ENVIRONMENTAL PROTECTION AGENCY, PETITIONER V. STATE OF OKLAHOMA,
ET AL.

   STATE OF ARKANSAS, ET AL., PETITIONER V. STATE OF OKLAHOMA, ET AL.

   No. 90-1266, No. 90-1262

   In The Supreme Court Of The United States

   October Term, 1990

   On Writs Of Certiorari To The United States Court Of Appeals For
The Tenth Circuit

   Brief For The Environmental Protection Agency

                      PARTIES TO THE PROCEEDINGS

   The parties to the proceedings in the court of appeals, in addition
to the United States Environmental Protection Agency, were the State
of Arkansas, The Arkansas Department of Pollution Control and Ecology,
The City of Fayetteville, Arkansas, the Beaver Water District, the
State of Oklahoma, the Oklahoma Scenic Rivers Commission, The Oklahoma
Pollution Control Coordinating Board, Save the Illinois River (STIR),
and the Oklahoma Wildlife Federation.

            TABLE OF CONTENTS
   Questions Presented
   Parties To The Proceedings
   Opinion below
   Jurisdiction
   Statutory and regulatory provisions involved
   Statement
   Summary of argument
   Argument:
      I. Federal law governs the interpretation and
         application of federally approved state water
         quality standards to out-of-state discharges
         A. This Court's decisions establish that interstate
            water pollution issues are to be resolved
            by application of federal law
         B. The Clean Water Act assigns to EPA the
            responsibility for resolution of disputes
            between states over the discharge of
            pollutants into interstate waters
         C. EPA's interpretation of the federally-approved
            Oklahoma standards is entitled
            to judicial deference
     II. There was no appropriate basis for rejecting
         EPA's interpretation and application of the
         Oklahoma standards
         A. EPA reasonably construed the state antidegradation
            provision to allow an out-of-state
            discharge where that discharge
            would have no detectable impact on the
            current water quality of the protected
            waters
         B. The court of appeals' policy choices are
            not required by the Clean Water Act or
            applicable regulations
    III. The court of appeals should have considered
         whether the record supported issuance of the
         permit under the interpretation of the
         Oklahoma standard adopted by EPA
   Conclusion

                             OPINION BELOW

   The opinion of the court of appeals (Pet. App. 1a-97a) /1/ is
reported at 908 F.2d 595.

                             JURISDICTION

   The judgment of the court of appeals was entered on July 11, 1990.
Petitions for rehearing were denied on October 11, 1990 (Pet. App.
98a-99a).  On December 29, 1990, Justice White extended the time for
filing a petition for a writ of certiorari to and including February
8, 1991.  The petitions were filed on that date, and granted on April
1, 1991.  The jurisdiction of this Court rests on 28 U.S.C. 1254(1).

             STATUTORY AND REGULATORY PROVISIONS INVOLVED

   The relevant provisions of the Clean Water Act, 33 U.S.C. 1251 et
seq., are reproduced at Pet. App. 100a-106a.  The relevant provisions
of the Oklahoma Water Quality Standards are reproduced at Pet. App.
96a-97a.

                          QUESTIONS PRESENTED

   1. Whether determination of the appropriate standards governing the
issuance of permits under the Clean Water Act for discharges into
interstate waters involves a question of federal law, requiring a
reviewing court to uphold the validity of the Environmental Protection
Agency's permitting action if that action was based upon a reasonable
interpretation and application of the federally approved water quality
standards of the receiving State.

   2. Whether the Environmental Protection Agency reasonably concluded
that the contemplated discharge would comply with the applicable water
quality standards because it would have no detectable impact on
current water quality within the receiving State.

   3. Whether the court exceeded the proper scope of judicial review.

                               STATEMENT

   1. The Clean Water Act, 33 U.S.C. 1251 et seq., is a comprehensive
statute designed "to restore and maintain the chemical, physical, and
biological integrity of the Nation's waters" through reduction and
eventual elimination of the discharge of pollutants into those waters.
 Section 101(a), 33 U.S.C. 1251(a).  The Act anticipates a partnership
between the federal government and the States to achieve this
fundamental goal.  The Administrator of the Environmental Protection
Agency (EPA) is, with certain explicit exceptions not relevant here,
responsible for administering the Act.  Section 101(d), 33 U.S.C.
1251(d).  A major responsibility of the Administrator under the Act is
the development and promulgation of uniform national technology-based
standards, known as "effluent limitations guidelines," for categories
and classes of discharges.  Sections 301 and 304, 33 U.S.C. 1311 and
1314.  E.I. duPont de Nemours & Co. v. Train, 430 U.S. 112, 126-136
(1977).  An "effluent limitation" is "a() restriction * * * on
quantities, rates, and concentrations of chemical, physical,
biological, and other constituents which are discharged from point
sources." Section 502(11), 33 U.S.C. 1362(11).  /2/

   A second major source of authority for reducing pollution is found
in Section 303, which directs States, with federal approval and
oversight, to institute a range of comprehensive requirements,
potentially more stringent than the federally imposed limitations, to
assure protection of the quality of all state waters.  Section 303(a),
(b), and (c)(1), 33 U.S.C. 1313(a), (b), and (c)(1).  These water
quality standards are not technology-based standards;  instead, they
are based on the desired uses and condition of the particular waterway
involved.  Congress utilized water quality standards "as a
supplementary basis * * * so that numerous point sources, despite
individual compliance with effluent limitations, may be further
regulated to prevent water quality from falling below acceptable
levels." EPA v. California ex rel. State Water Resources Control Bd.,
426 U.S. 200, 205 n.12 (1976).  Section 303(c)(2), 33 U.S.C.
1313(c)(2).  A water quality standard is a method of expressing the
desired condition of a waterway.  Water quality standards under the
Act generally consist of three elements:  (1) one or more designated
"uses" of that waterway (e.g., public water supply, recreation,
propagation of fish, or agriculture) consistent with the goals of the
Act as set forth in Section 101;  (2) "criteria" specifying the amount
of various pollutants that may be present in those waters and still
protect the designated uses, expressed in numerical concentration
limits or narrative form;  and (3) a provision restricting the
degradation of certain waters, i.e., an antidegradation policy.
Section 303(c)(2), 33 U.S.C. 1313(c)(2);  Section 303(d)(4)(B), 33
U.S.C. 1313(d)(4)(B);  40 C.F.R. Pt. 131, Subpt. B.  The States must
submit their water quality standards to EPA for review and approval.
Upon approval by EPA, a state-adopted water quality standard "shall
thereafter be the water quality standard for the applicable water of
that State." Section 303(c)(3), 33 U.S.C. 1313(c)(3).

   The primary means for achieving and enforcing effluent limitations
guidelines and state water quality requirements is the "national
pollutant discharge elimination system" (NPDES) permit program under
Section 402 of the Act, 33 U.S.C. 1342.  State Water Resources Control
Bd., 426 U.S. at 205.  The Act prohibits the discharge of any
pollutant /3/ into the waters of the United States except when
authorized by an NPDES permit or a Section 404 permit.  /4/ Section
301(a), 33 U.S.C. 1311(a).  Thus, an NPDES permit (which may include a
timetable for compliance) transforms generally applicable effluent
limitations guidelines and state water quality standards into
obligations of the individual discharger.  See 40 C.F.R. 122.44(d)(1).

   The Act provides that EPA will issue NPDES permits except in those
States where EPA has approved a state permit program pursuant to
Section 402(b), 33 U.S.C. 1342(b).  /5/ Even in those States with
approved permit programs, the State must submit to EPA a copy of each
proposed permit involving an interstate waterway before it may be
issued.  Section 402(d)(1) and (2), 33 U.S.C. 1342(d)(1) and (2);  40
C.F.R. 123.24(d).  EPA may object to issuance of an NPDES permit if it
determines that issuance would be "outside the guidelines and
requirements" of the Act.  Section 402(d)(2)(B), 33 U.S.C.
1342(d)(2)(B).  On receipt of an objection, the State may submit an
appropriately revised permit;  if it fails to do so, EPA will issue a
permit "in accordance with the guidelines and requirements" of the
Act.  Section 402(d)(4), 33 U.S.C. 1342(d)(4).

   The Clean Water Act also establishes mechanisms for resolving
interstate water pollution questions, i.e., situations where a
discharge in one State may affect the waters of another State.
Specifically, the statutory conditions for EPA approval of state
permit programs require each program to contain specified provisions
for dealing with such situations.  The source, or permit-issuing,
State must have procedures for notifying other States, "the waters of
which may be affected," of a permit application contemplating such
discharges.  Section 402(b)(3), 33 U.S.C. 1342(b)(3).  Each
potentially affected State must then be afforded an opportunity to
"submit written recommendations to the permitting State" and to EPA
regarding the application.  Section 402(b)(5), 33 U.S.C. 1342(b)(5).
If any part of those recommendations is not accepted by the permitting
State, that State must notify the affected State and EPA.  Section
402(b)(5), 33 U.S.C. 1342(b)(5).  EPA then has the right to object to
issuance of the permit, as provided in Section 402(d)(2)(A), 33 U.S.C.
1342(d)(2)(A).

   Where EPA itself retains permit-issuing authority, the statutory
procedures for resolution of interstate disputes are contained in the
provisions governing the issuance of federal licenses and permits that
may affect water quality.  Thus, Section 401(a), 33 U.S.C. 1341(a),
requires applicants for federal licenses or permits for activities
that may result in discharges to navigable waters to provide a
certification from the source State that the proposed discharge will
comply, inter alia, with applicable water quality standards.  If the
source State denies such a certification, no permit may be issued.
Section 401(a), 33 U.S.C. 1341(a).  Whenever EPA (or any other federal
permitting authority) determines that a discharge might affect water
quality in another State, it must notify that State.  Section
401(a)(2), 33 U.S.C. 1341(a)(2).  If the notified State determines
that the discharge will violate its water quality requirements, the
federal permitting authority must (if the State requests) hold a
hearing to consider the State's objections and EPA's recommendations,
and "condition such * * * permit in such manner as may be necessary to
insure compliance with applicable water quality requirements." Section
401(a), 33 U.S.C. 1341(a)(2).  /6/

   2. This case involves an interstate dispute concerning the waters
of the Illinois River, which originates in the State of Arkansas and
flows into the State of Oklahoma.  /7/ In the early 1980's the City of
Fayetteville, Arkansas, operated a sewage treatment plant that
discharged all of its wastewater into the White River (which is not a
tributary of the Illinois River).  /8/ The White River was unable to
assimilate that waste without violating Arkansas' water quality
standards.  To alleviate this situation, Fayetteville constructed a
new wastewater treatment plant, with federal financial assistance
provided by EPA under the Clean Water Act.  The plant was designed so
that its discharges into the White River would not cause a violation
of Arkansas water quality standards:  discharged pollutants were to be
greatly reduced, and half of the treated effluent was to be discharged
into a tributary of the Illinois River.  Pet. App. 2a, 5a.  /9/

   In 1985, Fayetteville applied to EPA for an NPDES permit for its
new treatment plant.  Following public notice and an informal public
hearing (see 40 C.F.R. Pt. 124), EPA issued an NPDES permit to
Fayetteville on November 5, 1985, to become effective on December 10,
1985.  The permit authorized split flow into both the White River and
the Illinois River tributary;  it contained stringent limits with
respect to oxygen demand, total suspended solids, and phosphorus.  It
also prohibited discharge of inadequately treated sewage, so that if
the plant malfunctioned, wastewater would have to be stored and
retreated.  Finally, a reopener provision in the permit specified that
if an ongoing study of water quality in the Illinois River showed a
need for more stringent limitations on Fayetteville's discharge to
ensure compliance with Oklahoma water quality standards, the permit
would be modified accordingly.  Pet. App. 5a-6a.

   Both Oklahoma and Arkansas requested an evidentiary hearing before
EPA on its issuance of the NPDES permit.  The sole issue addressed in
the evidentiary hearing was whether the Fayetteville discharge into
the tributary of the Illinois River would cause a violation of the
Oklahoma water quality standards (Oklahoma standards).  Ark. Pet. App.
98a.  The evidence at the hearing consisted largely of expert
testimony discussing various mathematical models designed to predict
the impact of the proposed flow on the waters of the Illinois River in
Oklahoma.  Id. at 99a.  Reliance on this type of evidence was
necessary not only because no actual effluent measurements were
available (since the Fayetteville plant was not yet in operation), but
also because the effluent was to be discharged at the Fayetteville
plant, 39 miles upstream from the Oklahoma state line.  It was
therefore necessary to predict the changes the effluent would undergo
while it was still in Arkansas -- e.g., changes resulting from the
assimilation of nutrients by biota in the river, and from
reoxygenation through aeration and turbulence.  See Ark. Pet. App.
99a, 129a, 139a.

   The relevant Oklahoma standards include numeric dissolved oxygen
requirements, limitations on the concentrations of nutrients
(phosphorous and nitrogen/phosphorous concentration ratio), and
numeric limitations on inorganic elements and organic chemicals.  Ark.
Pet. App. 127a, 136a-137a, 140a-142a.  In addition, the Oklahoma
standards include beneficial use and antidegradation provisions.  The
beneficial use provision prohibits "any new point source discharge of
wastes (into protected rivers) * * * except under conditions described
in Section 3." Oklahoma standard Section 5, Pet. App. 96a.  Section 3,
Oklahoma's antidegradation provision, in turn provides that "(n)o
further water quality degradation which would interfere with or become
injurious to existing instream water uses shall be allowed." Pet. App.
96a.  Recognizing that certain high quality waters currently exceed
their beneficial use standards, Section 3 also provides that "(n)o
degradation shall be allowed in high quality waters." Id. at 97a.
High quality waters include designated state scenic rivers such as the
Illinois River above the Tenkiller Reservoir.

   The EPA's Administrative Law Judge upheld the permit, finding that
the discharge into the Illinois River would not violate the Oklahoma
standards, including the state antidegradation provision, because the
discharge would not have an "undue impact" on Illinois River water
quality in Oklahoma.  Ark. Pet. App. 95a-107a.  On Oklahoma's appeal,
EPA's Chief Judicial Officer (acting pursuant to a delegation of
authority under 40 C.F.R. 124.72(b), see Ark. Pet. App. 145a n.4)
found that the ALJ had applied the wrong standard:  while compliance
with the Oklahoma standards was required, such compliance was to be
judged by whether there would be a "detectable" or "measurable"
violation of water quality standards at the boundary.  Id. at
115a-121a.

   On remand, the ALJ ruled that the proposed discharge would have no
"detectable" impact on the Oklahoma portion of the Illinois River and
thus upheld the permit.  Ark. Pet. App. 122a-144a.  Specifically, the
ALJ found that the phosphorous added to the Illinois River by the
Fayetteville discharge would largely be assimilated before the river
reached the Oklahoma border (id. at 129a).  /10/ Because this small
increase in phosphorous would not result in an increase in
eutrophication of waters in Oklahoma (ibid.), /11/ the ALJ ruled that
the Fayetteville discharge would not cause a violation of the Oklahoma
standards for nutrients.  Ark. Pet. App. 132a.  The ALJ also found
that the Fayetteville effluent would achieve complete oxygen recovery
before the river reached the Oklahoma border;  therefore there was no
violation of the Oklahoma standards for dissolved oxygen.  Id. at
140a.  Finally, the ALJ found that there would be no discernible
violation of aesthetic standards (id. at 134a) or of the numeric
criteria as to metals or organic chemicals.  Id. at 143a.  In sum, the
ALJ concluded that the proposed discharge would not cause a violation
of any of the Oklahoma water quality standards.

   Oklahoma filed an administrative appeal, and, in an order issued on
December 22, 1988, the Chief Judicial Officer declined further review.
 Ark. Pet. App. 145a-153a.  In that order, the Chief Judicial Officer
again stated that the governing interpretation of the antidegradation
provision is that "(f)or a (water) quality degradation to exist, there
must be a degradation caused by a change in some water quality
parameter such as nutrients, metals, dissolved oxygen, etc.  In his
Decision on Remand, the ALJ concluded that the Fayetteville discharge
would not cause a detect(a)ble change in any of these parameters." Id.
at 152a.  The Chief Judicial Officer upheld that conclusion (id. at
153a), and thus the permit went into effect.  Operations pursuant
thereto commenced on January 21, 1989.  /12/

   3. Three petitions for review were filed in early 1989.  The
Arkansas petition challenged EPA's authority to require that an
Arkansas discharger comply with Oklahoma water quality standards.
Petitions by the Oklahoma parties and by an environmental group, Save
The Illinois River (STIR), alleged violations of Oklahoma water
quality standards resulting from EPA's grant of the NPDES permit.
Arkansas' petition for review, which was initially filed in the Eighth
Circuit, was transferred to the Tenth Circuit and consolidated with
those of the Oklahoma parties and STIR.

   On July 11, 1990, the Tenth Circuit issued its opinion in this
matter.  Pet. App. 1a-97a.  Rejecting Arkansas' challenge, the court
first determined that EPA had properly interpreted the Act to require
it to consider, in the NPDES permit procedure, whether a proposed
discharge would violate the federally approved water quality standards
of a downstream State.  Id. at 14a-48a.  The court proceeded, however,
to reverse EPA's decision to issue the permit.  The court rejected
EPA's conclusion that the antidegradation provisions of the Oklahoma
water quality standards are satisfied so long as the Fayetteville
discharge does not result in any detectable change to any water
quality parameter at the Oklahoma state line.  Finding that EPA
"incorrectly construed and applied (the) Oklahoma regulations" (id. at
60a, 83a-84a), the court adopted a novel interpretation of the
antidegradation provisions of the Oklahoma standards not advanced by
any party.  Id. at 48a.  The court's approach was this:  In light of
its view of the federal policies embodied in the Clean Water Act and
EPA regulations, /13/ the court read the Oklahoma antidegradation
provisions as prohibiting any further release of pollutants that will
reach an "already degraded" river.  /14/ The court summarized its view
of the relevant provisions (id. at 90a-91a):

      (I)f a body of water is experiencing (water quality standard)
      violations and a proposed new source would discharge the same
      pollutants to which those standards apply, that source may not
      be permitted if its effluent will reach the degraded waters.

   Analyzing the record before EPA, the court concluded that there was
"ample evidence from which the ALJ could have concluded" (Pet. App.
63a) that the Illinois River in Oklahoma was already degraded (id. at
62a-73a), /15/ and that pollutants from the Fayetteville discharge
would reach the Oklahoma boundary (id. at 73a-76a) and would
contribute to the existing degradation of the river at that point (id.
at 76a-82a).  /16/ The court expressly "reject(ed) any notion that
once water quality standards have been violated (i.e., the quality of
the receiving waters has been degraded), the incremental impact of a
proposed additional discharge must itself be detectable." Id. at 90a.
Instead, the court was of the view that it was necessary to deny the
permit because "(a)t worst, (permitting the proposed discharges) will
increase the frequency and severity of ongoing violations;  at best,
it will thwart efforts to bring the river back into compliance with
the applicable standards." Id. at 91a.

   In sum, the court concluded that "EPA's failure to exercise its
authority to deny the Fayetteville permit is arbitrary and capricious
or otherwise not in accordance with law." Id. at 94a.  The court
flatly held that Fayetteville discharges "may not be permitted" (id.
at 61a) and that, accordingly, "the Fayetteville permit may not
issue." Id. at 83a n.49.  Instead of remanding to EPA for
reconsideration of the permit decision under the judicially prescribed
standards, the court of appeals simply "reverse(d) EPA's decision
authorizing Fayetteville's municipal treatment plant to discharge a
portion of its effluent to the Illinois River basin." Id. at 95a.
/17/

                          SUMMARY OF ARGUMENT

   Federal -- not state -- law governs the complex issues raised in
disputes involving interstate water pollution.  In the Clean Water
Act, Congress has entrusted to EPA the primary responsibility for
resolving such federal issues that arise in the context of its
consideration of applications for NPDES permits.  Before issuing a
permit authorizing discharges into an interstate waterway, EPA must
determine that the proposed permit will meet all applicable
requirements of the Act and implementing regulations, including
compliance with federally approved water quality standards of the
receiving State.  But in any interstate dispute involving the
application of a receiving State's water quality standards, the
statutory scheme provides that EPA -- not the receiving State -- is to
determine the proper application of the standards.  Accordingly, the
validity of EPA's decision to issue the Fayetteville permit depends on
whether the Agency reasonably interpreted and applied applicable
Oklahoma water quality standards, not on whether issuance of the
permit is consistent with the reviewing court's own interpretation of
those standards as a question of the law of the receiving State
simpliciter.

   In this case, EPA reasonably concluded that the Oklahoma
antidegradation standard permits a discharge that will have no
detectable impact on the current condition of Oklahoma's protected
waters.  The court of appeals, however, preferred a policy that would
prohibit any discharge that would theoretically reach waters that were
already degraded.  Under well-established principles of administrative
law, this preference was an impermissible basis for rejecting EPA's
contrary interpretation.  To make matters worse, the court's
interpretation would create serious practical difficulties in
implementing water quality requirements for interstate waterways.  The
court of appeals' error was compounded by the fact that the court
based its decision on issues not raised or briefed by the parties;
engaged in independent fact-finding that disregarded the scientific
expertise of the Agency;  and declined to remand the permit decision
to the Agency.  In short, the court of appeals not only ignored the
special role given EPA under the Clean Water Act but transgressed
basic principles of administrative law which require reviewing courts
to give appropriate deference to the administrative process.

                               ARGUMENT

   I. FEDERAL LAW GOVERNS THE INTERPRETATION AND APPLICATION OF
FEDERALLY APPROVED STATE WATER QUALITY STANDARDS TO OUT-OF-STATE
DISCHARGES

   The court of appeals fundamentally misconstrued the teachings of
the Court and the effect of the Clean Water Act in the context of an
interstate dispute.  Instead of interpreting the requirements of the
Clean Water Act in this context as a matter of federal law, the court
of appeals treated the question of how the Oklahoma water quality
standards (specifically, the beneficial use and antidegradation
provisions) should be interpreted in this case as entirely a question
of state law.  /18/ It then undertook to construe the provisions on
its own without first examining the reasonableness of EPA's
interpretation of the federally-approved standard.  Pet. App. at
53a-54a.

   A. This Court's Decisions Establish That Interstate Water Pollution
Issues Are To Be Resolved By Application Of Federal Law

   This Court's decisions make clear that when interstate water
pollution issues are involved, the interpretation of the Clean Water
Act's requirements is a matter of federal, not state, law.  See
Illinois v. City of Milwaukee, 406 U.S. 91, 102 (1972) (Milwaukee I);
International Paper Co. v. Ouellette, 479 U.S. 481, 492 (1987).
Furthermore, the Court has recognized that the 1972 Amendments to the
Federal Water Pollution Control Act (now the Clean Water Act)
"establish an all-encompassing program of water pollution regulation"
(City of Milwaukee v. Illinois, 451 U.S. 304, 318 (1981) (Milwaukee
II)), under which "(f)ederal courts lack authority to impose more
stringent effluent limitations * * * than those imposed by the agency
charged by Congress with administering this comprehensive scheme"
under the guise of applying federal common law.  Id. at 320.  /19/ And
in Ouellette, the Court specifically concluded that "the CWA precludes
a court from applying the (common) law of an affected State against an
out-of-state source." 479 U.S. at 494.  Instead, "the Act limits the
right to administer the permit system to the EPA and the source
States." Id. at 495.  It follows from this Court's precedents that the
question of the proper standards to be applied to the Fayetteville
discharges under the Clean Water Act ultimately involves a question of
federal law.

   B. The Clean Water Act Assigns To EPA The Responsibility For
Resolution Of Disputes Between States Over The Discharge Of Pollutants
Into Interstate Waters

   The Clean Water Act directs EPA to address interstate water
pollution issues in either of two ways, depending upon whether the
source State or EPA is the permit-issuing authority.  If the source
State's program has been approved by EPA under Section 402(b), 33
U.S.C. 1342(b), the State may issue the permit, unless EPA objects
pursuant to Section 402(d)(2), 33 U.S.C. 1342(d)(2).  /20/ Where, as
here, EPA is the permit-issuing authority, EPA is directly responsible
for determining whether a proposed permit will meet all applicable
requirements of the Act and implementing regulations (Section 402(a)).
 Although the federal permitting authority may not issue a permit if
the source State determines that the permit will not comply with its
water quality standards, the federal permitting authority need only
consider the "recommendations" of a receiving State in determining
whether the permit will comply with that State's standards.  Section
401(a)(1) and (2), 33 U.S.C. 1341(a)(1) and (2).  As this Court
explained in Ouellette, 479 U.S. at 491, "the Act makes it clear that
affected States occupy a subordinate position to source States in the
federal regulatory program." Thus, the text of the Clean Water Act
commits the determination of whether the permit will achieve
compliance with the receiving State's water quality standards to the
federal permitting agency:  /21/

      Such agency * * * shall condition such license or permit in such
      manner as may be necessary to insure compliance with applicable
      water quality requirements.

33 U.S.C. 1341(a)(2).  In determining compliance, the agency
necessarily has to make decisions concerning the proper interpretation
of the receiving State's water quality standards and how those
standards apply to an out-of-state discharger.  /22/

   As a result, in any interstate dispute involving the application of
a downstream State's water quality standards, the statutory scheme
provides that EPA -- not the downstream State -- is to determine the
proper application of the standards, either in reviewing the permits
for possible objection under Section 402(d) or in its role as permit
issuer.  This federal responsibility complements EPA's responsibility
under the Act to review and approve proposed state water quality
standards.  Section 303(c), 33 U.S.C. 1313(c).  Before granting
approval, EPA must determine that the proposed standard "meets the
requirements" of the Act.  Section 303(c)(3), 33 U.S.C. 1313(c)(3).
/23/ In determining whether a proposed standard meets the statutory
requirements, it is, of course, necessary for EPA to determine the
meaning of that standard.  Therefore, if a dispute concerning the
meaning of the standard subsequently arises in the context of a
permitting decision, /24/ EPA's interpretation of the disputed
provision, which presumably reflects its understanding of that
provision when approval was granted, should normally be dispositive.
/25/

   C. EPA's Interpretation Of The Federally-Approved Oklahoma
Standards Is Entitled To Judicial Deference

   In light of the key role assigned by the Clean Water Act to EPA as
arbiter of interstate water pollution disputes under the Act and EPA's
responsibility for approving state-submitted water quality standards,
EPA's interpretation of the water quality standards involved in this
case should, under established principles of administrative law, be
accorded deference.  It is beyond dispute that a reviewing court
should defer to an agency's reasonable interpretation of a regulation
it is charged with administering.  Ford Motor Credit Co. v. Milhollin,
444 U.S. 555, 566 (1980);  United States v. Larionoff, 431 U.S. 864,
872-873 (1977);  Udall v. Tallman, 380 U.S. 1, 16-17 (1965);  Navistar
Int'l Transp. Corp. v. EPA, 858 F.2d 282, 288 (6th Cir. 1988), cert.
denied, 490 U.S. 1039 (1989) (EPA's interpretation of a federally
approved state air quality standard is accorded the same deference by
a reviewing court as EPA's interpretation of its own regulations).
Cf. Chevron U.S.A. Inc. v. NRDC, Inc., 467 U.S. 837, 844 (1984).
Accordingly, to the extent that the terms of a federally approved
state standard are ambiguous or silent on a particular point at issue
in an interstate dispute, EPA's interpretation of the standard should
be followed "unless it is plainly erroneous or inconsistent with the
regulation." United States v. Larionoff, 431 U.S. at 872 (quoting
Bowles v. Seminole Rock & Sand Co., 325 U.S. 410, 414 (1945)).

   In short, the question is not whether EPA interpreted the water
quality standards applicable to the Oklahoma portion of the Illinois
River in the same way they would be interpreted by the reviewing court
or even by Oklahoma itself (see, e.g., Pet. App. 60a).  Instead, the
question, in reviewing the validity of EPA's administrative action, is
whether EPA's reading and application of those standards in the
permitting proceeding was reasonable.

   The court of appeals failed to address this issue.  Instead, it
candidly admitted that it was substituting its own interpretation for
that of EPA (Pet. App. 48a-49a, 54a-55a), adopted a restrictive
construction of the applicable standards not advanced by any party
(id. at 48a), and rejected EPA's construction out of hand.  Id. at
53a-57a.  /26/

   II. THERE WAS NO APPROPRIATE BASIS FOR REJECTING EPA'S
INTERPRETATION AND APPLICATION OF THE OKLAHOMA STANDARDS

   Before issuing the permit to Fayetteville to discharge effluent
into a tributary of the Illinois River, EPA as the permitting agency
had to determine whether the permit conditions would assure compliance
with the Oklahoma Water Quality Standards applicable to that river in
Oklahoma.  In particular, EPA had to interpret Oklahoma standard
Section 3, which provides that "(n)o degradation shall be allowed in
high quality waters," including the portion of the Illinois River
between the Oklahoma boundary and Tenkiller Reservoir.  EPA concluded
that Oklahoma standard Section 3 permits a discharge upstream from
protected waters so long as that discharge will have no detectable
impact on current water quality in the protected waters.  The court of
appeals rejected both the "no-detectable impact" and the "current
condition" aspects of EPA's interpretation of Oklahoma standard
Section 3 as inconsistent with its plain meaning (Pet. App. 53a).  The
court ruled that the antidegradation requirement prohibited the
issuance of any permit for a new discharge in Arkansas -- whether or
not that discharge would have any detectable impact on water quality
parameters in Oklahoma -- if the water quality in the waterway in
Oklahoma has been degraded compared to an historical benchmark (here,
1970, when the River was designated a "scenic river").  Id. at 62a,
90a.  In so concluding, the court improperly rejected EPA's reasonable
interpretation of the federally approved antidegradation standard.

   A. EPA Reasonably Construed The State Antidegradation Provision To
Allow An Out-Of-State Discharge Where That Discharge Would Have No
Detectable Impact On The Current Water Quality Of The Protected Waters

   In its operative provisions, Oklahoma Water Quality Standard
Section 3, which was adopted in 1982 (Pet. App. 50a n. 29), is a
verbatim replication of the federal antidegradation standard that was
then in effect.  /27/ Accordingly, in considering the Fayetteville
NPDES permit application, EPA interpreted the Oklahoma standard as
identical to the federal one.

   While a similar antidegradation standard may be adopted by any
State, /28/ there has been no national rulemaking or determination on
how to interpret and apply the terms of the standard.  /29/ Questions
can therefore arise as to what constitutes a "degradation" of water
quality, and as to the benchmark from which degradation is to be
measured.

   1. There is general agreement that the "no degradation of water
quality" requirement means that a new discharge should not result in a
lowering of water quality in an ONRW, /30/ but EPA has not attempted
to prescribe general standards for determining what constitutes a
"lowering" of water quality.  Instead, the individual decisionmaker,
i.e., the State or EPA, must determine on a case-by-case basis whether
addition of pollutants to a water body will result in a lowering of
water quality.  /31/

   In this interstate case, EPA's determination of what constitutes
degradation, or a lowering of water quality, was set forth in the
Chief Judicial Officer's initial decision of June 28, 1988 (Ark. Pet.
App. 117a):

      (A) mere theoretical impairment of Oklahoma's water quality
      standards -- i.e., an infinitesimal impairment predicted through
      modeling but not expected to be actually detectable or
      measurable -- should not by itself block the issuance of the
      permit.  In this case, the permit should be upheld if the record
      shows by a preponderance of the evidence that the authorized
      discharges would not cause an actual detectable violation of
      Oklahoma's water quality standards.

   The Chief Judicial Officer's order of December 22, 1988, clarified
the application of this interpretation to the State's antidegradation
policy.  The CJO explained that because the antidegradation policy for
waters subject to the highest degree of protection is in fact a
"policy," not a numeric standard, it would be violated if there were
any water quality degradation in such waters.  But "(f)or a quality
degradation to exist, there must be a degradation caused by a change
in some water quality parameter such as nutrients, metals, dissolved
oxygen, etc." Ark. Pet. App. 152a.  In other words, if a discharge
"will not cause a detect(a)ble change in any of the relevant water
quality parameters, it logically follows that there will not be a
'quality degradation.'" Id. at 152a-153a.  Thus, EPA interpreted the
antidegradation policy as permitting a discharge upstream from
protected waters so long as that discharge will have no detectable
impact on water quality parameters in the protected waters.  /32/

   This interpretation of the antidegradation provision was entirely
reasonable and consistent with the language of the Oklahoma standard,
the federal regulation on which it was based, and the policies and
purposes of the Clean Water Act.  At least where the effects of a
discharge are undetectable at the State boundary, the receiving State
can have little more than a theoretical basis for concluding that its
water has been degraded.  In such circumstances, it is at least
reasonable for EPA to conclude that the discharge is not prohibited.

   2. Determining whether a new discharge will degrade downstream
water quality requires identification of the water quality level to be
protected.  The parties to this case, and the EPA decisionmakers,
considered the relevant water quality to be that in existence at the
Oklahoma border at the time the permit was under consideration.
Again, this was a reasonable interpretation and application of the
antidegradation provisions of Oklahoma standard Section 3.  That
provision states only that "(n)o degradation shall be allowed in high
quality waters";  it does not provide a description of the water
quality to be maintained.  Nothing in the Oklahoma standards provides
a general benchmark date, nor is there in the standards any suggestion
that there is a particular benchmark date for the Illinois River.  In
these circumstances, EPA's reliance on current water quality at the
boundary as the applicable benchmark was entirely reasonable.  /33/

   The court found that the "plain language" of the Oklahoma
beneficial use and antidegradation provisions showed that they
prohibit discharges of pollutants into a scenic river if "its water
quality has been degraded or if the new source would degrade it." Pet.
App. 53a-54a.  But the court did not identify the specific regulatory
language upon which it relied, and in fact no language in the Oklahoma
standards indicates an intent to consider whether water quality "has
been degraded" from the standard it had at some point in the past.

   B. The Court of Appeals' Policy Choices Are Not Required By The
Clean Water Act or Applicable Regulations

   The court of appeals' reading of the EPA-approved state
antidegradation provision was based primarily on two conclusions:  (1)
that "degradation" must be measured from some historic benchmark date,
undefined in the provision itself, rather than from the current
condition of the waterway, and (2) that if current water quality is
adjudged poorer than it was at that prior time, no further upstream
discharges may be permitted.  Taken together, these conclusions
establish a "zero-discharge" requirement once the waters in question
fall below the historic benchmark.  /34/ Moreover, that requirement
extends beyond a receiving State's borders to preclude any discharges
in all upstream tributaries of the interstate waterway.  But the
conclusions reflected in the zero-discharge requirement represent
policy choices not required by the Clean Water Act, EPA's regulations,
or the federally approved Oklahoma standards.  The court's adoption of
those conclusions certainly does not suggest that EPA's decision in
this case, which reflected alternative permissible policy choices, was
in any way unreasonable.  /35/ Thus, the court had no authority to
impose a zero-discharge requirement.  /36/

   The practical difficulties occasioned by such judicial intrusion
into EPA's responsibilities are vividly illustrated by this case.  The
ruling of the court of appeals -- that no discharge may be permitted
upstream if the pollutants in the effluent would reach a degraded
downstream waterway -- would create serious problems of
implementation.  /37/ It may be nigh unto impossible to demonstrate
that pollutants in an upstream discharge will never reach a point
downstream.  While modelling or other available predictive techniques
may persuasively demonstrate that pollutants are unlikely to survive
in the water system, so that only a de minimis amount would reach
protected waters, it may be statistically impossible to show that no
amount of pollutant will ever pass into those waters.  The court's
zero-discharge standard does not consider whether there is an
exception for de minimis amounts of pollutants.  /38/ If there is to
be such an exception, it must be defined;  under the court's ruling,
the standard must be somewhere below the level of detectability, which
poses obvious problems for enforcement.  If there is to be no
exception for de minimis amounts of pollutants, then the consequences
of a state designation of high quality waters to be subject to the
suggested federal antidegradation policy are substantially different
from those anticipated by EPA (and, most likely, the States that have
adopted EPA's model standards).

   More generally, the Agency's responsibility for approving state
standards would be gravely undermined if its reasonable
interpretations of those standards could be jettisoned on judicial
review.  This is of fundamental practical importance, because EPA's
ability to perform effectively its statutory role in resolving
interstate disputes over the issuance of NPDES permits requires the
Agency to rely on its own reasonable construction of a state standard.
 Indeed, if reviewing courts may substitute their own interpretations
of an EPA-approved state standard, then similarly worded standards of
various States may well have different meanings in different circuits,
or even within the same circuit.  The resulting uncertainty and
confusion -- especially in lengthy river systems involving several
receiving States -- would lead to precisely the situation that
Congress sought to avoid by enacting the comprehensive Clean Water Act
Amendments to replace the former case-by-case approach of the federal
common law.  See Milwaukee II, 451 U.S. at 324-325.

   III. THE COURT OF APPEALS SHOULD HAVE CONSIDERED WHETHER THE RECORD
SUPPORTED ISSUANCE OF THE PERMIT UNDER THE INTERPRETATION OF THE
OKLAHOMA STANDARDS ADOPTED BY EPA

   Because the court of appeals rejected the standard EPA used in
determining that the Fayetteville discharge would be in compliance
with Oklahoma water quality standards, the court did not consider
whether the agency's factual findings were based on substantial
evidence in the administrative record.  See Pet. App. 89a.  /39/ Nor
did the court remand to EPA to reconsider the propriety of issuing a
permit to Fayetteville under the legal standards the court thought
proper.  Instead, the court undertook a totally inappropriate and
unjustified inquiry into whether the record compiled at the
administrative hearing supported the issuance of a permit to
Fayetteville under the legal standards the court set out.  This
displacement of EPA's fact-finding and decisionmaking authority
constituted clear error.

   Firmly established principles of administrative law required the
court to remand to EPA for further proceedings once it determined
(again, erroneously, in our view) that the original agency decision
was in error.  This is fundamental:  It is for the administrative
agency, not the court, to evaluate different permissible courses of
action and ultimately to make a choice.  Kleppe v. Sierra Club, 427
U.S. 390, 410 n.21 (1976);  Citizens to Preserve Overton Park, Inc. v.
Volpe, 401 U.S. 402, 416 (1971).  This Court stated the "guiding
principle" nearly forty years ago in FPC v. Idaho Power Co., 344 U.S.
17, 20 (1952):

      (T)he function of the reviewing court ends when an error of law
      is laid bare.  At that point the matter once more goes to the
      (agency) for reconsideration.

See also FCC v. Pottsville Broadcasting Co., 309 U.S. 134, 140-146
(1940).  And the Court has recently reaffirmed the principle, noting
that the agency's task on remand remains "infused with judgment and
discretion, requiring the accommodation of conflicting policies that
were committed to the agency's care." Department of the Treasury v.
FLRA, 110 S. Ct. 1623, 1629 (1990) (internal quotation marks omitted).
 "It is not a task (courts) ought to undertake on the agency's behalf
in reviewing its orders." Id. at 1630.

   In undertaking its own inquiry into whether an NPDES permit should
be issued, the court of appeals fundamentally misapplied the
"substantial evidence" standard of review of agency action.  The
"substantial evidence" test requires only "such relevant evidence as a
reasonable mind might accept as adequate to support a conclusion."
American Textile Mfrs. Inst. v. Donovan, 452 U.S. 490, 522 (1981).
The proper inquiry for the court is whether the administrative
agency's findings are supported by substantial evidence, and "(t)he
possibility of drawing two inconsistent conclusions from the evidence
does not prevent an administrative agency's finding from being
supported by substantial evidence." Consolo v. Federal Maritime
Commission, 383 U.S. 607, 620 (1966).  Adherence to the substantial
evidence test, when properly applied, "frees the reviewing courts of
the time-consuming and difficult task of weighing the evidence, it
gives proper respect to the expertise of the administrative tribunal
and it helps promote the uniform application of the statute." Ibid.

   The court of appeals turned this test on its head, searching the
voluminous administrative record to determine whether there was
"substantial evidence" to support its own, independent factual
determinations.  The court openly acknowledged that it was taking such
an approach:

      The record contains substantial evidence from which the ALJ
      could have found that the water quality of the Illinois scenic
      river has been degraded and that water quality standards were
      being violated prior to the onset of Fayetteville's discharge to
      the river * * * .

Pet. App. 61a (emphasis added).  Similarly, the court stated that its
review of the record indicated that there was substantial evidence
that the Illinois River had been degraded by the same types of
pollutants that would be contained in Fayetteville's effluent, and
that Fayetteville's effluent will be transported downstream to
Oklahoma.  Pet. App. 81a.  With this de novo review of the record, the
court of appeals substituted itself for the agency as the primary
factfinder in determining the scientific effects of issuing the
Fayetteville permit.

   Not content with displacing EPA as fact-finder, the court of
appeals went further and flatly "reversed" the issuance of the
Fayetteville permit without remanding to EPA.  Pet. App. 95a.  But the
Clean Water Act, 33 U.S.C. 1341(a)(2), places the duty on the
permit-issuing authority to "condition such * * * permit in such
manner as may be necessary to insure compliance" with water quality
standards.  Only if the permitting authority determines that "the
imposition of conditions cannot insure such compliance" is the agency
to deny the permit.  Section 401(a)(2), 33 U.S.C. 1341(a)(2).  EPA,
the permitting agency, has never made any such determination.  Prior
to the court of appeals' decision, the agency had no occasion to
determine the effects on Oklahoma water quality of placing further
conditions in the Fayetteville permit.  Accordingly, even if, contrary
to our contention, the court of appeals' decision were otherwise to be
upheld, the court's refusal to remand the case to the agency was
inconsistent with the governing statute.

   In sum, the court of appeals usurped EPA's statutorily prescribed
functions.  The court independently determined the legal standards
applicable to the issuance of the Fayetteville NPDES permit;  it
determined the facts from the record de novo;  and it issued a
remedial order independent of the statutory prescription.  Indeed, but
for the development of the record by the administrative agency, the
court's actions in this case closely mirrored the judicial role in a
suit based on the federal common law of nuisance.  In such cases, the
federal court determines the applicable legal standards, serves as
fact-finder, and develops a remedy.  But, as this Court stated in
Milwaukee II, 451 U.S. at 325, Congress vested decisionmaking
authority in interstate water disputes "in administrative agencies
possessing the necessary expertise" and displaced the federal common
law authority formerly exercised by the federal courts.  With this
decision, the court of appeals came full circle, reasserting plenary
authority under the guise of judicial review of agency action.

                              CONCLUSION

   The judgment of the court of appeals should be reversed as to the
questions presented in Petition No. 90-1266.

   Respectfully submitted.

   KENNETH W. STARR

      Solicitor General

   RICHARD B. STEWART

      Assistant Attorney General

   LAWRENCE G. WALLACE

      Deputy Solicitor General

   HARRIET S. SHAPIRO

      Assistant to the Solicitor General

   MICHAEL A. MCCORD

   ANNE S. ALMY

   GARY S. GUZY

      Attorney

   E. DONALD ELLIOTT

      General Counsel

   CATHERINE A. WINER

   PAT RANKIN

      Attorneys Environmental Protection Agency

   MAY 1991

   /1/ "Pet. App." refers to the petition appendix in No. 90-1266;
"Ark. Pet. App." refers to the petition appendix in No. 90-1262.

   /2/ A point source is "any discernible, confined and discrete
conveyance * * * from which pollutants are or may be discharged."
Section 502(14), 33 U.S.C. 1362(14).

   /3/ The term "pollutant" is defined in Section 502(6) of the Act,
33 U.S.C. 1362(6).

   /4/ Section 404 permits authorize the discharge of "dredged or fill
material," whereas NPDES permits authorize the discharge of all other
pollutants.  Section 404(a), 33 U.S.C. 1344(a).  The permit at issue
here is an NPDES permit.

   /5/ EPA had permit-issuing authority in this case, which involves
discharges arising in Arkansas, because Arkansas did not have an
approved permit program at the time the permit application was made.
EPA has subsequently approved the Arkansas permit program.

   /6/ If EPA is itself the permitting agency, the hearing is held
pursuant to the provisions of Section 402(a), 33 U.S.C. 1342(a).

   /7/ In 1970, Oklahoma designated the portion of the Illinois River
from the state line to the Tenkiller Reservoir a state scenic river.
Pet. App. 50a, 62a;  Okla. Stat. Ann. tit. 82, Section 1452(b)(1)
(West 1990).

   /8/ The sewage treatment plants of other Arkansas communities have,
however, historically discharged their effluent into the Illinois
River above the state line.  See Ark. Pet. App. 128a.

   /9/ Fayetteville's plans prompted the State of Oklahoma to move
this Court for leave to file an original action against the State of
Arkansas (and other entities) alleging causes of action under the
federal and state common law of nuisance.  Oklahoma v. Arkansas, No.
93 Orig.  In response to the Court's invitation, the United States
filed a brief opposing the motion for leave to file the complaint, on
the ground that the Clean Water Act permitting procedures would afford
the State an adequate remedy for any threat to its water quality
standards.  This Court denied the motion for leave to file the
complaint.  460 U.S. 1020 (1983).

   /10/ The ALJ calculated that if the Fayetteville plant released the
maximum permissible daily effluent of 3.5 million gallons, 6 pounds of
phosphorous per day would reach the Oklahoma state line.  Ark. Pet.
App. 129a.  Other Arkansas entities currently discharge approximately
750 pounds of phosphorous per day into the Illinois river, but new
treatment plants under construction at three Arkansas cities will
permit "large phosphorus reductions" in their effluent -- resulting in
an estimated 54% reduction of total phosphorus loading to the Illinois
River basin.  Ark. Pet. App. 128a, 132a.

   /11/ The ALJ explained (Ark. Pet. App. 127a, quoting Oklahoma
standard Section 7.10(b)) that eutrophication is:

      the normally slow aging process by which a lake evolves into a
      bog or marsh and ultimately assumes a terrestrial state.  During
      eutrophication the lake becomes so rich in nutritive compounds
      (especially nitrogen and phosphorus) that algae and other
      microscopic plant life become superabundant, thereby "chocking"
      the lake, and causing the lake to advance in serial stages.

   /12/ In the course of the administrative proceedings, several
rulings were made to which Arkansas objected;  Arkansas thereupon
moved this Court for leave to file an original action against Oklahoma
concerning the application of Oklahoma's water quality standards to an
Arkansas permittee.  Arkansas v. Oklahoma, No. 115 Orig.  The United
States filed a brief as amicus curiae, arguing that Arkansas was
attempting to bypass the established administrative procedures for
resolving this interstate dispute.  The State's remedy, the brief
argued, was to let the permitting process run its course and to seek
judicial review under the Clean Water Act if it was displeased with
the result.  The Court denied leave to file an original action.  488
U.S. 1000 (1989).

   /13/ See, e.g., Pet. App. 85a-90a (discussing Clean Water Act
policy and legislative history), 54a (court's examination of state
policy is "guided by the minimum requirements * * * set forth in EPA's
regulation"), 85a (EPA's position inconsistent with "federal water
pollution control strategy engineered by the Clean Water Act and
enhanced by Oklahoma law"), 90a ("We will not ascribe to the (Clean
Water) Act either the gaping loophole or the irrational purpose
necessary to uphold EPA's action."), 94a (EPA "decision is
inconsistent with the language of the Clean Water Act, as interpreted
in light of the legislative history, and frustrates the policy that
Congress sought to implement").

   /14/ The court used 1970, the date of Oklahoma's designation of the
relevant portion of the Illinois River as a "scenic river" (see note
7, supra), as the benchmark from which to determine whether water
quality had been degraded.  Pet. App. 62a.

   /15/ Because the parties had not considered the historic water
quality of the Illinois River significant to the propriety of the
issuance of the permit, the court's factual findings on this aspect of
the case constitute gleanings from "a record that consists of five
boxes and four years of briefs, orders, transcripts, prepared
testimony, correspondence, technical reports, and miscellaneous other
documents" (Pet. App. 62a) on a matter that had not been addressed in
the EPA proceedings, nor briefed and argued by the parties.  See id.
at 61a n.40.

   /16/ The court was not deterred by its recognition that this latter
issue involves "more a scientific question than it is a legal one."
Pet. App. 76a.

   /17/ On October 31, 1990, the court granted Arkansas' motion to
stay the issuance of the mandate pending this Court's action on
petitions for certiorari;  accordingly, the discharges from the
Fayetteville plant are continuing.

   /18/ For instance, the court noted that "(t)he Oklahoma courts
apparently have not interpreted these provisions" and in a footnote
concluded that an opinion of the Oklahoma Attorney General discussing
the provisions seemed contrary to the language of the provisions
themselves.  Pet. App. 53a.

   /19/ In explaining why courts should not invoke federal common law
to supplement the comprehensive statutory scheme, the Court noted (451
U.S. at 325):  "(n)ot only are the technical problems difficult --
doubtless the reason Congress vested authority to administer the Act
in administrative agencies possessing the necessary expertise -- but
the general area is particularly unsuited to the (case-by-case)
approach inevitable under a regime of federal common law." These same
considerations, of course, counsel reliance on the expert agency's
interpretation and application of the relevant federal requirements.

   /20/ That provision sets forth two grounds for an objection.  See
Champion Int'l Corp. v. EPA, 850 F.2d 182, 185 (4th Cir. 1988).  Under
Section 402(d)(2)(A), EPA may object when there is an unresolved
interstate dispute that has been brought to EPA's attention under the
procedures in Section 402(b)(5) (providing for notification to EPA of
a receiving State's objections to the issuance of the permit, and of
the permitting State's action with regard to those objections).  Under
Section 402(d)(2)(B), EPA may -- even in the absence of a state
complaint -- object to the issuance of any permit "as being outside
the guidelines and requirements" of the Act.

   /21/ The permitting authority's responsibility under federal law to
determine whether the issuance of the permit will comply with the
downstream State's standards suggests a fully sufficient alternative
basis for affirming the EPA decision to issue a permit in this case.
The threshold question of the showing necessary to determine under the
CWA whether there is compliance with any particular state standard is
itself a matter of federal, not state, law.  Therefore, EPA's decision
that "the permit should be upheld if the record shows by a
preponderance of the evidence that the authorized discharges would not
cause an actual detectable violation of Oklahoma's water quality
standards" (Ark. Pet. App. 117a) represents an EPA interpretation of
the federal statute's requirement for compliance in the context of
this case, rather than an interpretation of any Oklahoma standard at
all.  Under this alternative analysis, the "detectability" requirement
simply represents an intensely practical conclusion that, as a matter
of federal law, the threshold question of whether an issue of
compliance with the receiving State's standards is even presented is
definitively answered in the negative where the effect of the proposed
discharge cannot be detected at the critical point -- the receiving
State's boundary.  Id. at 118a n. 16.

   /22/ The Arkansas petition correctly recognizes that, in
determining whether to issue a permit for a discharge into interstate
waters, EPA has authority "to assess compliance with downstream
standards." Ark. Pet. 13.  But Arkansas also appears to suggest that
EPA is free to ignore the receiving State's standards altogether, or
to balance the respective interests of the States through which an
interstate waterway passes.  Id. at 13-16.  EPA has never asserted
such authority, in this or any other case, and the terms of the NPDES
permit issued by EPA to Fayetteville would not have been affected if
EPA had agreed with Arkansas' interpretation.  It is therefore
unnecessary for this Court to consider whether the Act gives EPA the
authority claimed for it by Arkansas.

   /23/ If EPA cannot make that finding, it must allow the State to
make the changes necessary to bring the standards into conformity with
the Act.  If the State fails to do so in a timely manner, EPA will
promulgate the water quality standards for the State.  Section
303(c)(3) and (4), 33 U.S.C. 1313(c)(3) and (4).

   Arkansas suggests (90-1262 Pet. 14) that EPA has no authority to
disapprove a state water quality standard on the ground that it has a
discriminatory impact on out-of-state dischargers.  EPA has never
disapproved a state standard on the ground that it has such a
"predatory" effect, and accordingly has not considered the extent of
its power to do so, or, if such power exists, the criteria to be
applied to identify a predatory standard.  Because there was no such
disapproval of the Oklahoma standards in this case, the Court need not
address that issue here.

   /24/ Since many water quality standards are, like the Oklahoma
antidegradation provision at issue here, in narrative form and thus
necessarily expressed in rather general terms, disagreements as to
their meaning will often surface only when the standards are applied
in the context of a specific permit proceeding -- as happened here.

   /25/ To guide the States in the promulgation of water quality
standards, EPA regulations set out (at 40 C.F.R. Pt. 131) model water
quality standards satisfying the requirements of Section 303 of the
Clean Water Act, 33 U.S.C. 1313.  Where, as here, the water quality
standard adopted by the State is based on the EPA model (see note 27,
infra), and there is no clear indication at the time the proposed
standard was submitted to EPA for approval that the State intended a
different meaning, it is surely reasonable and appropriate for EPA to
construe the state standard as being consistent with the model
provision.

   /26/ Thus, the court stated without elaboration that the "ALJ's
interpretation defies the plain language of the Beneficial Use
Limitations and the Anti-Degradation Policy that it references." Pet.
App. 57a.  The court ignored the fact that the governing
interpretation was set forth in the Chief Judicial Officer's opinion
of June 28, 1988 (Ark. Pet. App. 117a) and was reaffirmed in his order
of December 22, 1988, denying review.  Id. at 152a-153a.

   /27/ Even the court of appeals noted the similarities between the
state provision and EPA's model provision (Pet. App. 54a n.34).
Compare the antidegradation provision of Oklahoma standard Section 3:

      No degradation shall be allowed in high quality waters which
      constitute an outstanding resource or in waters of exceptional
      recreational or ecological significance.

with the corresponding language in EPA's model antidegradation
regulations in effect until 1983 (40 C.F.R. 35.1550(e)(2) (1981)):

      Additionally, no degradation shall be allowed in high quality
      waters which constitute an outstanding National resource, such
      as waters * * * of exceptional recreational or ecological
      significance.

   The current regulations provide that high quality waters "shall be
maintained and protected" (40 C.F.R. 131.12(a)(3)).  This change was
to allow for temporary degradation associated with construction
projects.  The change did not affect the restrictions for long-term
sources of pollutants.  48 Fed. Reg. 51,402-51,403 (1983).

   /28/ The antidegradation requirements of the federal model water
quality standards were created by administrative action.  The
antidegradation policy was first enunciated by Secretary Udall of the
Interior Department in 1968.  The instant antidegradation standard was
adopted by EPA in 1975.  Congress subsequently referred to the
antidegradation policy in the 1987 Amendments to the Clean Water Act.
See 33 U.S.C. 1313(d)(4)(B).

   /29/ This standard is termed a Tier III antidegradation standard,
and the waters protected by it are known as "outstanding national
resource waters," or ONRW.

   /30/ See, e.g., Region IV, Questions and Answers on Implementation
of Tier III of the Federal Antidegradation Policy:  Protection of
Outstanding National Resource Waters (Apr. 20, 1989), which states
that there should be no new discharge of pollutants directly into an
ONRW;  discharges to tributaries are permissible if they do not lower
water quality at the boundary of the ONRW.

   /31/ See, e.g., Region V, Guidance for Antidegradation Policy
Implementation for High Quality Waters (Dec. 3, 1986);  Region IX,
Guidance on Implementing the Antidegradation Provisions of 40 C.F.R.
131.12 (June 3, 1987).

   /32/ Indeed, Oklahoma took essentially the same position in
briefing before EPA.  It there stated, "any detectible (sic) increase
in any 'wastes', defined as '(i)ndustrial waste and all other liquid,
gaseous or solid substances which may pollute or tend to pollute any
waters of the State,' will be a violation of the (scenic river)
designation" (emphasis added).  A.R. Doc. B146, at 45.

   /33/ States must affirmatively designate water bodies to be
outstanding national resource waters protected from degradation under
Tier III standards.  Modern designations often do contain a reference
date or a description of the water quality to be maintained.  The
application of such an antidegradation provision could, of course,
raise issues not relevant to this case.  In any event, a State is
highly unlikely to adopt as a benchmark date a time substantially
antedating the application of the protective standard to the waterway
involved.  Compare Okla. Stat. Ann. tit. 82 Section 1452(b)(1) (West
1990) (designation as scenic river) with id. Section 1457
(authorization to impose pollution controls on scenic rivers).

   /34/ It is not entirely clear whether the court intended this
requirement to apply only to "high quality waters" subject to an
antidegradation policy similar to Oklahoma's, or whether it was
intended -- as Arkansas assumes (Ark. Pet. 20-23) -- to apply to any
application for a permit to discharge into waters upstream from waters
not presently in compliance with any applicable standard.

   /35/ Moreover, if the court's zero-discharge requirement was
intended to apply to water quality standards generally (see note 34,
supra), the court ignored EPA's regulation specifically addressing the
circumstances under which a discharge may be allowed into waters that
do not currently meet the applicable standards.  40 C.F.R. 122.4(i).

   /36/ As this Court explained in discussing judicial interpretations
of the requirements of the Clean Air Act in Chevron, 467 U.S. at 865:

      Judges are not experts in the field, and are not part of either
      political branch of the Government.  Courts must, in some cases,
      reconcile competing political interests, but not on the basis of
      the judges' personal policy preferences.  In contrast, an agency
      to which Congress has delegated policymaking responsibilities
      may, within the limits of that delegation, properly rely upon
      the incumbent administration's views of wise policy to inform
      its judgments.

   /37/ Moreover, the court of appeals' analysis leaves no room for
considering whether a discharge will actually dilute, and thereby
improve, the ambient concentration of pollutants in the affected
stream.  For most pollutants, the effect of a discharge on ambient
water quality is a function of the relative concentration of the
stream and the discharge.  If the discharge has a lower concentration
of pollutants than the stream, it will dilute, and thereby improve,
the stream.  Thus, logically even where a stream is in violation of a
numerical water quality standard, a high volume discharge containing
the pollutant of concern may nonetheless not only not exacerbate the
violation, but it may even mitigate or cure that violation, if the
concentration of the pollutant in the discharge is low enough.

   /38/ Compare Ark. Pet. App. 128a-132a (ALJ's findings that maximum
permissible daily effluent from the Fayetteville plant would result in
increase of six pounds of phosphorus per day at Oklahoma boundary,
although other Arkansas entities currently discharge 750 pounds of
phosphorus per day into Illinois River in Arkansas) with Pet. App.
73a-76a (court determination that sufficient phosphorus will reach the
Illinois line from the Fayetteville plant to violate antidegradation
standard).  See note 10, supra.

   /39/ The court there stated:

      EPA and the Arkansas parties urge that the Fayetteville
      discharge should be permitted because its individual impact on
      Illinois River water quality will not be detectable.  While this
      may prove true (and we pass no judgment thereon), we reject the
      argument because of its unavoidable results.