COEUR ALASKA, INC. v. SOUTHEAST ALASKA CONSERVATION COUNCIL et al.

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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” technique,
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 compli
ance” with the CWA, § 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 together define “fill mate
rial” as any “material [that] has the effect of . . . [c]hanging the bottom
elevation” of water, including “slurry . . . or similar mining-related mate
rials.” 40 CFR § 232.2. Coeur Alaska obtained a § 404 permit for the
slurry discharge from the Corps and a § 402 permit for the lakewater
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
lakewater 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 discharge “proc
ess wastewater,” which includes solid wastes, 40 CFR § 440.104(b)(1).
Coeur Alaska and petitioner Alaska intervened as defendants. 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. 273–277.
*Together with No. 07–990, Alaska v. Southeast Alaska Conservation
Council et al., also on certiorari to the same court.

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(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 under
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]is
charges 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 author
ity to do so. If so, the EPA may not regulate. Pp. 273–275.
(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 in
tended to burden industry with the confusing division of permitting au
thority that SEACC’s contrary reading would create. Pp. 275–277.
2. The Corps acted in accordance with law in issuing the slurry dis
charge permit to Coeur Alaska. Pp. 277–291.
(a) The CWA alone does not resolve these cases. Pp. 278–282.
(i) SEACC contends that because the EPA’s performance stand
ard forbids even minute solid waste discharges, 40 CFR § 440.104(b)(1),
it also forbids Coeur Alaska’s slurry discharge, 30 percent 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 per
formance applicable to such source.” Pp. 278–280.
(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. 280–281.
(iii) 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 per
formance standard is “unlawful”—without an exception for fill material.
On the other hand, § 404 grants the Corps blanket authority to permit
the discharge of fill material—without mentioning § 306. This tension

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indicates that Congress has not “directly spoken” to the “precise ques
tion” at issue. Chevron U. S. A. Inc. v. Natural Resources Defense
Council, Inc., 467 U. S. 837, 842. Pp. 281–282.
(b) Although the agencies’ regulations construing the CWA are
entitled to deference if they resolve the statutory ambiguity in a reason
able 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 without refer
ence to the other. The EPA’s performance standard contains no excep
tion for fill material, and it forbids any discharge of “process wastewa
ter,” 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. 282–283.
(c) In light of the ambiguities in the CWA and the pertinent regula
tions, 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 agen
cies’ practice and policy, as recited in the EPA’s internal “Regas Memo
randum” (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 because it is not
“plainly erroneous or inconsistent with the regulation[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 standards; (2) guards
against the possibility of evasion of those standards; (3) employs the
Corps’ expertise in evaluating the effects of fill material on the aquatic
environment; (4) does not allow toxic compounds to be discharged into
navigable waters; and (5) reconciles §§ 306, 402, and 404, and the regula
tions 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. 283–286.
(d) The Court rejects SEACC’s contention that the Memorandum
is not entitled to deference because it contradicts the agencies’ published
statements and prior practice. Though SEACC cites three such state
ments, its arguments are not convincing. Pp. 286–291.
(i) Although a 1986 memorandum of agreement (MOA) between
the EPA and the Corps seeking to reconcile their then-differing “fill
material” definitions suggests, as SEACC asserts, that § 402 will “nor

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mally” apply to discharges of “suspended”—i. e., solid—pollutants, that
statement is not contrary to the Memorandum, which acknowledges that
the EPA retains authority under § 402 to regulate the discharge of sus
pended solids from the lake into downstream waters. The MOA does
not address the question presented by these cases, and answered by the
Memorandum, and is, in fact, consistent with the agencies’ determina
tion that the Corps regulates all discharges of fill material and that § 306
does not apply to these discharges. Pp. 286–288.
(ii) Despite SEACC’s assertion that the fill regulation’s preamble
demonstrates that the fill rule was not intended to displace the pre
existing froth-flotation gold mine performance standard, the preamble
is consistent with the Memorandum when it explicitly notes that the
EPA has “never sought to regulate fill material under effluent guide
lines,” 67 Fed. Reg. 31135. If a discharge does not qualify as fill, the
EPA’s new source performance standard applies. If the discharge qual
ifies as fill, the performance standard does not apply; and there was no
earlier agency practice or policy to the contrary. Pp. 288–289.
(iii) Remarks made by the two agencies in promulgating the fill
regulation, which pledge that the EPA’s “previou[s] determination[s]”
with regard to the application of performance standards “remai[n]
valid,” are not conclusive of the question at issue. The 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 discharges of fill mate
rial. Pp. 289–290.
(iv) While SEACC cites no instance in which the EPA has applied
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 illus
trate that the agencies did not have a prior practice of applying EPA
performance standards to discharges of mining wastes that qualify as
fill material. Pp. 290–291.
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, post, p. 291.
Scalia, J., filed an opinion concurring in part and concurring in the judg
ment, post, p. 295. Ginsburg, J., filed a dissenting opinion, in which Ste
vens and Souter, JJ., joined, post, p. 296.
Theodore B. Olson argued the cause for petitioners in both
cases. With him on the briefs for petitioner Coeur Alaska,

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Inc., were Matthew D. McGill, Aaron D. Lindstrom, and
Robert A. Maynard. Talis J. Colberg, Attorney General of
Alaska, Cameron M. Leonard, Assistant Attorney General,
Jonathan S. Franklin, and Tillman J. Breckenridge filed
briefs for petitioner State of Alaska.
Former Solicitor General Garre argued the cause for the
federal respondents urging reversal in both cases. With
him on the briefs were Assistant Attorney General Tenpas,
Deputy Solicitor General Stewart, Pratik A. Shah, Lane
McFadden, Earl H. Stockdale, and Marc L. Kesselman.
David C. Crosby filed briefs for respondent Goldbelt, Inc.,
under this Court’s Rule 12.6 urging reversal in both cases.
Thomas S. Waldo argued the cause for respondent South
east Alaska Conservation Council et al. With him on the
brief was Scott L. Nelson.†
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 En
gineers, or instead to the Environmental Protection Agency
(EPA or Agency), to issue a permit for the discharge of min
†Briefs of amici curiae urging reversal in both cases were filed for the
Council of Alaska Producers by Paul Lawrence and Wilson L. Condon;
for the Mountain States Legal Foundation by William Perry Pendley; for
the National Association of Home Builders by Duane J. Desiderio,
Thomas J. Ward, and Amy C. Chai; for the National Mining Association
et al. by Christopher T. Handman and Harold P. Quinn, Jr.; for the Pacific
Legal Foundation et al. by James S. Burling; and for the Resource Devel
opment Council for Alaska, Inc., by Michael Jungreis.
Briefs of amici curiae urging affirmance in both cases were filed for
American Rivers et al. by Deborah A. Sivas and Leah J. Russin; for the
Nondalton Tribal Council et al. by Seth P. Waxman, Paul R. Q. Wolfson,
Ethan G. Shenkman, Brian Litmans, and Victoria Clark; for Members
of Congress by David C. Vladeck; and for the Honorable G. Tracy Mehan
III by Amy J. Wildermuth.
Jeffrey C. Parsons and Roger Flynn filed a brief for David M. Chambers
et al. as amici curiae in both cases.

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ing waste, called slurry. The Corps of Engineers (or Corps)
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
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 accord
ance with law.” 5 U. S. C. § 706(2)(A). The environmental
groups are Southeast Alaska Conservation Council, Sierra
Club, and Lynn Canal Conservation (collectively, SEACC).
The State of Alaska and Coeur Alaska are petitioners here.
SEACC argues that the permit from the Corps is unlawful
because the discharge of slurry would violate an EPA regula
tion 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

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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.
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 vol
ume 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 proposes
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 sub
ject 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 lake

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bed 50 feet—to what is now the lake’s surface—and will in
crease 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 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 ap
proved 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 mate
rial.” 33 U. S. C. § 1344(a). The Corps and the EPA have
together defined “fill material” to mean any “material [that]
has the effect of . . . [c]hanging the bottom elevation” 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 Corps issued Coeur Alaska a permit
to pump the slurry into Lower Slate Lake. App. 340a–378a.

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In granting the permit the Corps followed the steps set
forth by § 404. Section 404(b) requires the Corps to consider
the environmental consequences of every discharge it allows.
33 U. S. C. § 1344(b). The Corps must apply guidelines writ
ten by the EPA pursuant to § 404(b). See ibid.; 40 CFR pt.
230 (EPA guidelines). Applying those guidelines 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 pur
pose. 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 “re
cla[im]” the lake by “[c]apping” the tailings with about four
inches of “native material.” App. 361a; id., at 309a. The
Corps concluded that
“[t]he reclamation of the lake will result in more emer
gent wetlands/vegetated shallows with moderate values
for fish habitat, nutrient recycling, carbon/detrital ex
port 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

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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 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 permanently 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 tail
ings in the lake was not the “environmentally preferable”
means of disposing of them. App. 300a. By declining to
exercise its veto, the EPA in effect deferred to the judgment
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 downstream 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 author
ity to regulate the amount of pollutants that certain catego

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ries of new sources may discharge into 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 restricting 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 alumi
num, 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, speci
fied 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 regard
less of which agency issued the permit, the discharge itself
is unlawful because it will violate the EPA new source per
formance 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 ar
gued that this performance standard also applies to the dis
charge of slurry into the lake. It contended further that the
performance standard is a binding implementation of § 306.

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Section 306(e) of the CWA makes it “unlawful” for Coeur
Alaska to “operate” the mine “in violation of ” the EPA’s per
formance standard. 33 U. S. C. § 1316(e).
Coeur Alaska and the State of Alaska intervened as de
fendants. 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 Engineers’
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 definition of ‘fill mate
rial,’ ” 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 dis
charges from froth-flotation mills.” Ibid. The Court of Ap
peals 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 promul
gating their current and prior definitions of “fill material.”
These statements, in the Court of Appeals’ view, demon
strated the agencies’ intent that the EPA’s new source per
formance standard govern discharges like Coeur Alaska’s.
Id., at 648–654.
The Court of Appeals concluded that Coeur Alaska re
quired a § 402 permit for its slurry discharge, that the Corps
lacked authority to issue such a permit under § 404, and that
the proposed discharge was unlawful because it would vio
late the EPA new source performance standard and § 306(e).

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Opinion of the Court
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. 931 (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 governing
this discharge.
A
Section 402 gives the EPA authority to issue “permit[s] for
the discharge of any pollutant,” with one important excep
tion: 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 require
ments under [CWA § 301, 33 U. S. C. § 1311; 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 de
termines are necessary to carry out the provisions of
this chapter.” 33 U. S. C. § 1342(a)(1) (emphasis added).
Section 402 thus prohibits the EPA from exercising permit
ting authority that is “provided [to the Corps] in” § 404.

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This is not to say the EPA has no role with respect to the
environmental consequences of fill. The EPA’s function is
different, in regulating fill, from its function in regulating
other pollutants, but the Agency does exercise some author
ity. Section 404 assigns the EPA two tasks in regard to
fill material. First, the EPA must write guidelines for the
Corps to follow in determining whether to permit a dis
charge 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 dis
posal 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 provide
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
“[d]ischarges of . . . fill material” are “regulated under sec
tion 404.” Ibid.
The agencies, however, have interpreted this regulation
otherwise. In the agencies’ view the regulation essentially
restates the text of § 402, and prohibits the EPA from issuing
permits for discharges that “are regulated under section
404.” 40 CFR § 122.3(b); cf. CWA § 402(a) (“[e]xcept as pro
vided in . . . [§ 404], the Administrator may . . . issue a per
mit”). Before us, the EPA confirms this reading of the regu
lation. Brief for Federal Respondents 27. The Agency’s
interpretation is not “plainly erroneous or inconsistent with

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the regulation”; and so we accept it as correct. Auer v. Rob
bins, 519 U. S. 452, 461 (1997) (internal quotation 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 permits . . .
for the discharge of dredged or fill material.” 33 U. S. C.
§ 1344(a). As all parties concede, the slurry meets the defi
nition 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 un
derstanding 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 expresses a
concern that Coeur Alaska’s interpretation of the statute will
lead to § 404 permits authorizing the discharges of other sol
ids 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 pre
sented by the cases now before us. If, in a future case, a
discharger of one of these solids were to seek a § 404 permit,

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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 agen
cies 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 in
terpretation 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 qual
ification. Nor do the EPA regulations support SEACC’s
reading of § 404. The EPA has enacted guidelines, 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 difficul
ties for the regulated industry. As the regulatory regime
stands now, a discharger must ask a simple question—is the
substance to be discharged fill material or not? The fill reg
ulation, 40 CFR § 232.2, offers a clear answer to that ques
tion; 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 dis
charger consider whether any EPA performance standard

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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 stat
ute gives no indication that Congress intended to burden in
dustry with that confusing division of permit authority.
The regulatory scheme discloses a defined, and workable,
line for determining whether the Corps or the EPA has the
permit authority. Under this framework, the Corps of En
gineers, 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 permit 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 an
swer the question: Do EPA performance standards, and
§ 306(e), apply to discharges of fill material?
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 discharges
of fill material, the statute alone does not resolve the case.
Chevron U. S. A. Inc. v. Natural Resources Defense Council,
Inc., 467 U. S. 837, 842 (1984). We look first to the agency

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regulations, which are entitled to deference 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 agen
cies’ subsequent interpretation of those regulations. Id., at
234–238; Auer, 519 U. S., at 461. In an internal memoran
dum 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 regula
tion[s],” and so we accept it as correct. Ibid. (internal quo
tation 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 state
ments and of the regulatory 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 contrast,
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
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 stand
ard 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

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§ 440.104(a) (limiting the amount of TSS from other kinds of
mines); see also EPA Development Document for Effluent
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’ dis
charges); 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 solu
ble pollutants, the Agency’s action in these cases would re
solve 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 re
quirements set by the performance standard. This demon
strates that the performance standard regulates solid waste.
The EPA’s permit not only restricts the amount of total sus
pended solids, App. 327a (Table 3), but also prohibits the
mine from allowing any “floating solids” to flow from the
lake. Id., at 328a. No party disputes the EPA’s authority
to regulate these discharges of solid mining waste; and no
party questions the validity of the EPA’s new source per
formance standard when it is applicable.
When the performance standard applies to a point source,
§ 306(e) makes it “unlawful” for that point source to vio
late 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), prohibits
the mine from discharging slurry into Lower Slate Lake.

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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 application
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 circumstances. And so,
SEACC reasons, it follows that because the new source per
formance standard forbids even minute discharges of solid
waste, it also forbids the slurry discharge, 30 percent of
which is solid waste.
2
For their part, the State of Alaska and the federal agencies
claim that the Act is unambiguous in the opposite direction.
They rely on § 404 of the Act. As explained above, that sec
tion authorizes the Corps of Engineers to determine whether
to issue a permit allowing the discharge of the slurry. Peti
tioners 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 consider the
EPA’s new source performance standard or the § 306(e) pro
hibition. That silence advances the argument that § 404’s
grant of authority to “issue permits” contradicts § 306(e)’s
declaration that discharges in violation of new source per
formance 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 sec
tion . . . 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

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§ 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 permittee from lawsuits alleging
violations of CWA § 301 (which bars the discharge of “any
pollutant” “[e]xcept 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 permittee from a lawsuit al
leging 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 provi
sion in § 402 does protect a § 402 permittee from an enforce
ment 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 dis
charges of fill material. If § 306 did apply, then the Corps
would be required to evaluate each permit application 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 permittee would be
protected from a suit seeking a judicial determination that
the discharge violates § 306.
3
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 any exception for fill material. On the other hand,
§ 404 grants the Corps blanket authority to permit the dis
charge of fill material—without any mention of § 306. This
tension indicates that Congress has not “directly spoken” to

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the “precise question” 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 stand
ards promulgated under it, applies to § 404 permits and the
discharges they authorize. There is no regulation, for ex
ample, interpreting § 306(e)’s text—“standard of perform
ance applicable to such source”—to mean that a performance
standard ceases to be “applicable” the moment 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 princi
pal regulations, which have been mentioned above, seems
to stand on its own without reference to the other. The
EPA’s new source performance standard contains no excep
tion 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 in
cludes “slurry, or tailings or similar mining-related materi
als” in its definition of a “discharge of fill material,” 40 CFR
§ 232.2; and it contains no exception for slurry that is regu
lated by an EPA performance standard.
The parties point to additional regulations, but these pro
visions do not offer a clear basis of reconciliation. An EPA
regulation, mentioned above, provides that “[d]ischarges of

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dredged or fill material into waters of the United States
which are regulated under section 404 of CWA” “do not re
quire [§ 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 writ
ten by the EPA to guide the Corps permitting decision. See
40 CFR pt. 230. The agencies note that these guidelines do
not expressly require the Corps, in issuing a permit, to con
sider whether the discharge would violate EPA’s perform
ance standards. Here we think failure to mention § 306 or
the EPA new source performance standards does offer some
indication that these are not relevant to the § 404 permit,
though the argument falls short of being conclusive. The
Corps’ own regulations require the agency to evaluate per
mit applications “for compliance with applicable [EPA] ef
fluent limitations.” 33 CFR § 320.4(d) (2008). The regula
tions do not answer whether the new source performance
standard is “applicable” to a 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 interpreta
tion and agency application of the regulations are instructive
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 agencies, 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 re
gional Office of Water with responsibility over the mine.
App. 141a–149a (Regas Memorandum). The Memorandum,

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though not subject to sufficiently formal procedures to merit
Chevron deference, see Mead, supra, at 234–238, is entitled
to a measure of deference 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 limitations
guidelines and standards, such as those applicable 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: “Discharges of dredged or fill ma
terial into waters of the United States which are regulated
under section 404 of CWA” “do not require [§ 402] permits.”
The Regas Memorandum takes an instructive interpretive
step when it explains that because the discharge “do[es] not
require” an EPA permit, ibid., the EPA’s performance stand
ard “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 erroneous or inconsistent with the reg
ulation[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 regulating the dis
charge into surrounding waters. The Memorandum does
not purport to invalidate the EPA’s performance standard.

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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 Ken
sington Mine is not, for example, a project that smuggles a
discharge of EPA-regulated pollutants into a separate dis
charge of Corps-regulated fill material. The instant cases
do not present a process or plan designed to manipulate the
outer boundaries of the definition of “fill material” by label
ing minute quantities of EPA-regulated solids as fill. The
Memorandum states that when a discharge has only an “inci
dental filling effect,” the EPA’s performance standard con
tinues 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 determi
nation. Applying it, the Corps determined 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, furthermore, that the alterna
tive—a heap of tailings larger than the Pentagon placed upon
wetlands—would cause more harm to the environment. Be
cause the Memorandum 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 dan
gerous pollutants, such as slurry) to enter the navigable wa
ters. The EPA has regulated toxic pollutants under a sepa
rate 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 Memorandum,
we find it a sensible and rational construction that reconciles
§§ 306, 402, and 404, and the regulations implementing them,

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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. 1219
(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, however, 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 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 agencies’
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 possibility of
evasion of those standards; it employs the Corps’ expertise
in evaluating the effects of fill material on the aquatic envi
ronment; 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 conclusion that its per
formance 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 downstream creek.
D
SEACC argues against deference to the Regas Memoran
dum. In its view the Regas Memorandum is contrary to
published agency statements and earlier agency practice.
SEACC cites three agency statements: A 1986 “memoran
dum of understanding” between the EPA and the Corps re

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garding 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 “memorandum 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 Federal 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 subject
to section 402 if it is a discharge in liquid, semi-liquid,
or suspended form or if it is a discharge of solid mate
rial of a homogeneous nature normally associated with
single industry wastes . . . . These materials include
placer mining wastes, phosphate mining wastes, tita
nium mining wastes, sand and gravel wastes, fly ash, and
drilling muds. As appropriate, EPA and the Corps will
identify additional such materials.” 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 discharge
of suspended solids from Lower Slate Lake into downstream
waters. This passage does not address the question pre
sented by these cases, and answered by the Regas Memoran
dum, as to whether the EPA’s performance standard applies
when the discharge qualifies as fill material. In fact, the
MOA’s preamble suggests that when a discharge qualifies as

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Opinion of the Court
“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’ determina
tion that the Corps regulates all discharges of fill material
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 “Effluent
Guideline Limitations and 402 Permits”:
“[W]e emphasize that today’s rule generally is intended
to maintain our existing approach to regulating pollut
ants under either section 402 or 404 of the CWA. Ef
fluent limitation guidelines and new source performance
standards (‘effluent guidelines’) promulgated under sec
tion 304 and 306 of the CWA establish limitations and
standards for specified wastestreams from industrial
categories, and those limitations and standards are in

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corporated into permits issued under section 402 of the
Act. EPA has never sought to regulate fill material
under effluent guidelines. Rather, effluent guidelines
restrict discharges of pollutants from identified waste
streams based upon the pollutant reduction capabilities
of available treatment technologies. Recognizing that
some discharges (such as suspended or settleable solids)
can have the associated effect, over time, of raising the
bottom elevation of a water due to settling of water
borne pollutants, we 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 effluent 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 under 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 guide
lines.” Ibid. The preamble, then, is consistent with the
Regas Memorandum. If a discharge does not qualify as fill
material, the EPA’s new source performance standard ap
plies. 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 re
sponse to public comments on the proposed fill material regu
lation. App. 22a–127a. These remarks were incorporated
by reference into the administrative record. 67 Fed. Reg.
31131.

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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 fur
ther that the placement of ‘overburden, slurry, or tail
ings or similar mining-related materials’ is considered
a discharge of fill material. Nevertheless, if EPA has
previously determined that certain materials are sub
ject to an [effluent limitation guideline] under specific
circumstances, then that determination remains valid.
Moreover, . . . permits issued pursuant to section 402 are
intended to regulate process water and provide effluent
limits that are protective of receiving water quality.
This distinction provides the framework 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 “remai[n] valid.” But,
as noted above, the Regas Memorandum has followed this
policy by applying the EPA’s performance standard to the
discharge of water from the lake into the downstream creek.
The response does not state that the EPA will apply its per
formance 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 mate

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rial. By contrast, Coeur Alaska cites two instances in which
the Corps issued a § 404 permit authorizing a mine to dis
charge 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 tail
ings to construct useful structures—a dam in one case, a tail
ings pond in another. Here, by contrast, SEACC contends
that the primary purpose of the discharge is to use a naviga
ble 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 prac
tice 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 consistent
with this opinion.
It is so ordered.
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 environ
mental 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

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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 “pol
lutant.” The Environmental Protection Agency (EPA) ap
plies § 306 new source “performance standards” to a wide
variety of discharges, ranging, for example, from those in
volved in the processing of apples into apple juice or apple
cider, 40 CFR § 407.10 (2008); to the manufacturing of ce
ment, § 411.10; to the production of fresh meat cuts by a
meatcutter, § 432.60; and to the manufacture of pharmaceuti
cal 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 sub
stances produced by that point source; in the case of fer
mentation 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 Administra
tor determines to be achievable through application of the
best available demonstrated control technology . . . including,
where practicable, a standard permitting no discharge of pol
lutants.” 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) (defining “pollut
ant” 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 applica

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ble regulations as allowing the use of such material, say,
crushed rock, as “fill” in some of these situations. Cf. Chev
ron 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 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 302
(dissenting opinion).
Yet there are safeguards against that occurring. For one
thing, as the Court recognizes, see ante, at 275, 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 discharges 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 re
tain 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 sup
plies, shellfish beds and fishery areas . . . , wildlife, or recre
ational areas.” § 1344(c). Finally, the EPA’s decision not to
apply § 306, but to allow permitting to proceed under § 404,
must be a reasonable decision; and court review will help
ensure 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 reason
able, hence lawful. Lower Slate Lake, located roughly three

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Breyer, J., concurring
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 268–270, the EPA arrived at a compro
mise. On the one hand, it would treat mine tailings placed
directly into the lake as “fill” under the § 404 permitting pro
gram. 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
standard 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 rec
ognized 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 pollut
ants.” 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 (sub
ject 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.

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Opinion of Scalia, J.
Justice Scalia, concurring in part and concurring in the
judgment.
I join the opinion of the Court, except for its protestation,
ante, at 283–284, 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 Watersheds,
to the Director of the EPA’s regional Office of Water with
responsibility over the Coeur Alaska mine—an interpreta
tion consistently followed by both the EPA and the Corps of
Engineers, and adopted by both agencies in the proceedings
before this Court. See Chevron U. S. A. Inc. v. Natural
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 interpreta
tion of “the agencies’ own regulatory scheme” and “ ‘the reg
ulatory regime,’ ” ante, at 284 (citing Auer v. Robbins, 519
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 ac
cepts the agency interpretation, includes not just the agen
cies’ own regulations but also (and indeed primarily) the con
formity of those regulations with the ambiguous governing
statute, which is the primary dispute here.
Surely the Court is not adding to our already inscrutable
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 ambiguous statute but also
an ambiguous regulation. One must conclude, then, that if
today’s opinion is not according the agencies’ reasonable and
authoritative interpretation of the Clean Water Act Chevron
deference, it is according some new type of deference—per
haps to be called in the future Coeur Alaska deference—
which is identical to Chevron deference except for the name.

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The Court’s deference to the EPA and the Corps of Engi
neers 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 com
mitted to the charge of executive agencies without the as
surance that reviewing courts will accept reasonable and
authoritative agency interpretation of ambiguous 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 pro
duced so much confusion in the lower courts* that there has
now appeared the phenomenon of Chevron avoidance—the
practice of declining to opine whether Chevron applies or
not. See Bressman, How Mead Has Muddled Judicial Re
view 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.
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
*Compare, e. g., Kruse v. Wells Fargo Home Mortgage, Inc., 383 F. 3d
49, 61 (CA2 2004) (according Chevron deference to policy statements is
sued by Department of Housing and Urban Development), and Schuetz 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 Chev
ron deference to same policy statements). Compare American Federa
tion of Govt. Employees, AFL–CIO, Local 446 v. Nicholson, 475 F. 3d 341,
353–354 (CADC 2007) (according Chevron deference to informal adjudica
tion 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 rulemaking 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).

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Lake, a 23-acre subalpine lake in Tongass National Forest.
The “tailings slurry” would contain concentrations of alumi
num, 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 Environmen
tal Protection Agency (EPA) performance standard forbid
ding 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 performance standards,
33 U. S. C. § 1316(a), and declares it unlawful for any dis
charger 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 (Corps). The Corps has authority,
under § 404 of the Act, 3 U. S. C. § 1344(a), to issue permits
for discharges 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 perform
ance standards. See ante, at 284; Brief for Petitioner Coeur
Alaska 26; Brief for Respondent Southeast Alaska Conserva
tion 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 ma
1 Whether aquatic life will eventually be able to inhabit the lake again
is uncertain. Compare ante, at 269, with App. 201a–202a and Southeast
Alaska Conservation Council v. United States Army Corps of Engineers,
486 F. 3d 638, 642 (CA9 2007).

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terial? In agreement with the Court of Appeals, I would
answer no. The statute’s text, structure, and purpose 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 restore
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 treat
ment system,” the Act’s drafters stated, “is 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 pri
marily in Subchapter III, “Standards and Enforcement”—
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 provided . . . , the
Administrator of [EPA] shall administer this [Act].”).
The Act instructs EPA to establish various technology
based, increasingly stringent effluent limitations for catego
ries 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

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(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(e).
That section makes it “unlawful for any . . . new source to
operate . . . in violation of ” an applicable performance stand
ard. 33 U. S. C. § 1316(e) (emphasis added). In line with
Congress’ aim “to insure . . . ‘maximum feasible control of
new sources,’ ” du Pont, 430 U. S., at 138, the preferred
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 ap
plicable limitations. 430 U. S., at 138.3
In 1982, EPA promulgated new source performance stand
ards for facilities engaged in mining, including those using a
froth-flotation milling process. See Ore Mining and Dress
ing Point Source Category Effluent Limitations Guidelines
and New Source Performance Standards, 47 Fed. Reg. 54598.
Existing mills, EPA found, were already achieving zero dis
charge; 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.
2 In addition, the Act requires States to institute comprehensive water
quality standards for intrastate waters, subject to EPA approval. See
§ 1313. This program supplements the technology-based standards, serv
ing 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).
3 Even the provision allowing the President to exempt federal installa
tions 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).

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B
The nationwide pollution-control requirements just de
scribed are implemented through the National Pollution Dis
charge 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 transforms gen
erally applicable effluent limitations into the individual obli
gations of each discharger. EPA v. California 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 an NPDES permit. E. g., EPA v. Na
tional 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, ad
ministered 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 269.
As the above-described statutory background indicates,
Coeur Alaska’s claim to a § 404 permit carries weighty impli
cations. 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) eligible
to receive a § 404 permit as a discharge of fill material? All

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agree on preliminary matters. Only one agency, the Corps
or EPA, can issue a permit for the discharge. See ante, at
274, 286. Only EPA, through the NPDES program, issues
permits that implement § 306. See supra, at 297–298. Fur
ther, § 306(e) and EPA’s froth-flotation performance stand
ard, unless inapplicable here, bar Coeur Alaska’s proposed
discharge. See ante, at 278–279.
No part of the statutory scheme, in my view, calls into
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 wa
ters from mills that use the froth-flotation process” for min
ing 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 276. 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 material” eligible for a § 404 per
mit is read in harmony with § 306. Doing so yields a simple
rule: Discharges governed by EPA performance standards
are subject to EPA’s administration 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 re
spects Congress’ special concern for new sources. Leaving
pollution-related decisions to EPA, moreover, is consistent
with Congress’ delegation to that Agency of primary respon
sibility to administer the Act. Most fundamental, adhering

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302 COEUR ALASKA, INC. v. SOUTHEAST ALASKA
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Ginsburg, J., dissenting
to § 306(e)’s instruction honors the overriding statutory goal
of eliminating water pollution, and Congress’ particular re
jection of the use of navigable waters as waste disposal sites.
See supra, at 298–301. See also 33 U. S. C. § 1324 (creating
“clean lakes” program requiring States to identify and re
store polluted lakes).4
The Court’s reading, in contrast, strains credulity. A dis
charge of a pollutant, otherwise prohibited by firm statutory
command, becomes lawful if it contains sufficient solid matter
to raise the bottom of a water body, transformed into a waste
disposal facility. Whole categories of regulated industries
can thereby gain immunity from a variety of pollution
control standards. The loophole would swallow not only
standards governing mining activities, see 40 CFR pt. 440
(effluent limitations and new source performance standards
for ore mining and dressing); id., pt. 434 (coal mining); id.,
4 The Court asserts that “numerous difficulties” will ensue if a discharge
governed by a new source performance standard is ineligible for a § 404
permit. Ante, at 276. Namely, the Court notes, the discharger will have
to determine whether a performance standard applies to it. Ante, at 277.
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 270.
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 292 (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 industrial processes. See,
e. g., 40 CFR § 411.10 (performance standard for particular cement manu
facturing process). Levee construction generally is undertaken by devel
opers or government, entities not subject to performance standards for
such a project. This litigation, furthermore, does not illustrate the “diffi
culty” Justice Breyer perceives. See ante, at 292. 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.

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303 Cite as: 557 U. S. 261 (2009)
Ginsburg, J., dissenting
pt. 436 (mineral mining), but also standards for dozens of
other categories of regulated point sources, see, e. g., id., pt.
411 (cement manufacturing); id., pt. 425 (leather tanning and
finishing); 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 specifically
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 funda
mental details of a regulatory scheme in vague terms or an
cillary 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 alteration of
that kind is just what today’s decision imagines. Congress,
as the Court reads the Act, silently upended, in an ancil
lary permitting provision, its painstaking pollution-control
scheme. See ante, at 281. Congress did so, the Court holds,
notwithstanding the lawmakers’ stated effort “to restore and
maintain the chemical, physical, and biological integrity” of
5 The “safeguards” Justice Breyer identifies are hardly reassuring.
See ante, at 293 (concurring opinion). Given today’s decision, it is optimis
tic 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 encompassing more
than 1 million permit applications, see Brief for American 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, under
mines Congress’ aim to install uniform water-pollution regulation.

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Ginsburg, J., dissenting
the waters of the United States, 33 U. S. C. § 1251(a); their
assignment to EPA of the Herculean task of setting strict
effluent limitations for many categories of industrial sources;
and their insistence that new sources meet even more am
bitious standards, not subject to exception or variance.
Would a rational legislature 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 anti
thetical to the text, structure, and purpose of the Clean
Water Act.
* * *
For the reasons stated, I would affirm the judgment of the
Ninth Circuit.