Natural Resources Defense Council, Inc. v. County of Los Angeles ( 2013 )


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  •                  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