                 FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

NORTHWEST COALITION FOR               
ALTERNATIVES TO PESTICIDES
(NCAP),
                        Petitioner,
                                            No. 05-75255
                                      
               v.
                                              EPA No.
UNITED STATES ENVIRONMENTAL
                                            Clear Air Act
PROTECTION AGENCY,
                      Respondent,
CROPLIFE AMERICA,
                       Intervenor.
                                      

NATURAL RESOURCES DEFENSE             
COUNCIL, INC.,
                                            No. 05-76807
                      Petitioner,
               v.                            EPA No.
                                          70 Fed Reg 46706
UNITED STATES ENVIRONMENTAL
                                              OPINION
PROTECTION AGENCY,
                     Respondent.
                                      
         On Petition for Review of an Order of the
            Environmental Protection Agency

                  Argued and Submitted
            June 6, 2007—Seattle, Washington

                 Filed September 19, 2008




                           13239
13240             NORTHWEST COALITION v. EPA
Before: Harry Pregerson and Sandra S. Ikuta, Circuit Judges,
         and Barry T. Moskowitz,* District Judge.

               Opinion by Judge Pregerson;
   Partial Concurrence and Partial Dissent by Judge Ikuta




  *The Honorable Barry T. Moskowitz, District Judge for the Southern
District of California, sitting by designation.
13242           NORTHWEST COALITION v. EPA


                        COUNSEL

Aaron Colangelo and Erik D. Olsen, National Resource
Defense Council, Washington, D.C.; Shelley Davis, Farm-
worker Justice Fund, Washington, D.C.; Patti Goldman,
Earthjustice, Seattle, Washington, for petitioners-appellants
Northwest Coalition for Alternatives to Pesticides and
National Resources Defense Council.

Jonathan J. Fleuchaus, Environmental Protection Agency,
Washington, D.C.; Sue Ellen Woodridge, Attorney General,
John C. Cruden, Deputy Assistant Attorney General, and Kent
E. Hanson, Environment and Natural Resources Division,
United States Department of Justice, Washington, D.C., for
respondent-appellee Environmental Protection Agency.

Kenneth W. Weinstein, Claudia M. O’Brien, and Cassandra
Sturkie, Latham & Watkins LLP, Washington, D.C., for
respondent-intervenor CropLife America.
                 NORTHWEST COALITION v. EPA               13243
                          OPINION

PREGERSON, Circuit Judge:

   Petitioners are two environmental groups challenging the
Environmental Protection Agency’s (“EPA”) establishment of
tolerances for seven pesticides used mostly on fruit and vege-
table crops. We grant the petition in part, deny it in part, and
remand to the EPA.

                      BACKGROUND

                               I.

   The EPA regulates pesticides under two statutes: the Fed-
eral Insecticide, Fungicide, and Rodenticide Act (“FIFRA”),
7 U.S.C. § 136-136y, and the Federal Food, Drug, and Cos-
metic Act (“FDCA”), 21 U.S.C. § 346a.

   Under FIFRA, pesticides sold in the United States must be
registered by the EPA. 7 U.S.C. § 136a. The EPA may not
register a pesticide unless the pesticide will perform its
intended function without causing “any unreasonable adverse
effects on the environment.” 7 U.S.C. § 136a(c)(5)(C).

   The FDCA authorizes the EPA to set “tolerances” for pesti-
cide residues in food. 21 U.S.C. § 346a(b). “A tolerance is the
maximum allowable amount of pesticide that may remain in
or on a commodity.” Nader v. EPA, 859 F.2d 747, 748 (9th
Cir. 1988). The EPA may “establish or leave in effect a toler-
ance for a pesticide chemical residue in or on a food only if
[the EPA] determines that the tolerance is safe.” 21 U.S.C.
§ 346a(b)(2)(A)(i). The term “safe” is defined to mean that
“there is a reasonable certainty that no harm will result from
aggregate exposure to the pesticide chemical residue, includ-
ing all anticipated dietary exposures and all other exposures
for which there is reliable information.” 21 U.S.C.
13244                NORTHWEST COALITION v. EPA
§ 346a(b)(2)(A)(ii). Any tolerance that is not “safe” must be
modified or revoked. 21 U.S.C. § 346a(b)(2)(A)(i).

   Tolerances are established by rulemaking. 21 U.S.C.
§ 346a(d). Pesticide manufacturers initiate the rulemaking
process by petitioning the EPA to set a tolerance. 21 U.S.C.
§ 346a(d)(1). The EPA publishes notices of these petitions in
the Federal Register. 21 U.S.C. § 346a(d)(3). After reviewing
a petition and any comments received on it, the EPA may
issue: (1) a final rule establishing a tolerance, (2) a proposed
rule, or (3) an order denying the petition. 21 U.S.C.
§ 346a(d)(4).

   Once the EPA takes final action on a petition, any affected
party has sixty days to file objections with the EPA and to
seek an evidentiary hearing on those objections. 21 U.S.C.
§ 346a(g)(2). The EPA’s final order in response to those
objections is subject to judicial review. 21 U.S.C.
§ 346a(h)(1).

                                     II.

   In 1996, Congress amended the FDCA by enacting the
Food Quality Protection Act (“FQPA”), Pub. L. No. 104-170,
110 Stat. 1489. One of the key provisions of the FQPA
requires the EPA to give special consideration to risks posed
to infants and children when establishing pesticide tolerances.
Specifically, the FQPA directs the EPA to use “an additional1
tenfold margin of safety . . . to take into account potential pre-
and post-natal toxicity and completeness of the data with
respect to exposure and toxicity to infants and children.” 21
  1
   This margin of safety is “additional” to two safety factors that the EPA
has long used to account for other uncertainties: a tenfold factor for inter-
species differences (to account for the possibility that people are more sus-
ceptible than animals studied in laboratory experiments), and a tenfold
safety factor for intra-species differences (to account for the wide range
of sensitivities in the human population).
                    NORTHWEST COALITION v. EPA                    13245
U.S.C. § 346a(b)(2)(C). This tenfold (or “10x”) child safety
factor is presumptively applied to all tolerances. Thus, in
making tolerance decisions, the EPA must assume that the
risk to children from the use of a particular pesticide on food
is ten times greater than for adults. The EPA may “use a dif-
ferent margin of safety for the pesticide chemical residue only
if, on the basis of reliable data, such margin will be safe for
infants and children.” Id. (emphasis added).

  Unfortunately, the FQPA does not define “reliable data.”
The dispute before us turns on the definition of this term.

   Between December 2001 and April 2002, the EPA pub-
lished seven regulations establishing tolerances for the pesti-
cides    acetamiprid,      fenhexamid,     halosulfuron-methyl,
isoxadifen-ethyl, mepiquat, pymetrozine, and zeta-
cypermethrin used on many foods, including fruits, vegeta-
bles, nuts, cereal grains, milk, and eggs.2 Each regulation was
promulgated in response to an industry petition to establish
tolerances.

   The EPA did not apply the presumptive 10x child safety
factor to any of these seven pesticides. The EPA reduced the
10x child safety factor to 3x for four of the pesticides
(acetamiprid, fenhexamid, isoxadifen-ethyl, and pymetro-
zine). For the remaining three pesticides (halosulfuron,
mepiquat, and zeta-cypermethrin), the EPA did not apply a
child safety factor at all.
  2
   For the EPA’s individual tolerance rulings, see Acetamiprid; Pesticide
Tolerance, 67 Fed. Reg. 14,649 (Mar. 27, 2002); Fenhexamid; Pesticide
Tolerance, 67 Fed. Reg. 19,114 (Apr. 18, 2002); Halosulfuron-methyl;
Pesticide Tolerance, 66 Fed. Reg. 66,333 (Dec. 26, 2001); Isoxadifen-
ethyl; Pesticide Tolerance, 67 Fed. Reg. 12,875 (Mar. 20, 2002);
Mepiquat; Pesticide Tolerance, 67 Fed. Reg. 3,113 (Jan. 23, 2002);
Pymetrozine; Pesticide Tolerance, 66 Fed. Reg. 66,786 (Dec. 27, 2001);
Zeta-cypermethrin and its Inactive R-isonomers; Pesticide Tolerance, 67
Fed. Reg. 6,422 (Feb. 15, 2002).
13246              NORTHWEST COALITION v. EPA
   In 2002, Natural Resources Defense Council, Inc.
(“NRDC”) filed objections to each of the tolerances based on
the EPA’s decision to reduce or remove the child safety factor.3
NRDC argued that the EPA did not have “reliable data”
allowing it to deviate from the child safety factor.

   On August 10, 2005, the EPA issued its final order reject-
ing NRDC’s objections. See Order Denying Objections to
Issuances of Tolerances, 70 Fed. Reg. 46,706 (Aug. 10, 2005)
(hereinafter “Final Order”). The Final Order upheld the 3x
child safety factor for acetamiprid, fenhexamid, isoxadifen-
ethyl, and pymetrozine, and a 1x child safety factor (i.e., no
safety factor) for halosulfuron, mepiquat, and zeta-
cypermethrin. Id. at 46,711-13, 46,736.

   NRDC and the Northwest Coalition for Alternatives to Pes-
ticides (“NCAP”) each petitioned for review of the Final
Order.

                         JURISDICTION

   We have jurisdiction under the FDCA, which provides that
“any person who will be adversely affected” by an EPA order
denying tolerance objections may file a petition for review in
the Court of Appeals within 60 days of the EPA’s order. 21
U.S.C. § 346a(h)(1).

   NRDC filed administrative objections to the tolerances in
2002. The EPA published its Final Order denying those objec-
tions on August 10, 2005. Within 60 days, NRDC filed a peti-
tion for review in the Second Circuit, and NCAP filed a
petition for review in this court. The Judicial Panel on Mul-
tidistrict Litigation transferred NRDC’s petition for review to
this court pursuant to 28 U.S.C. § 2112, and NRDC and
NCAP filed joint briefs on appeal.
  3
   NRDC did not request an evidentiary hearing on its objections.
                  NORTHWEST COALITION v. EPA               13247
                  STANDARD OF REVIEW

   The FDCA does not establish a standard for reviewing pes-
ticide tolerances that are established without a public evidenti-
ary hearing. See 21 U.S.C. § 346a(h)(2). In the absence of
such a standard, our review is governed by section 706 of the
Administrative Procedure Act (“APA”). See 5 U.S.C. § 706;
City of Sausalito v. O’Neill, 386 F.3d 1186, 1205-06 (9th Cir.
2004).

    Under the APA, we must set aside an agency’s decision if
it is “arbitrary, capricious, an abuse of discretion, or otherwise
not in accordance with law.” 5 U.S.C. § 706(2)(A). An
agency decision would normally be arbitrary and capricious
if “the agency has relied on factors which Congress has not
intended it to consider, entirely failed to consider an important
aspect of the problem, offered an explanation for its decision
that runs counter to the evidence before the agency, or is so
implausible that it could not be ascribed to a difference in
view or the product of agency expertise.” Mfrs’ Ass’n v. State
Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43 (1983).

   “The scope of review under the ‘arbitrary and capricious’
standard is narrow and a court is not to substitute its judgment
for that of the agency.” Id. “Nevertheless, the agency must
examine the relevant data and articulate a satisfactory expla-
nation for its action including a ‘rational connection between
the facts found and the choice made.’ ” Id. (citation omitted).
“In reviewing that explanation, [the court] must consider
whether the decision was based on a consideration of the rele-
vant factors and whether there has been a clear error of judg-
ment.” Id. (citation omitted).

   Although we will “uphold a decision of less than ideal clar-
ity if the agency’s path may be reasonably discerned,” we
“may not supply a reasoned basis for the agency’s action that
the agency itself has not given.” Id. (citations omitted).
13248              NORTHWEST COALITION v. EPA
                            ANALYSIS

   Petitioners challenge seven tolerances (acetamiprid, fen-
hexamid, halosulfuron-methyl, isoxadifen-ethyl, mepiquat,
pymetrozine, and zeta-cypermethrin) based on the EPA’s fail-
ure to gather drinking water data as part of its exposure analy-
sis. Petitioners also challenge three tolerances (acetamiprid,
mepiquat, and pymetrozine) based on the absence of certain
toxicity studies, and based on the EPA’s failure to explain
why it had reliable data in the absence of those toxicity studies.4
We address these challenges in turn.

                                   I.

  [1] The FQPA directs the EPA to use an additional tenfold
margin of safety to take into account completeness of data
with respect to pesticide “exposure to infants and children.”
21 U.S.C. § 346a(b)(2)(C) (emphasis added).

   As required by the FQPA, the EPA monitors whether
infants and children will be exposed to unsafe levels of pesti-
cides in drinking water. However, the EPA lacks sufficient
drinking water exposure data for several pesticides, including
the ones at issue in this case. Therefore, the EPA used com-
puter modeling to determine drinking water exposure for the
seven pesticides. Because the modeling results revealed little-
to-no risk of pesticide exposure in drinking water, the EPA
reduced or removed the child safety factor for each of the pes-
ticide tolerances.

   Petitioners argue that because the EPA used modeling
instead of actual sampling data to determine drinking water
exposure to these pesticides, the EPA does not have “reliable
  4
  Petitioners also initially challenged the tolerances for halosulfuron-
methyl and zeta-cypermethrin on these grounds. They now acknowledge,
however, that subsequent agency actions have rendered those challenges
moot.
                    NORTHWEST COALITION v. EPA                    13249
data” justifying its use of a lower than 10x margin of safety
for the pesticide tolerances. See 21 U.S.C. § 346a(b)(2)(C). In
short, Petitioners argue that modeling results can never consti-
tute reliable data within the meaning of the FQPA.

   [2] We disagree. Petitioners have presented no evidence
that modeling does not yield reliable data. There is nothing
inherently unreliable about the use of models in scientific
assessments. See, e.g., Small Refiner Lead Phase-Down Task
Force v. EPA, 705 F.2d 506, 535 (D.C. Cir. 1983)
(“[A]dministrative agencies have undoubted power to use pre-
dictive models.”). Moreover, because of the difficulty in sam-
pling the entire nation’s water supply, modeling is necessary
to determine whether drinking water has been contaminated
by pesticides. Topography, geology, and hydrology differ
greatly across the nation and constantly change. In many
cases, computer modeling can more accurately incorporate
these elements and provide more reliable data than actual
water sampling data can provide.5

   [3] Therefore, we are unwilling to adopt the narrow con-
struction of “reliable data” that Petitioners advance. Although
the FQPA does not define “reliable data,” we are confident
that modeling results can satisfy this statutory requirement.

   [4] Furthermore, in this case, the EPA provided a specific,
detailed explanation of why its drinking water exposure mod-
els do yield reliable data. The Final Order states:

         Lack of comprehensive drinking water (DW) mon-
      itoring data. NRDC contends that, because EPA
      used a model for calculating drinking water expo-
  5
    See FIFRA Scientific Advisory Panel, A Set of Scientific Issues Being
Considered by the Agency in Connection with Estimating Drinking Water
Exposure as a Component of Dietary Risk Assessment, 4-7 (Dec. 1997),
available     at     http://epa.gov/scipoly/sap/meetings/1997/december/
finaldec.pdf.
13250           NORTHWEST COALITION v. EPA
    sure, EPA does not have, as a definitional matter,
    “reliable data” for choosing a factor different than
    the 10X default value. Similar comments were made
    during the development of EPA’s Children’s Safety
    Policy. This issue was addressed at length in the
    response to the imidacloprid objections. That
    response is incorporated herein and is summarized
    below.

       Although the availability of drinking water moni-
    toring data has increased dramatically in the last sev-
    eral years, EPA still finds it necessary to rely for
    most pesticides upon various exposure models to
    estimate exposure levels in drinking water. These
    models are based on generic data regarding fate and
    transport of pesticides in the environment, and they
    operate by combining this generic data with
    pesticide-specific data on chemical properties to esti-
    mate exposure. EPA has primarily used its drinking
    water models to “screen” those pesticides that may
    pose unacceptable risks due to exposures in drinking
    water from pesticides not likely to result in such
    exposures. To accomplish this goal, the models are
    based on data from studies at sites that are highly
    vulnerable to runoff of pesticides to surface water or
    leaching of pesticides to ground water. If a pesticide
    fails this conservative (health-protective) screen,
    EPA would investigate whether the model is signifi-
    cantly overstating the residue levels that actually
    occur.

      EPA has developed models for estimating expo-
    sure in both surface water and ground water. EPA
    uses a two-tiered approach to modeling pesticide
    exposure in surface water. In the initial tier, EPA
    uses the FQPA Index Reservoir Screening Tool
    (FIRST) model. FIRST replaces the Generic Esti-
    mated Environmental Concentrations (GENEEC)
                NORTHWEST COALITION v. EPA              13251
    model that was used as the first tier screen by EPA
    from 1995-1999. If the first tier model suggests that
    pesticide levels in water may be unacceptably high,
    a more refined model is used as a second tier assess-
    ment. The second tier model is actually a combina-
    tion of the models, Pesticide Root Zone Model
    (PRZM) and the Exposure Analysis Model System
    (EXAMS). For estimating pesticide residues in
    groundwater, EPA uses the Screening Concentration
    In Ground Water (SCI-GROW) model. Currently,
    EPA has no second tier groundwater model.

       Whether EPA assesses pesticide exposure in
    drinking water through monitoring data or model-
    ing, EPA uses the higher of the two values from sur-
    face and ground water in assessing overall exposure
    to the pesticide. In most cases, pesticide residues in
    surface water are significantly higher than in ground
    water.

       In the Imidacloprid Order, EPA analyzed each of
    its water models extensively. Based on the results of
    design characteristics of the models, outside peer
    review of the models, validation of the models, and
    comparison between the models’ predictions and
    extensive water monitoring data, EPA concluded
    that the models are based on reliable data and will
    produce estimates that are unlikely to underestimate
    exposure to pesticides in drinking water.

       Accordingly, EPA reaffirms its earlier conclusion
    that its drinking water models provide a reliable
    basis for finding that exposure to pesticide residues
    in water are not underestimated.

Final Order at 46,726-29 (internal citations omitted) (empha-
sis added). Thus, the EPA addressed at length the reliability
of its models. The EPA explained that the models yield con-
13252                NORTHWEST COALITION v. EPA
servative data because the models incorporate the higher of
the two values from surface and ground water in assessing the
overall risk of exposure to the pesticides. Petitioners have not
established that the EPA’s explanation regarding the reliabil-
ity of its models is faulty or suspect.

   [5] Accordingly, we conclude that the computer modeling
used by the EPA to calculate the safety of drinking water was
neither contrary to law nor arbitrary and capricious.6 We
affirm this aspect of the Final Order.

                                     II.

  In addition to NRDC’s challenge to the completeness of
exposure data, Petitioners also raise two arguments regarding
whether reliable toxicity data supported a reduction in the
child safety factor.

                                     A.

   NRDC first challenges the EPA’s failure to wait for the
results of certain developmental neurotoxicity studies (“DNT
studies”) before establishing tolerances for acetamiprid,
mepiquat, and pymetrozine. The EPA specifically required
the registrants of these pesticides to conduct DNT studies.
However, the EPA did not wait for the results of the DNT
studies before making its tolerance determinations.
  6
    Our conclusion, of course, is not meant to suggest that the EPA’s mod-
els are flawless. Petitioners have raised some concerns about the EPA’s
water exposure models that may warrant further scrutiny. To give one
example, the EPA first performs a model-based water exposure test using
conservative criteria; if the test results reveal unacceptable exposure
levels, the EPA runs a second test to ensure that the first result was accu-
rate. The EPA does not run a second test, however, if the initial test results
reveal acceptable exposure levels. Although we are required to defer to
the EPA’s technical expertise in this area, see, e.g., Envtl Def. Ctr., Inc.
v. EPA, 344 F.3d 832, 869 (9th Cir. 2003), we note that the EPA may wish
to revisit this methodology.
                 NORTHWEST COALITION v. EPA                13253
   Petitioners contend that DNT studies are essential for
assessing pesticide effects. Petitioners explain that DNT
studies are the best available studies for examining neurologi-
cal effects in children because DNT studies are more sensitive
than other studies, address areas that are not covered by other
studies, and sometimes reveal developmental harm that is sig-
nificant enough to require more stringent regulation. Petition-
ers argue that the EPA acted arbitrarily and capriciously by
requesting DNT studies but failing to wait for the results of
those studies before removing the child safety factor.

   [6] Petitioners’ position, however, is inconsistent with the
Supreme Court’s decision in National Ass’n of Home Builders
v. Defenders of Wildlife, 127 S. Ct. 2518 (2007). In Home
Builders, our court rejected a final order of the EPA as “arbi-
trary and capricious” because the EPA had relied on “legally
contradictory positions” before arriving at its final administra-
tive decision. 127 S. Ct. at 2529. The Supreme Court, how-
ever, reversed our opinion. The Court held that the mere fact
that the EPA might have adopted “internally inconsistent”
positions throughout the decision-making process did not ren-
der the EPA’s final decision arbitrary and capricious. 127
S. Ct. at 2530. The Court explained that as long as agencies
follow the proper administrative procedures, they have the
authority to change their minds before issuing a final order.
Id.

   [7] Thus, Home Builders appears to foreclose Petitioners’
argument. Even though the EPA initially thought that the
DNT studies were needed, the EPA later determined that the
DNT studies were not needed. Under Home Builders, the
EPA’s later determination does not automatically render the
EPA’s Final Order arbitrary and capricious. Notably, Petition-
ers have not identified any procedures that were violated
when the EPA decided not to wait for the requested DNT
studies before setting the tolerances. Moreover, the Final
Order provided a reasoned explanation of why DNT studies
are not actually required in every case where there is a reduc-
13254            NORTHWEST COALITION v. EPA
tion of the 10x child safety factor. Final Order at 46,711-12,
46,723-24.

   [8] Therefore, we reject Petitioner’s argument that the EPA
acted arbitrarily and capriciously by establishing the pesticide
tolerances for acetamiprid, mepiquat, and pymetrozine before
receiving the DNT studies. While Petitioners’ concerns about
the EPA’s apparent change of heart are understandable, on
such questions of scientific judgment, we are required to defer
to the EPA.

                              B.

   [9] NRDC also disputes that the EPA’s decision to deviate
from the 10x presumptive child safety factor imposed by Con-
gress was supported by reliable data establishing, with reason-
able certainty, that the lower margin of safety for acetamiprid,
mepiquat, and pymetrozine would not harm infants and chil-
dren. 21 U.S.C. § 346a(b)(2)(A), (C). Even though the EPA
was not necessarily required to wait for the results of the DNT
studies, the decision to reduce the 10x child safety factor for
these three pesticides must still be based on reliable data.
Moreover, the EPA must tell the public why its data are reli-
able.

   [10] The problem in this case is that the EPA’s Final Order
is vague, making it impossible for us to determine whether the
EPA’s deviations from the 10x child safety factor for acetami-
prid, mepiquat, and pymetrozine were in fact supported by
reliable data, even in the absence of the DNT studies. For
example, with respect to pymetrozine, the Final Order states:

    NRDC challenged a December 27, 2001 action
    establishing tolerances for pymetrozine on cotton
    seed, cotton gin byproducts, the fruiting vegetables
    crop group, the cucurbit vegetables crop group, the
    leafy vegetables crop group (except Brassica), head
    and stem Brassica, leafy Brassica, turnip greens,
                NORTHWEST COALITION v. EPA              13255
    dried hops, and pecans. (66 FR 66786, December 27,
    2001). Given pymetrozine’s exposure pattern and
    toxicological characteristics, EPA determined that
    pymetrozine potentially presented acute, chronic,
    short-term, and cancer risks and EPA quantitatively
    assessed these risks in making its safety determina-
    tion. (66 FR at 66791-66792). All of these risks were
    found to be below the Agency’s level of concern.
    (Id.). Although a DNT study was outstanding, EPA
    determined that the additional 10X children’s safety
    factor could generally be reduced to 3X because the
    toxicological data showed no evidence of greater
    sensitivity to the young and there was no evidence of
    abnormalities in the development of the fetal ner-
    vous system. (64 FR 52438, 52444, September 29,
    1999).

Final Order at 46,711.

   The Final Order recites that the “toxicological data”
showed no evidence of increased sensitivity for developing
fetuses or the “young.” However, the Final Order does not
explain the connection between the toxicological data and the
3x margin of safety selected by the EPA in place of the 10x
standard. This same critique applies to the Final Order’s rea-
soning with respect to acetamiprid and mepiquat. As a result,
it is entirely unclear why the EPA chose safety factors of 3x
for pymetrozine and acetamiprid, and 1x for mepiquat, as
opposed to 4x or 5x or 8x or 9x. As far as we can tell from
the record, it appears that the EPA chose these lower safety
levels arbitrarily—to acknowledge certain concerns about
each pesticide, but with no specific evidence that these lower
safety factors would actually account for the risks to infants
and children.

   [11] In sum, the Final Order does not provide enough infor-
mation to demonstrate a rational connection between the fac-
tors that the EPA examined and the conclusions it reached.
13256                 NORTHWEST COALITION v. EPA
See State Farm, 463 U.S. at 43. We are therefore unable to
determine whether there was reliable data supporting the
EPA’s reductions of the 10x child safety factor. Although on
remand the EPA may be able to explain why a 3x or 1x factor
is appropriate, we cannot conclude it is appropriate on this
record. To do so would abdicate our responsibility to ensure
compliance with Congress’s expressed desire to have a pre-
sumptive 10x child safety factor. Accordingly, we remand the
tolerance regulations for acetamiprid, mepiquat, and pymetro-
zine to the EPA. See, e.g., State Farm, 463 U.S. at 57
(remanding where the agency failed to supply the requisite
“reasoned analysis”); Safe Food & Fertilizer v. EPA, 350 F.3d
1263, 1271 (D.C. Cir. 2003) (remanding for the EPA to pro-
vide “further explanation” of an exemption level for chro-
mium found in zinc fertilizers).7
  7
    While we are aware that the scope of our review under the APA is nar-
row, we are also mindful that we should not endorse the removal of the
statutorily presumed child safety factor if we cannot determine that the
EPA’s conclusions are rationally supported. As Judge J. Skelly Wright of
the D.C. Circuit elucidated, there is an important difference between the
depth of our review of an agency’s action and the scope of that review:
         Judicial review of agency action requires that the reviewing
      court consider whether the [agency’s] decision was based on a
      consideration of the relevant factors and whether there has been
      a clear error of judgment. As noted by this court in International
      Ladies Garment Workers Union v. Donovan, 722 F.2d 795, 815
      (D.C. Cir. 1983), cert. denied, 469 U.S. 820 (1984), such review
      “is not merely perfunctory. We are to engage in a ‘searching and
      careful’ inquiry, the keystone of which is to ensure that the
      [agency] engaged in reasoned decisionmaking.”
         This formulation points to an acknowledged disparity between
      the depth of our review and the ultimate scope of that review:
      Although the ultimate scope may be narrow, the depth must be
      sufficient for us to be able to comprehend the agency’s handling
      of the evidence cited or relied upon. The purpose of this in-depth
      review is to educate ourselves so that we can properly perform
      our reviewing function: determining whether the agency’s con-
      clusions are rationally supported. For, although data interpreta-
      tion and analysis are functions that often lie within an agency’s
                     NORTHWEST COALITION v. EPA                        13257
   The EPA and the dissent argue that Petitioners did not raise
this argument below and therefore cannot assert it now. We
disagree. In its administrative objections, NRDC challenged
the basis for the reduced safety levels as inadequate. In partic-
ular, NRDC argued that, absent the DNT studies, the EPA had
no reliable data to reduce the 10x child safety factor. NRDC’s
objection was a direct challenge to the lower child safety
levels set by the EPA. To justify its decision to set a 3x or 1x
child safety factor without the DNT studies, the EPA needed
to explain why the data in its possession was reliable and sup-
ported such reductions. As noted above, the EPA explained
why the absence of the DNT studies does not necessarily
mean that there is a lack of reliable data justifying a down-
ward deviation from the 10x child safety factor. However, the
EPA failed to explain why, in the case of the three pesticides
at issue, the available information justified the specific safety
reductions. Because the NRDC challenged the EPA to pro-
vide that explanation, the EPA’s failure to do so is properly
before us for review.

                             CONCLUSION

   Because the EPA failed to adequately explain the basis for
its deviations from the 10x child safety factor for acetamiprid,

    realm of expertise, it is our duty to review those functions to
    ascertain whether the agency’s actions were complete, reasoned,
    and adequately explained. The mere fact that an agency is operat-
    ing in a field of its expertise does not excuse us from our custom-
    ary review responsibilities. And, where the agency’s reasoning,
    although complex, is rational, clear, and complete, we must
    affirm. Contrarily, where the agency’s reasoning is irrational,
    unclear, or not supported by the data it purports to interpret, we
    must disapprove the agency’s action.
Center for Auto Safety v. Peck, 751 F.2d 1336, 1373 (D.C. Cir. 1985)
(Wright, J., dissenting) (internal citations and quotation marks omitted).
See also Riverkeeper, Inc. v. United States Environmental Protection
Agency, 475 F.3d 83, 103-04 (2d Cir. 2007) (“In a technical area of this
sort, it is difficult for judges or interested parties to determine the propri-
ety of the Agency’s action without a justification for the action supported
by clearly identified substantial evidence whose import is explained.”).
13258            NORTHWEST COALITION v. EPA
mepiquat, and pymetrozine, we grant the petitions for review
in part and remand to the EPA for further proceedings consis-
tent with this opinion. On all other issues, we deny the peti-
tions for review.

  Each side to bear its own costs on appeal.

 GRANTED IN PART, DENIED IN PART, AND
REMANDED.



IKUTA, Circuit Judge, concurring in part and dissenting in
part:

   I agree with the majority’s conclusion that “the computer
modeling used by the EPA to calculate the safety of drinking
water was neither contrary to law nor arbitrary and capri-
cious.” Maj. Op. at 13252; see also The Lands Council v.
McNair, ___ F.3d ___, 2008 WL 2640001, at *6-10 (9th Cir.
2008) (en banc). I also agree with the majority’s holding that
National Ass’n of Home Builders v. Defenders of Wildlife,
127 S. Ct. 2518, 2529-30 (2007), forecloses petitioners’ argu-
ment “that the EPA acted arbitrarily and capriciously by
establishing the pesticide tolerances for acetamiprid,
mepiquat, and pymetrozine before receiving . . . DNT
studies.” Maj. Op. at 13254.

   I disagree, however, with the majority’s conclusion that the
tolerance regulations for acetamiprid, mepiquat, and pymetro-
zine must be remanded to the EPA because “it is entirely
unclear why the EPA chose safety factors of 3x for pymetro-
zine and acetamiprid, and 1x for mepiquat,” and therefore
“the Final Order [did] not provide enough information to
demonstrate a rational connection between the factors the
EPA examined and the conclusions it reached.” Maj. Op. at
13255. The petitioners failed to raise this argument in their
objections to the EPA prior to the issuance of the Final Rule.
                     NORTHWEST COALITION v. EPA                      13259
See Order Denying Objections to Issuances of Tolerances, 70
Fed. Reg. 46,706 (Aug. 10, 2005) [hereinafter, Final Rule],
and therefore the EPA was given no opportunity to explain its
rationale for adopting the 3x and 1x safety factors. Because
we may review only the objections raised before the EPA, see
21 U.S.C. § 346a(g)-(h); 40 C.F.R. §§ 178.25(a)(2),
180.30(b), the issue is not properly before us. Even if the peti-
tioners had raised this objection, there is no doubt the EPA
could have provided information sufficient to demonstrate a
rational basis for selecting these safety factors. Indeed, the
record establishes that the EPA drew upon its expertise to
select uncertainty factors based on principles well established
in the scientific community. There is no basis for the majori-
ty’s conclusion that the agency’s path is not reasonably dis-
cernable in this case. See, e.g., Motor Vehicle Mfrs. Ass’n v.
State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43 (1983).
Accordingly, I dissent from Part IIB of the majority opinion.1

                                     A

   As noted by the majority, the tolerance rules at issue in this
appeal have substantially similar histories.2 While the devel-
opment of its safety factor policy was in process, the EPA
received pesticide petitions requesting the issuance of toler-
  1
     I also dissent from footnote 6 of the majority opinion. The majority’s
suggestion that the “EPA may wish to revisit [its] methodology” regarding
its “model-based water exposure test[s]” conflicts directly with the teach-
ing of our en banc panel in Lands Council. Lands Council emphasized that
it “is not a proper role for a federal appellate court” to “act as a panel of
scientists that instructs the [agency] how to validate its hypotheses,”
“chooses among scientific studies,” and requires the agency to “explain
every possible scientific uncertainty.” 2008 WL 2640001, at *4. The
majority errs in this case by doing that which Lands Council expressly for-
bids.
   2
     The three pesticides at issue are acetamiprid, mepiquat, and pymetro-
zine. For the individual tolerance rulings, see Acetamiprid; Pesticide Tol-
erance, 67 Fed. Reg. 14,649 (Mar. 27, 2002); Mepiquat; Pesticide
Tolerance, 67 Fed. Reg. 3,113 (Jan. 23, 2002); Pymetrozine; Pesticide
Tolerance, 66 Fed. Reg. 66,786 (Dec. 27, 2001).
13260                 NORTHWEST COALITION v. EPA
ances under the FFDCA for the three pesticides at issue. As
required in the FFDCA, the EPA reviewed the scientific data
and other information, evaluated their completeness and reli-
ability, and considered “the relationship of the results of such
studies to human risk.” 21 U.S.C. § 346a(b)(2)(D)(iii); see,
e.g., Pymetrozine; Pesticide Tolerance, 66 Fed. Reg. 66,786,
66,787 (Dec. 27, 2001). The EPA determined that the child
safety factor was not necessary, or could be reduced to 3x, for
each of the pesticides based on its analysis of potential expo-
sure levels for the given pesticide, the extent to which the pes-
ticide affected fetal development, and the effects, if any, on
infants as observed in multi-generational studies of mammals.
In each case, the EPA provided a reasoned explanation for
eliminating or reducing the child safety factor.3
  3
   In its order establishing the tolerance for acetamiprid, the EPA
explained:
      [T]he safety factor could be reduced to 3x for acetamiprid
      because the toxicology database is complete; there is no quantita-
      tive or qualitative evidence of increased susceptibility following
      in utero exposure of rat and rabbit fetuses; the dietary (food and
      water) and residential exposure assessments will not underesti-
      mate the potential exposures for infants, children, and/or women
      of childbearing age; and the requirement of a developmental neu-
      rotoxicity study is not based on criteria reflecting special concern
      for the developing fetuses or young which are generally used for
      requiring a DNT study and a safety factor.
Acetamiprid; Pesticide Tolerance, 67 Fed. Reg. at 14,655.
   The EPA removed the additional child safety factor for mepiquat
(reducing it to 1x) because it had already satisfied itself of the safety of
another “salt” of mepiquat that it determined was identical in terms of its
environmental distribution and toxicology. Mepiquat; Pesticide Tolerance,
67 Fed. Reg. at 3,115-16. It explained:
      The Agency published a risk assessment for mepiquat chloride on
      January 12, 2000, that discusses use on cotton as well as all other
      registered uses of mepiquat chloride. In that analysis risk esti-
      mates for exposure to mepiquat chloride were below the Agen-
      cy’s level of concern. The Agency has reviewed a dissociation
      study for mepiquat pentaborate that demonstrates that mepiquat
      pentaborate dissociates in an identical physical manner to
                      NORTHWEST COALITION v. EPA                      13261
   In 2002, the NRDC filed objections to the final rules for
each of the pesticides based on the EPA’s decision to reduce
the 10x safety factor to 3x or 1x. The NRDC’s objections
were based on the theory that the EPA did not have “reliable
data” which would allow it to reduce the child safety factor
because the EPA had not yet received the results of a DNT
study for each pesticide, and because the EPA relied on drink-
ing water exposure models rather than on pesticide-specific

      mepiquat chloride in water. Therefore, the analysis performed for
      mepiquat chloride or the “chloride salt,” also pertains to this
      mepiquat “pentaborate salt” use because the use rate, maximum
      seasonal use rate and other pertinent use factors remain the same
      for mepiquat chloride or the “chloride salt.” . . .
         Margins of safety are incorporated into EPA risk assessments
      either directly through use of a margin of exposure (MOE) analy-
      sis or through using uncertainty (safety) factors in calculating a
      dose level that poses no appreciable risk to humans.
        The Agency has determined that the FQPA safety factor for
      mepiquat is 1X. See the Agency’s risk assessment for mepiquat
      chloride dated January 12, 2000, for details. The facts are that
      mepiquat pentaborate is another “salt” of mepiquat and that
      mepiquat pentaborate disassociates to mepiquat and therefore the
      basic toxicology data base for mepiquat chloride pertains to
      mepiquat pentaborate.
Id.
  In establishing the tolerance for pymetrozine, the EPA stated:
      There is a complete toxicity database for pymetrozine and expo-
      sure data are complete or are estimated based on data that reason-
      ably accounts for potential exposures. EPA determined that the
      10X safety factor to protect infants and children could be reduced
      to 3. The FQPA factor is reduced after assessing the potential for
      additional sensitivity of infants and children to residues of
      pymetrozine in the following studies: developmental toxicity
      studies in rabbit and rat and two-generation reproduction study in
      the rat. There was no evidence of increased susceptibility in these
      studies. The FQPA safety factor was not reduced to one due to
      the need for a developmental neurotoxicity study.
Pymetrozine; Pesticide Tolerance, 66 Fed. Reg. at 66,791.
13262               NORTHWEST COALITION v. EPA
drinking water monitoring data.4 Notably, the NRDC did not
object on the ground that the EPA failed to justify its choice
of a safety factor of 3x or 1x relative to some other safety fac-
tor, such as “4x or 5x or 8x or 9x.” Maj. Op. at 13255.5 The
EPA rejected NRDC’s objections in the Final Rule, and pro-
vided a detailed explanation of its basis for concluding that it
had reliable data notwithstanding the absence of certain DNT
studies and the use of exposure models, and why such reliable
data supported the EPA’s conclusion that it could safely
reduce the child safety factor. See generally 70 Fed. Reg.
46,706. The Final Rule upheld the 3x child safety factor for
acetamiprid and pymetrozine, and the 1x child safety factor
for mepiquat. Id. at 46,711-13, 46,736.

                                    B

   In concluding that remand is required because the EPA
failed to explain why it chose a 3x uncertainty factor for
acetamiprid and pymetrozine and a 1x uncertainty factor for
mepiquat instead of “4x or 5x or 8x or 9x,” Maj. Op. at
  4
     Natural Resources Defense Council, Objections to the Establishment of
Tolerances for Pesticide Chemical Residues: Halosulfuron-methyl and
Pymetrozine Tolerances (filed Feb. 25, 2002); Natural Resources Defense
Council, Objections to the Establishment of Tolerances for Pesticide
Chemical Residues: Imidacloprid, Mepiquat, Bifenazate, Zeta-
cypermethrin, and Diflubenzuron Tolerances (filed May 19, 2002); Natu-
ral Resources Defense Council, Objections to the Establishment of Toler-
ances for Pesticide Chemical Residues: Isoxadifen-ethyl, Acetamiprid,
Propiconazole, Furilazole, Fenhexamid, and Fluazinam Tolerances (filed
May 20, 2002).
   5
     The NRDC also objected to the three tolerances on a number of other
grounds, including the failure to consider farm children adequately, a fail-
ure to consider worker risk adequately, an inadequate aggregate risk
assessment, an improper reliance on a “lowest observed adverse effect
level” (LOAEL) rather than a “no observed adverse effect level”
(NOAEL), a residue “percentile” assumption that inadequately protected
infants and children, and an improper assessment of chronic dietary expo-
sure, among others. The NRDC did not raise these issues to us on appeal.
See supra Note 4; Final Rule, 70 Fed. Reg. at 46,713-14, 46,717-36.
                  NORTHWEST COALITION v. EPA                13263
13255, the majority is reaching an argument not properly
before us. The regulations applicable to the FFDCA require
exhaustion of administrative remedies. See 40 C.F.R.
§ 180.30(b) (providing that “judicial review is not available
unless an adversely affected party exhausts the[ ] objection
procedures, and any petition procedures preliminary thereto”).
In order to exhaust the objection procedure provided by the
FFDCA, petitioners must raise their objections to the agency
with specificity. See 21 U.S.C. § 346a(g)(2)(A) (requiring
objections to an EPA order establishing a tolerance to specify
“with particularity the provisions of the regulation or order
deemed objectionable”); 40 C.F.R. § 178.25(a)(2) (“To be
considered by the Administrator, an objection must: Specify
with particularity the provision(s) of the order, regulation, or
denial objected to, the basis for the objection(s), and the relief
sought.”). The purpose of this administrative exhaustion
requirement is to give notice to an agency of specific errors
or issues, so the agency can “bring the Agency’s experience
to bear on a contested question,” Nader v. EPA, 859 F.2d 747,
754 (9th Cir. 1988), and either correct the error or provide a
reasoned explanation.

   The NRDC objected to the EPA’s decision that a 10x safety
factor was not required for each of the three pesticide toler-
ances, and based this objection on the ground that the EPA
lacked reliable data because it had failed to obtain a DNT
study and had relied on drinking water exposure models. The
majority rests its decision that the tolerances for acetamiprid,
mepiquat, and pymetrozine must be remanded to the EPA on
a different ground, namely that the EPA failed to explain why
it chose a 3x uncertainty factor for acetamiprid and pymetro-
zine and a 1x uncertainty factor for mepiquat instead of “4x
or 5x or 8x or 9x,” Maj. Op. at 13255. Because the NRDC did
not object to the EPA’s decision on the ground that the EPA
had failed to give a clear explanation of the 3x or 1x safety
factor in lieu of “4x or 5x or 8x or 9x,” id., the issue identified
by the majority is not exhausted, and we are precluded from
reviewing it.
13264                NORTHWEST COALITION v. EPA
   The majority attempts to justify addressing issues that the
NRDC did not raise to the EPA by turning the administrative
exhaustion requirement on its head. As noted above, under the
regulations requiring exhaustion of administrative remedies,
parties objecting to proposed regulations bear the initial bur-
den, and must raise their specific objections to the agency;
any issues not raised are waived and need not be considered
by the agency or by the court on appeal. 40 C.F.R.
§§ 178.25(a)(2), 180.30. Here, the majority shifts the burden
to the EPA to identify, raise, and resolve additional issues that
petitioners failed to raise at all, let alone frame with the requi-
site “particularity.” Id. § 178.25(a)(2).

   The majority first notes that “the NRDC argued that, absent
the DNT studies, the EPA had no reliable data to reduce the
10x child safety factor.” Maj. Op. at 13257. This is indeed the
specific objection raised by the NRDC. The majority then
recharacterizes this specific objection as being a more general
“challenge to the lower child safety levels set by the EPA.”
Maj. Op. at 13257.6 From this generalization, the majority
leaps to the conclusion that the NRDC’s specific objection
places a burden on the EPA to “explain why the data in its
possession” supported its decision to set a 3x or 1x child
safety factor for the pesticides at issue “as opposed to 4x or
5x or 8x or 9x.” Maj. Op at 13255, 13257. There is no basis
in our case law for taking such a leap or placing such a burden
on the EPA. We have never required an agency to interpret a
specific objection as being, at some level of generality, a dif-
ferent, broader objection, and responding to that different
objection. See, e.g., High Country Resources v. FERC, 255
F.3d 741, 745-46 (9th Cir. 2001) (stating that a petitioner can-
not “implicitly” raise an issue to a regulatory agency in order
to exhaust administrative remedies, but must provide “much
  6
   As noted supra, however, a valid objection cannot be this general; it
must “[s]pecify with particularity the provision(s) of the order, regulation
or denial objected to, the basis for the objection(s), and the relief sought.”
40 C.F.R. § 178.25.
                     NORTHWEST COALITION v. EPA                       13265
more specificity in the statement of objection” and present the
issue “squarely” to the agency.). Nor would it be reasonable
or consistent with the purpose of the administrative exhaus-
tion requirement to do so. Here, the EPA responded to the
NRDC’s specific objection by carefully explaining why the
absence of DNT studies did not require the retention of the
10x safety factor. The EPA satisfied its burden, and had no
additional obligation to make a further response.

   In short, we have no authority to reverse an agency deci-
sion based on an objection that was not raised. The Supreme
Court has long warned us not to invent new issues as part of
our review of objections raised to an administrative agency.
“A reviewing court usurps the agency’s function when it sets
aside the administrative determination upon a ground not
theretofore presented and deprives the [administrative agency]
of an opportunity to consider the matter, make its ruling, and
state the reasons for its action.” Unemployment Comp. Com’n
v. Aragon, 329 U.S. 143, 155 (1946); see also Woodford v.
Ngo, 548 U.S. 81, 89 (2006). The EPA addressed, with ade-
quate thoroughness and detail, see, e.g., Balt. Gas and Elec.
Co., 462 U.S. at 105-06, each of the objections filed by the
NRDC. These objections create the compass of our limited
review. 21 U.S.C. § 346a(h)(1), (5); 40 C.F.R. § 178.25(a)(2).7
                                               (Text continued on page 13267)

   7
     The majority also relies in part upon the dissent of Judge Wright in
Center for Auto Safety v. Peck, 751 F.2d 1336, 1373 (D.C. Cir. 1985)
(Wright, J., dissenting). Maj. Op. at 13256-57 n.7. However, Judge (now
Justice) Scalia’s opinion for the majority in that case captures the dissent’s
error, and, concomitantly, the majority’s mistake in this case when it
warns that “we must be implacably skeptical of belated recognition at the
appellate stage that elements of scientific analysis unchallenged during a
contested proceeding are incomprehensible without further explanation.
To credit such post-appeal pleas of inadequate information is to threaten
the integrity of all rulemaking in fields beyond our own limited scientific
ken.” Id. at 1361. The entirety of the passage bears repeating:
    The dissent’s response is equally unsatisfactory, consisting essen-
    tially of the assertion that late presentation of the issue must be
    disregarded because validity of the [data] curves is essential to
13266              NORTHWEST COALITION v. EPA
   validity of the agency’s conclusion. It is simply not the case,
   however, that all of the essential postulates for an agency rule
   must be contained in the record. Every judgment of any conse-
   quence is constructed upon an infinitude of other judgments, of
   greater or lesser certitude, in a progression of logical dependency
   terminating in a first principle the equivalent of 1 + 1 = 2. They
   cannot all possibly be included in the statement of basis and pur-
   pose for a rulemaking. We do not have authority to require that
   all elements underlying a rule be set forth in a fashion “under-
   standable to a layman,” see Vermont Yankee Nuclear Power
   Corp. v. Natural Resources Defense Council, Inc., 435 U.S. 519,
   557, 98 S. Ct. 1197, 1218, 55 L. Ed. 2d 460 (1978). And it may
   as well be disclosed that in scientific fields we judges ourselves
   are laymen, ill equipped to determine where the line falls
   between requisite explanation of problematic analysis and useless
   replication of what for the cognoscenti amounts to a textbook on
   basic physics. Thus, our “feel” for the adequacy of an analysis in
   such cases is necessarily governed by the reaction that it elicits
   from knowledgeable commenters. From the point at which it
   reaches common ground we can reasonably assume that no fur-
   ther explication is required. We will hear on appeal assertions
   that needful elaborations fairly requested were not provided; but
   we must be implacably skeptical of belated recognition at the
   appellate stage that elements of scientific analysis unchallenged
   during a contested proceeding are incomprehensible without fur-
   ther explanation. To credit such post-appeal pleas of inadequate
   information is to threaten the integrity of all rulemaking in fields
   beyond our own limited scientific ken. The present challenge to
   the effectiveness curves presents the threat in a particularly fla-
   grant form. NHTSA specifically asked the petitioners (and other
   rulemaking participants) in 1979: “Do the existing analyses rep-
   resent the most appropriate methods of approaching a study of
   bumper standards at different impact speeds and levels of damage
   resistance? If not, what method should be used?” Though State
   Farm and IIHS, among others, responded with substantial com-
   ments there was not even a suggestion that the effectiveness
   curves represented a fundamentally invalid methodology. The
   dissent provides a list of reasons why petitioners might not have
   raised these objections during the rulemaking proceeding, Dissent
   at 1387-88 all of which boil down to petitioners’ probable reluc-
   tance to upset favorable determinations. Even if that were the
                    NORTHWEST COALITION v. EPA                       13267
                                     C

   Even were it proper for us to address the adequacy of the
EPA’s consideration of an issue not raised, the record pro-
vides an adequate basis for us to conclude that the EPA’s
selection of a 3x and 1x uncertainty factor was not arbitrary,
as the majority erroneously concludes. Maj. Op. at 13255.

  The record in this case contains the EPA’s published guid-
ance for determination of an appropriate FQPA safety factor.
See Office of Pesticide Programs, EPA, Determination of the

    only consideration, it would be of questionable wisdom to reward
    their tactical decision to leave the agency in the dark—and thus
    encourage benighted agency action in the future. But in any
    event, the dissent’s speculations do not explain why the propo-
    nents of the 2.5 mph standard did not raise these arguments. In
    fact, some commenters on the June 1979 Final Assessment
    (which supported the 5.0 mph standard) did object that the “ef-
    fectiveness ratios for 5.0 mph systems are overstated to a consid-
    erable extent,” but that objection was based upon the lack of
    correspondence with repair cost data rather than theoretical inad-
    equacy of the effectiveness curves.
       We conclude that the curves were considered part of the com-
    mon ground of expert analysis that required no further explana-
    tion. Petitioners’ objections on this score put us in mind of the
    Supreme Court’s injunction in Vermont Yankee that administra-
    tive proceedings should not be a game or a forum to engage in
    unjustified obstructionism by making cryptic and obscure refer-
    ence to matters that “ought to be” considered and then, after fail-
    ing to do more to bring the matter to the agency’s attention,
    seeking to have that agency determination vacated on the ground
    that the agency failed to consider matters “forcefully presented.”
    435 U.S. at 553-54, 98 S. Ct. at 1217. These instructions are even
    more appropriate when cryptic and obscure reference to theoreti-
    cal inadequacy—or in fact, even less than that, mere assertion of
    lack of explanation of theoretical adequacy—is first made on
    appeal.
Id. at 1361-62 (emphases in original, internal citations to the record omit-
ted).
13268             NORTHWEST COALITION v. EPA
Appropriate FQPA Safety Factor(s) in Tolerance Assessment
10 (Feb. 28, 2002). As explained in this guidance document,
“when evaluating whether reliable data are available to sup-
port a FQPA safety factor different from the default 10x
FQPA safety factor and what level of ‘different’ FQPA safety
factor would be safe for infants and children,” id. at 19, the
EPA may, in the exercise of its scientific judgment, consider
the 3x uncertainty factor that has traditionally been used for
evaluating risks posed by pesticide exposure in a related con-
text. See id. at 26; see also id. at 9-10 (noting that in evaluat-
ing the risks posed by pesticide exposure, “often a value of 3x
is used to address database deficiencies . . . .”). However, in
“the optimal case” in “which there is a high level of confi-
dence that the hazard and exposure assessments are suffi-
ciently conservative[,] and there are no residual uncertainties
in the assessment,” the EPA will remove the safety factor, i.e.,
it will apply a “safety factor of 1X,” deeming the existing
threshold “sufficient to protect infants and children.” Id. at
51-52. See also Office of Pesticide Programs, EPA, Office of
Pesticide Programs’ Policy on The Determination of The
Appropriate FQPA Safety Factor(s) For Use in The
Tolerance-setting Process: Response to Public Comments
OPP Docket OPP-00610 97 (Feb. 28, 2002) (internal citation
omitted) (further explaining the long-standing basis for “im-
posing a database uncertainty factor of 3X if one key study is
missing from the database and a factor of 10X if more than
one is missing.”).

   Other EPA tolerance-setting regulations reflect the
approach described in its guidance documents for selecting a
FQPA safety factor different from the default 10x FQPA
safety factor. See, e.g., Fenarimol; Pesticide Tolerance, 71
Fed. Reg. 32,841, 32,844-45 (June 7, 2006) (noting that the
EPA originally reduced the FQPA Safety factor from 10x to
3x subject to receiving additional data, and subsequently rec-
ommended reducing the 3x FQPA Safety factor to 1x when
it obtained adequate data); Thiacloprid; Pesticide Tolerances,
68 Fed. Reg. 55,503, 55,509 (Sept. 26, 2003) (“Although the
                  NORTHWEST COALITION v. EPA               13269
lack of morphometric assessments in the DNT raised some
uncertainty, EPA determined that there were sufficient reli-
able data to select an additional safety factor of 3X instead of
10X.”). The EPA relied on this long-established approach in
setting the safety factors for the three pesticides at issue here,
see supra at nn.2 & 3.

   Because the petitioners did not challenge the absence of an
explanation as to why the EPA picked a 3x or 1x factor rather
than a “4x or 5x or 8x or 9x” factor, we are deprived of the
EPA’s more detailed explanation as to why the scientific
community relies on the 3x uncertainty factor when database
deficiencies are identified. Nevertheless, the record indicates
that use of the 3x uncertainty factor is generally accepted by
the scientific community. See Michael L. Dourson et al., Evo-
lution of Science-Based Uncertainty Factors in Noncancer
Risk Assessment, 24 Regulatory Toxicology and Pharmacol-
ogy 108 (1996) (generally discussing the science underlying
the use of 10x and 3x default uncertainty factors). Indeed, the
lack of any controversy regarding the rationale underlying the
selection of a 3x safety factor rather than a “4x or 5x or 8x
or 9x” factor may explain why the NRDC did not argue in its
objections to the EPA that the agency needed a special justifi-
cation for selecting a 3x safety factor, once the EPA deter-
mined that the additional 10x factor was not required. In light
of the EPA’s reliance on a long-established and widely
accepted protocol, the majority’s statement that “the EPA
chose these lower safety levels arbitrarily” is not supported by
the record, and is contrary to our obligation to defer to the sci-
entific analysis and judgments made by an agency operating
within its area of special expertise. Balt. Gas and Elec. Co.,
462 U.S. at 103.

   As we have recently emphasized, “[w]e are to be most def-
erential when the agency is making predictions, within its area
of special expertise, at the frontiers of science.” Lands Coun-
cil, 2008 WL 2640001, at *9 (internal quotation marks and
alterations omitted). Lands Council prohibits us from indulg-
13270            NORTHWEST COALITION v. EPA
ing the temptation to “act as a panel of scientists.” Id. at *4.
Nor can we require the agency “to always demonstrate the
reliability of its scientific methodology or the hypotheses
underlying the [agency’s] methodology.” Id. at *7 (internal
quotation marks omitted). Lands Council teaches that our
proper role is simply to ensure that the agency, in its exper-
tise, made no clear error of judgment rendering its action arbi-
trary and capricious. See id. at *9-10. The EPA’s choices in
this case were neither arbitrary nor capricious and we must
defer to its judgment. See 5 U.S.C. § 706(2)(A); Balt. Gas and
Elec. Co., 462 U.S. at 103-05. Accordingly, I would deny the
petition for review in its entirety.
