City of Pomona v. Sqm North America Corp. ( 2017 )


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  •                 FOR PUBLICATION
    UNITED STATES COURT OF APPEALS
    FOR THE NINTH CIRCUIT
    CITY OF POMONA,                          No. 15-56062
    Plaintiff-Appellant,
    D.C. No.
    v.                     2:11-cv-00167-
    RGK-VBK
    SQM NORTH AMERICA
    CORPORATION,
    Defendant-Appellee.           OPINION
    Appeal from the United States District Court
    for the Central District of California
    R. Gary Klausner, District Judge, Presiding
    Argued and Submitted May 10, 2017
    Pasadena, California
    Filed August 7, 2017
    Before: J. Clifford Wallace, Morgan Christen,
    and Paul J. Watford, Circuit Judges.
    Opinion by Judge Wallace
    2        CITY OF POMONA V. SQM NORTH AMERICA
    SUMMARY*
    Expert Testimony
    The panel vacated the district court’s judgment, which
    found that SQM North America Corporation was not liable
    for causing perchlorate contamination in the City of
    Pomona’s water system, and held that the district court
    abused its discretion by limiting the testimony of one of the
    City’s experts and failing to make sufficient findings before
    admitting the testimony of one of SQM’s experts.
    Dr. Neil Sturchio developed a methodology for collecting
    and analyzing perchlorate isotopes from groundwater, and he
    concluded that most of the perchlorate in the City’s water had
    come from the Atacama Desert in Chile. The City filed this
    products-liability action, alleging that SQM’s importation of
    perchlorate-containing fertilizer products from the Atacama
    Desert caused the contamination in the City’s water supply.
    First, the panel addressed the district court’s denial of the
    City’s motion to update Dr. Sturchio’s report, which resulted
    in the exclusion of any testimony regarding post-2011
    developments in Dr. Sturchio’s research. The panel held that
    in denying the City’s motion, the district court identified the
    correct legal standard. The panel held, however, that the
    district court applied the legal standard in an “illogical”
    manner, and thus committed an abuse of discretion. The
    panel further held that the district court’s exclusion of Dr.
    Sturchio’s testimony was prejudicial.
    *
    This summary constitutes no part of the opinion of the court. It has
    been prepared by court staff for the convenience of the reader.
    CITY OF POMONA V. SQM NORTH AMERICA                  3
    Second, the panel considered the district court’s denial
    of the City’s motion to exclude the testimony of SQM’s
    alternative source expert, Dr. Richard Laton, who opined that
    the perchlorate at issue might have flowed from hundreds of
    potential alternative sources other than SQM’s fertilizer. The
    panel held that the manner in which the district court denied
    the City’s Daubert motion as to Dr. Laton constituted an
    abuse of discretion. Specifically, the panel held that the
    district court’s failure to make any findings regarding the
    efficacy of Dr. Laton’s expert opinions constituted an
    abdication of the district court’s gatekeeping role, and was
    necessarily an abuse of discretion. The panel also held that
    based on the circumstances presented by the case, the City
    did enough to preserve its objection. Finally, the panel held
    that the erroneous inclusion of Dr. Laton’s testimony,
    combined with the erroneous partial exclusion of Dr.
    Sturchio’s testimony, was prejudicial.
    On remand, the panel directed the district court to allow
    Dr. Sturchio to update his expert report, and testify to the
    state of stable isotope research up to the present. The panel
    also directed the district court to make findings regarding the
    scientific reliability of Dr. Laton’s proposed opinions, and
    hold a Daubert hearing if deemed necessary.
    COUNSEL
    Susannah Weaver (argued), Donahue & Goldberg LLP,
    Washington, D.C.; Esther L. Klisura, Kathleen S. Kizer, SL
    Environmental Law Group, San Francisco, California; Robert
    S. Chapman, Sauer & Wagner, Los Angeles, California;
    Andrew L. Jared, Assistant City Attorney; Arnold M.
    Alvarez-Glasman, City Attorney; Office of the City Attorney
    4        CITY OF POMONA V. SQM NORTH AMERICA
    of the City of Pomona, Pomona, California; for Plaintiff-
    Appellant.
    R. Gaylord Smith (argued), Lann G. McIntyre, Michael K.
    Johnson, and Malissa Hathaway McKeith, Lewis Brisbois
    Bisgaard & Smith LLP, San Diego, California, for
    Defendant-Appellee.
    Anthony Z. Roisman, Weathersfield, Vermont; Ned
    Miltenberg, National Legal Scholars Law Firm P.C.,
    Washington, D.C.; Kevin J. Madonna, Kennedy & Madonna
    LLP, Hurley, New York; for Amicus Curiae Law Professors
    Stephen A. Saltzburg, Michael M. Martin, and Joëlle Anne
    Moreno.
    OPINION
    WALLACE, Senior Circuit Judge:
    After a seven-day trial, a jury found SQM North America
    Corporation (SQM) not liable for causing perchlorate
    contamination in the City of Pomona’s (Pomona) water
    system. Pomona now appeals from that judgment. We have
    jurisdiction pursuant to 
    28 U.S.C. § 1291
    . We hold that the
    district court abused its discretion by limiting the testimony
    of one of Pomona’s experts and failing to make sufficient
    findings before admitting the testimony of one of SQM’s
    experts. These errors, in combination, were prejudicial.
    Accordingly, we vacate the district court’s judgment and
    remand for a new trial.1
    1
    We resolve two other issues raised by Pomona in a concurrently
    filed memorandum disposition.
    CITY OF POMONA V. SQM NORTH AMERICA                 5
    I.
    Pomona owns and operates a public water system to
    provide its residents with clean drinking water. The State of
    California regulates the quality of that water by imposing
    maximum contaminant levels (MCL), which limit the amount
    of a given chemical that can be present in the water. In 2007,
    California established that the MCL for perchlorate, a
    chemical that interferes with the ability of the thyroid gland
    to produce hormones, would be six parts per billion. Shortly
    thereafter, Pomona discovered that fourteen of its wells
    possessed perchlorate levels in excess of the MCL. In
    response, Pomona shut down non-compliant wells, purchased
    water from other sources, and took other steps to remedy the
    perchlorate contamination in its drinking water.
    In 2010, Pomona filed this products-liability action
    against SQM. SQM began importing fertilizer from the
    Atacama Desert in Chile in 1927, and from 1931 to 1968
    imported a substantial portion of the Chilean nitrate (a
    component of that fertilizer) brought from Chile into the
    United States. The theory of Pomona’s case is that SQM’s
    importation of perchlorate-containing fertilizer products from
    the Atacama Desert, which were used in areas around
    Pomona’s wells, caused the contamination in Pomona’s water
    supply. Thus, Pomona sought to recover over $32 million in
    past and future costs associated with investigating and
    remediating the perchlorate contamination.
    The case progressed towards a January 2012 trial date.
    Unsurprisingly, the case involved several scientific experts,
    as the key dispute centered around whether the perchlorate
    from SQM’s fertilizer had migrated into Pomona’s wells and
    caused the contamination present in Pomona’s water system.
    6        CITY OF POMONA V. SQM NORTH AMERICA
    Five days before trial, the district court conducted a Daubert
    hearing to consider whether the testimony of Pomona’s expert
    witness, Dr. Neil Sturchio, should be excluded. Dr. Sturchio,
    who was then the Head of the Department of Earth and
    Environmental Sciences at the University of Illinois at
    Chicago,2 had developed a peer-reviewed methodology for
    collecting and analyzing perchlorate isotopes from
    groundwater. Dr. Sturchio’s research concluded that
    perchlorate from the Atacama Desert in Chile has a distinct
    isotopic fingerprint. Thus, by analyzing the chlorine and
    oxygen isotopes taken from Pomona’s wells, Dr. Sturchio
    determined that roughly ninety percent of the perchlorate
    present in Pomona’s groundwater matched the isotopic
    fingerprint of perchlorate unique to the Atacama Desert. Put
    simply, Dr. Sturchio concluded that most of the perchlorate
    in Pomona’s water had come from the Atacama Desert.
    Four days before trial was to begin, the district court
    granted SQM’s motion to exclude Dr. Sturchio’s testimony.
    In a one half-page minute order, the district court held that
    Dr. Sturchio’s opinions had “not been generally accepted by
    the scientific community,” had “not been tested by other
    laboratories,” and that “Dr. Sturchio’s reference database
    [was] too limited.” As Dr. Sturchio was one of Pomona’s key
    witnesses, the parties stipulated to dismiss the case and
    allowed Pomona to appeal the exclusion of his testimony.
    We reversed the district court’s exclusion of Dr.
    Sturchio’s expert testimony. City of Pomona v. SQM North
    America Corp., 
    750 F.3d 1036
     (9th Cir. 2014) (Pomona I).
    We held that the “district court’s ruling [was] unpersuasive
    2
    Dr. Sturchio is now the Chair of the Department of Geological
    Sciences at the University of Delaware.
    CITY OF POMONA V. SQM NORTH AMERICA                   7
    because both grounds for exclusion [were] without adequate
    support in the record.” 
    Id. at 1047
    . Accordingly, we
    remanded the case for trial. The mandate from our court
    issued in December 2014.
    Upon remand, the district court ordered a status
    conference for January 12, 2015. At that conference, Pomona
    requested to reopen fact and expert discovery to reflect
    scientific developments that had been advanced during the
    three years in which the case was on appeal. The district court
    requested that Pomona file a written motion to reopen
    discovery and set trial to begin June 2, 2015, less than five
    months from the date of the first post-remand status
    conference.
    On February 9, 2015, Pomona filed its formal motion to
    reopen discovery. As to Dr. Sturchio, Pomona requested
    leave to supplement his expert report to reflect additional data
    concerning isotopic analysis of perchlorate that had been
    developed while the appeal had been pending. The motion
    contained a sworn declaration from Dr. Sturchio, in which he
    described the new developments in the science of isotopic
    analysis of perchlorate. Dr. Sturchio and other scientists had
    conducted new interlaboratory comparisons and the database
    sizes for their research had increased, which buttressed Dr.
    Sturchio’s conclusions and repelled the main criticisms of his
    research. On March 26, 2015, the district court denied
    Pomona’s motion to supplement Dr. Sturchio’s report. The
    district court concluded that Pomona failed to demonstrate
    that the information was material and determined that
    updating Dr. Sturchio’s report would “create back-and-forth
    discovery, which could delay trial.”
    8       CITY OF POMONA V. SQM NORTH AMERICA
    The case proceeded towards the June 2, 2015, trial date.
    Still pending, however, were the parties’ motions in limine,
    which had been filed in 2011, before the original trial date. At
    that juncture, before the case made its first trip through our
    court, the district court had issued tentative rulings on the
    motions in limine. On May 29, 2015, four days before trial,
    the district court issued new rulings on the parties’ motions in
    limine. Relevant for our purposes is the district court’s ruling
    on Pomona’s motion to exclude the testimony of SQM’s
    expert, Dr. Richard Laton. Dr. Laton’s proffered testimony
    contended that the perchlorate contamination present in
    Pomona’s water system could have come from hundreds of
    alternative sources other than SQM’s importation of fertilizer
    from the Atacama Desert. For example, Dr. Laton opined that
    the perchlorate in Pomona’s water system could have come
    from “household bleach,” “swimming pools,” “septic tanks,”
    “photographic flash powder,” or even “fireworks.” Pomona’s
    motion asserted that Dr. Laton’s testimony was unreliable
    under the standard set forth in Daubert v. Merrell Dow
    Pharmaceuticals, Inc., 
    509 U.S. 579
     (1993). Before the first
    appeal, the district court denied Pomona’s Daubert motion as
    to Dr. Laton, without explanation, in a ruling that was
    explicitly labeled as tentative. The district court’s May 29,
    2015, ruling on Pomona’s motion to exclude Dr. Laton did
    not include any analysis.
    At trial, Dr. Sturchio testified to the circumstances as they
    existed in 2011. As the district court had denied Pomona’s
    motion to update Dr. Sturchio’s expert report, he was
    prohibited from testifying about the significant scientific
    progress that had taken place while the case had been on
    appeal. Furthermore, Dr. Laton testified that the perchlorate
    contamination could have arisen from many potential sources.
    After seven days of testimony and argument, the jury returned
    CITY OF POMONA V. SQM NORTH AMERICA                    9
    its verdict, finding that SQM’s sodium nitrate fertilizer was
    not a substantial factor in causing harm to Pomona—a
    complete defense verdict in favor of SQM.
    This appeal followed, in which Pomona challenges the
    district court’s denial of its motion to update Dr. Sturchio’s
    expert report, which resulted in the exclusion of testimony
    regarding new scientific developments. Pomona also
    challenges the district court’s denial of its motion to exclude
    Dr. Laton’s testimony.
    II.
    “We review evidentiary rulings for abuse of discretion
    and reverse if the exercise of discretion is both erroneous and
    prejudicial.” Pomona I, 750 F.3d at 1043. Furthermore, “[t]he
    district court is given broad discretion in supervising the
    pretrial phase of litigation, and its decisions regarding the
    preclusive effect of a pretrial order . . . will not be disturbed
    unless they evidence a clear abuse of discretion.” Johnson v.
    Mammoth Recreations, Inc., 
    975 F.2d 604
    , 607 (9th Cir.
    1992) (second alteration in original) (citation and internal
    quotation marks omitted).
    “[T]he first step of our abuse of discretion test is to
    determine de novo whether the trial court identified the
    correct legal rule to apply to the relief requested.” United
    States v. Hinkson, 
    585 F.3d 1247
    , 1261–62 (9th Cir. 2009)
    (en banc). “[T]he second step of our abuse of discretion test
    is to determine whether the trial court’s application of the
    correct legal standard was (1) illogical, (2) implausible, or
    (3) without support in inferences that may be drawn from the
    facts in the record.” 
    Id. at 1262
     (citations and internal
    quotation marks omitted).
    10      CITY OF POMONA V. SQM NORTH AMERICA
    III.
    A.
    First, we turn to the district court’s denial of Pomona’s
    motion to update Dr. Sturchio’s report, which resulted in the
    exclusion of any testimony regarding post-2011
    developments in Dr. Sturchio’s research.
    In his 2011 expert report, Dr. Sturchio concluded that a
    substantial majority of the perchlorate in Pomona’s water
    system had come from the Atacama Desert in Chile. The
    strongest criticisms of Dr. Sturchio’s 2011 report were that
    the reference database he used was too small, and, that when
    the 2011 report was composed, Dr. Sturchio’s specific
    method had not been tested widely and confirmed by other
    laboratories. Thus, upon remand in 2015, Pomona moved to
    update Dr. Sturchio’s expert report, so his testimony would
    reflect the current state of knowledge in the scientific
    community in these areas. Pomona’s motion included a sworn
    declaration from Dr. Sturchio, in which he described the
    developments that had taken place. Dr. Sturchio explained
    that “a number of laboratories, other than [his] own, have
    continued to engage in perchlorate isotopic analysis,”
    resulting in “additional interlaboratory comparisons that fully
    verify the methods used and the results obtained in [his]
    previous research.” Moreover, by 2015, “the database for
    natural perchlorate samples [had] become larger, and
    [included] samples from other locations across the US and
    around the world.”
    Despite these relevant scientific developments, the district
    court denied Pomona’s motion to reopen discovery and
    update Dr. Sturchio’s expert report, thus limiting his trial
    CITY OF POMONA V. SQM NORTH AMERICA                   11
    testimony to the scientific world as it existed in 2011. The
    district court’s three-sentence analysis of the issue provided
    two reasons for prohibiting Dr. Sturchio from updating his
    report, and thus testifying at trial to the then-current state of
    stable isotope research. First, the district court concluded that
    allowing Dr. Sturchio to update his report might “create back-
    and-forth discovery, which could delay trial.” Second, the
    district court determined that the updates to Dr. Sturchio’s
    report were not material.
    When ruling on a motion to amend a Rule 16 scheduling
    order to reopen discovery, we instruct district courts to
    consider the following factors:
    1) whether trial is imminent, 2) whether the
    request is opposed, 3) whether the non-
    moving party would be prejudiced, 4) whether
    the moving party was diligent in obtaining
    discovery within the guidelines established by
    the court, 5) the foreseeability of the need for
    additional discovery in light of the time
    allowed for discovery by the district court,
    and 6) the likelihood that the discovery will
    lead to relevant evidence.
    United States ex rel. Schumer v. Hughes Aircraft Co., 
    63 F.3d 1512
    , 1526 (9th Cir. 1995) (citation omitted), vacated on
    other grounds, 
    520 U.S. 939
     (1997).
    In denying Pomona’s motion, the district court identified
    the correct legal standard, which satisfies the first step of our
    abuse of discretion test. Hinkson, 
    585 F.3d at
    1261–62. We
    hold, however, that the district court applied that legal
    standard in an “illogical” manner, thus committing an abuse
    12      CITY OF POMONA V. SQM NORTH AMERICA
    of discretion. 
    Id. at 1262
    . As to the first reason the district
    court provided, any potential for the updated expert report to
    delay trial was of the district court’s own making. Upon
    remand, the district court set a June trial date at the initial
    status conference, following which Pomona promptly filed its
    motion to reopen discovery. By the time the district court
    ruled on the motion, roughly two months before trial,
    reopening discovery would likely have caused delay. Any
    potential delay, however, was brought about by the
    combination of an expeditious trial date and the amount of
    time Pomona’s motion sat undecided. The problem was not
    the result of a lack of diligence by Pomona.
    The district court’s second proffered reason for denying
    the motion, lack of materiality, was also illogical. SQM has
    acknowledged that “Sturchio was Pomona’s key witness, and
    much of the case involved his forensic methods.” As such, the
    level of support for his conclusions was critical and it was
    important that his proffered testimony be accurate and reflect
    the current state of knowledge in the scientific community.
    The main attack on Dr. Sturchio’s testimony (as it stood in
    2011) was that it had not been reproduced by other
    laboratories and that his reference database was too small.
    The proffered updates to Dr. Sturchio’s report directly
    combated those criticisms. Based on Dr. Sturchio’s sworn
    declaration (which accompanied Pomona’s motion), and the
    fact that the first appeal focused heavily on Dr. Sturchio’s
    testimony, the district court should have been on notice that
    the updates to Dr. Sturchio’s report were material.
    In defense of the district court’s decision, SQM argues
    that Pomona was not diligent. Primarily, SQM asserts that
    Pomona should have updated Dr. Sturchio’s report, and
    should have moved to do so, in May 2014, after we decided
    CITY OF POMONA V. SQM NORTH AMERICA                 13
    Pomona I. Thus, by making its motion in February 2015,
    Pomona waited too long. But in May 2014, the appeal was
    still alive, a certiorari petition was pending, and the mandate
    had not issued. Pomona moved promptly once the case
    returned to the district court.
    SQM also asserts that Pomona lacked diligence because
    it did not provide SQM with Dr. Sturchio’s full updated
    expert report until eleven days before trial. This argument is
    irrelevant. By that time, the district court had already issued
    a firm ruling denying Pomona’s motion to update Dr.
    Sturchio’s report. Although the record would have been more
    complete had Pomona included the updated report with its
    February 2015 motion, Dr. Sturchio’s declaration, attached to
    the motion, was sufficient to put the district court and SQM
    on notice of what the updated expert report would say.
    SQM’s attempt to shift the relevant date to eleven days before
    trial, rather than when Pomona filed its motion four months
    before trial, has not convinced us.
    SQM further argues that the updates Pomona sought to
    include in Dr. Sturchio’s expert report were immaterial. In
    doing so, SQM asserts, as the district court did, that the
    updates were cumulative, did not change Dr. Sturchio’s
    conclusions, and merely buttressed his previously-expressed
    opinion. We disagree. As expressed above, the parties knew
    Dr. Sturchio’s causation analysis would be a key factor at
    trial. Thus, the degree of support for his conclusions was
    critical and the updates Pomona sought were material.
    B.
    Having determined that the district court’s exclusion of
    Dr. Sturchio’s testimony regarding post-2011 developments
    14      CITY OF POMONA V. SQM NORTH AMERICA
    was erroneous, we now must resolve whether that error was
    prejudicial. “[A] showing of prejudice is required for
    reversal.” Ollier v. Sweetwater Union High Sch. Dist.,
    
    768 F.3d 843
    , 859 (9th Cir. 2014). Here, we hold that the
    exclusion of Dr. Sturchio’s testimony regarding post-2011
    developments, combined with the erroneous inclusion of Dr.
    Laton’s expert testimony (as discussed in Section IV), more
    probably than not affected the verdict and was thus
    prejudicial.
    After presentation of the evidence at trial, but before the
    jury had rendered its verdict, the district court described the
    trial as “a battle of the experts.” In keeping with this theme,
    SQM sought to discredit Dr. Sturchio, who it recognized
    “was Pomona’s key witness.” For example, SQM elicited the
    following testimony from its geochemical expert, Dr. Ramon
    Aravena, regarding Dr. Sturchio’s conclusions:
    [T]he two main criticism[s] that I have on Dr.
    Sturchio[’s] research. One is that it’s the
    failure to reproduce his method and result by
    other laboratories. And second is – basically
    is the failure to have basically a complete
    database for interpretation of the data for the
    sources of perchlorate.
    *       *       *
    Q: In your prior chart where you had the two
    critiques of Dr. Sturchio’s method, the second
    one was failure to assemble a complete
    isotope database for sources of perchlorate.
    Do you have an opinion as to whether Dr.
    CITY OF POMONA V. SQM NORTH AMERICA                  15
    Sturchio’s interpretation of the isotopic data
    that he has developed is reasonable?
    A: I have an opinion.
    Q: What is your opinion, sir?
    A: My opinion is that the database is
    incomplete.
    Furthermore, during its closing argument to the jury, SQM
    asserted the following, regarding the scientific support for Dr.
    Sturchio’s conclusions:
    [Dr. Sturchio] also admitted his is the one and
    the only laboratory to do his technique. Now,
    I saw a big false sign next to my statement in
    my opening statement where I said that he
    was the one and only lab. Well, I didn’t make
    that up, folks. That comes from Dr. Sturchio.
    *        *       *
    Isotope ratios don’t give you a unique
    fingerprint. What they give you is a range of
    values, and those range of values are not
    unique from one place to one place or even
    within one place. It is so important to have a
    complete comparison database, and that’s
    where Sturchio has dragged his feet. He says
    there’s only 16 samples from Chile. An area
    of the Atacama desert, a vast area, 16 samples
    doesn’t even tell us where those samples were
    taken from in Chile. And not one independent
    16      CITY OF POMONA V. SQM NORTH AMERICA
    lab has analyzed the isotopic signature or
    composition of those samples. You only have
    four samples from all of California.
    *       *       *
    Because Pomona is presenting weaker
    evidence when they had it in their power to
    present stronger evidence, you should
    disregard Dr. Sturchio.
    These criticisms of Dr. Sturchio were accurate in 2011. By
    2015, however, these characterizations of Dr. Sturchio’s
    research were false, and counsel making them had to know
    they were false, based on the evidence SQM successfully kept
    from the jury. By the time of trial, Dr. Sturchio, along with
    other scientists, had amassed 50 samples from the Atacama
    Desert, 55 samples of naturally occurring perchlorate from
    other locations, and 79 samples of synthetic perchlorate. Had
    the district court allowed Dr. Sturchio to update his
    testimony, Pomona could have easily rebutted much of
    SQM’s criticism of his research during trial. Given that Dr.
    Sturchio was Pomona’s “key witness,” that his credibility and
    the level of support for his conclusions was paramount, and
    that SQM attacked directly the level of support as it existed
    in 2011, we conclude that the district court’s refusal to allow
    Dr. Sturchio to testify to scientific developments occurring
    between 2011 and 2015 was prejudicial.
    In response, SQM’s main argument is that even if the
    district court committed error, any such error was harmless.
    Put simply, SQM asserts that even if the jury agreed with Dr.
    Sturchio’s conclusions, it could still have reasonably found
    that SQM did not cause the perchlorate contamination in
    CITY OF POMONA V. SQM NORTH AMERICA                   17
    Pomona’s water system. The record shows that from 1931 to
    1968, SQM imported a substantial portion of the sodium
    nitrate brought from Chile to the United States. Other
    companies, however, imported Chilean nitrate before 1931.
    Accordingly, as Dr. Sturchio conceded that he could not age
    date the perchlorate found in Pomona’s wells, the perchlorate,
    even if it had come from Chile, could have been imported by
    an entity other than SQM. This argument is buttressed, SQM
    argues, by the fact that some of the well sites below the
    historic orchards in the well capture zone tested non-detect
    for perchlorate. Had SQM’s fertilizer (which was originally
    used in the orchards) been the cause of contamination, those
    sites should have tested positive for perchlorate
    contamination.
    But the jury did not need to find that all of the perchlorate
    found in Pomona’s water system came from SQM. Rather,
    the jury instructions asked whether SQM’s importation of
    fertilizer was a “substantial factor in causing” the
    contamination, which the jury instructions defined as “more
    than a remote or trivial factor.” Dr. Sturchio’s ultimate
    conclusion was that ninety percent of the perchlorate
    contamination found in Pomona’s wells came from the
    Atacama Desert in Chile. The record further shows that from
    1931 to 1968, SQM imported substantially all of the Chilean
    nitrate coming into the United States, and imported especially
    large amounts during 1941 and 1942. Taking these facts into
    account, along with the erroneous inclusion of Dr. Laton’s
    testimony (described below), we conclude that the preclusion
    of Dr. Sturchio’s updated report and testimony more probably
    than not affected the verdict. Thus, the exclusion of Dr.
    Sturchio’s testimony regarding post-2011 scientific
    developments was prejudicial.
    18      CITY OF POMONA V. SQM NORTH AMERICA
    IV.
    A.
    Next, we turn to the district court’s denial of Pomona’s
    motion to exclude the testimony of SQM’s alternative source
    expert, Dr. Richard Laton. Dr. Laton opined that the
    perchlorate at issue might have flowed from hundreds of
    potential alternative sources other than SQM’s fertilizer.
    Pomona first moved to exclude Dr. Laton’s testimony under
    Daubert before the scheduled 2012 trial. The district court
    denied this motion in what was explicitly a “tentative” one-
    sentence ruling. On remand, Pomona again challenged Dr.
    Laton under Daubert. Pomona argued that Dr. Laton’s
    proffered testimony failed to show any scientifically valid
    grounds for asserting that any of his alternative sources
    contained the specific type of perchlorate actually found in
    Pomona’s groundwater. In a one-word ruling on Pomona’s
    2015 Daubert motion, the district court stated “DENY.” Dr.
    Laton proceeded to testify at the 2015 trial.
    The manner in which the district court denied the Daubert
    motion as to Dr. Laton constituted an abuse of discretion. In
    Estate of Barabin v. AstenJohnson, Inc., 
    740 F.3d 457
     (9th
    Cir. 2014) (en banc), we held the district court had abdicated
    its gatekeeping authority, in denying a Daubert motion,
    because “[a]bsent from the explanation is any indication that
    the district court assessed, or made findings regarding, the
    scientific validity or methodology of [the expert’s] proposed
    testimony. Therefore, the district court failed to assume its
    role as gatekeeper with respect to [the expert’s] testimony.”
    
    Id. at 464
    . Furthermore, in Pyramid Technologies, Inc. v.
    Hartford Casualty Insurance Co., 
    752 F.3d 807
     (9th Cir.
    2014), we held that a district court abuses its discretion when
    CITY OF POMONA V. SQM NORTH AMERICA                 19
    it fails to provide any “analysis or explanation” for its
    decision regarding expert testimony under Daubert. 
    Id. at 814
    . In Pyramid, the district court abused its discretion by
    denying a Daubert motion “[i]n two conclusory sentences and
    without analysis or explanation.” 
    Id.
    So too here. The district court denied Pomona’s Daubert
    motion as to Dr. Laton with a one-word “DENY.” Under the
    standard we set in Estate of Barabin and Pyramid, the failure
    to make any findings regarding the efficacy of Dr. Laton’s
    expert opinions constituted an abdication of the district
    court’s gatekeeping role, and necessarily an abuse of
    discretion.
    SQM’s main argument in response is that Pomona waived
    its right to appeal the denial of its Daubert motion. Under
    Federal Rule of Evidence 103(b), “[o]nce the court rules
    definitively on the record—either before or at trial—a party
    need not renew an objection or offer of proof to preserve a
    claim of error for appeal.” Here, SQM argues that by failing
    to appeal the district court’s tentative ruling in 2011, which
    denied the Daubert motion as to Dr. Laton, Pomona waived
    any right to appeal the district court’s 2015 ruling. We
    disagree. The district court’s 2011 ruling was explicitly
    tentative, and thus not definitive within the meaning of Rule
    103. During the 2011 pretrial conference, in which the district
    court made oral rulings, the district court stressed several
    times that its rulings were tentative. Furthermore, the minute
    order expressing the motion in limine rulings stated the
    rulings were all “tentative.” “[I]n order to appeal an issue on
    which the district court ruled in limine, a party must first
    receive a final ruling on the issue.” Adkins v. Mireles,
    
    526 F.3d 531
    , 542 (9th Cir. 2008). Thus, Pomona could not
    have appealed the original tentative ruling.
    20      CITY OF POMONA V. SQM NORTH AMERICA
    Next, SQM argues that Pomona waived its right to appeal
    because it did not object to Dr. Laton’s testimony at the 2015
    trial. Unlike the 2011 ruling, however, the district court’s
    2015 “DENY” ruling did not contain the tentative label in the
    minute order. Instead, the “tentative” heading on the district
    court’s motion in limine rulings was conspicuously omitted.
    On the first day of trial, the district court stated as follows
    regarding its written rulings on the parties’ motions in limine:
    As to motions in limine, I think they’re pretty
    clearly stated on my findings that I sent
    you. . . . [M]otions in limine almost always
    deal with evidentiary issues, evidentiary
    issues that come up during the trial. Any
    ruling on a motion in limine may or may not
    be revisited as the evidence comes in. It may
    or may not change, but these are the rulings
    until and unless the Court decides that it can
    come in. Some evidence may come up that
    may make something relevant that the Court
    had determined that up until the time that that
    comes in is not relevant. So all I’m telling you
    is, is that they’re quasi tentative, depending on
    how the evidence comes in.
    Thus, SQM’s only relevant argument is that the district
    court’s statement, that its in limine rulings were “quasi
    tentative,” meant that Pomona was required to object to Dr.
    Laton’s testimony during trial to preserve its right to appeal,
    which Pomona did not do explicitly.
    Pretrial motions, such as motions in limine, “are useful
    tools to resolve issues which would otherwise clutter up the
    trial.” Palmerin v. City of Riverside, 
    794 F.2d 1409
    , 1413 (9th
    CITY OF POMONA V. SQM NORTH AMERICA                    21
    Cir. 1986) (internal quotation marks omitted). Furthermore,
    “a ruling on a motion in limine is essentially a preliminary
    opinion that falls entirely within the discretion of the district
    court. The district court may change its ruling at trial because
    testimony may bring facts to the district court’s attention that
    it did not anticipate at the time of its initial ruling.” United
    States v. Bensimon, 
    172 F.3d 1121
    , 1127 (9th Cir. 1999)
    (emphasis added) (internal citation omitted). “Still, parties
    expect a district court to adhere to its earlier ruling if no facts
    or circumstances arise to warrant a reversal.” 
    Id.
     When a
    district court makes a pretrial ruling on a motion in limine
    that is subject to limitations regarding how the evidence
    actually comes in, and if the testimony “stay[s] within [those]
    parameters,” then “no additional objection [is] necessary.”
    Mukhtar v. Cal. State Univ., Hayward, 
    299 F.3d 1053
    , 1063
    (9th Cir. 2002), overruled in part on other grounds by Estate
    of Barabin, 740 F.3d at 467.
    Our reading of the district court’s statement on the first
    day of trial, quoted above, is that it was merely reiterating
    what we said in Bensimon—that a district court may change
    an in limine ruling at trial if facts or circumstances arise to
    warrant the change. The district court had denied the Daubert
    motion as to Dr. Laton in a written ruling without any
    tentative heading. As trial progressed, before Dr. Laton’s
    testimony, the district court had denied objections, making
    clear that it was “not going to argue with you in front of the
    jury” and later, that “we do not argue objections in front of
    the jury.” By the time Dr. Laton rose to testify, no facts or
    circumstances had arisen that would have warranted reversal
    of the district court’s pretrial ruling. In fact, during Dr.
    Laton’s testimony, Pomona’s counsel asked if it could briefly
    voir dire the witness, which request was quickly denied. By
    making this request, Pomona renewed its challenge to Dr.
    22      CITY OF POMONA V. SQM NORTH AMERICA
    Laton’s testimony concerning alternative sources to
    perchlorate, giving the district court another opportunity to
    rule on the issue. Additionally, Pomona’s counsel tried to
    object to Dr. Laton’s “shotgun” testimony about potential
    sources of perchlorate, but the district court overruled him
    while he was midsentence.
    Thus, we must decide whether Pomona preserved its
    objection to Dr. Laton’s testimony. Without doubt, Pomona
    could have simplified this issue by restating its Daubert
    objection just before Dr. Laton testified, or by raising the
    objection during a recess. Nevertheless, given the importance
    of expert testimony in this case, the fact that the first appeal
    focused on a Daubert issue, and the district court’s focus on
    moving the trial along briskly, Pomona’s hesitation to object
    once more, and risk further irritating the district court, was
    understandable. Accordingly, based on the circumstances
    presented here, we hold that Pomona did enough to preserve
    its objection.
    B.
    Having determined that the district court abdicated its
    gatekeeping role by failing to make any findings of reliability
    as to Dr. Laton, we next must decide whether that error was
    prejudicial. “We treat the erroneous admission of expert
    testimony the same as all other evidentiary errors, by
    subjecting it to harmless error review. We reverse only if the
    error affect[ed] a substantial right of the party. In other
    words, we require a finding of prejudice.” Estate of Barabin,
    740 F.3d at 464 (internal citations and quotation marks
    omitted). Furthermore, “[p]rejudice is at its apex when the
    district court erroneously admits evidence that is critical to
    the proponent’s case.” Id. at 465.
    CITY OF POMONA V. SQM NORTH AMERICA                   23
    Here, there can be no doubt that Dr. Laton’s testimony
    was critical to SQM’s case. Dr. Laton essentially testified
    about all the ways in which the perchlorate contamination
    could have manifested in Pomona’s water system that had
    nothing to do with SQM. Dr. Laton’s testimony undercut
    directly the testimony of Dr. Sturchio, Pomona’s “key
    witness,” as well as Dr. Stephen Wheatcraft, Pomona’s
    hydrology expert, who testified about the manner in which
    the perchlorate flowed from the orchards into Pomona’s water
    system. On direct examination, Dr. Laton testified as follows:
    Q: Did you reach an opinion as to whether the
    City’s experts, Dr. Sturchio, Dr. Wheatcraft,
    conducted a complete environmental
    investigation in Pomona?
    A: No, they did not.
    Q: And what do you base your opinion on?
    A: The reports that I reviewed that were
    submitted on behalf of the City.
    Dr. Laton’s testimony went on with a further attack on Dr.
    Sturchio’s and Dr. Wheatcraft’s conclusions.
    Dr. Laton’s testimony, and that of Dr. Sturchio and Dr.
    Wheatcraft, went to the crux of the case—whether SQM’s
    importation of fertilizer was a substantial factor in causing the
    perchlorate contamination in Pomona’s water system. Dr.
    Laton was a key player in what the district court aptly
    described as “a battle of the experts.” Therefore, the
    erroneous inclusion of Dr. Laton’s testimony, combined with
    24      CITY OF POMONA V. SQM NORTH AMERICA
    the erroneous partial exclusion of Dr. Sturchio’s testimony,
    was prejudicial.
    We do not decide, one way or the other, whether Dr.
    Laton’s proffered opinions satisfy the Daubert standard.
    Rather, we merely hold that the record lacks “any indication
    that the district court assessed, or made findings regarding,
    the scientific validity or methodology of [Dr. Laton’s]
    proposed testimony.” Estate of Barabin, 740 F.3d at 464.
    V.
    We are sympathetic with the district court’s desire to keep
    this case on a fast track. A civil action may meander through
    discovery far too slowly and our system benefits when district
    judges keep the wheels of justice turning by employing
    effective case management. But there are limits. The record
    demonstrates that the science of stable isotope analysis
    evolved significantly during this case’s first journey through
    the appellate system. By constraining Dr. Sturchio to his 2011
    report, the district court abused its discretion. Furthermore,
    the district court’s failure to make any findings regarding the
    reliability of Dr. Laton’s testimony, despite Pomona’s
    Daubert motion, was an abuse of discretion. These errors, in
    combination, were prejudicial.
    Accordingly, the district court’s judgment is vacated and
    this case is remanded for a new trial. On remand, the district
    court shall allow Dr. Sturchio to update his expert report and
    testify to the state of stable isotope research up to the present.
    In addition, the district court shall make findings regarding
    the scientific reliability of Dr. Laton’s proposed opinions, and
    CITY OF POMONA V. SQM NORTH AMERICA                25
    hold a Daubert hearing if the district court determines one is
    necessary.
    VACATED and REMANDED.