FOR PUBLICATION

UNITED STATES COURT OF APPEALS

FOR THE NINTH CIRCUIT

CITY OF POMONA,

Plaintiff-Appellant,

v.

SQM NORTH AMERICA

CORPORATION,

Defendant-Appellee.

No. 15-56062

D.C. No.

2:11-cv-00167-

RGK-VBK

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 PlaintiffAppellant.

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,2had 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 manypotential 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

communityin 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 backand-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 nonmoving partywould be prejudiced, 4) whether

the moving party was diligent in obtaining

discoverywithin 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 promptlyfiled 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

theywere 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 “keywitness,” 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 testimonymore 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” onesentence 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 Daubertmotion “[i]n two conclusorysentences 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

discoveryfar 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. Byconstraining 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.