                 FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,             
               Plaintiff-Appellant,
               v.
                                            No. 06-30472
W. R. GRACE; ALAN R. STRINGER;
HENRY A. ESCHENBACH; JACK W.                 D.C. No.
WOLTER; J. MCCAIG; ROBERT J.              CR-05-00007-DWM
BETTACCHI; O. MARIO FAVORITO;
ROBERT C. WALSH,
            Defendants-Appellees.
                                      

UNITED STATES OF AMERICA,             
               Plaintiff-Appellant,
               v.                           No. 06-30524
W. R. GRACE; ALAN R. STRINGER;
HENRY A. ESCHENBACH; JACK W.                 D.C. No.
                                          CR-05-00007-DWM
WOLTER; WILLIAM MCCAIG;
                                              OPINION
ROBERT J. BETTACCHI; O. MARIO
FAVORITO; ROBERT C. WALSH,
            Defendants-Appellees.
                                      
       Appeal from the United States District Court
               for the District of Montana
       Donald W. Molloy, District Judge, Presiding
                  Argued and Submitted
            June 4, 2007—Seattle, Washington
                 Filed September 20, 2007
      Before: Betty B. Fletcher, Harry Pregerson, and
           Warren J. Ferguson, Circuit Judges.

                           12669
12670   UNITED STATES v. W. R. GRACE
        Opinion by Judge B. Fletcher
12674           UNITED STATES v. W. R. GRACE
                        COUNSEL

Todd S. Aagaard, Dept. of Justice Environment and Natural
Resources Division, Washington, D.C., and Kris A. McLean,
Assistant United States Attorney, Missoula, Montana, argued
for the government. With them on the briefs were Sue Ellen
Wooldridge, Assistant Attorney General; William W. Mercer,
United States Attorney; Eric E. Nelson, Linda Kato, Special
Assistant United States Attorneys; Kevin M. Cassidy, and
Allen M. Brabender, Attorneys, United States Dept. of Justice
Environment and Natural Resources Division.

Christopher Landau, Washington, D.C., argued for defendant-
appellee W.R. Grace & Co. With him on the brief were Lau-
rence A. Urgenson, Tyler D. Mace, Michael D. Shumsky,
Washington, D.C.; Stephen R. Brown, Charles E. McNeil,
Kathleen L. DeSoto, Missoula, Montana, for defendant-
appellee W.R. Grace & Co.; Angelo J. Calfo, Seattle, Wash-
ington; Michael F. Bailey, Missoula, Montana, for defendant-
appellee Alan R. Stringer; Ronald F. Waterman, Helena,
Montana; David S. Krakoff, Gary A. Winters, Washington,
D.C., for defendant-appellee Henry A. Eschenbach; Mike
Milodragovich, W. Adam Duerk, Missoula, Montana; Mark
Holscher, Jeremy Maltby, Los Angeles, California, for
defendant-appellee Jack W. Wolter; Palmer Hoovestal,
Helena, Montana, Elizabeth Van Doren Gray, Columbia,
South Carolina, William A. Coates, Greenville, South Caro-
lina, for defendant-appellee William J. McCaig; Brian Gallik,
Bozeman, Montana, Thomas C. Frongillo, Boston, Massachu-
setts, Vernon S. Broderick, New York, New York, for
defendant-appellee Robert J. Bettacchi; C.J. Johnson, Mis-
soula, Montana, Stephen A. Jonas, Robert Keefe, Boston,
Massachusetts, for defendant-appellee O. Mario Favorito;
Catherine A. Laughner, Aimee M. Grmoljez, Helena, Mon-
tana, Stephen R. Spivack, Washington, D.C., David E. Roth,
Birmingham, Alabama, for defendant-appellee Robert C.
Walsh.
                 UNITED STATES v. W. R. GRACE              12675
                          OPINION

B. FLETCHER, Circuit Judge:

   From 1963 until the early 1990s, W. R. Grace (“W. R.
Grace” or “Grace”) mined and processed a rich supply of ver-
miculite ore outside of Libby, Montana. In response to on-
going serious health problems suffered by Libby residents, the
government obtained an indictment charging W. R. Grace and
seven of its executives (together “Grace”) with criminal con-
duct arising from Grace’s vermiculite operation in Libby. The
superseding indictment charges defendants-appellees with (1)
conspiring knowingly to release asbestos, a hazardous air pol-
lutant, into the ambient air, thereby knowingly placing per-
sons in imminent danger of death or serious bodily injury in
violation of 42 U.S.C. § 7413(c)(5)(A) and (2) conspiring to
defraud the United States in violation of 18 U.S.C. § 371. In
addition to the dual-object conspiracy alleged in Count I, the
indictment charged defendants-appellees with three counts of
knowing endangerment under the Clean Air Act, 42 U.S.C.
§ 7413(c)(5)(A), and four counts of obstruction of justice in
violation of 18 U.S.C. §§ 1505 and 1515(b).

   This interlocutory appeal brought by the government con-
cerns six orders grouped into four sections: the first order dis-
missed the knowing endangerment object of Count I’s
conspiracy charge; the second adopted a particular definition
of asbestos and excluded evidence inconsistent with that defi-
nition; the third denied a motion to exclude evidence related
to an affirmative defense and relied on an emission standard
for asbestos contained in certain Environmental Protection
Agency (“EPA”) regulations, see, e.g., 40 C.F.R.
§§ 61.142-61.149; and the fourth through sixth orders
excluded certain evidence and expert testimony. In addition,
we rule on defendants-appellees’ motion to strike documents
attached to the government’s reply brief. We have jurisdiction
to hear this appeal pursuant to 18 U.S.C. § 3131, and we
reverse in part, affirm in part, and remand.
12676            UNITED STATES v. W. R. GRACE
  I.    Dismissal of the Knowing Endangerment Object

                       1.   Background

   In the original indictment, filed February 7, 2005, the gov-
ernment charged defendants with participating in a dual-
object conspiracy. According to Count I of the indictment,
which details the scope of the conspiracy, defendants con-
spired (1) to knowingly release asbestos, a hazardous air pol-
lutant, and thus knowingly to endanger both EPA employees
and members of the Libby community in violation of 42
U.S.C. § 7413(c)(5)(A) (“knowing endangerment object”);
and (2) to defraud the United States by impairing, impeding,
and frustrating government agency investigations and clean-
up operations in violation of 18 U.S.C. § 371 (“defrauding
object”). On March 20, 2006, defendants moved to dismiss
the knowing endangerment object of the conspiracy, arguing
that the government had failed to allege an overt act in fur-
therance of the alleged conspiracy within the statute of limita-
tions period. United States v. W. R. Grace, 434 F. Supp. 2d
879, 883 (D. Mont. 2006).

   Defendants’ argument relied primarily on Yates v. United
States, 354 U.S. 298 (1957) (holding that the statute of limita-
tions must be satisfied as to each object of the conspiracy
when the government charges a multi-object conspiracy),
overruled on other grounds by Burks v. United States, 437
U.S. 1, 2 (1978). Because the government supposedly had
failed to allege a requisite overt act before the statute of limi-
tations ran on November 3, 2004, defendants asserted that the
knowing endangerment object was time-barred.

   The government disputed defendants’ characterization of
the indictment, claiming that certain overt acts alleged in the
indictment could support both the fraud object and the know-
ing endangerment object of Count I’s conspiracy charge.
Towards this end, the government directed the district court’s
attention to paragraphs 143, 149, and 173-184 of the indict-
                 UNITED STATES v. W. R. GRACE              12677
ment. W. R. Grace, 434 F. Supp. 2d at 885-87. The para-
graphs cited by the government alleged that defendants had
failed to remove asbestos-contaminated material from sites in
the Libby community, had misled various individuals regard-
ing current asbestos contamination, and had failed to disclose
the existence of numerous asbestos-contaminated sites. What
the paragraphs purportedly failed to allege was that defen-
dants released, or conspired to release, asbestos during the rel-
evant time period.

   Analyzing both the text of the specified paragraphs and the
structure of the indictment, in which the cited paragraphs
were listed under the sub-heading “Obstruction of EPA’s
Superfund Clean-Up,” the district court concluded that the
indictment “more plausibly suggests a completed operation
than a conspiracy still at work.” Id. at 887. To the extent that
overt acts were alleged, the district court found that they were
acts of obstruction, not acts of wrongful endangerment. Id.
Thus, the district court dismissed as time-barred the knowing
endangerment object of the Count I conspiracy. Id. at 888.

   Two weeks after the district court’s first order, dismissing
a portion of the indictment, the government obtained a super-
seding indictment. The new indictment was substantially sim-
ilar to the original indictment, amending only paragraphs 173-
183, which had been the focus of the district court’s previous
order. In the superseding indictment, the government changed
the section heading under which the disputed paragraphs had
been listed from “Obstruction of Superfund Clean-Up” to
“Knowing Endangerment of EPA Employees and the Libby
Community and Obstruction of the EPA’s Superfund Clean-
Up.” It also changed paragraphs 173, 174, 176-80, 182 and
183, by adding at the end of each original paragraph the
phrase, “thereby concealing the true hazardous nature of the
asbestos contamination, delaying EPA’s investigation and
12678             UNITED STATES v. W. R. GRACE
causing releases of asbestos into the air in the Libby Communi-
ty.”1

   Defendants then moved to dismiss the “knowing endanger-
ment” object of the superseding indictment, arguing that the
government had failed to fix the original indictment because
the new indictment alleged no new overt acts, was barred by
the previous dismissal “with prejudice,” and was time-barred
because the statute of limitations had run. The district court
rejected the first two arguments, but agreed with defendants
that the new indictment was time-barred. Under the district
court’s reading, the superseding indictment was not protected
by the savings clause of 18 U.S.C. § 3288. Order at 17,
United States v. W. R. Grace, 9:05-cr-00007-DWM (“Order
Dismissing Indictment”) (July 27, 2006) (Docket # 690). The
government now appeals that determination.

                    2.   Standard of Review

   We review de novo a district court’s decision to dismiss
part of an indictment, United States v. Barrera-Moreno, 951
F.2d 1089, 1091 (9th Cir. 1991), as we review, also de novo,
the district court’s interpretation of 18 U.S.C. § 3288. United
States v. Gorman, 314 F.3d 1105, 1110 (9th Cir. 2002).

                           3.   Analysis

   [1] If a district court dismisses an indictment (or portion
thereof), the savings clause of 18 U.S.C. § 3288 permits the
government to return a new indictment after the statute of lim-
itations has expired, as long as it is done within six months
of the dismissal. The statute reads as follows:

      Whenever an indictment or information charging a
      felony is dismissed for any reason after the period
      prescribed by the applicable statute of limitations has
  1
   Paragraph 175 was changed significantly.
                 UNITED STATES v. W. R. GRACE              12679
    expired, a new indictment may be returned in the
    appropriate jurisdiction within six calendar months
    of the date of the dismissal of the indictment or
    information . . . , which new indictment shall not be
    barred by any statute of limitations. This section
    does not permit the filing of a new indictment or
    information where the reason for the dismissal was
    the failure to file the indictment or information
    within the period prescribed by the applicable statute
    of limitations, or some other reason that would bar
    a new prosecution.

   [2] The dispute in the instant case stems from the parties’
divergent interpretations of the final sentence of § 3288. This
sentence explains that the savings clause does not extend to
indictments initially filed outside of the statute of limitations.
The government takes the position that this does not bar the
return of the new indictment because the original indictment
was obtained before the statute of limitations expired. Thus,
the government argues, § 3288 permits amendment by a
superseding indictment. Defendants disagree, arguing that the
government failed to allege an overt act for the knowing
endangerment object of the conspiracy before the statute of
limitations expired. The district court agreed with defendants
and dismissed the knowing endangerment object as time-
barred.

   [3] Defendants’ argument is premised on a conflation of the
terms “time-barred” and “not timely filed.” The last sentence
of § 3288 refers to indictments that were not timely filed, i.e.,
indictments that were not filed within the statute of limita-
tions. Here, there is no dispute that the government filed its
indictment within the statute of limitations period. The district
court dismissed the knowing endangerment object in the orig-
inal indictment as “time-barred” because it failed to allege an
overt act within the statute of limitations, not because the
indictment was untimely filed. The district court erred. If the
indictment is filed within six months of the dismissal order,
12680            UNITED STATES v. W. R. GRACE
§ 3288 does not bar the government from filing a superseding
indictment: the savings clause of § 3288 permits amendment
when the original was structurally flawed but timely filed.
United States v. Clawson, 104 F.3d 250 (9th Cir. 1996).

   In Clawson, the defendant was indicted for mail fraud on
June 10, 1993. Id. at 251. Defendant immediately moved to
dismiss the indictment for failure to allege an overt act within
the five-year statute of limitations. Id. The indictment alleged
overt acts that occurred before the limitation period began on
June 10, 1988, or after defendant’s withdrawal from the con-
spiracy on July 5, 1988. Id. The district court granted defen-
dant’s motion to dismiss the indictment and the government
responded by obtaining a First Superseding Indictment, which
alleged overt acts occurring in the window between June 10,
1988, and July 5, 1988. Id. Defendant then moved to dismiss
the new indictment, arguing that the statute had run before the
government obtained the First Superseding Indictment and
that § 3288 did not extend to indictments dismissed for failure
to comply with the statute of limitations. Id. The district court
denied his motion and we affirmed. Id. at 251-52.

   Clawson noted that when “[r]ead in its entirety, th[e] last
sentence [of § 3288] cuts off the six-month grace period only
where the defect — whether it’s a limitations problem ‘or
some other’ problem — is not capable of being cured.” Id. at
252. In the instant case, the district court held (and defendants
now argue) that the defect in the original indictment obtained
by the government is not capable of being cured because the
original indictment did not allege an overt act for the knowing
endangerment object before the statute of limitations expired.
This position, however, is precluded by Clawson.

   In Clawson we distinguished between a timely filed, but
flawed, indictment, to which the savings clause of § 3288
does apply, and an untimely filed indictment, to which it does
not.
                 UNITED STATES v. W. R. GRACE              12681
    “[I]f the original indictment was brought after the
    limitations period ran on all the alleged criminal con-
    duct, allowing reindictment under section 3288
    would obliterate the statute of limitations: A defen-
    dant could be indicted two years after the statute had
    run and, when the court dismissed, the prosecution
    could simply reindict within six months, free from
    the limitations bar.” Id.

   For obvious reasons, reindictment is prohibited by § 3288
in such circumstances. Id.

    “The matter is much different where the original
    indictment is brought within the limitations period,
    but is dismissed for failure to allege the exact ele-
    ments of the crime, or some other technical reason.
    In the latter circumstance, a valid indictment could
    have been brought in a timely fashion; the six-month
    grace period merely allows the government to do
    what it had a right to do in the first place.” Id.

   The latter circumstance describes the facts of both Clawson
and the instant case. In both cases, the government timely
indicted defendants for a particular crime, but originally failed
to allege a valid overt act. The government then obtained
superseding indictments charging defendants with the exact
same crimes, but adding the necessary overt act allegations.
Thus, each defendant was charged “with the exact crime for
which he could have been prosecuted had there not been a
defect in the indictment. Section 3288 was designed to apply
in this situation.” Id.; see also United States v. Charnay, 537
F.2d 341, 354 (9th Cir. 1976) (“[The] underlying concept of
§ 3288 is that if the defendant was indicted within time, then
approximately the same facts may be used for the basis of any
new indictment [obtained after the statute has run] . . . , if the
earlier indictment runs into legal pitfalls.”).

  [4] When discussing “timeliness,” both Clawson and
Charnay refer to the time of the original filing of the indict-
12682            UNITED STATES v. W. R. GRACE
ment. They do not consider whether the original indictment
included all of the relevant acts or elements necessary to
charge defendants with the crime. As long as the original
indictment is filed within the statute of limitations and
charges the same crime, based upon approximately the same
facts charged in the superseding indictment, § 3288 allows the
government to file a superseding indictment within six
months. See 18 U.S.C. § 3288; Clawson, 104 F.3d at 251-52;
Charnay, 537 F.2d at 354. Here, the parties do not dispute
that the original indictment was timely filed. The district
court’s holding that the indictment was time-barred referred
only to its failure to allege the necessary overt acts in the orig-
inal indictment — a flaw that can be cured through re-
indictment under § 3288.

   The district court attempted to distinguish Clawson, stating
that in Clawson the government alleged overt acts in the origi-
nal indictment, which was filed within the limitations period.
This distinction is irrelevant. While the government did allege
overt acts before the limitations period expired in Clawson, it
failed to allege an overt act sufficient to support the conspir-
acy charge since the only overt acts alleged occurred outside
the statute of limitations or subsequent to Clawson’s with-
drawal from the conspiracy. Thus, the government originally
failed to allege any relevant overt acts in Clawson, just as in
the instant case.

  Moreover, Clawson did not turn on the distinction
advanced by the district court: as we have explained, § 3288
applies when an indictment (though defective) is brought
within the limitations period, and the superseding indictment
charges defendant with the same exact crime with which he
was initially charged, based on approximately the same facts.
The only addition in the new indictment considered in Claw-
son was the inclusion of new overt acts that the government
could have used in the original indictment. The fact that the
government had timely alleged inapplicable overt acts was
wholly extraneous to the Clawson court’s decision.
                 UNITED STATES v. W. R. GRACE              12683
   The district court’s misapprehension of both Clawson and
§ 3288 is also clear from its statement that “[t]o allow the
government a six-month grace period in this case would
extend the statute of limitations for the improper purpose of
affording the prosecution a second opportunity to do what it
failed to do in the beginning.” Order Dismissing Indictment
at 16. Yet this is exactly what § 3288 does. It extends the stat-
ute of limitations by six months to allow the prosecution a
second opportunity to do what it failed to do in the beginning:
namely, file an indictment free of legal defects.

   This reading of § 3288 does not, as the district court sug-
gests, “require a defendant to remain subject to an indefinite
threat of prosecution, held open beyond the statute of limita-
tions period, while he and the court wait for the government
to finish tinkering with the indictment.” Id. What § 3288 does
is twofold: First, it eliminates the incentive for criminal defen-
dants to move for dismissal of an indictment at the end of the
statute of limitations, thereby winning dismissal at a time
when the government cannot re-indict. And second, it subjects
defendants to the threat of prosecution for six months after the
dismissal of the original indictment — not an indefinite threat
of prosecution as the district court suggests — and only if the
government has timely filed an indictment charging the exact
same crimes based on approximately the same facts.

   [5] For the reasons articulated herein, we reverse the dis-
trict court’s dismissal of the knowing endangerment object of
Count I in the superseding indictment and reinstate that por-
tion of the count.

                 II.   Definition of Asbestos

                       1.   Background

   We now turn to the question of whether Congress’s use of
the term “asbestos” to identify a hazardous air pollutant cre-
ated ambiguity as to what substance was meant by that term.
12684            UNITED STATES v. W. R. GRACE
The parties filed cross motions in limine to exclude evidence
that fell outside their respective interpretations of the term.
Govt. Mot. in Limine #2 Re: Definition of Asbestos (Docket
# 462); Defs’ Mot. in Limine Re: Definition of Asbestos
(Docket # 474). The district court held that the term “asbes-
tos” has no inherent meaning and therefore its use in the crim-
inal provisions of the Clean Air Act violated the rule of lenity
and the Due Process Clause of the Fourteenth Amendment. It
interpreted asbestos for purposes of the Clean Air Act’s
knowing endangerment provision to mean the six minerals
covered by EPA’s civil regulatory scheme. Order at 2 & 20,
United States v. W. R. Grace, 9:05-cr-00007-DWM (“Order
Defining Asbestos”) (Aug. 8, 2006) (Docket # 701). That reg-
ulation defines the civilly regulated species of asbestos as “the
asbestiform varieties of serpentinite (chrysotile), riebeckite
(crocidolite), cummingtonite-grunerite, anthophyllite, and
actinolite-tremolite.” Definitions for National Emission Stan-
dards for Hazardous Air Pollutants (“NESHAPs”), 40 C.F.R.
§ 61.141 (2007).

   The district court imported the civil regulatory definition of
“asbestos” into the criminal provisions of the Clean Air Act,
and then ruled that evidence of asbestos releases offered at
trial would be limited to those relevant to proving releases of
the six minerals included in the regulatory definition; evi-
dence of releases of other asbestiform minerals would be
excluded. Order Defining Asbestos at 22. This ruling elimi-
nated from trial evidence of releases of 95% of the contami-
nents in the Libby vermiculite — which are asbestiform
minerals but fall outside of the six minerals in the civil regula-
tory definition — as well as excluding government data that
did not differentiate between the six regulated minerals and
unregulated asbestiform minerals. The government appeals,
asserting that the definition contained in the criminal portion
of the statute is the applicable definition.

                  2.   Standards of Review

  We review de novo the district court’s construction of the
Clean Air Act, as we do rulings on the admissibility of evi-
                   UNITED STATES v. W. R. GRACE                    12685
dence in which issues of law predominate. See United States
v. Mateo-Mendez, 215 F.3d 1039, 1042 (9th Cir. 2000).

                             3.   Analysis

   [6] The Clean Air Act’s knowing endangerment provision
prohibits the knowing and dangerous release into the ambient
air of “any hazardous air pollutant listed pursuant to § 7412.”
42 U.S.C. § 7413(c)(5)(A).2 Section 7412(b) lists “asbestos,”
also identified by its Chemical Abstracts Service (“CAS”)3
Registry number 1332-21-4, as a hazardous air pollutant. 42
U.S.C. § 7412(b). Thus, § 7412(b) identifies asbestos by name
and defines it through reference to CAS Registry # 1332-21-
4.
  2
   42 U.S.C. § 7413(c)(5)(A) reads in relevant part:
      Any person who knowingly releases into the ambient air any haz-
      ardous air pollutant listed pursuant to section 7412 of this title
      . . . , and who knows at the time that he thereby places another
      person in imminent danger of death or serious bodily injury shall,
      upon conviction, be punished by a fine under Title 18, or by
      imprisonment of not more than 15 years, or both. Any person
      committing such violation which is an organization shall, upon
      conviction under this paragraph, be subject to a fine of not more
      than $1,000,000 for each violation. If a conviction of any person
      under this paragraph is for a violation committed after a first con-
      viction of such person under this paragraph, the maximum pun-
      ishment shall be doubled with respect to both the fine and
      imprisonment. For any air pollutant for which the Administrator
      has set an emissions standard or for any source for which a per-
      mit has been issued under subchapter V of this chapter, a release
      of such pollutant in accordance with that standard or permit shall
      not constitute a violation of this paragraph or paragraph (4).
   3
     The Chemical Abstracts Service Registry, maintained by the American
Chemical Society, is an authoritative database of chemical information.
The Registry assigns each chemical substance a unique numeric identifier.
Searches in the Registry require subscription. However, EPA maintains on
its website a free “Substance Registry System” containing CAS Registry
information, including the CAS definition of asbestos. http://
www.epa.gov/srs/ (search “asbestos”; follow link associated with 1332-
21-4) (last visited Aug. 3, 2007).
12686             UNITED STATES v. W. R. GRACE
   The government contends that a statute may have two defi-
nitions for one term, one definition civil and one criminal.
Further, it argues that the definition of asbestos applicable to
the Clean Air Act’s criminal knowing endangerment provi-
sion covers the minerals involved in this case. We agree on
both points.

   The district court found § 7412(b)’s “one-word definition”4
to be “unsatisfactory” as a matter of law. However, Congress
need not define every word in a criminal statute for the statute
to pass Constitutional muster. When Congress does not define
a term in a statute, we construe that term “according to [its]
ordinary, contemporary, common meaning[ ].” United States
v. Cabaccang, 332 F.3d 622, 626 (9th Cir. 2003) (en banc)
(internal quotation marks omitted). It is well known that
asbestos has a common meaning; it is a fibrous, non-
combustible compound that can be composed of several sub-
stances, typically including magnesium. Or, as defined by the
CAS Registry, and incorporated by reference into § 7412(b),
it is a “grayish non-combustible material” that “consists pri-
marily of impure magnesium silicates.” CAS Registry number
1332-21-4, available at http://iaspub.epa.gov/srs/srs_proc_
qry.navigate?P_SUB_ID=85282. This definition has been
established for decades, as was elucidated in the motions in
limine. See Defs’ Mot. in Limine Re: Definition of Asbestos
n.4 (Expert Witness Disclosure of Gregory P. Meeker,
Appendix A) (May 31, 2006) (noting that asbestos was first
defined in 1920).

   [7] In addition, defendants had actual notice in this case of
the risks from the fibrous content of the asbestiform minerals
in their products. Defendants are an industrial chemical com-
pany and seven of its top executives. They are all familiar
with asbestos. Since at least 1976, defendants have known of
the health risks posed by the asbestiform minerals in their
products. It is clear that defendants knew or should have
  4
   I.e., “1332214 Asbestos”
                UNITED STATES v. W. R. GRACE              12687
known that their mining, milling, and distribution activities
risked the release of asbestos into the ambient air. In light of
the clear statutory language, including § 7412(b)’s incorpora-
tion by reference of the CAS Registry asbestos definition, and
defendants’ knowledge of the industrial chemicals field, the
district court erred in misdefining “asbestos” as used in the
criminal statute and in invoking the rule of lenity. See Musca-
rello v. United States, 524 U.S. 125, 138 (1998) (“The rule of
lenity applies only if, after seizing everything from which aid
can be derived, . . . we can make no more than a guess as to
what Congress intended.”) (alteration in original) (internal
quotation marks omitted); United States v. Lanier, 520 U.S.
259, 266 (1997) (The “rule of lenity[ ] ensures fair warning by
so resolving ambiguity in a criminal statute as to apply [the
statute] only to conduct clearly covered.”).

   The district court’s conclusion that ambiguity exists simply
because of the existence of two oversight structures — a civil
regulatory structure and a criminal enforcement provision —
that use different definitions of the term “asbestos” is errone-
ous. As we determined in United States v. Hagberg, 207 F.3d
569, 573 (9th Cir. 2000), Congress validly may create multi-
ple enforcement mechanisms that each draw on different defi-
nitions for the same term or phrase.

   In Hagberg, defendant was indicted for allegedly dumping
sewage along a public road in violation of the Clean Water
Act, 33 U.S.C. §§ 1319(c)(2), 1345(e). Hagberg at 570. Mov-
ing to dismiss the indictment, Hagberg argued that his actions
did not fit within the statutory definition of the crime because
the material he dumped was not “sewage sludge” as defined
by the regulations for permitting waste disposal. Id. at 571.
Accepting Hagberg’s argument, the district court dismissed
the indictment. The government appealed. Id. We reversed
because the district court improperly had conflated the regula-
tory and direct enforcement provisions of the Clean Water
Act, and the relevant definition — supplied by the direct
enforcement provision — covered the material dumped by
12688            UNITED STATES v. W. R. GRACE
defendant. Id. at 571-72, 575. We explained that “some terms
found in the [direct enforcement provision] are defined differ-
ently when used in the context of [the civil permitting] regula-
tions.” Id. at 572.

   Like the Clean Water Act provisions at issue in Hagberg,
the Clean Air Act creates multiple enforcement mechanisms:
a civil regulatory structure and a direct enforcement mecha-
nism. In the instant case, as in Hagberg, defendants are
charged with violating the directly enforceable provision of
the statute that pulls its definitions from a separate provision
than does the regulatory provision. The civil regulatory sys-
tem draws its definition of asbestos from 40 C.F.R. § 61.141,
the knowing endangerment provision from 42 U.S.C.
§ 7412(b). See 42 U.S.C. §§ 7412(a)(6); 7413(c)(5)(A). The
civil regulatory system regulates major sources of hazardous
air pollutants, 42 U.S.C. § 7412(c)-(g), and therefore under-
standably focuses on a subset of asbestifom minerals deemed
to have commercial potential; market forces preclude com-
mercially non-viable species of asbestos from becoming
major sources of pollution from asbestos mills and mines and
other covered sources. The direct enforcement mechanism
created in 42 U.S.C. § 7413 focuses on risks to health. There-
fore it provides oversight of release of hazardous pollutants
whether or not they come from major sources of pollution.
We defer to Congress’s decision to create two enforcement
structures and hold the district court’s conflation of the two to
be error.

   [8] In sum, the district court improperly limited the term
“asbestos” to the six minerals covered by the civil regulations.
Asbestos is adequately defined as a term and need not include
mineral-by-mineral classifications to provide notice of its haz-
ardous nature, particularly to these knowledgeable defendants.
Accordingly, we reverse the order limiting evidence to that
fitting within the civil regulations.
                 UNITED STATES v. W. R. GRACE              12689
                       III.    Mandamus

                       1.     Background

   [9] The knowing endangerment provision of the Clean Air
Act establishes an affirmative defense for hazardous air pollu-
tants released “in accordance with” an applicable National
Emissions Standards for Hazardous Air Pollutants
(“NESHAP”). See 42 U.S.C. § 7413(c)(5)(A). In the proceed-
ings before the district court, the government argued that
defendants could not avail themselves of this affirmative
defense because no NESHAP applied to W.R. Grace’s opera-
tions in Libby; thus, compliance with an “applicable”
NESHAP was impossible. The district court rejected this
argument, finding that the regulations created an emissions
standard of “no visible emissions” for asbestos. Accordingly,
the district court ruled that it would allow defendants to intro-
duce evidence at trial to try to prove their affirmative defense.
Because the district court did not exclude any of the govern-
ment’s emissions evidence as a result of this ruling, the gov-
ernment cannot appeal the district court’s decision. Instead, it
now seeks a writ of mandamus to overturn the decision.

                  2.   Standard of Review

   The writ of mandamus is codified at 28 U.S.C. § 1651(a):
“The Supreme Court and all courts established by Act of Con-
gress may issue all writs necessary or appropriate in aid of
their respective jurisdictions and agreeable to the usages and
principles of law.” This court has developed a five-factor test
for determining whether a writ may issue. We must consider
whether:

    (1) The party seeking the writ has no other adequate
    means, such as direct appeal, to attain the relief he
    or she desires.

    (2) The petitioner will be damaged or prejudiced in
    a way not correctable on appeal.
12690            UNITED STATES v. W. R. GRACE
    (3) The district court’s order is clearly erroneous as
    a matter of law.

    (4) The district court’s order is an oft-repeated error,
    or manifests a persistent disregard of the federal
    rules.

    (5) The district court’s order raises new and impor-
    tant problems, or issues of law of first impression.

Clemens v. U. S. Dist. Ct., 428 F.3d 1175, 1177-78 (9th Cir.
2005) (quoting Bauman v. United States Dist. Ct., 557 F.2d
650, 654-55 (9th Cir. 1977)). Not every factor must be present
to warrant mandamus relief, see id. at 1178, and in this case
the only disputed issue is whether the district court made a
clear error as a matter of law.

                         3.   Analysis

   Where, as here, the district court’s order involves issues of
statutory interpretation, the order is clearly erroneous as a
matter of law if the reviewing court is left with “a definite and
firm conviction that the district court’s interpretation of the
statute was incorrect.” DeGeorge v. United States Dist. Court,
219 F.3d 930, 936 (9th Cir. 2000) (citing In re Cement Anti-
trust Litig., 688 F.2d 1297, 1306 (9th Cir. 1982)); see also
United States v. Ye, 436 F.3d 1117, 1123 (9th Cir. 2006).
Here, the plain language of the statute makes clear that the
affirmative defense is not applicable to defendants’ actions.

   [10] In relevant part, § 7413(c)(5)(A) states, “[f]or any air
pollutant for which the Administrator has set an emissions
standard . . . , a release of such pollutant in accordance with
that standard . . . shall not constitute a violation of this para-
graph.” The first clause of the affirmative defense makes it
inapplicable to Grace’s alleged asbestos releases. Quite sim-
ply, asbestos is not an “air pollutant for which the Administra-
tor has set an emissions standard.” § 7413(c)(5)(A) (emphasis
                   UNITED STATES v. W. R. GRACE                   12691
added). Rather, the Administrator has set several emissions
standards, each of which is source dependent. Some asbestos
emissions standards make no reference at all to “visible emis-
sions.” See 40 C.F.R. §§ 61.143, 61.145, & 61.148. Others
include additional procedural requirements, above and beyond
the “no visible emissions” requirement. See 40 C.F.R.
§§ 61.142, 61.144, 61.146, 61.149, & 61.150. In short, there
is simply no trans-categorical emissions standard for asbestos;
neither is there an emissions standard for asbestos releases
from mining operations.5 Therefore, it is inconceivable that
the alleged Grace releases were “in accordance with that stan-
dard.” § 7413(c)(5)(A). The plain language of the statute
makes clear that the affirmative defense simply doesn’t apply
in this case. The district court’s order to the contrary leaves
us with a “a definite and firm conviction” that it got the law
wrong. DeGeorge, 219 F.3d at 936. Consequently, we grant
the government’s petition for writ of mandamus, and hold that
W.R. Grace can not avail itself at trial of the affirmative
defense articulated in 42 U.S.C. § 7413(c)(5)(A).

                    IV.    Evidentiary Rulings

                          1.   Introduction

   As stated above, Counts II-IV of the superseding indict-
ment allege violations of 42 U.S.C. § 7413(c)(5)(A), the
Clean Air Act’s knowing endangerment provision, which
creates criminal penalties for a person who “knowingly
releases into the ambient air any hazardous air pollutant listed
pursuant to section 7412 of this title . . . and who knows at
the time that he thereby places another person in imminent
danger of death or serious bodily injury.” Defendants filed
motions in limine seeking to exclude evidence related to, or
  5
   A perusal of the table of contents for 40 C.F.R. § 61 shows that most
hazardous pollutants do in fact have a single emissions standard, enumer-
ated in a single code section. See, e.g., §§ 61.22, 61.32, 61.42, 61.52.
Asbestos, however, does not. See §§ 61.142-.151.
12692           UNITED STATES v. W. R. GRACE
testimony based on, certain studies — EPA indoor air studies
(“Indoor Air studies”), Grace’s historic testing of its vermicu-
lite products (“Historic Testing”), a report of the Agency for
Toxic Substances and Disease Registry based on a medical
screening study of residents of Libby, Montana (“ATSDR
Report”), and the results of the screening study published as
an article in a peer-reviewed journal (“Peipins Publication”).
Ruling that these studies were unreliable, irrelevant, or unduly
prejudicial, the district court barred government experts from
relying on them in forming opinions regarding the knowing
endangerment charges, and, as to the indoor air studies, the
ATSDR Report, and the Peipins Publication, excluding the
studies, report, and publication themselves for most or all pur-
poses. Order, United States v. W. R. Grace, 9:05-cr-00007-
DWM (Aug. 21, 2006) (“Indoor Air Order”); Order, United
States v. W. R. Grace, 9:05-cr-00007-DWM (Aug. 28, 2006)
(“Historical Testing Order”); Order, United States v. W. R.
Grace, 9:05-cr-00007-DWM (Aug. 31, 2006) (“ATSDR and
Peipins Order”). The government appeals.

                  2.    Standard of Review

   This court reviews de novo the district court’s interpreta-
tion of the Federal Rules of Evidence. United States v. Sioux,
362 F.3d 1241, 1244 n.5 (9th Cir. 2004). In general, this court
reviews for abuse of discretion a district court’s decision to
admit or exclude scientific evidence and expert testimony.
United States v. Finley, 301 F.3d 1000, 1007 (9th Cir. 2002).
“[A] trial court has ‘broad discretion’ in assessing the rele-
vance and reliability of expert testimony.” Id. (quoting United
States v. Murillo, 255 F.3d 1169, 1178 (9th Cir. 2001)).

                       3.   Relevant Rules

   Federal Rule of Evidence 401 defines “relevant evidence”
as that which has “any tendency to make the existence of any
fact that is of consequence to the determination of the action
more probable or less probable than it would be without the
                   UNITED STATES v. W. R. GRACE                    12693
evidence.” Rule 402 provides that relevant evidence is admis-
sible, except as limited by the Constitution, statutes, or other
rules of evidence. Rule 403 provides a balancing test for the
exclusion of relevant evidence on the grounds of prejudice:
relevant evidence may be excluded if “probative value is sub-
stantially outweighed by the danger of unfair prejudice, con-
fusion of the issues, or misleading the jury. . . .”6

   Several rules apply specifically to testimony by experts.
Under Rule 702, an expert witness may provide opinion testi-
mony if “the testimony is based upon sufficient facts or data”
and “is the product of reliable principles and methods,” which
have been “applied . . . reliably to the facts of the case.” The
rule “affirms the court’s role as gatekeeper and provides some
general standards that the trial court must use to assess the
reliability and helpfulness of proffered expert testimony.”
Advisory Comm. Notes, Rule 702 (2000).

   Under Rule 703, the “facts or data . . . upon which an
expert bases an opinion or inference may be those perceived
by or made known to the expert at or before the hearing. If
of a type reasonably relied upon by experts in the particular
field in forming opinions or inferences upon the subject, the
facts or data need not be admissible in evidence in order for
the opinion or inference to be admitted.” However, if the
expert relies on facts or data that are otherwise inadmissible,
then those facts “shall not be disclosed to the jury by the pro-
ponent of the opinion or inference unless the court determines
that their probative value in assisting the jury to evaluate the
expert’s opinion substantially outweighs their prejudicial
effect.”7
  6
     Advisory committee notes from 1972 discuss the meaning of unfair
prejudice — the “undue tendency to suggest decision on an improper
basis, commonly . . . an emotional one” — and observe that the “availabil-
ity of other means of proof may also be an appropriate factor” of deter-
mining when there is unfair prejudice.
   7
     To the extent that inadmissible evidence is reasonably relied upon by
an expert, a limiting instruction typically is needed — i.e., the evidence
12694               UNITED STATES v. W. R. GRACE
                             4.    Analysis

                      A.    Indoor Air Releases

                            i.    Background

  On May 31, 2006, Defendants filed a motion in limine to
exclude evidence of or derived from indoor asbestos releases.
Defendants sought to exclude documents and studies, includ-
ing EPA’s Phase II air sampling charts, as well as expert testi-
mony that relied upon these studies. See Defs’ Mot. in Limine
Re: Indoor Air Releases at 4-6 (Docket # 473).

   On August 28, 2006, the district court granted defendants’
motion “with respect to evidence of or derived from indoor
releases offered for the purpose of proving an ‘ambient air’
release in violation of 42 U.S.C. § 7413(c)(5)(A).” Indoor Air
Order at 11. The district court held that “[i]ndoor sampling
performed by EPA in the course of its CERCLA activities,
and testimony based upon this sampling, is not relevant
[under Fed. R. Evid. 402] to whether Defendants committed
a release in violation of the Clean Air Act, and is not admissi-
ble for the purpose of proving such a release.” Id. at 8. The
court stated that, under Federal Rules of Evidence 403,
“[e]vidence derived from EPA testing and sample collection
performed as part of its CERCLA analysis has the potential
to be highly confusing and prejudicial,” id. at 10, and barred
the evidence for most purposes related to the Clean Air Act
counts. However, the court held that the evidence had proba-
tive value with respect to defendants’ “knowledge of the dan-
gerousness of the asbestos contaminated vermiculite,” id. at 8,

is admitted only to help the jury evaluate the expert’s evidence. E.g.,
United States v. 0.59 Acres of Land, 109 F.3d 1493, 1496 (9th Cir. 1997)
(error to admit hearsay offered as the basis of an expert opinion without
a limiting instruction). There is a presumption against disclosure to the
jury of inadmissible information used as the basis for expert’s opinion. See
Advisory Comm. Notes, Rule 703 (2000).
                 UNITED STATES v. W. R. GRACE              12695
relevant to the government’s argument that defendants know-
ingly “place[d] another person in imminent danger of death or
serious bodily injury,” 42 U.S.C. § 7413(c)(5)(A), by releas-
ing vermiculite into the community. In addition, the district
court held the evidence relevant to the defrauding object of
Count I’s conspiracy charge and to the four counts of obstruc-
tion of justice in the superseding indictment. The district court
thus denied the motion with respect to establishing knowledge
of risk for the Clean Air Act charges and with respect to prov-
ing the obstruction and conspiracy counts. The government
appeals the exclusion of the Indoor Air studies and expert tes-
timony based upon them with regard to the knowing endan-
germent counts.

                         ii.   Analysis

   [11] The government argues that EPA’s Phase II tests show
the propensity of the Libby asbestos to release fibers when-
ever it was disturbed and regardless of the form the vermicu-
lite took and therefore should be admitted to form the basis
of expert testimony. The government also makes an argument
that the Indoor Air studies should themselves be admitted as
relevant. However, although the government makes a valid
argument about the friability of Libby asbestos being the
same whether indoors or outdoors, the probative value of the
EPA studies is possibly outweighed by the danger of unfair
prejudice. First, the studies’ overall probative value is low
because they largely concern the asbestos releases at various
indoor locations in Grace’s Libby mining and milling opera-
tion. There is some information in the studies regarding the
friable character of Libby asbestos, but not much. There is a
risk of unfair prejudice because the indoor releases may not
reflect the level of releases into the ambient air, and there is
some language in the studies regarding asbestos-related dis-
eases in Libby that may mislead or confuse the jury into
believing that releases into indoor air proves releases into
ambient air. Finally, even if this court disagreed with the dis-
trict court’s Rule 403 balancing, “[a]n appellate court will not
12696               UNITED STATES v. W. R. GRACE
reengage in a balancing of the probative value and prejudicial
effect.” Rogers v. Raymark Industries, Inc., 922 F.2d 1426,
1430 (9th Cir. 1991). The district court’s decision to bar the
use of documents and studies derived from indoor air releases
for the purpose of proving a release into the ambient air was
within its discretion.

   [12] It is a separate question, however, whether the district
court abused its discretion in excluding expert testimony
based on documents and studies derived from indoor air
releases. The district court did not conduct an inquiry under
Rule 7028 or 7039 in its August 28th order. Rule 703 provides,
“If of a type reasonably relied upon by experts in the particu-
lar field in forming opinions or inferences upon the subject,
the facts or data need not be admissible in evidence in order
for the opinion or inference to be admitted.” (Emphasis
added.) The government persuasively argues that the proper
remedy for the problems associated with the indoor air studies
is to prevent an expert from disclosing the prejudicial facts
instead of preventing the expert from relying on them alto-
gether. Allowing expert testimony based on the EPA studies
“will assist the trier of fact to understand the evidence or to
determine a fact in issue” under Rule 702 because the studies
may show the propensity of the asbestos-contaminated ver-
  8
     Fed. R. Evid. 702 provides, “If scientific, technical, or other special-
ized knowledge will assist the trier of fact to understand the evidence or
to determine a fact in issue, a witness qualified as an expert by knowledge,
skill, experience, training, or education, may testify thereto in the form of
an opinion or otherwise.”
   9
     Fed. R. Evid. 703 provides, “The facts or data in the particular case
upon which an expert bases an opinion or inference may be those per-
ceived by or made known to the expert at or before the hearing. If of a
type reasonably relied upon by experts in the particular field in forming
opinions or inferences upon the subject, the facts or data need not be
admissible in evidence in order for the opinion or inference to be admitted.
Facts or data that are otherwise inadmissible shall not be disclosed to the
jury by the proponent of the opinion or inference unless the court deter-
mines that their probative value in assisting the jury to evaluate the
expert’s opinion substantially outweighs their prejudicial effect.”
                         UNITED STATES v. W. R. GRACE      12697
miculite to release asbestos fibers into the ambient air. While
the specific asbestos concentration levels discussed in the
studies are not relevant because the studies largely measured
indoor air releases and gathered data under conditions differ-
ent from the ambient air releases relevant to the statute, the
government’s experts should be permitted to opine generally
about the friability of Libby asbestos based in part on the data
in the studies. The data from the indoor sampling is relevant
to the propensity of Libby asbestos to release fibers upon dis-
turbance. Based on these data, an expert could testify about
friability and whether a release of asbestos would occur if
asbestos-contaminated vermiculite were exposed or disturbed.
Because the district court did not inquire into whether the data
provided by the indoor air tests is of the type reasonably
relied upon by experts in the field, see Fed. R. Evid. 703, or
whether the data fits under Rule 702, we remand so that the
district court can conduct these inquiries in the first instance.

          B.       W.R. Grace’s Historic Product Testing

                               i.   Background

   On May 31, 2006, defendants filed a motion in limine to
exclude expert opinions regarding Grace’s historical, non-
ambient air product and commercial testing. Defendants
sought to exclude the testimony of Dr. Richard Lemen,10 Dr.
Vernon Rose,11 Paul Peronard,12 Dr. Aubrey Miller,13 Dr.
Chris Weis,14 and other government witnesses who might “at-
tempt to draw unsupportable correlations between Grace’s
historical product and commercial tests and expected ambient
air exposures from disturbances of vermiculite materials
  10
     Docket   #   287.
  11
     Docket   #   283.
  12
     Docket   #   281.
  13
     Docket   #   279.
  14
     Docket   #   286.
12698            UNITED STATES v. W. R. GRACE
found in the town of Libby.” Defs’ Mot. in Limine Re: His-
toric Testing at 4 (Docket # 496). On August 29, 2006, the
district court granted defendants’ motion to exclude expert
testimony based on historic testing offered to prove a release
in violation of 42 U.S.C. § 7413(c)(5)(A). Historic Testing
Order at 7. The district court denied defendants’ motion with
respect to expert testimony based on historic testing offered
for the purpose of showing defendants’ knowledge of the dan-
gerousness of the asbestos contaminated vermiculite. Id.

                         ii.   Analysis

   Rule 702 authorizes expert testimony that “will assist the
trier of fact” when the testimony “is based upon sufficient
facts or data,” the testimony is produced through “reliable
principles and methods,” and the expert witness “has applied
the principles and methods reliably to the facts of the case.”
Generally, an inquiry under Rule 702 examines the expert’s
testimony as a whole. The 702 inquiry typically does not
examine the reliability or relevance of particular data sets that
underlie the expert testimony, although this approach does no
harm where the expert testifies on only one study or where no
combination or addition of data could make the data in ques-
tion a proper, reliable basis for making a given claim. In con-
trast to Rule 702’s holistic focus on an expert’s testimony,
Rule 703 governs the inquiry into the reliability of particular
data underlying expert testimony. Fed. R. Evid. 703; see also
Claar v. Burlington Northern R. Co., 29 F.3d 499, 501 (9th
Cir. 1994).

   [13] Here, the district court excluded the historic testing
data under Rule 702. This document-based approach creates
the problem that one cannot know fully whether or in what
ways other information sources are meant to, in combination
with the challenged data sources, form the premise for the
expert testimony. Each document must be dispositive under
the district court’s approach, a requirement we do not impose
under Rule 702. On remand, the district court shall conduct
                    UNITED STATES v. W. R. GRACE                     12699
the Rule 702 analysis in light of the expert’s reasoning and
methodology as a whole.

   [14] Faced with this new 702 analysis, defendants presum-
ably will argue, as they do on appeal, that the historic testing
evidence fails the “fit” test under Daubert v. Merrell Dow
Pharm., Inc., 509 U.S. 579 (1993).15 In response, the govern-
ment argues that its experts do not plan to rely on the historic
testing data to estimate the fiber concentrations from the
charged releases, but only to opine generally on the hazardous
characteristics16 of Libby asbestos contaminated vermiculite.
This limited use of the study to inform experts’ opinions is
permissible, because the propensity of Libby asbestos to
release fibers fits the release element of the knowing endan-
germent provision. The district court did not consider this
propensity-to-release inquiry, thus abusing its discretion by
excluding this evidence under 702.

  Defendants make two additional, ultimately unsupportable
arguments. First, they argue that the testimony’s exclusion
under Rule 702 was proper because the government’s experts
“do not need” the evidence on historic air releases to testify
about the friability of Libby asbestos. This argument miscon-
ceives Rule 702’s inquiry, which focuses on fitness, rele-
vance, and reliability, not on whether an expert potentially has
other evidence on which to base an opinion. Second, defen-
dants argue that the district court properly excluded the testi-
mony under Rule 403 in addition to Rule 702. Contrary to
defendants’ assertion, however, the district court did not rely
on Rule 403 in its historic testing order but discussed the
admissibility of expert testimony only under Rule 702. More-
over, an expert reasonably may rely on inadmissible evidence
  15
      This phrasing of the argument improperly focuses the 702 inquiry on
a document-by-document approach that we disapproved supra.
   16
      I.e., the propensity of Libby asbestos to break down and release fibers
into the ambient air.
12700           UNITED STATES v. W. R. GRACE
in forming an opinion or delivering testimony. See Fed. R.
Evid. 703.

   [15] The question remains whether data concerning indoor
air quality are of the type reasonably relied on by other
experts in the field. See Fed. R. Evid. 703. Although it
appears that the district court never conducted this 703
inquiry, the second step of the Rule 702 analysis — that the
study was “the product of reliable principles and methods” —
presumably answers this question in the affirmative. See Rule
702; see also Claar, 29 F.3d at 501 (“Rule 703 merely
relaxes, for experts, the requirement that witnesses have per-
sonal knowledge of the matter to which they testify,” not
whether the requirements of 702 are properly met). Although
not stated explicitly, the order implicitly found the historic
testing reliable in finding it admissible under 702 to show
knowledge. Historic Testing Order at 3-4. Thus, the historic
testing is admissible for purposes of expert opinion formation
and testimony regarding the propensity of Libby vermiculite
to release asbestos as relevant to 42 U.S.C. § 7413(c)(5)(A).
Accordingly, we reverse the district court order excluding
such testimony.

     C.   Medical Screening Study: ATSDR and Peipins
                        Publication

                       i.   Background

   In 2000-2001, the Agency for Toxic Substances and Dis-
ease Registry (“ATSDR”) conducted a medical screening
study in Libby (the “ATSDR Report”) to detect pleural abnor-
malities in Libby residents and to inform priority-setting in
EPA’s asbestos clean-up operation. The study entailed inter-
viewing and medically testing individuals who had lived,
worked, attended school, or participated in other activities in
Libby for at least six months before 1990. Questions were
asked to identify individuals who had accessed potential “ex-
posure pathways” to asbestos and vermiculite prior to Decem-
                UNITED STATES v. W. R. GRACE              12701
ber 31, 1990. For example, “pathways” included employment
at W. R. Grace, living with W. R. Grace workers, using ver-
miculite for gardening, and engaging in recreational activities
in certain locations known to contain vermiculite. Information
about other basic demographic variables and risk factors was
also gathered, e.g., age, sex, smoking status, history of pulmo-
nary disease and various other self-reported health conditions.

  ATSDR published an initial report of the study’s findings
in February 2001. The complete results of the study (the
“Peipins Publication”) were published in November 2003 in
Environmental Medicine, a peer-reviewed journal. The
Peipins Publication analysis used regression modeling to esti-
mate the risk of respiratory abnormalities for each of the
exposure pathways while controlling for all other pathways
and other established and suggested risk factors.

   The study showed that certain factors — including expo-
sure to particular pathways — were associated with respira-
tory illness and abnormalities. The factors most strongly
associated with abnormalities were: being a former W. R.
Grace employee, being older, having had household contact
with a former W. R. Grace worker, and being male. (The
study also demonstrated “a statistically significant increase in
the prevalence of pleural abnormalities with an increasing
number of exposure pathways.” While “participants reporting
more pathways might be expected to have more cumulative
exposure than would those reporting fewer pathways,” this
was not data gathered by the study; the study identified ave-
nues for exposure but did not quantify the duration or inten-
sity of individuals’ exposures.

   Both the interim ATSDR Report and the final Peipins Pub-
lication noted that the study had no control group and “no
directly comparable Montana or U.S. population studies
[were] available.” The researchers were able to compare the
data gathered with studies of other groups with substantive
work-related asbestos exposure. The levels of pleural abnor-
12702               UNITED STATES v. W. R. GRACE
malities were higher in Libby than in studies of other groups,
but the study did not engage in any direct quantitative compari-
son.17

   On May 31, 2006, defendants filed a motion in limine “to
exclude expert evidence relating to the ATSDR Medical Test-
ing Program.” Defs’ Mot. in Limine Re: ATSDR (Docket
# 500, 502). The district court characterized the motion as one
to exclude “any evidence or expert testimony relating to” the
medical screening study conducted in Libby by the Agency
for Toxic Substances and Disease Registry. ATSDR Order at
1. The government did not object to the court’s characteriza-
tion of defendants’ motion. On August 31, 2006, the district
court granted defendants’ motion. The court ruled that the
ATSDR Report and Peipins Publication, and any expert testi-
mony based thereon, were excluded under Rules 403 and 702
for any purpose relating to the Clean Air Act knowing endan-
germent counts. Id. at 31.

                              ii.   Analysis

  [16] The district court acted within its discretion in exclud-
ing the ATSDR Report and Peipins Publication themselves
under Rule 403 for purposes of the knowing endangerment
counts. There are limits to the probative value18 of the particu-
  17
      The results of the ATSDR Report were also compared with “control
groups or general populations found in other studies.” That comparison
showed that the levels of pleural abnormalities were also higher in Libby
for those who claimed “no apparent exposure” to particular pathways than
subjects in other studies. This supported the study’s conclusion that it was
unlikely that there were individuals in Libby who had not been exposed
to some degree.
   18
      The study demonstrated an association between negative health out-
comes and an individual’s unquantified exposure to vermiculite via partic-
ular “pathways” prior to the statutory period. The existence of association
— and not causation — goes to the probative value of the evidence. The
reported findings did not indicate that all exposure pathways were signifi-
cantly associated with lung abnormalities (for example, gardening with
                   UNITED STATES v. W. R. GRACE                     12703
lar correlations the ATSDR Report revealed and potentially
prejudicial aspects to the data. Moreover, the government
failed to contest the district court’s undue prejudice conclu-
sion. Because Rule 403 requires the district court to balance
the probative value and the prejudicial effects of a piece of
evidence, failure to raise and argue prejudice generally waives
the argument. See United States v. Wilson, 966 F.2d 243, 245-
46 (7th Cir. 1992).

   [17] However, in excluding this evidence from informing
expert opinion and testimony, the district court erred. The
expert is, in the first instance, the judge of what resources
would help him to form an opinion, and he can filter out as
irrelevant prejudicial information. The trial judge is to assure
the reliability of evidence by vetting under Rule 703 the bases
underlying the expert’s testimony and by examining under
Rule 702 the expert’s methodology. Here, however, the trial
judge misapplied Rule 702 and replaced inappropriately the
Rule 703 analysis with one under Rule 403.

   To begin, the district court concluded that the ATSDR
medical screening program and resulting analyses did not
establish a causal link between exposure to Libby’s vermicu-
lite and the development of asbestos-related disease. The
ATSDR Report acknowledged repeatedly that the testing pro-
gram was not designed as an epidemiological study to show
causality. Notably, there was no internal control group and the
participants were self-selected, rather than randomly selected.
In light of this, the district court concluded that the data could
not provide experts with a reliable basis for opining as to cau-

vermiculite is not one of the factors mentioned as one being associated
with such abnormalities). Because the data were gathered before the statu-
tory period, it is questionable how reliable a basis they provide for draw-
ing conclusions about the extent of the dangers posed by ambient releases
during the statutory period, i.e., concentration or duration of releases.
However, this is more an issue for the expert than the court.
12704           UNITED STATES v. W. R. GRACE
sality (i.e., the danger posed by the releases from Libby ver-
miculite).

   Nonetheless, one of the main objectives of the ATSDR
Report was to examine the association between pleural and
interstitial abnormalities and participants’ exposure histories
— measured in broad terms by the participants’ overall con-
tact with exposure pathways. As the district court acknowl-
edged, the government’s experts did not claim that they
intended to use the study to show causation, but rather indi-
cated that they would rely on the evidence to show that there
were some associations or correlations between exposure to
vermiculite in Libby and pleural abnormalities.

   The district court took the view that the jury would be
unlikely to distinguish between evidence of an association and
evidence of causation and therefore would likely be misled,
and would place undue reliance on the evidence. In this
respect, the court substantially underestimated the capacity of
jury instructions to distinguish these relationships, and the
potential efficacy of a limiting instruction.

   Further, the fact that a study is associational — rather than
an epidemiological study intended to show causation — does
not bar it from being used to inform an expert’s opinion about
the dangers of asbestos releases, assuming the study is “of the
type typically relied upon” by experts in the field. Fed. R.
Evid. 703. Of course, the expert’s opinion testimony must sat-
isfy the requirements of Rule 702—but that requires consider-
ation of the overall sufficiency of the underlying facts and
data, and the reliability of the methods, as well as the fit of
the methods to the facts of the case. Fed. R. Evid. 702.

   Here, the district court failed to consider the Rule 702
requirements with regard to causation. Instead, as with the
historical testing, the court conducted a document-by-
document Rule 702 analysis that deconstructed the experts’
testimony in a manner not contemplated by Rule 702. More-
                 UNITED STATES v. W. R. GRACE              12705
over, the study, which was published in a peer-reviewed jour-
nal and relevant to association, is adequate under 702. The
study’s failure to establish causation goes to the weight it
should be accorded, but does not mean that an expert could
not rely on it in forming an opinion.

   Nor did the district court consider the possibility of expert
reliance on the ATSDR Report without disclosure of the study
itself to the jury, as provided for by Rule 703 (“If of a type
reasonably relied upon by experts in the particular field in
forming opinions or inferences upon the subject, the facts or
data need not be admissible in evidence in order for the opin-
ion or inference to be admitted.”). In fact, the district court
generally failed to conduct a 703 analysis, such as considering
whether this study was “of the type” relied upon by experts
in the field, or whether the ATSDR Report’s “probative value
. . . substantially outweighs [its] prejudicial effect.” Fed. R.
Evid. 703.

  [18] Instead, the district court excluded expert testimony
regarding the ATSDR Report under Rule 403. This ruling
improperly replaced 703 balancing with 403 balancing, cf.
Fed. R. Evid. 703 (providing balancing test applicable to
expert testimony), and the exclusion of the ATSDR Report
and Peipins Publication as bases for expert testimony or opin-
ion formation was error. While Rule 403 supplies a basis for
holding the underlying ATSDR Report inadmissible, it does
not contemplate barring an expert from relying on it. Cf. Fed.
R. Evid. 403. The exclusion of the ATSDR Report and the
Peipins Publication from expert consideration and testimony
was error, and thus we reverse that part of the ATSDR Order.

                    V.   Motion to Strike

   In its reply brief to this court, the government submitted six
documents not included in the record below—two excerpts of
the federal register (addenda 1 and 3), a report of the National
Research Council (addendum 2), published scientific articles
12706            UNITED STATES v. W. R. GRACE
(addenda 5 and 6), and search results presumably from the
CAS Registry (addendum 4). Defendants moved to strike four
of the documents (addenda 2, 4, 5, and 6) on the grounds that
they were not part of the record below, were misleading, and,
by virtue of their submission in the reply brief, were presented
without giving defendants an opportunity to respond.

   [19] In general, we consider only the record that was before
the district court. We have made exceptions to this general
rule in three situations: (1) to “correct inadvertent omissions
from the record,” (2) to “take judicial notice,” and (3) to “ex-
ercise inherent authority . . . in extraordinary cases.” Lowry v.
Barnhart, 329 F.3d 1019, 1024 (9th Cir. 2003). Consider-
ations of institutional expertise and notice support our limita-
tion of these exceptions to “unusual circumstances.” Id.

   [20] The search results in addendum item 4 fit none of
these exceptions. Addendum items 2, 5, and 6 fit within the
second exception—we have discretion to take judicial notice
under Rule 201 of the existence and content of published arti-
cles. See Bell Atlantic Corp. v. Twombly, ___ U.S. ___, ___
n.13, 127 S. Ct. 1955, 1973 n.13 (2007); United States v. Rut-
gard, 116 F.3d 1270, 1278 (9th Cir. 1997). However, as we
have stated before, the appropriate manner to supplement the
record on appeal is “by motion or formal request so that the
court and opposing counsel are properly apprised of the status
of the documents in question.” Lowry, 329 F.3d at 1025. The
government failed to so move, and thus we grant defendants’
motion to strike. However, due to the reversal and remand on
certain issues, our ruling here does not preclude application to
the district court for inclusion in the district court’s record for
whatever use is appropriate.

                          CONCLUSION

  We reverse the order dismissing the knowing endanger-
ment object of Count I of the superseding indictment. We
reverse the order adopting the regulatory definition of asbes-
                UNITED STATES v. W. R. GRACE                 12707
tos used for civil regulation and direct that the definition in
the criminal statute, i.e., the definition provided in 42 U.S.C.
§ 7412(b), applies. We grant the government’s request for a
writ of mandate. We affirm the exclusion of the indoor air
studies, the ATSDR Report, and the Peipins Publication them-
selves. However we reverse their exclusion — and the exclu-
sion of the historic testing — as bases underlying an expert’s
opinion or testimony. Finally, we grant defendants’ motion to
strike the documents included with the government’s reply
brief to this court.

 AFFIRMED          in   part,   REVERSED        in   part,    and
REMANDED.

  WRIT OF MANDAMUS GRANTED on one issue.
