                 FOR PUBLICATION

  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT


NATURAL RESOURCES DEFENSE                 No. 10-56017
COUNCIL, INC.; SANTA MONICA
BAYKEEPER,                                   D.C. No.
               Plaintiffs-Appellants,     2:08-cv-01467-
                                            AHM-PLA
                  v.

COUNTY OF LOS ANGELES; LOS                  OPINION
ANGELES COUNTY FLOOD CONTROL
DISTRICT; MICHAEL ANTONOVICH,
in his official capacity as Supervisor;
YVONNE BURKE, in her official
capacity as Supervisor; GLORIA
MOLINA, in her official capacity as
Supervisor; ZEV YAROSLAVSKY, in
his official capacity as Supervisor;
DEAN D. EFSTATHIOU, in his official
capacity as Acting Director of Los
Angeles County Department of
Public Works; DON KNABE, in his
official capacity as Supervisor,
                 Defendants-Appellees.
2               NRDC V. CNTY. OF LOS ANGELES

        On Remand From The United States Supreme Court

                       Filed August 8, 2013

    Before: Harry Pregerson and Milan D. Smith, Jr., Circuit
     Judges, and H. Russel Holland, Senior District Judge.*

              Opinion by Judge Milan D. Smith, Jr.


                           SUMMARY**


                       Environmental Law

    On remand from the United States Supreme Court, the
panel reversed the district court’s grant of summary judgment
and held that pollution exceedances detected at monitoring
stations of the County of Los Angeles and the Los Angeles
County Flood Control District were sufficient to establish the
County defendants’ liability as a matter of law for violations
of the terms of their National Pollutant Discharge Elimination
System permit issued pursuant to the Clean Water Act.

    In Los Angeles Cnty. Flood Control Dist. v. Natural Res.
Def. Council, Inc., 133 S. Ct. 710 (2013), the Supreme Court
held that a discharge of pollutants does not occur when
polluted water flows from one portion of a river that is


    *
   The Honorable H. Russel Holland, Senior District Judge for the U.S.
District Court for the District of Alaska, sitting by designation.
  **
     This summary constitutes no part of the opinion of the court. It has
been prepared by court staff for the convenience of the reader.
              NRDC V. CNTY. OF LOS ANGELES                      3

navigable water of the United States, through a concrete
channel or other engineered improvement in the river, and
then into a lower portion of the same river. The Supreme
Court declined to address the plaintiffs’ argument that the
County defendants’ monitoring data established their liability
for permit violations as a matter of law. On remand, the
panel held that this court’s previous rejection of the plaintiffs’
argument was not a final decision, nor was it law of the case.

    The panel held that, under the plain language of the
NPDES permit, the data collected at the monitoring stations
was intended to determine whether the permittees were in
compliance with the permit. Accordingly, if the District’s
monitoring data showed that the level of pollutants in
federally protected water bodies exceeded those allowed
under the permit, then, as a matter of permit construction, the
monitoring data conclusively demonstrated that the
defendants were not in compliance with the permit conditions
and were liable for permit violations. The panel held that
extrinsic considerations, including the Clean Water Act’s
monitoring requirements, also supported its holding. The
panel remanded the case to the district court for further
proceedings, including a determination of the proper remedy
for the County defendants’ violations.
4            NRDC V. CNTY. OF LOS ANGELES

                        COUNSEL

Aaron Colangelo, Natural Resources Defense Council,
Washington, D.C.; Daniel Cooper, Lawyers for Clean Water,
San Francisco, California, for Plaintiffs-Appellants.

Andrea Sheridan Ordin, Judith A. Fries, Laurie Dods, Los
Angeles County Department of County Counsel, Los
Angeles, California; Howard Gest and David W. Burhenn,
Burhenn & Gest LLP, Los Angeles, California, for
Defendants-Appellees.


                        OPINION

M. SMITH, Circuit Judge:

    Plaintiffs-Appellants Natural Resources Defense Council
and Santa Monica Baykeeper (collectively, the Plaintiffs)
filed suit against the County of Los Angeles and the Los
Angeles County Flood Control District (collectively, the
County Defendants) alleging that the County Defendants are
discharging polluted stormwater in violation of the terms of
their National Pollutant Discharge Elimination System
(NPDES) permit, issued pursuant to the Federal Water
Pollution Control Act (the Clean Water Act, Act, or CWA),
86 Stat. 816, codified as amended at 33 U.S.C. §§ 1251, et
seq. The district court granted the County Defendants’
motion for summary judgment, reasoning that Plaintiffs failed
to prove that any individual defendant had discharged
pollutants in violation of the Clean Water Act, where
Plaintiffs’ only evidence of violations was monitoring data
taken downstream of the County Defendants’ (and others’)
discharge points, as opposed to data sampled at the relevant
             NRDC V. CNTY. OF LOS ANGELES                     5

discharge points themselves. On appeal, we affirmed the
district court’s judgment in part and reversed in part. Natural
Res. Def. Council, Inc. v. Cnty. of L.A., 673 F.3d 880 (9th Cir.
2011). On January 8, 2013, the Supreme Court reversed our
judgment and remanded this case to us for further
proceedings. L.A. Cnty. Flood Control Dist. v. Natural Res.
Def. Council, Inc., 133 S. Ct. 710 (2013). On February 19,
2013, we ordered the parties to file supplemental briefs
addressing the implications of the Supreme Court’s ruling.
Having considered the Supreme Court’s ruling, the responses
of the parties in their supplemental briefs, and other matters
noted herein, we now conclude that the pollution exceedances
detected at the County Defendants’ monitoring stations are
sufficient to establish the County Defendants’ liability for
NPDES permit violations as a matter of law. Accordingly,
we once again reverse the district court’s grant of summary
judgment in favor of the County Defendants, and remand to
the district court for a determination of the appropriate
remedy for the County Defendants’ violations.

               FACTUAL BACKGROUND

I. Stormwater Runoff in Los Angeles County

    Stormwater runoff is surface water generated by
precipitation events, such as rainstorms, which flows over
streets, parking lots, commercial sites, and other developed
parcels of land. When stormwater courses over urban
environs, it frequently becomes polluted with contaminants,
such as “suspended metals, sediments, algae-promoting
nutrients (nitrogen and phosphorus), floatable trash, used
6               NRDC V. CNTY. OF LOS ANGELES

motor oil, raw sewage, [and] pesticides[.]”1 Envtl. Def. Ctr.,
Inc. v. EPA, 344 F.3d 832, 840 (9th Cir. 2003). This polluted
stormwater often makes its way into storm drains and sewers,
which “generally channel collected runoff into federally
protected water bodies,” id., such as rivers and oceans.
Consequently, stormwater runoff has been recognized as “one
of the most significant sources of water pollution in the
nation, at times comparable to, if not greater than,
contamination from industrial and sewage sources.” Id.
(citation omitted).

    Los Angeles County (the County) is home to more than
10 million people and covers a sprawling amalgam of
populous incorporated cities and significant swaths of
unincorporated land. The Los Angeles County Flood Control
District (the District) is a public entity governed by the Los
Angeles County Board of Supervisors and the Los Angeles
County Department of Public Works. The District comprises
84 cities and some unincorporated areas of the County. The
County and the District are separate legal entities.




    1
     Whereas natural, vegetated soil can absorb rainwater and capture
pollutants, paved surfaces and developed land can do neither. Paved
facilities with particularly high volumes of motor vehicle traffic—such as
parking lots, retail gasoline outlets, and fast food restaurants—are
typically responsible for producing higher concentrations of pollutants in
storm water runoff.
                 NRDC V. CNTY. OF LOS ANGELES                            7

    Each city in the District operates a municipal separate
storm sewer system (ms4)2 that is composed of gutters, catch
basins, storm drains, and pipes that collect and convey
stormwater. The County also operates its own ms4 that
primarily collects and conveys stormwater runoff in the
unincorporated areas of the County. Each of these ms4s
connects to the District’s substantially larger ms4, an
extensive flood-control and storm-sewer infrastructure
consisting of approximately 500 miles of open channels and


 2
     Federal Regulations define an ms4 as:

          a conveyance or system of conveyances (including
          roads with drainage systems, municipal streets, catch
          basins, curbs, gutters, ditches, man-made channels, or
          storm drains):

          (i) Owned or operated by a State, city, town, borough,
          county, parish, district, association, or other public
          body . . . having jurisdiction over disposal of sewage,
          industrial wastes, storm water, or other wastes,
          including special districts under State law such as a
          sewer district, flood control district or drainage district,
          or similar entity . . . ;

          (ii) Designed or used for collecting or conveying storm
          water;

          (iii) Which is not a combined sewer; and

          (iv) Which is not part of a Publicly Owned Treatment
          Works . . . .

40 C.F.R. § 122.26(b)(8). Unlike a sanitary sewer system, which
transports municipal sewage for treatment at a wastewater facility, or a
combined sewer system, which transports sewage and stormwater for
treatment, an ms4 conveys only untreated stormwater. See 40 C.F.R.
§ 122.26(a)(7), (b)(8).
8               NRDC V. CNTY. OF LOS ANGELES

2,800 miles of storm drains. Because a comprehensive map
of the County Defendants’ storm sewer system does not exist,
no one knows the exact size of the LA MS43 or the locations
of all of its storm drain connections and outfalls.4 But while
the number and location of storm drains and outfalls are too
numerous to catalog, it is undisputed that the LA MS4
collects and channels stormwater runoff from across the
County. It is similarly undisputed that untreated stormwater
is discharged from LA MS4 outfalls into various
watercourses, including the Los Angeles and San Gabriel
Rivers.5 These rivers, in turn, drain into several coastal
waters, including, among others, the Santa Monica Bay and
the Pacific Ocean.



 3
   Throughout this Opinion, reference is made to both “ms4” and the “LA
MS4.” The former is a generic reference to an individual municipal
separate storm sewer system without regard to its particular location,
while the latter specifically refers to the entire flood control and storm-
sewer infrastructure described supra that exists in Los Angeles County,
and which is made up of the various interconnected ms4s that are
controlled by the County, the District, and the incorporated cities within
the District.
     4
      An “outfall” is defined as a “point source . . . at the point where a
municipal separate storm sewer discharges to waters of the United States.
. . .” 40 C.F.R. § 122.26(b)(9). It is estimated that the LA MS4 contains
tens of thousands of outfalls where stormwater runoff is discharged into
federally protected water bodies.
         5
      Plaintiffs originally complained about the County Defendants’
discharges into four water bodies: the Los Angeles River, the San Gabriel
River, the Santa Clara River, and Malibu Creek. See Natural Res. Def.
Council, 673 F.3d at 883. On remand to this court, however, Plaintiffs
only seek review of the district court’s summary judgment ruling
regarding the County Defendants’ discharges into the Los Angeles and
San Gabriel Rivers.
                NRDC V. CNTY. OF LOS ANGELES                            9

II. The County Defendants’ NPDES Permit

    Section 301(a) of the CWA prohibits the “discharge of
any pollutant” from any “point source” into “navigable
waters” unless the discharge complies with certain other
sections of the CWA.6 See 33 U.S.C. § 1311(a). One of
those sections is section 402, which provides for the issuance
of NPDES permits. 33 U.S.C. § 1342. In nearly all cases, an
NPDES permit is required before anyone may lawfully
discharge a pollutant from a point source into the navigable
waters of the United States. See Arkansas v. Oklahoma,
503 U.S. 91, 101–02 (1992); Environmental Law Handbook
323 (Thomas F. P. Sullivan ed., 21st ed. 2011).

    Congress has empowered the EPA Administrator to
delegate NPDES permitting authority to state agencies.
33 U.S.C. § 1342(b). Pursuant to this authority, the EPA has
authorized the State of California to develop water quality
standards and issue NPDES permits. Pursuant to the Porter-
Cologne Water Quality Control Act, California state law
designates the State Water Resources Control Board and nine
regional boards as the principal state agencies charged with
enforcing federal and state water pollution laws and issuing


  6
    A point source is defined as “any discernible, confined and discrete
conveyance, including but not limited to any pipe, ditch, channel, tunnel,
conduit, well, discrete fissure, container, rolling stock, concentrated
animal feeding operation, or vessel or other floating craft, from which
pollutants are or may be discharged.” 33 U.S.C. § 1362(14). Throughout
this litigation, there has been confusion regarding whether the LA MS4 is
a “point source” under the CWA. See Natural Res. Def. Council, 673 F.3d
at 898 (accepting Plaintiffs’ argument that “[u]nder the Clean Water Act,
the [LA] MS4 is a ‘Point Source.’”). The LA MS4 is not a single point
source. Rather, the LA MS4 is a collection of point sources, including
outfalls, that discharge into the navigable waters of the United States.
10           NRDC V. CNTY. OF LOS ANGELES

NPDES permits. See Cal. Water Code §§ 13000 et seq. The
entity responsible for issuing permits in the Los Angeles area
is the California State Water Resources Control Board for the
Los Angeles Region (the Regional Board).

      On June 18, 1990, the Regional Board first issued an
NPDES permit (the Permit) regulating stormwater discharges
by the County, the District, and the 84 incorporated
municipalities in the District (collectively, the Permittees).
The Permit has subsequently been renewed or amended
several times, and the version of the Permit at issue in this
litigation came into force on December 13, 2001.7 The
Permit covers all relevant discharges that occur “within the
boundaries of the Permittee municipalities . . . over which
[the municipalities have] regulatory jurisdiction as well as
unincorporated areas in Los Angeles County within the
jurisdiction of the Regional Board.”

    The Permit runs to 99 pages and contains a myriad of
rules, regulations, and conditions regarding the Permittees’
operation of the LA MS4. However, only two sets of the
Permit’s provisions are particularly relevant to this appeal;
those contained in Part 2, titled “Receiving Water
Limitations,” and those contained in the section titled
“Monitoring and Reporting Program.”

    Part 2 places limits on the type and amount of pollutants
the Permittees may lawfully discharge from the LA MS4.
Specifically, Part 2 prohibits “discharges from the [LA] MS4
that cause or contribute to the violation of the Water Quality



  7
    On November 8, 2012, the Regional Board issued a new NPDES
permit to the County Defendants and various other permittees.
                NRDC V. CNTY. OF LOS ANGELES                           11

Standards or water quality objectives.”8 The Permit defines
“Water Quality Standards and Water Quality Objectives” as
“water quality criteria contained in the Basin Plan, the
California Ocean Plan, the National Toxics Rule, the
California Toxics Rule, and other state or federal approved
surface water quality plans.”9 Succinctly put, the Permit
incorporates the pollution standards promulgated in other
agency documents such as the Basin Plan, and prohibits
stormwater discharges that “cause or contribute to the
violation” of those incorporated standards. The Permit
further provides that the Permittees “shall comply” with the
LA MS4 discharge prohibitions outlined in Part 2 “through
timely implementation of control measures and other actions
to reduce pollutants in the[ir LA MS4] discharges . . . .”

     The Monitoring and Reporting Program complements
Part 2. Under that program, the Permittees are required to
monitor the impacts of their LA MS4 discharges on water
quality and to publish the results of all pollution monitoring
at least annually. The primary objectives of the monitoring
program include “assessing compliance” with the Permit,
“measuring and improving the effectiveness” of the Los
Angeles Countywide Stormwater Quality Management


  8
   Part 2 also mandates that “[d]ischarges from the [LA] MS4 of storm
water, or non-storm water, for which a Permittee is responsible for [sic],
shall not cause or contribute to a condition of nuisance.”
 9
   Under California law, regional boards are required to formulate water
quality plans, called “basin plans,” which designate the beneficial uses of
protected water bodies within the boards’ jurisdiction, establish water
quality objectives for those water bodies, and establish a program for
implementing the basin plan. See City of Burbank v. State Water Res.
Control Bd., 108 P.3d 862, 865 (Cal. 2005) (citing Cal. Water Code
§ 13050(j)).
12             NRDC V. CNTY. OF LOS ANGELES

Program (SQMP),10 and assessing the environmental impact
of urban runoff on the receiving waters in the County.

    One of the principal ways the Permittees are required to
monitor their LA MS4 discharges is through mass-emissions
monitoring. Mass-emissions monitoring measures all
constituents present in water, and the readings give a
cumulative picture of the pollutant load in a waterbody. The
Permit requires the District, as Principal Permittee, to conduct
mass-emissions monitoring at seven enumerated monitoring
stations located throughout the County. The District is also
responsible for analyzing the resulting data and submitting a
comprehensive report of its findings.11 According to the
Permit, the purpose of mass-emissions monitoring is to: (1)
estimate the mass emissions from the LA MS4; (2) assess
trends in the mass emissions over time; and (3) determine if
the LA MS4 is contributing to exceedances of Water Quality
Standards by comparing the monitoring results to the
applicable pollution standards promulgated in the Basin Plan
and similar documents.

    The Permittees sited a mass-emissions monitoring station
in both the Los Angeles and San Gabriel Rivers (collectively,
the Monitoring Stations). The Los Angeles River monitoring
station is located in a channelized portion of the Los Angeles


  10
      The Permit defines the SQMP as “the Los Angeles Countywide
Stormwater Quality Management Program, which includes descriptions
of programs, collectively developed by the Permittees in accordance with
the provisions of the NPDES permit, to comply with applicable federal
and state law. . . .”
 11
    The District publishes these “Stormwater Monitoring Reports” on the
internet at: http://ladpw.org/wmd/NPDES/report_directory.cfm. (last
accessed August 1, 2013).
                NRDC V. CNTY. OF LOS ANGELES                           13

River that runs through the City of Long Beach.12 The San
Gabriel River monitoring station is located in a channelized
portion of the San Gabriel River that runs through the City of
Pico Rivera.       The Monitoring Stations are located
downstream of numerous LA MS4 outfalls controlled by the
County Defendants and various other non-party Permittees.

    Between 2002 and 2008, when this case was filed, the
District published annual monitoring reports that contain the
data that the District collected at the Monitoring Stations.
According to those reports, the Monitoring Stations identified
140 separate exceedances of the Permit’s water quality
standards, including excessive levels of aluminum, copper,
cyanide, zinc, and fecal coliform bacteria in both the Los
Angeles and San Gabriel Rivers. The County Defendants do
not dispute the accuracy of the monitoring data.

 12
    In a declaration submitted to the district court, the County Defendants
described both Monitoring Stations as being located “in a portion of the
District’s flood control channel.”          See also“Section Two: Site
Descriptions,” Los Angeles Cnty. Dept. of Pub. Works, available at
http://dpw.lacounty.gov/wmd/npdes/9899_report/SiteDesc.pdf (last
accessed August 1, 2013). Thus, it appears that the pertinent river
segments are part of both the LA MS4 itself and “the waters of the United
States” that the CWA protects. But regardless of whether the mass-
emissions monitoring stations are also part of the LA MS4, there is no
dispute that the mass-emissions monitoring stations are located within the
Los Angeles and San Gabriel Rivers, downstream of a significant number
of the County Defendants’ LA MS4 outfalls. We misconstrued some of
the data before us when we previously held otherwise. See Natural Res.
Def. Council, 673 F.3d at 899 (“As a matter of law and fact, the [LA] MS4
is distinct from the two navigable rivers; the [LA] MS4 is an intra-state
man-made construction—not a naturally occurring Watershed River”); see
also 53 Fed. Reg. 49,416, 49,453 (Dec. 7, 1988) (EPA observes that “[i]n
many situations, waters of the United States that receive discharges from
municipal storm sewers can be mistakenly considered to be part of the
storm sewer system.”).
14              NRDC V. CNTY. OF LOS ANGELES

               PROCEDURAL BACKGROUND

    Using the monitoring data self-reported by the District,
Plaintiffs cataloged the water quality exceedances measured
in various receiving waters in the County. Beginning on May
31, 2007, Plaintiffs sent a series of notice letters to the
County Defendants informing them that Plaintiffs believed
that they were violating the terms of the Permit.13
Specifically, Plaintiffs contended that the water quality
exceedances documented in the District’s monitoring reports
demonstrated liability under the CWA. Dissatisfied with the
County Defendants’ response to these letters, Plaintiffs
brought this citizen-enforcement action on March 3, 2008.
After the district court dismissed certain elements of the
Plaintiffs’ initial complaint because notice of the Permit
violations was defective, Plaintiffs sent the County
Defendants an adequate notice letter on July 3, 2008.

    Plaintiffs filed their First Amended Complaint on
September 18, 2008. In the complaint, Plaintiffs asserted six
causes of action under the CWA. Four of the Plaintiffs’
claims, which the district court designated the “Watershed
Claims,” were initially before us on appeal. The first three
Watershed Claims allege that, beginning in 2002 or 2003, the
County Defendants caused or contributed to exceedances of
water quality standards in the Santa Clara River (Claim 1),
the Los Angeles River (Claim 2), and the San Gabriel River
(Claim 3), in violation of 33 U.S.C. §§ 1311(a), 1342(p). The
fourth Watershed Claim alleges that, beginning in 2002,
County Defendants caused or contributed to exceedances of


  13
    The CWA requires plaintiffs to provide 60 days notice to an alleged
violator, the State in which the violation is alleged to be occurring, and the
EPA, before filing suit. 33 U.S.C. § 1365(b)(1)(A).
              NRDC V. CNTY. OF LOS ANGELES                       15

the water quality standards and violated the total maximum
daily load limits in Malibu Creek. All of the Watershed
Claims rest on the same premise: (1) the Permit incorporates
water-quality limits for each receiving water body; (2) mass-
emissions monitoring stations have recorded pollutant loads
in the receiving water bodies that exceed those permitted
under the relevant standards; (3) an exceedance constitutes
non-compliance with the Permit and, thereby, the Clean
Water Act; and (4) County Defendants, as holders of the
Permit and joint operators of the LA MS4, are liable for these
exceedances under the Act.

    Early in the litigation, the district court bifurcated liability
and remedy, and all proceedings related to remedy were
stayed until liability was determined. On March 2, 2010, the
district court denied all parties’ cross-motions for summary
judgment with regard to liability. NRDC v. Cnty. of L.A., No.
CV 08-1467-AHM, 2010 WL 761287 (C.D. Cal. Mar. 2,
2010), amended on other grounds, 2011 WL 666875 (C.D.
Cal. Jan. 27, 2011). Although the district court accepted
Plaintiffs’ arguments that the Permit “clearly prohibits
‘discharges from the [LA] MS4 that cause or contribute to the
violation of Water Quality Standards or water quality
objectives,’” 2010 WL 761287, at *6, and that mass-
monitoring stations “are the proper monitoring locations to
determine if the [LA] MS4 is contributing to exceedances” of
the Water Quality Standards or water quality objectives, id.,
the district court held that Plaintiffs were improperly
attempting to use the District’s self-reported monitoring data
to establish liability without presenting evidence that any
individual defendant was discharging pollutants that
“cause[d] or contribute[d] to the violation” of the water
quality standards. Id. The district court observed that
although “the District is responsible for the pollutants in the
16           NRDC V. CNTY. OF LOS ANGELES

[LA] MS4” at the time they pass the Monitoring Stations,
“that does not necessarily determine the question of whether
the water passing by these points is a ‘discharge’ within the
meaning of the Permit and the Clean Water Act.” Id. at *7.
Unable to determine whether any of the County Defendants’
upstream LA MS4 outflows were contributing polluted
stormwater to navigable waters, the district court stated that
“Plaintiffs would need to present some evidence (monitoring
data or an admission) that some amount of a standards-
exceeding pollutant is being discharged through at least one
District outlet.” Id. at *8.

    Following supplemental briefing, the district court again
determined that “Plaintiffs failed to present evidence that the
standards-exceeding pollutants passed through the
Defendants’ [LA] MS4 outflows at or near the time the
exceedances were observed. Nor did Plaintiffs provide any
evidence that the mass emissions stations themselves are
located at or near a Defendant’s outflow.” The district court
thus entered summary judgment for the County Defendants
on the Watershed Claims.

    On June 9, 2010, the district court entered a partial final
judgment on the Watershed Claims under Fed. R. Civ. P.
54(b). The court reasoned that an interlocutory appeal was
appropriate because the Watershed Claims are “factually and
legally severable” from the Plaintiffs’ other claims and “[t]he
parties and the Court would benefit from appellate resolution
of the central legal question underlying the watershed claims:
what level of proof is necessary to establish defendants’
liability.” The Plaintiffs timely appealed.

    On appeal, the Plaintiffs pressed the same legal argument
they advanced in the district court: that the data published in
              NRDC V. CNTY. OF LOS ANGELES                     17

the County Defendants’ annual monitoring reports—data
which shows undisputed pollution exceedances at the mass-
emissions monitoring stations—conclusively establishes the
County Defendants’ liability for Permit violations as a matter
of law. Like the district court, we rejected this contention and
held that the Plaintiffs must submit at least some additional
proof of the County Defendants’ individual contributions to
the measured Permit violations. See Natural Res. Def.
Council, 673 F.3d at 898 (noting that “the Clean Water Act
does not prohibit ‘undisputed’ exceedances; it prohibits
‘discharges’ that are not in compliance with the Act. . . .
While it may be undisputed that exceedances have been
detected, responsibility for those exceedances requires proof
that some entity discharged a pollutant.”).

     Nonetheless, we held the District liable for CWA
violations in the Los Angeles and San Gabriel Rivers because
we concluded that the mass-emissions monitoring stations for
each river are “located in a section of the [LA] MS4 owned
and operated by the District” and that “when pollutants were
detected, they had not yet exited the point source into
navigable waters.” Id. at 899. We further clarified that “[t]he
[relevant] discharge from a point source occurred when the
still-polluted stormwater flowed out of the concrete channels
where the Monitoring Stations are located, through an outfall,
and into the navigable waterways. We agree with Plaintiffs
that the precise location of each outfall is ultimately irrelevant
because there is no dispute that [the LA] MS4 eventually adds
stormwater to the Los Angeles and San Gabriel Rivers
downstream from the Monitoring Stations.” Id. at 900.

    On October 11, 2011, the District filed a petition for writ
of certiorari, 2011 WL 4874090, which was granted in part on
June 25, 2012. L.A. Cnty. Flood Control Dist. v. Natural Res.
18            NRDC V. CNTY. OF LOS ANGELES

Def. Council, Inc., 133 S. Ct. 23 (2012). The Supreme Court
granted review in order to answer a single question: “Under
the CWA, does a discharge of pollutants occur when polluted
water flows from one portion of a river that is navigable
water of the United States, through a concrete channel or
other engineered improvement in the river, and then into a
lower portion of the same river?” L.A. Cnty. Flood Control
Dist., 133 S. Ct. at 712–13 (internal quotation marks omitted).
The Court answered in the negative, and re-affirmed its
holding in S. Fla. Water Mgmt. Dist. v. Miccosukee Tribe of
Indians, 541 U.S. 95 (2004), that “pumping polluted water
from one part of a water body into another part of the same
body is not a discharge of pollutants under the CWA.” L.A.
Cnty. Flood Control Dist., 133 S. Ct. at 711. The Court did
not address any other basis for the District’s potential liability
for Permit violations and instead reversed our prior judgment
and remanded this case to us for additional proceedings. Id.
at 713–14.

     JURISDICTION AND STANDARD OF REVIEW

    We have jurisdiction under 28 U.S.C. § 1291. We review
the district court’s grant of summary judgment de novo.
Assoc. to Protect Hammersley, Eld, & Totten Inlets v. Taylor
Res., Inc., 299 F.3d 1007, 1009 (9th Cir. 2002).

                        DISCUSSION

                                I.

     Plaintiffs return from the Supreme Court with the same
argument they have consistently advanced throughout this
litigation—that the County Defendants’ monitoring data
establishes their liability for Permit violations as a matter of
               NRDC V. CNTY. OF LOS ANGELES                          19

law. We previously rejected this argument, see Natural Res.
Def. Council, 673 F.3d at 898, and the Supreme Court
explicitly declined to address it.14

    On remand, the County Defendants argue that we may not
reconsider our earlier decision because it has become “final,”
and because “reconsideration of Appellants’ monitoring
argument would fly in the face of the finality given to
decisions of this Court after denial of rehearing or expiration
of the time in which to seek such further review.”
Alternatively, the County Defendants argue that our earlier
disposition should be left undisturbed because it has become
the law of the case. The County Defendants are mistaken on
both counts.

    “No opinion of this circuit becomes final until the
mandate issues[.]” Carver v. Lehman, 558 F.3d 869, 878 (9th
Cir. 2009); see also Fed R. App. P. 41(c), 1998 Adv. Comm.
Note (“A court of appeals’ judgment or order is not final until
issuance of the mandate[.]”). Thus, we have explained that
a “court of appeals may modify or revoke its judgment at any
time prior to issuance of the mandate, sua sponte or by
motion of the parties.” United States v. Foumai, 910 F.2d
617, 620 (9th Cir. 1990). The mandate in this case has not
issued. Consequently, our earlier judgment is not final.
Carver, 558 F.3d at 878. Nor can it be considered the law of

 14
    See L.A. Cnty. Flood Control Dist., 133 S. Ct. at 713–14 (“Under the
permit’s terms, the NRDC and Baykeeper maintain, the exceedances
detected at instream monitoring stations are by themselves sufficient to
establish the District’s liability under the CWA for its upstream
discharges. This argument failed below. It is not embraced within, or
even touched by, the narrow question on which we granted certiorari. We
therefore do not address, and indicate no opinion on, the issue NRDC and
Baykeeper seek to substitute for the question we took up for review.”).
20           NRDC V. CNTY. OF LOS ANGELES

the case. See id. at 878 n.16 (“[U]ntil the mandate issues, an
opinion is not fixed as settled Ninth Circuit law, and reliance
on the opinion is a gamble.” (citation omitted)); see also Key
Enters. of Del., Inc. v. Venice Hosp., 9 F.3d 893, 898 (11th
Cir. 1993) (“[B]ecause the panel’s mandate had not issued,
the panel’s decision was never the ‘law of the case.’”). Put
simply, we are free to reconsider the merits of Plaintiffs’
argument, and we now do so.

                              II.

    Where a permittee discharges pollutants in compliance
with the terms of its NPDES permit, the permit acts to
“shield” the permittee from liability under the CWA.
33 U.S.C. § 1342(k). The permit shield is a major benefit to
a permittee because it protects the permittee from any
obligation to meet more stringent limitations promulgated by
the EPA unless and until the permit expires. See Piney Run
Pres. Ass’n v. Cnty. Comm’rs of Carroll Cnty., 268 F.3d 255,
266–69 (4th Cir. 2001); see also The Clean Water Act
Handbook 67 (Mark A. Ryan ed., 3rd ed. 2011). Of course,
with every benefit comes a cost: a permittee violates the
CWA when it discharges pollutants in excess of the levels
specified in the permit, or where the permittee otherwise
violates the permit’s terms. See Russian River Watershed
Prot. Comm. v. City of Santa Rosa, 142 F.3d 1136, 1138 (9th
Cir. 1998); see also 40 C.F.R. § 122.41(a) (“Any permit
noncompliance constitutes a violation of the Clean Water Act
and is grounds for [an] enforcement action”); Nw. Envtl.
Advocates v. City of Portland, 56 F.3d 979, 986 (9th Cir.
1995) (noting that “[t]he plain language of [the CWA citizen
suit provision] authorizes citizens to enforce all permit
conditions”); Environmental Law Handbook 327 (“The
             NRDC V. CNTY. OF LOS ANGELES                   21

primary purpose of NPDES permits is to establish
enforceable effluent limitations.”).

     Plaintiffs allege that the County Defendants are violating
the terms of the Permit by discharging pollutants into the Los
Angeles and San Gabriel Rivers in excess of the permitted
levels. County Defendants do not dispute that they are
discharging pollutants from the LA MS4 into these rivers.
Nor can the County Defendants dispute that their own
monitoring reports demonstrate that pollution levels recorded
at the Monitoring Stations are in excess of those allowed
under the Permit. Rather, the County Defendants focus on
their perception of the evidentiary burden Plaintiffs must
satisfy in order to hold any individual defendant liable for
these pollution exceedances. Plaintiffs contend that they may
rely exclusively on the District’s monitoring reports to
establish liability. County Defendants, however, argue that
they cannot be held liable for Permit violations based solely
on the data published in the District’s monitoring reports
because: (1) the mass-emissions monitoring required under
the Permit was “neither designed nor intended” to measure
the compliance of any Permittee; and (2) the monitoring data
cannot parse out precisely whose discharge(s) contributed to
any given exceedance because the Monitoring Stations
sample pollution levels downstream from a legion of
discharge points (e.g., LA MS4 outfalls) controlled by
various Permittees and other non-party entities, as opposed to
at the discharge points themselves.

    To resolve the parties’ contentions, we must interpret the
language of the Permit. Although the NPDES permitting
scheme can be complex, a court’s task in interpreting and
enforcing an NPDES permit is not—NPDES permits are
treated like any other contract. See Nw. Envtl. Advocates,
22              NRDC V. CNTY. OF LOS ANGELES

56 F.3d at 982 (“We review the district court’s interpretation
of the 1984 permit as we would the interpretation of a
contract or other legal document.”).15 If the language of the
permit, considered in light of the structure of the permit as a
whole, “is plain and capable of legal construction, the
language alone must determine the permit’s meaning.” Piney
Run Pres. Ass’n, 268 F.3d at 270 (citation omitted). If,
however, the permit’s language is ambiguous, we may turn to
extrinsic evidence to interpret its terms. Id. Our sole task at
this point of the case is to determine what Plaintiffs are
required to show in order to establish liability under the terms
of this particular NPDES permit.16

A. The Plain Language of the Permit

    “[NPDES permit] terms are to be given their ordinary
meaning, and when the terms of a [permit] are clear, the
intent of the parties must be ascertained from the [permit]


  15
     See also Piney Run Pres. Ass’n, 268 F.3d at 269–70; Am. Canoe
Ass’n, Inc. v. D.C. Water & Sewer Auth., 306 F. Supp. 2d 30, 42 (D.D.C.
2004).
 16
    The question before us is not whether the Clean Water Act mandates
any particular result. An NPDES permitting authority has wide discretion
concerning the terms of a permit. It could, for example, lawfully write an
ms4 permit that provides that all permittees will share liability in some
ratio for any measured exceedance of applicable pollutant limits. Or, as
a further example, a permitting authority could lawfully write a permit
providing that only the co-permittee(s) whose specific discharges are
connected to a particular pollutant exceedance may be held liable for the
permit violation. See 33 U.S.C. § 1342(a)(2) (“The Administrator shall
prescribe conditions for [NPDES] permits to assure compliance with the
requirements of [33 U.S.C. § 1342(a)(1)], including conditions on data and
information collection, reporting, and such other requirements as he deems
appropriate.”).
             NRDC V. CNTY. OF LOS ANGELES                   23

itself.” Klamath Water Users Protective Ass’n v. Patterson,
204 F.3d 1206, 1210 (9th Cir. 1999). Plaintiffs argue that the
text of the County Defendants’ Permit is clear, and provides
that the District’s mass-emissions monitoring data will be
used to assess the County Defendants’ compliance with the
Permit, and particularly Part 2, which prohibits “discharges
from the [LA] MS4 that cause or contribute to the violation
of Water Quality Standards or water quality objectives.” The
County Defendants dispute this notion, and first claim that the
District’s mass-emissions monitoring is intended to serve
only a hortatory purpose. As County Defendants state, “the
mass emission monitoring program . . . neither measures nor
was designed to measure any individual permittee’s
compliance with the Permit.” This argument is clearly belied
by the text of the Permit and is rejected.

    The Permit establishes a “Monitoring and Reporting
Program” with the stated objectives of both characterizing
stormwater discharges and assessing compliance with water-
quality standards. The Permit language could not be more
explicit in this regard, stating that “[a]ssessing compliance
with this [Permit]” is one of the “primary objectives of the
Monitoring Program.” “The fact that the parties dispute a
[permit’s] meaning does not establish that the [permit] is
ambiguous; it is only ambiguous if reasonable people could
find its terms susceptible to more than one interpretation.”
Klamath Water Users Protective Ass’n, 204 F.3d at 1210. No
reasonable person could find even the slightest ambiguity in
the phrase “[t]he primary objectives of the Monitoring
Program include, but are not limited to: Assessing
compliance with this [Permit].” Consequently, we decline to
embrace the County Defendants’ initial argument that “the
mass-emission monitoring stations, as a matter of fact, do not
assess the compliance of any permittee with the Permit . . . .”
24            NRDC V. CNTY. OF LOS ANGELES

    County Defendants’ alternative argument, while more
facially appealing, fares no better. Specifically, the County
Defendants point to certain Permit language they claim shows
that the Regional Board did not intend for the
mass–emissions monitoring data to be used to establish
liability for Permit violations. For instance, the County
Defendants note that the Permit provides that “[e]ach
permittee is responsible only for a discharge for which it is
the operator.” County Defendants also cite language in Part
2 that reads: “Discharges from the [LA] MS4 of storm water,
or non-storm water, for which a Permittee is responsible for
[sic], shall not cause or contribute to a condition of nuisance.”
The County Defendants read this language as precluding a
finding of liability against them—or any other
Permittee—without independent monitoring data establishing
that discharges from a particular entity’s ms4 outfalls
exceeded standards.

    “[A] court must give effect to every word or term” in an
NPDES permit “and reject none as meaningless or
surplussage. . . .” In re Crystal Props., Ltd., L.P., 268 F.3d
743, 748 (9th Cir. 2001) (quotations omitted); see also
Restatement (Second) of Contracts § 203(a) (1981) (“[A]n
interpretation which gives a reasonable, lawful, and effective
meaning to all the terms is preferred to an interpretation
which leaves a part unreasonable, unlawful, or of no effect.”).
“Therefore, we must interpret the [Permit] in a manner that
gives full meaning and effect to all of the [Permit’s]
provisions and avoid a construction of the [Permit] that
focuses only on” a few isolated provisions. In re Crystal
Props., 268 F.3d at 748.

    The County Defendants’ interpretation of the Permit
ultimately must be rejected because it would create an
                NRDC V. CNTY. OF LOS ANGELES                          25

unreasonable result. Reading the clause that “[e]ach
permittee is responsible only for a discharge for which it is
the operator” to preclude use of the mass–emission
monitoring data to “assess[] compliance with this [Permit]”
would render the monitoring provisions of the Permit largely
meaningless. Under the County Defendants’ reading of the
Permit, individual Permittees could discharge an unlimited
amount of pollutants from the LA MS4 but never be held
liable for those discharges based on the results of the
mass–emissions monitoring, even though that monitoring is
explicitly intended to assess whether Permittees are in
compliance with Part 2’s discharge limitations. We are
unwilling to accept such a strained interpretation. See
Mastrobuono v. Shearson Lehman Hutton, Inc., 514 U.S. 52,
63 (1995) (holding that courts should be guided by the
“cardinal principle of contract construction: that a document
should be read to give effect to all of its provisions and to
render them consistent with each other”). A better reading of
the Permit’s putatively conflicting provisions, therefore, is the
one proposed by Plaintiffs.          Limiting a Permittee’s
responsibility to “discharge[s] for which it is the operator”
applies to the appropriate remedy for Permit violations, not to
liability for those violations. Indeed, Plaintiffs’ reading is
consistent with the remedial scheme of the Permit itself. If
the LA MS4 is found to be contributing to water quality
violations, each Permittee must take appropriate remedial
measures with respect to its own discharges.17 Thus, a finding
of liability against the County Defendants would not, as



 17
    The relevant Permit provision states: “Each Permittee is required to
comply with the requirements of this Order applicable to discharges within
its boundaries . . . and not for the implementation of the provisions
applicable to the Principal Permittee or other Permittees.”
26           NRDC V. CNTY. OF LOS ANGELES

defendants argue, hold any County Defendant responsible for
discharges for which they are not “the operator.”

    In sum, and contrary to the County Defendants’
contentions, the language of the Permit is clear—the data
collected at the Monitoring Stations is intended to determine
whether the Permittees are in compliance with the Permit. If
the District’s monitoring data shows that the level of
pollutants in federally protected water bodies exceeds those
allowed under the Permit, then, as a matter of permit
construction, the monitoring data conclusively demonstrate
that the County Defendants are not “in compliance” with the
Permit conditions. Thus, the County Defendants are liable
for Permit violations.

B. Extrinsic Considerations

    Although we believe the plain language of the Permit
clearly contemplates that the County Defendants’ monitoring
data will be used to assess Permit compliance (i.e., establish
liability for CWA violations), we note that numerous
extrinsic considerations also undercut the County Defendants’
position.

    First and foremost, the Clean Water Act requires every
NPDES permittee to monitor its discharges into the navigable
waters of the United States in a manner sufficient to
determine whether it is in compliance with the relevant
NPDES permit. 33 U.S.C. § 1342(a)(2); 40 C.F.R.
§ 122.44(i)(1) (“[E]ach NPDES permit shall include
conditions meeting the following . . . monitoring
requirements . . . to assure compliance with permit
limitations.”). That is, an NPDES permit is unlawful if a
permittee is not required to effectively monitor its permit
             NRDC V. CNTY. OF LOS ANGELES                   27

compliance. See 40 C.F.R. § 122.26(d)(2)(i)(F) (“Permit
applications for discharges from large and medium municipal
storm sewers . . . shall include . . . monitoring procedures
necessary to determine compliance and noncompliance with
permit conditions . . . .”). As previously noted, the County
Defendants contend that the mass–emissions monitoring
program “neither measures nor was designed to measure any
individual permittee’s compliance with the Permit.” But if
the County Defendants are correct, the Permit would be
unlawful under the CWA. We must interpret the provisions
of the Permit like any other contract and reject an
interpretation that would render the Permit unenforceable.
See Walsh v. Schlecht, 429 U.S. 401, 408 (1977) (noting that
“contracts should not be interpreted to render them illegal and
unenforceable where the wording lends itself to a logically
acceptable construction that renders them legal and
enforceable”); see also Nw. Envtl. Advocates, 56 F.3d at 984;
Restatement (Second) of Contracts § 203.

    Second, the County Defendants’ position has been
explicitly rejected by the Regional Board, the entity that
issued the Permit. This is important because one of our
obligations in interpreting an NPDES permit is “to determine
the intent of the permitting authority. . . .” Piney Run Pres.
Ass’n, 268 F.3d at 270. Thus, we give significant weight to
any extrinsic evidence that evinces the permitting authority’s
interpretation of the relevant permit. See Nw. Envtl.
Advocates, 56 F.3d at 985 (relying on “significant evidence
from [the state permitting agency], the permit author,” to
determine the proper scope of an NPDES permit).
28             NRDC V. CNTY. OF LOS ANGELES

    Here, the record contains an amicus brief filed by the
Regional Board in a lawsuit nearly identical to this one.18 In
that suit, these same Plaintiffs sued the City of Malibu, one of
the County Defendants’ co-permittees, for violating the
NPDES Permit at issue in this case. In its brief, the Regional
Board stated its position that:

        The Permit recognizes that the inter-
        connected nature of the system means that it
        may be difficult to determine exactly where
        [pollutants] originated within the [LA] MS4.
        This does not mean, however, that the Permit
        assumes only one permittee may be
        responsible. Instead, it recognizes that in such
        an integrated storm sewer system, one or more
        Permittees may have caused or contributed to
        violations. . . . Having constructed a joint
        sewer system that, by design, co-mingles the
        [Permittees’] discharges, they cannot avoid
        enforcement because one cannot determine
        the original source of pollutants in the waste
        stream.

    The Regional Board also noted that “the monitoring
program that the permittees requested (and were granted)
does not readily generate the permittee–by–permittee outfall
data that the [County Defendants] would require as a
precondition to enforcement.” As a result, the Regional
Board disagreed with any construction of the Permit that
would require individualized proof of a Permittees’
discharges in order to establish liability. Simply put, the

  18
     Santa Monica Baykeeper, et al. v. City of Malibu, No. CV-08-01465
(AHM) (C.D. Cal. Mar. 3, 2008).
               NRDC V. CNTY. OF LOS ANGELES                         29

Regional Board indicated that it “does not agree” that the
“burden [of proving Permit violations] rests upon the
enforcing entity.” Although we do not defer to the Regional
Board’s interpretation of the Permit, see Orthopaedic Hosp.
v. Belshe, 103 F.3d 1491, 1495 (9th Cir. 1997), its rejection
of the County Defendants’ position is clearly instructive.

    Finally, the County Defendants’ arguments run counter to
the purposes of the CWA, and ignore the inherent complexity
of ensuring an ms4’s compliance with an NPDES permit that
covers thousands of different point sources and outfalls. As
we have previously recognized, “[t]he NPDES program
fundamentally relies on self-monitoring.” Sierra Club v.
Union Oil Co. of Cal., 813 F.2d 1480, 1491 (9th Cir. 1987),
vacated and remanded on other grounds, 485 U.S. 931
(1988), and reinstated and amended by 853 F.2d 667 (9th Cir.
1988). Congress’ purpose in adopting this self-monitoring
mechanism was to promote straightforward enforcement of
the Act. See id. at 1492 (noting that Congress wished to
“avoid the necessity of lengthy fact finding, investigations,
and negotiations at the time of enforcement. Enforcement of
violations of requirements under this Act should be based on
relatively narrow fact situations requiring a minimum of
discretionary decision making or delay”) (quoting S. Rep. No.
92–414, 92nd Cong., 1st Sess. 64, reprinted in 1972 U.S.
Code Cong. & Ad. News 3668, 3730)).19 Or, as one treatise
writer has described enforcement of the Act:

        The CWA is viewed by many as the easiest of
        the federal environmental statutes to enforce.
        This is because persons regulated under the

   19
      See also 44 Fed. Reg. 32,854, 32,863 (June 7, 1979) (“Congress
intended that prosecution for permit violations be swift and simple.”).
30           NRDC V. CNTY. OF LOS ANGELES

       act normally must report their own
       compliance and noncompliance to the
       regulating agency. For example, holders of
       NPDES permits must file periodic discharge
       monitoring reports (or DMRs), which must
       contain the results of all monitoring of
       discharges, and must indicate where those
       discharges exceed permit limitations. . . .
       Thus, enforcement actions may be brought
       based on little, if anything, more than the
       DMRs and other reports submitted by the
       permittee itself.

Environmental Law Handbook at 357–58.

    Admittedly, regulating pollution from ms4s is
substantially more complicated than regulating pollution from
a few defined point sources. Like the LA MS4 at issue here,
municipal separate storm sewer systems often cover many
square miles and comprise numerous, geographically
scattered, and sometimes uncharted sources of pollution,
including streets, catch basins, gutters, man-made channels,
and storm drains. Faced with the difficult task of regulating
millions of storm-sewer point sources, Congress amended the
CWA in 1987 to grant the EPA the express authority to create
a separate permitting program for ms4s. 33 U.S.C.
§ 1342(p)(2), (3). In enacting these amendments, Congress
recognized that for large urban areas like Los Angeles, ms4
permitting cannot be accomplished on a source-by-source
basis. The amendments therefore give the EPA, or a state
like California to which the EPA has delegated permitting
authority, broad discretion to issue permits “on a system-wide
or jurisdiction-wide basis,” 40 C.F.R. § 122.26(a)(1)(v),
rather than requiring cities and counties to obtain separate
                NRDC V. CNTY. OF LOS ANGELES                           31

permits for millions of individual stormwater discharge
points. This increased flexibility is crucial in easing the
burden of issuing stormwater permits for both permitting
authorities and permittees.20

    But while otherwise more flexible than the traditional
NPDES permitting system, nothing in the ms4 permitting
scheme relieves permittees of the obligation to monitor their
compliance with their NPDES permit in some fashion. See
33 U.S.C. § 1342(a)(2) (“The Administrator shall prescribe
conditions for [NPDES] permits to assure compliance with
the requirements of [the permit], including conditions on data
and information collection, reporting, and such other
requirements as he deems appropriate.”); 40 C.F.R.
§ 122.44(i)(1) (establishing that every permit “shall include”
monitoring “[t]o assure compliance with the permit
limitations”). Rather, EPA regulations make clear that while
ms4 NPDES permits need not require monitoring of each
stormwater source at the precise point of discharge, they may
instead establish a monitoring scheme “sufficient to yield
data which are representative of the monitored activity. . . .”
40 C.F.R. § 122.48(b) (emphasis added). In fact, EPA
regulations require permittees, like the County Defendants
here, to propose a “monitoring program for representative
data collection for the term of the permit that describes the
location of outfalls or field screening points to be sampled (or
the location of instream stations)” and explain “why the

 20
    See 55 Fed. Reg. 47,990, 48,046 (Nov. 16, 1990) (noting that issuing
individual permits to cover all ms4 discharges to the waters of the United
States is “unmanageable”); id. at 48,049–48,050 (“Given the complex,
variable nature of storm water discharges from municipal systems, EPA
favors a permit scheme where the . . . [p]ermit writers have the necessary
flexibility to develop monitoring requirements that more accurately reflect
the true nature of highly variable and complex discharges.”).
32              NRDC V. CNTY. OF LOS ANGELES

[chosen] location is representative. . . .” 40 C.F.R.
§ 122.26(d)(2)(iii)(D) (emphases added). Here, the County
Defendants did just that. County Defendants themselves
chose the locations of the Monitoring Stations, locations that
are downstream from a significant number of their outfalls.21
And, as required by law, the County Defendants chose
locations that they certified were necessarily “representative”
of the monitored activity (i.e., the Permittees’ discharges of
stormwater runoff into the navigable waters of the United
States).22 Now, however, County Defendants claim that their
compliance with the Permit cannot be measured using the
results of the representative monitoring they themselves
agreed to, that the Regional Board approved, and that the
Permit itself contemplates is to be used to assess compliance
with its terms. We take this opportunity to reevaluate and
reject County Defendants’ arguments.

                          CONCLUSION

  Because the results of County Defendants’ pollution
monitoring conclusively demonstrate that pollution levels in

      21
     “Q: Does the County’s ms4 outlet to any tributaries of the Los
Angeles River? A: Yes. Q: Does it outlet to tributaries of the Los
Angeles River upstream of the mass emissions station? A: Yes. . . . Q:
Does [the County’s ms4] outlet to the San Gabriel River upstream of the
mass emissions station? A: Yes.” Pestrella Dep. 697:7–698:6, June 2,
2009.
 22
    “Q: Who selected the location of those stations, do you know? A: The
County selected those locations for a particular purpose. And the purpose
was [to be] far enough away from tidal influence so that you would be
characterizing the stormwater runoff as opposed to ocean waters. Q: And
the locations were then approved by Regional Board staff; is that correct?
A: Correct.” Wamikannu Dep. 130:13–130:19, July 1, 2009 (emphasis
added).
             NRDC V. CNTY. OF LOS ANGELES                  33

the Los Angeles and San Gabriel Rivers are in excess of those
allowed under the Permit, the County Defendants are liable
for Permit violations as a matter of law. This case is
remanded to the district court for further proceedings
consistent with this opinion, including a determination of the
appropriate remedy for the County Defendants’ violations.

   REVERSED and REMANDED.
34   NRDC V. CNTY. OF LOS ANGELES




            APPENDICES
Appendix A
Appendix B
