                         PUBLISHED

UNITED STATES COURT OF APPEALS
               FOR THE FOURTH CIRCUIT


THE PINEY RUN PRESERVATION            
ASSOCIATION,
                Plaintiff-Appellee,
                v.
COUNTY COMMISSIONERS OF CARROLL
COUNTY, MARYLAND,
             Defendant-Appellant.
ASSOCIATION OF METROPOLITAN
SEWERAGE AGENCIES; WATER
ENVIRONMENT FEDERATION;
MARYLAND ASSOCIATION OF
MUNICIPAL WASTEWATER AGENCIES,
INCORPORATED; VIRGINIA
ASSOCIATION OF MUNICIPAL
                                         No. 00-1283
WASTEWATER AGENCIES,
INCORPORATED; WEST VIRGINIA
MUNICIPAL WATER QUALITY
ASSOCIATION, INCORPORATED;
AMERICAN CHEMISTRY COUNCIL;
AMERICAN FOREST AND PAPER
ASSOCIATION; CHAMBER OF
COMMERCE OF THE UNITED STATES OF
AMERICA; GENERAL ELECTRIC
COMPANY; NATIONAL ASSOCIATION OF
MANUFACTURERS; UTILITY WATER
ACT GROUP; VIRGINIA
MANUFACTURERS ASSOCIATION;
                                      
2            PINEY RUN v. COMMRS OF CARROLL COUNTY


M.A.D.E. IN MARYLAND;                  
ALLIANCE OF AUTOMOBILE
MANUFACTURERS; AMERICAN IRON AND
STEEL INSTITUTE; AMERICAN
PETROLEUM INSTITUTE;
ENVIRONMENTAL FEDERATION OF
OKLAHOMA; MICHIGAN
MANUFACTURERS ASSOCIATIONS;            
MISSISSIPPI MANUFACTURERS
ASSOCIATION; NATIONAL
PETROCHEMICAL AND REFINERS
ASSOCIATION; NUCLEAR ENERGY
INSTITUTE; WESTERN STATES
PETROLEUM ASSOCIATION,
                      Amici Curiae.
                                       
THE PINEY RUN PRESERVATION             
ASSOCIATION,
                Plaintiff-Appellant,
                 v.
COUNTY COMMISSIONERS OF CARROLL
COUNTY, MARYLAND,
              Defendant-Appellee.

                                       
ASSOCIATION OF METROPOLITAN
SEWERAGE AGENCIES; WATER                    No. 00-1322
ENVIRONMENT FEDERATION;
MARYLAND ASSOCIATION OF
MUNICIPAL WASTEWATER AGENCIES,
INCORPORATED; VIRGINIA
ASSOCIATION OF MUNICIPAL
WASTEWATER AGENCIES,
INCORPORATED; WEST VIRGINIA
MUNICIPAL WATER QUALITY
ASSOCIATION, INCORPORATED;
                                       
             PINEY RUN v. COMMRS OF CARROLL COUNTY        3


AMERICAN CHEMISTRY COUNCIL;           
AMERICAN FOREST AND PAPER
ASSOCIATION; CHAMBER OF
COMMERCE OF THE UNITED STATES OF
AMERICA; GENERAL ELECTRIC
COMPANY; NATIONAL ASSOCIATION OF
MANUFACTURERS; UTILITY WATER
ACT GROUP; VIRGINIA
MANUFACTURERS ASSOCIATION;
M.A.D.E. IN MARYLAND;
ALLIANCE OF AUTOMOBILE
MANUFACTURERS; AMERICAN IRON AND
STEEL INSTITUTE; AMERICAN             
PETROLEUM INSTITUTE;
ENVIRONMENTAL FEDERATION OF
OKLAHOMA; MICHIGAN
MANUFACTURERS ASSOCIATIONS;
MISSISSIPPI MANUFACTURERS
ASSOCIATION; NATIONAL
PETROCHEMICAL AND REFINERS
ASSOCIATION; NUCLEAR ENERGY
INSTITUTE; WESTERN STATES
PETROLEUM ASSOCIATION,
                      Amici Curiae.
                                      
          Appeals from the United States District Court
           for the District of Maryland, at Baltimore.
            Joseph H. Young, Senior District Judge.
                         (CA-98-3124-Y)

                     Argued: April 5, 2001

                   Decided: October 10, 2001

    Before WILKINS, KING, and GREGORY, Circuit Judges.
4             PINEY RUN v. COMMRS OF CARROLL COUNTY
Vacated and remanded by published opinion. Judge King wrote the
opinion, in which Judge Wilkins and Judge Gregory joined.


                             COUNSEL

ARGUED: Linda S. Woolf, GOODELL, DEVRIES, LEECH &
GRAY, L.L.P., Baltimore, Maryland, for Appellant. Christopher Don-
ald Pomeroy, MCGUIRE WOODS, L.L.P., Richmond, Virginia, for
Amici Curiae State Associations. Guerdon Macy Nelson, Towson,
Maryland, for Appellee. ON BRIEF: Michael B. MacWilliams, Ian
Gallacher, GOODELL, DEVRIES, LEECH & GRAY, L.L.P., Balti-
more, Maryland, for Appellant. F. Paul Calamita, MCGUIRE
WOODS, L.L.P., Richmond, Virginia, for Amici Curiae State Associ-
ations. D. Randall Benn, Paul C. Freeman, LEBOEUF, LAMB,
GREENE & MACRAE, L.L.P., Washington, D.C., for Amici Curiae
Sewerage Agencies, et al. James N. Christman, HUNTON & WIL-
LIAMS, Richmond, Virginia, for Amici Curiae Industry Groups.
Robert G. Smith, Anthony M. Carey, VENABLE, BAETJER &
HOWARD, L.L.P., Baltimore, Maryland, for Amicus Curiae
M.A.D.E. in Maryland. Scott M. DuBoff, Kenneth S. Kaufman,
WRIGHT & TALISMAN, P.C., Washington, D.C., for Amici Curiae
Automobile Manufacturers, et al.


                              OPINION

KING, Circuit Judge:

   The Piney Run Preservation Association sued the Commissioners
of Carroll County, Maryland, claiming that a county-operated waste
treatment plant was discharging warm water into a local stream, Piney
Run, in violation of the Clean Water Act. The district court construed
the plant’s NPDES permit as not prohibiting the discharge of heat.
Nonetheless, the court decided that the Commissioners were liable
under the Clean Water Act for the discharge of pollutants not
expressly authorized by the permit. On appeal, the Commissioners
maintain that the "permit shield" defense, embodied in 33 U.S.C.
§ 1342(k), bars suit against a permit holder for the discharge of pollu-
              PINEY RUN v. COMMRS OF CARROLL COUNTY                    5
tants not expressly listed in the permit. Although we do not accept the
Commissioners’ position on the permit shield defense, we also dis-
agree with the district court’s interpretation of the Clean Water Act.
Utilizing the two-part test spelled out in Chevron, U.S.A., Inc. v. Nat-
ural Resources Defense Council,1 467 U.S. 837 (1984), we adhere to
the interpretation provided by the EPA. We therefore view the
NPDES permit as shielding its holder from liability under the Clean
Water Act as long as (1) the permit holder complies with the express
terms of the permit and with the Clean Water Act’s disclosure
requirements and (2) the permit holder does not make a discharge of
pollutants that was not within the reasonable contemplation of the
permitting authority at the time the permit was granted. Applying this
rule, we conclude that the Commissioners did not violate the Clean
Water Act because (1) they complied with the discharge limitations
and reporting requirements of their permit, and (2) their discharges of
heat were within the reasonable contemplation of the permitting
authority at the time the permit was issued. Accordingly, we vacate
the judgment of the district court, and we remand for entry of judg-
ment in favor of the Commissioners.

                                   I.

   Piney Run is a small stream with its headwaters near the border of
Carroll and Baltimore counties in Maryland. The Maryland Depart-
ment of the Environment ("MDE") has classified Piney Run as a
Class III-P stream, which means that it is protected as a source of
public drinking water and as a body capable of supporting a self-
sustaining trout population. See Md. Regs. Code ("COMAR") tit. 26,
§ 26.08.02.02(B)(5). Carroll County operates the Hampstead Waste-
water Treatment Plant ("Plant"), which serves approximately 4200
residential and commercial users. As part of the treatment process, the
Plant discharges effluent, i.e., treated wastewater, into Piney Run.

  Because of the Plant’s discharge of effluent into Piney Run, the
Plant is subject to the Clean Water Act ("CWA"). See 33 U.S.C.
  1
   The Chevron doctrine provides that interpretations of governing stat-
utes by authorized administrative agencies receive deference from the
courts if (1) the statutory language is ambiguous and (2) the administra-
tive interpretation is reasonable. 467 U.S. at 844.
6              PINEY RUN v. COMMRS OF CARROLL COUNTY
§ 1311(a). Under the CWA, dischargers must operate pursuant to a
National Pollutant Discharge Elimination System ("NPDES") permit
obtained from either the Environmental Protection Agency ("EPA")
or an authorized state agency. See id. §§ 1311(a), 1342(a), (c); see
also Md. Code Ann. Envir. § 9-323. Beginning in 1975, the Plant has
operated under a series of NPDES permits granted by the MDE as the
authorized state agency. The most recent NPDES permit was issued
to the Plant in 1990.

   Under the CWA, the various states are required to promulgate
water quality standards for certain waters within their borders. See 33
U.S.C. § 1313. Such standards denote designated uses of particular
bodies of water and establish water quality criteria designed to protect
those uses. See 40 C.F.R. §§ 131.10(a), 131.11. In order to grant a
permit or a permit modification, the MDE must determine that the
discharger will not violate these water quality standards. See Md.
Code Ann. Envir. § 9-324(a); COMAR tit. 26, § 26.08.04.02(A)
(1)(b).

   The Piney Run Preservation Association ("Association"), which is
dedicated to the protection of Piney Run, filed this lawsuit in the Dis-
trict of Maryland in 1998. The Association sued the Commissioners
under section 505 of the CWA, 33 U.S.C. § 1365(a),2 claiming that
the Plant’s NPDES permit limited the amount of heated effluent it
could discharge into Piney Run, and that the Plant regularly exceeded
this limit.3 The Plant’s 1990 permit contained express limitations on
    2
     Section 505 provides, in pertinent part, that "any citizen may com-
mence a civil action on his own behalf against any person . . . who is
alleged to be in violation of an effluent standard or limitation under this
chapter." 33 U.S.C. § 1365(a). This provision of the CWA allows citi-
zens "to bring suit against any NPDES permit holder who has allegedly
violated its permit" and "a successful suit may result in the award of
injunctive relief and the imposition of civil penalties payable to the
United States Treasury." Friends of the Earth, Inc. v. Gaston Copper
Recycling Corp., 204 F.3d 149, 152 (4th Cir. 2000).
   3
     In 1991, the Plant petitioned the MDE for a modification of its 1990
permit to allow it to increase its daily discharge of effluent. The MDE
proposed granting the modification, but several neighboring landowners
challenged the change and contended that the MDE had not sufficiently
               PINEY RUN v. COMMRS OF CARROLL COUNTY                      7
the amount of certain pollutants that may be discharged. Heat, a statu-
tory pollutant under the CWA, was not listed in the 1990 permit as
one of these pollutants.4 See id. § 1362(6). In its lawsuit, the Associa-
tion claimed that a footnote of the Plant’s NPDES permit flatly pro-
hibited the discharge of any pollutants that were not expressly listed
in the permit. In the alternative, the Association argued that a permit
holder may be liable under the CWA for the discharge of any pollu-
tant not expressly allowed by its permit. The Association claimed that
under either of these theories, the Plant was in violation of the CWA
if it discharged any level of heat whatsoever. In May 1999, the district
court construed the Commissioners’ permit as allowing for the dis-
charge of heat, but held that the CWA prohibits the discharge of any
pollutant that is not limited by the permit. Using Maryland water
quality standards, the court concluded that heat constituted a pollutant
in violation of the CWA when effluent was discharged "with a tem-
perature exceeding the greater of either 68 degrees [Fahrenheit] or the
ambient temperature of Piney Run." Piney Run Pres. Ass’n. v. County

analyzed whether the Plant would comply with state water quality tem-
perature standards in discharging the increased effluent. Although the
MDE adjudicatory bodies and the Circuit Court for Baltimore County
dismissed the landowners’ claim, the Court of Special Appeals of Mary-
land upheld the landowners’ challenge and remanded the case to the
MDE to measure the ambient temperature of Piney Run and to ascertain
whether the Plant violated Maryland water quality standards at its current
or proposed levels of discharge. Therefore, because the Plant has not
received final approval for a modified permit, the 1990 permit is the rele-
vant permit for this case.
   4
     Although the Association asserts that the Plant discharged heat in vio-
lation of the NPDES permit, the crux of the Association’s challenge is
that the Plant discharged water into Piney Run that was warmer than the
baseline temperature, or "ambient temperature," of the stream. In
essence, the Association contends that heat was discharged into Piney
Run in violation of the CWA any time the temperature of the water dis-
charged exceeded that of Piney Run, even if the difference in tempera-
ture between the two was slight. For example, the Association claims
that the Commissioners violated the CWA even though the Plant’s efflu-
ent was less than ten degrees Fahrenheit warmer than the temperature of
Piney Run, and the discharged water was never measured as exceeding
approximately 75.2 degrees Fahrenheit.
8                  PINEY RUN v. COMMRS OF CARROLL COUNTY
Comm’rs., 82 F. Supp. 2d 464, 466 (D. Md. 2000) (citing COMAR
tit. 26, § 26.08.02.03-3E). The court then calculated the "ambient
temperature" of the stream, and found on partial summary judgment
that the Commissioners had violated the CWA on 183 occasions.5 In
January 2000, the court conducted a bench trial in connection with the
discharges in dispute, and it found an additional 107 CWA violations
against the Commissioners. Accordingly, the court in February 2000
entered judgment for the Association, enjoined the Commissioners
from further violations, assessed them $400,000 in civil penalties pay-
able to the United States Treasury, and awarded the Association its
litigation costs and reasonable attorneys’ fees.

   Both the Association and the Commissioners appeal from the dis-
trict court’s final order of February 10, 2000. The Association claims
that the district court erred in holding that the Plant only violated the
CWA when its discharge of heat exceeded state temperature stan-
dards. It contends that the Plant violated the CWA whenever it dis-
charged any level of heat whatsoever. Accordingly, the Association
seeks remand of this case on the issue of damages. The Commission-
ers, on the other hand, claim that the permit shield defense in 33
U.S.C. § 1342(k) bars holding a permit holder liable for the discharge
of pollutants not expressly regulated by the permit.6 The Commission-
    5
     The Commissioners subsequently moved for reconsideration by the
district court of its summary judgment ruling or, in the alternative, for
certification of an interlocutory appeal, pursuant to 28 U.S.C. § 1292(b).
In order to grant certification under § 1292(b), a district court must find
that the order at issue "involves a controlling question of law as to which
there is substantial ground for difference of opinion." The district court
denied the Commissioners’ motion to reconsider, but properly certified
its summary judgment ruling for interlocutory appeal. On August 30,
1999, however, we denied the Commissioners’ petition for interlocutory
review. The Commissioners then filed a second motion for reconsidera-
tion in the district court, which was also denied.
   6
     The permit shield defense is derived from the provisions of 33 U.S.C.
§ 1342(k), which provides:
        Compliance with a permit issued pursuant to this section shall be
        deemed compliance, for purposes of sections 1319 and 1365 of
        this title, with sections 1311, 1312, 1316, 1317, and 1343 of this
        title, except any standard imposed under section 1317 of this title
        for a toxic pollutant injurious to human health.
               PINEY RUN v. COMMRS OF CARROLL COUNTY                         9
ers also challenge the Article III standing of the Association to sue,
and they assert that the doctrine of primary jurisdiction precludes the
district court’s findings with respect to the ambient temperature of
Piney Run.7 We possess jurisdiction pursuant to 28 U.S.C. § 1291.

                                      II.

   The Commissioners claim that the Association lacks Article III
standing. Pursuant to Article III of the Constitution, federal courts are
restricted to the adjudication of "cases" and "controversies." The
standing requirement therefore "ensures that a plaintiff has a suffi-
cient personal stake in a dispute to render judicial resolution appropri-
ate." Friends of the Earth, Inc. v. Gaston Copper Recycling Corp.,
204 F.3d 149, 153 (4th Cir. 2000). Moreover, the standing inquiry
also "tends to assure that the legal questions presented to the court
will be resolved, not in the rarefied atmosphere of a debating society,
but in a concrete factual context conducive to a realistic appreciation
of the consequences of judicial action." Valley Forge Christian Col-
lege v. Americans United for Separation of Church and State, Inc.,
454 U.S. 464, 472 (1982). In analyzing a decision on Article III stand-
ing, we review the district court’s factual findings for clear error. We
consider the legal question of whether the Association possesses
standing to sue as a de novo matter. See Marshall v. Meadows, 105
F.3d 904, 905-06 (4th Cir. 1997).
  7
    The doctrine of primary jurisdiction "is a doctrine specifically appli-
cable to claims properly cognizable in court that contain some issue
within the special competence of an administrative agency. It requires
the court to enable a ‘referral’ to the agency, staying further proceedings
so as to give the parties reasonable opportunity to seek an administrative
ruling." Reiter v. Cooper, 507 U.S. 258, 268 (1993). The doctrine has
been deemed to apply in circumstances in which federal litigation raises
a difficult, technical question that falls within the expertise of a particular
agency. See, e.g., American Auto. Mfrs. Ass’n. v. Mass. Dept. of Envt’l.
Prot., 163 F.3d 74, 81 (1st Cir. 1998). In this case, the Commissioners
contend that the district court should have deferred to the MDE to calcu-
late the ambient temperature of Piney Run. Although the Commission-
ers’ point may be compelling, we need not reach this issue because the
ambient temperature of Piney Run has no bearing on our disposition of
this appeal.
10            PINEY RUN v. COMMRS OF CARROLL COUNTY
   An association, as the representative of its members who have been
harmed, possesses standing to sue if it can show: (1) at least one
member would otherwise have individual standing, (2) the interests at
stake in the litigation are germane to the organization’s purpose, and
(3) neither the claim asserted nor the relief requested requires the par-
ticipation of individual members in the lawsuit. See Friends of the
Earth, Inc. v. Laidlaw Envt’l. Servs. (TOC), Inc., 528 U.S. 167, 181
(2000); Warth v. Seldin, 422 U.S. 490, 511 (1975). On appeal, the
Commissioners only contest the first prong of this three-part test, i.e.,
whether any member of the Association has individual standing to
sue. An individual possesses Article III standing if (1) he or she has
suffered an "injury in fact," (2) that is fairly traceable to the chal-
lenged action of the defendant, and (3) it is likely that the injury will
be redressed by a favorable decision. See Laidlaw, 528 U.S. at 180-
81. In this proceeding, the Commissioners challenge the first two ele-
ments of the individual standing test: they assert that no member of
the Association has suffered an "injury in fact," and that even if an
Association member has suffered such an injury, it is not "fairly trace-
able" to the Plant’s operation. They correctly point out that the ele-
ments of standing are "not mere pleading requirements," but rather
must be supported by sufficient evidence. Lujan v. Defenders of Wild-
life, 504 U.S. 555, 561 (1992).

   A plaintiff can show an "injury in fact" when he or she suffers "an
invasion of a legally protected interest which is concrete and particu-
larized, as well as actual or imminent." Gaston Copper, 204 F.3d at
154; see also Defenders of Wildlife, 504 U.S. at 560. In an environ-
mental case, the question is whether the plaintiff has suffered an
injury, as opposed to whether the environment has actually been
harmed. See Laidlaw, 528 U.S. at 181. Specifically, a plaintiff need
only show that he used the affected area, and that he is an individual
"for whom the aesthetic and recreational values of the area [are] less-
ened" by the defendant’s activity. Sierra Club v. Morton, 405 U.S.
727, 735 (1972); see also Laidlaw, 528 U.S. at 184 (holding that
plaintiffs had established an injury in fact because the challenged
activity directly affected their "recreational, aesthetic, and economic
interests"); Defenders of Wildlife, 504 U.S. at 562-63 ("[T]he desire
to use or observe an animal species, even for purely aesthetic pur-
poses, is undeniably a cognizable interest for the purpose of stand-
ing."); Gaston Copper, 204 F.3d at 159 (concluding that individuals’
              PINEY RUN v. COMMRS OF CARROLL COUNTY                   11
allegations that they would make greater recreational use of waterway
except for concern over defendant’s discharges sufficient for injury in
fact).

   In this case, Dorothy Rowland, a member of the Association, is
able to show that she has suffered an injury in fact. Piney Run flows
through Rowland’s property. She testified that when she purchased
her property in 1967, Piney Run was "very pristine," but that in the
last several years the stream had acquired a high concentration of
green algae. Rowland stated that the green algae significantly inter-
fered with her use and enjoyment of Piney Run. For example, the
algae made the stream’s rocks slippery, and therefore difficult to
cross. Because the water is no longer clear, she stopped allowing her
horses to drink from Piney Run. Further, according to Rowland, the
green algae made the stream less desirable to observe. In sum, Row-
land demonstrated that her enjoyment of Piney Run has been dimin-
ished, and accordingly, she has sufficiently shown an "injury in fact."

    Rowland can also show that her injury was "fairly traceable" to the
Plant’s operation. The plaintiff’s injury must be fairly traceable to the
challenged action of the defendant and not the result of some indepen-
dent action. See, e.g., Defenders of Wildlife, 504 U.S. at 561. The
Commissioners maintain that the Association failed to provide suffi-
cient scientific evidence that the concentration of green algae in Piney
Run was caused by the Plant’s discharge of heat. According to the
Commissioners, the Association had to show that, but for the Plant’s
operation, the algae would not have developed in the stream. The
Commissioners, however, misapprehend what the Association must
demonstrate to show traceability. Traceability "does not mean that
plaintiffs must show to a scientific certainty that defendant’s effluent
. . . caused the precise harm suffered by the plaintiffs." Natural Res.
Def. Council, Inc. v. Watkins, 954 F.2d 974, 980 n.7 (4th Cir. 1992)
(internal quotation marks omitted); see also Gaston Copper, 204 F.3d
at 161 (same). Rather, a plaintiff "must merely show that a defendant
discharges a pollutant that causes or contributes to the kinds of inju-
ries alleged." Watkins, 954 F.2d at 980 (internal quotation marks
omitted); see also Gaston Copper, 204 F.3d at 161 (same).

   In this case, the Association presented evidence that the Plant is
discharging heat into Piney Run. Dr. Stauffer, a professor of ichthyol-
12             PINEY RUN v. COMMRS OF CARROLL COUNTY
ogy (the study of fish), testified that heat can cause green algae to prolif-
erate.8 Rowland therefore has sufficiently shown that her alleged
injury is "fairly traceable" to the challenged actions of the Plant. Row-
land has demonstrated that she would possess individual standing if
she were to sue the Commissioners for unlawfully operating the Plant.
Because Rowland would have individual standing, the Association
has standing to sue as a representative of its members.

                                    III.

   We turn now to the district court’s interpretation and application of
the CWA. The court found that the Plant’s NPDES permit contained
no prohibition on discharging heat, but concluded that the Plant was
liable under the CWA because the discharge of heat was not expressly
allowed by the permit. We are, however, constrained to disagree. In
these circumstances, because the Commissioners adequately disclosed
that the Plant was discharging heat and because their discharges were
within the reasonable contemplation of the MDE during the permit
application process, the NPDES permit allowed the Plant to discharge
heat. To explain our view on this point, a brief overview of the history
and structure of the CWA is required.

                                     A.

   Prior to enactment of the CWA in 1972, the Water Pollution Con-
trol Act of 1948, as amended by the Water Quality Act of 1965, was
the primary means of federal regulation of water pollution. See gener-
ally EPA v. California ex rel. State Water Res. Control Bd., 426 U.S.
200, 202 (1976); Martin A. McCrory, Standing in the Ever-Changing
Stream: The Clean Water Act, Article III Standing, and Post-
Compliance Adjudication, 20 Stan. Envtl. L.J. 73, 79-81 (2001).
  8
   The Commissioners contend that the district court abused its discre-
tion in allowing Dr. Stauffer to opine that the Plant’s discharge of heat
was affecting Piney Run’s trout population. Specifically, the Commis-
sioners claim that Dr. Stauffer’s testimony did not meet the standards for
admissibility. Regardless, because of the broad discretion accorded trial
courts in such matters, and due to Dr. Stauffer’s qualifications and the
nature of his testimony, it was not erroneous for the district court to con-
sider his evidence.
              PINEY RUN v. COMMRS OF CARROLL COUNTY                   13
Under this regulatory scheme, states were required to promulgate
water quality standards for certain bodies of water within their bor-
ders. See Friends of the Earth v. Gaston Copper Recycling Corp., 204
F.3d 149, 151 (4th Cir. 2000). Operators could discharge pollutants
so long as their discharges did not reduce water quality below these
standards. This water quality standard scheme, however, was plagued
with many problems. Significantly, it was often difficult to formulate
precise water quality standards and even more difficult to prove that
a particular operator’s discharge reduced water quality below these
standards. See S. Rep. No. 92-414 (1971); see also Gaston Copper,
204 F.3d at 151.

   The CWA (and its later amendments) represented a fundamental
change in the manner of federal regulation of water pollution. The
CWA "shifted the focus away from water quality standards to direct
limitations on the discharge of pollutants." Gaston Copper, 204 F.3d
at 151 (citing 33 U.S.C. § 1311). Regulators no longer had to deter-
mine whether there was a causal link between the degradation of
water quality and the pollutant in question; they simply had to deter-
mine whether the entity was discharging more pollutant into water
than allowed by the CWA. Id. The CWA also established a default
regime of strict liability. Unless a discharge fit within one of the
CWA’s limited exceptions, the entity discharging the pollutant vio-
lated the CWA, regardless of the quantity of pollutant emitted. Id.
Thus, the "centerpiece of the Clean Water Act," § 301(a), provides
that "[e]xcept as in compliance with this section and [other sections
of the Act], the discharge of any pollutant by any person shall be
unlawful." Gaston Copper, 204 F.3d at 151 (quoting 33 U.S.C.
§ 1311(a)).

   The primary exception to the blanket liability imposed by the CWA
is the NPDES permitting system. See Natural Res. Def. Council, Inc.
v. Costle, 568 F.2d 1369, 1374 (D.C. Cir. 1977) ("[T]he legislative
history makes clear that Congress intended the NPDES permit to be
the only means by which a discharger from a point source may escape
the total prohibition of [§] 301(a)."). Although Congress intended the
CWA to lead to the long-term elimination of pollutants in the nation’s
waterways, Congress recognized the technological infeasibility of
prohibiting all pollutants in the short term. See id. at 1373. Therefore,
under § 402 of the CWA, individuals may apply for NPDES permits
14            PINEY RUN v. COMMRS OF CARROLL COUNTY
to discharge a limited amount of effluent. See 33 U.S.C. § 1311(a),
1342(a) & (c). The EPA issues NPDES permits; however, the EPA
suspends its issuance of permits if it approves a state permitting pro-
gram. See id. § 1342(c)(1). The EPA has authorized approximately
forty states, including Maryland, to issue NPDES permits. See 57 Fed.
Reg. 43,733, 43,734-35 (1992) (listing states with permitting author-
ity). Permit holders, no matter the issuing authority, are required to
comply "not only with the limitations on the amount of pollutants
they may discharge, but also with a variety of monitoring, testing, and
reporting requirements." Gaston Copper, 204 F.3d at 151. Assuming
that they follow the terms of their NPDES permits, however, permit
holders avoid CWA liability.

   In crafting a permit, the permitting authority (either the EPA or the
designated state authority, in this case, the MDE), must take account
of two central concepts. The CWA requires that "every permit contain
(1) effluent limitations that reflect the pollution reduction achievable
by using technologically practicable controls and (2) any more strin-
gent pollutant release limitations necessary for the waterway receiv-
ing the pollutant to meet ‘water quality standards.’" American Paper
Inst., Inc. v. United States Envt’l. Prot. Agency, 996 F.2d 346, 349
(D.C. Cir. 1993) (citing 33 U.S.C. § 1311(b)(1)) (internal citations
omitted). Thus, despite the CWA’s shift in focus of environmental
regulation towards the discharge of pollutants, water quality standards
still have an important role in the CWA regulatory scheme.9 Before
issuing a permit the permitting authority must, with reference to what
is technologically feasible, incorporate "discharge limitations neces-
sary to satisfy [the state water quality] standard." Id. at 350 (citing
§ 301 of the CWA).

  The effectiveness of the permitting process is heavily dependent on
permit holder compliance with the CWA’s monitoring and reporting
  9
    Under the CWA, states have the primary role in promulgating water
quality standards. The CWA requires that states review their water qual-
ity standards at least once every three years in "a process commonly
known as triennial review" to ensure that the standards "‘protect the pub-
lic health or welfare, enhance the quality of water and serve the pur-
poses’ of the Act." American Paper Inst., 996 F.2d at 349 (quoting 33
U.S.C. § 1313(c)(2)(A)).
              PINEY RUN v. COMMRS OF CARROLL COUNTY                  15
requirements. See 33 U.S.C. § 1318. The permitting authority receives
discharge information from all relevant parties and then calibrates
each individual permit to maintain overall state water quality stan-
dards. NPDES permits are therefore somewhat interdependent; the
permitting authority must account for the effluent discharge of others
in calculating the appropriate levels for an individual permit holder.

                                  B.

   Having briefly reviewed the history and structure of the CWA, we
now turn to the central question on appeal, the nature of the Commis-
sioners’ liability, if any, under the CWA. The district court concluded
that the CWA prohibits the discharge of any pollutant not expressly
allowed by an operator’s NPDES permit. The Commissioners chal-
lenge that ruling, contending that the permit shield defense bars suit
against NPDES permit holders under the CWA except for violations
of the express conditions of the permit. We view each of these inter-
pretations as being at variance with the CWA’s liability scheme;
although the CWA does prohibit the discharge of pollutants not con-
tained within the NPDES permit, the protection offered by the permit
is broader than the district court suggests.

   At issue is the scope of the permit shield defense. As noted previ-
ously, the NPDES permit sets out the allowable departures from the
CWA’s baseline of total liability for discharges of effluent. Natural
Res. Def. Council, Inc. v. Costle, 568 F.2d at 1374. It is clear, there-
fore, that if a permit holder discharges pollutants precisely in accor-
dance with the terms of its permit, the permit will "shield" its holder
from CWA liability. The permit shield defense, however, raises two
additional questions that are slightly more difficult: (1) what com-
prises the scope or terms of an NPDES permit, and (2) whether the
permit shield bars CWA liability for discharges not expressly allowed
by the permit when the holder has complied with the permit’s express
restrictions. It is to these matters that we now turn.

   The central issue in determining the scope of a NPDES permit is
whether the permit implicitly incorporates pollutant discharges dis-
closed by the permit holder to the permitting authority that are not
explicitly allowed in the permit. Put more simply, although an opera-
tor may report multiple discharges of pollutants to the licensing body,
16            PINEY RUN v. COMMRS OF CARROLL COUNTY
the permit may only contain explicit limitations for some of those pol-
lutants. The question, in that circumstance, is whether the permit
holder may continue to empty the unlisted pollutants into the water,
or whether it may only discharge those pollutants that are specifically
listed in the permit.

   Determining the proper scope of an NPDES permit requires us to
examine the language of the CWA. See Atlantic States Legal Found.,
Inc. v. Eastman Kodak Co., 12 F.3d 353, 358 (2d Cir. 1993). In con-
struing the application of the CWA’s provisions in this case, we find
it necessary and appropriate to perform a Chevron analysis. See Chev-
ron, U.S.A., Inc. v. Natural Res. Def. Council, Inc., 467 U.S. 837,
842-43 (1984). Under Chevron, we are required to apply a two-part
test. First, we examine the language of the statute to see if "Congress
has directly spoken to the precise question at issue." Id. at 842. If
Congressional intent is clear, "that is the end of the matter; for the
court, as well as the agency, must give effect to the unambiguously
expressed intent of Congress." Id. at 843. If the statute is ambiguous,
then we apply Chevron’s second step, and we defer to the agency’s
interpretation of its governing statute and regulations, as long as (1)
the agency has promulgated that interpretation pursuant to a notice-
and-comment rulemaking or a formal adjudication, Christensen v.
Harris County, 529 U.S. 576, 587 (2000), and (2) the agency’s inter-
pretation is reasonable. Chevron, 467 U.S. at 843. In analyzing the
reasonableness of the EPA’s interpretation of the CWA, "we need not
find that [the EPA’s interpretation] is the only permissible construc-
tion that EPA might have adopted but only that EPA’s understanding
of this very ‘complex statute’ is a sufficiently rational one to preclude
a court from substituting its judgment for that of EPA." Chemical
Mfrs. Ass’n. v. Natural Res. Def. Council, Inc., 470 U.S. 116, 125
(1985) (quoting Train v. Natural Res. Def. Council, Inc., 421 U.S. 60,
75, 87 (1975)) (emphasis added).

   In applying step one of Chevron, we view the crucial language of
the CWA as ambiguous. The permit shield provision, 33 U.S.C.
§ 1342(k), specifies that "compliance with a permit issued pursuant to
this section shall be deemed compliance, for purposes of sections
1319 and 1365 of this title, with sections 1311, 1312, 1316, 1317, and
1343 of this title." Although this statutory language makes clear that
compliance with a permit constitutes an exception to the general strict
              PINEY RUN v. COMMRS OF CARROLL COUNTY                  17
liability of the CWA, we must agree with the Second Circuit’s con-
clusion that § 1342(k) does not explicitly explain the scope of permit
protection. See Atlantic States Legal Found., 12 F.3d at 357-58 (con-
cluding that permit shield language ambiguous with respect to scope
of coverage). Therefore, because Congressional intent is not clear, we
must turn to the second step of the Chevron analysis.

   In applying step two of Chevron, we observe that the EPA has pro-
mulgated, pursuant to a formal adjudication, an interpretation of the
permit shield provision that is reasonable. The EPA is authorized both
to administer and enforce the CWA. See 33 U.S.C. § 1251(d). In a
1998 formal adjudication proceeding before the EPA’s Environmental
Appeals Board,10 In re Ketchikan Pulp Co., the Board determined that
the NPDES permit covers all pollutants disclosed to the permitting
authority during the permit application process. 7 E.A.D. 605 (EPA
1998), 1998 WL 284964 (E.P.A.) at *12-13 ("[W]hen the permittee
has made adequate disclosures during the application process regard-
ing the nature of its discharges, unlisted pollutants may be considered
to be within the scope of an NPDES permit, even though the permit
does not expressly mention those pollutants."). In explaining this rul-
ing, the Ketchikan Board observed that the EPA had already acknowl-
edged that "it is impossible to identify and rationally limit every
chemical or compound present in the discharge of pollutants" and that
the EPA consequently had determined that the "goals of the CWA
may be more effectively achieved by focusing on the chief pollutants
and wastestreams established in effluent guidelines and disclosed by
permittees in their permit applications." Id. at *11. The Board, adopt-
ing the reasoning of the Second Circuit in Atlantic States Legal
Foundation, therefore held that "[t]he proper interpretation of the
[CWA] regulations is that . . . [w]ater quality based limits are estab-
lished where the permitting authority reasonably anticipates the dis-
charge of pollutants by the permittee at levels that have the reasonable
potential to cause or contribute to an excursion above any state water
quality criterion." Id. at *11 (quoting Atlantic States Legal Found., 12
F.3d at 358).
  10
    The EPA Administrator has delegated authority to review NPDES
permit violations to the Environmental Appeals Board. See 40 C.F.R.
§§ 1.25, 124.2.
18             PINEY RUN v. COMMRS OF CARROLL COUNTY
   The Ketchikan decision therefore made clear that a permit holder
is in compliance with the CWA even if it discharges pollutants that
are not listed in its permit, as long as it only discharges pollutants that
have been adequately disclosed to the permitting authority. Id. at *17
("[T]he discharge of unlisted pollutants is in violation of the CWA
unless the applicant makes adequate disclosures to permit authorities
during the application process about the source and nature of its dis-
charges."). To the extent that a permit holder discharges a pollutant
that it did not disclose, it violates the NPDES permit and the CWA.
Id. at *13 ("[W]here the discharger has not adequately disclosed the
nature of its discharges to permit authorities, and as a result thereof
the permit authorities are unaware that unlisted pollutants are being
discharged, the discharge of unlisted pollutants has been held to be
outside the scope of the permit.").

   The EPA in Ketchikan therefore outlined the proper structure for
the permitting process. The applicant discloses the nature of its efflu-
ent discharges to the permitting authority. The permitting authority
analyzes the environmental risk posed by the discharge, and places
limits on those pollutants that, in the words of the Second Circuit and
EPA, it "reasonably anticipates" could damage the environmental
integrity of the affected waterway. Id. at *11; Atlantic States Legal
Found., 12 F.3d at 358 (internal citations omitted). Thus, as long as
a permit holder complies with the CWA’s reporting and disclosure
requirements, it may discharge pollutants not expressly mentioned in
the permit. Ketchikan, 1998 WL 284964 at *11. The only other limi-
tation on the permit holder’s ability to discharge such pollutants is
that the discharges must be reasonably anticipated by, or within the
reasonable contemplation of, the permitting authority. Id. at *11.
Because the permitting scheme is dependent on the permitting author-
ity being able to judge whether the discharge of a particular pollutant
constitutes a significant threat to the environment, discharges not
within the reasonable contemplation of the permitting authority dur-
ing the permit application process, whether spills or otherwise, do not
come within the protection of the permit shield. We see the EPA’s
interpretation of the permit shield as a rational construction of the
CWA’s statutory ambiguity; as such, we deem it "reasonable" within
the meaning of a Chevron analysis. See Chemical Mfrs., 470 U.S. at
125. Therefore, because the CWA provision in question, § 1342(k),
is ambiguous, and because the EPA’s interpretation of this provision
                 PINEY RUN v. COMMRS OF CARROLL COUNTY                    19
is reasonable, we must defer under Chevron to the EPA’s interpreta-
tion of the scope of an NPDES permit.11

   Thus, the scope of the permit shield defense is relatively straight-
forward. An NPDES permit holder is shielded from CWA liability for
discharges in compliance with its permit, and is liable for any dis-
charges not in compliance with its permit. As the EPA has deter-
mined, however, compliance is a broader concept than merely
obeying the express restrictions set forth on the face of the NPDES
permit; all discharges adequately disclosed to the permitting authority
are within the scope of the permit’s protection. Having examined the
nature of liability under the CWA, we turn to whether, in this case,
the Plant’s discharge of heat during the period in question was in vio-
lation of its NPDES permit and the CWA.

                                     C.

                                     1.

   The Commissioners would be in violation of their NPDES permit
through the Plant’s discharge of heat if either: (1) the permit specifi-
cally barred such discharges; or (2) the Commissioners did not ade-
quately disclose them to the MDE. Section I of the Commissioners’
  11
    Prior to its Ketchikan decision, the EPA in 1994 published a policy
statement on the scope of the permit shield defense that mirrors its hold-
ing in Ketchikan. That statement provides in relevant part:
       A permit provides authorization and therefore a shield for the
       following pollutants resulting from facility processes, waste-
       streams and operations that have been clearly identified in the
       permit application process when discharged from specified out-
       falls:
       ...
          2) Pollutants for which the permit authority has not estab-
       lished limits or other permit conditions, but which are specifi-
       cally identified as present in facility discharges during the
       permit application process[.]
Policy Statement on Scope of Discharge Authorization and Shield Asso-
ciated with NPDES permits at 2-3 (July 1, 1994) (emphasis added).
20            PINEY RUN v. COMMRS OF CARROLL COUNTY
NPDES permit expressly limits the discharge of certain pollutants,
such as dissolved oxygen and fecal coliforms, but makes no mention
of heat. Under the permitting process previously explained, that
would indicate, assuming proper disclosure of its heat discharges, that
the Commissioners did not violate the CWA. A footnote to the list of
pollutants in the Commissioners’ NPDES permit provides, however,
that the "discharge of pollutants not shown shall be illegal." J.A.
1553. A plain application of this footnote, which is urged upon us by
the Association, is that it is illegal for the Plant to discharge any pol-
lutants not specifically listed in the permit at any level. Because heat
is not listed in the NPDES permit, imparting this meaning to the foot-
note provision would render illegal the discharge of heated effluent
by the Plant. The Commissioners, however, view the footnote as pro-
hibiting only those pollutants that were not disclosed to the MDE dur-
ing the permitting process. In other words, the Commissioners read
the footnote as providing, "the discharge of pollutants not shown [to
the MDE during the permitting process] shall be illegal."

   In analyzing a provision of an NPDES permit, we review the dis-
trict court’s interpretation in the same manner as we would contracts
or other legal documents. See Hendricks v. Central Reserve Life Ins.
Co., 39 F.3d 507, 512 (4th Cir. 1993) (applying rules of contract
interpretation to benefit plan provision in ERISA lawsuit); see also
Northwest Envt’l. Advocates v. Portland, 56 F.3d 979, 982 (9th Cir.
1995) (applying principles of contract interpretation to NPDES per-
mit). We review the district court’s application of contract principles
de novo, but review its findings of fact with respect to extrinsic mat-
ters for clear error. Hendricks, 39 F.3d at 512.

   A proper interpretation of the footnote requires that we first deter-
mine whether it is ambiguous; if "the language is plain and capable
of legal construction, the language alone must determine" the permit’s
meaning. FDIC v. Prince George Corp., 58 F.3d 1041, 1046 (4th Cir.
1995). If the footnote is ambiguous, however, then we must look to
extrinsic evidence to determine the correct understanding of the per-
mit. See Northwest Envt’l. Advocates, 56 F.3d at 983-984. Having
carefully examined the footnote, we conclude that it is ambiguous.
Although the footnote specifies that "the discharge of pollutants not
shown shall be illegal," it fails to indicate either to whom or where
the pollutants must be shown in order to fall within the NPDES per-
               PINEY RUN v. COMMRS OF CARROLL COUNTY                    21
mit’s protection. Both of the interpretations offered by the parties, i.e.,
(1) that the pollutants must be shown in the language of the permit,
and (2) that the pollutants must be shown during the permit applica-
tion process, are entirely reasonable readings of the footnote. Given
this ambiguity, we must turn to extrinsic evidence to determine the
intent of the permitting authority in drafting this footnote.

   Examining the footnote in the context of the entire NPDES permit
and the permitting process persuades us that the interpretation offered
by the Commissioners is the correct one. Indeed, another section of
the NPDES permit anticipates that the Plant will discharge new,
unlisted pollutants. Pursuant to Section II.A.1 of the permit, titled
"Change in Discharge":

     Any anticipated facility expansions, production increases, or
     process modifications which will result in new, different, or
     increased discharge of pollutants shall be reported by the
     permittee by submission of a new application at least 180
     days prior to the commencement of the changed discharge
     or, if such changes will not violate the effluent limitations
     specified in this permit, by notice to the Department.

J.A. 1561. This subsection of the NPDES permit indicates that the
MDE contemplated, in its issuance, that the Plant would in fact dis-
charge pollutants other than those expressly listed. To suggest, there-
fore, that the footnote constitutes a blanket ban on all pollutants not
listed in the NPDES permit is problematic. Indeed, the Second Cir-
cuit, in its Atlantic States Legal Foundation decision in 1993, inter-
preted a similar permit provision as inconsistent with a general
prohibition on the discharge of new pollutants. Atlantic States Legal
Found., 12 F.3d at 359.

   In fact, the structure laid out in the "Change in Discharge" provi-
sion reflects the permitting process as a whole. Because the focus of
that process is to ensure that the MDE possesses sufficient informa-
tion to calibrate discharge levels so that state water quality standards
are met, the NPDES permit mandates that the Plant inform the MDE
of future changes in what it discharges. This allows the MDE time to
calculate the effects of the change and, if necessary, to modify the
permit in order to maintain state water quality standards. If the permit
22            PINEY RUN v. COMMRS OF CARROLL COUNTY
holder is discharging less of a pollutant than originally disclosed,
however, the change in discharge poses no risk to the environmental
integrity of the system. Therefore, it is no surprise that the "Change
in Discharge" provision exempts such cases from the new application
process.

    Moreover, the logic of the Commissioners’ position is apparent
when the practical implications of interpreting the footnote as prohib-
iting the discharge of all pollutants not expressly listed, at any level,
are considered. The CWA defines pollutant as "dredged spoil, solid
waste, incinerator residue, sewage, garbage, sewage sludge, muni-
tions, chemical wastes, biological materials, radioactive materials,
heat, wrecked or discarded equipment, rock, sand, cellar dirt and
industrial, municipal, and agricultural waste discharged into water."
See 33 U.S.C. § 1362(6). This definition is extremely broad, covering
innumerable individual substances. See, e.g., Sierra Club, Lone Star
Chapter v. Cedar Point Oil Co., 73 F.3d 546, 566 (5th Cir. 1996)
("[T]he definition of "pollutant" is meant to leave out very little
. . . ."); Atlantic States Legal Found., 12 F.3d at 357 (noting that there
is "no principled reason why water itself, which is conceded to be a
chemical, would not be considered a ‘pollutant’ under . . . the Act").
Thus, if we were to adopt the interpretation urged by the Association,
the Plant would violate the terms of its NPDES permit (thereby giving
rise to monetary and injunctive relief under the CWA) if it discharges
an unlisted pollutant even at an infinitesimal amount.

   We are not persuaded that the MDE either intended or contem-
plated such consequences when it issued the Commissioners’ NPDES
permit. The provision at issue, an eight-word footnote in a twenty-one
page NPDES permit, deals with significantly less controversial topics
in great detail. For example, the permit contains a half-page descrip-
tion of the MDE’s and EPA’s rights of entry. Further, the record con-
tains no evidence that the MDE or any other party discussed this
footnote, its provisions, its possible ramifications, or its proper inter-
pretation during the permitting process. If the MDE had intended to
impose liability on the Commissioners for the discharge of a fully dis-
closed but unlisted pollutant at any level, we would expect to find an
extended discussion of the consequences of such a decision. Thus,
having reviewed and carefully considered the extrinsic evidence con-
cerning the MDE’s intent in granting the Commissioners their permit,
               PINEY RUN v. COMMRS OF CARROLL COUNTY                    23
we must conclude that the language of the permit itself contains no
bar to the Plant’s discharges of heat.12

                                    2.

   The final questions that we must address are whether the Commis-
sioners adequately disclosed the Plant’s discharges of heated effluent
to the MDE during and after the permit application process, and
whether the Plant’s discharges of heat were reasonably contemplated
by the MDE. If both of these conditions are satisfied, then the Com-
missioners are protected by the permit shield defense and they are not
liable under the CWA.

   The record clearly demonstrates that both of these conditions were
in fact met. The MDE and the Commissioners each testified that the
Commissioners informed the permitting authority that the Plant was
discharging heat during the permit application process. See J.A. 1213-
21, 1338-44. The record also contains a significant compilation of the
daily reports on water temperature and heat discharges provided by
the Commissioners to the MDE after the permit was issued in 1990;
in addition, there is testimony from the MDE and the Commissioners
that the Commissioners filed such reports as required by the permit-
ting authority. The evidence thus demonstrates that the Commission-
ers complied with permit and CWA disclosure requirements.
Furthermore, the testimony of the MDE and the Commissioners
shows that the MDE reasonably contemplated that the Plant would
discharge heat pursuant to its permit, and the temperature records
demonstrate that the Plant did not act outside that reasonable contem-
plation. Therefore, the Commissioners are entitled to the full protec-
tion of the permit shield, and they are not liable under the CWA.

  12
    Although adopting the Commissioners’ interpretation of the footnote
suggests that it simply represents the codification of the preexisting per-
mit shield defense, it is important to recognize that the permit was issued
in 1990, eight years before the EPA’s decision in Ketchikan. When the
permit was issued the scope of the permit shield defense was not clear,
and therefore an effort by the MDE to shield all properly disclosed pollu-
tants from CWA liability was not redundant.
24           PINEY RUN v. COMMRS OF CARROLL COUNTY
                                IV.

  For the foregoing reasons, the judgment of the district court must
be vacated, and we remand for the entry of judgment in favor of the
Commissioners.

                                      VACATED AND REMANDED
