F OR P UBLICATION



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

S A N D R A L

. B A H R ; D A

V I D M A T U S O W , Petitioners
,

v

.

U.S. E N V I R O N M E N T A L P R

O T E C T I O N A G E N C Y ; G I N A M C C A R

T H Y , Administrator, United States Environmental Protection Ag ency ; J A R E D B L U M E N F E L D , Reg ional Administrator, EPA Reg ion I X,

Respondents
,

S T A T E O F A R

I Z O N A , Respondent-Intervenor

. N o. 14-72327

OPI NI ON

O n Petition for Review of an Order of the Environmental Protection Ag ency

Arg ued and Submitted J une 17, 2016 San F rancisco, California

F iled September 12, 2016B A H R V

. U.S. EPA 2

B efore: Richard R. Clifton and Sandra S. I kuta, Circuit J udg es, and W illiam Q. Hay es, * District J udg e.

Opinion by

J udg e I k uta; Partial Concurrence and Partial Dissent by J udg e Clifton

SUMMARY * *

Environm ental Law

The panel g ranted in part and denied in part a p etition for review of an order of the United States Environmental Protection Ag ency approving Ariz ona’s F ive Percent Plan for airborne particulate matter a round Maricopa County
, promulg a ted under the Clean Air Act.

Ariz ona submitted a new State I mplementation Plan revision on May 25, 2 012

– the F ive Percent Plan – to achieve a five percent annual reduction in PM-10, a harmful air pollutant.

Petitioners alleg ed that the EPA acted contrary to law b y failing to require that Ariz ona include an updated analy sis o f best available control measures a n d most string ent measures in the F ive Percent Plan, e x cluding 135 ex ceedances from the monitoring data as “ex ceptional events,” and allowing

* T h e H o n orab le W illiam Q. H ay es, Un ited States District J u dg e f or th e So u t h ern District o f

Calif o rn ia, sittin g b y

d esig n atio n

.

** T h is su m m ary co n stitu

t es n o p art o f th e o p in io n o f th e co u rt. It h as b een p rep ared b y

co u rt staf

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

th e read er.B A H R V

. U.S. EPA 3

Ariz ona to satisfy t h e “conting ency measures” r equirement with previously

implemented control measures.

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

. Natural Resources Defense Council, I nc. , 467 U.S. 837 (1984), deference to the EPA’s interpretation of the Clean Air Act issued in connection w i t h a State I mplementation Plan approval.

The p anel u

pheld the EPA’s de t e r

m i nation that the control

measures in Ariz ona’s F ive Percent Plan did not n ee d to be

u p d ated, and that the 1 35 ex ceedances were ex ception al
event s that were ex cluded from consideration under the EPA’s reg ulation and g uidance documents.

The panel d id not defer to the EPA’s interpretation of the conting ency

measures requirement, however, because under the plain lang uag e of 4 2 U .S.C. § 75 0 2 (c)(9) conting ency

measures are measures that will b e taken in the future, not

measures that have already been implemented. T h e p a n el remanded to the E PA for further consideration of this portion of the State I mplementation Plan, bu t otherwise d e nied the petition.

J u d g e Clifton concurred in sections I -I V of the majority opin i o n, a

nd dissented from the majority ’s conclusion in section V that EPA’s approval of the conting en cy measures in Ariz ona’s State I mplementat i o n Plan was contrary to the clear lang uag e of the Clean Air Act. I n h is view, the scope o f the Clean A ir Ac t’s c o n ting ency measures requirement was ambig uous and EPA’s reasonable interpretation of that requirement was entitled to deference.B A H R V

. U.S. EPA 4

COUNSEL

J oy E

. H err-Cardill o (arg ued) and Timothy M. Hog an, Ariz ona Center for L aw in the Public I nterest, Tucson, Ariz ona, for Petitioners.

Ala n D

. Greenberg (arg

ued), Attorney ; Sam Hirsch, A cting Assistant Attorney General; Environment & Natural Resources Di v ision, United States Department of J ustice, Denver, Colorado ; G e offrey W ilcox
, Office of General Counsel; Kara Christenson, Office of Reg ional C o unsel, Reg ion 9; United S tates Environmental Protection Ag ency , San F rancisco, California; for Respondents.

Monique Coady
, Assistant Attorney General, Office of the Attorney General, Phoenix
, Ariz ona, for RespondentI ntervenor.

OP INION

I KUTA, Circuit J udg e:

Sandra B ahr and David Matusow petition for review of a final r u l e issued by the Environmental Protection Ag ency (EPA) approving Ariz ona’s F ive Percent Plan for a irborne particulate matter around Maricopa County

. They arg ue that the EPA e rred in approving this plan be c a u s e i t did not include best available control measures (B AC M) and most st r i n g e n t control measures (MSM) as of 2012. The petitioners also arg ue that the EPA failed to follow i t s o wn published g uidance in approvi n g Ariz ona’s claim that 135

ex c e edances of the air emission s t a n d a r d could b e ex cluded from consideration. See 42 U.S.C. § 7619(b)(1)(A). F inally
,B A H R V

. U.S. EPA 5

the petitioners arg ue t h a t the EPA’s approval of the conting ency measures included in Ariz ona’s F ive Percent Plan was contrary t o 4 2 U .S.C. § 7502(c)(9) because the

measures had already been implemented. W e uphold the EPA’s determination that the control measures in Ariz o n a ’s F ive Percent Plan did not need to be updated, and that the 135

ex c e edances w ere ex ceptional events that are ex cluded from consider at ion under the EPA’s reg ulation and g uidance documents. W e do n ot defer to the EPA’s interpre t a t i o n o f the conting ency measures requirement, h o wever, because under the plain lang uag e of § 7 502(c)(9) conting ency

measures are measures that will b e taken in the future, not measures that have already been implemented.

I

W e beg in by briefly describing t h e statutory framework. The Clean Air Act (CAA )
, 4 2 U

. S.C. § 7401 et seq., establishes “cooperative F ederal, State, reg ion a l
, and local
prog r ams to prevent and control air pollution,” id

. § 7401(a)(4). Under the CAA, the E P A is required to “publish

. . . a list w hich inclu d e s e ach air pollutant

. . . emissions o f which, in [ the EPA’s] ju d g ment, cause o r contribute to air p ollution which may r easonably be anticipated to en d a n g er p ublic health or welfare.” Id

. § 7408(a)(1). The EPA is then required to “p r e s c rib[ e] a national primary ambient air quality standard” (NAAQS) for that pollutant. Id . § 7409(a).

One such harmful air pollutant is “PM-10,” d efi n e d a s “particulate matter with an aerody namic diameter less than o rB A H R V

. U.S. EPA 6

equal to a nominal ten micrometers.” Id

. § 7602(t). According to the EPA, “PM-10 cau s es adverse health effects by penetr a ting deep into the lung s, ag g ravating the cardiopulmonary sy s t e m.” Approval and Promulg ation of I mplement a t i o n P l a n s

— M ar i copa County PM-10 Nonattainment Area, 79 F ed. Reg

. 7118, 7118 (F eb. 6, 2014). The E PA establi s h e d a N AAQS for PM-10 of 150 microg rams p e r cubic meter, averag ed over a 24-hour period. 40 C.F

. R. § 50.6(a). This standard, which is sometimes referred to as the “24-hour P M

- 10 standard,” is “attained when the ex p ected number of da y s p e r calendar y ear with a 24-hour averag e concentration a bove 150 ì g /m3 . . . is equal to or less than one.” Id

.

The CAA provides that “[ e] a ch S tate shall h ave the primary responsibility for assuring air quality ” w i thin the
state “by submitting an implementation plan” ex plaining h ow t h e state will meet and maintain the NAAQS and other

s t a n dards. 42 U.S.C. § 7407(a). An area within a sta t e t h at does not meet a NAAQS is desig nated as a “nonattainment”
area, id

. § 7407(d). E ach state’s implementation plan ( called

a State I mplementation Plan or SI P) must provide f o r t h e “implementation, maintenance, and enf o r cement” o f the N A A Q S

. Id

. § 7410(a)(1). T h e CAA requires each SI P f o r

a nonattainment area to c ontain specified information, including a r equirement for reasonable further p rog ress, id. § 7502(c)(2), an emissions inventory
, id. § 7502(c)(3), and a li st of “conting ency measures” to “be undertaken if the area fails to mak e reasonable further prog ress, or to attain theB A H R V

. U.S. EPA 7

national primary ambi e nt 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 f

or PM-10, with increasing ly string ent requirements if a state misses a deadline. Id

. § § 7513–7513b. The sequence is as follows:

A nonattainment a

rea is initia lly desig nated as a “moderate” area. Id

. § 7513(a). A SI P for a “moderate” PM10 nonattainment area must ex plain how that a re a will meet the PM-10 NAAQS by the “attainment date,” w hich for nonattainment areas desig nated by Cong ress was no later than December 31, 1994. Id

. § 7 513(c)(1). The SI P must “assure that reasonably

available c ontrol measures for the control of PM-10” are implemented. I d . § 7513a(a).

I f a moderate nonattainment area fails to meet the PM-10 NAAQS by the attainment d ate, the EPA must reclassify it a s

a “Serious PM-10 nonattainment area.” Id

. § 7 513(b). After redesig nation, the state must submit a SI P that demonstrates how the area will meet the PM-10 NAAQS within 10 y ears o f

1 4 2 U.S.C. § 7 5 0 2 (c)(9 ) states:

(9 ) Co n t in g en cy

m easu res

Su ch p l an sh all p ro v id e f o r th e im

plem en tatio n of
sp ecif ic m easu res t o b e un d ertak en i f t

h e area f ails to

m ak e r e aso n ab le f

u rth er p ro g ress, o r to attain th e

n atio n al p rim ary am

b i en t air q u ality s tan d ard b y th e attain m e n t date ap p licab le u n d er th is p art. Su ch

m easu res sh all b e in clu d ed in th e p lan rev i sio n as

co n t in g en cy m easu res to tak e ef f ect i n a n y su ch case

w ith o u t f u rth er actio n b y t

h e State o r th e A d m in i strato r.B A H R V

. U.S. EPA 8

t h e o r i g inal nonattainment desig n ation, or, for areas orig inally desig nated as nonattainment b y Cong r e s s , no later than December 31, 2001. Id

. § 7513(c)(2). A SI P for a seri o us

no n a t t ainment area must also “assure that the best available control measures [ B ACM] f or the control of PM-10 shall be implemented.” Id . § 7513a(b). 2

I f a state fails to meet the deadline for bring ing a Serious Area into c ompliance, the EPA may g rant the state a s ing le five-y ear ex tension of the de a d line to meet the NAAQS for PM-10, but o nly if the state submits a SI P that “includes the
most string ent 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 4 2 U.S.C. § 7 5 1 3 a(b ) p ro v id es:

(b ) Serio u s A reas

(1 ) P lan p ro v isio n s. In ad d iti o n t o th e pro v isio n s

su bm itted to m eet t h e r e q u irem en ts of p arag rap h [1 ] (a)(1 ) (relatin g to Mo d erate A reas), each State in w h ich all o r p art o f a Serio u s A rea is lo cated sh all su b m i t an im p lem en tatio n p lan f

o r su ch area th at in clu d es each of th e f o llo w in g : . . .

(B ) P ro v isio n s to assu

re t h at th e b est av ailab le co n tro l

m easu res f

o r th e co n tro l o f P M- 1 0 sh a l l b e im p lem en ted n o later th an 4 y ears af ter t h e d ate th e area is classif ied (o r reclassif

ied ) as a Serio u s A rea.

3 4 2 U.S.C. § 7 5 1 3 (e) p ro v i d es in p ertin en t p art:

(e) Ex ten sio n

o f attain m en t d ate f

o r Serio u s A reas

Up o n ap p licatio n b y an y State, th e A d m in istrato r m ayB A H R V

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I f a Serious Area fai l s to achieve compliance by the attainment date after r eceiving the one-time five-y e ar

ex tension under § 7513(e), the CAA r equires the s t at e to “submit within 12 months after the applicable atta i nment date, plan revisions which provide for attainment of the PM10 air q uality standard.” Id . § 7513a(d). 4 The SI P revisions

ex ten d th e attain m e n t d ate f o r a Serio u s A rea b ey o n d th e d ate sp ecif

ied u n d er s u

bsectio n (c) o f th is sectio n , if a t t a in m en t b y th e d ate estab l ish ed u n d er su b sectio n (c) o f th is sectio n w o u ld b e im p racticab le, th e State h as

c om p lied w ith all req u irem en ts an d co m m itm e n t s p ertain in g to th at area in th e im p lem en tatio n p lan , an d
t h e State d em on strates to th e satisf actio n o f th e Ad m in istrato r th at th e p lan f o r th at area in clu d es t h e

m o st strin g en t m easu res t h at are in clu d ed in th e im p lem e n t a t i o n p lan o f an y State o r are ach iev ed in
p ractice in an y

State, an d can f

easib ly b e im

p lem en ted in th e area.

. . . T h e A d m in istrato r m ay n o t ap p ro v e an

ex ten sio n u n til t

h e S tate su

b m i ts an att a i n m en t d em on stratio n f

or th e area. T h e A d m in istrato r m ay g ran t at m ost o n e su ch ex t e n s io n f or an area, o f n o

m o re th an

5 y ears.

4 4 2 U.S.C. § 7 5 1 3 a(d ) states:

(d ) Failu re to attain

In th e case o f a Serio u s P M- 1 0 n o n attain m en t area in

w h ich th e P M-1 0 s tan dard is n o t attain ed b y th e ap plicab le attain m en t d ate, th e State in w h ich su ch area is lo cated sh all, af

ter n otice an d o p p ortu n ity f o r pu b l ic

co m m en t, su b m it w ith in 1 2 m o n t

h s af ter th e ap p licab le
att a i n m en t d ate, p l an rev i sio n s w h ich p ro v id e f

or attain m en t o f th e P M- 1 0 air q u ality stan d ard an d
, f ro m th e d ate o f su ch s u

bm issio n u n til attain m en t , f or an

an n u al r e d u ctio n in P M- 1 0 o r P M- 1 0 p recu rso r

e m issio n s w ith in th e area o f n o t less th an 5 p er c e n t o fB A H R V

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must p rovide for an annual five percent reduction in PM-10

w i t hin the Serious Area from the date the SI P revision w a s submitted to the EPA u n til the state attains the NAAQS in that area. Id

.

States are required to c onduct ambient air quality

mon i t o r ing to determine whether a g eog raphical reg ion o r

area in the state is mee t i n g t h e NAAQS for PM-10. Id

. § 7410(a)(2)(B )(i). State air quality monitoring sy stems must

use the c riteria and methodolog y established by the EPA. Id

. § 7619( a). Cong ress recog niz ed that air quality monitoring data c o u l d be affected by ex ceptional e vents that could not reasonably

be controlled by

the states, and directed the EPA
to promul g a te reg u lations “g o verning the review a nd handling o f air qu al i t y monitoring data influenced b y

ex c e ptional events.” Id. § 7619(b)(2)(A). The statute defines

an “ex ceptional event” as an event that “(i) affects air quality ; (ii) is not r easonably controllable or preventable; (iii) is an

e v e nt caused by human activity that is unlikely to rec u r a t a particular location o r a natural event; and (iv) is de termined by the Administrator throug h the pro ce s s established in the
reg ulations promulg ated under parag r aph (2) t o b e an

ex c e ptional event.” Id. § 7619(b)(1)(A).

P u rsuant to this direction, the E PA promulg ated th e “Ex ceptional E vents Ru l e , ” 40 C.F .R. § 50.14. The rule repeats t h e statute’s definition of “ex ceptional event,” id

.

th e am o u n t o f su ch em issio n s as rep o rted in th e m ost

recen t in v en to ry

p rep ared f

o r su ch area.B A H R V

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§ 50.1(j), 5 and allows a state to “request E PA to ex clude data showing ex ceedances or violations of the national a mbient air quality standard that a

re d irectly d

ue to an ex ceptional event,” id

. § 50.14(a)(1). I n order to o btain EPA approval to ex clude

ex c e ptional event d ata, a state must provide evidence t h at “[ t] he event satisfies the c riteria set forth in 40 C.F .R 50.1(j)” and meets other c riteria. Id

. § 50.14(c)(3)(iv). I f a state makes the required showing
, the “EPA shall e x c lude [ the

ex c e ptional event] data from use in determinations o f

ex c e edances and NAAQS violations.” Id . § 50.14(b)(1).

The EPA has recog niz ed that PM-10 leve l s can be affected by natural events such as dust storms, see id

. § 50.1(j)–(k), an d h a s therefore developed g uidance for apply ing the Ex ceptional Events Ru l e to hig h wind events. See Treatment of D ata I nflu e n c e d by Ex ceptional Events, 72 F ed. Reg

. 13560 (Mar. 22, 2007) ( T r e a t m e nt of Data Guidance). The Treatment o f Data G uidan c e states that increased particulate matter c o ncentrations “ra i sed b y unusually h ig h winds will b e treated as due to uncontrollable natural events where ( 1) the dust origi n a t e d from nonanthropog enic sources, or (2) the dust o r ig inated from

5 4 0 C.F.R. § 5 0.1 (j ) p ro v id es:

(j ) Excep tio n a l even t m ean s an ev en t t h a t af f ects air
q u ality
, i s n o t reaso n ab ly co n tro l lab le o r p rev en tab le, is

an ev en t cau s ed b y h u m an activ ity t h at is u n lik ely to

recu r at a p articu lar l o catio n o r a n atu ral ev en t, an d is d eter m i n ed by th e A dm in i strato r in acco rd an ce w i th 4 0 CFR 5 0

. 1 4 t o b e an ex cep tio n al ev en t. It d o es n o t in clu d e stag n atio n o f air m asses or m eteo ro lo g i cal i n v ersio n s, a m eteo ro lo g ical ev en t in v o lv in g h i gh
tem p era t u r e s o r lack o f precip itatio n , o r air p o llu tio n relatin g to so u

rce n o n co m

p lian ce.B A H R V

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anthropog enic sources within the Stat e , t hat are determined
to have b een r e asonably well-controlled at the time that the
event occurred, or fro m anthropog enic sources outside the State.” Id . at 13576 (emphasis added).

I n May 2 013, the E PA published additional “g uidance and interpretation” ex p lai n i n g how the Ex ceptional Events Rule and the Treatment of Data Guidance ap p lies to hig h wind events. See EPA, I nterim Guidance on the Preparation of Demon s t r a tions in Support of Requests to Ex clude Ambient A ir Q uality Data Affected by H ig h W inds Under the Ex ceptional Events Rule (May 20 1 3 ) ( I nterim Guidance). 6 The I nterim Guidance addresses when an anthropog e n i c

source within the State is “ r e asonably well-controlled at the time that the e vent occurred,” 72 Fe d

. R e g. at 13576, a s required by the Treatment of Data Guidance.

I I

W e now pro v i d e the backg round of this case. Cong ress desig nated Maricopa County
, A riz ona, as a “moderate” PM10 nonattainment area in 1990. 42 U

. S

. C

. § 7407(d)(4)(B ); PM1 0 G r o u p I and Group I I Areas, 52 F ed. Reg

. 29383, 29384 (Aug

. 7, 1987). The desig nated nonat t a i n ment area, termed the “Maricopa County PM-10 N onattainment A rea” (Maricopa Area), cover s the eastern portion of Maricopa County
, including the cities of Phoenix
, Mesa, Scottsdale,

6 T h e In te r im G u id an ce is av ailab le at: h ttp s://w w w .ep a.g o v /

s i t e s / p r o d u c t i o n / f

i l e s / 2 0 1 5

- 0 9 / d o c u m e n t s / e x c e p t e v e n t s

_ h i g h wi n d s

_ g u id e_ 1 3 0 5 1 0 .p d f

; see a lso Draf

t G u id an ce T o Im

p lem en t Req u i rem en ts f o r th e T reatm en t o f Ai r Q u ality Mo n i to rin g Data In f lu en ced b y Ex cep tio n al Ev en ts, 7 7 Fed

. Reg

. 3 9 9 5 9
, 3 9 9 6 0 (J u l y 6
, 20 1 2) (an n o u n cin g th e av ailab i lity of a d raf t v ersio n of th e In terim Gu id an ce on th e EP A ’ s w eb site).B A H R V

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Tempe, Chandler, and Glendale. 79 F ed. Reg

. at 7118. I t also covers unincorporated parts of Maricopa County a nd portions of Pinal County

. Id

.

B e cause the M aricopa Area was desig nated as a nonattainment area by Cong r ess, Ariz ona’s first deadline for meeting the NAAQS for PM-10 was December 31, 1994. 42 U.S.C. § 7513(c). T h e Maricopa Area was n ot in attainmen t by 1994, so the EPA reclassified the Maricopa Area as a Serious PM-10 nonattainment area. 4 2 U .S.C. § 7513(b)(2); Clean Air Act Reclassification; A r i z onaPhoenix Nonattainment Area; PM-10, 6 1 F ed. Reg

. 2137 2
, 21373 (May 10, 1996). T h i s required Ariz ona to submit a SI P that wou l d demonstrate how the Maricopa Area would
meet the NAAQS for PM-10 by D ecember 3 1, 2001, see 42 U.S.C. § 7513(c)(2), a nd to ex pl a i n 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 2 001. Rather, in 2000 Ari z o n a preemptively applied for a five-y e ar ex tension ( until D ecember 2006) under § 7 513(e) and at the s am e time submitted a SI P for the Maricopa A re a ( t h e 2 000 SI P). The 2000 SI P proposed to implement over 70 best available control measures for major dust sources, Approval and Promulg ation of I mplementation Plans; Ar iz ona—Maricopa County PM-10 Nonattainment Area; Serious Area Plan for Attainment of the Annual PM-10 Standard, 65 F ed. Reg

. 1 9964, 1 9972–83 (Apr. 13, 2000), a nd stated that its measures wer e “t he most string ent measures that are included in the implementation plan of any State, or

are achieved in practice in any State,” id

. at 19984. I n 2002, the EPA issued a final rule approving t h e 2000 SI P a nd
g ranting the requested ex tension

. A p p r o v a l a n d P romulg ationB A H R V

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of I mplementation Plans; Ariz ona–Maricopa County PM-10 Nonattainment Area; Serious Area Plan for Attainment o f the PM-10 Standards, 6 7 Fe d. Reg

. 48718, 48718–19 (J uly 25, 2002) (the 2002 F inal Rule). The 2002 F inal Rule stated that the control measures in the 2000 S I P met the B ACM a nd MSM standards. Id

. 7

B y December 2006, the Maricopa Area had still failed to meet the NAAQS f

o r P M

- 1 0

. See F inding s of F a ilure T o Attain; State of Ariz o na, Phoenix Nonattainment Area; State of California, Owens Valley Nonattainment Area; Particulate Matter of 10 Microns or L ess, 72 F ed. Reg

. 31183, 31184–85 (J une 6, 200 7 ). A t that point, the CAA g ave Ariz ona 12 months to submit revisio n s to the SI P that would achieve attainment o f the NAAQS for PM-10, provide for an annual five percent reduction in P M

- 10 in the Maricopa Area, 42 U.S.C. § 7513a(d), and contain ap p ropriate conting ency measures, id . § 7502(c)(9).

Ariz ona submitted revisions to the Maricopa Area SI P in December 2007 (the 2007 SI P). I n addition to proposing 53 control measures, the 2007 SI P proposed revising a previously approved ag ricultural control measure, namely an ag ricultural g eneral permit specify ing best manag ement practices f

or reducing PM-10 from ag ricultural activities. See Approval and Promulg ation of I mplementatio n P lans— Maricopa County (Phoenix ) P M-10 Nonattainment Area;

7 W e co n sid ered a ch allen g e to EP A ’ s 2 0 0 2 Fin al Ru le ap p ro v in g th e 2 0 0 0 SIP an d h eld th at th e EP A ’ s ap p ro v al o f A rizo n a ’s r e j e c tio n o f a

m easu re req u i r i n g th e u se of a ref o rm u lated d iesel f

u el as B A C M w as arb itrary an d cap ricio u s

. Vig il v. L ea vitt
, 3 8 1 F.3 d 8 2 6
, 8 4 1

– 4 6 (9 t h Cir. 2 0 0 4 ). We u

p h eld th e rest o f th e EP A ’ s ap p ro v al, in clu din g its ap p ro v al

o f A rizo n a’ s g en e r al p erm it ru le f or ag ricu ltu

ral em issio n s o f P M- 1 0 as B A CM. Id

. at 8 3 6

– 3 8 , 8 4 7

.B A H R V

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S er i ous Area Plan for A ttainment of the 24-Hour PM- 1 0 Standard; Clean Air A ct Section 189(d), 75 F ed. Reg

. 54806, 54810, 54812–13 ( Sept. 9, 2 0 10) (the 2010 Proposed Rule). The 2 010 Proposed Rule sta t e d that the EPA would disapprove this revision to the ag r icultural g eneral permit rule

on the g round that other states and local ag e ncies h ad “acquired additi o n a l e x pertise about how to control emissions from these sources,” a

n d a s a result the EPA no long er believed that the requirements in the ag ricultura l g eneral permit rule in the 2000 SI P were best available cont r o l

me asures. Id

. To avoid a partial disapproval, A riz o na withdrew the plan in 2011. 79 F ed. Reg

. at 7119. As a result of th i s w i thdrawal of the 2007 SI P, the EPA found that Ariz ona had failed to make a required SI P submittal. F inding of F ail u r e T o Submit State I mplementation Plan Revisions for Particulate Matter, PM-10, Maricopa County ( Phoenix ) PM10 Nonattainment Area, AZ
, 76 F e d. R eg

. 8300, 8300–01 (F eb. 14, 2011). This finding r equir e d A r iz o na to submit another SI P by

2013. I d . at 8301; 42 U.S.C. § 7509(a).

Ariz ona submitted a new SI P revision on May 25, 2012. S e e 79 F ed. Reg

. at 7119. B ecause this SI P was p r ep a r e d pursuant to § 7513a(d), which r e q u ires a state to achieve a five percent annual reduction in PM-10, we adopt the E PA’s
term and r efer to it a s the “F ive P e rcent Plan.” T h e F ive Perc e n t Plan p roposed to achieve the five percent annual reducti o n r e q

uired by § 7513a(d) by implementing many o f the 53 control measures p reviously p r oposed in the 2 007 SI P,

as well as ad o p t ing a new emissions control measure, the “Dust Action General Permit.” Unlike the 2007 SI P, the F ive Percent Plan did not propose any chang es to the ag ricultural
g eneral permit.B A H R V

. U.S. EPA 16

As required by § 7 502(c)(9), the F ive Percent Plan proposed a number of conting ency measures. 79 F ed. Reg

. at 7124. F our of the five measures were permanent chang es to infrastructure that had been completed in the y ear s 2 0 0 8 throug h 2011, namely
, paving ex isting dirt roads and alley s, paving and stabiliz ing u npaved shoulders, r epaving o r overlay ing paved roads with r

ubberiz ed asphalt, and lowering speed limits on dirt roa d s a n d alley s. Id

. The f ifth conting ency measure required the purc hase of PM-10 certified sweepers (which had already been accomplished b y the end of 2 0 09), and ong oing sweeping of ramps, freeway s, and frontag e roads. Id

.

Ariz ona also acknowledg ed that there had been a number of ex ceedances of the 2 4-ho u r P M -10 standard during 2011 and 2012, but claimed they sho u ld be deemed “ex ceptional events” and ex cluded from a deter m i n ation of whether the Maricopa A rea met the NAAQS f or PM-10. I n su p p o r t o f this claim, A riz ona submitted document a t i o n to the E PA to demonstrate that 137 ex ceedances of the NAAQS for PM-10

on 27 day s d

uring the period from 2011 to 2012 were the result of “ex c eptional events,” namely hig h wind dust events. 79 F ed. Reg

. at 7122. 8 The E P A w r o t e separate r eports on each of Ariz ona’s submissions. T he reports analy z ed the data and concluded that the f lag g ed ex ceedances met “th e definition of an ex ceptional event: the ex ceedances affected

a i r quality
, were not reasonably controllable or preventabl e, and meet the definition of a natural event.”

I n F ebruary 2 014, the EPA p ublished its proposed decision reg a

rding Ariz ona’s F ive Percent Plan. 79 F ed. Reg

.

8 T h ou g h th e EP A ’ s p ro p osed ru lem ak in g m en t io n e d 1 3 3

ex ceed an ces, th e p arties ag ree th at A rizo n a req u ested ap p ro v al o f 1 3 7

.B A H R V

. U.S. EPA 17

at 7118. The EPA n oted that the monitori n g d a t a f or the Maricopa Area showed 133 ex ceedances of the 24-hour PM10 NAAQS during the 2 011–2012 time period, but stated that 131 of those e x ceedances “ were caused by hig h wind

ex c e ptional events,” and “should not be used for reg ulatory purposes,” including for evaluation of the F ive Percent Plan. Id

. at 7122. Ex cluding these ex ceedances, the EPA proposed
to d etermine that the Maricopa Area had attained the NAAQS for 24-hour PM-10 by December 31, 2 012. Id

. at 7125. The EP A a l so p roposed to approve Ariz ona’s conting ency

measures. Id

. at 7124. I n d oing so, the EPA ex plained that it h ad previously “interpreted [ 42 U.S.C. § 75 02(c)(9)] to allow states to implement conting ency measures before they

are t r i gge r ed by a failure o f

. . . attainment as long as those

measures are intended to a c hieve e m ission reductions over and bey ond those relied on in the attainment and [ reasonable further progress] demonstrations.” 79 F ed. Reg

. at 7124.

The EPA issued a f

inal rule on J u ne 10, 2014, approving the F ive Percent Plan “as meeting all rele v a nt statutory a nd

r eg ulatory requirements.” Approval and Promulg ation o f I m p l e m e n t a t i o n P l a n s

— M a r i c o p a C o u n t y P M

- 1 0 Nonattainment Area; F ive Percent Plan f or Attainment of the 24-Hour PM-10 Standard, 79 F ed. Reg

. 33107, 33107 (J u ne 10, 2014) (2014 F inal Rule). The 2014 F inal Rule stated that the EPA was ex cluding 135 ex ceedances 9 from the monitoring data a s ex ceptional events. I d

. at 3 3111. F or e ach of the events that EPA d etermine d w a s ex c eptional, “ EPA found that the event was n ot reasonab l y c o n trollable o r preventable,” a

nd that “reasonable controls” were in place for

9 T h e EP A ’ s f

in al ru le clarif

ied t h a t th e n

u m b er o f ap p ro v ed

ex ceed an ces w as 1 3 5
, w h ich o ccu rred on 2 5 d ay s o v e r th e p erio d of 2 0 1 0

– 1 2 . 7 9 Fed . Reg . at 3 3 11 0– 1 1

.B A H R V

. U.S. EPA 18

anthropog enic sources of dust. I d

. The EPA r e ached its conclusion that “reasonable controls” w ere in place by rely ing

on its 2002 F inal Rule approving Ariz ona’s 2000 SI P a s including best available control measures and most string ent control measures. Id

. a t 33112. T h e EPA also determined
t h a t Ariz ona sufficiently demonstrated that d ust sources outside the Maricopa Area were reasonably controlled. Id

. at 33113.

Th e 2014 F inal Rule included the EPA’s response to comments made by p e t itioners Sandra B ahr a nd David Matusow, two residents o f Phoenix

. F irst, the EPA addressed petitioners’ a r gu ment that the EPA should have r equired Ariz ona to update its control measures to en s u r e that they

were B ACM and MSM, r a t h e r than letting Ariz ona rely on the EPA’s approval of the 2000 S I P. 79 F ed. Reg

. at 33108–10. The EPA rejected this claim, ex plaining that “the requirement for B ACM is trig g ered by a specific event: The reclassification of a moderate PM-10 no n attainment area to serious.” Id. at 33108. L ikewise, th e E PA ex plained that § 7513(e) provides “ that the requirement for MSM is trig g ered by a particular event: E P A’s g ranting o f a state’s request for an ex tension of the attainment d e a d line for a serious nonattainment a

r ea. ” Id. The EPA then stated that § 7513(d) ( the section requiring the submiss i o n o f a five percent plan) “does not contain a specific requirement that the
state update the previously a pproved requirements for B ACM and MSM as a consequence of failing to reach attainment b y the applicable deadline for serious P M

- 1 0 nonattainment areas.” Id . at 33109. B ecause there was no statutory trig g er requiring Ariz ona to update its demonstration that its control

measures w ere best a v a i l able and most string ent, the EPA

ex p lained, the F ive Perce n t Plan could rely on the E PA’s approval of B ACM and MSM in the 2000 SI P. Id. The EPAB A H R V

. U.S. EPA 19

also disag reed with petitione r ’s comment that the F ive Percent Plan w as inadequate because the ag ricultural control

measures were not B ACM, as indicated by the E P A ’ s 2010 Proposed Rule disapproving of Ariz ona’s proposed revision
t o its ag ricultural g eneral permit. I n response to t h i s comment, the E PA stated that the F ive Percent Plan satisfied the requirements in § 7513a(d) “without rely ing on additional emissi o n s reductions from ag ricultural sources.” Id

. at 33109.

Second, the EPA addressed petitioners’ arg ument that its determination that the 135 e x cee dances constituted

ex c e ptional events w as contrary to the I nterim G uidance. Petitioners interpreted the I nterim G uidance as preventing the EPA from concurring that be s t available control measures

were in place unless the EPA h ad de t e rmined control

measures for w indblown dust to be BACM within the past three y ears. 79 F ed. Reg

. a t 33111–12. The EPA disag reed with this interpretation and concluded that Ariz ona’s c ontrols

were reasonable. Id. at 33112. The EPA also rejected petitioners’ arg ument that Ariz o na h ad failed to provide an adequate description of upwind sources and control measures as required by

the I n terim Guidance. I

d . at 33113–14.

F inally
, the EPA d ismissed petitioners’ comment that the EPA erred in accepting Ariz ona’s “conting ency measures” in its F ive Percent Plan because the measures had already been implemented. I

d

. a t 3 3114–15. The petitioners arg ued that because § 7502(c)(9) requires conting ency measures that “are automatically an d i mmediately implemented if a milestone for r easonable further prog r ess or attainment is not met,” the previously implemented m easures in the F ive Percent Plan could n ot qualify

. Id

. a t 33114. I n rejecting this c omment, the EPA stated it interpreted § 7 5 0 2 ( c )(9) as r equiring onlyB A H R V

. U.S. EPA 20

that “[ c] onting ency measures must provide f or additional emission r eductions” that were not otherwise included “ in the attainment demonstration,” and that “[ n] othing in the statute precludes a state from implementing such measures b e fore they are trig g ered,” rely ing o n the F ifth Circuit d ecision in Louisiana Environmental A ction N e twork v. EPA
, 382 F .3d 575 (5th Cir. 2004). 79 F e d. Reg . at 33114.

The plaintiffs filed a petition for review o f the 2014 F inal Rule on J u ly

29, 2014.

I I I

Under 42 U .S.C. § 7607(b)(1), we have jurisdiction over “[ a] petition for review of the Ad m i n i s t rator’s a ction in approving or promulg ating any implementation plan.”

I n r eviewing a c halleng e to the EPA’s a p p r o val o f a SI P under § 7607(b)(1), we apply “the g eneral standard of r eview for a g ency actions set forth in the Admini s t r a t ive Procedure Act (APA).” Latino Issues Forum v. EPA
, 558 F .3d 936, 941 (9th Cir. 2009); see a lso Vigil v

. Leavitt
, 381 F .3d 826, 833 (9th Cir. 2004). Under the APA, we must uphold a n ag ency action unles s i t i s “arbitrary
, capricious, an abuse o f di s c r etion, o r otherwise not in accordance w ith law.” 5 U.S.C. § 7 06(2)(A). This standard is “hig hly deferential, presuming the ag ency action to be valid and af f i r m i ng the
ag ency action if a reasonable basis ex ists for its d ec i s i o n

. ” Ranchers Cattlemen Action Legal Fund United Stockgrowers of A m. v. U.S. D ep’t of

Agric.
, 499 F .3d 1108, 1115 (9th Cir. 2007). Generally
, “[ a] n age n cy d e cision will be upheld a s long as there is a rational connection between the facts f ound and the conclusions made.” Barnes v. U.S. Dep’t of Transp
., 655 F .3d 1 124, 1132 (9th Cir. 2 0 1 1 )

. W e will deem anB A H R V

. U.S. EPA 21

ag ency action to be a r

b i trary a nd capricious only “if the
ag ency h as relied on f

actors which Cong r ess has not intended it to consider, entirely

failed to consider an important aspect of t h e p r oblem, offered an ex planation for its decision that

r u n s counter to the evidence before the ag ency , o r is s o implausible that it could not be ascribed to a diffe r e n c e i n vie w o r the product o f ag ency ex pertise.” Motor Vehicle Mfrs. Ass’n of the U.S. v

. State Farm Mut. Auto. I n s. Co
., 463 U.S. 29, 43 (1983). W he re the question presented for review is a factual dispute which implicates “a hig h lev el o f technical ex pertise” w e def e r to “the informed discretion o f the responsible federal ag encies.” Kleppe v. S ierra Club
, 427 U.S. 390, 412 ( 1976). “ E ven when an ag ency ex plains its decision with ‘less than ideal clarity ,’ a reviewing court will
not ups e t the decision on that a ccount ‘if the ag e ncy ' s p ath
may reasonably be discerne d

. ’” Alaska Dep’t of Envtl. Conservation v. EPA
, 540 U .S. 4 61
, 4 9 7 ( 2004) (quoting Bowman Transp., I

nc. v. A rk.-Best Freight Sys

. , I n c. , 419 U.S. 281, 286 (1974)).

W h ere t h e petitioner challeng es the ag e ncy ’s action a s in consistent w ith the ag ency ’ s own policies, we ex amine whether the ag ency has actually d eparted from its policy and, if so, w hether the ag e ncy has offered a reasoned ex planation for such departure. See Encino Motorcars, LLC v

. Navarro
, 136 S. Ct. 2117, 2125–26 (2016). Generally
, “[ a] g encies a re free to chang e their ex isting policies as long as they provide

a reasoned ex planation for the chang e.” Id. at 2 1 2 5

. I n

c ontrast, where the ag ency is not offering a policy

ex p lanation but is instead interpretin g a binding reg ulation, the ag ency ’s interpretation is “controlling ” u n less “plainly

erroneous or inconsist e nt w ith the reg ulation.” Auer v

. Robbins , 519 U.S. 452, 461 (1997).B A H R V

. U.S. EPA 22

W h ere the ag ency ’s action is an interpretation of a statute that the ag ency administers, “we follow the two-step approach set out in C hevron U.S.A. Inc. v

. Natural Resources Defense Council, I

nc. , 467 U

. S

. 8 3 7 (1984).” Latino Issues Forum
, 558 F .3d at 941. F irst, “if Cong ress has ‘dir e c t ly spoken to the precise question at issue,’ then the matter is capable of but one interpretation b y which the c o u r t an d the
ag ency must abide.” Vigil
, 381 F .3d at 834 (q uoting Chevron , 467 U.S. at 842).

At the second step o f C h e v r on , if we determine that Co n gr e s s w as silent on the issue, or the statute is subject to multiple interpretations, we mus t d e termine the d eg ree o f d e f e rence to g ive the ag ency ’s interpretation of a statut e. United States v. Mead Corp.
, 533 U.S. 218, 227–29 (2001). “Not a ll ag ency statutory interpret a t i o n s are entitled to Chevron d eference.” Sierra Club v. EPA
, 671 F

. 3d 955, 962 (9th Cir. 2012). “Rather, Chevron deference i s appropriate where ‘the ag ency c an demonstrate that i t has the g eneral
power to make rules carry ing the force o f law a

nd that the challeng ed action was taken in the ex ercise of th at authority .’” Id. ( quoting W ilderness Soc’

y v. U .S. F ish & W ildlif e S e r v. , 353 F

. 3d 1051, 1067 (9th Cir. 2 003) (en banc)). W e g enerally deem Cong r ess to have deleg ated such authority when it a u thoriz es the ag ency to eng ag e in noticeand-comment rulemaking

. Mead
, 533 U.S. at 2 2 9

– 3 0

. I n such circumstances, a court should a ccept the ag e ncy ’s in t e r p r e tation “if Cong ress h as not previously spoken to the point at issue and the ag ency ’s interpretation is reasonable.” Id . at 229.

Thoug h w e have previously applied Chevron deference to the EPA’s interpretation of the CAA issued in connection with a SI P approval, see A ssociation o f Irritated Residents v

.B A H R V

. U.S. EPA 23

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

ex p ressly held that such deference is a ppropriate, b u t rather have held the que stion open, see Vigil
, 381 F .3d at 835 (declining to address “whether the EPA’s interpretation of the Act in the course of appr o v i n g A riz ona’s SI P is entitled to Chevron d eference”). B ut because “[ a] very g ood ind icator of deleg a tion meriting Chevron treatment [ is] ex press cong ressional au thoriz ations to eng ag e in the rulemaking o r adjudication process that produces the reg ulations or ruling s for which de f

e r ence is c laimed,” Mead Corp.
, 533 U.S. at 229, a nd b ecause the EPA eng ag es in s u c h a rulemaking
proc e s s in a

pproving a SI P, we ag ree with the F ifth Circuit
t h a t “EPA’s f

inal rules approving the [ A riz ona] SI P, to the

ex tent they involve the reasonable resolution of ambig uities in the CAA, will be a ff

o rded Chevron deference,” BCCA Appeal Grp. v. EPA , 355 F .3d 817, 825 (5th Cir. 2003).

I V

On appeal, petitioners argue that the EPA acted contrary
to law by failing to require that Ari z o n a include an updated analy sis of best available control measures and most string ent

measures in the F ive Percen t P l a n

. They also arg ue that the EPA abused its discretion by ex c luding 135 ex ceedances from the monitoring data as “ex ceptional events.” F inally
, they arg ue that the EPA violated the C A A b y allowing Ariz ona to satisfy the “ c onting ency measures” r e quirement with previously implemented control measures. W e consider each arg ument in turn.

A

W e first consider petitioners’ arg ume n t that the E PA’s

a p p roval of the F ive Percent Plan constituted an abus e o fB A H R V

. U.S. EPA 24

discretion because the EPA d id not require A riz ona t o demonstrate that the p l an included best available control

measures (B ACM) or most string ent measures (MSM) for the control o f PM-10. A ccording to petitioners, the F ive Percent Plan must demonstrate that Ariz ona’s control measures meet the B ACM and MSM s t a n d ards b ecause Ariz ona has a continuing oblig ation to c o m ply with § 7513a(b)(1)(B ) a nd § 7513(e), which set the co n t r o l requirements for serious nonattainment areas. Petitioners arg ue that ha d a BA CM demonstratio n b e en required, the F ive Percent Plan would have failed b ecause the ag ricultural control measures in Ariz ona’s 2000 SI P are no long er B ACM, as stated in E PA’s 2010 Proposed Rule. F urther, petitioners argu e , t he E PA’s
statement in the 2 010 Proposed Rule reg arding Ariz ona’s failure to meet the B ACM standard is evidence that the EPA
g enerally requires an updated B ACM demonstration in each SI P, meaning that the EPA acted inconsistently by not requiring such a demonstration in the F ive Percent Plan.

W e disag ree with these a

rg uments. The EPA’s decision
not to require an updated demonstration of B A CM a nd MSM in t h e F ive Percent Plan was n ot an abuse of discretion because i t was not contrary to any lang uag e in the CAA. Section 7513a(d), which g overns fi v e p e r cent plans such a s the o ne b e f

o re us here, p rovides only that if a state fails to achieve attainment after receiving the five-y ear ex tension, it
must submit plan revisions providing for “attainment o f the PM-10 air quality standard,” and a n an nual five percent reduction in PM-10 within the Serious Area. I t does not mention B ACM or MSM. The CAA sections that do require B AC M and MSM demonstrations do not ex pressly apply to

a f ive percent plan. Section § 7513a(b) provides that when the EPA reclassifies a Moderate Area as a Serious Area, the
state must then submit a S I P t hat “assure[ s] that the bestB A H R V

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available control measures for the control of PM-10 shall be implemented.” I t does not require t h e s t ate to update that

assurance when submitting a five percent plan, nor does it require the E PA to review its previous B ACM determination. S imilarly
, § 7513(e) provides that when the EPA g rant s a state a five-y ear ex tension of t he d eadline to meet the N AAQS for PM-10, the state must submit a SI P t h at “includes the mo st string e nt measures” that are included in
any SI P o r a chieved in any state. Again, this lang u ag e does
not require the state to include a n updated d e monstration o f MSM when submitting a five percent plan.

W e also d isag ree with petitioners’ a r g ument that the EPA acted inc o n s istently in failing to require an updated demonstration of B ACM and MSM in the F ive Percent Plan. Even thoug h the EPA h ad previously reviewed and proposed
to disapprove the a g r icultural control measure i n Ar i zona’s 2007 SI P as n ot meetin g the B ACM standard, the EPA provided a reasonable interpretation of it s a p p roach in the 2014 F inal Rule. A ccording to the EPA, the CAA lay s o ut a series of escalating control measures th a t a r e trig g e red by a finding of noncompliance with a series of statutory requirements. The EP A wi l l assess compliance with the control measures that were trig g ered at each step, but will not

reassess compliance w ith those measures at subsequent steps unless a state proposes chang es to c o n trol measures that were previously approved. 79 F ed. Reg

. at 33108–09. This approach is consistent w ith the CAA, which does not require the EPA to reassess a state’s controls in each SI P submission. Here, the EPA’s 2010 Proposed Rule reasses s e d Ariz ona’s
ag ricultural control measures under the B ACM standard because Ariz ona proposed to revise ag ricultural cont r o l

measures that were pr ev i o u s ly approved as B ACM in the 2002 F inal Rule. Ariz ona did not propose any revisions to itsB A H R V

. U.S. EPA 26

ag ricultural controls in the F ive Per c e n t Plan, however, so EPA did not have any occasion to reevaluate those measures. Given the EPA’s reasonable e x planation for its approach, a nd the lack of any contrar

y s t a tutory command in the CAA, we conclude that the EPA di d n o t a buse its discretion or act contrary to law by d eclining to require an u pdated demonstration of B ACM or MSM in the F ive Percent Plan.

Petitioners also arg ue that t h e E PA acted in an arbitrary and capricio u s m an ner in reviewing the F ive Percent Plan because it evalua t ed Ariz ona’s compliance with CAA requirements reg a

r ding emission inventories, reasonable further progr e s s , and conting ency measures, but ig nored B ACM a nd M S M

. We also reject this arg ument. T he EPA reasonably ex plained that those particular CAA requirements

are procedural or otherwise applicable to all SI P submissions,

see 42 U.S.C. §§ 7410(a), 7502(c), 7506(c), 7513a(c)(1), a nd the EPA re v i e ws such measures whenever it r eviews a proposed SI P. B y contrast, the B ACM and MSM requirements are not applicable to all SI P submissions, and so t h e EPA reviews them only when the state is required t o demonstrate compliance with these requirements.

B

W e n ex t turn to the p etitioners’ arg u ment t h at the EPA acted contrary to law by ex cluding 135 ex ceeda n c es in the Maricopa Area from Ariz ona’s air quality monitoring data.

Petitioners raise several arg uments as to why the EPA erred in concluding that the dust sources causing the 135

ex c e edances w e re from anthropog enic sources that were “reasonably well-controlled,” and therefore were ex cludable

a s ex ceptional events. See 40 C.F

. R. § 50.14(b)(1). T h eB A H R V

. U.S. EPA 27

petitioners beg in by pointing to the statement in the I n terim Guidance that “ [ g ] enerally
, the EPA will consider windblown dust B A CM to c onstitute reasonable controls i f these

measures have been reviewed and a p proved in the contex t o f

a SI P revision for the em i s sion source area within the past three y ears.” I nterim Guidance at 15. The EPA’s de c i s i on

was inconsistent with this g uidance, p etitioners arg ue, for two

reason s

. Fi r st, Ariz ona’s dust control measures for the Maricopa Area had not been approved since 2002, w ell over three y ears before the 2014 F inal Rule. Second, ag ricultural emissions are a m o n g the sources of windblown dust in the Maricopa Area, and the EPA’s 2010 Proposed Rule h ad proposed to disapprov e o f Ariz o na’s ag ricultural control

measures because they were not B A C M

. Moreover, petitioners arg ue, the EP A f ailed to offer a reasonable

ex p lanation for its departure from its g uidance.

W e disag r ee; the EPA’s 2 014 F inal Rule did n o t conflict with the I nterim Guidance. F irst, nothing in the I n terim Guidance indicates that EPA must find that control measures for windblown dust have been reviewed and approved a s B ACM within the past three y ears in order for the dust to be deemed r e asonably well-controlled. Rather, the I n terim Guidance g ives the EPA flex ibility to consider a wide rang e of issues, and emphasiz es that a prior B ACM d e termination “may be a reference point, but not the sole means, by which the EPA as s e s s the reasonableness of controls.” I n terim Gu idance at 15. The EPA’s interpretation is therefore consistent wi th the I nterim G uidance a nd is a reasonable interpretation of the Ex cept i o n a l Events Rule, to which we owe deference. Auer , 519 U.S. at 461.

Second, the EPA provided a r easonable e x planation a s to why the Marico pa Area had reasonable controls forB A H R V

. U.S. EPA 28

w indblown dust even thoug h the 2010 Proposed Rule h a d proposed to disapprove of Ariz o na’s ag ricult u r a l control

measures. The EPA’s 2002 F inal Rule determined t hat the 2000 SI P c ontained the best available control measures for the hig hest emitters of PM-10 (including unpaved roads and alley s, construction, p a v e d road d ust, a nd non-ag ricultural windblown dust). 79 F ed. Reg

. at 3 3111–13. The 2014 F inal Rule then ex plained that it was still appropriate to rely on that determination because n either the hig hest emitters of PM-10

nor the techniques for controlli n g fug itive dust had chang ed sig nificantly since 2002. Id

. a t 33112. Moreover, A riz o na made its dust control r u l e s even more string ent in the y ears following its 2000 SI P, further bolstering the conclusion that the c ontrols remained reasonable. Id

. A lthoug h the EPA h ad proposed to disapprove of the ag ricultural controls as not meeting the B ACM standard in 2010, data showed that
ag ricultural sources were o nly a minimal contrib u t o r to the Maricopa Area’s overall level of PM-10 e missions. Id

. According ly
, t he EPA’s judg ment was that the control

measures in the 2000 SI P ensured tha t anthropog enic windblown dust was reasonably control l ed for purposes o f the Ex ceptional Events Rule.

“[ W ] e g enerally must be at [ our] most deferential when reviewing scientific judg ments and technical analy ses within the ag ency ’s e x pertise.” Lands Council v. McNair
, 629 F .3d 1070, 1074 (9th Cir. 2010) (second alteration in orig inal) (internal quotation marks omitted). Here, the EPA c o n s i dered the relevant factors and a r ti c u l a ted a rational connection between the facts found and t h e choice made. As a g eneral rule, a determination that p a r t i cular control measures a re reasonable relies on technical c onsiderations that a reB A H R V

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“properly left to the informe d discretion of” the EPA. Kleppe , 427 U.S. at 412. W e defer to its conclusion here. 1 0

C

Petitioners also claim that t h e EPA’s approval o f Ariz ona’s 135 ex ceedances as ex ceptional events violated the I nterim Guidance because the EPA failed to adequately address the controls in upwi n d areas outside the Maricopa Area. T o qualify as an ex ceptional event under the Ex ceptional Events Rule, an ex ceedance must be “ caused b y human a ctivity that is unlikely to recur at a particular location

or a natural e v e n t

. ” 40 C.F .R. §§ 50.1(j), 50.14. The Treatment of Data Guidance states that h ig h wind events will be considered “natural” when “(1) the d ust o r i gi nated from nonanthropog enic sources, or (2) th e d ust orig inated from anthropog enic sources within the State, that are d e t ermined
to have been reasonably well-controlled at the time t hat the
event occurred, or from anthropog e nic s ources outside the State.” 7 2 Fe d

. Reg

. at 13576. To assist the EPA in determining c ompliance with this require m e n t, the I n terim Guidance requires a state to prov i d e “ a brief description” o f “all contributing emi s sion sources in upwind areas a nd provide evidence that those sources w e re reasonably controlled, w heth er anthropog enic or natural.” I n terim Guidance at 42.

Petitioners a

rg ue that Ariz o na’s submissions were inadequate because Ariz ona did not identify all contributing emission sources outside the Maricopa Area, fai l e d to

10 B ecau se w e co n clu d e t

h at th e EP A

d id n o t d ep art f

ro m its In terim Gu i d an ce, w e d o n o t reach th e petitio n ers’ arg u m en t th at th e EP A

f ailed
to p ro v id e a reaso n ed ex p lan atio n f o r d ep artin g f

ro m its g u id an ce.B A H R V

. U.S. EPA 30

d isting uish between n atural a n d anthropog enic sources, a n d failed to submit evidence that Pinal County had reasonab l e controls in place.

W e ag ain disag ree. Under the Treatment o f Data G u i dance, a hig h wind e v ent may meet the criteria of the Ex ceptional E vents Rule when the dust orig inated f r o m nonanthropog enic sources, o r from a nthropog enic sources that are reasonably

well-controlled at the time that the event occurred. 72 F ed. Reg

. at 13576–77. Ariz ona ex plained that the hig h wind e v e nts causing the 1 35 e x ceedances stemmed from monsoonal dust storms. B ec a use “outflow from thund er s t o r m s c an c ar r y dust o ver vast distances encompassing many source areas,” Ariz ona could not clearly disting uish between n onanthropog enic and anthropog enic sources of dust. Nevertheless, Ariz o na adequately provided

a “brief description” o f contributing dust sources outside the Maricopa Area and demonstrated that r e a s o nable c ontrols

were in place for any anthropog e nic sources of dust. F o r instance, in describing ex ceedances that occurred during the Aug ust 1 1, 2012, event, A riz ona p rovided a “conceptual model” identify ing a nonanthropog enic source, the “undeveloped lands south o f Maricopa County ,” as being the primary contributing source areas in Pima and Pinal Counties. Ar i z o n a also provided evidence that any anthropog enic

sources of dust in those areas w e re r easonably controlled, pointing to two Pinal County rules applicable to fug itive dust and construction sites. A riz ona compiled similar su b m i s s i o ns for each of its ex ceptional event submittals. Ariz ona’s submissions provided enoug h detail for the EP A to reasonably conclude t h a t the dust o rig inated either from “nonanthropog enic sources” or “anthropog enic sources” that

w ere “reasonably well-controlled.” I nterim G uidance at 42. According ly
, the EPA’s conclusio n t h a t A r i zo n a ’ s d escriptionB A H R V

. U.S. EPA 31

of the upwind sources w as adequate was not an abuse o f discretion.

Petitioners also arg ue t h a t the EPA ig nored the I n terim Guidance and thus abused its discretion in concluding that the anthropog enic dust sources in th e areas of Pinal County
out s i d e of the Maricopa Area were reasonably controlled. The I nterim Guidance states t h a t “ [ f] or the anthropog enic

sources to be considered to be reasonably controlled, the EPA anticipates that it is reasonable for an air age n c y t o h ave the controls required for an area’s attainment status.” I n terim Guidance at 15. “[ T] he E PA does not e x pect areas classified

as attainment, unclassifiable, o r maintenance for a NAAQS
to have the same level of controls as areas that a re nonattainment for the same NAAQS.” Id

. I n o ther words, an

area that is in attainment should have the control m e a s u r e s appropriate for an a ttainment area, while an area that has been desig nated a serious n onattainment ar e a should have the

c ontrol measures appropriate for that level of classification. Id

. W here “an area has b een recentl y d esig nated to nonattainment but has not y et been r equired t o i m p lement controls, the E PA will ex pect the l e v el of controls that is appropriate for the planning stag e.” Id

.

Un d e r the I nterim Guidance, the EPA did not abuse its discretion in concluding that the anthropog e nic dust sources in the areas of Pinal County o utside of the Ma r i c o p a Area

were r easonably well-controlled. The EPA provided a reasoned ex planation as to why it deemed the Pin a l County

area to have the controls required for t h a t area’s attainment
status. The 135 ex ceedances approved b y t h e EPA all

o c curred between 2010 and 2012. 79 F ed. Reg

. at 331 1 1

. F rom J anuary 2011 to J une 2012, Pinal County (ex cluding the portion within the Maricopa Area) w as an attainment area,B A H R V

. U.S. EPA 32

and had a dopted two rules addressing fug itive dust emissions that were appropriate for this status. Althoug h Pinal County

was redesig nated a nonattainment area in J uly 2012, it w a s not required to submit a SI P u ntil 18 months a fter redesig nation, leaving it i n the planning stag e for the remainder of 2012. See D esig n ation of A reas for Air Quality Pla n n ing Purposes; State of Ariz ona; Pinal County ; PM10, 77 F ed

. Reg

. 32024, 32030 (May 31, 2012). B ecause Pinal County had not y et been required to implement controls, the EPA reasonably

concluded that Pinal County ’s fug itive dust rules were appropriate for the planning stag e.

V

F inally
, we turn to petitioners’ arg u ment that the EPA erred in a

pproving the conting ency measures in the F ive Percent Plan because those measures had a l r e ady been implemented. As noted above, four of fi ve conting ency

measures in the F ive Percent Plan w ere permanent chang es to infrastructure that had been completed b y 2012 (paving a nd stabiliz ing e x isting public dirt roads an d a l l ey s, p aving a nd stabiliz ing unpaved shoulders, repaving or overlay ing paved roads with r

ubberiz ed asphalt, and lowering speed limits on dirt roads and alley s). The f i f t h conting ency measure in volved the purchase of PM-10 certified sweepers a nd sweeping of freeway s, thoug h the purchase occurred in 2009 and Ariz ona had procured contracts for sweeping services b y 2010. The CAA provides that a nonattainment SI P:

[ S ] hall provide for the implementation o f specific measures to be undertaken if the area fails to make reasonable further prog r ess, o r to attain the national p rimary a m b ient air quality standard b y the attainment dateB A H R V

. U.S. EPA 33

a p p licable under this part. Such measures shall b e included in the p lan rev i s i on a s conting ency measures to t a k e e ffect in any such case without f

urther action by the State or the Administrator.

42 U. S

. C. § 7502(c)(9). I n its 2014 F inal Rule, the EPA

ex p lai n ed i ts interpretation o f this requirement. W hile “[ c] onting ency measures must provide for addit i o nal emission r eductions that a r e not r elied on for RF P [ reasonable further prog ress] or a ttainment and that are not included in the attainment demonstration,” the EPA concl u ded that “[ n] othing in the statute precludes a state from implementing such measures before they are trig g ered.” 7 9 Fed. Reg

. at 33114.

Althoug h w e defer to the EPA’s interpreta t i o n of the C AA contained in a final rule approving a SI P i f t h at interpretation involves the reasonable i n t erpretation o f ambig uous statutory terms, see supra at 22, we cannot defer
to the EPA’s interpretation of § 7502(c)(9) h e re. W here Cong r ess has “directly spoken to the precise question at issue

. . . that is the e nd of the matter; for the court, a s we l l as the
ag ency , must gi ve effect to the u nambig uously ex pressed intent of Cong ress.” Chevron
, 467 U.S. at 842–43. The statutory lang uag e in § 7502(c)(9) is c lear: it requires the SI P
to provide for the implementation of measures “ to be undertaken” in the f

uture, trig g ered b y the state’s failure “to make r easonable further prog r e ss” or to attain the N AAQS. These measures a r e included in the SI P as “conting ency measures” and are “ to take effect” a utomatically in the future. Althoug h the statute d oes not define the word “conting ency , ” the meaning of the term is n ot ambig uous. According to the dictionary d efinition, it means “a possible future event o rB A H R V

. U.S. EPA 34

c o n dition or an unforeseen o ccurrence that may necessitat e special measures.” W ebster’s Third New I nternational Dictionary (2002). B e c ause Cong r ess was clear that “conting ency measures” are c ontrol measures that w i ll be i m p lemented in the future, and the statutory lang uag e is n o t susceptible to multiple interpretations, we must g ive effect to its plain meaning

. Chevron
, 467 U.S. at 842–43.

I n arg uing that its interpretation of § 7502(c) is e ntitled to deference d espite the clear langu a ge of the statute, the EPA relies on the F ifth Circuit’s decision in Louis i ana Envtl. Action Network v. EPA
, 382 F .3d 5 7 5
, 580 (5th Cir. 2004). I n Louisiana E

nvtl. Action Network
, the petitio n e rs challeng e d t he EPA’s 2002 approval of L ouisiana’s SI P because the conting e ncy mea s u r e in the SI P (a compressor station’s permanent reduction o f its emissions) had been implemented in 1 998, and therefore w as not a measure “to be undertaken” or “to take effect” in the future, as § 7502(c)(9) requires. Id

. at 582. The F ifth Circuit first a c k n o wledg ed that “a plain reading of the terms ‘to take effect’ a n d ‘ to be

u n d e r t a k e n’ i m p l y a p ro s p e c t i v e, f o r w a r d l o o k i n g orientation” that would “preclud e t h e use of past reductions which have a lready failed to achieve attainment.” Id. at 583. Nevertheless, the F ifth Circuit h e ld that § 7502(c)(9) was ambig uous because it “neither affirms nor prohibit s continuing emissions reductions—measures which orig inate prior to the SI P failing
, b u t w hose effects continue to manifest an effect a fter the plan fails—from being utiliz ed a s

a conting ency m e asure.” Id. (emphasis omitted). Having found this “ambig uity ,” it deferred to the EPA’s interpretation that “conting ency measures” could include measures that h ad already been implemented by

the state.B A H R V

. U.S. EPA 35

W e cann o t ag ree with the F ifth Circuit’s interpretative approach. Having determined that t h e “plain r eading of the terms” indicates a forward looking approach, the F ifth Circuit

was bound by Chevron to g ive effect to the plain meaning o f the statute. W e disag r ee that the lack of any discussion in § 7 502(c)(9) reg arding treatment of continuing emissions reductions makes the statute a mbig uous. Rather, unless such continuing emissions reductions are “ to be undertaken” in the
event of a conting ency , they d o n o t fit the definition o f “conting ency measures” provid ed i n § 7502(c)(9). W e also disag ree with the dissent’s contention that p reviously implemented control measures that prov i de continuing emissions r e ductions “take effect” and are “undertaken” both “at the time they are first i mplemented but also thereafter.” Dissent a t 38. T his is a misreading of the s t a t u te, which defines conting ency measures as measures “ to be u nd e r t a ken”

or “ to take effect” if a future event occurs, namely “ if the area fails to make reasonable further prog ress, or to attain the [ NAAQS] .” 42 U.S.C. § 7 5 0 2 ( c )(9) (emphases added). Control measures that have already b e e n implemented are not

measures “to be u ndertaken” or “to take effect” in the future, and the statute cannot reasonably be so interpreted.

The E PA arg ues that its interpretation is c o n sistent with the CAA’s policy g oals, because permittin g e arly implementation o f conting ency measures is con s i stent with the o verall policy of the CAA to reduce p articulate emissions

an d p rotect public health. La. Envtl. Action Network
, 382 F .3d at 583. T he F ifth Circuit likewise relied o n th ese policy considerations, stating that allowing states to implement measures before the conting en c y occurs was consistent with the CAA’s purpose of c r eating incentives for
states to reach NAAQS compliance earlier and m o re efficiently

. I

d. at 583–84. The dissent ag rees, ad opting theB A H R V

. U.S. EPA 36

Fi fth Circuit’s policy analy sis. 1 1 Dissent at 39–40. E ven if

we ag reed that the EPA’s policy c o nsiderations a re compelling
, such considerations cannot override the plain lang uag e of the statut e

. W e therefore cannot g ive them controlling weig ht here.

B e cause the “continge n cy measures” in Ariz ona’s SI P

were not “specific measures to be undertaken if the a rea f ails to make reasonable further p r og ress, or to attain the national primary ambient air quality standard b y the attainment date applicable under this part,” the EPA’s approval of this p art o f the F ive Percent Plan was contrary to the CAA. A c cording ly
, we re m and to the EPA f or further consideration of this portion of the SI P but otherwise deny the petition. 1 2

P ETITION G RANTED IN P ART AND DENIED IN P A RT

.

11 In ad d iti o n to rely in g on th e Fif t h Circu it’ s p o licy arg u m en ts, th e d issen t arg u es th at p reclu din g th e u se o f p rev io u sly im p lem en ted co n t

ro ls

as co n tin g en cy m easu res “ im po ses an ad d itio n al an d u n n ecessary b u rd en

u p o n s tates w

h ere th e f ailu re to attain th e N A A QS also trig g ers a b u m p u p

o f an area’ s classif

ic a t i o n un d er th e A ct” b ecau se states w ill n o t b e ab le
to “ f o cu s th eir ef

f o rts o n i m p lem en tin g th e n ew ly im

p osed req u irem en ts.” Dissen t at 4 0. T h is is i n co rrect: b ecau se co n tin g en cy m easu res

au to m atically tak e ef

f ect w h en th e co n tin g en cy o ccu rs, “ w i th o u t f u rth er actio n b y th e State,” 4 2 U.S.C. § 7 5 0 2 (c)(9 ), th e im p l em en t atio n of

co n tin g en cy m easu res can n o t d istract a state f ro m m eetin g th e o th er CA A
req u irem en ts.

12 Each p arty

is to b ear its o w

n co sts o n ap peal.B A H R V

. U.S. EPA 37

CL I F TON, Circuit J ud ge , c oncurring in part and dissenting in part:

I fully concur in sections I –I V of the majority opinio n

. I disag ree, however, with the majority ’s conclusion in section V that EPA’s approval o f t h e conting ency measures in Ariz ona’s SI P is co n t r ary to the clear lang uag e of the CAA. I n my view, the scope of the CAA’s continge n cy measures

r e q u i r e m e n t i s a m b i g u o u s a n d E P A ’ s r e a s o n a b l e interpretation of that requirement is entitled to deference.

L ike th e m ajority

, I beg in by analy z ing the tex t of the relevant statutory provision, 42 U .S.C. § 750 2 (c)(9). That section of the CAA requires state nonattainment plans to include conting ency me a sures “ to b e undertaken” and “to take effect” in the event that a n area “ fails to make reasonable further p rog ress, or to attain” the N AAQS by the applicable attainment date. Id. Althoug h I ag ree with the major ity that this lang uag e most o ften r efers to meas u r e s t h a t are to be implemented in the f

uture, in the event that the other

measures included in a state’s SI P are n o t s u f ficient to meet CAA requirements, I am not persuaded that t h e provision’s
tex t forecloses the i nterpretation advanced by E PA a nd applied in this case.

The lang uag e of the statute prohibits states from labeling

as “conting e ncy measures” the same proposed reduc tions relied upon to achieve NAAQS com pliance. S ee La. Envtl. Action Networ k v. EPA
, 382 F .3d 575, 583 (5th Cir. 2 004) (“Such a prospec t i v e reading of the tex t would seeming ly preclude the use of past reductions which have already failed
to achieve attainment. ” )

. I t requires states to identify additional measures that m u s t be put into effect without further action by the state or EPA if reasonable prog ress isB A H R V

. U.S. EPA 38

not made or the a ir quality s t a n d a rd is not met b y the attainment d a t e

. Those additional measures are what the statute describes as “conting e n cy measures.”

Ariz ona’s SI P identified additional measures that were not relied upon to obtain t h e anticipated compliance. The practical issue before us in this case is whether Ariz ona was prohibited from putting those additional measures into effect in advance. The majority opinion conc l u d e s that it was, that the state’s conting ency measures must be left undone, sitting

on the sidelines in reserve. I do not believe that the lang uag e or intent of the statute requires that conclusion.

The early implementation of infrastructure improvements that are ex pected to result in additional and continuing emissions reductions is con s i stent with the lang uag e o f § 7 5 0 2(c)(9). These early

- implemented cont i n g e n c y m e a s u r e s result in a net reduction in emissions f ollowing their implementation. They “take e ffect” and are “undertaken” not only at the time they a

re first implemented but also thereafter, including at the time they mig h t formally be required due to nonattainment. So long as these reductions are not relied upon to meet o ther CAA requirements, they funct i o n a s a backup plan, reducing the lik e l ihood that the state will fail to attain th e NAAQS e ven in the “conting ency ” that the measures

ex p licitly included in the SI P for that purpose are not enoug h.

The majority responds by asserting that the statute “defines conting ency m easures a s measures ‘ to be undertaken’ or ‘ to take effect’ if a f u ture event occurs, namely ‘ if the area fails to make reasonable further prog ress,

or to a ttain the [ NAAQS]

. ’” Majority opinion at 35 (emphasis in orig inal). B ut this lang uag e fits just as well with E PA’s interpretation as it does w ith the view of the majority

. I n bothB A H R V

. U.S. EPA 39

scenarios, the c o n t i n gency measures must be in effect a t the time an area f

a i l s to achieve the g o als outlined in the SI P. W h at is at issue here is whethe r s t a t es are prohibited from also implementing the measures before that “future e v ent occurs.” T he lang uag e quoted by the majority contains no

s u ch prohibition and it is not our role to read one i n t o t h e statute.

EPA’s interpretation also c omports well with the purpose of the CAA. “I n determining whether Cong ress has specifically addressed the question at issue, a reviewing court should not confine itself to ex amining a p articular statutory p r o vision in isolation.

. . . I t is a ‘fundamental canon o f statutory c onstruction that the words of a statute must be read in their contex t a

nd with a v iew to their place in the overall statutory scheme.’” FDA v. B r o w n & W illiamson Tobacco Corp.
, 529 U.S. 1 20, 132–33 (2000) (quoting Davis v

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

Allowing states to implement conting ency measures before they are trig g ered makes sens e i n l i g ht of that same provision’s requirement that such measures “take effect

. . . without further action by the State o r the A dministrator.” That requirement, read in contex t with the Act’s mandate th at states implement e m i s s i o n

- c o n t r o l m e a s u r e s “ a s e xp e d itiously

as practicable,” id. § 7502(c)(1), e v inces a clear cong ressional preference that conting ency mea sures operate to reduce the emission of har mful pollutants in as efficient and timely a

manner as p o s s ible. Taking this statutory purpose into account, “it seems illog ical to penaliz e nonattainme n t areas that are taking ex tra steps, such a s implementing conting ency

measures prior to a deadline” as a c ushion to ensure NAAQS

c o m pliance a

nd prevent the need for the conting ency

measures requirement to b e trig ge red in the first place. La.B A H R V

. U.S. EPA 40

Envtl. Action Network
, 382 F .3d a t 58 4

. I t does not benefit ordinary citiz ens to read the CAA to incentiviz e states to hold off from purchasing ne w s treet sweepers or repaving their roads until the conting e n cy measures requirement is trig g ered.

The m ajority ’s interpretation also imposes an additional and u nnecessary burden u pon s t a tes in circumstances where the failure to attain the N AAQS also trig g ers a bump up of an area’s classification under the Act. F o r ex ample, the fa i lure of a moderate n o n a t tainment area to achieve NAAQS compliance by the applicable deadline trig g ers both § 7502(c)(9) ’ s conting ency measures requirement and the additional requirements imposed upon serious nonattainment

areas. 42 U.S.C. § 7 513(b)(2). The early implementation o f conting ency

measures allows states in this situation to focus their efforts on implementing the newly imposed requirements w hile the conting ency measures continue to operate in the interim. See La. Envtl. Action N e t w o r k
, 382 F .3d at 583. 1

1 T h e m a j o r i ty arg u es t

h at b ecau se co n tin g en cy m easu res m u st tak e ef f ect “ w ith o u t f

u rth er actio n b y t h e S tate” o r EP A
, 4 2 U.S.C. § 7 5 0 2 (c)(9 ), th ey “ can n o t d istract a s tat e f ro m m eetin g th e oth er CA A
req u irem en ts.” Maj o rity o p in io n at 3 6 n

. 1 1

. Ho w ev er, EP A h as in terp reted th i s l a n g u ag e t o req u ire o n ly “ th at n o f u rth er ru lem ak in g activ ities b y th e State o r EP A w o u l d b e n eed ed to im plem en t th e

co n tin g en cy m easu res.” Green b au m v. EPA
, 3 7 0 F.3 d 5 2 7
, 5 4 1 (6 th Cir. 2 0 0 4 ) (q u otin g State Im

p lem en tatio n P lan s; Gen eral P ream b l e f o r th e Im p lem en tatio n o f T itle I o f th e C lean A ir A ct A m en d m e n t s o f 1 9 9 0
, 5 7 Fed . Reg . 1 34 9 8 , 1 3 5 1 2 (A p r. 1 6 , 1 9 92 )). T h u s, u n d er th e m aj o rity ’ s in terp retatio n , states w o u ld still b e req u ired to p erf o rm th e actu al b u sin ess

o f i m plem en tin g th e id en tif

ied co n tin g en cy m easu res at th e sam e t i m e th ey ad dress o th er req u irem en ts im p o sed b y a f

ailu re to attain th e NA A QS.B A H R V

. U.S. EPA 41

I recog niz e that what is lost by EPA’s interpretation of the
statute is the advance identification of “still more” measures aimed at improvi ng a ir q uality that can b e newly a nd

a dditionally implemented in the e vent of nonattainment

. I f Ariz ona’s SI P does not r e a ch i t s g oal, then reliance upon conting ency measures t h a t have already been put into effect will not further reduce airborne particulate matter, and more will have to be done a t that point. B ut EP A a p p l i e d its

ex p ertise and e x e rcised its judg ment in concluding that the
g oal was likely to be r eached by the measures proposed in the SI P, w i t h o ut reg ard to the additional conting ency measures. B y letting A riz ona identify actions that have a l r e a d y been implemented a s conting e ncy measures, EPA has obtained a cushion. I t i s n o t an unreasonable judg ment for EPA to conclude that implementing the cus h i on rig h t away is more valuable than advance identification of what else mig ht be done, if necessary

.

F or these reasons, I would g ive Chevron d eference to the EPA’s interpretation of § 7502(c)(9). I respectfully dissent from the majority ’s conclusion to the contrary

.