F OR P UBLICATION



### UNIT E D ST AT E S CO URT O F APPE AL S FO R T H E NINT H CIRCUIT

C I T Y O F P O M O

N A , Plaintiff-Appellant
,

v

. SQM N O R

T H A M E R

I C A C O R P O R A T I O N , Defendant-Appellee. N o. 15-56062

D.C. No. 2:11-cv-00167- RGK-VB K

OPI NI ON

Appeal from the United States District Court for the Central District of California R. Gary Klausner, District J udg e, Presiding

Arg ued and Submitted May 10, 2017 Pasadena, California

F iled Aug ust 7, 2017

B efore: J . Clifford W allace, Morg an Christen, and Paul J . W atford, Circuit J udg es.
Opinion by

J udg e W allaceC I T Y O F P O M O N A V

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SUMMARY *

Expert Testim o ny

The panel vacated the district court’s judg ment, which found that SQM North America Corporation was n o t liable f o r causing perchlorate contamination in the City o f Pomona’s water sy stem, and h eld that the district court ab u s e d its discretion by limiting the testimony of one of the City ’ s ex perts and f

ailing to make sufficient finding s b e f o r e admitting the testimony

of one of SQM’s ex perts.

Dr. N eil Sturchio developed a methodolog y for collecting and analy z ing perchlorate isotopes from g roundwater, a nd he concluded that most o f the perchlorate in the City ’s w ater h ad

come from the Atacama Desert in Chile. The City filed this products-liability a c tion, alleg ing that SQM’s importation o f perchlorate-containing fertiliz er products from the Atacama Desert caused the contamination in the City ’s water supply

.

F irst, the p anel a d dressed the district court’s denial of the City ’ s motion to update D r. Sturchio’s report, which resulted in the e x clusion of any testimony reg arding post-2011 developments in Dr. Sturchio’s research. The panel held that in deny ing the City ’s motion, the district court identified the
correct leg al standard. The panel held, however, that the district court applied t h e l eg a l standard in an “illog ical”
manner, and thus committed an abuse of discr e t i o n

. The panel f urther h eld that the district c ourt’s e x clusion of Dr. Sturchio’s testimony was prejudicial.

* T h is su m m ary co n stitu

tes n o p art o f th e o pin io n o f th e co urt. It h as b eenp rep ared b y

co urt staf

f f o r th e co n v en i en ce o f

th e read er.C I T Y O F P O M O N A V

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Second, the p a

n el considered the district court’s denial of the City ’s motion to ex c lude the t e s t i m ony of SQM’s alternative source ex pert, Dr. Richard L aton, who opined that the perchlorate at issue mig ht h ave flowed from hundreds o f potential alternative sources other than SQM’s fertiliz er. The panel held that the manner in which the district court denied the C i ty ’s D aubert motion as to Dr. L aton constituted an abuse of discretion. Specifically
, the p anel held t h a t the district cour t’s failure to make any finding s reg arding the efficacy o f Dr. L aton’s ex pert opinion s c o nstituted an abdication of the district c ourt’s g atekeeping role, a nd was necessarily an abuse of discretion. The p a n el also held that based on the circumstances presented by the case, the City did enoug h to preserve its objection. F inally
, the panel held that the erroneous inclusion of D r. L aton’s testimony
, combined with the e rroneous pa r t i a l ex c lusion of Dr. Sturchio’s testimony
, was prejudicial.

On r emand, the panel directed the dist r i ct c ourt to allow Dr. Sturchio to update h is ex pert report, a n d t estify to the
state of stable isotope r esearch up to the present. The panel also d irected the district court to make finding s reg a rding the scientific reliability of Dr. L aton’s proposed opinions, a nd hold a Daubert

hearing if deemed necessary

.

COUNSEL

Susannah W eaver (arg

ued), Donahue & G oldberg L L P, W a shing ton, D.C.; Esther L

. Klisura
, K a t hleen S. Kiz er, SL Environmental L aw Group, San F ranc i s c o , California; Robert S. Ch a p m a n , Sauer & W ag ner, L o s A ng eles, California; Andrew L

. J ared, Assistant City Attorney ; Arnold M. Alvarez -Glasman, City Attorney ; O ffice of the City AttorneyC I T Y O F P O M O N A V

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of the City o f Pomon a, P o mona, California; for PlaintiffAppellant.

R. Gaylord Smith (arg

u e d )
, L ann G. McI nty

re, Michael K

. J ohnson, and Malissa Hathaway McKe ith, L ewis B risbois B isg a ard & Smith L L P, San Dieg o, California, for Defendant-Appellee.

Anthony Z

. Roisman, W e a t hersfield, Vermont; Ned Mi l t e nberg
, National L eg al Scholars L a w F irm P.C., W a shing ton, D .C.; Kevin J

. Madonna, Kennedy & Madonna L L P, Hurley
, New York; for Amicus Curiae L a w Professors Stephen A. Saltz burg
, Michael M. Martin, and J oëlle Anne Moreno.

OP INION

W A L L ACE, Senior Circuit J udg e:

After a seven-day trial, a jury found SQM North America C orporation (SQM) not liable for c ausing perchlorat e contaminat i o n in the City of Pomona’s (Pomona) water sy stem. Pomona now a

ppeals from tha t j udg ment. W e have jurisdiction pursuant to 28 U .S

. C

. § 1 291. W e hold that the distric t c o u r t abused its discretion by limiting the testimony of one of Pomona’s ex perts and failing to make suffic i ent finding s b efore admitting the testimony o f one of SQM’s

ex p erts. These error s, in combination, were prejudicial. According ly
, w e vacate t h e district court’s judg ment a nd remand for a new trial. 1

1 W e reso l v e tw o o th er i ssu es raised by P o m o n a in a co n cu rr e n t l y f iled m em o ran d u m

d isp ositio n

.C I T Y O F P O M O N A V

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I

.

Pomona o wns and operates a p u b l i c water sy stem to provide its residents w ith clean drin king water. The State o f California regu lates the quality of that water by imp o s i ng

max imum contaminant levels (MCL ), which limit the amount of a g iven c hemical that c an be present in the water. I n 2007, California established t h at the MCL for perchlorate, a chemical that interferes with t h e a bility of the thy

roid g land to produce h ormones, would b e six parts per billion. Shortly thereafter, Pom o n a d iscovered that fourteen of its wells possessed perchlorate levels in ex cess of th e M CL

. I n response, Pomona shut down non-c o m p liant wells, purchased
water f rom other sources, and took other steps to remedy the perchlorate contamination in its drinking water.

I n 2010, Pomona filed this p roducts-liabi l i t y action

a ga inst SQM. SQM beg an importing fertiliz er f r om the Atacama Desert in Chile in 1927, and from 1931 t o 1968 imported a substantial portion o f the Chil e a n n itrate (a component of that fertiliz er) broug ht fr o m Chile into the United States. The theory of Pomona’s case is that SQM’s importation o f perchlorate- c o n t a i n i ng fertiliz er products from the Atacama Desert, which were used i n a r eas around Pomona’s wells, caused the contam i n a t ion in Pomona’s water supply

. Thus, Pomona soug ht to recover over $32 million in past and future costs assoc i a t ed with investig ating a nd remediating the perchlorate contamination.

The c ase prog res sed towards a J anuary 2012 trial date. Unsurprising ly
, the case involved several scientific ex p erts,

as the key d ispute centere d a round whether the p erchlorate from SQM’s f

ertiliz e r had mig rated into Pomona’s wells a nd caused the contamination present in Pomona’s water sy stem.C I T Y O F P O M O N A V

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F ive day s before trial, the district court conducted a Daubert hearing to c o nsider whether the testimony of Pomona’s ex pert witness, Dr. Neil Sturchio, should be ex cluded. Dr. Sturchio, who w as then the Head of the D epartment of Earth a nd Environmental Sciences at t he University of I llinois at Chicag o, 2 had developed a peer-reviewed methodolog y for collect i n g a n d analy

z ing perchlorate isotopes from
g roundwater. Dr. Sturchio’s research concluded that perchlorate fr o m the Atacama Desert in Chile has a d istinct isotopic fing erprint. Thus, b y analy zing the chlorine a

nd

ox yg en isotopes taken from Pomona’s wells, Dr. Sturchio determined that roug hly ninety percent of the p erchlorate present in Pomona’s g roundwater matched the isotopic fing erprint of perchlorate unique to the Atacama Desert. Put simply
, Dr. Sturchio concluded that most of the perchl o r a te in Pomona’s water had come from the Atacama Desert.

F our day s before trial was to beg in, t h e district court g ranted SQM’s motion to e x clude D r. Sturchio’s testimony

. I n a one half-pag e minute order, the d istrict co u rt held that Dr. Sturchio’s opinions had “not been g enerally accepted by the scientific community
, ” had “not been tested b y o t h er laboratories,” and that “Dr. Sturch i o ’ s reference database [ was] too limited.” As Dr. Sturchio was one of Pomona’s key witnesses, the parties stipulated to d ismiss t h e c ase a nd allowed Pomona to appeal the ex clusion of his testimony

.

W e reverse d the d istrict court’s ex c lusion o f Dr. Sturchio’s ex p e r t testimony

. City o f Pomona v. SQM North America Corp.
, 7 5 0 F .3d 1 036 ( 9th Cir. 2014) ( Pomona I

). W e held that the “district court’s ruling [ was] u n p ersuasive

2 Dr. Stu r c h i o i s n o w th e Ch air o f th e Dep artm en t o f Geo lo g i cal Scien ces at th e Un iv ersity o f Delaw are.C I T Y O F P O M O N A V

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because b oth g rounds for ex clusion [were] without adequate support in the record.” Id

. at 1047. According ly
, we remanded the case for trial. T h e mandate from our court issued in December 2014.

Upon remand, the d i s trict court ordered a status conference for J anuary 12, 2015. At that conference, Pomona
reques ted to r eopen fact and ex pert discovery to reflect scientific developments that had been advanced during the three y e ars in which the case was on appeal. The district court requested that Pomona file a writte n m o t i on to r eopen discovery and set trial to beg in J une 2
, 2 0 1 5
, l e s s than five months from the d ate of the first post-remand sta t us conference.

On F ebruary 9, 2015, Pomon a f iled its formal motion to reopen discovery

. As to Dr. Sturc h i o , Pomona requested leave to supplement his ex pert report to reflect a dditional data concerning isotopic analy sis of perchl orate that had been developed while the appeal had been pending

. Th e m o tion contained a sworn declaration from Dr. Sturchio, in which he described the new developments in the sci e nce of isotopic analy sis of perchlorate. Dr. Sturchio and other scientists had conducted new interlaboratory comparisons and the database siz es for their r e s earch h ad increased, w hich buttressed Dr. Sturchio’s conclusions and repelled the main criticisms of his research. On March 2 6, 2015, the d istrict court d enied Pomona’s m otion to supplement Dr. Sturchio’s report. The district court concluded that P o m ona failed to demonstrate that the information was material and determine d t hat updating Dr. Sturchio’s report would “create back-and-forth discovery , which could delay trial.”C I T Y O F P O M O N A V

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The case proceeded towards the J une 2, 20 1 5
, t r ial date. Still pendin g, however, were the parties’ motions in limine
, which had been filed in 2011, before the orig inal trial date. At that junctur e , b e f

ore the case made its first trip throug h our court, the district court had i s s u ed tentative r uling s on the motions in limine

. On M a y 2 9, 2015, four day s before trial, the district court issued new ruling s on the parties’ motions in limine

. Relevant for our purposes is the district court’s ruling

on Po m o n a ’s motion to ex clude the testimony of SQM’s

ex p ert, Dr. Richard L aton. Dr. L aton’s proffered t e stimony

co n tended that the perchlorate contamination p resent in P o mona’s water sy stem could have come from hundreds o f alternative sources other than SQM’s importation o f fertiliz er from the Atacama Desert. F or ex ample, Dr. L aton opined that the perchlorate in Pomona’s w a t e r sy stem c ould have come from “household bleach,” “ swimming pools,” “septic tanks,” “photog raphic flash powder,” or e v en “fireworks.” Pomona’s motion asserted that Dr. L aton’s testimony was unreliable under the standard set f orth in D aubert v. Merr e ll Dow Pharmaceuticals, Inc.
, 509 U.S. 579 (1993). B efore the first appeal, the district court denied Pomona’s Daubert motion a s to D r

. L aton, without e x planation, in a ruling that was

ex p licitly labeled as tent a t i v e. The district court’s May 29, 2 0 1 5, ruling on Pomona’s motion to e x clude Dr. L a ton d i d not include any

analy sis.

At trial, Dr. Sturchio testified to the circumstances as they

ex isted in 2011. As the distri ct c o u r t had denied Pomona’s motion to update D r. Sturchio’s ex pert r e p ort, he was prohibite d from testify ing about the sig nificant scientific
prog r ess that had t a k e n place while the case had been on appeal. F urthermore, Dr. L aton testified that the p erchlorate contamination could have a risen from m a

ny p o t e n t i a l sources. After seven day s of testimony a nd argument, the jury r eturnedC I T Y O F P O M O N A V

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its verdict, finding that SQM’s sodium nitrate fertiliz er w a s not a substantial factor in caus i n g h a rm to Pomona—a complete defense verdict in favor of SQM.

This appeal f

o llowed, in w hich Pomona challeng es the district court’s denial of its motion to update D r. Stur c hio’s

ex p ert report, whic h r esulted in the ex clusion o f testimony
reg arding new scientif i c d e v elopments. Pomona also challeng es the district court’s denial of its motion to ex clude Dr. L aton’s testimony

.

I I

.

“W e review e v identiary ruling s for abuse of discretion and reverse if the ex ercise of discretion is both e rroneous a nd prejudicial.” Pomona I

, 750 F .3d at 1043. F urthermore, “[ t] he district court is g iven broad discretion in supe rv i sing the
p r e t r i a l phase of litig ation, and its decisions reg arding the preclusive effect of a pretrial order

. . . will n ot be disturbed unless they evidence a clear abuse of discretion.” Johnson v

. Mammoth R ecreations, Inc.
, 975 F .2d 604, 607 (9th Cir. 1992) (second alteration in origi n a l) ( citation and internal quotation marks omitted).

“[ T] he first step o f o u r abuse of discretion test is to dete rmine de novo whether the trial court identified the
correct l eg al rule to apply to the relief requested.” United States v

. Hinkson
, 585 F .3d 1247, 1 261–62 (9th C i r

. 2 009) (en banc). “[ T] he second step o f our abuse of d iscretion test is to d etermine w hether the trial court’s applicatio n of the
correct leg al standard was (1) i l l o gi cal, (2) implausible, o r (3) without support in inferences that may be drawn from the facts in the record.” Id

. at 1 262 (citations and int e rnal quotation marks omitted).C I T Y O F P O M O N A V

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I I I

.

A.

F irst, we turn to the d i s t r ict court’s denial of Pomona’s motion to update Dr. Sturchio’s report, which resulted in the

e x c l u s i o n o f a n y t e s t i m o n y r e g a r d i n g p o s t

- 2 0 1 1 developments in Dr. Sturchio’s research.

I n his 2011 e x p e rt report, Dr. Sturchio concluded that a substantial majority of the pe r c h lorate in Pomona’s water sy stem had come from the Atacama Desert in Chile. The strong est critici s m s o f Dr. Sturchio’s 2011 report w ere that the reference database he used was too small, and, that when the 2011 report wa s c o mposed, Dr. Sturchio’s specific method had not been tested wid e l y and confirmed by other laboratories. Thus, upon remand in 2015, Pomona moved to update Dr. Sturchio’s e x pert report, so h is testimony would reflect the current state of knowledg e in the scientific community in these areas. Pomona’s mot ion included a sworn declaration from Dr. Sturchio, in which he de s c r i bed the developments that had taken p lace. Dr. St u r c hio ex p lained that “a number of laboratories, oth e r t h a n [ his] o wn, have continued to eng a g e in perch l o rate isotopic analy sis,” resulting in “additional interlaboratory comparisons that f ully verify the methods used a nd the results obtained in [ his] previou s r esearch.” Moreover, by 2015, “ the database for
natura l p e r chlorate samples [ had] become larg er, a nd [ included] samples from other locations across t h e U S a nd around the world.”

D espite these relevant scientific developm e n t s , t h e d i s t r i c t court d en i e d Pomona’s motion to r eopen discovery a nd update Dr. Sturchio’s ex pert rep o r t , thus limiting his trialC I T Y O F P O M O N A V

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testimony to the s c i e n t i f

ic world as it ex isted in 2011. The district court’s three-sentenc e analy sis o f the issue provided
t w o reasons f

or prohibiting D r. Sturchio from updating h i s

re p o r t , and thus testify ing a t trial to the then-current state o f stable isotope research. F irst, the district court concluded that allowing Dr. Sturchio to update his report mig ht “create backand-forth discovery
, which could delay trial.” Seco n d
, the district court d etermined that the updates to Dr. Sturchio’s report were not material.

W h en r uling on a motion to amend a Rule 16 scheduling order to reopen discovery
, we i n s t ru c t district c ourts to consider the following

factors:

1) whether t rial is imminent, 2 ) whether the request is opposed, 3) whether the nonmoving party would b e prejudiced, 4) whether the moving party was d ilig en t i n obtaining discovery within the g uidelines established b y the court, 5) the foreseeability of the need for addi t i o n al discovery in lig ht of the time allowed for disc o v e ry by the district court, and 6) the likelihood that the discovery will lead to relevant evidence.

United States ex rel. Schumer v. H ughes Aircraft Co.
, 6 3 F .3d 1512, 1526 (9th Cir. 1995) (citation omitted), vacated on other grounds
, 520 U.S. 939 (1997).

I n denying Pomona’s motion, the district court identified the correct leg a l standard, which satisfies the first step of our abuse of d iscretion test. H i n k s on , 585 F .3d at 1261–62. W e hold, h owever, that the district court applied that l e ga l standard in an “illog ical” manner, thus committing an abuseC I T Y O F P O M O N A V

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of discretion. Id

. a t 1 2 6 2

. As to the first reason the district
court provided, any potential for the updated ex pert report to delay trial was of the district court’s o wn mak i n g. Upon remand, the district c ourt set a J une trial date a t the initial
status conference, f

ollowing which Pomona promptly f iled its motion to reopen discovery

. B y the time the district co u r t ruled o n the motion, roug hly two months before trial, reopening discovery would likely h ave caus e d delay

. Any potential delay
, however, w as broug ht a b o u t b y the combination of an ex p e d itious trial date and the a m o u nt o f ti m e P omona’s motion sat undecided. The p roblem was not the result of a lack of dilig e nce by Pomona.

The district court’s sec o n d p roffered reason for denying the mot i o n , lack of materiality
, was also illog ical. SQM has acknowledg ed that “Sturchio was Pomona’s k ey witness, a nd much of the case involved h is forensic methods.” As such, the level of support for his conclusions was critical an d it was important that his proffered testimony be accurate and reflect the current state of knowledg e in the s c ientific community

. The main attack on Dr. Sturchio’s te s t i m o n y ( as it stood in 2011) was that it had not been r e produced by other laboratories and that his refe r ence database w as too small. The proffere d u p dates to Dr. Sturchio’s report directly combated those criticisms. B ased on Dr. Sturchio’s sworn declaration (which accompanied Pomona’s motion), and the fact th a t the first appeal focused heavily on Dr. Sturchio’s testimony
, the district court should h ave been on no t i c e t hat the updates to Dr. Sturchio’s report were material.

I n d efense of the district court’s decision, SQ M a r gu e s that Pomona was not dilig ent. Primarily
, SQM assert s t hat Pomona should have up d a ted Dr. Sturchio’s r eport, a nd should have moved to do so, in May 2014, after we dec i d e dC I T Y O F P O M O N A V

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Pomona I

. Thus, by making its m o t i o n in F ebruary 2015, Pomona waite d too long

. B ut in May 2014, the appeal was still alive, a certiorari petition was pending
, and the mandate had n o t issued. Pomona moved p romptly o nce the case returned to the district court.

S Q M a lso asserts that Pomona lacked d ilig ence becaus e it did n o t p rovide SQM with Dr. Sturchio’s f u l l updated

ex p ert report until eleven day s before trial. This arg ument is irrelevant. B y that time, the district court ha d a lready issued

a firm r uling denying P o m o na’s motion to update Dr. Sturchio’s report. A lthoug h the record w ould have b een more complete had Pomona i n c l u ded the updated report with its F ebruary 2 015 motion, D r. Sturchio’s declaration, attached to the mot i o n , w as sufficient to put the district court a nd SQM

on notice o f what the upda t e d ex pert report would say

. SQM’s attempt to shift the relevant date to eleven day s before trial, rather than when Pomona f iled its motion four months before trial, has not convinced us.

SQM further argu es that the updat e s P o mona soug ht to include in Dr. Sturchio’s ex p ert r e port were immaterial. I n doing so, SQM asserts, as the distr i c t c o u rt did, that the updates were cumulative, did n o t chang e Dr. Sturchio’s conclusions, and merely buttressed his previously -ex pressed opinion. W e disag ree. As ex p ressed above, the parties knew Dr. Sturchio’s causation analy s i s w o uld be a key factor at trial. Thus, the d eg ree o f support for h is conclusions was critical and the updates Pomona soug h t were material.

B

. Having determined that th e d istrict court’s ex clusion o f Dr. Sturchio’s testimony reg arding post-2011 d evelopm entsC I T Y O F P O M O N A V

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was erroneous, we no w must r esolve w hether that error was prejudicial. “ [ A] showing of prejudi c e is required for reversal.” O llier v. Sweetwater Union H igh S ch

. Dist.
, 768 F .3d 843, 859 (9th C i r

. 2014). Here, we h old that the

ex c lusion o f Dr. Sturchi o ’s testimony reg arding post-2011 developments, combined with the erroneous inclusion of Dr. L aton’s ex pert test i m o ny ( as discussed in Section I V), more probably than not affected the ve r d ict and was thus prejudicial.

After presentation of the evidence at trial, but before the jury had rendered its ver dict, the d istrict court described the trial as “a ba t t l e o f the ex perts.” I n keeping w ith this theme, SQM soug h t to discredit Dr. Sturchio, who it recog niz ed “was Pomona’s key witness.” F or e x ample, SQM elicited the following testimony f

rom its g eochemical ex pert, Dr. Ramon Aravena, reg arding Dr. Sturchio’s conclusions:

[ T] he two main criticism[ s] that I have on Dr. Stur c hio[ ’s] research. One is that it’s the failure to reproduce h is method a nd r e sult b y other laboratorie s. And second is – basically is th e failure to have basically a complete database for interpretatio n o f the data for the sources of perchlorate.

* * *

Q: I n y our prior c hart w here y ou had t h e t wo critiques of Dr. Sturchio’s method, the second

one was f

ailure to assemble a complete isotope database for s o urces of perchlorate. Do y ou have an o p inion as to whether D r.C I T Y O F P O M O N A V

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S t urchio’s interpretation o f the isotopic dat a that he has developed is reasonable?

A: Ihave an opinion.

Q: W hat is y our opinion, sir?

A: My opinion is that th e d a tabase is incomplete.

F urthermore, during its closin g argument to the jury
, SQM asserted the f

ollowing
, reg arding the scientific support for Dr. Sturchio’s conclusions:

[ Dr. Sturchio] a lso admitted h is is the one a nd the only laboratory to do his technique. Now, Isaw a bigfalse sig n nex t to my statement in
my opening statement w here I s a i d that he

was the one a

nd o nly lab. W ell, I didn’t make that up, folks. That comes from Dr. Sturchio.

* * *

I sotope ratios don’t g iv e y ou a unique fi n g e r p r int. W hat they g ive y ou is a rang e o f value s, and those rang e of v alues are not unique from o n e p lace to one place or even within one place. I t i s s o i m p ortant to have a complete comparis o n database, and that’s where Sturch io has drag g ed his feet. He say s there’s only 16 sample s f r o m 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 independentC I T Y O F P O M O N A V

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lab has analy

z e d the isotopic sig nature o r composition of those samples. You only have four samples from all of California.

* * *

B e cause Pomona is presenting weaker evidence when they had it in their power to present strong er evidence, y ou s hould disreg ard Dr. Sturchio.

These criticisms of Dr. Sturchio w ere accurate in 2 011. B y 2015, however, these c haracteriz ations of Dr. Sturchio’s research were false, and counsel making them had to know they were false, based on the e v idence SQM successfully k ept from the jury

. By t h e time of trial, Dr. Sturchio, along with other scientists, h ad amassed 50 sam p l e s from the Atacama Desert, 55 samples of naturally occurrin g p erchlorate from other locations, and 79 samples o f sy nthetic perchlorate. Had the distri c t c ourt a llowed Dr. Sturchio to update his testimony
, Pomona could have easi l y r e butted much o f SQM’s criticism of his research d u r i n g trial. Given that Dr. Sturchio was Pomona’s “key witness,” that his c redibility a nd the level of support f

o r hi s conclusions was paramount, a nd that SQM att ac k e d directly the level of support as it e x isted in 2 011, we conclude that the d istrict c ourt’s refusal to allow Dr. Stu rchio to testify to scientific developments occurring between 2011 and 2015 was prejudicial.

I n response, SQM’s main argument is that even if the district court committed error, any such error w a s harmless. Put simply
, SQM asserts that even if the jury ag reed with Dr. Sturchio’s c onclusions, it could stil l have reasonably f ound that SQM did not cause the perchlorate contamination inC I T Y O F P O M O N A V

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Pomona’s water sy stem. The record shows that from 1931 to 1968, SQM imported a substantial portion of the sodium nitrate broug ht from Chile to the United St a t e s

. Other companies, however, imported Chilean nitrate b efore 1931. According ly
, as Dr. Sturchio conceded that he could not ag e date the perchlorate found in Pomona’s wells, the perchlorate,

even if it h ad come from Chile, could have been imported b y

an entity other than SQM. This argument is buttressed, SQM
argues, b y the fact that som e o f the well sites below the historic orchards in the well cap ture z o n e tested n on-detect for per c h l o rate. Had SQM’s fertiliz er (which was orig inally used in the orchards) been the cause of contamination, those

s i t e s s h o u l d h a v e t e s t e d p o s i t i v e f o r p e r c h l o r a t e contamination.

B u t the jury d id not need to find that all of the p erchlorate found in Pomona’s w ater sy stem came from SQM. Rather, the jury instructions asked w hether SQM’s importation o f fertiliz er w a s a “substantial factor in causing ” the contamination, which the jury instructions d e fined as “more than a remote o r trivial factor.” Dr. St u r c h i o ’s ultimate conclusion was that ninety percent of the p erchlorate contamination found in P o mona’s w ells came f rom the Atacama Desert in Chile. The r ecord further shows that from 1931 to 1968, SQM imported substantially all of the Chilean nitrate coming into the United States, and imported especially larg e amounts during 1941 and 1942. T aking these facts into account, along with the errone o u s inclusion of Dr. L aton’s testimony (described below), we conclude that the preclusion of Dr. Sturchio’s updated report and testimony more probably than n ot affected the verdict. T hus, the ex clusion o f D r. S t u r c h i o ’ s t es t i m o n y r ega r d i n g p o s t

- 2 0 1 1 s c i en t i fi c developments was prejudicial.C I T Y O F P O M O N A V

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I V.

A.

Nex t, we turn to the district court’s denial of Pomon a’s motion to ex clude the testimony of SQM’s alternative source

ex p ert, D r. Richard L aton. Dr. L ato n o p i ned that the perchlorate at issue mig ht h ave f lowed fro m hundreds o f potential alternative sources other than SQM’s f e rtiliz er. Pomona first moved to ex clude Dr. L aton’s testimony under Daubert b e fore the scheduled 2012 trial. The district court denied this motion in wh a t was e x plicitly a “tentative” onesentence rul i n g. On remand, Pomona ag ain c halleng ed Dr. L aton und e r Daubert

. Pomona argued that Dr. L aton’s proffered testimony failed to show any scientifically v alid
g rounds for asserting that any o f h i s a l ternative sources contained the specific ty

pe of perchlorate actually found in Pomona’s g roundwater. I n a one-word ruli n g o n Pomona’s 2015 Daubert

motion, the district court stated “DENY.” Dr. L aton proceeded to testify at the 2015 trial.

The manner in which the district c ourt denied the Daubert motion as to Dr. L a ton constituted an a b use of discretion. I

n Estate of Barabin v. AstenJohnson, I n c

. , 740 F

. 3d 457 (9th Cir. 2014) (en banc), we held the district court had abdicated its g a tekeeping author i t y , in denying a Daubert motion, because “[ a] bsent from the ex planation is any indication that th e d i s t rict court assessed, or made finding s reg arding
, the scientific validity o r methodolog y of [ the ex pert’s] proposed testimony

. Therefore, the district cou r t failed to assume its role a s g atekeeper with respect t o [ the ex pert’s] testimony

. ” Id. at 464. F urthermore, in Pyramid Technologies, I nc. v

. Hartford Casualty Insurance Co.
, 752 F .3d 807 (9th Cir. 2014), we held that a district c o urt abuses its discretion whenC I T Y O F P O M O N A V

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it fails to provide a n y “analy sis or ex planation” for its decision r eg arding ex pert testimony under Daubert

. I d

. at 814. I n Pyramid
, the d istrict c o urt abused its discretion b y denying a Daubert motion “ [ i] n two c onclusory sentences a nd without analy sis or ex planation.” I d

.

So too here. The d istrict court denied Pomona’s Daubert motion as to Dr. L aton with a one-word “DENY.” Under the standard we set in E

state of Barabin and Pyramid
, the failure
to make any finding s r eg arding the efficacy of D r

. L a ton’s

ex p ert opinions constituted an abdication of the district court’s g atekeeping role, and necessarily an a b u s e o f discretion.

SQM’s main argument in response is that Pomona waived its rig ht to appeal the denial of its Daubert motio n

. Under F ederal Rule of Evidence 103(b), “ [ o] nce the court rules definitively on the record—either before or at trial

— a p a r ty need not renew a

n objection or offer of proof to preserve a claim of error for appeal.” Here, SQM a rg ues that by

failing
to appeal the district court’s tentative ruli n g in 2011, which denied the Daubert

motion as to Dr. L aton, Pomona waived
any rig ht to a

ppeal the d istrict court’s 2015 rulin g. W e disag ree. The district court’s 2011 ruling w as ex plicitly tentative, and thus not definitive within the meaning of Rule 103. During the 2011 pretrial conference, in which the district
court m a d e o r al ruling s, the district court stressed several times that its ruling s were tentative. F urthermore, the minute order ex press i n g the motion in limine ruling s stated the ruling s were a ll “ tentative.” “ [I ] n order to appeal an issue on which the district court ruled in limine
, a par ty 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 orig inal tentative ruling

.C I T Y O F P O M O N A V

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Nex t, SQM argues that Pomona waived its rig ht to appeal because it d id not object to Dr. L aton’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 o rder. I nstead, the “tentative” heading on the district court’s motion in limine ruling s was conspicuously omitted. On the first day of trial, the district court stated as follows
reg arding its written ruling s o n the parties’ motions in limine :

As to motions in limine
, I think they ’re pretty cl ea r l y stated on my finding s that I sent y ou.

. . . [ M] otions in limine almost alway s deal with evidentiary issues, evidentiary issues that come u

p during the trial. Any ruling on a motion in limine ma y o r may not be revisited as the evidence c o mes in. I t may

or may not ch a n ge , b ut these are the ruling s until and unless the C o u r t decides that it can

c o m e in. Some evidence may c ome up tha t may ma k e something relevant that the Court had determined that up until the time that that

comes in is n ot relevant. So all I ’m telling y ou is, is that they ’re quasi tentative, depending on how the evidence comes in.

Thus, SQM’s only relev a n t argument is that the district court’s statement, that its in limine ruling s were “quasi tentative,” mea n t t hat Pomona was required to object to Dr. L aton’s testimony

during trial to preserve its right to appeal, which Pomona did not do ex plicitly

.

Pretrial motions, such as motions in limine
, “are useful tools to resolve issues which would o t h e r w i se clutter up the trial.” Palmerin v. City o

f Riverside
, 794 F .2d 1409, 1413 (9thC I T Y O F P O M O N A V

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Cir. 1986) (internal quotation marks o m i t ted). F urthermore, “a ruling on a m otion in limine is essentially a preliminary opinion that falls entirely within the discretion of the district
court. T he district court may chang e its ruling at trial because testimony may bring f

acts to the district court’s attention that i t d i d not anticipate a t the time of its initial ruling .” United States v. Bensimon
, 172 F .3d 1121, 11 2 7 (9th Cir. 1 999) (emphasis a d ded) ( internal citation omitted). “Still, parties

ex p ect a district c ourt to a d h ere to its earlier ruling if no facts

or circumstances a

rise to warr a nt a reversal.” Id

. W hen a district court makes a pret r i al ruling on a motion in limine that is subject to limitations r e ga r d ing how the evidence actually c omes in, a

nd 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 o n other grounds by Estate of Barabin , 740 F .3d at 467.

Our reading of the district court’s sta tement on the first day of trial, quoted above, is that it was mere l y reiterating what we said in Bensimon —that a district c ourt may chang e

an in limine ruling at trial if facts o r c i rcumstances arise to warrant the chang e. The district c ourt had denied the Daubert motion as to Dr. L aton in a w r i tten ruling without any tentative heading

. As trial p rog ressed, before Dr. L aton’s testimony
, the distri c t court had denied objections, making

c lear that it was “ not g oing to argu e with y ou in fro n t o f t h e jury ” and later, that “ we do not argue objections in f r o n t o f the jury .” B y the time Dr. L aton rose to test i f y , no facts o r circumstances had arisen that would have warranted reversal of the district court’s pretrial ruling

. I n fac t , during Dr. L aton’s testimony
, Pomona’s counsel asked if it could briefly

v o i r dire the witness, which request was quickly denied. B y making this r equest, Pomona r en e w ed its challeng e to Dr.C I T Y O F P O M O N A V

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L aton’s testimony concerning alternative sources to perchlorate, g iving the district court another oppo r t unity to rule on the issue. Additionally
, Pomona’s counsel tried to object to Dr. L aton’s “ s h o tg un” testimony about potential

sources of perchlorate, b ut the district court overruled h im while he was midsentence.

Thus, we must decide whether Pomona preserved its objection to Dr. L aton’s tes timony

. W ithout doubt, Pomona could have simplified this is s u e by restating its Daubert objection just before Dr. L a t o n testified, or by raising the objection during a recess. N evertheless, g iven the importance of ex pert testimony in this case, the f ac t 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 i r r itating the district court, was understandable. According ly
, bas e d on the circumstances presented here, we hold that Pomona did enoug h to preserve its objection.

B

. Having d e termined that the district court abdicated its
g atekeeping role by failing to make any f inding s of reliability

as to Dr. L aton, we nex t m u st decide w hether that error was prej u d i c ial. “W e treat the erroneous admission of ex pert testimony the same as a ll other evidentiary e rror s , b y subjecting it to harmless error review. W e reverse only if the

error affect[ ed] a substantial rig ht of the party

. I n other words, w e require a finding o f prejudice.” Estate of Barabin
, 740 F .3d at 464 (internal c itations and quotati o n m arks omi t t e d ). F urthermore, “[ p] rejudice is at its apex when the district court erroneously admits e v idence that is c ritical to the proponent’s case.” Id. at 465.C I T Y O F P O M O N A V

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Here, there can be no doubt t hat Dr. L aton’s testimony

was critical to SQM’s case. Dr. L a t o n e s sentially testified about all the way s in w h ich the p erchlorate contamination could h ave manifested i n Pomona’s water sy stem that h ad
not h i ng to do with SQM. Dr. L aton’s testimony undercut directly the testimony of Dr. Sturchio, Pom o n a’s “key

w itness,” as well as Dr. Stephen W heatcraft, Pomona’ s hy drolog y ex pert, who testi f i e d about the manner in which the perchlorate flowed from the orcha r d s into Pomona’s water sy stem. On direct ex amination, Dr. L aton testified as follows:

Q: D id y ou r each an o pinion as to whether the City ’ s ex perts, D r

. Sturchio, Dr. W heatcraft,

c o n d u c t e d a c o m p l e t e e n v i r o n m e n t a l investig ation in Pomona?

A: No, they

did not.

Q: And what do y ou base y our opinion on?

A: T he reports that I r eviewed that were submitted on behalf of the City

.

Dr. L aton’s testimony went on with a further a ttack on Dr. Sturchio’s and Dr. W heatcraft’s conclusions.

Dr. L aton’s testimony
, and that of D r. Sturchio and Dr. W h e atcraft, went to the crux of the case—whether SQM’s importation of fertiliz er was a substantial factor in causing the perchlorate c ontamination in Pomona’s wate r s y stem. Dr. L a ton was a key play er in w hat the district cou r t a p t l y described a s “a battle of the e x perts.” Therefore, the

erroneous inclusion of Dr. L aton’s testimony
, combined withC I T Y O F P O M O N A V

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the erroneous par t ial ex clusion of Dr. Sturchio’s testimony
, was prejudicial.

W e do not decide, one way or the o t h er, whether Dr. L aton’s proffered opinions satisfy the Daubert standard. Rather, we merely

hold that the record lacks “any indication that the distric t c ourt a ssessed, o r made finding s reg arding
, the scientific validity or methodolog y o f [ D r

. L aton’s] proposed testimony .” E

state of Barabin
, 740 F .3d at 464.

V.

W e are sy mpathetic with the district court’s desire to keep this case on a fast track. A civil action may meander throug h discovery f

ar too slowly and o ur sy stem benefits when district judg es keep the wheels of justice turning b y employ ing effective case manag ement. B ut there are limits. T h e record demonstrates that the science of sta b l e i sotope analy sis evolved sig nificantly during this case’s first journey throug h the appellate sy stem. B y c onstraining Dr. Sturchio to his 2011 report, the d istrict court abused its d iscret ion. F urthermore, the district court’s failure to make any finding s reg arding the reliability of Dr. L a t on’s testimony
, despite Pomona’s Daubert motion, was an a b use of d iscretion. These errors, in combination, were prejudicial.

According ly
, the district court’s judg ment is vacated a nd this case is remanded for a new trial. On remand, the district
court shall allow Dr. Sturchio to update his ex pert report a nd testify to the state of stable isotope research up to the present. I n addition, the district court shall make finding s reg arding the scientific reliability of Dr. L aton’s proposed opinions, a ndC I T Y O F P O M O N A V

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hold a Daubert hearing if the district c ourt determines one is
necessary

.

VACATED and REMANDED.