, respondents here,
sued the Corps under the Administrative Procedure Act,
arguing that the issuance of the permit by the Corps was
“not in accordance with law.” 5 U. S. C. §706(2)(A). The
environmental groups are Southeast Alaska Conservation
Council, Sierra Club, and Lynn Canal Conservation (col
lectively, SEACC). The State of Alaska and Coeur Alaska
are petitioners here.
   SEACC argues that the permit from the Corps is unlaw
ful because the discharge of slurry would violate an EPA
regulation promulgated under §306(b) of the CWA, 33
U. S. C. §1316(b). The EPA regulation, which is called a
“new source performance standard,” forbids mines like
Coeur Alaska’s from discharging “process wastewater” into
the navigable waters. 40 CFR §440.104(b)(1). Coeur
Alaska, the State of Alaska, and the federal agencies
maintain that the Corps permit is lawful nonetheless
because the EPA’s performance standard does not apply to
discharges of fill material.
   Reversing the judgment of the District Court, the Court
of Appeals held that the EPA’s performance standard
applies to this discharge so that the permit from the Corps
is unlawful.
                 Cite as: 557 U. S. ____ (2009)            3

                     Opinion of the Court

                               I

                              A

   Petitioner Coeur Alaska plans to reopen the Kensington
Gold Mine, located some 45 miles north of Juneau, Alaska.
The mine has been closed since 1928, but Coeur Alaska
seeks to make it profitable once more by using a technique
known as “froth flotation.” Coeur Alaska will churn the
mine’s crushed rock in tanks of frothing water. Chemicals
in the water will cause gold-bearing minerals to float to
the surface, where they will be skimmed off.
   At issue is Coeur Alaska’s plan to dispose of the mixture
of crushed rock and water left behind in the tanks. This
mixture is called slurry. Some 30 percent of the slurry’s
volume is crushed rock, resembling wet sand, which is
called tailings. The rest is water.
   The standard way to dispose of slurry is to pump it into
a tailings pond. The slurry separates in the pond. Solid
tailings sink to the bottom, and water on the surface
returns to the mine to be used again.
   Rather than build a tailings pond, Coeur Alaska pro
poses to use Lower Slate Lake, located some three miles
from the mine in the Tongass National Forest. This lake
is small—800 feet at its widest crossing, 2,000 feet at its
longest, and 23 acres in area. See App. 138a, 212a.
Though small, the lake is 51 feet deep at its maximum.
The parties agree the lake is a navigable water of the
United States and so is subject to the CWA. They also
agree there can be no discharge into the lake except as the
CWA and any lawful permit allow.
   Over the life of the mine, Coeur Alaska intends to put
4.5 million tons of tailings in the lake. This will raise the
lakebed 50 feet—to what is now the lake’s surface—and
will increase the lake’s area from 23 to about 60 acres. Id.,
at 361a (62 acres), 212a (56 acres). To contain this wider,
shallower body of water, Coeur Alaska will dam the lake’s
downstream shore. The transformed lake will be isolated
4        COEUR ALASKA, INC. v. SOUTHEAST ALASKA
                CONSERVATION COUNCIL
                   Opinion of the Court

from other surface water. Creeks and stormwater runoff
will detour around it. Id., at 298a. Ultimately, lakewater
will be cleaned by purification systems and will flow from
the lake to a stream and thence onward. Id., at 309a–
312a.
                            B
  Numerous state and federal agencies reviewed and
approved Coeur Alaska’s plans. At issue here are actions
by two of those agencies: the Corps of Engineers and the
EPA.
                               1
  The CWA classifies crushed rock as a “pollutant.” 33
U. S. C. §1362(6). On the one hand, the Act forbids Coeur
Alaska’s discharge of crushed rock “[e]xcept as in compli
ance” with the Act. CWA §301(a), 33 U. S. C. §1311(a).
Section 404(a) of the CWA, on the other hand, empowers
the Corps to authorize the discharge of “dredged or fill
material.” 33 U. S. C. §1344(a). The Corps and the EPA
have together defined “fill material” to mean any “mate
rial [that] has the effect of . . . [c]hanging the bottom ele
vation” of water. 40 CFR §232.2. The agencies have
further defined the “discharge of fill material” to include
“placement of . . . slurry, or tailings or similar mining
related materials.” Ibid.
  In these cases the Corps and the EPA agree that the
slurry meets their regulatory definition of “fill material.”
On that premise the Corps evaluated the mine’s plan for a
§404 permit. After considering the environmental factors
required by §404(b), the Corp issued Coeur Alaska a per
mit to pump the slurry into Lower Slate Lake. App. 340a–
378a.
  In granting the permit the Corps followed the steps set
forth by §404. Section 404(b) requires the Corps to con
sider the environmental consequences of every discharge it
                 Cite as: 557 U. S. ____ (2009)           5

                     Opinion of the Court

allows. 33 U. S. C. §1344(b). The Corps must apply guide
lines written by the EPA pursuant to §404(b). See ibid.;
40 CFR pt. 230 (EPA guidelines). Applying those guide
lines here, the Corps determined that Coeur Alaska’s plan
to use Lower Slate Lake as a tailings pond was the “least
environmentally damaging practicable” way to dispose of
the tailings. App. 366a. To conduct that analysis, the
Corps compared the plan to the proposed alternatives.
   The Corps determined that the environmental damage
caused by placing slurry in the lake will be temporary.
And during that temporary disruption, Coeur Alaska will
divert waters around the lake through pipelines built for
this purpose. Id., at 298a. Coeur Alaska will also treat
water flowing from the lake into downstream waters,
pursuant to strict EPA criteria. Ibid.; see Part I–B–2,
infra. Though the slurry will at first destroy the lake’s
small population of common fish, that population may
later be replaced. After mining operations are completed,
Coeur Alaska will help “recla[im]” the lake by “[c]apping”
the tailings with about 4 inches of “native material.” App.
361a; id., at 309a. The Corps concluded that
    “[t]he reclamation of the lake will result in more
    emergent wetlands/vegetated shallows with moderate
    values for fish habitat, nutrient recycling, car
    bon/detrital export and sediment/toxicant retention,
    and high values for wildlife habitat.” Id., at 361a.
   If the tailings did not go into the lake, they would be
placed on nearby wetlands. The resulting pile would rise
twice as high as the Pentagon and cover three times as
many acres. Reply Brief for Petitioner Coeur Alaska 27.
If it were chosen, that alternative would destroy dozens of
acres of wetlands—a permanent loss. App. 365a–366a.
On the premise that when the mining ends the lake will
be at least as environmentally hospitable, if not more so,
than now, the Corps concluded that placing the tailings in
6        COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

                CONSERVATION COUNCIL

                   Opinion of the Court 


the lake will cause less damage to the environment than
storing them above ground: The reclaimed lake will be
“more valuable to the aquatic ecosystem than a perma
nently filled wetland . . . that has lost all aquatic functions
and values.” Id., at 361a; see also id., at 366a.
                              2
   The EPA had the statutory authority to veto the Corps
permit, and prohibit the discharge, if it found the plan to
have “an unacceptable adverse effect on municipal water
supplies, shellfish beds and fishery areas . . . , wildlife, or
recreational areas.” CWA §404(c), 33 U. S. C. §1344(c).
After considering the Corps findings, the EPA did not veto
the Corps permit, even though, in its view, placing the
tailings in the lake was not the “environmentally prefer
able” means of disposing of them. App. 300a. By declining
to exercise its veto, the EPA in effect deferred to the judg
ment of the Corps on this point.
   The EPA’s involvement extended beyond the agency’s
veto consideration. The EPA also issued a permit of its
own—not for the discharge from the mine into the lake but
for the discharge from the lake into a downstream creek.
Id., at 287a–331a. Section 402 grants the EPA authority
to “issue a permit for the discharge of any pollutant,”
“[e]xcept as provided in [CWA §404].”             33 U. S. C.
§1342(a). The EPA’s §402 permit authorizes Coeur Alaska
to discharge water from Lower Slate Lake into the down
stream creek, subject to strict water-quality limits that
Coeur Alaska must regularly monitor. App. 303a–304a,
309a.
   The EPA’s authority to regulate this discharge comes
from a regulation, termed a “new source performance
standard,” that it has promulgated under authority
granted to it by §306(b) of the CWA. Section 306(b) gives
the EPA authority to regulate the amount of pollutants
that certain categories of new sources may discharge into
                 Cite as: 557 U. S. ____ (2009)           7

                     Opinion of the Court

the navigable waters of the United States. 33 U. S. C.
§1316(b). Pursuant to this authority, the EPA in 1982
promulgated a new source performance standard restrict
ing discharges from new froth-flotation gold mines like
Coeur Alaska’s. The standard is stringent: It allows “no
discharge of process wastewater” from these mines. 40
CFR §440.104(b)(1).
   Applying that standard to the discharge of water from
Lower Slate Lake into the downstream creek, the EPA’s
§402 permit sets strict limits on the amount of pollutants
the water may contain. The permit requires Coeur Alaska
to treat the water using “reverse osmosis” to remove alu
minum, suspended solids, and other pollutants. App.
298a; id., at 304a. Coeur Alaska must monitor the water
flowing from the lake to be sure that the pollutants are
kept to low, specified minimums. Id., at 326a–330a.
                               C
  SEACC brought suit against the Corps of Engineers and
various of its officials in the United States District Court
for the District of Alaska. The Corps permit was not in
accordance with law, SEACC argued, for two reasons.
First, in SEACC’s view, the permit was issued by the
wrong agency—Coeur Alaska ought to have sought a §402
permit from the EPA, just as the company did for the
discharge of water from the lake into the downstream
creek. See Part I–B–2, supra. Second, SEACC contended
that regardless of which agency issued the permit, the
discharge itself is unlawful because it will violate the EPA
new source performance standard for froth-flotation gold
mines. (This is the same performance standard described
above, which the EPA has already applied to the discharge
of water from the lake into the downstream creek. See
ibid.) SEACC argued that this performance standard also
applies to the discharge of slurry into the lake. It con
tended further that the performance standard is a binding
8        COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

                CONSERVATION COUNCIL

                   Opinion of the Court 


implementation of §306. Section 306(e) of the CWA makes
it “unlawful” for Coeur Alaska to “operate” the mine “in
violation of” the EPA’s performance standard. 33 U. S. C.
§1316(e).
   Coeur Alaska and the State of Alaska intervened as
defendants. Both sides moved for summary judgment.
The District Court granted summary judgment in favor of
the defendants.
   The Court of Appeals for the Ninth Circuit reversed and
ordered the District Court to vacate the Corps of Engi
neers’ permit. Southeast Alaska Conservation Council v.
United States Army Corps of Engs., 486 F. 3d 638, 654–
655 (2007). The court acknowledged that Coeur Alaska’s
slurry “facially meets the Corps’ current regulatory defini
tion of ‘fill material,’ ” id., at 644, because it would have
the effect of raising the lake’s bottom elevation. But the
court also noted that the EPA’s new source performance
standard “prohibits discharges from froth-flotation mills.”
Ibid. The Court of Appeals concluded that “[b]oth of the
regulations appear to apply in this case, yet they are at
odds.” Ibid. To resolve the conflict, the court turned to
what it viewed as “the plain language of the Clean Water
Act.” Ibid. The court held that the EPA’s new source
performance standard “applies to discharges from the
froth-flotation mill at Coeur Alaska’s Kensington Gold
Mine into Lower Slate Lake.” Ibid.
   In addition to the text of the CWA, the Court of Appeals
also relied on the agencies’ statements made when prom
ulgating their current and prior definitions of “fill mate
rial.” These statements, in the Court of Appeals’ view,
demonstrated the agencies’ intent that the EPA’s new
source performance standard govern discharges like Coeur
Alaska’s. Id., at 648–654.
   The Court of Appeals concluded that Coeur Alaska
required a §402 permit for its slurry discharge, that the
Corps lacked authority to issue such a permit under §404,
                 Cite as: 557 U. S. ____ (2009)           9

                     Opinion of the Court

and that the proposed discharge was unlawful because it
would violate the EPA new source performance standard
and §306(e).
  The decision of the Court of Appeals in effect reallocated
the division of responsibility that the Corps and the EPA
had been following. The Court granted certiorari. 554
U. S. ___ (2008). We now hold that the decision of the
Court of Appeals was incorrect.
                            II
  The question of which agency has authority to consider
whether to permit the slurry discharge is our beginning
inquiry. We consider first the authority of the EPA and
second the authority of the Corps. Our conclusion is that
under the CWA the Corps had authority to determine
whether Coeur Alaska was entitled to the permit govern
ing this discharge.
                           A
  Section 402 gives the EPA authority to issue “permit[s]
for the discharge of any pollutant,” with one important
exception: The EPA may not issue permits for fill material
that fall under the Corps’ §404 permitting authority.
Section 402(a) states:
    “Except as provided in . . . [CWA §404, 33 U. S. C.
    §1344], the Administrator may . . . issue a permit for
    the discharge of any pollutant, . . . notwithstanding
    [CWA §301(a), 33 U. S. C. §1311(a)], upon condition
    that such discharge will meet either (A) all applicable
    requirements under [CWA §301, 33 U. S. C. §1311(a);
    CWA §302, 33 U. S. C. §1312; CWA §306, 33 U. S. C.
    §1316; CWA §307, 33 U. S. C. §1317; CWA §308, 33
    U. S. C. §1318; CWA §403, 33 U. S. C. §1343], or (B)
    prior to the taking of necessary implementing actions
    relating to all such requirements, such conditions as
    the Administrator determines are necessary to carry
10       COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

                CONSERVATION COUNCIL

                   Opinion of the Court 


     out the provisions of this chapter.”       33 U. S. C.
     §1342(a)(1) (emphasis added).
Section 402 thus forbids the EPA from exercising permit
ting authority that is “provided [to the Corps] in” §404.
   This is not to say the EPA has no role with respect to
the environmental consequences of fill. The EPA’s func
tion is different, in regulating fill, from its function in
regulating other pollutants, but the agency does exercise
some authority. Section 404 assigns the EPA two tasks in
regard to fill material. First, the EPA must write guide
lines for the Corps to follow in determining whether to
permit a discharge of fill material. CWA §404(b); 33
U. S. C. §1344(b). Second, the Act gives the EPA authority
to “prohibit” any decision by the Corps to issue a permit
for a particular disposal site. CWA §404(c); 33 U. S. C.
§1344(c). We, and the parties, refer to this as the EPA’s
power to veto a permit.
   The Act is best understood to provide that if the Corps
has authority to issue a permit for a discharge under §404,
then the EPA lacks authority to do so under §402.
   Even if there were ambiguity on this point, the EPA’s
own regulations would resolve it. Those regulations pro
vide that “[d]ischarges of dredged or fill material into
waters of the United States which are regulated under
section 404 of CWA” “do not require [§402] permits” from
the EPA. 40 CFR §122.3.
   In SEACC’s view, this regulation implies that some “fill
material” discharges are not regulated under §404—else,
SEACC asks, why would the regulation lack a comma
before the word “which,” and thereby imply that only a
subset of “discharges of . . . fill material” are “regulated
under section 404.” Ibid.
   The agencies, however, have interpreted this regulation
otherwise. In the agencies’ view the regulation essentially
restates the text of §402, and forbids the EPA from issuing
                 Cite as: 557 U. S. ____ (2009)           11

                     Opinion of the Court

permits for discharges that “are regulated under section
404.” 40 CFR §122.3(b); cf. CWA §402(a) (“[e]xcept as
provided in . . . [§404], the Administrator may . . . issue a
permit”). Before us, the EPA confirms this reading of the
regulation. Brief for Federal Respondents 27. The
agency’s interpretation is not “plainly erroneous or incon
sistent with the regulation”; and so we accept it as correct.
Auer v. Robbins, 519 U. S. 452, 461 (1997) (internal quota
tion marks omitted).
   The question whether the EPA is the proper agency to
regulate the slurry discharge thus depends on whether the
Corps of Engineers has authority to do so. If the Corps
has authority to issue a permit, then the EPA may not do
so. We turn to the Corps’ authority under §404.
                               B
  Section 404(a) gives the Corps power to “issue per
mits . . . for the discharge of dredged or fill material.” 33
U. S. C. §1344(a). As all parties concede, the slurry meets
the definition of fill material agreed upon by the agencies
in a joint regulation promulgated in 2002. That regulation
defines “fill material” to mean any “material [that] has the
effect of . . . [c]hanging the bottom elevation” of water—a
definition that includes “slurry, or tailings or similar
mining-related materials.” 40 CFR §232.2.
  SEACC concedes that the slurry to be discharged meets
the regulation’s definition of fill material. Brief for Re
spondent SEACC et al. 20. Its concession on this point is
appropriate because slurry falls well within the central
understanding of the term “fill,” as shown by the examples
given by the regulation. See 40 CFR §232.2 (“Examples of
such fill material include, but are not limited to: rock,
sand, soil, clay . . . .”). The regulation further excludes
“trash or garbage” from its definition. Ibid. SEACC ex
presses a concern that Coeur Alaska’s interpretation of the
statute will lead to §404 permits authorizing the dis
12       COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

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                   Opinion of the Court 


charges of other solids that are now restricted by EPA
standards. Brief for Respondent SEACC et al. 44–45
(listing, for example, “feces and uneaten feed,” “ litter, ”
and waste produced in “battery manufacturing”). But
these extreme instances are not presented by the cases
now before us. If, in a future case, a discharger of one of
these solids were to seek a §404 permit, the dispositive
question for the agencies would be whether the solid at
issue—for instance, “feces and uneaten feed”—came
within the regulation’s definition of “fill.” SEACC cites no
instance in which the agencies have so interpreted their
fill regulation. If that instance did arise, and the agencies
were to interpret the fill regulation as SEACC fears, then
SEACC could challenge that decision as an unlawful
interpretation of the fill regulation; or SEACC could claim
that the fill regulation as interpreted is an unreasonable
interpretation of §404. The difficulties are not presented
here, however, because the slurry meets the regulation’s
definition of fill.
   Rather than challenge the agencies’ decision to define
the slurry as fill, SEACC instead contends that §404
contains an implicit exception. According to SEACC, §404
does not authorize the Corps to permit a discharge of fill
material if that material is subject to an EPA new source
performance standard.
   But §404’s text does not limit its grant of power in this
way. Instead, §404 refers to all “fill material” without
qualification.      Nor do the EPA regulations support
SEACC’s reading of §404. The EPA has enacted guide
lines, pursuant to §404(b), to guide the Corps permitting
decision. 40 CFR pt. 230. Those guidelines do not strip
the Corps of power to issue permits for fill in cases where
the fill is also subject to an EPA new source performance
standard.
   SEACC’s reading of §404 would create numerous diffi
culties for the regulated industry. As the regulatory re
                 Cite as: 557 U. S. ____ (2009)          13

                     Opinion of the Court

gime stands now, a discharger must ask a simple ques
tion—is the substance to be discharged fill material or
not? The fill regulation, 40 CFR §232.2, offers a clear
answer to that question; and under the agencies’ view,
that answer decides the matter—if the discharge is fill,
the discharger must seek a §404 permit from the Corps; if
not, only then must the discharger consider whether any
EPA performance standard applies, so that the discharger
requires a §402 permit from the EPA.
   Under SEACC’s interpretation, however, the discharger
would face a more difficult problem. The discharger would
have to ask—is the fill material also subject to one of the
many hundreds of EPA performance standards, so that
the permit must come from the EPA, not the Corps? The
statute gives no indication that Congress intended to
burden industry with that confusing division of permit
authority.
   The regulatory scheme discloses a defined, and worka
ble, line for determining whether the Corps or the EPA
has the permit authority. Under this framework, the
Corps of Engineers, and not the EPA, has authority to
permit Coeur Alaska’s discharge of the slurry.
                            III
  A second question remains: In issuing the permit did the
Corps act in violation of a statutory mandate so that the
issuance was “not in accordance with law”? 5 U. S. C.
§706(2)(A). SEACC contends that the slurry discharge
will violate the EPA’s new source performance standard
and that the Corps permit is made “unlawful” by CWA
§306(e). Petitioners and the agencies argue that the per
mit is lawful because the EPA performance standard, and
§306(e), do not apply to fill material regulated by the
Corps. In order to determine whether the Corps permit is
lawful we must answer the question: Do EPA performance
standards, and §306(e), apply to discharges of fill mate
14      COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

               CONSERVATION COUNCIL

                  Opinion of the Court 


rial?
   We address in turn the statutory text of the CWA, the
agencies’ regulations construing it, and the EPA’s subse
quent interpretation of those regulations. Because Con
gress has not “directly spoken” to the “precise question” of
whether an EPA performance standard applies to dis
charges of fill material, the statute alone does not resolve
the case. Chevron U. S. A. Inc. v. Natural Resources De
fense Council, Inc., 467 U. S. 837, 842 (1984). We look
first to the agency regulations, which are entitled to defer
ence if they resolve the ambiguity in a reasonable manner.
Ibid.; see United States v. Mead Corp., 533 U. S. 218, 226–
227 (2001). But the regulations, too, are ambiguous, so we
next turn to the agencies’ subsequent interpretation of
those regulations. Id., at 234–238; Auer, 519 U. S., at 461.
In an internal memorandum the EPA explained that its
performance standards do not apply to discharges of fill
material. That interpretation is not “plainly erroneous or
inconsistent with the regulation[s],” and so we accept it as
correct. Ibid. (internal quotation marks omitted). Though
SEACC contends that the agencies’ interpretation is not
entitled to deference because it contradicts the agencies’
published statements and prior practice, we disagree with
SEACC’s reading of those statements and of the regula
tory record.
                            A
  As for the statutory argument, SEACC claims the CWA
§404 permit is unlawful because §306(e) forbids the slurry
discharge. Petitioners and the federal agencies, in con
trast, contend that §306(e) does not apply to the slurry
discharge.
                           1
  To address SEACC’s statutory argument, it is necessary
to review the EPA’s responsibilities under the CWA. As
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                      Opinion of the Court

noted, §306 empowers the EPA to regulate the froth
flotation gold mining industry. See 33 U. S. C. §1316(b).
Pursuant to this authority, EPA promulgated the new
source performance standard relied upon by SEACC. The
standard is stringent. If it were to apply here, it would
allow “no discharge of process wastewater” from the mine.
40 CFR §440.104(b)(1).
   The term “process wastewater” includes solid waste. So
the regulation forbids not only pollutants that dissolve in
water but also solid pollutants suspended in water—what
the agency terms “total suspended solids,” or TSS. See
§440.104(a) (limiting the amount of TSS from other kinds
of mines); see also EPA Development Document for Efflu
ent Limitations Guidelines and Standards for the Ore
Mining and Dressing Point Source Category 157–158
(Nov. 1982) (the amount of TSS in “wastewater” from
froth-flotation mines is “generally high”); id., at 175 (Table
VI–6) (measuring the amounts of TSS in samples of froth
flotation mines’ discharges); id., at 194 (stating an intent
to “regulat[e]” TSS); id., at 402 (evaluating the costs of
constructing a “settling pond”); id., at 535 (concluding that
even in mountainous regions, a froth-flotation mine will be
able to construct a “tailings impoundment” to “provide a
disposal area for mill tailings”).
   Were there any doubt about whether the EPA’s new
source performance standard forbade solids as well as
soluble pollutants, the agency’s action in these cases
would resolve it. Here, the EPA’s §402 permit authorizes
Coeur Alaska to discharge water from Lower Slate Lake
into a downstream creek, provided the water meets the
quality requirements set by the performance standard.
This demonstrates that the performance standard regu
lates solid waste. The EPA’s permit not only restricts the
amount of total suspended solids, App. 327a (Table 3), but
also forbids the mine from allowing any “floating solids” to
flow from the lake. Id., at 328a. No party disputes the
16       COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

                CONSERVATION COUNCIL

                   Opinion of the Court 


EPA’s authority to regulate these discharges of solid min
ing waste; and no party questions the validity of the EPA’s
new source performance standard when it is applicable.
   When the performance standard applies to a point
source, §306(e) makes it “unlawful” for that point source to
violate it: “[I]t shall be unlawful for any owner or operator
of any new source to operate such source in violation of
any standard of performance applicable to such source.”
CWA §306(e), 33 U. S. C. §1316(e).
   SEACC argues that this provision, §306(e), forbids the
mine from discharging slurry into Lower Slate Lake.
SEACC contends the new source performance standard is,
in the words of §306(e), “applicable to” the mine. Both the
text of the performance standard and the EPA’s applica
tion of it to the discharge of mining waste from Lower
Slate Lake demonstrate that the performance standard is
“applicable to” Coeur Alaska’s mine in some circum
stances. And so, SEACC reasons, it follows that because
the new source performance standard forbids even minute
discharges of solid waste, it also forbids the slurry dis
charge, 30% of which is solid waste.
                              2
  For their part, the State of Alaska and the federal agen
cies claim that the Act is unambiguous in the opposite
direction. They rely on §404 of the Act. As explained
above, that section authorizes the Corps of Engineers to
determine whether to issue a permit allowing the dis
charge of the slurry. Petitioners and the agencies argue
that §404 grants the Corps authority to do so without
regard to the EPA’s new source performance standard or
the §306(e) prohibition discussed above.
  Petitioners and the agencies make two statutory argu
ments based on §404’s silence in regard to §306. First,
they note that nothing in §404 requires the Corps to con
sider the EPA’s new source performance standard or the
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                     Opinion of the Court

§306(e) prohibition. That silence advances the argument
that §404’s grant of authority to “issue permits” contra
dicts §306(e)’s declaration that discharges in violation of
new source performance standards are “unlawful.”
  Second, petitioners and the agencies point to §404(p),
which protects §404 permitees from enforcement actions
by the EPA or private citizens:
    “Compliance with a permit issued pursuant to this
    section . . . shall be deemed compliance, for purposes
    of sections 1319 [CWA §309] and 1365 [CWA §505] of
    this title, with sections 1311 [CWA §301], 1317 [CWA
    §307], and 1343 [CWA §403] of this title.” 33 U. S. C.
    §1344(p).
Here again, their argument is that silence is significant.
Section 404(p) protects the permitee from lawsuits alleg
ing violations of CWA §301 (which bars the discharge of
“any pollutant” “except as in compliance” with the Act),
§307 (which bars the discharge of “toxic pollutants”); and
§403 (which bars discharges into the sea). But §404(p)
does not in express terms protect the permitee from a
lawsuit alleging a violation of §306(e) or of the EPA’s new
source performance standards. Section 404(p)’s silence
regarding §306 is made even more significant because a
parallel provision in §402 does protect a §402 permitee
from an enforcement action alleging a violation of §306.
CWA §402(k), 33 U. S. C. §1342(k).
   In our view, Congress’ omission of §306 from §404, and
its inclusion of §306 in §402(k), is evidence that Congress
did not intend §306(e) to apply to Corps §404 permits or to
discharges of fill material. If §306 did apply, then the
Corps would be required to evaluate each permit applica
tion for compliance with §306, and issue a permit only if it
found the discharge would comply with §306. But even if
that finding were made, it is not clear that the §404 per
mitee would be protected from a suit seeking a judicial
18      COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

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                  Opinion of the Court 


determination that the discharge violates §306.
                               3
  The CWA is ambiguous on the question whether §306
applies to discharges of fill material regulated under §404.
On the one hand, §306 provides that a discharge that
violates an EPA new source performance standard is
“unlawful”—without any exception for fill material. On
the other hand, §404 grants the Corps blanket authority to
permit the discharge of fill material—without any mention
of §306. This tension indicates that Congress has not
“directly spoken” to the “precise question” of whether §306
applies to discharges of fill material. Chevron, 467 U. S.,
at 842.
                             B
  Before turning to how the agencies have resolved that
question, we consider the formal regulations that bear on
§§306 and 404. See Mead, 533 U. S., at 234–238. The
regulations, like the statutes, do not address the question
whether §306, and the EPA new source performance stan
dards promulgated under it, apply to §404 permits and the
discharges they authorize. There is no regulation, for
example, interpreting §306(e)’s text—“standard of per
formance applicable to such source”—to mean that a
performance standard ceases to be “applicable” the mo
ment the discharge qualifies as fill material, which would
resolve the cases in petitioners’ favor. Nor is there a
regulation providing that the Corps, in deciding whether
to grant a permit under §404, must deny that permit if the
discharge would violate §306(e), which would decide the
cases for SEACC.
  Rather than address the tension between §§306 and
404, the regulations instead implement the statutory
framework without elaboration on this point. Each of the
two principal regulations, which have been mentioned
above, seems to stand on its own without reference to the
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                     Opinion of the Court

other. The EPA’s new source performance standard con
tains no exception for fill material; and it forbids any
discharge of “process wastewater,” a term that includes
solid wastes. 40 CFR §440.104(b)(1); see Part III–A–1,
supra. The agencies’ joint regulation defining fill material
is also unqualified. It includes “slurry, or tailings or simi
lar mining-related materials” in its definition of a “dis
charge of fill material,” 40 CFR §232.2; and it contains no
exception for slurry that is regulated by an EPA perform
ance standard.
   The parties point to additional regulations, but these
provisions do not offer a clear basis of reconciliation. An
EPA regulation, mentioned above, provides that
“[d]ischarges of dredged or fill material into waters of the
United States which are regulated under section 404 of
CWA” “do not require [§402] permits” from the EPA.
§122.3. As we have explained, however, this merely states
that a permit for this discharge cannot be issued by the
EPA. See Part II, supra. The regulation does not answer
the question whether the EPA’s new source performance
standard, and §306(e), apply to a discharge regulated by
the Corps under §404.
   The agencies also direct us to the §404(b) guidelines
written by the EPA to guide the Corps permitting decision.
See 40 CFR pt. 230. The agencies note that these guide
lines do not expressly require the Corps, in issuing a
permit, to consider whether the discharge would violate
EPA’s performance standards. Here we think failure to
mention §306 or the EPA new source performance stan
dards does offer some indication that these are not rele
vant to the §404 permit, though the argument falls short
of being conclusive. The Corps’ own regulations require
the agency to evaluate permit applications “for compliance
with applicable [EPA] effluent limitations.” 33 CFR
§320.4(d) (2008). The regulations do not answer whether
the new source performance standard is “applicable” to a
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                   Opinion of the Court 


discharge of fill material.
                             C
  The regulations do not give a definitive answer to the
question whether §306 applies to discharges regulated by
the Corps under §404, but we do find that agency interpre
tation and agency application of the regulations are in
structive and to the point. Auer, 519 U. S., at 461. The
question is addressed and resolved in a reasonable and
coherent way by the practice and policy of the two agen
cies, all as recited in a memorandum written in May 2004
by Diane Regas, then the Director of the EPA’s Office of
Wetlands, Oceans and Watersheds, to Randy Smith, the
Director of the EPA’s regional Office of Water with re
sponsibility over the mine. App. 141a–149a (Regas Memo
randum). The Memorandum, though not subject to suffi
ciently formal procedures to merit Chevron deference, see
Mead, supra, at 234–238, is entitled to a measure of defer
ence because it interprets the agencies’ own regulatory
scheme. See Auer, supra, at 461.
  The Regas Memorandum explains:
     “As a result [of the fact that the discharge is regulated
     under §404], the regulatory regime applicable to dis
     charges under section 402, including effluent limita
     tions guidelines and standards, such as those applica
     ble to gold ore mining . . . do not apply to the
     placement of tailings into the proposed impoundment
     [of Lower Slate Lake]. See 40 CFR §122.3(b).” App.
     144a–145a.
The regulation that the Memorandum cites—40 CFR
§122.3—is one we considered above and found ambiguous.
That regulation provides: “[d]ischarges of dredged or fill
material into waters of the United States which are regu
lated under section 404 of CWA” “do not require [§402]
permits.” The Regas Memorandum takes an instructive
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                     Opinion of the Court

interpretive step when it explains that because the dis
charge “do[es] not require” an EPA permit, ibid., the
EPA’s performance standard “do[es] not apply” to the
discharge. App. 145a. The Memorandum presents a
reasonable interpretation of the regulatory regime. We
defer to the interpretation because it is not “plainly erro
neous or inconsistent with the regulation[s].” Auer, supra,
at 461 (internal quotation marks omitted). Five factors
inform that conclusion.
  First, the Memorandum preserves a role for the EPA’s
performance standard. It confines the Memorandum’s
scope to closed bodies of water, like the lake here. App.
142a–143a, n. 1. When slurry is discharged into a closed
body of water, the Memorandum explains, the EPA’s
performance standard retains an important role in regu
lating the discharge into surrounding waters. The Memo
randum does not purport to invalidate the EPA’s perform
ance standard.
  Second, the Memorandum acknowledges that this is not
an instance in which the discharger attempts to evade the
requirements of the EPA’s performance standard. The
Kensington Mine is not, for example, a project that smug
gles a discharge of EPA-regulated pollutants into a sepa
rate discharge of Corps-regulated fill material. The in
stant cases do not present a process or plan designed to
manipulate the outer boundaries of the definition of “fill
material” by labeling minute quantities of EPA-regulated
solids as fill. The Memorandum states that when a dis
charge has only an “incidental filling effect,” the EPA’s
performance standard continues to govern that discharge.
Id., at 145a.
  Third, the Memorandum’s interpretation preserves the
Corps’ authority to determine whether a discharge is in
the public interest. See 33 CFR §320.4(a)(1); 40 CFR
§230.10. The Corps has significant expertise in making
this determination. Applying it, the Corps determined
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                  Opinion of the Court 


that placing slurry in the lake will improve that body of
water by making it wider, shallower, and so more capable
of sustaining aquatic life. The Corps determined, fur
thermore, that the alternative—a heap of tailings larger
than the Pentagon placed upon wetlands—would cause
more harm to the environment. Because the Memoran
dum preserves an important role for the Corps’ expertise,
its conclusion that the EPA’s performance standard does
not apply is a reasonable one.
   Fourth, the Regas Memorandum’s interpretation does
not allow toxic pollutants (as distinguished from other,
less dangerous pollutants, such as slurry) to enter the
navigable waters. The EPA has regulated toxic pollutants
under a separate provision, §307 of the CWA, and the
EPA’s §404(b) guidelines require the Corps to deny a §404
permit for any discharge that would violate the EPA’s
§307 toxic-effluent limitations. 40 CFR §230.10(b)(2).
   Fifth, as a final reason to defer to the Regas Memoran
dum, we find it a sensible and rational construction that
reconciles §§306, 402, and 404, and the regulations im
plementing them, which the alternatives put forward by
the parties do not. SEACC’s argument, that §402 applies
to this discharge and not §404, is not consistent with the
statute and regulations, as already noted. See Part II,
supra.
   The Court requested the parties to submit supplemental
briefs addressing whether the CWA contemplated that
both agencies would issue a permit for a discharge. 556
U. S. ___ (2009). A two-permit regime would allow the
EPA to apply its performance standard, while the Corps
could apply its §404(b) criteria. The parties agree, how
ever, that a two-permit regime is contrary to the statute
and the regulations. We conclude that this is correct. A
two-permit regime would cause confusion, delay, expense,
and uncertainty in the permitting process. In agreement
with all of the parties, we conclude that, when a permit is
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                     Opinion of the Court

required to discharge fill material, either a §402 or a §404
permit is necessary. Here, we now hold, §404 applies, not
§402. See Part II, supra.
  The Regas Memorandum’s interpretation of the agen
cies’ regulations is consistent with the regulatory scheme
as a whole. The Memorandum preserves a role for the
EPA’s performance standards; it guards against the possi
bility of evasion of those standards; it employs the Corps’
expertise in evaluating the effects of fill material on the
aquatic environment; it does not allow toxic pollutants to
be discharged; and we have been offered no better way to
harmonize the regulations. We defer to the EPA’s conclu
sion that its performance standard does not apply to the
initial discharge of slurry into the lake but applies only to
the later discharge of water from the lake into the down
stream creek.
                            D
   SEACC argues against deference to the Regas Memo
randum. In its view the Regas Memorandum is contrary
to published agency statements and earlier agency prac
tice. SEACC cites three agency statements: A 1986
“memorandum of understanding” between the EPA and
the Corps regarding the definition of fill material; the
preamble to the agencies’ current 2002 fill regulation; and
comments made by the agencies in promulgating the 2002
fill regulation. These arguments are not convincing.
                             1
   In 1986, to reconcile their then-differing definitions of
“fill material,” the EPA and the Corps issued a “memoran
dum of agreement.” 51 Fed. Reg. 8871 (MOA). The
memorandum was not made subject to notice-and
comment procedures, but it was published in the Federal
Register. It defined the statutory term “fill material” until
the current definition took effect in 2002. Brief for Fed
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                   Opinion of the Court 


eral Respondents 30–31, n. 8.
  SEACC points to paragraph B(5) of the MOA, which
reads:
     “[A] pollutant (other than dredged material) will nor
     mally be considered by EPA and the Corps to be sub
     ject to section 402 if it is a discharge in liquid, semi
     liquid, or suspended form or if it is a discharge of solid
     material of a homogeneous nature normally associ
     ated with single industry wastes . . . . These materials
     include placer mining wastes, phosphate mining
     wastes, titanium mining wastes, sand and gravel
     wastes, fly ash, and drilling muds. As appropriate,
     EPA and the Corps will identify additional such mate
     rials.” 51 Fed. Reg. 8872.
It is true, as SEACC notes, that this passage suggests that
§402 will “normally” apply to discharges of “suspended”—
i.e., solid—pollutants. But that statement is not contrary
to the Regas Memorandum, which acknowledges that the
EPA retains authority under §402 to regulate the dis
charge of suspended solids from Lower Slate Lake into
downstream waters. This passage does not address the
question presented by these cases, and answered by the
Regas Memorandum, as to whether the EPA’s perform
ance standard applies when the discharge qualifies as fill
material. In fact, the MOA’s preamble suggests that when
a discharge qualifies as “fill material,” the Corps retains
authority to regulate it under §404:
     “Discharges listed in the Corps definition of ‘discharge
     of fill material,’ . . . remain subject to section 404 even
     if they occur in association with discharges of wastes
     meeting the criteria in the agreement for section 402
     discharges.” Id., at 8871.
  The MOA is quite consistent with the agencies’ determi
nation that the Corps regulates all discharges of fill mate
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                     Opinion of the Court

rial and that §306 does not apply to these discharges.
                               2
   SEACC draws our attention to the preamble of the
current fill material regulation. 67 Fed. Reg. 31129 (2002)
(final rule). It cites the opening passages of the preamble,
which state:
    “[T]oday’s rule is generally consistent with current
    agency practice and so it does not expand the types of
    discharges that will be covered under section 404.”
    Id., at 31133.
In SEACC’s view, this passage demonstrates that the fill
rule was not intended to displace the pre-existing froth
flotation gold mine performance standard, which has been
on the books since 1982.
   The preamble goes on to say, in a section entitled “Efflu
ent Guideline Limitations and 402 Permits”:
    “[W]e emphasize that today’s rule generally is in
    tended to maintain our existing approach to regulat
    ing pollutants under either section 402 or 404 of the
    CWA. Effluent limitation guidelines and new source
    performance standards (‘effluent guidelines’) promul
    gated under section 304 and 306 of the CWA establish
    limitations and standards for specified wastestreams
    from industrial categories, and those limitations and
    standards are incorporated into permits issued under
    section 402 of the Act. EPA has never sought to regu
    late fill material under effluent guidelines. Rather,
    effluent guidelines restrict discharges of pollutants
    from identified wastestreams based upon the pollut
    ant reduction capabilities of available treatment tech
    nologies. Recognizing that some discharges (such as
    suspended or settleable solids) can have the associ
    ated effect, over time, of raising the bottom elevation
    of a water due to settling of waterborne pollutants, we
26       COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

                CONSERVATION COUNCIL

                   Opinion of the Court 


     do not consider such pollutants to be ‘fill material,’
     and nothing in today’s rule changes that view. Nor
     does today’s rule change any determination we have
     made regarding discharges that are subject to an ef
     fluent limitation guideline and standards, which will
     continue to be regulated under section 402 of the
     CWA. Similarly, this rule does not alter the manner
     in which water quality standards currently apply un
     der the section 402 or the section 404 programs.” Id.,
     at 31135.
Although the preamble asserts it does not change agency
policy with regard to EPA performance standards and
§402 permitting decisions, it is explicit in noting that the
EPA has “never sought to regulate fill material under
effluent guidelines.” Ibid. The preamble, then, is consis
tent with the Regas Memorandum. If a discharge does not
qualify as fill material, the EPA’s new source performance
standard applies. If the discharge qualifies as fill, the
performance standard does not apply; and there was no
earlier agency practice or policy to the contrary.
                             3
  SEACC also cites remarks made by the agencies in
response to public comments on the proposed fill material
regulation. App. 22a–127a. These remarks were incorpo
rated by reference into the administrative record. 67 Fed.
Reg. 31131.
  Responding to a question about whether “mine tailings”
would be “subject to section 404 regulation as opposed to
section 402” under the 2002 fill regulation, the agencies
stated:
     “Today’s final rule clarifies that any material that has
     the effect of fill is regulated under section 404 and
     further that the placement of ‘overburden, slurry, or
     tailings or similar mining-related materials’ is consid
                 Cite as: 557 U. S. ____ (2009)          27

                     Opinion of the Court

    ered a discharge of fill material. Nevertheless, if EPA
    has previously determined that certain materials are
    subject to an [effluent limitation guideline] under spe
    cific circumstances, then that determination remains
    valid. Moreover, . . . permits issued pursuant to sec
    tion 402 are intended to regulate process water and
    provide effluent limits that are protective of receiving
    water quality. This distinction provides the frame
    work for today’s rule.” App. 48a.
This statement is not conclusive of the issue. SEACC
notes that this response, like the regulation’s preamble,
pledges that EPA’s “previou[s] . . . determination[s]” with
regard to the application of performance standards “re
mai[n] valid.” But, as noted above, the Regas Memoran
dum has followed this policy by applying the EPA’s per
formance standard to the discharge of water from the lake
into the downstream creek. The response does not state
that the EPA will apply its performance standards to
discharges of fill material.
                             4
   The agencies’ published statements indicate adherence
to the EPA’s previous application and interpretation of its
performance standards. SEACC cannot show that the
agencies have changed their interpretation or application
of their regulations.
   SEACC cites no instance in which the EPA has applied
one of its performance standards to a discharge of fill
material. By contrast, Coeur Alaska cites two instances in
which the Corps issued a §404 permit authorizing a mine
to discharge solid waste (tailings) as fill material. See
Brief for Petitioner Coeur Alaska 40–42. SEACC objects
that those two §404 permits authorized discharges that
used the tailings to construct useful structures—a dam in
one case, a tailings pond in another. Here, by contrast,
SEACC contends that the primary purpose of the dis
28      COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

               CONSERVATION COUNCIL

                  Opinion of the Court 


charge is to use a navigable water to dispose of waste.
Ibid. But that objection misses the point. The two §404
permits cited by Coeur Alaska illustrate that the agencies
did not have a prior practice of applying EPA performance
standards to discharges of mining wastes that qualify as
fill material.
   SEACC has not demonstrated that the agencies have
changed their policy, and it cannot show that the Regas
Memorandum is contrary to the agencies’ published
statements.
                         *    *   *
  We accord deference to the agencies’ reasonable decision
to continue their prior practice.
  The judgment of the Court of Appeals is reversed, and
these cases are remanded for further proceedings consis
tent with this opinion.
                                           It is so ordered.
                 Cite as: 557 U. S. ____ (2009)           1

                    BREYER, J., concurring

SUPREME COURT OF THE UNITED STATES
                         _________________

                   Nos. 07–984 and 07–990
                         _________________


       COEUR ALASKA, INC., PETITIONER
07–984              v.
  SOUTHEAST ALASKA CONSERVATION COUNCIL
                  ET AL.


            ALASKA, PETITIONER
07–990               v.
  SOUTHEAST ALASKA CONSERVATION COUNCIL
                  ET AL.

ON WRITS OF CERTIORARI TO THE UNITED STATES COURT OF
            APPEALS FOR THE NINTH CIRCUIT
                        [June 22, 2009]

  JUSTICE BREYER, concurring.
  As I understand the Court’s opinion, it recognizes a
legal zone within which the regulating agencies might
reasonably classify material either as “dredged or fill
material” subject to §404 of the Clean Water Act, 33
U. S. C. §1344(a), or as a “pollutant,” subject to §§402 and
306, 33 U. S. C. §§1342(a), 1316(a). Within this zone, the
law authorizes the environmental agencies to classify
material as the one or the other, so long as they act within
the bounds of relevant regulations, and provided that the
classification, considered in terms of the purposes of the
statutes and relevant regulations, is reasonable.
  This approach reflects the difficulty of applying §§402
and 306 literally to every new-source-related discharge of a
“pollutant.” The Environmental Protection Agency (EPA)
applies §306 new source “performance standards” to a
wide variety of discharges, ranging, for example, from
2        COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

                CONSERVATION COUNCIL

                   BREYER, J., concurring


those involved in the processing of apples into apple juice
or apple cider, 40 CFR §407.10 (2008); to the manufactur
ing of cement, §411.10; to the production of fresh meat
cuts by a meat cutter, §432.60; and to the manufacture of
pharmaceutical products by fermentation, §439.10. See
generally 40 CFR pts. 405–471 (containing more than 800
pages of “new source performance” and effluent limitation
regulations). At the same time the regulations for any one
point source often regulate numerous chemicals, minerals,
and other substances produced by that point source; in the
case of fermentation products, for example, the regulations
provide performance standards for roughly 30 different
chemicals. §439.15. These “standards of performance”
“reflect the greatest degree of effluent reduction which the
Administrator determines to be achievable through appli
cation of the best available demonstrated control technol
ogy . . . including, where practicable, a standard permit
ting no discharge of pollutants.” 33 U. S. C. §1316(a)(1).
   To literally apply these performance standards so as to
forbid the use of any of these substances as “fill,” even
when, say, they constitute no more than trace elements in
dirt, crushed rock, or sand that is clearly being used as
“fill” to build a levee or to replace dirt removed from a lake
bottom may prove unnecessarily strict, cf. §1362(6) (defin
ing “pollutant” to include “rock”), to the point that such
application would undermine the objective of §404, which
foresees the use of “dredged or fill material” in certain
circumstances and with approval of the relevant agencies.
§1344. At minimum, the EPA might reasonably read the
statute and the applicable regulations as allowing the use
of such material, say crushed rock, as “fill” in some of
these situations. Cf. Chevron U. S. A. Inc. v. Natural
Resources Defense Council, Inc., 467 U. S. 837, 842–844
(1984); Auer v. Robbins, 519 U. S. 452, 461 (1997).
   At the same time, I recognize the danger that JUSTICE
GINSBURG warns against, namely, that “[w]hole categories
                  Cite as: 557 U. S. ____ (2009)            3

                     BREYER, J., concurring

of regulated industries” might “gain immunity from a
variety of pollution-control standards,” if, say, a §404
permit applicant simply adds “sufficient solid matter” to a
pollutant “to raise the bottom of a water body,” thereby
turning a “pollutant” governed by §306 into “fill” governed
by §404. Post, at 7 (dissenting opinion).
   Yet there are safeguards against that occurring. For
one thing, as the Court recognizes, see ante, at 11, it is not
the case that any material that has the “ ‘effect of . . .
[c]hanging the bottom elevation’ ” of the body of water is
automatically subject to §404, not §402. The EPA has
never suggested that it would interpret the regulations so
as to turn §404 into a loophole, permitting evasion of a
“performance standard” simply because a polluter dis
charges enough pollutant to raise the bottom elevation of
the body of water. For another thing, even where a matter
is determined reasonably to be “fill” and consequently falls
within §404, the EPA can retain an important role in the
permitting process. That is because the EPA may veto
any §404 plan that it finds has an “unacceptable adverse
effect on municipal water supplies, shellfish beds and
fishery areas . . . , wildlife, or recreational areas.”
§1344(c). Finally, EPA’s decision not to apply §306, but to
allow permitting to proceed under §404, must be a reason
able decision; and court review will help assure that is so.
5 U. S. C. §706.
   In these cases, it seems to me that the EPA’s interpreta
tion of the statute as permitting the EPA/Corps of Engi
neers “fill” definition to apply to the cases at hand is rea
sonable, hence lawful. Lower Slate Lake, located roughly
three miles from the Kensington Gold Mine, is 51 feet
deep, 800 feet wide, and 2,000 feet long; downstream from
the lake is Slate Creek. Faced with a difficult choice
between creating a huge pile of slurry on nearby wetlands
or using part of the lake as a storage facility for mine
tailings, see App. 294a–298a; see also ante, at 5–8, the
4        COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

                CONSERVATION COUNCIL

                   BREYER, J., concurring


EPA arrived at a compromise. On the one hand, it would
treat mine tailings placed directly into the lake as “fill”
under the §404 permitting program. App. 144a. The
tailings, the EPA recognized, would have the “immediate
effect of filling the areas of water into which they are
discharged.” Ibid. But it would also treat any spillover of
the tailings, or chemicals from the tailings, into any
nearby waterway, most particularly Slate Creek (running
out of Slate Lake) as requiring a §402 permit. The EPA’s
§306 “performance standard” would apply and that stan
dard insists upon no discharge of process wastewater at
all. Id., at 145a; see also 40 CFR §440.104(b). The EPA
reached this result because it recognized that, even though
pollutants discharged into the creek might come “in the
form of suspended and settleable solids,” such solids would
“have, at most, an incidental filling effect.” App. 145a.
The EPA thereby sought to apply the distinction it had
previously recognized between discharges that have the
immediate effect of raising the bottom elevation of water,
and those that only have the “associated effect, over time,
of raising the bottom elevation of a water due to settling of
waterborne pollutants.” See 67 Fed. Reg. 31135 (2002)
(concluding that §402 applies to the latter); see also Brief
for G. Tracy Mehan III as Amicus Curiae 22–23.
   I cannot say whether the EPA’s compromise represents
the best overall environmental result; but I do believe it
amounts to the kind of detailed decision that the statutes
delegate authority to the EPA, not the courts, to make
(subject to the bounds of reasonableness). I believe the
Court’s views are consistent with those I here express.
And with that understanding, I join its opinion.
                 Cite as: 557 U. S. ____ (2009)            1

                     Opinion of SCALIA, J.

SUPREME COURT OF THE UNITED STATES
                         _________________

                    Nos. 07–984 and 07–990
                         _________________


       COEUR ALASKA, INC., PETITIONER
07–984              v.
  SOUTHEAST ALASKA CONSERVATION COUNCIL
                  ET AL.


            ALASKA, PETITIONER
07–990               v.
  SOUTHEAST ALASKA CONSERVATION COUNCIL
                  ET AL.

ON WRITS OF CERTIORARI TO THE UNITED STATES COURT OF
            APPEALS FOR THE NINTH CIRCUIT
                        [June 22, 2009]

   JUSTICE SCALIA, concurring in part and concurring in
the judgment.
   I join the opinion of the Court, except for its protesta
tion, ante, at 20, that it is not according Chevron deference
to the reasonable interpretation set forth in the memoran
dum sent by the Director of the Environmental Protection
Agency’s (EPA) Office of Wetlands, Oceans and Water
sheds, to the Director of the EPA’s regional Office of Water
with responsibility over the Coeur Alaska mine—an inter
pretation consistently followed by both EPA and the Corps
of Engineers, and adopted by both agencies in the proceed
ings before this Court. See Chevron U. S. A. Inc. v. Natu
ral Resources Defense Council, Inc., 467 U. S. 837 (1984).
The opinion purports to give this agency interpretation “a
measure of deference” because it involves an interpretation
of “the agencies’ own regulatory scheme,” and “ ‘the regu-
latory regime,’ ” ante, at 20 (citing Auer v. Robbins, 519
2           COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

                   CONSERVATION COUNCIL

                      Opinion of SCALIA, J. 


U. S. 452, 461 (1997)). Auer, however, stands only for the
principle that we defer to an agency’s interpretation of its
own ambiguous regulation. But it becomes obvious from
the ensuing discussion that the referenced “regulatory
scheme,” and “regulatory regime” for which the Court
accepts the agency interpretation includes not just the
agencies’ own regulations but also (and indeed primarily)
the conformity of those regulations with the ambiguous
governing statute, which is the primary dispute here.
   Surely the Court is not adding to our already inscruta
ble opinion in United States v. Mead Corp., 533 U. S. 218
(2001), the irrational fillip that an agency position which
otherwise does not qualify for Chevron deference does
receive Chevron deference if it clarifies not just an am
biguous statute but also an ambiguous regulation. One
must conclude, then, that if today’s opinion is not accord
ing the agencies’ reasonable and authoritative interpreta
tion of the Clean Water Act Chevron deference, it is ac
cording some new type of deference—perhaps to be called
in the future Coeur Alaska deference—which is identical
to Chevron deference except for the name.
   The Court’s deference to the EPA and the Corps of
Engineers in today’s cases is eminently reasonable. It is
quite impossible to achieve predictable (and relatively
litigation-free) administration of the vast body of complex
laws committed to the charge of executive agencies with
out the assurance that reviewing courts will accept rea
sonable and authoritative agency interpretation of am
biguous provisions. If we must not call that practice
Chevron deference, then we have to rechristen the rose.
Of course the only reason a new name is required is our
misguided opinion in Mead, whose incomprehensible
criteria for Chevron deference have produced so much
confusion in the lower courts* that there has now appeared
——————
    * Compare, e.g., Kruse v. Wells Fargo Home Mortgage, Inc., 383 F. 3d
                    Cite as: 557 U. S. ____ (2009)                  3

                        Opinion of SCALIA, J.

the phenomenon of Chevron avoidance—the practice of
declining to opine whether Chevron applies or not. See
Bressman, How Mead Has Muddled Judicial Review of
Agency Action, 58 Vand. L. Rev. 1443, 1464 (2005).
   I favor overruling Mead. Failing that, I am pleased to
join an opinion that effectively ignores it.




——————
49, 61 (CA2 2004) (according Chevron deference to policy statements
issued by Department of Housing and Urban Development) and Schu
etz v. Banc One Mortgage Corp., 292 F. 3d 1004, 1012 (CA9 2002)
(same), with Krzalic v. Republic Title Co., 314 F. 3d 875, 881 (CA7
2002) (denying Chevron deference to same policy statements). Compare
American Federation of Govt. Employees, AFL–CIO, Local 446 v.
Nicholson, 475 F. 3d 341, 353–354 (CADC 2007) (according Chevron
deference to informal adjudication by Department of Veterans Affairs),
with American Federation of Govt. Employees, AFL–CIO, Local 2152 v.
Principi, 464 F. 3d 1049, 1057 (CA9 2006) (denying Chevron deference
to similar action). It is not even clear that notice-and-comment rule
making will assure Chevron deference to agency interpretation of an
ambiguous statute. See Rubie’s Costume Co. v. United States, 337 F. 3d
1350, 1355 (CA Fed. 2003) (customs classification).
                    Cite as: 557 U. S. ____ (2009)                 1

                      GINSBURG, J., dissenting

SUPREME COURT OF THE UNITED STATES
                            _________________

                      Nos. 07–984 and 07–990
                            _________________


       COEUR ALASKA, INC., PETITIONER
07–984              v.
  SOUTHEAST ALASKA CONSERVATION COUNCIL
                  ET AL.


            ALASKA, PETITIONER
07–990               v.
  SOUTHEAST ALASKA CONSERVATION COUNCIL
                  ET AL.

ON WRITS OF CERTIORARI TO THE UNITED STATES COURT OF
            APPEALS FOR THE NINTH CIRCUIT
                           [June 22, 2009]

   JUSTICE GINSBURG, with whom JUSTICE STEVENS and
JUSTICE SOUTER join, dissenting.
   Petitioner Coeur Alaska, Inc., proposes to discharge
210,000 gallons per day of mining waste into Lower Slate
Lake, a 23-acre subalpine lake in Tongass National For
est. The “tailings slurry” would contain concentrations of
aluminum, copper, lead, and mercury. Over the life of the
mine, roughly 4.5 million tons of solid tailings would enter
the lake, raising the bottom elevation by 50 feet. It is
undisputed that the discharge would kill all of the lake’s
fish and nearly all of its other aquatic life.1
   Coeur Alaska’s proposal is prohibited by the Environ
mental Protection Agency (EPA) performance standard
——————
  1 Whether  aquatic life will eventually be able to inhabit the lake
again is uncertain. Compare ante, at 5, with App. 201a–202a; and
Southeast Alaska Conservation Council v. United States Army Corps of
Engineers, 486 F. 3d 638, 642 (CA9 2007).
2       COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

               CONSERVATION COUNCIL

                 GINSBURG, J., dissenting 


forbidding any discharge of process wastewater from new
“froth-flotation” mills into waters of the United States.
See 40 CFR §440.104(b)(1) (2008). Section 306 of the
Clean Water Act directs EPA to promulgate such perform
ance standards, 33 U. S. C. §1316(a), and declares it
unlawful for any discharger to violate them, §1316(e).
Ordinarily, that would be the end of the inquiry.
   Coeur Alaska contends, however, that its discharge is
not subject to EPA’s regulatory regime, but is governed,
instead, by the mutually exclusive permitting authority of
the Army Corps of Engineers. The Corps has authority,
under §404 of the Act, §1344(a), to issue permits for dis
charges of “dredged or fill material.” By regulation, a
discharge that has the effect of raising a water body’s
bottom elevation qualifies as “fill material.” See 33 CFR
§323.2(e) (2008). Discharges properly within the Corps’
permitting authority, it is undisputed, are not subject to
EPA performance standards. See ante, at 20; Brief for
Petitioner Coeur Alaska 26; Brief for Respondent South
east Alaska Conservation Council et al. 37.
   The litigation before the Court thus presents a single
question: Is a pollutant discharge prohibited under §306 of
the Act eligible for a §404 permit as a discharge of fill
material? In agreement with the Court of Appeals, I
would answer no. The statute’s text, structure, and pur
pose all mandate adherence to EPA pollution-control
requirements. A discharge covered by a performance
standard must be authorized, if at all, by EPA.
                              I

                             A

  Congress enacted the Clean Water Act in 1972 “to re
store and maintain the chemical, physical, and biological
integrity” of the waters of the United States. 33 U. S. C.
§1251(a). “The use of any river, lake, stream or ocean as a
waste treatment system,” the Act’s drafters stated, “is
                     Cite as: 557 U. S. ____ (2009)                    3

                        GINSBURG, J., dissenting

unacceptable.” S. Rep. No. 92–414, p. 7 (1971). Congress
announced in the Act itself an ambitious objective: to
eliminate, by 1985, the discharge of all pollutants into the
Nation’s navigable waters. 33 U. S. C. §1251(a).
   In service of its goals, Congress issued a core command:
“[T]he discharge of any pollutant by any person shall be
unlawful,” except in compliance with the Act’s terms.
§1311(a). The Act’s substantive requirements—housed
primarily in Subchapter III, “Standards and Enforce
ment”—establish “a comprehensive regulatory program
supervised by an expert administrative agency,” EPA.
Milwaukee v. Illinois, 451 U. S. 304, 317 (1981). See also
33 U. S. C. §1251(d) (“Except as otherwise expressly pro
vided . . . , the Administrator of [EPA] shall administer
this [Act].”).
   The Act instructs EPA to establish various technology
based, increasingly stringent effluent limitations for cate
gories of point sources. E.g., §§1311, 1314. These limita
tions, formulated as restrictions “on quantities, rates, and
concentrations of chemical, physical, biological, and other
constituents,” §1362(11), were imposed to achieve national
uniformity among categories of sources. See, e.g., E. I. du
Pont de Nemours & Co. v. Train, 430 U. S. 112, 129–130
(1977). The limitations for a given discharge depend on
the type of pollutant and source at issue.2
   Of key importance, new sources must meet stringent
“standards of performance” adopted by EPA under §306.
That section makes it “unlawful for any . . . new source to
operate . . . in violation of” an applicable performance
——————
  2 In addition, the Act requires States to institute comprehensive wa

ter quality standards for intrastate waters, subject to EPA approval.
See §1313. This program supplements the technology-based standards,
serving to “prevent water quality from falling below acceptable levels”
even when point sources comply with effluent limitations. EPA v.
California ex rel. State Water Resources Control Bd., 426 U. S. 200, 205,
n. 12 (1976).
4         COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

                 CONSERVATION COUNCIL

                   GINSBURG, J., dissenting 


standard. 33 U. S. C. §1316(e) (emphasis added). In line
with Congress’ aim “to insure . . .‘maximum feasible con
trol of new sources,’ ” du Pont, 430 U. S., at 138, the pre
ferred standard for a new source is one “ ‘permitting no
discharge of pollutants,’ ” id., at 137–138 (quoting 33
U. S. C. §1316(a)(1) (emphasis added)). Moreover, new
sources, unlike existing sources, are not eligible for EPA
granted variances from applicable limitations. 430 U. S.,
at 138.3
  In 1982, EPA promulgated new source performance
standards for facilities engaged in mining, including those
using a froth-flotation milling process. See Ore Mining
and Dressing Point Source Category Effluent Limitations
Guidelines and New Source Performance Standards, 47
Fed. Reg. 54598 (1982). Existing mills, the Agency found,
were already achieving zero discharge; it was therefore
practicable, EPA concluded, for new mills to do as well.
Id., at 54602. Accordingly, under 40 CFR §440.104(b)(1),
new mines using the froth-flotation method, as Coeur
Alaska proposes to do, may not discharge wastewater
directly into waters of the United States.
                             B
  The nationwide pollution-control requirements just
described are implemented through the National Pollution
Discharge Elimination System (NPDES), a permitting
scheme set forth in §402 and administered by EPA and the
States. The NPDES is the linchpin of the Act, for it trans
forms generally applicable effluent limitations into the
individual obligations of each discharger. EPA v. Califor
——————
   3 Even the provision allowing the President to exempt federal instal

lations from compliance with the Act’s requirements—“if he determines
it to be in the paramount interest of the United States to do so”—does
not extend to new source standards: “[N]o exemption may be granted
from the requirements of section [306] or [307] of this [Act].” 33
U. S. C. §1323(a).
                 Cite as: 557 U. S. ____ (2009)            5

                    GINSBURG, J., dissenting

nia ex rel. State Water Resources Control Bd., 426 U. S.
200, 205 (1976). The discharge of a pollutant is generally
prohibited unless the source has obtained a NPDES per
mit. E.g., EPA v. National Crushed Stone Assn., 449 U. S.
64, 71 (1980) (“Section 402 authorizes the establishment of
the [NPDES], under which every discharger of pollutants
is required to obtain a permit.”).
   The Act also establishes a separate permitting scheme,
administered by the Corps, for discharges of “dredged or
fill material.” 33 U. S. C. §1344(a). Section 404 hews to
the Corps’ established expertise in matters of navigability
and construction. The §404 program does not implement
the uniform, technology-based pollution-control standards
set out, inter alia, in §306. Instead, §404 permits are
subject to regulatory guidelines based generally on the
impact of a discharge on the receiving environment. See
§1344(b); ante, at 4–5.
   As the above-described statutory background indicates,
Coeur Alaska’s claim to a §404 permit carries weighty
implications. If eligible for that permit, Coeur Alaska can
evade the exacting performance standard prescribed by
EPA for froth-flotation mills. It may, instead, use Lower
Slate Lake “as the settling pond and disposal site for the
tailings.” App. 360a (Corps’ Record of Decision).
                             II
  Is a pollutant discharge prohibited under §306(e) eligi
ble to receive a §404 permit as a discharge of fill material?
All agree on preliminary matters. Only one agency, the
Corps or EPA, can issue a permit for the discharge. See
ante, at 10, 22. Only EPA, through the NPDES program,
issues permits that implement §306. See supra, at 2.
Further, §306(e) and EPA’s froth-flotation performance
standard, unless inapplicable here, bar Coeur Alaska’s
proposed discharge. See ante, at 14–15.
  No part of the statutory scheme, in my view, calls into
6        COEUR ALASKA, INC. v. SOUTHEAST ALASKA
                CONSERVATION COUNCIL
                  GINSBURG, J., dissenting

question the governance of EPA’s performance standard.
The text of §306(e) states a clear proscription: “[I]t shall be
unlawful for any owner or operator of any new source to
operate such source in violation of any standard of per
formance applicable to such source.” 33 U. S. C. §1316(e).
Under the standard of performance relevant here, “there
shall be no discharge of process wastewater to navigable
waters from mills that use the froth-flotation process” for
mining gold. 40 CFR §440.104(b)(1). The Act imposes
these requirements without qualification.
   Section 404, stating that the Corps “may issue permits”
for the discharge of “dredged or fill material,” does not
create an exception to §306(e)’s plain command. 33
U. S. C. §1344(a). Cf. ante, at 12. Section 404 neither
mentions §306 nor states a contrary requirement. The Act
can be home to both provisions, with no words added or
omitted, so long as the category of “dredged or fill mate
rial” eligible for a §404 permit is read in harmony with
§306. Doing so yields a simple rule: Discharges governed
by EPA performance standards are subject to EPA’s ad
ministration and receive permits under the NPDES, not
§404.
   This reading accords with the Act’s structure and objec
tives. It retains, through the NPDES, uniform application
of the Act’s core pollution-control requirements, and it
respects Congress’ special concern for new sources. Leav
ing pollution-related decisions to EPA, moreover, is consis
tent with Congress’ delegation to that agency of primary
responsibility to administer the Act. Most fundamental,
adhering to §306(e)’s instruction honors the overriding
statutory goal of eliminating water pollution, and Con
gress’ particular rejection of the use of navigable waters as
waste disposal sites. See supra, at 2–3. See also 33
U. S. C. §1324 (creating “clean lakes” program requiring
                     Cite as: 557 U. S. ____ (2009)                   7

                       GINSBURG, J., dissenting

States to identify and restore polluted lakes).4
   The Court’s reading, in contrast, strains credulity. A
discharge of a pollutant, otherwise prohibited by firm
statutory command, becomes lawful if it contains suffi
cient solid matter to raise the bottom of a water body,
transformed into a waste disposal facility. Whole catego
ries of regulated industries can thereby gain immunity
from a variety of pollution-control standards. The loophole
would swallow not only standards governing mining ac
tivities, see 40 CFR pt. 440 (effluent limitations and new
source performance standards for ore mining and dress
ing); id., pt. 434 (coal mining); id., pt. 436 (mineral min
ing), but also standards for dozens of other categories of
regulated point sources, see, e.g., id., pt. 411 (cement
——————
  4 The   Court asserts that “numerous difficulties” will ensue if a dis
charge governed by a new source performance standard is ineligible for
a §404 permit. Ante, at 12. Namely, the Court notes, the discharger
will have to determine whether a performance standard applies to it.
Ante, at 13. That is not only the usual inquiry under the Clean Water
Act; it is one Coeur Alaska answered, without apparent difficulty, when
it sought and obtained an EPA permit for the proposed discharge from
the lake into a downstream creek. See ante, at 6.
   JUSTICE BREYER fears that “litera[l] appl[ication]” of performance
standards would interfere with efforts “to build a levee or to replace
dirt removed from a lake bottom,” and thus “may prove unnecessarily
strict.” Ante, at 2 (concurring opinion). His concerns are imaginative,
but it is questionable whether they are real. Apple juice processors,
meatcutters, cement manufacturers, and pharmaceutical producers do
not ordinarily build levees—and it is almost inconceivable that they
would do so using the waste generated by their highly specific indus
trial processes. See, e.g., 40 CFR §411.10 (performance standard for
particular cement manufacturing process). Levee construction gener
ally is undertaken by developers or government, entities not subject to
performance standards for such a project. This litigation, furthermore,
does not illustrate the “difficulty” JUSTICE BREYER perceives. See ante,
at 1. Coeur Alaska does not seek to build a levee or return dirt to a
lake; it simply wants to use Lower Slate Lake as a waste disposal site.
8         COEUR ALASKA, INC. v. SOUTHEAST ALASKA 

                 CONSERVATION COUNCIL

                   GINSBURG, J., dissenting 


manufacturing); id., pt. 425 (leather tanning and finish
ing); id., pt. 432 (meat and poultry products processing).
See also Brief for American Rivers et al. as Amici Curiae
26–27 (observing that discharges in these categories “typi
cally contain high volumes of solids”). Providing an escape
hatch for polluters whose discharges contain solid matter,
it bears noting, is particularly perverse; the Act specifi
cally focuses on solids as harmful pollutants. See 33
U. S. C. §1314(a)(4) (requiring EPA to publish information
regarding “conventional pollutants,” including “suspended
solids”); Brief for American Rivers, supra, at 28–29, and
n. 18 (identifying over 50 effluent limitations that restrict
total suspended solids).5
   Congress, we have recognized, does not “alter the fun
damental details of a regulatory scheme in vague terms or
ancillary provisions—it does not, one might say, hide
elephants in mouseholes.” Whitman v. American Trucking
Assns., Inc., 531 U. S. 457, 467–468 (2001). Yet an altera
tion of that kind is just what today’s decision imagines.
Congress, as the Court reads the Act, silently upended, in
an ancillary permitting provision, its painstaking pollu
tion-control scheme. See ante, at 17. Congress did so, the
Court holds, notwithstanding the lawmakers’ stated effort
“to restore and maintain the chemical, physical, and bio
logical integrity” of the waters of the United States, 33
——————
  5 The “safeguards” JUSTICE BREYER identifies are hardly reassuring.

See ante, at 3 (concurring opinion). Given today’s decision, it is opti
mistic to expect that EPA or the courts will act vigorously to prevent
evasion of performance standards. Nor is EPA’s veto power under
§404(c) of the Clean Water Act an adequate substitute for adherence to
§306. That power—exercised only a dozen times over 36 years encom
passing more than one million permit applications, see Brief for Ameri
can Rivers 14—hinges on a finding of “unacceptable adverse effect,” 33
U. S. C. §1344(c). Destruction of nearly all aquatic life in a pristine
lake apparently does not qualify as “unacceptable.” Reliance on ad hoc
vetoes, moreover, undermines Congress’ aim to install uniform water
pollution regulation.
                  Cite as: 557 U. S. ____ (2009)            9

                    GINSBURG, J., dissenting

U. S. C. §1251(a); their assignment to EPA of the Hercu
lean task of setting strict effluent limitations for many
categories of industrial sources; and their insistence that
new sources meet even more ambitious standards, not
subject to exception or variance. Would a rational legisla
ture order exacting pollution limits, yet call all bets off if
the pollutant, discharged into a lake, will raise the water
body’s elevation? To say the least, I am persuaded, that
is not how Congress intended the Clean Water Act to
operate.
   In sum, it is neither necessary nor proper to read the
statute as allowing mines to bypass EPA’s zero-discharge
standard by classifying slurry as “fill material.” The use
of waters of the United States as “settling ponds” for
harmful mining waste, the Court of Appeals correctly held,
is antithetical to the text, structure, and purpose of the
Clean Water Act.
                      *     *    *
  For the reasons stated, I would affirm the judgment of
the Ninth Circuit.
