MARTHA VIGIL, ANDY BLACKLEDGE and ROBIN SILVER, Petitioners, v.

MICHAEL O. LEAVITT, * Administrator, United States Environmental Protection

Agency; WAYNE NASTRI, Regional Administrator, Region IX; and UNITED

STATES ENVIRONMENTAL PROTECTION AGENCY, Respondents.

* Pursuant to Fed. R. App. P. 43(c), Michael O. Leavitt is automatically

substituted as a party respondent for Christie Whitman.

No. 02-72424

UNITED STATES COURT OF APPEALS FOR THE NINTH CIRCUIT

366 F.3d 1025; 2004 U.S. App. LEXIS 9069; 58 ERC (BNA) 1481

June 9, 2003, Argued and Submitted, San Francisco, California

May 10, 2004, Filed

SUBSEQUENT HISTORY: Amended by, Rehearing

granted by, in part, Rehearing denied by, in part Vigil v.

Leavitt, 381 F.3d 826, 2004 U.S. App. LEXIS 18495 (9th

Cir., Sept. 1, 2004)

Reprinted as amended at Vigil v. Leavitt, 2004 U.S. App.

LEXIS 18547 (9th Cir., Sept. 1, 2004)

PRIOR HISTORY: [**1] On Petition for Review of

an Order of the Environmental Protection Agency.

DISPOSITION: Petition was granted in part and

denied in part; costs to petitioners.

COUNSEL: Joy E. Herr-Cardillo, Arizona Center for

Law in the Public Interest, Tucson, Arizona, for the

petitioners.

Angeline Purdy, Trial Attorney, Environmental Defense

Section, Environment and Natural Resources Division,

U.S. Department of Justice, Washington, D.C., and

Daniel W. Pinkston, Senior Trial Attorney, Denver,

Colorado, for the respondents.

Richard S. Moskowitz, American Trucking Associations,

Inc., Alexandria, Virginia, for the amicus curiae.

JUDGES: Before: Susan P. Graber, Kim McLane

Wardlaw, and Jay S. Bybee, Circuit Judges. Opinion by

Judge Bybee.

OPINION BY: Jay S. Bybee

OPINION

[*1028] BYBEE, Circuit Judge:

Martha Vigil, Andy Blackledge and Robin Silver

petition for review of a final rule approved by the

Environmental Protection Agency (EPA) under the Clean

Air Act, 42 U.S.C. §§ 7401-7671q. On July 25, 2002,

EPA approved Arizona's serious area state

implementation plan for airborne particulate matter in the

metropolitan Phoenix (Maricopa County) area and

granted Arizona's request for an extension of the statutory

[**2] attainment deadline from December 31, 2001, to

December 31, 2006. 1

1 Various state, county, municipal, and regional

governments or associations of governments have

played a role in the proceedings before EPA. For

convenience, in this opinion we will generally

refer to these entities as "Arizona."

Page 1
Petitioners, who are interested Phoenix residents,

assert that EPA's actions are arbitrary and capricious or

otherwise not in accordance with the Act because EPA

approved Arizona's general permit rule for controlling

agricultural emissions without requiring all feasible

measures and, specifically, controls currently

implemented in the South Coast region of California.

Petitioners also argue that EPA approved the plan without

requiring Arizona to mandate the use of CARB diesel, a

fuel standard adopted by the California Air Resources

Board. Finally, petitioners argue that it was arbitrary and

capricious for EPA to grant an extension of the statutory

deadline to December 31, 2006. We grant the petition in

part, vacate [**3] portions of EPA's final approval of

Arizona's state implementation plan for Maricopa

County, and remand to EPA.

[*1029] FACTS AND PROCEEDINGS BELOW

A. Regulatory Background

The Clean Air Act sets forth a cooperative

state-federal scheme for improving the nation's air

quality. Under the Act, the EPA publishes a list of air

pollutants and then establishes national ambient air

quality standards (NAAQS) for each pollutant that it has

identified. 42 U.S.C. §§ 7408(a), 7409(a). EPA has

identified airborne particulate matter of diameter 10

micrometers or less (PM-10) as an air pollutant that

"affects the respiratory system and can cause damage to

lung tissue and premature death. The elderly, children,

and people with chronic lung disease, influenza, or

asthma are especially sensitive to high levels of

particulate matter." Promulgation of Federal

Implementation Plan for Arizona--Phoenix PM-10

Moderate Area; Disapproval of State Implementation

Plan for Arizona--Phoenix PM-10 Moderate Area, 63

Fed. Reg. 41,326, 41,326 (Aug. 3, 1998). EPA has

established two national air quality standards for PM-10,

a 24-hour standard and an annual standard. 40 C.F.R. §

50.6(a) [**4] , (b); see Sierra Club v. EPA, 346 F.3d

955, 957-58 (9th Cir.), amended by 352 F.3d 1186 (9th

Cir. 2003); Ober v. EPA, 84 F.3d 304, 306 & n.1 (9th Cir.

1996) (Ober I).

Under the Clean Air Act Amendments of 1990,

Congress designated certain areas as "nonattainment" for

the PM-10 standards. See Pub. L. No. 101-549, § 101(a),

104 Stat. 2399, 2403 (codified at 42 U.S.C. §

7407(d)(4)(B)). Congress further required that these

PM-10 nonattainment areas be classified by law as

"moderate area[s]." 42 U.S.C. § 7513(a). Moderate

PM-10 nonattainment areas may be reclassified as serious

PM-10 nonattainment areas under specified

circumstances; among other things, any area that fails to

reach attainment by the applicable date "shall be

reclassified by operation of law as a Serious Area." 42

U.S.C. § 7513(b)(2)(A).

Each state has "primary responsibility for assuring

air quality" within the region comprising such state, 42

U.S.C. § 7407(a), and each state must submit a state

implementation plan (SIP) proposing the manner in

which the state will [**5] satisfy the NAAQS, see id. §

7410(a). In the event that a state does not submit a SIP or

does not submit a satisfactory plan within the specified

time, the EPA Administrator shall promulgate a federal

implementation plan (FIP). See id. § 7410(c).

The Act specifies different standards that SIPs in

particulate matter nonattainment areas must satisfy,

depending on whether an area is designated as

"moderate" or "serious." A SIP for a PM-10 moderate

area must, among other things, include assurances that

"reasonably available control measures" (RACM) will be

implemented by the specified implementation deadlines.

42 U.S.C. § 7513a(a)(1)(C) (emphasis added); see also

id. § 7502(c)(1). All moderate areas were to reach

attainment by December 31, 1994. 42 U.S.C. §

7513(c)(1). By contrast, a state implementation plan for a

PM-10 serious area must satisfy the requirements for a

moderate area and must further demonstrate that the "best

avail-able control measures" (BACM) will be

implemented within four years after the area is classified

as "serious." 42 U.S.C. § 7513a(b)(1)(B) (emphasis

added). All [**6] serious areas were to reach attainment

by December 31, 2001. 42 U.S.C. § 7513(c)(2).

Finally, the Administrator may extend the attainment

date for a PM-10 serious area under various conditions

and after various procedures are satisfied. 42 U.S.C. §

7513(e). These include that attainment by the specified

date would be "impracticable," that the state "has

complied with all requirements and commitments

pertaining to that area in the implementation [*1030]

plan," and that 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." Id. The last of those three standards is referred

Page 2

366 F.3d 1025, *1028; 2004 U.S. App. LEXIS 9069, **2;

58 ERC (BNA) 1481
to as "most stringent measures" (MSM).

B. Proceedings Below

The proceedings below are both numerous and

complex. This is the fourth petition for review filed

before us concerning implementation of the particulate

matter NAAQS in the Phoenix metropolitan area. We

issued published opinions in the first two petitions and

dismissed the third petition [**7] as moot. Ober I, 84

F.3d 304; Ober v. Whitman, 243 F.3d 1190 (9th Cir.

2001) (Ober II); Ober v. Browner, No. 99-71107 (9th Cir.

Nov. 7, 2001) (order dismissing petition as moot); see

also Delaney v. EPA, 898 F.2d 687 (9th Cir. 1990)

(decided prior to the Clean Air Act Amendments of

1990), abrogation recognized by Ober I, 84 F.3d at 311.

Under the Act as amended in 1990, Phoenix was

designated by law as a moderate nonattainment area for

PM-10. 42 U.S.C. § 7513(a). In November 1991, Arizona

submitted its moderate area PM-10 state implementation

plan, which EPA rejected as incomplete. See Approval

and Promulgation of Implementation Plans; Arizona --

Phoenix Nonattainment Area; PM[10], 59 Fed. Reg.

38,402, 38,403 (July 28, 1994). Arizona submitted a

revised plan in 1994, which EPA approved. Approval and

Promulgation of Implementation Plans; Arizona --

Phoenix Nonattainment Area; PM[10], 60 Fed. Reg.

18,010 (Apr. 10, 1995). Phoenix residents petitioned this

court for review of EPA's action. We granted the petition

on the grounds that EPA failed to address [**8]

"reasonably available control measures" and other aspects

of the implementation plan for the 24-hour standard. We

held that the Act required Arizona to reduce violations of

the 24-hour standard irrespective of whether such

measures would contribute to attaining the annual

standard. Ober I, 84 F.3d at 309-11.

Contemporaneously with our decision, EPA found

that Arizona had not attained either the 24-hour standard

or the annual standard for PM-10 by the statutory

deadline, December 31, 1994. Clean Air Act

Reclassification; Arizona-Phoenix Nonattainment Area;

PM[10], 61 Fed. Reg. 21,372, 21,372-73 (May 10, 1996).

As a result of this finding, Arizona was reclassified as a

serious PM-10 nonattainment area by operation of law.

42 U.S.C. § 7513(b)(2)(A). Under the Act, Arizona had

to submit a new state implementation plan within

eighteen months. Id. § 7513a(b)(2).

Following our decision in Ober I and Arizona's

reclassification as a serious nonattainment area, EPA and

Arizona agreed that Arizona should divide its planning

efforts into two stages: the state would address the

moderate area and serious area requirements for the [**9]

24-hour standard first, and then would address the

requirements for the annual standard. In May 1997,

Arizona submitted its Plan for Attainment of the 24-hour

PM-10 Standard--Maricopa County PM-10

Nonattainment Area, known as the "Microscale Plan,"

which EPA approved in part and disapproved in part.

Approval and Promulgation of Implementation Plans:

Arizona--Maricopa County PM-10 Nonattainment Area,

62 Fed. Reg. 41,856, 41,856-57 (Aug. 4, 1997).

As a result of a consent decree entered in another

suit, EPA adopted its own moderate area FIP for Arizona.

Promulgation of Federal Implementation Plan for

Arizona--Phoenix PM-10 Moderate Area; Disapproval of

State Implementation Plan for Arizona--Phoenix PM-10

Moderate [*1031] Area, 63 Fed. Reg. 41,326, 41,328

(Aug. 3, 1998); see also 42 U.S.C. § 7410(c)(1). Phoenix

residents again petitioned for review in this court, and we

denied the petition. Ober II, 243 F.3d 1190. In 1999,

Arizona submitted a revised SIP with legislation

requiring adoption of a rule--known as the "general

permit rule"--addressing agricultural sources of PM-10.

EPA approved the new legislation as meeting the [**10]

RACM requirement and withdrew the FIP. Approval and

Promulgation of Implementation Plans;

Arizona--Maricopa Nonattainment Area; PM-10, 64 Fed.

Reg. 34,726 (June 29, 1999).

By early 2000, Arizona submitted its Revised MAG

[Maricopa Association of Governments] 1999 Serious

Area Particulate Plan for PM-10 for the Maricopa County

Nonattainment Area (Feb. 2000) (MAG Plan). The MAG

Plan, a substantially revised version of Arizona's SIP,

addressed both the annual and the 24-hour PM-10

standards for the first time. In April 2000, EPA proposed

to approve Arizona's SIP for the annual PM-10 standard

and solicited comments. 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. 19,964 (Apr.

13, 2000). In October 2001, EPA did the same with

respect to the 24-hour standard. Approval and

Promulgation of Implementation Plans;

Arizona--Maricopa County PM-10 Nonattainment Area;

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

Standard and Contingency Measures, 66 Fed. Reg.

Page 3

366 F.3d 1025, *1030; 2004 U.S. App. LEXIS 9069, **6;

58 ERC (BNA) 1481
50,252 (Oct. 2, 2001). That same month EPA approved

Arizona's [**11] general permit rule for control of

PM-10 from agricultural sources (regulations adopted

under the legislation EPA had approved as RACM in

1999) as satisfying the RACM standard. Approval and

Promulgation of Implementation Plans;

Arizona-Maricopa Nonattainment Area; PM-10, 66 Fed.

Reg. 51,869 (Oct. 11, 2001).

On July 25, 2002, EPA issued final approval of

Arizona's SIP for the Phoenix area for the 24-hour and

annual standards, and it granted Arizona's request to

extend the deadline for attaining those standards from

December 31, 2001, to December 31, 2006. Approval and

Promulgation of Implementation Plans;

Arizona--Maricopa County PM-10 Nonattainment Area;

Serious Area Plan for Attainment of the PM-10

Standards, 67 Fed. Reg. 48,718 (July 25, 2002). As EPA

noted, by this action EPA "had now approved all

elements of the serious area PM-10 plan for the Phoenix

area." 67 FR at 48,718. This petition for review of EPA's

final rule followed.

STANDARD OF REVIEW

We have jurisdiction to review EPA's approval of the

SIP under 42 U.S.C. § 7607(b)(1). This section does not

specify a standard of review, so we apply the general

standard [**12] of review for agency actions in the

Administrative Procedure Act: whether EPA's actions

were "arbitrary, capricious, an abuse of discretion, or

otherwise not in accordance with law." 5 U.S.C. §

706(2)(A). See Alaska Dep't of Envtl. Conservation v.

EPA, 540 U.S. 461, 157 L. Ed. 2d 967, 124 S. Ct. 983,

1006 & n.18 (2004); Arizona v. Thomas, 824 F.2d 745,

748 (9th Cir. 1987). We have stated that this standard

requires "the agency to 'articulate[] a rational connection

between the facts found and the choice made.'" Sierra

Club, 346 F.3d at 961 (quoting Ariz. Cattle Growers'

Ass'n v. United States Fish & Wildlife, 273 F.3d 1229,

1236 (9th Cir. 2001)). We have recently repeated that

courts must carefully review the record

to ensure that agency decisions are

founded on a reasoned evaluation of the

relevant factors, and may not rubber

[*1032] stamp . . . administrative

decisions that they deem inconsistent with

a statutory mandate or that frustrate the

congressional policy underlying a statute .

. . . Nevertheless, we may not substitute

[our] judgment for that of the agency . . . .

Friends of Yosemite Valley v. Norton, 348 F.3d 789, 793

(9th Cir. 2003) [**13] (citations and internal quotation

marks omitted). In particular, "where, as here, a court

reviews an agency action 'involving primarily issues of

fact,' and where 'analysis of the relevant documents

requires a high level of technical expertise,' we must

'defer to the informed discretion of the responsible

federal agencies.'" Sierra Club, 346 F.3d at 961 (quoting

Marsh v. Or. Natural Res. Council, 490 U.S. 360, 377,

104 L. Ed. 2d 377, 109 S. Ct. 1851 (1989)). "Even when

an agency explains its decision with 'less than ideal

clarity,'" we "will not upset the decision on that account

'if the agency's path may reasonably be discerned.'"

Alaska Dep't of Envtl. Conservation, 124 S. Ct. at 1006

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

Inc., 419 U.S. 281, 286, 42 L. Ed. 2d 447, 95 S. Ct. 438

(1974)).

When the court reviews EPA's construction of a

statute and the statute is either ambiguous or silent, the

question is whether "the agency's answer is based on a

permissible construction of the statute." Chevron U.S.A.

Inc. v. Natural Res. Def. Council, Inc., 467 U.S. 837, 843,

81 L. Ed. 2d 694, 104 S. Ct. 2778 (1984). Because there

is some question [**14] whether EPA has in fact

construed the provisions at issue here, we discuss the

legal standards set forth in the Clean Air Act and EPA's

efforts to construe them.

Under 42 U.S.C. § 7513a(b)(1)(B), each state

classified as a serious area for PM-10 shall submit an

implementation plan including "provisions to assure that

the best available control measures for the control of

PM-10 shall be implemented" no later than four years

after the area is classified as serious. This requirement is

in addition to the statutory mandate for moderate area

plans to include "provisions to assure that reasonably

available control measures for the control of PM-10 shall

be implemented" by a specified deadline. 42 U.S.C. §

7513a(a)(1)(C). The terms "reasonably available control

measures" and "best available control measures" are not

defined by the Act.

Congress has given EPA general rulemaking

authority, 42 U.S.C. § 7601(a)(1), which, when exercised,

requires our deference in accordance with Chevron.

Chevron, 467 U.S. at 843-44; Ober I, 84 F.3d at 307; see

Page 4

366 F.3d 1025, *1031; 2004 U.S. App. LEXIS 9069, **10;

58 ERC (BNA) 1481
also 42 U.S.C. § 7513b [**15] (requiring the

Administrator to issue technical guidance on RACM and

BACM for urban fugitive dust and other emissions by a

specified date). EPA has not, in fact, exercised its general

rulemaking authority to define these terms. Instead,

shortly after the enactment of the Clean Air Act

Amendments of 1990, EPA provided its "preliminary

views" on RACM and BACM in the form of "advance

notice of how EPA generally intends to take action on

SIP submissions and to interpret various PM-10 related

title I provisions." State Implementation Plans for Serious

PM-10 Nonattainment Areas, and Attainment Date

Waivers for PM-10 Nonattainment Areas Generally;

Addendum to the General Preamble for the

Implementation of Title I of the Clean Air Act

Amendments of 1990, 59 Fed. Reg. 41,998, 41,998 (Aug.

16, 1994) ("Addendum"); State Implementation Plans;

General Preamble for the Implementation of Title I of the

Clean Air Act Amendments of 1990, 57 Fed. Reg.

13,498, 13,498 (Apr. 16, 1992) ("General Preamble").

EPA advised that the views expressed in the Addendum

were "EPA's preliminary interpretations, and thus do not

bind the States and the public as a matter of law."

Addendum, [**16] 59 Fed. Reg. [*1033] at 41,999; see

also General Preamble, 57 Fed. Reg. at 13,498. Indeed,

EPA announced that its rules would be developed later,

through notice-and-comment rulemaking on state SIP

revisions or through subsequent notice-and-comment

rulemakings on Clean Air Act provisions. General

Preamble, 57 Fed. Reg. at 13,498. The General Preamble

and Addendum were simply "advance notice of how EPA

generally intended, in those subsequent rulemakings, to

take action." Id. EPA has never undertaken the

notice-and-comment rulemakings to which it adverted.

Furthermore, in the Addendum, EPA indicated that it

would issue future guidance on what constituted "most

stringent measures" for granting an extension of the

attainment date. 59 Fed. Reg. at 42,002. EPA has never

issued such guidance. Thus, the only guidance we have

from EPA is its "preliminary interpretations" that "do not

bind the States and the public as a matter of law," and

EPA's ruling in this matter, which binds Arizona.

Under the familiar two-step analysis in Chevron, if

Congress has "directly spoken to the precise question at

issue," then the matter is capable of but [**17] one

interpretation by which the court and the agency must

abide. Chevron, 467 U.S. at 842. By contrast, where we

determine that a statute is not clear, "the question for the

court is whether the agency's answer is based on a

permissible construction of the statute." Id. at 843. The

principal statutory terms at issue here-- "reasonably

available control measures," "best available control

measures," and "most stringent control measures"--are

not terms as to which there can be but one view of the

law. Indeed, they fairly exude ambiguity and invite

debate. Congress has left it to EPA to fill the gaps in

meaning in these provisions.

Chevron deference, however, does not apply to the

General Preamble and Addendum, as they specifically

recite that they constitute EPA's preliminary guidance

and do not have the force of law. "Interpretations such as

those . . . contained in policy statements, agency manuals,

and enforcement guidelines, all of which lack the force of

law--do not warrant Chevron-style deference."

Christensen v. Harris County, 529 U.S. 576, 587, 146 L.

Ed. 2d 621, 120 S. Ct. 1655 (2000); see Hall v. EPA, 273

F.3d 1146, 1155-56 (9th Cir. 2001). [**18] Such views,

however, even if not authoritative for purposes of

Chevron, are entitled to so-called Skidmore deference

insofar as they "constitute a body of experience and

informed judgment to which courts and litigants may

properly resort for guidance." Skidmore v. Swift & Co.,

323 U.S. 134, 140, 89 L. Ed. 124, 65 S. Ct. 161 (1944).

"Cogent administrative interpretations . . . not the

products of formal rulemaking . . . nevertheless warrant

respect." Alaska Dep't of Envtl. Conservation, 124 S. Ct.

at 1001 (citation, internal quotation marks, and brackets

omitted); see also United States v. Mead Corp., 533 U.S.

218, 227-31, 150 L. Ed. 2d 292, 121 S. Ct. 2164 (2001);

Wilderness Soc'y v. United States Fish & Wildlife Serv.,

353 F.3d 1051, 1059-60, 1067-69 (9th Cir. 2003) (en

banc), amended by 360 F.3d 1374 (9th Cir. 2004) (en

banc); Pronsolino v. Nastri, 291 F.3d 1123, 1131 (9th

Cir. 2002), cert. denied, 539 U.S. 926, 123 S. Ct. 2573,

156 L. Ed. 2d 602 (2003). EPA's interpretations of the

Act, as expressed previously in the General Preamble and

Addendum and applied here in the approval of Arizona's

[**19] SIP, are entitled to respect.

ANALYSIS

Petitioners challenge three aspects of EPA's final

rule. First, petitioners claim that Arizona's general permit

rule for agricultural PM-10 emissions does not [*1034]

constitute either BACM or MSM. Second, petitioners

argue that Arizona's controls of diesel emissions do not

constitute BACM or MSM. Consequently, petitioners

argue, EPA's approval of Arizona's plan was arbitrary and

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58 ERC (BNA) 1481
capricious or otherwise not in accordance with law.

Third, petitioners claim that the Administrator abused his

discretion when he extended the attainment date for

Arizona to 2006. We consider each of these arguments in

turn.

A. Arizona's General Permit Rule for Agriculture

In May 1998, the Arizona legislature enacted

legislation creating an agricultural best management

practices (BMP) committee. ARIZ. REV. STAT. §

49-457(A) (1998). The committee--which consisted of a

representative of the Arizona Department of

Environmental Quality, representatives of state and

federal agricultural agencies, agriculture experts from the

University of Arizona, and farmers, id. § 49-457(B) --was

required to adopt an "agricultural general permit

specifying [**20] best management practices for

regulated agricultural activities to reduce pm-10

particulate emissions," id. § 49-457(H). The committee

considered 65 management practices and evaluated them

using available information on technological feasibility,

costs, and energy and environmental impacts. See 66 Fed.

Reg. at 50,268. "After an analysis of the limited

information available and numerous public discussions,"

the committee decided to include 34 of the practices in

the general permit rule and divided them among three

categories of farm activities (tillage and harvest,

noncropland, and cropland) specified in the statute. 66 FR

at 50268-69. In May 2000, the Arizona Department of

Environmental Quality adopted the rule as ARIZ.

ADMIN. CODE § R18-2-611 (2000). The regulation

establishes the three categories of farm activities, sets out

the 34 BMPs (dividing them among the three categories),

and requires commercial farmers to implement at least

one BMP per category. Id. The only exception is that a

person may develop PM-10 reduction practices not listed

in the rule, but such practices must be "proven effective

through on-farm demonstration trials" and [**21]

submitted to the committee for review. Id. §

R18-2-611(H).

In October 2001, EPA approved Arizona's general

permit rule as RACM and observed that the rule in fact

"far exceeded the RACM requirements." 66 Fed. Reg. at

51,871 n.7. Petitioners did not challenge EPA's final rule.

Petitioners now challenge the general permit rule on

two grounds. First, petitioners argue that, because BACM

requires a stricter showing than RACM and RACM

requires implementation of "all reasonably available

control measures," 42 U.S.C. § 7502(c)(1) (emphasis

added), but the general permit rule mandates only one

BMP in each category, the rule cannot satisfy BACM.

Second, petitioners argue that the general permit rule

cannot satisfy the MSM requirement because it fails to

adopt practices implemented in California's South Coast

region.

1. Arizona's general permit rule as BACM

Petitioners do not challenge any particular practice

adopted as BACM. 2 Rather, petitioners contend that

there is no reason why Arizona could not require farmers

to [*1035] implement more than one control measure in

each category. Petitioners point out that because, in one

sense, Arizona has already [**22] found these measures

to be "feasible," more than one measure must be

implemented. As a matter of theory, petitioners are, of

course, correct. Intuitively, it seems obvious to say that if

one measure per category is good, two or more would be

better. Petitioners' argument proves too much, however.

By petitioners' logic, if two are better than one, three are

better than two, and so forth. We have little doubt that if

Arizona required all of these measures, it would achieve

greater reductions than under its present plan.

2 Any challenge to EPA's approval of the rule

under the RACM standard --an action EPA took

in October 2001, see 66 Fed. Reg. 51,869 (Oct.

11, 2001)--is untimely. See 42 U.S.C. § 7607(b)

("Any petition for review under this subsection

shall be filed within sixty days from the date

notice of such promulgation, approval, or action

appears in the Federal Register."); 67 Fed. Reg. at

48,728.

Petitioners' argument would be compelling if the

[**23] Act required a state to reduce its emissions to the

maximum extent possible, regardless of cost. EPA,

however, has concluded that "best available control

measures" means

the maximum degree of emissions

reduction of PM-10 and PM-10 precursors

from a source . . . which is determined on

a case-by-case basis, taking into account

energy, environmental, and economic

impacts and other costs, to be achievable

for such source through application of

production processes and available

methods, systems, and techniques for

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58 ERC (BNA) 1481
control of each such pollutant.

Addendum, 59 Fed. Reg. at 42,010. Petitioners do not

challenge this longstanding interpretation of the Act, and

we cannot say that the interpretation is impermissible.

See Alaska Dep't of Envtl. Conservation, 124 S. Ct. at

1001; cf. 42 U.S.C. § 7479(3) (similarly defining the term

"best available control technology" for purposes of the

Prevention of Significant Deterioration program). Our

task, therefore, is to determine whether EPA has properly

concluded that Arizona has provided for the maximum

degree of emissions reduction, all things considered.

In its state implementation [**24] plan, Arizona

explained why it listed 34 BMPs in three categories, yet

required farmers to implement only three BMPs (one

BMP in each category). Arizona reported that an

effective agricultural PM-10 control strategy is "highly

dependent on specific local factors," such as "regional

climate, wind strength and direction, soil types, growing

season, crop types, cropping systems, moisture

conditions, water availability, and relation to urban

centers." Air Quality Div., Ariz. Dep't of Envtl. Quality,

Maricopa County PM[10] Serious Area State

Implementation Plan Revision: Agricultural Best

Management Practices, Enclosure 3 at 17-18 (June 13,

2001) (BMP Plan). Thus, "each PM[10] agricultural

strategy must be based on local circumstances and a

single BMP will not work equally well for all growers."

Id. at 17. Arizona's plan stated that farmers were

"encouraged to implement more than one BMP," but "it

is not reasonable to require more than one BMP because

in some instances one may be enough for a particular

farm." Id. at 18 (emphasis added). The committee "could

not determine that requiring more than one BMP would

be reasonable given the cost and emission reduction

uncertainties. [**25] " Id. at 18.

EPA concluded that the committee's review was

thorough and found that the general permit rule met

BACM. 66 Fed. Reg. at 50,268-69; see also 67 Fed. Reg.

at 48,731; U.S. Envtl. Prot. Agency, Final Technical

Support Document 233, 238-40 (Jan. 14, 2002) (TSD). 3

"Based on the BMP committee's findings regarding

technological [*1036] feasibility and economic effects

of requiring more than one BMP per category, we believe

that the BMP rule provides the maximum degree of

emission reductions achievable from the agriculture

source category in the Phoenix area and, therefore, meets

the BACM requirement." 66 Fed. Reg. at 50,269; TSD at

238. EPA found that listing options was "an acceptable

form for the implementation of BACM," as it accounts

for the variable nature of farming and the varying

economic circumstances of farmers. TSD at 239.

Allowing an individual source to select the control

method is a

common and accepted practice for the

control of dust. . . . Allowing sources the

discretion to choose from a range of

specified options is particularly important

for the agricultural sector because of the

variable nature of farming. As [**26] a

technical matter, neither we nor the State

is in a position to dictate what precise

control method is appropriate for a given

farm activity at a given time in a given

locale . . . . Moreover, the economic

circumstances of farmers vary

considerably. As a result, it is imperative

that flexibility be built into any PM-10

control measure for the agricultural source

category.

66 Fed. Reg. at 50,269; see also TSD at 239. 4 EPA

concluded that the "general permit rule represents a

comprehensive, sensible approach" and satisfied BACM

with respect to both the 24-hour and the annual standards.

TSD at 240.

3 Page references to the TSD correspond with

the version available in three sections on the

EPA's website at

http://www.epa.gov/region9/air/phoenixpm

/tsd10102.pdf,

http://www.epa.gov/region9/air/phoenixpm

/tsd20102.pdf, and

http://www.epa.gov/region9/air/phoenixpm

/tsd30102.pdf.

4 EPA noted that listing options is a common

method for controlling dust from other sources,

such as unpaved roads, and that EPA has

approved similar rules for fugitive dust control as

both RACM and BACM. 66 Fed. Reg. at 51,871.

[**27] In developing the BMPs for the general

permit rule, the Arizona committee considered

agricultural PM-10 controls adopted by the South Coast

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58 ERC (BNA) 1481
region of California. BMP Plan at 15, 18. It noted,

however, that the South Coast was the only other area in

the United States to require the implementation of BMPs

to reduce agricultural PM-10 and that information

concerning the effectiveness and cost of these BMPs was

therefore limited. Id. at 18. EPA accepted Arizona's

conclusions that agricultural production differs from farm

to farm and that it was not possible to compare directly

Arizona agriculture and California agriculture.

"Agricultural PM-10 strategies must be based on local

factors because of the variety, complexity, and

uniqueness of farming operations and because

agricultural sources vary by factors such as regional

climate, soil type, growing season, crop type, water

availability, and relation to urban centers." 67 Fed. Reg.

at 48,730; see also 66 Fed. Reg. at 50,269. Agricultural

sources are unlike other stationary sources and are unlike

sources such as automobiles that have common design

features and may be subjected to a common or uniform

control [**28] measure. EPA also acknowledged that the

BMP committee had very limited information regarding

the technological feasibility, costs, and energy and

environmental impacts of the potential BMPs. Id. Indeed,

EPA found that Arizona could not evaluate the South

Coast's practices because "the South Coast did not

attempt to estimate the reductions and cost from each

conservation practice." TSD at 236. EPA reported that, in

developing the FIP in 1998, it considered the South Coast

rules; but because "the two areas differ in a number of

key characteristics," EPA decided not to propose the

South Coast rules for Arizona "because the Agency could

not reasonably conclude that their implementation would

in fact result in air quality benefits for the Maricopa

nonattainment area." 66 Fed. Reg. at 51,872.

[*1037] EPA not only examined Arizona's final

rule and rationale, it looked closely at the process by

which Arizona arrived at its BMP Plan. Arizona

assembled representatives from agriculture, state and

federal agencies, and the University of Arizona--"a

multi-year endeavor involving an array of agricultural

experts familiar with Maricopa County agriculture." 67

Fed. Reg. at 48,730; [**29] see also TSD at 240; 66 Fed.

Reg. at 50,268-70. The BMP Committee held public

hearings and received public comments. It thoroughly

reviewed the South Coast rules and found that certain

aspects of them were not adapted to Arizona's conditions.

Taking into account the uncertainties involved in

pre-scribing agricultural rules, the measures that Arizona

adopted, and the process by which Arizona arrived at its

BMPs, we cannot conclude that EPA's approval of

Arizona's general permit rule as BACM was arbitrary and

capricious. Even as EPA approved the general permit rule

as RACM in 2001, EPA concluded that the rule "far

exceeded" the RACM standard. 66 Fed. Reg. at 51,871

n.7. EPA's approval of the general permit rule as BACM

is thus consistent with its long-standing view that BACM

suggests "a generally higher standard of performance"

than RACM. Addendum, 59 Fed. Reg. at 42,010. Arizona

has offered a reasoned explanation for the choices it

made, and EPA was within the bounds of its judgment

and expertise to approve it.

2. Arizona's general permit rule as MSM

Petitioners argue that Arizona's plan does not

implement MSM because Arizona has not adopted [**30]

certain measures that California implemented in the

South Coast Air Quality Management District (District).

The District includes the South Coast Air Basin (Basin)

(encompassing Orange County and portions of Los

Angeles, Riverside, and San Bernardino Counties), the

Coachella Valley, and other territory. Specifically,

petitioners claim that the District requires growers to

cease tilling on high wind days and to adopt more BMPs.

In contrast to BACM, MSM requires a comparative

inquiry. The Act does not define MSM, but refers to it as

"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." 42 U.S.C. § 7513(e) (emphasis added). The

Act also explicitly permits the EPA Administrator, in

determining whether to grant an extension and how long

it should be, to consider, among other things, "the

technological and economic feasibility of various control

measures." Id. § 7513(e). EPA has defined MSM as "the

maximum degree of emission reduction that has been

required or achieved from a source or source category in

other SIPs or in practice in other [**31] states and can be

feasibly implemented in the area." 66 Fed. Reg. at

50,282. EPA interprets MSM "to not require any measure

that is infeasible on technological or economic grounds,

any measure for insignificant source categories, and any

measure or group of measures that would not contribute

to expeditious attainment." 67 Fed. Reg. at 48,729.

As noted above, petitioners argue that Arizona's

general permit rule fails to adopt MSM in two respects: it

requires producers to implement fewer BMPs than the

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58 ERC (BNA) 1481
District's Handbook requires, and it does not mandate

cessation of tilling on high-wind days as the District

does. As a preliminary matter, petitioners

oversimplify--and overstate--the District's requirements,

as EPA explained. 67 Fed. Reg. at 48,729-30. The true

comparative baseline for MSM would take into account

the many exceptions and exemptions to the District's

requirements. See, e.g., Rule 403(h)(1)(A) (exempting all

farms outside the Basin and all [*1038] small farms

within the Basin from the dust-reducing BMPs);

Handbook at 1 n.1, 4-5, 11-12 (detailing various

exceptions). Yet, even with a more realistic

understanding of the substance of the District's [**32]

requirements, two questions remain: Are the District's

requirements more stringent than Arizona's? If so, must

Arizona adopt the District's requirements in order to

satisfy the MSM standard?

EPA found that, even without petitioners'

exaggerations, the District's requirements are "likely to be

more stringent than [Arizona's] general permit rule." 67

Fed. Reg. at 48,730. Given the exemptions and

alternatives available in the District, it is not clear what

basis EPA had for this assumption. For example, the

District's Handbook exempts entirely harvesting,

orchards, vine crops, nurseries, range land, and irrigated

pasture. Arizona's general permit rule does not exempt

any agricultural activities. In this regard, Arizona's rule is

stricter than the Handbook. Nevertheless, we will accept

EPA's assumption that the Handbook is likely to be more

stringent.

Once the District's requirements are determined to be

more stringent, Arizona must adopt those of the District's

requirements [*1039] that "can feasibly be

implemented" in Arizona, taking into consideration the

"technological and economic feasibility of various

control measures." 42 U.S.C. § 7513(e). EPA concluded

[**33] that the District's requirements were not feasible

for Arizona and, therefore, that Arizona need not adopt

the requirements to satisfy MSM. As we explain below,

this conclusion was not arbitrary or capricious.

EPA agreed "with the State's assessment that the

South Coast requirements are infeasible for the Phoenix

area and that the general permit rule represents the most

stringent economically and technologically feasible

agricultural control program for the area." 67 Fed. Reg. at

48,730. Arizona pointed out that agriculture is bound by

conditions specific to each locale and that generalizations

in this area are not helpful. Id. Arizona's topography, soil

conditions, crops, and irrigation methods differ

substantially from California's. Id. For example, the three

biggest crops in Maricopa County are upland cotton,

durum wheat, and alfalfa, with cotton comprising more

than the combined acreage of wheat and alfalfa. TSD at

224. By contrast, no cotton is grown in the South Coast

Air Basin. Id. at 236. Arizona's farmers irrigate by

flooding their fields, whereas farmers in the South Coast

region dry farm, irrigate, or use sprinkler irrigation. 67

Fed. Reg. at 48,730; [**34] BMP Plan at 27. As Arizona

found, "'the actual amount of irrigation water and

frequency of irrigation can effect [sic] wind erosion

estimates and the effectiveness of different control

measures under different conditions.'" 67 Fed. Reg. at

48,730 (quoting BMP Plan at 27). The application of

more than one BMP at a time for a particular category

"'would only provide incremental PM-10 reductions,

sometimes at an uneconomical cost.'" Id. (Implicitly, the

same objection applies to imposing a mandatory no-till

rule plus other BMPs.) The declining trend in the number

of farms operating in Maricopa County and uncertainty

about the "continued viability of agriculture in Maricopa

County" added to EPA's concerns about the economic

feasibility of requiring more BMPs. Id. Finally, as in the

BACM analysis, EPA noted that the process by which

Arizona developed the general permit rule "was a

multi-year endeavor involving an array of agricultural

experts familiar with Maricopa County agriculture." Id.

EPA concluded that the Handbook's requirements "are

neither technologically nor economically feasible for

Maricopa County." Id.

This conclusion was not arbitrary or capricious.

[**35] As noted above, 42 U.S.C. § 7513(e) specifically

limits MSM to measures that "can feasibly be

implemented in the area," and specifically allows the

Administrator to consider the "technological and

economic feasibility" of proposed measures. Here, EPA

did precisely that, and its conclusion was reasonable.

Regarding cessation of tilling during high-wind

conditions, Arizona explained, and EPA agreed, that

wind conditions in Arizona are quite different from those

in the Coachella Valley (which is subject to Rule 403.1,

the District's most stringent no-till rule). 67 Fed. Reg. at

48,729. Arizona studies determined that it was not the

active tilling of a field that primarily contributed

windblown dust, but instead it was dust from an already

tilled field. Id. A tilling-cessation rule would not address

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58 ERC (BNA) 1481
the source of fugitive dust unless it forbade tilling

altogether. The studies showed that the Coachella Valley

experiences winds of greater duration and speed than

Arizona. The Coachella Valley reports high winds (over

25 mph) on 47 days per year. Id. By contrast, Arizona

estimated that in 1995 Maricopa County had only 11 days

of winds over 15 mph. [**36] Id. Arizona further found

that only 15 percent of the tilling takes place during the

area's high wind season (March through September), and

only 4 percent of the days during that time experience

high winds (over 15 mph). Id. Arizona concluded that

any benefits from a tilling-cessation rule would be

minimal and such a rule would be no more effective than

other BMPs. TSD at 236. "More PM[10] reductions will

be achieved by implementing practices which control

PM[10] emissions throughout the year or during critical

erosions periods." BMP Plan at 27. According to

Arizona, EPA observed, a tilling-cessation rule on high

wind days would not be reasonable "since it would

impact a small number of growers and provide minimal

reductions." 67 Fed. Reg. at 48,729. EPA concluded that

this justification was sufficient because (1) the rule was

not necessary for expeditious attainment and (2) Arizona

had determined that "the requirement for one BMP per

category is the most effective economically and

technologically feasible control measure for agricultural

sources in the Phoenix area." Id.; see also TSD at 240-41.

In other words, EPA declined to require Arizona to adopt

[**37] the Coachella Valley's no-till rule based on

attainment and feasibility considerations. As noted above,

the Act explicitly allows EPA to take technological and

economic feasibility into account in determining whether

a state has satisfied the MSM standard, and EPA properly

did so here.

B. Arizona's Rejection of CARB Diesel

1. CARB Diesel as BACM

Petitioners do not challenge the bulk of Arizona's

plan for addressing on-road and non-road emissions.

Instead, they have confined their challenge to one aspect

of Arizona's plan, its rejection of CARB diesel, a

reformulated diesel fuel required by the California Air

Resources Board since 1993. Petitioners offer two points.

First, they argue that diesel emissions, considered alone,

constitute a significant source of emissions. Petitioners

contend that EPA allowed Arizona to reject CARB diesel

as BACM because EPA considered diesel emissions to be

a de minimis source. Second, petitioners argue that EPA

has not offered an adequate explanation for rejecting

CARB diesel as BACM.

EPA generally requires state implementation plans to

address all significant source categories and permits

states to ignore "de minimis" source categories. [**38]

See 67 Fed. Reg. at 48,720 ("EPA interprets the [Clean

Air Act] to not require a state to apply BACM to any

source or source category that it has demonstrated to be

de minimis"). 5 EPA has stated it [*1040] will "not

consider a source category or groups of source categories

to be de minimis if applying BACM to it or them . . .

would make the difference between attainment and

nonattainment by December 31, 2001 in areas requesting

an extension." 67 Fed. Reg. at 48,721. But EPA does not

require that each significant source be addressed as a

separate category. In theory, a state might define its

source categories so narrowly that all of its categories

would be de minimis. See Ober II, 243 F.3d at 1198 n.4.

Conversely, a state might define its source categories so

broadly that a single source category might include

several significant sources.

5 EPA has established a de minimis threshold of

5 g/m[3] for the 24-hour standard and a 1 g/m[3]

de minimis threshold for the annual standard. 67

Fed. Reg. at 48,720; see also 66 Fed. Reg. at

50,257 & n.12.

[**39] In its state implementation plan, Arizona

identified eight significant source categories--paved road

travel, unpaved road travel, industrial paved road travel,

construction site preparation, agricultural tilling,

residential wood combustion, on-road and non-road

motor vehicle exhaust, and secondary ammonium

nitrate--and twelve categories of "de minimis" sources. 6

MAG Plan, Table 9-1 at 9-9; 65 Fed. Reg. at 19,972.

Although Arizona determined that motor vehicle exhaust

was a significant source of PM-10, it also found that

exhaust was a relatively small source of PM-10. Arizona

found, for example, that non-road engine exhaust

contributed only 4.3 percent of total regional PM-10

emissions in 1995, and on-road vehicle exhaust just 2.3

percent, compared with construction/earth moving dust,

construction trackout, paved road dust, unpaved road

dust, and disturbed vacant land and agricultural

wind-blown dust, which contributed 23.4, 13.0, 17.7,

12.9, and 14.9 percent, respectively. MAG Plan, Figure

3-1. EPA found that "no significant source categories

were excluded," and even that Arizona "may have

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58 ERC (BNA) 1481
included more source categories in its significant source

list than are strictly [**40] needed." 65 Fed. Reg. at

19,972. Arizona proposed a series of controls to address

each source category.

6 The twelve de minimis sources were: fuel

combustion (excluding residential wood

combustion), waste/open burning, agricultural

harvesting, cattle feedlots, structural/vehicle fires,

charbroiling/frying meat, marine vessel exhaust,

airport ground support exhaust, railroad

locomotive exhaust, fluvial channels, and wild

fires. MAG Plan, Table 9-a, at 9-11.

Arizona's "on-road and non-road motor vehicle

exhaust" category included vehicles powered by gasoline,

diesel, and other sources. EPA observed that gasoline and

diesel vehicles could be considered distinct categories,

and it suggested that the category identified by Arizona

"constituted at least four if not more distinct categories of

emissions: gasoline on-road, diesel on-road, gasoline

nonroad, and diesel nonroad." TSD at 82 n.10. EPA also

acknowledged that "each of these individual categories

may or may not be significant itself." Id. [**41] EPA

noted, nonetheless, that it would

treat gasoline-[]and diesel-powered

vehicles together here to preserve to the

extent practicable the significant source

groupings in the MAG plan; however, we

believe they are in fact distinct categories.

Almost 95 percent of diesel PM-10

emissions come from heavy-duty diesel

trucks while 75 percent of gasoline PM-10

comes from the family car, that is, light

duty cars and trucks . . . . There is almost

no overlap in the controls for the family

car and those for heavy duty diesel trucks,

key evidence that they are in fact distinct

source categories.

65 Fed. Reg. at 19,972 n.10. In the end, EPA chose to

analyze Arizona's "on-road and non-road motor vehicle

exhaust" category [*1041] as two categories: on-road

exhaust and non-road exhaust.

With respect to petitioners' first point--that diesel

emissions are a significant source--EPA did treat diesel

emissions as significant (not de minimis) for purposes of

the BACM analysis. EPA analyzed whether Arizona's

plan adequately controlled emissions from two source

categories, on-road exhaust and non-road exhaust. Each

of those categories included diesel engine exhaust.

Petitioners would [**42] prefer that EPA have

treated both on-road and non-road diesel emissions as a

single source, separate from all other on-road and

non-road exhaust. Under EPA's guidelines, Arizona had

to address all significant source categories, and diesel

emissions were included in the on-road/non-road

emissions category, which Arizona properly treated as a

significant source category. It might have been possible

for Arizona to classify diesel emissions as its own source

category--as EPA suggested would have been useful --but

it was not arbitrary and capricious for EPA to approve

Arizona's listing of the broader categories. That Arizona

might have done something different does not render its

plan violative of the Act, nor EPA's approval arbitrary

and capricious. Even if Arizona had classified diesel

emissions alone as a significant source category, the mere

classification would not tell us whether Arizona had to

adopt CARB diesel.

What petitioners' argument fairly questions is

whether Arizona has adequately addressed diesel

emissions as BACM. Arizona evaluated approximately

30 suggested measures for on-road emissions and 8 for

non-road emissions, most of which it adopted in whole or

in part. TSD, [**43] Table OR-4 at 112-25, Table

NRM-3 at 155-57. The Arizona plan adopted several

programs to address on-road and non-road diesel

emissions in particular. For example, the state requires

certain pre-1988, heavy-duty diesel-powered vehicles to

meet 1988 federal emission standards; it establishes a

voluntary vehicle repair and retrofit program for older

heavy-duty diesel vehicles; it requires public agencies to

install oxidation catalysts on the heavy-duty diesel

vehicles in their fleets if the agencies receive a waiver to

opt out of alternative fuel requirements; it increases the

waiver repair amounts for heavy-duty diesel vehicles that

fail to meet emission standards; it requires heavy-duty

diesel vehicles to take an annual snap acceleration test

and authorizes random roadside emission tests for diesel

vehicles; it limits sulfur content of diesel oil to 500 ppm;

and it adopts non-road emission standards for certain

diesel engines. Id. Thus, Arizona has addressed diesel

emissions with numerous measures for reducing them.

Despite the manifest evidence of Arizona's efforts to

address diesel emissions, we cannot conclude on this

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58 ERC (BNA) 1481
record that EPA has adequately considered whether

CARB diesel [**44] is BACM for diesel emissions in

the Phoenix area. Our determination follows from the

way in which EPA reviewed Arizona's rejection of

CARB diesel. EPA ignored Arizona's proffered reason

for omitting CARB diesel from its plan. The MAG Plan

rejected CARB diesel as BACM because "it was not

technologically and economically feasible to implement

[CARB diesel] at this time." MAG Plan at 9-46. The

MAG Plan explained that "it is unclear whether there is

an adequate supply of CARB Diesel fuel for the Arizona

market and whether the increased demand resulting from

an Arizona regulation would have a significant impact on

the cost of the fuel (which is currently estimated to cost 6

[cent] more per gallon than the # 2 Diesel sold in Arizona

at this time)." Id. 7 The Plan noted that [*1042] other

actions Arizona had taken to control PM-10 emissions

from diesel-fueled vehicles "represent some of the most

stringent measures in the country." Id.

7 Amicus American Trucking Association

elaborated on this point, claiming that the Arizona

legislature found that the only refineries currently

producing CARB diesel are in California, and

observing that Arizona has no refineries of its

own. The Association also argued that, according

to the Arizona legislature, if Arizona imposed

CARB diesel only in the affected air quality

region--the Phoenix metropolitan area-- diesel

users could refuel outside the attainment area and

thereby reduce the effectiveness of the measure.

Neither EPA nor Arizona specifically addressed

these arguments.

[**45] EPA made no explicit comments on

Arizona's cost objection in its discussion of CARB diesel

as BACM (it did comment on the objection, but only with

regard to MSM). Instead, with respect to on-road

emissions, EPA concluded that Arizona's plan for

addressing them was "one of the nation's most

comprehensive programs." 67 Fed. Reg. at 48,725; see

also 66 Fed. Reg. at 50,259; 65 Fed. Reg. at 19,973. EPA

found that the overall mobile source program was

"strengthened and goes beyond the existing federal

program," that "strengthening and expanding existing

programs are key criteria for demonstrating the

implementation of BACM," and that "where the MAG

plan has rejected potential BACM, it provides a reasoned

and acceptable justification for the rejection." 66 Fed.

Reg. at 50,259.

With respect to non-road emissions, EPA similarly

found that Arizona had evaluated "a comprehensive set of

potential measures for nonroad engines." 66 Fed. Reg. at

50,260; 65 Fed. Reg. at 19,974. EPA noted that it had

previously adopted federal non-road engine emission

standards and that these standards applied in Arizona and

"constituted [**46] at a minimum a RACM-level

program." 66 Fed. Reg. at 50,260. EPA concluded that

Arizona's "overall nonroad engine program is

strengthened and goes beyond the existing federal

program," that "strengthening and expanding existing

programs are key criteria for demonstrating the

implementation of BACM," and that "where the MAG

plan has rejected potential BACM, it provides a reasoned

justification for the rejection." Id.

On appeal, EPA contends that its statements that

Arizona had strengthened and expanded existing on-road

and non-road emissions controls should suffice as an

explanation of why these controls satisfied the BACM

standard. EPA also, however, referred to the Arizona plan

as having provided a reasoned justification when it

rejected potential BACM--with good reason, as EPA has

described one of the steps for identifying BACM as

"providing for the implementation of the BACM or

providing a reasoned justification for rejecting any

potential BACM." 66 Fed. Reg. at 50,281.

We are unable to find the reasoned justification for

rejecting CARB diesel as BACM to which EPA refers.

Neither the proposed rules nor the final rule provides any

reasoning relevant [**47] to CARB diesel and BACM

beyond what we have quoted above. The justification

cannot be cost, as suggested by the state. In explaining

why CARB diesel was not required as MSM, EPA

specifically declined to take a position on that particular

justification. 67 Fed. Reg. at 48,725. In the part of the

TSD concerning on-road measures, EPA's comment on

why BACM does not require CARB diesel simply

cross-references the MSM discussion of CARB diesel,

without further explanation. TSD, Table OR-4, at 123.

Yet, the TSD section on non-road measures does not list

CARB diesel as a suggested BACM at all. TSD, Table

NRM-3, at 155-57.

[*1043] We are left puzzled by a record that

approves Arizona's diesel emissions measures as BACM

but refers to MSM. This would not pose a problem if

BACM were equivalent to, or a subset of, MSM. But

EPA has not found that BACM and MSM are the same; it

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58 ERC (BNA) 1481
regards the BACM and MSM inquiries as overlapping in

some respects, but distinct. 66 Fed. Reg. at 50,283. In

particular, EPA interprets MSM to allow consideration of

whether the measures in question will advance attainment

of the NAAQS. 66 FR at 50,284. In fact, the agency

rejected CARB diesel [**48] as MSM on the grounds

that the measure would not advance attainment. 67 Fed.

Reg. at 48,275. In contrast, EPA has stated that the

BACM analysis should be conducted generally

independent of attainment. Addendum, 59 Fed. Reg. at

42,011. Thus, the justification that EPA offered for

rejecting CARB diesel under the MSM standard does not

support rejecting it under the BACM standard. In short,

EPA's approval of the rejection of CARB diesel under the

BACM standard referred to a nonexistent justification

and was therefore arbitrary and capricious.

We wish to make clear that we have not concluded

that it would be arbitrary and capricious for EPA to reject

CARB diesel as BACM in Arizona. There may be a good

explanation for why CARB diesel is not BACM in

Arizona. It may be that diesel emissions are "de

minimis," or that CARB diesel is not economically

feasible, or that there is not an adequate supply, or that

CARB diesel would not significantly reduce diesel

emissions. It may be that EPA has revised its

interpretation of BACM to allow consideration of

attainment (and can explain the revision), or that EPA has

revised its interpretation of BACM not to require the state

[**49] to justify rejecting each potential BACM on an

individual basis (and can explain the revision). But EPA

has not done the hard work. Arizona has offered one

explanation, which EPA has declined to ratify, and EPA

has not proffered an adequate explanation of its own.

"Whether the result of inadvertence or of an unexplained

change of course," EPA's failure to give a full

explanation of whether CARB diesel is BACM is

arbitrary and capricious. Sierra Club v. EPA, 352 U.S.

App. D.C. 357, 294 F.3d 155, 163 (D.C. Cir. 2002). We

cannot discern EPA's reasoning on the basis of the record

before us, and we must remand for further consideration.

Hall, 273 F.3d at 1161.

2. CARB Diesel as MSM

Petitioners argue that 42 U.S.C. § 7513(e) requires

that attainment be as "expeditious" as possible and that

adopting CARB diesel would contribute to attainment.

Therefore, they conclude, Arizona must adopt CARB

diesel. Petitioners fault EPA for not requiring Arizona to

adopt CARB diesel when it was "indisputably a more

stringent measure."

In its final rule, EPA specifically responded to

petitioners' criticism. EPA took note that Arizona had

rejected [**50] CARB diesel as infeasible because of its

cost. 67 Fed. Reg. at 48,725. Acknowledging that it could

not verify Arizona's claim because of "uncertainties

regarding [the] cost estimate," EPA framed the question

as "whether we could still approve the MSM

demonstration without CARB diesel and absent a

reasoned justification for not including it." Id. EPA stated

that its "sole criterion for determining if the plan provides

for MSM" was whether Arizona "has excluded any

feasible MSM or a group of feasible MSMs that, if

adopted and implemented early, would result in

attainment of the PM-10 standards more expeditiously."

Id. EPA found that implementation of CARB diesel

would reduce emissions from on-road and non-road

engines only, and these were "not implicated in 24-hour

exceedances of [*1044] the PM-10 standard." Id.

Rather, with one exception, the exceedances in Phoenix

were due "exclusively" to windblown dust. Id.

Accordingly, "introducing CARB diesel would not

contribute to expeditious attainment of the 24-hour

standard." Id. EPA further found that adoption of CARB

diesel would not contribute to meeting the annual

NAAQS for PM-10. Id. Fugitive dust remained [**51]

the largest contributor to the annual standard

exceedances, with the on-road and non-road sources

"contributing little." Id. Thus, "the small emission

reduction associated with the introduction of CARB

diesel would not advance the attainment date in the area,

either by itself or in combination with other measures."

Id.; see also TSD, Table OR-4 at 126, Table NRM-3 at

157-58.

We need not decide whether EPA's explanations are

reasonable. In light of our disposition with respect to

CARB diesel as BACM, we remand to EPA for further

consideration of whether CARB diesel satisfies MSM as

well. We do so because it appears that MSM is at least

"similar" to BACM, and any determination EPA makes

about CARB diesel under the BACM standard may

inform its judgment under the MSM standard.

C. EPA's Extension of Arizona's Attainment Deadline

Finally, aside from the issue whether Arizona has

adopted MSM, petitioners claim that EPA abused its

discretion when it granted Arizona a five-year extension

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58 ERC (BNA) 1481
under 42 U.S.C. § 7513(e). Satisfaction of the MSM

standard is not the only requirement for a state to qualify

for an extension of the serious area attainment [**52]

date under § 7513(e). The provision details various

conditions and procedures for determining whether the

state qualifies, including that the Administrator may grant

the extension only "if attainment by the date established

under subsection (c) of this section [here, December 31,

2001,] would be impracticable, [and] the State has

complied with all requirements and commitments

pertaining to that area in the implementation plan." §

7513(e).

Petitioners argue that Arizona has not satisfied either

of these conditions. As to the first condition, they claim

that Arizona is very close to attaining the annual standard

and fault EPA for approving Arizona's determination that

attainment is impracticable based on the proposed plan,

rather than determining whether attainment would be

practicable if the state adopted CARB diesel and other

agricultural controls. This objection is unpersuasive. EPA

interprets § 7513(e)'s requirement that the plan

demonstrate the impracticability of attainment by the

deadline to mean that "the implementation of BACM on

significant . . . source categories will not bring the area

into attainment by December 31, 2001." 66 Fed. Reg. at

50,282. This [**53] is a reasonable interpretation of the

Act. In context, the requirement that attainment by the

deadline must be "impracticable" implies that the state

need only include the best practicable measures--not

every possible measure--in its showing. If a state satisfies

the BACM standard, it has already established that the

controls it has adopted are the best practicable. Arizona

does not have to demonstrate that it cannot meet the

deadline if it adopted other proposals that are not already

required under the BACM standard. Cf. Ober II, 243 F.3d

at 1193, 1198. We reject petitioners' attempt to bootstrap

a new BACM determination into the impracticability

showing.

Petitioners also claim that EPA should not grant

Arizona an extension because Arizona has not complied

with the requirements of the Act. For this proposition,

they cite § 7513(e)'s instruction that to qualify for an

extension, the state must [*1045] have complied with

"all requirements and commitments pertaining to that

area in the implementation plan." Specifically, petitioners

contend that Arizona did not meet prior implementation

deadlines, including a RACM deadline of December 10,

1993, and failed to submit acceptable [**54] plans in the

past. Petitioners argue that by failing to meet these

requirements of the Act, Arizona has rendered itself

ineligible for an extension.

Petitioners' construction of § 7513(e) is

unreasonable. The statute requires the state to have

"complied with all requirements and commitments

pertaining to that area in the implementation plan," not

the Act. § 7513(e) (emphasis added). Nowhere does the

provision limit extensions to those states that never made

a misstep in their efforts to comply with the Act. If

petitioners were correct, it is unlikely, if not impossible,

that any state could ever secure an extension. Section

7513 establishes a deadline for serious areas of December

31, 2001, and grants the Administrator the power to

extend that deadline. Nowhere does the statute render

ineligible a state that has missed a prior deadline. Indeed,

if a state had met its deadline, it would not need an

extension; only states that can-not meet their deadlines

have need of an extension.

Because § 7513(e) requires satisfaction of the MSM

standard, our remand on whether Arizona must adopt

CARB diesel under that standard necessarily implicates

Arizona's eligibility for the extension. [**55] Subject to

the MSM question, however, we cannot say that the

Administrator has abused his discretion here.

CONCLUSION

We remand to the EPA for further consideration of

whether Arizona's decision to reject CARB diesel as an

emissions control measure satisfies BACM and MSM.

We also remand the question of Arizona's eligibility for

the extension, insofar as that question depends on EPA's

determination regarding MSM. Under 42 U.S.C. §

7607(f), we award petitioners the "costs of litigation

(including reasonable attorney and expert witness fees)"

related to this appeal. We refer the determination of such

costs to the court's Appellate Commissioner, Peter L.

Shaw. See Ober I, 84 F.3d at 316. In all other respects the

petition is denied.

PETITION GRANTED IN PART AND DENIED IN

PART; COSTS TO PETITIONERS.

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