FOR PUBLICATION

UNITED STATES COURT OF APPEALS

FOR THE NINTH CIRCUIT

SANDRA L. BAHR; DAVID

MATUSOW,

Petitioners,

v.

U.S. ENVIRONMENTAL PROTECTION

AGENCY; GINA MCCARTHY,

Administrator, United States

Environmental Protection Agency;

JARED BLUMENFELD, Regional

Administrator, EPA Region IX,

Respondents,

STATE OF ARIZONA,

Respondent-Intervenor.

No. 14-72327

OPINION

On Petition for Review of an Order of the

Environmental Protection Agency

Argued and Submitted June 17, 2016

San Francisco, California

Filed September 12, 2016
2 BAHR V. U.S. EPA

Before: Richard R. Clifton and Sandra S. Ikuta, Circuit

Judges, and William Q. Hayes,* District Judge.

Opinion by Judge Ikuta;

Partial Concurrence and Partial Dissent by Judge Clifton

SUMMARY**

Environmental Law

The panel granted in part and denied in part a petition for

review of an order of the United States Environmental

Protection Agencyapproving Arizona’s Five Percent Plan for

airborne particulate matter around Maricopa County,

promulgated under the Clean Air Act.

Arizona submitted a new State Implementation Plan

revision on May 25, 2012 – the Five Percent Plan – to

achieve a five percent annual reduction in PM-10, a harmful

air pollutant.

Petitioners alleged that the EPA acted contrary to law by

failing to require that Arizona include an updated analysis of

best available control measures and most stringent measures

in the Five Percent Plan, excluding 135 exceedances from the

monitoring data as “exceptional events,” and allowing

* The Honorable William Q. Hayes, United States District Judge for

the Southern District of California, sitting by designation.

** This summary constitutes no part of the opinion of the court. It has

been prepared by court staff for the convenience of the reader.
BAHR V. U.S. EPA 3

Arizona to satisfy the “contingency measures” requirement

with previously implemented control measures.

The panel held that it would apply Chevron U.S.A. Inc. v.

Natural Resources Defense Council, Inc., 467 U.S. 837

(1984), deference to the EPA’s interpretation of the Clean Air

Act issued in connection with a State Implementation Plan

approval.

The panel upheld the EPA’s determination that the control

measures in Arizona’s Five Percent Plan did not need to be

updated, and that the 135 exceedances were exceptional

events that were excluded from consideration under the

EPA’s regulation and guidance documents. 

The panel did not defer to the EPA’s interpretation of the

contingency measures requirement, however, because under

the plain language of 42 U.S.C. § 7502(c)(9) contingency

measures are measures that will be taken in the future, not

measures that have already been implemented. The panel

remanded to the EPA for further consideration of this portion

of the State Implementation Plan, but otherwise denied the

petition.

Judge Clifton concurred in sections I-IV of the majority

opinion, and dissented from the majority’s conclusion in

section V that EPA’s approval of the contingency measures

in Arizona’s State Implementation Plan was contrary to the

clear language of the Clean Air Act. In his view, the scope of

the Clean Air Act’s contingency measures requirement was

ambiguous and EPA’s reasonable interpretation of that

requirement was entitled to deference. 
4 BAHR V. U.S. EPA

COUNSEL

Joy E. Herr-Cardillo (argued) and Timothy M. Hogan,

Arizona Center for Law in the Public Interest, Tucson,

Arizona, for Petitioners.

Alan D. Greenberg (argued), Attorney; Sam Hirsch, Acting

Assistant Attorney General; Environment & Natural

Resources Division, United States Department of Justice,

Denver, Colorado; Geoffrey Wilcox, Office of General

Counsel; Kara Christenson, Office of Regional Counsel,

Region 9; United States Environmental Protection Agency,

San Francisco, California; for Respondents.

Monique Coady, Assistant Attorney General, Office of the

Attorney General, Phoenix, Arizona, for RespondentIntervenor.

OPINION

IKUTA, Circuit Judge:

Sandra Bahr and David Matusow petition for review of a

final rule issued by the Environmental Protection Agency

(EPA) approving Arizona’s Five Percent Plan for airborne

particulate matter around Maricopa County. They argue that

the EPA erred in approving this plan because it did not

include best available control measures (BACM) and most

stringent control measures (MSM) as of 2012. The

petitioners also argue that the EPA failed to follow its own

published guidance in approving Arizona’s claim that 135

exceedances of the air emission standard could be excluded

from consideration. See 42 U.S.C. § 7619(b)(1)(A). Finally,
BAHR V. U.S. EPA 5

the petitioners argue that the EPA’s approval of the

contingency measures included in Arizona’s Five Percent

Plan was contrary to 42 U.S.C. § 7502(c)(9) because the

measures had already been implemented. We uphold the

EPA’s determination that the control measures in Arizona’s

Five Percent Plan did not need to be updated, and that the 135

exceedances were exceptional events that are excluded from

consideration under the EPA’s regulation and guidance

documents. We do not defer to the EPA’s interpretation of

the contingency measures requirement, however, because

under the plain language of § 7502(c)(9) contingency

measures are measures that will be taken in the future, not

measures that have already been implemented.

I

We begin by briefly describing the statutory framework. 

The Clean Air Act (CAA), 42 U.S.C. § 7401 et seq.,

establishes “cooperative Federal, State, regional, and local

programs to prevent and control air pollution,” id.

§ 7401(a)(4). Under the CAA, the EPA is required to

“publish . . . a list which includes each air pollutant . . .

emissions of which, in [the EPA’s] judgment, cause or

contribute to air pollution which may reasonably be

anticipated to endanger public health or welfare.” Id.

§ 7408(a)(1). The EPA is then required to “prescrib[e] a

national primary ambient air quality standard” (NAAQS) for

that pollutant. Id. § 7409(a).

One such harmful air pollutant is “PM-10,” defined as

“particulate matter with an aerodynamic diameter less than or
6 BAHR V. U.S. EPA

equal to a nominal ten micrometers.” Id. § 7602(t). 

According to the EPA, “PM-10 causes adverse health

effects by penetrating deep into the lungs, aggravating

the cardiopulmonary system.” Approval and Promulgation

of Implementation Plans—Maricopa County PM-10

Nonattainment Area, 79 Fed. Reg. 7118, 7118 (Feb. 6, 2014). 

The EPA established a NAAQS for PM-10 of 150

micrograms per cubic meter, averaged over a 24-hour period. 

40 C.F.R. § 50.6(a). This standard, which is sometimes

referred to as the “24-hour PM-10 standard,” is “attained

when the expected number of days per calendar year with a

24-hour average concentration above 150 ìg/m3 . . . is equal

to or less than one.” Id.

The CAA provides that “[e]ach State shall have the

primary responsibility for assuring air quality” within the

state “by submitting an implementation plan” explaining how

the state will meet and maintain the NAAQS and other

standards. 42 U.S.C. § 7407(a). An area within a state that

does not meet a NAAQS is designated as a “nonattainment”

area, id. § 7407(d). Each state’s implementation plan (called

a State Implementation Plan or SIP) must provide for the

“implementation, maintenance, and enforcement” of the

NAAQS. Id. § 7410(a)(1). The CAA requires each SIP for

a nonattainment area to contain specified information,

including a requirement for reasonable further progress, id.

§ 7502(c)(2), an emissions inventory, id. § 7502(c)(3), and a

list of “contingency measures” to “be undertaken if the area

fails to make reasonable further progress, or to attain the
BAHR V. U.S. EPA 7

national primary ambient air quality standard by the

attainment date applicable under this part,” id. § 7502(c)(9).1

The CAA sets out a series of deadlines for states to meet

the NAAQS for PM-10, with increasingly stringent

requirements if a state misses a deadline. Id. §§ 7513–7513b. 

The sequence is as follows:

A nonattainment area is initially designated as a

“moderate” area. Id. § 7513(a). A SIP for a “moderate” PM10 nonattainment area must explain how that area will meet

the PM-10 NAAQS by the “attainment date,” which for

nonattainment areas designated byCongress was no later than

December 31, 1994. Id. § 7513(c)(1). The SIP must “assure

that reasonably available control measures for the control of

PM-10” are implemented. Id. § 7513a(a).

If a moderate nonattainment area fails to meet the PM-10

NAAQS by the attainment date, the EPA must reclassify it as

a “Serious PM-10 nonattainment area.” Id. § 7513(b). After

redesignation, the state must submit a SIP that demonstrates

how the area will meet the PM-10 NAAQS within 10 years of

1

 42 U.S.C. § 7502(c)(9) states:

(9) Contingency measures

Such plan shall provide for the implementation of

specific measures to be undertaken if the area fails to

make reasonable further progress, or to attain the

national primary ambient air quality standard by the

attainment date applicable under this part. Such

measures shall be included in the plan revision as

contingency measures to take effect in any such case

without further action by the State or the Administrator.
8 BAHR V. U.S. EPA

the original nonattainment designation, or, for areas originally

designated as nonattainment by Congress, no later than

December 31, 2001. Id. § 7513(c)(2). A SIP for a serious

nonattainment area must also “assure that the best available

control measures [BACM] for the control of PM-10 shall be

implemented.” Id. § 7513a(b).2

If a state fails to meet the deadline for bringing a Serious

Area into compliance, the EPA may grant the state a single

five-year extension of the deadline to meet the NAAQS for

PM-10, but only if the state submits a SIP that “includes the

most stringent measures [MSM] that are included in the

implementation plan of any State or are achieved in practice

in any State, and can feasibly be implemented in the area.” 

Id. § 7513(e).3

2

 42 U.S.C. § 7513a(b) provides:

(b) Serious Areas

(1) Plan provisions. In addition to the provisions

submitted to meet the requirements of paragraph [1]

(a)(1) (relating to Moderate Areas), each State in which

all or part of a Serious Area is located shall submit an

implementation plan for such area that includes each of

the following: . . .

(B) Provisions to assure that the best available control

measures for the control of PM-10 shall be

implemented no later than 4 years after the date the area

is classified (or reclassified) as a Serious Area.

3

 42 U.S.C. § 7513(e) provides in pertinent part:

(e) Extension of attainment date for Serious Areas

Upon application by any State, the Administrator may
BAHR V. U.S. EPA 9

If a Serious Area fails to achieve compliance by the

attainment date after receiving the one-time five-year

extension under § 7513(e), the CAA requires the state to

“submit within 12 months after the applicable attainment

date, plan revisions which provide for attainment of the PM10 air quality standard.” Id. § 7513a(d).4

 The SIP revisions

extend the attainment date for a Serious Area beyond

the date specified under subsection (c) of this section,

if attainment by the date established under subsection

(c) of this section would be impracticable, the State has

complied with all requirements and commitments

pertaining to that area in the implementation plan, and

the State demonstrates to the satisfaction of the

Administrator that the plan for that area includes the

most stringent measures that are included in the

implementation plan of any State or are achieved in

practice in any State, and can feasibly be implemented

in the area. . . . The Administrator may not approve an

extension until the State submits an attainment

demonstration for the area. The Administrator may

grant at most one such extension for an area, of no

more than 5 years.

4

 42 U.S.C. § 7513a(d) states:

(d) Failure to attain

In the case of a Serious PM-10 nonattainment area in

which the PM-10 standard is not attained by the

applicable attainment date, the State in which such area

is located shall, after notice and opportunity for public

comment, submit within 12 months after the applicable

attainment date, plan revisions which provide for

attainment of the PM-10 air quality standard and, from

the date of such submission until attainment, for an

annual reduction in PM-10 or PM-10 precursor

emissions within the area of not less than 5 percent of
10 BAHR V. U.S. EPA

must provide for an annual five percent reduction in PM-10

within the Serious Area from the date the SIP revision was

submitted to the EPA until the state attains the NAAQS in

that area. Id.

States are required to conduct ambient air quality

monitoring to determine whether a geographical region or

area in the state is meeting the NAAQS for PM-10. Id.

§ 7410(a)(2)(B)(i). State air qualitymonitoring systems must

use the criteria and methodology established by the EPA. Id.

§ 7619(a). Congress recognized that air quality monitoring

data could be affected by exceptional events that could not

reasonably be controlled by the states, and directed the EPA

to promulgate regulations “governing the review and

handling of air quality monitoring data influenced by

exceptional events.” Id. § 7619(b)(2)(A). The statute defines

an “exceptional event” as an event that “(i) affects air quality;

(ii) is not reasonably controllable or preventable; (iii) is an

event caused by human activity that is unlikely to recur at a

particular location or a natural event; and (iv) is determined

by the Administrator through the process established in the

regulations promulgated under paragraph (2) to be an

exceptional event.” Id. § 7619(b)(1)(A).

Pursuant to this direction, the EPA promulgated the

“Exceptional Events Rule,” 40 C.F.R. § 50.14. The rule

repeats the statute’s definition of “exceptional event,” id.

the amount of such emissions as reported in the most

recent inventory prepared for such area.
BAHR V. U.S. EPA 11

§ 50.1(j),5and allows a state to “request EPA to exclude data

showing exceedances or violations of the national ambient air

quality standard that are directly due to an exceptional event,”

id. § 50.14(a)(1). In order to obtain EPA approval to exclude

exceptional event data, a state must provide evidence that

“[t]he event satisfies the criteria set forth in 40 C.F.R 50.1(j)”

and meets other criteria. Id. § 50.14(c)(3)(iv). If a state

makes the required showing, the “EPA shall exclude [the

exceptional event] data from use in determinations of

exceedances and NAAQS violations.” Id. § 50.14(b)(1).

The EPA has recognized that PM-10 levels can be

affected by natural events such as dust storms, see id.

§ 50.1(j)–(k), and has therefore developed guidance for

applying the Exceptional Events Rule to high wind events. 

See Treatment of Data Influenced by Exceptional Events,

72 Fed. Reg. 13560 (Mar. 22, 2007) (Treatment of Data

Guidance). The Treatment of Data Guidance states that

increased particulate matter concentrations “raised by

unusually high winds will be treated as due to uncontrollable

natural events where (1) the dust originated from

nonanthropogenic sources, or (2) the dust originated from

5

 40 C.F.R. § 50.1(j) provides:

(j) Exceptional event means an event that affects air

quality, is not reasonably controllable or preventable, is

an event caused by human activity that is unlikely to

recur at a particular location or a natural event, and is

determined by the Administrator in accordance with

40 CFR 50.14 to be an exceptional event. It does not

include stagnation of air masses or meteorological

inversions, a meteorological event involving high

temperatures or lack of precipitation, or air pollution

relating to source noncompliance.
12 BAHR V. U.S. EPA

anthropogenic sources within the State, that are determined

to have been reasonably well-controlled at the time that the

event occurred, or from anthropogenic sources outside the

State.” Id. at 13576 (emphasis added).

In May 2013, the EPA published additional “guidance

and interpretation” explaining how the Exceptional Events

Rule and the Treatment of Data Guidance applies to high

wind events. See EPA, Interim Guidance on the Preparation

of Demonstrations in Support of Requests to Exclude

Ambient Air QualityData Affected byHigh Winds Under the

Exceptional Events Rule (May 2013) (Interim Guidance).6

The Interim Guidance addresses when an anthropogenic

source within the State is “reasonably well-controlled at the

time that the event occurred,” 72 Fed. Reg. at 13576, as

required by the Treatment of Data Guidance.

II

We now provide the background of this case. Congress

designated Maricopa County, Arizona, as a “moderate” PM10 nonattainment area in 1990. 42 U.S.C. § 7407(d)(4)(B);

PM10 Group I and Group II Areas, 52 Fed. Reg. 29383,

29384 (Aug. 7, 1987). The designated nonattainment area,

termed the “Maricopa County PM-10 Nonattainment Area”

(Maricopa Area), covers the eastern portion of Maricopa

County, including the cities of Phoenix, Mesa, Scottsdale,

6 The Interim Guidance is available at: https://www.epa.gov/

sites/production/files/2015-09/documents/exceptevents_highwinds_

guide_130510.pdf; see also Draft Guidance To Implement Requirements

for the Treatment of Air Quality Monitoring Data Influenced by

Exceptional Events, 77 Fed. Reg. 39959, 39960 (July 6, 2012)

(announcing the availability of a draft version of the Interim Guidance on

the EPA’s website).
BAHR V. U.S. EPA 13

Tempe, Chandler, and Glendale. 79 Fed. Reg. at 7118. It

also covers unincorporated parts of Maricopa County and

portions of Pinal County. Id.

Because the Maricopa Area was designated as a

nonattainment area by Congress, Arizona’s first deadline for

meeting the NAAQS for PM-10 was December 31, 1994. 

42 U.S.C. § 7513(c). The Maricopa Area was not in

attainment by 1994, so the EPA reclassified the Maricopa

Area as a Serious PM-10 nonattainment area. 42 U.S.C.

§ 7513(b)(2); Clean Air Act Reclassification; ArizonaPhoenix Nonattainment Area; PM-10, 61 Fed. Reg. 21372,

21373 (May 10, 1996). This required Arizona to submit a

SIP that would demonstrate how the Maricopa Area would

meet the NAAQS for PM-10 by December 31, 2001, see

42 U.S.C. § 7513(c)(2), and to explain how it would

implement the best available control measures for PM-10, id.

§ 7513a(b).

The Maricopa Area did not meet the NAAQS for PM-10

by the end of 2001. Rather, in 2000 Arizona preemptively

applied for a five-year extension (until December 2006) under

§ 7513(e) and at the same time submitted a SIP for the

Maricopa Area (the 2000 SIP). The 2000 SIP proposed to

implement over 70 best available control measures for major

dust sources, Approval and Promulgation of Implementation

Plans; Arizona—Maricopa County PM-10 Nonattainment

Area; Serious Area Plan for Attainment of the Annual PM-10

Standard, 65 Fed. Reg. 19964, 19972–83 (Apr. 13, 2000), and

stated that its measures were “the most stringent measures

that are included in the implementation plan of any State, or

are achieved in practice in any State,” id. at 19984. In 2002,

the EPA issued a final rule approving the 2000 SIP and

granting the requested extension. Approval andPromulgation
14 BAHR V. U.S. EPA

of Implementation Plans; Arizona–Maricopa County PM-10

Nonattainment Area; Serious Area Plan for Attainment of the

PM-10 Standards, 67 Fed. Reg. 48718, 48718–19 (July 25,

2002) (the 2002 Final Rule). The 2002 Final Rule stated that

the control measures in the 2000 SIP met the BACM and

MSM standards. Id.

7

By December 2006, the Maricopa Area had still failed to

meet the NAAQS for PM-10. See Findings of Failure To

Attain; State of Arizona, Phoenix Nonattainment Area; State

of California, Owens ValleyNonattainment Area; Particulate

Matter of 10 Microns or Less, 72 Fed. Reg. 31183, 31184–85

(June 6, 2007). At that point, the CAA gave Arizona 12

months to submit revisions to the SIP that would achieve

attainment of the NAAQS for PM-10, provide for an annual

five percent reduction in PM-10 in the Maricopa Area,

42 U.S.C. § 7513a(d), and contain appropriate contingency

measures, id. § 7502(c)(9).

Arizona submitted revisions to the Maricopa Area SIP in

December 2007 (the 2007 SIP). In addition to proposing 53

control measures, the 2007 SIP proposed revising a

previously approved agricultural control measure, namely an

agricultural general permit specifying best management

practices for reducing PM-10 from agricultural activities. See

Approval and Promulgation of Implementation Plans—

Maricopa County (Phoenix) PM-10 Nonattainment Area;

7 We considered a challenge to EPA’s 2002 Final Rule approving the

2000 SIP and held that the EPA’s approval of Arizona’s rejection of a

measure requiring the use of a reformulated diesel fuel as BACM was

arbitrary and capricious. Vigil v. Leavitt, 381 F.3d 826, 841–46 (9th Cir.

2004). We upheld the rest of the EPA’s approval, including its approval

of Arizona’s general permit rule for agricultural emissions of PM-10 as

BACM. Id. at 836–38, 847.
BAHR V. U.S. EPA 15

Serious Area Plan for Attainment of the 24-Hour PM-10

Standard; Clean Air Act Section 189(d), 75 Fed. Reg. 54806,

54810, 54812–13 (Sept. 9, 2010) (the 2010 Proposed Rule). 

The 2010 Proposed Rule stated that the EPA would

disapprove this revision to the agricultural general permit rule

on the ground that other states and local agencies had

“acquired additional expertise about how to control emissions

from these sources,” and as a result the EPA no longer

believed that the requirements in the agricultural general

permit rule in the 2000 SIP were best available control

measures. Id. To avoid a partial disapproval, Arizona

withdrew the plan in 2011. 79 Fed. Reg. at 7119. As a result

of this withdrawal of the 2007 SIP, the EPA found that

Arizona had failed to make a required SIP submittal. Finding

of FailureTo Submit State Implementation Plan Revisions for

Particulate Matter, PM-10, Maricopa County (Phoenix) PM10 Nonattainment Area, AZ, 76 Fed. Reg. 8300, 8300–01

(Feb. 14, 2011). This finding required Arizona to submit

another SIP by 2013. Id. at 8301; 42 U.S.C. § 7509(a).

Arizona submitted a new SIP revision on May 25, 2012. 

See 79 Fed. Reg. at 7119. Because this SIP was prepared

pursuant to § 7513a(d), which requires a state to achieve a

five percent annual reduction in PM-10, we adopt the EPA’s

term and refer to it as the “Five Percent Plan.” The Five

Percent Plan proposed to achieve the five percent annual

reduction required by § 7513a(d) by implementing many of

the 53 control measures previously proposed in the 2007 SIP,

as well as adopting a new emissions control measure, the

“Dust Action General Permit.” Unlike the 2007 SIP, the Five

Percent Plan did not propose any changes to the agricultural

general permit.
16 BAHR V. U.S. EPA

As required by § 7502(c)(9), the Five Percent Plan

proposed a number of contingencymeasures. 79 Fed. Reg. at

7124. Four of the five measures were permanent changes to

infrastructure that had been completed in the years 2008

through 2011, namely, paving existing dirt roads and alleys,

paving and stabilizing unpaved shoulders, repaving or

overlaying paved roads with rubberized asphalt, and lowering

speed limits on dirt roads and alleys. Id. The fifth

contingency measure required the purchase of PM-10

certified sweepers (which had already been accomplished by

the end of 2009), and ongoing sweeping of ramps, freeways,

and frontage roads. Id.

Arizona also acknowledged that there had been a number

of exceedances of the 24-hour PM-10 standard during 2011

and 2012, but claimed they should be deemed “exceptional

events” and excluded from a determination of whether the

Maricopa Area met the NAAQS for PM-10. In support of

this claim, Arizona submitted documentation to the EPA to

demonstrate that 137 exceedances of the NAAQS for PM-10

on 27 days during the period from 2011 to 2012 were the

result of “exceptional events,” namely high wind dust events. 

79 Fed. Reg. at 7122.8 The EPA wrote separate reports on

each of Arizona’s submissions. The reports analyzed the data

and concluded that the flagged exceedances met “the

definition of an exceptional event: the exceedances affected

air quality, were not reasonably controllable or preventable,

and meet the definition of a natural event.”

In February 2014, the EPA published its proposed

decision regarding Arizona’s Five Percent Plan. 79 Fed. Reg.

8 Though the EPA’s proposed rulemaking mentioned 133

exceedances, the parties agree that Arizona requested approval of 137.
BAHR V. U.S. EPA 17

at 7118. The EPA noted that the monitoring data for the

Maricopa Area showed 133 exceedances of the 24-hour PM10 NAAQS during the 2011–2012 time period, but stated that

131 of those exceedances “were caused by high wind

exceptional events,” and “should not be used for regulatory

purposes,” including for evaluation of the Five Percent Plan. 

Id. at 7122. Excluding these exceedances, the EPA proposed

to determine that the Maricopa Area had attained the NAAQS

for 24-hour PM-10 by December 31, 2012. Id. at 7125. The

EPA also proposed to approve Arizona’s contingency

measures. Id. at 7124. In doing so, the EPA explained that

it had previously “interpreted [42 U.S.C. § 7502(c)(9)] to

allow states to implement contingency measures before they

are triggered by a failure of . . . attainment as long as those

measures are intended to achieve emission reductions over

and beyond those relied on in the attainment and [reasonable

further progress] demonstrations.” 79 Fed. Reg. at 7124.

The EPA issued a final rule on June 10, 2014, approving

the Five Percent Plan “as meeting all relevant statutory and

regulatory requirements.” Approval and Promulgation of

Implementation Plans—Maricopa County PM-10

Nonattainment Area; Five Percent Plan for Attainment of the

24-Hour PM-10 Standard, 79 Fed. Reg. 33107, 33107 (June

10, 2014) (2014 Final Rule). The 2014 Final Rule stated that

the EPA was excluding 135 exceedances9from the

monitoring data as exceptional events. Id. at 33111. For each

of the events that EPA determined was exceptional, “EPA

found that the event was not reasonably controllable or

preventable,” and that “reasonable controls” were in place for

9 The EPA’s final rule clarified that the number of approved

exceedances was 135, which occurred on 25 days over the period of

2010–12. 79 Fed. Reg. at 33110–11.
18 BAHR V. U.S. EPA

anthropogenic sources of dust. Id. The EPA reached its

conclusion that “reasonable controls” were in place byrelying

on its 2002 Final Rule approving Arizona’s 2000 SIP as

including best available control measures and most stringent

control measures. Id. at 33112. The EPA also determined

that Arizona sufficiently demonstrated that dust sources

outside the Maricopa Area were reasonably controlled. Id. at

33113.

The 2014 Final Rule included the EPA’s response to

comments made by petitioners Sandra Bahr and David

Matusow, two residents of Phoenix. First, the EPA addressed

petitioners’ argument that the EPA should have required

Arizona to update its control measures to ensure that they

were BACM and MSM, rather than letting Arizona rely on

the EPA’s approval of the 2000 SIP. 79 Fed. Reg. at

33108–10. The EPA rejected this claim, explaining that “the

requirement for BACM is triggered by a specific event: The

reclassification of a moderate PM-10 nonattainment area to

serious.” Id. at 33108. Likewise, the EPA explained that

§ 7513(e) provides “that the requirement for MSM is

triggered by a particular event: EPA’s granting of a state’s

request for an extension of the attainment deadline for a

serious nonattainment area.” Id. The EPA then stated that

§ 7513(d) (the section requiring the submission of a five

percent plan) “does not contain a specific requirement that the

state update the previously approved requirements for BACM

and MSM as a consequence of failing to reach attainment by

the applicable deadline for serious PM-10 nonattainment

areas.” Id. at 33109. Because there was no statutory trigger

requiring Arizona to update its demonstration that its control

measures were best available and most stringent, the EPA

explained, the Five Percent Plan could rely on the EPA’s

approval of BACM and MSM in the 2000 SIP. Id. The EPA
BAHR V. U.S. EPA 19

also disagreed with petitioner’s comment that the Five

Percent Plan was inadequate because the agricultural control

measures were not BACM, as indicated by the EPA’s 2010

Proposed Rule disapproving of Arizona’s proposed revision

to its agricultural general permit. In response to this

comment, the EPA stated that the Five Percent Plan satisfied

the requirements in § 7513a(d) “without relying on additional

emissions reductions from agricultural sources.” Id. at

33109.

Second, the EPA addressed petitioners’ argument that its

determination that the 135 exceedances constituted

exceptional events was contrary to the Interim Guidance. 

Petitioners interpreted the Interim Guidance as preventing the

EPA from concurring that best available control measures

were in place unless the EPA had determined control

measures for windblown dust to be BACM within the past

three years. 79 Fed. Reg. at 33111–12. The EPA disagreed

with this interpretation and concluded that Arizona’s controls

were reasonable. Id. at 33112. The EPA also rejected

petitioners’ argument that Arizona had failed to provide an

adequate description of upwind sources and control measures

as required by the Interim Guidance. Id. at 33113–14.

Finally, the EPA dismissed petitioners’ comment that the

EPA erred in accepting Arizona’s “contingencymeasures” in

its Five Percent Plan because the measures had already been

implemented. Id. at 33114–15. The petitioners argued that

because § 7502(c)(9) requires contingencymeasures that “are

automatically and immediately implemented if a milestone

for reasonable further progress or attainment is not met,” the

previously implemented measures in the Five Percent Plan

could not qualify. Id. at 33114. In rejecting this comment,

the EPA stated it interpreted § 7502(c)(9) as requiring only
20 BAHR V. U.S. EPA

that “[c]ontingency measures must provide for additional

emission reductions” that were not otherwise included “in the

attainment demonstration,” and that “[n]othing in the statute

precludes a state from implementing such measures before

they are triggered,” relying on the Fifth Circuit decision in

Louisiana Environmental Action Network v. EPA, 382 F.3d

575 (5th Cir. 2004). 79 Fed. Reg. at 33114.

The plaintiffs filed a petition for review of the 2014 Final

Rule on July 29, 2014.

III

Under 42 U.S.C. § 7607(b)(1), we have jurisdiction over

“[a] petition for review of the Administrator’s action in

approving or promulgating any implementation plan.”

In reviewing a challenge to the EPA’s approval of a SIP

under § 7607(b)(1), we apply “the general standard of review

for agency actions set forth in the Administrative Procedure

Act (APA).” Latino Issues Forum v. EPA, 558 F.3d 936, 941

(9th Cir. 2009); see also Vigil v. Leavitt, 381 F.3d 826, 833

(9th Cir. 2004). Under the APA, we must uphold an agency

action unless it is “arbitrary, capricious, an abuse of

discretion, or otherwise not in accordance with law.” 

5 U.S.C. § 706(2)(A). This standard is “highly deferential,

presuming the agency action to be valid and affirming the

agency action if a reasonable basis exists for its decision.” 

Ranchers Cattlemen Action Legal Fund United Stockgrowers

of Am. v. U.S. Dep’t of Agric., 499 F.3d 1108, 1115 (9th Cir.

2007). Generally, “[a]n agency decision will be upheld as

long as there is a rational connection between the facts found

and the conclusions made.” Barnes v. U.S. Dep’t of Transp.,

655 F.3d 1124, 1132 (9th Cir. 2011). We will deem an
BAHR V. U.S. EPA 21

agency action to be arbitrary and capricious only “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.” Motor Vehicle

Mfrs. Ass’n of the U.S. v. State Farm Mut. Auto. Ins. Co.,

463 U.S. 29, 43 (1983). Where the question presented for

review is a factual dispute which implicates “a high level of

technical expertise” we defer to “the informed discretion of

the responsible federal agencies.” Kleppe v. Sierra Club,

427 U.S. 390, 412 (1976). “Even when an agency explains its

decision with ‘less than ideal clarity,’ a reviewing court will

not upset the decision on that account ‘if the agency's path

may reasonably be discerned.’” Alaska Dep’t of Envtl.

Conservation v. EPA, 540 U.S. 461, 497 (2004) (quoting

Bowman Transp., Inc. v. Ark.-Best Freight Sys., Inc.,

419 U.S. 281, 286 (1974)).

Where the petitioner challenges the agency’s action as

inconsistent with the agency’s own policies, we examine

whether the agency has actually departed from its policy and,

if so, whether the agency has offered a reasoned explanation

for such departure. See Encino Motorcars, LLC v. Navarro,

136 S. Ct. 2117, 2125–26 (2016). Generally, “[a]gencies are

free to change their existing policies as long as they provide

a reasoned explanation for the change.” Id. at 2125. In

contrast, where the agency is not offering a policy

explanation but is instead interpreting a binding regulation,

the agency’s interpretation is “controlling” unless “plainly

erroneous or inconsistent with the regulation.” Auer v.

Robbins, 519 U.S. 452, 461 (1997).
22 BAHR V. U.S. EPA

Where the agency’s action is an interpretation of a statute

that the agency administers, “we follow the two-step

approach set out in Chevron U.S.A. Inc. v. Natural Resources

Defense Council, Inc., 467 U.S. 837 (1984).” Latino Issues

Forum, 558 F.3d at 941. First, “if Congress has ‘directly

spoken to the precise question at issue,’ then the matter is

capable of but one interpretation by which the court and the

agency must abide.” Vigil, 381 F.3d at 834 (quoting

Chevron, 467 U.S. at 842).

At the second step of Chevron, if we determine that

Congress was silent on the issue, or the statute is subject to

multiple interpretations, we must determine the degree of

deference to give the agency’s interpretation of a statute. 

United States v. Mead Corp., 533 U.S. 218, 227–29 (2001). 

“Not all agency statutory interpretations are entitled to

Chevron deference.” Sierra Club v. EPA, 671 F.3d 955, 962

(9th Cir. 2012). “Rather, Chevron deference is appropriate

where ‘the agency can demonstrate that it has the general

power to make rules carrying the force of law and that the

challenged action was taken in the exercise of that

authority.’” Id. (quoting Wilderness Soc’y v. U.S. Fish &

Wildlife Serv., 353 F.3d 1051, 1067 (9th Cir. 2003) (en

banc)). We generally deem Congress to have delegated such

authority when it authorizes the agency to engage in noticeand-comment rulemaking. Mead, 533 U.S. at 229–30. In

such circumstances, a court should accept the agency’s

interpretation “if Congress has not previously spoken to the

point at issue and the agency’s interpretation is reasonable.” 

Id. at 229.

Though we have previously applied Chevron deference to

the EPA’s interpretation of the CAA issued in connection

with a SIP approval, see Association of Irritated Residents v.
BAHR V. U.S. EPA 23

EPA, 686 F.3d 668, 679–81 (9th Cir. 2011), we have never

expressly held that such deference is appropriate, but rather

have held the question open, see Vigil, 381 F.3d at 835

(declining to address “whether the EPA’s interpretation of the

Act in the course of approving Arizona’s SIP is entitled to

Chevron deference”). But because “[a] very good indicator

of delegation meriting Chevron treatment [is] express

congressional authorizations to engage in the rulemaking or

adjudication process that produces the regulations or rulings

for which deference is claimed,” Mead Corp., 533 U.S. at

229, and because the EPA engages in such a rulemaking

process in approving a SIP, we agree with the Fifth Circuit

that “EPA’s final rules approving the [Arizona] SIP, to the

extent they involve the reasonable resolution of ambiguities

in the CAA, will be afforded Chevron deference,” BCCA

Appeal Grp. v. EPA, 355 F.3d 817, 825 (5th Cir. 2003).

IV

On appeal, petitioners argue that the EPA acted contrary

to law by failing to require that Arizona include an updated

analysis of best available control measures and most stringent

measures in the Five Percent Plan. They also argue that the

EPA abused its discretion by excluding 135 exceedances

from the monitoring data as “exceptional events.” Finally,

they argue that the EPA violated the CAA by allowing

Arizona to satisfy the “contingency measures” requirement

with previously implemented control measures. We consider

each argument in turn.

A

We first consider petitioners’ argument that the EPA’s

approval of the Five Percent Plan constituted an abuse of
24 BAHR V. U.S. EPA

discretion because the EPA did not require Arizona to

demonstrate that the plan included best available control

measures (BACM) or most stringent measures (MSM) for the

control of PM-10. According to petitioners, the Five Percent

Plan must demonstrate that Arizona’s control measures meet

the BACM and MSM standards because Arizona has a

continuing obligation to comply with § 7513a(b)(1)(B) and

§ 7513(e), which set the control requirements for serious

nonattainment areas. Petitioners argue that had a BACM

demonstration been required, the Five Percent Plan would

have failed because the agricultural control measures in

Arizona’s 2000 SIP are no longer BACM, as stated in EPA’s

2010 Proposed Rule. Further, petitioners argue, the EPA’s

statement in the 2010 Proposed Rule regarding Arizona’s

failure to meet the BACM standard is evidence that the EPA

generally requires an updated BACM demonstration in each

SIP, meaning that the EPA acted inconsistently by not

requiring such a demonstration in the Five Percent Plan.

We disagree with these arguments. The EPA’s decision

not to require an updated demonstration of BACM and MSM

in the Five Percent Plan was not an abuse of discretion

because it was not contrary to any language in the CAA. 

Section 7513a(d), which governs five percent plans such as

the one before us here, provides only that if a state fails to

achieve attainment after receiving the five-year extension, it

must submit plan revisions providing for “attainment of the

PM-10 air quality standard,” and an annual five percent

reduction in PM-10 within the Serious Area. It does not

mention BACM or MSM. The CAA sections that do require

BACM and MSM demonstrations do not expressly apply to

a five percent plan. Section § 7513a(b) provides that when

the EPA reclassifies a Moderate Area as a Serious Area, the

state must then submit a SIP that “assure[s] that the best
BAHR V. U.S. EPA 25

available control measures for the control of PM-10 shall be

implemented.” It does not require the state to update that

assurance when submitting a five percent plan, nor does it

require the EPA to review its previous BACM determination. 

Similarly, § 7513(e) provides that when the EPA grants a

state a five-year extension of the deadline to meet the

NAAQS for PM-10, the state must submit a SIP that

“includes the most stringent measures” that are included in

any SIP or achieved in any state. Again, this language does

not require the state to include an updated demonstration of

MSM when submitting a five percent plan.

We also disagree with petitioners’ argument that the EPA

acted inconsistently in failing to require an updated

demonstration of BACM and MSM in the Five Percent Plan. 

Even though the EPA had previously reviewed and proposed

to disapprove the agricultural control measure in Arizona’s

2007 SIP as not meeting the BACM standard, the EPA

provided a reasonable interpretation of its approach in the

2014 Final Rule. According to the EPA, the CAA lays out a

series of escalating control measures that are triggered by a

finding of noncompliance with a series of statutory

requirements. The EPA will assess compliance with the

control measures that were triggered at each step, but will not

reassess compliance with those measures at subsequent steps

unless a state proposes changes to control measures that were

previously approved. 79 Fed. Reg. at 33108–09. This

approach is consistent with the CAA, which does not require

the EPA to reassess a state’s controls in each SIP submission. 

Here, the EPA’s 2010 Proposed Rule reassessed Arizona’s

agricultural control measures under the BACM standard

because Arizona proposed to revise agricultural control

measures that were previously approved as BACM in the

2002 Final Rule. Arizona did not propose any revisions to its
26 BAHR V. U.S. EPA

agricultural controls in the Five Percent Plan, however, so

EPA did not have any occasion to reevaluate those measures. 

Given the EPA’s reasonable explanation for its approach, and

the lack of any contrary statutory command in the CAA, we

conclude that the EPA did not abuse its discretion or act

contrary to law by declining to require an updated

demonstration of BACM or MSM in the Five Percent Plan.

Petitioners also argue that the EPA acted in an arbitrary

and capricious manner in reviewing the Five Percent Plan

because it evaluated Arizona’s compliance with CAA

requirements regarding emission inventories, reasonable

further progress, and contingency measures, but ignored

BACM and MSM. We also reject this argument. The EPA

reasonably explained that those particular CAA requirements

are procedural or otherwise applicable to all SIP submissions,

see 42 U.S.C. §§ 7410(a), 7502(c), 7506(c), 7513a(c)(1), and

the EPA reviews such measures whenever it reviews a

proposed SIP. By contrast, the BACM and MSM

requirements are not applicable to all SIP submissions, and so

the EPA reviews them only when the state is required to

demonstrate compliance with these requirements.

B

We next turn to the petitioners’ argument that the EPA

acted contrary to law by excluding 135 exceedances in the

Maricopa Area from Arizona’s air quality monitoring data.

Petitioners raise several arguments as to why the EPA

erred in concluding that the dust sources causing the 135

exceedances were from anthropogenic sources that were

“reasonably well-controlled,” and therefore were excludable

as exceptional events. See 40 C.F.R. § 50.14(b)(1). The
BAHR V. U.S. EPA 27

petitioners begin by pointing to the statement in the Interim

Guidance that “[g]enerally, the EPA will consider windblown

dust BACM to constitute reasonable controls if these

measures have been reviewed and approved in the context of

a SIP revision for the emission source area within the past

three years.” Interim Guidance at 15. The EPA’s decision

was inconsistent with this guidance, petitioners argue, for two

reasons. First, Arizona’s dust control measures for the

Maricopa Area had not been approved since 2002, well over

three years before the 2014 Final Rule. Second, agricultural

emissions are among the sources of windblown dust in the

Maricopa Area, and the EPA’s 2010 Proposed Rule had

proposed to disapprove of Arizona’s agricultural control

measures because they were not BACM. Moreover,

petitioners argue, the EPA failed to offer a reasonable

explanation for its departure from its guidance.

We disagree; the EPA’s 2014 Final Rule did not conflict

with the Interim Guidance. First, nothing in the Interim

Guidance indicates that EPA must find that control measures

for windblown dust have been reviewed and approved as

BACM within the past three years in order for the dust to be

deemed reasonably well-controlled. Rather, the Interim

Guidance gives the EPA flexibility to consider a wide range

of issues, and emphasizes that a prior BACM determination

“may be a reference point, but not the sole means, by which

the EPA assess the reasonableness of controls.” Interim

Guidance at 15. The EPA’s interpretation is therefore

consistent with the Interim Guidance and is a reasonable

interpretation of the Exceptional Events Rule, to which we

owe deference. Auer, 519 U.S. at 461.

Second, the EPA provided a reasonable explanation as to

why the Maricopa Area had reasonable controls for
28 BAHR V. U.S. EPA

windblown dust even though the 2010 Proposed Rule had

proposed to disapprove of Arizona’s agricultural control

measures. The EPA’s 2002 Final Rule determined that the

2000 SIP contained the best available control measures for

the highest emitters of PM-10 (including unpaved roads and

alleys, construction, paved road dust, and non-agricultural

windblown dust). 79 Fed. Reg. at 33111–13. The 2014 Final

Rule then explained that it was still appropriate to rely on that

determination because neither the highest emitters of PM-10

nor the techniques for controlling fugitive dust had changed

significantly since 2002. Id. at 33112. Moreover, Arizona

made its dust control rules even more stringent in the years

following its 2000 SIP, further bolstering the conclusion that

the controls remained reasonable. Id. Although the EPA had

proposed to disapprove of the agricultural controls as not

meeting the BACM standard in 2010, data showed that

agricultural sources were only a minimal contributor to the

Maricopa Area’s overall level of PM-10 emissions. Id. 

Accordingly, the EPA’s judgment was that the control

measures in the 2000 SIP ensured that anthropogenic

windblown dust was reasonablycontrolled for purposes of the

Exceptional Events Rule.

“[W]e generally must be at [our] most deferential when

reviewing scientific judgments and technical analyses within

the agency’s expertise.” Lands Council v. McNair, 629 F.3d

1070, 1074 (9th Cir. 2010) (second alteration in original)

(internal quotation marks omitted). Here, the EPA considered

the relevant factors and articulated a rational connection

between the facts found and the choice made. As a general

rule, a determination that particular control measures are

reasonable relies on technical considerations that are
BAHR V. U.S. EPA 29

“properly left to the informed discretion of” the EPA. 

Kleppe, 427 U.S. at 412. We defer to its conclusion here.10

C

Petitioners also claim that the EPA’s approval of

Arizona’s 135 exceedances as exceptional events violated the

Interim Guidance because the EPA failed to adequately

address the controls in upwind areas outside the Maricopa

Area. To qualify as an exceptional event under the

Exceptional Events Rule, an exceedance must be “caused by

human activity that is unlikely to recur at a particular location

or a natural event.” 40 C.F.R. §§ 50.1(j), 50.14. The

Treatment of Data Guidance states that high wind events will

be considered “natural” when “(1) the dust originated from

nonanthropogenic sources, or (2) the dust originated from

anthropogenic sources within the State, that are determined

to have been reasonably well-controlled at the time that the

event occurred, or from anthropogenic sources outside the

State.” 72 Fed. Reg. at 13576. To assist the EPA in

determining compliance with this requirement, the Interim

Guidance requires a state to provide “a brief description” of

“all contributing emission sources in upwind areas and

provide evidence that those sources were reasonably

controlled, whether anthropogenic or natural.” Interim

Guidance at 42.

Petitioners argue that Arizona’s submissions were

inadequate because Arizona did not identify all contributing

emission sources outside the Maricopa Area, failed to

10 Because we conclude that the EPA did not depart from its Interim

Guidance, we do not reach the petitioners’ argument that the EPA failed

to provide a reasoned explanation for departing from its guidance.
30 BAHR V. U.S. EPA

distinguish between natural and anthropogenic sources, and

failed to submit evidence that Pinal County had reasonable

controls in place.

We again disagree. Under the Treatment of Data

Guidance, a high wind event may meet the criteria of the

Exceptional Events Rule when the dust originated from

nonanthropogenic sources, or from anthropogenic sources

that are reasonably well-controlled at the time that the event

occurred. 72 Fed. Reg. at 13576–77. Arizona explained that

the high wind events causing the 135 exceedances stemmed

from monsoonal dust storms. Because “outflow from

thunderstorms can carry dust over vast distances

encompassing many source areas,” Arizona could not clearly

distinguish between nonanthropogenic and anthropogenic

sources of dust. Nevertheless, Arizona adequately provided

a “brief description” of contributing dust sources outside the

Maricopa Area and demonstrated that reasonable controls

were in place for any anthropogenic sources of dust. For

instance, in describing exceedances that occurred during the

August 11, 2012, event, Arizona provided a “conceptual

model” identifying a nonanthropogenic source, the

“undeveloped lands south of Maricopa County,” as being the

primarycontributing source areas in Pima and Pinal Counties. 

Arizona also provided evidence that any anthropogenic

sources of dust in those areas were reasonably controlled,

pointing to two Pinal County rules applicable to fugitive dust

and construction sites. Arizona compiled similar submissions

for each of its exceptional event submittals. Arizona’s

submissions provided enough detail for the EPA to

reasonably conclude that the dust originated either from

“nonanthropogenic sources” or “anthropogenic sources” that

were “reasonably well-controlled.” Interim Guidance at 42.

Accordingly, the EPA’s conclusion thatArizona’s description
BAHR V. U.S. EPA 31

of the upwind sources was adequate was not an abuse of

discretion.

Petitioners also argue that the EPA ignored the Interim

Guidance and thus abused its discretion in concluding that the

anthropogenic dust sources in the areas of Pinal County

outside of the Maricopa Area were reasonably controlled. 

The Interim Guidance states that “[f]or the anthropogenic

sources to be considered to be reasonably controlled, the EPA

anticipates that it is reasonable for an air agency to have the

controls required for an area’s attainment status.” Interim

Guidance at 15. “[T]he EPA does not expect areas classified

as attainment, unclassifiable, or maintenance for a NAAQS

to have the same level of controls as areas that are

nonattainment for the same NAAQS.” Id. In other words, an

area that is in attainment should have the control measures

appropriate for an attainment area, while an area that has been

designated a serious nonattainment area should have the

control measures appropriate for that level of classification. 

Id. Where “an area has been recently designated to

nonattainment but has not yet been required to implement

controls, the EPA will expect the level of controls that is

appropriate for the planning stage.” Id.

Under the Interim Guidance, the EPA did not abuse its

discretion in concluding that the anthropogenic dust sources

in the areas of Pinal County outside of the Maricopa Area

were reasonably well-controlled. The EPA provided a

reasoned explanation as to why it deemed the Pinal County

area to have the controls required for that area’s attainment

status. The 135 exceedances approved by the EPA all

occurred between 2010 and 2012. 79 Fed. Reg. at 33111. 

From January2011 to June 2012, Pinal County (excluding the

portion within the Maricopa Area) was an attainment area,
32 BAHR V. U.S. EPA

and had adopted two rules addressing fugitive dust emissions

that were appropriate for this status. Although Pinal County

was redesignated a nonattainment area in July 2012, it was

not required to submit a SIP until 18 months after

redesignation, leaving it in the planning stage for the

remainder of 2012. See Designation of Areas for Air Quality

Planning Purposes; State of Arizona; Pinal County; PM10,

77 Fed. Reg. 32024, 32030 (May 31, 2012). Because Pinal

County had not yet been required to implement controls, the

EPA reasonably concluded that Pinal County’s fugitive dust

rules were appropriate for the planning stage.

V

Finally, we turn to petitioners’ argument that the EPA

erred in approving the contingency measures in the Five

Percent Plan because those measures had already been

implemented. As noted above, four of five contingency

measures in the Five Percent Plan were permanent changes to

infrastructure that had been completed by 2012 (paving and

stabilizing existing public dirt roads and alleys, paving and

stabilizing unpaved shoulders, repaving or overlaying paved

roads with rubberized asphalt, and lowering speed limits on

dirt roads and alleys). The fifth contingency measure

involved the purchase of PM-10 certified sweepers and

sweeping of freeways, though the purchase occurred in 2009

and Arizona had procured contracts for sweeping services by

2010. The CAA provides that a nonattainment SIP:

[S]hall provide for the implementation of

specific measures to be undertaken if the area

fails to make reasonable further progress, or

to attain the national primary ambient air

quality standard by the attainment date
BAHR V. U.S. EPA 33

applicable under this part. Such measures

shall be included in the plan revision as

contingency measures to take effect in any

such case without further action by the State

or the Administrator.

42 U.S.C. § 7502(c)(9). In its 2014 Final Rule, the EPA

explained its interpretation of this requirement. While

“[c]ontingency measures must provide for additional

emission reductions that are not relied on for RFP [reasonable

further progress] or attainment and that are not included in

the attainment demonstration,” the EPA concluded that

“[n]othing in the statute precludes a state from implementing

such measures before they are triggered.” 79 Fed. Reg. at

33114.

Although we defer to the EPA’s interpretation of the

CAA contained in a final rule approving a SIP if that

interpretation involves the reasonable interpretation of

ambiguous statutory terms, see supra at 22, we cannot defer

to the EPA’s interpretation of § 7502(c)(9) here. Where

Congress has “directly spoken to the precise question at issue

. . . that is the end of the matter; for the court, as well as the

agency, must give effect to the unambiguously expressed

intent of Congress.” Chevron, 467 U.S. at 842–43. The

statutory language in § 7502(c)(9) is clear: it requires the SIP

to provide for the implementation of measures “to be

undertaken” in the future, triggered by the state’s failure “to

make reasonable further progress” or to attain the NAAQS. 

These measures are included in the SIP as “contingency

measures” and are “to take effect” automatically in the future. 

Although the statute does not define the word “contingency,”

the meaning of the term is not ambiguous. According to the

dictionary definition, it means “a possible future event or
34 BAHR V. U.S. EPA

condition or an unforeseen occurrence that may necessitate

special measures.” Webster’s Third New International

Dictionary (2002). Because Congress was clear that

“contingency measures” are control measures that will be

implemented in the future, and the statutory language is not

susceptible to multiple interpretations, we must give effect to

its plain meaning. Chevron, 467 U.S. at 842–43.

In arguing that its interpretation of § 7502(c) is entitled to

deference despite the clear language of the statute, the EPA

relies on the Fifth Circuit’s decision in Louisiana Envtl.

Action Network v. EPA, 382 F.3d 575, 580 (5th Cir. 2004). 

In Louisiana Envtl. Action Network, the petitioners

challenged the EPA’s 2002 approval of Louisiana’s SIP

because the contingency measure in the SIP (a compressor

station’s permanent reduction of its emissions) had been

implemented in 1998, and therefore was not a measure “to be

undertaken” or “to take effect” in the future, as § 7502(c)(9)

requires. Id. at 582. The Fifth Circuit first acknowledged

that “a plain reading of the terms ‘to take effect’ and ‘to be

undertaken’ imply a prospective, forward looking

orientation” that would “preclude the use of past reductions

which have already failed to achieve attainment.” Id. at 583. 

Nevertheless, the Fifth Circuit held that § 7502(c)(9) was

ambiguous because it “neither affirms nor prohibits

continuing emissions reductions—measures which originate

prior to the SIP failing, but whose effects continue to

manifest an effect after the plan fails—from being utilized as

a contingency measure.” Id. (emphasis omitted). Having

found this “ambiguity,” it deferred to the EPA’s interpretation

that “contingencymeasures” could include measures that had

already been implemented by the state.
BAHR V. U.S. EPA 35

We cannot agree with the Fifth Circuit’s interpretative

approach. Having determined that the “plain reading of the

terms” indicates a forward looking approach, the Fifth Circuit

was bound by Chevron to give effect to the plain meaning of

the statute. We disagree that the lack of any discussion in

§ 7502(c)(9) regarding treatment of continuing emissions

reductions makes the statute ambiguous. Rather, unless such

continuing emissions reductions are “to be undertaken” in the

event of a contingency, they do not fit the definition of 

“contingency measures” provided in § 7502(c)(9). We also

disagree with the dissent’s contention that previously

implemented control measures that provide continuing

emissions reductions “take effect” and are “undertaken” both

“at the time they are first implemented but also thereafter.” 

Dissent at 38. This is a misreading of the statute, which

defines contingencymeasures as measures “to be undertaken”

or “to take effect” if a future event occurs, namely “if the area

fails to make reasonable further progress, or to attain the

[NAAQS].” 42 U.S.C. § 7502(c)(9) (emphases added). 

Control measures that have already been implemented are not

measures “to be undertaken” or “to take effect” in the future,

and the statute cannot reasonably be so interpreted.

The EPA argues that its interpretation is consistent with

the CAA’s policy goals, because permitting early

implementation of contingency measures is consistent with

the overall policy of the CAA to reduce particulate emissions

and protect public health. La. Envtl. Action Network,

382 F.3d at 583. The Fifth Circuit likewise relied on these

policy considerations, stating that allowing states to

implement measures before the contingency occurs was

consistent with the CAA’s purpose of creating incentives for

states to reach NAAQS compliance earlier and more

efficiently. Id. at 583–84. The dissent agrees, adopting the
36 BAHR V. U.S. EPA

Fifth Circuit’s policy analysis.11 Dissent at 39–40. Even if

we agreed that the EPA’s policy considerations are

compelling, such considerations cannot override the plain

language of the statute. We therefore cannot give them

controlling weight here.

Because the “contingency measures” in Arizona’s SIP

were not “specific measures to be undertaken if the area fails

to make reasonable further progress, or to attain the national

primary ambient air quality standard by the attainment date

applicable under this part,” the EPA’s approval of this part of

the Five Percent Plan was contrary to the CAA. Accordingly,

we remand to the EPA for further consideration of this

portion of the SIP but otherwise deny the petition.12

PETITION GRANTED IN PART AND DENIED IN

PART.

11 In addition to relying on the Fifth Circuit’s policy arguments, the

dissent argues that precluding the use of previously implemented controls

as contingency measures “imposes an additional and unnecessary burden

upon states where the failure to attain the NAAQS also triggers a bump up

of an area’s classification under the Act” because states will not be able

to “focustheir efforts on implementing the newly imposed requirements.”

Dissent at 40. This is incorrect: because contingency measures

automatically take effect when the contingency occurs, “without further

action by the State,” 42 U.S.C. § 7502(c)(9), the implementation of

contingency measures cannot distract a state from meeting the other CAA

requirements.

12 Each party is to bear its own costs on appeal.
BAHR V. U.S. EPA 37

CLIFTON, Circuit Judge, concurring in part and dissenting

in part:

I fully concur in sections I–IV of the majority opinion. I

disagree, however, with the majority’s conclusion in section

V that EPA’s approval of the contingency measures in

Arizona’s SIP is contrary to the clear language of the CAA.

In my view, the scope of the CAA’s contingency measures

requirement is ambiguous and EPA’s reasonable

interpretation of that requirement is entitled to deference.

Like the majority, I begin by analyzing the text of the

relevant statutory provision, 42 U.S.C. § 7502(c)(9). That

section of the CAA requires state nonattainment plans to

include contingency measures “to be undertaken” and “to

take effect” in the event that an area “fails to make reasonable

further progress, or to attain” the NAAQS by the applicable

attainment date. Id. Although I agree with the majority that

this language most often refers to measures that are to be

implemented in the future, in the event that the other

measures included in a state’s SIP are not sufficient to meet

CAA requirements, I am not persuaded that the provision’s

text forecloses the interpretation advanced by EPA and

applied in this case.

The language of the statute prohibits states from labeling

as “contingency measures” the same proposed reductions

relied upon to achieve NAAQS compliance. See La. Envtl.

Action Network v. EPA, 382 F.3d 575, 583 (5th Cir. 2004)

(“Such a prospective reading of the text would seemingly

preclude the use of past reductions which have already failed

to achieve attainment.”). It requires states to identify

additional measures that must be put into effect without

further action by the state or EPA if reasonable progress is
38 BAHR V. U.S. EPA

not made or the air quality standard is not met by the

attainment date. Those additional measures are what the

statute describes as “contingency measures.”

Arizona’s SIP identified additional measures that were

not relied upon to obtain the anticipated compliance. The

practical issue before us in this case is whether Arizona was

prohibited from putting those additional measures into effect

in advance. The majority opinion concludes that it was, that

the state’s contingency measures must be left undone, sitting

on the sidelines in reserve. I do not believe that the language

or intent of the statute requires that conclusion.

The earlyimplementation of infrastructure improvements

that are expected to result in additional and continuing

emissions reductions is consistent with the language of

§ 7502(c)(9). These early-implemented contingencymeasures

result in a net reduction in emissions following their

implementation. They “take effect” and are “undertaken” not

only at the time they are first implemented but also thereafter,

including at the time they might formally be required due to

nonattainment. So long as these reductions are not relied upon

to meet other CAA requirements, they function as a backup

plan, reducing the likelihood that the state will fail to attain

the NAAQS even in the “contingency” that the measures

explicitly included in the SIP for that purpose are not enough.

The majority responds by asserting that the statute

“defines contingency measures as measures ‘to be

undertaken’ or ‘to take effect’ if a future event occurs,

namely ‘if the area fails to make reasonable further progress,

or to attain the [NAAQS].’” Majority opinion at 35 (emphasis

in original). But this language fits just as well with EPA’s

interpretation as it does with the view of the majority. In both
BAHR V. U.S. EPA 39

scenarios, the contingency measures must be in effect at the

time an area fails to achieve the goals outlined in the SIP.

What is at issue here is whether states are prohibited from

also implementing the measures before that “future event

occurs.” The language quoted by the majority contains no

such prohibition and it is not our role to read one into the

statute.

EPA’s interpretation also comports well with the purpose

of the CAA. “In determining whether Congress has

specifically addressed the question at issue, a reviewing court

should not confine itself to examining a particular statutory

provision in isolation. . . . It is a ‘fundamental canon of

statutory construction that the words of a statute must be read

in their context and with a view to their place in the overall

statutory scheme.’” FDA v. Brown & Williamson Tobacco

Corp., 529 U.S. 120, 132–33 (2000) (quoting Davis v. Mich.

Dept. of Treasury, 489 U.S. 803, 809 (1989)).

Allowing states to implement contingency measures

before they are triggered makes sense in light of that same

provision’s requirement that such measures “take effect . . .

without further action bythe State or the Administrator.” That

requirement, read in context with the Act’s mandate that

states implement emission-controlmeasures “as expeditiously

as practicable,” id. § 7502(c)(1), evinces a clear congressional

preference that contingency measures operate to reduce the

emission of harmful pollutants in as efficient and timely a

manner as possible. Taking this statutory purpose into

account, “it seems illogical to penalize nonattainment areas

that are taking extra steps, such as implementing contingency

measures prior to a deadline” as a cushion to ensure NAAQS

compliance and prevent the need for the contingency

measures requirement to be triggered in the first place. La.
40 BAHR V. U.S. EPA

Envtl. Action Network, 382 F.3d at 584. It does not benefit

ordinary citizens to read the CAA to incentivize states to hold

off from purchasing new street sweepers or repaving their

roads until the contingency measures requirement is

triggered.

The majority’s interpretation also imposes an additional

and unnecessary burden upon states in circumstances where

the failure to attain the NAAQS also triggers a bump up of an

area’s classification under the Act. For example, the failure

of a moderate nonattainment area to achieve NAAQS

compliance by the applicable deadline triggers both

§ 7502(c)(9)’s contingency measures requirement and the

additional requirements imposed upon serious nonattainment

areas. 42 U.S.C. § 7513(b)(2). The early implementation of

contingency measures allows states in this situation to focus

their efforts on implementing the newly imposed

requirements while the contingency measures continue to

operate in the interim. See La. Envtl. Action Network,

382 F.3d at 583.1

1 The majority argues that because contingency measures must take

effect “without further action by the State” or EPA, 42 U.S.C.

§ 7502(c)(9), they “cannot distract a state from meeting the other CAA

requirements.” Majority opinion at 36 n. 11. However, EPA has

interpreted this language to require only “that no further rulemaking

activities by the State or EPA would be needed to implement the

contingency measures.” Greenbaum v. EPA, 370 F.3d 527, 541 (6th Cir.

2004) (quoting State Implementation Plans; General Preamble for the

Implementation of Title I of the Clean Air Act Amendments of 1990,

57 Fed. Reg. 13498, 13512 (Apr. 16, 1992)). Thus, under the majority’s

interpretation, states would still be required to perform the actual business

of implementing the identified contingency measures at the same time

they address other requirements imposed by a failure to attain the

NAAQS.
BAHR V. U.S. EPA 41

Irecognize that what is lost byEPA’s interpretation of the

statute is the advance identification of “still more” measures

aimed at improving air quality that can be newly and

additionally implemented in the event of nonattainment. If

Arizona’s SIP does not reach its goal, then reliance upon

contingency measures that have already been put into effect

will not further reduce airborne particulate matter, and more

will have to be done at that point. But EPA applied its

expertise and exercised its judgment in concluding that the

goal was likely to be reached by the measures proposed in the

SIP, without regard to the additional contingency measures.

By letting Arizona identify actions that have already been

implemented as contingency measures, EPA has obtained a

cushion. It is not an unreasonable judgment for EPA to

conclude that implementing the cushion right away is more

valuable than advance identification of what else might be

done, if necessary.

For these reasons, I would give Chevron deference to the

EPA’s interpretation of § 7502(c)(9). I respectfully dissent

from the majority’s conclusion to the contrary.