FOR PUBLICATION

UNITED STATES COURT OF APPEALS

FOR THE NINTH CIRCUIT

MONTANA SULPHUR & CHEMICAL 

COMPANY,

Petitioner,

v.  No. 02-71657

UNITED STATES ENVIRONMENTAL

PROTECTION AGENCY,

Respondent. 

MONTANA SULPHUR & CHEMICAL 

COMPANY, No. 08-72642

Petitioner, EPA No.

v.  EPA-R08-OAR2006-0098 UNITED STATES ENVIRONMENTAL

PROTECTION AGENCY, OPINION

Respondent. 

On Petition for Review of an Order of the

Environmental Protection Agency

Argued and Submitted

August 31, 2011—Seattle, Washington

Filed January 19, 2012

425

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Before: Michael Daly Hawkins and M. Margaret McKeown,

Circuit Judges, and John W. Sedwick, District Judge.*

Opinion by Judge Hawkins

*The Honorable John W. Sedwick, United States District Judge for the

District of Alaska, sitting by designation. 

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COUNSEL

Robert K. Baldwin, Goetz, Gallik & Baldwin, PC, Bozeman,

Montana, for the petitioner. 

Martin F. McDermott, United States Department of Justice,

Environment & Natural Resources Division, Washington,

D.C., for the respondent.

Leslie Sue Ritts, Ritts Law Group, PLLC, Alexandria, Virginia, for Amicus National Environmental Development

Association’s Clean Air Project.

Russell S. Frye, FryeLaw, PLLC, Washington, D.C., for

Amicus American Petroleum Institute.

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OPINION

HAWKINS, Senior Circuit Judge:

In these appeals, consolidated for decision,1 we address the

propriety of various actions taken by the United States Environmental Protection Agency (“EPA”) under the Clean Air

Act with respect to Montana air quality from 1993 to 2008.

In No. 02-71657, Montana Sulphur & Chemical Company

(“Montana Sulphur”) seeks review of the EPA’s final rule

which partially disapproved a proposed revision to Montana’s

State Implementation Plan (“SIP”) governing sulfur dioxide

(“SO2”) emissions. 67 Fed. Reg. 22,168 (May 2, 2002). Montana Sulphur also seeks review of a prior EPA action in 1993

known as a “SIP Call,” which preceded the formal SIP revision and started the review process. 58 Fed. Reg. 41,430

(Aug. 4, 1993). The final agency action incorporated documents supporting its SIP Call—in particular EPA reliance on

various modeling calculations—into the administrative record

for partial disapproval of the SIP. 

In No. 08-72642, Montana Sulphur seeks review of the

EPA’s April 2008 final rule promulgating a Federal Implementation Plan (“FIP”) for the State of Montana’s SO2 emissions. 73 Fed. Reg. 21,418 (April 21, 2008). The FIP is

designed to fill perceived gaps the EPA identified in the SIP.

This later appeal focuses on the EPA’s authority to promulgate the FIP and the reasonableness of certain specific

requirements set forth therein. Because we conclude that the

agency did not act arbitrarily or capriciously with respect to

either the SIP or FIP, we deny both petitions for review.

1We initially denied the EPA’s motion to consolidate case No. 08-

72642 with 02-71657, but ordered the cases be calendared together after

briefing. Montana Sulphur now acknowledges that the cases involve

“many of the same issues” and that relief on the 02-71657 petition “might

wholly or partially moot” the FIP challenge. We have therefore decided

to address both appeals in a single opinion. 

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STATUTORY BACKGROUND

The Clean Air Act directs states to develop implementation

plans—SIPs—that “assure” attainment and maintenance of

national ambient air quality standards (“NAAQS”) through

enforceable emission limitations. 42 U.S.C. §§ 7407(a),

7410(a)(2)(A). The EPA has developed a list of pollutants that

cause or contribute to air pollution that “may reasonably be

anticipated to endanger public health or welfare.” 42 U.S.C.

§ 7408(a)(1)(A). For each criteria pollutant, the EPA sets

NAAQS sufficient to protect public health with an adequate

margin of safety and to protect the public welfare, 42 U.S.C.

§ 7409(b), pursuant to which it has promulgated NAAQS for

SO2, 40 C.F.R. §§ 50.4 & 50.5.

A SIP must “provide for the performance of such air quality modeling as the Administrator may prescribe for the purpose of predicting the effect on ambient air quality of any

emissions of any [NAAQS-regulated] air pollutant.” 42

U.S.C. § 7410(a)(2)(K)(i). As reflected in relevant regulations, emissions limitations may be demonstrated through

modeling. 40 C.F.R. § 51.112(a)(1) (“adequacy of a control

strategy shall be demonstrated by means of applicable air

quality models, data bases, and other requirements specified

in appendix W . . . (Guideline on Air Quality Models)”).

There is also a Federal Reference Method for measuring

ambient levels of SO2 pollutants. 40 C.F.R. § 58.1. The EPA

uses this data and engages in formal notice-and-comment

rulemaking to designate “attainment areas,” “nonattainment

areas,” and areas that are not classifiable. 42 U.S.C.§ 7407(d).

The Clean Air Act gives the EPA significant national oversight power over air quality standards, to be exercised pursuant to statutory specifications, and provides the EPA with

regulatory discretion in key respects relevant to SIP calls and

determinations about the attainment of NAAQS. Yet, the Act

also anticipates states’ shared responsibility for air quality

control. 42 U.S.C. §§ 7407(a), 7410 (giving states duty of

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developing implementation plans). The Clean Air Act “left

with the states, so long as the [NAAQS] were met, the power

to determine which sources would be burdened by regulation

and to what extent.” Union Elec. Co. v. EPA, 427 U.S. 246,

269 (1976) (emphasis added); see also Train v. Natural Res.

Def. Council, Inc., 421 U.S. 60, 98 (1975). A state must

develop implementation plans that will satisfy national standards; if it does so, it may “adopt whatever mix of emissions

limitations it deems best suited to its particular situation.”

Train, 421 U.S. at 79. But when the state plan is inadequate

to attain and maintain NAAQS, then the EPA is empowered

to step in and fill any deficiencies with a FIP. 42 U.S.C.

§ 7410(c).

PROCEDURAL BACKGROUND

The dispute between Montana Sulphur and the EPA is

long-standing, spanning over seventeen years and centering

on regulations governing emissions from industrial facilities

located near Billings, Montana. Montana Sulphur operates a

sulfur recovery plant northeast of Billings. The plant is

located next to a petroleum refinery owned by ExxonMobil.

Pipes from the refinery bring a continuous stream of high sulfur gas—a by-product of the refining process—to Montana

Sulphur. Montana Sulphur recovers 95-98% of the sulfur as

a marketable product. The remainder is emitted in the form of

SO2. SO2 is a “highly reactive colorless” gas primarily

derived from fossil fuel combustion, “best known for causing

‘acid rain’ at elevated concentrations in the ambient air.”

American Lung Ass’n v. EPA, 134 F.3d 388, 389 (D.C. Cir.

1998). 

In 1978, the EPA made a formal determination that the Billings area met the primary standards for SO2. 43 Fed. Reg.

40,412 (Sept. 11, 1978). Neighboring Laurel was designated

“nonattainment” in 1978, due to measured and modeled violations of the primary SO2 standards. 43 Fed. Reg. 8,962 (Mar.

3, 1978). Dispersion modeling conducted by the EPA during

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the 1970s, however, indicated that potential violations of the

SO2 standards were also occurring in the Billings area due to

SO2 emissions from a variety of sources, including Montana

Sulphur.

In 1980, the EPA approved Montana’s SIP for attaining and

maintaining SO2 NAAQS in the Billings/Laurel area. 45 Fed.

Reg. 2,034 (Jan. 10, 1980). Actual monitoring subsequent to

that approval showed some individual “exceedances” of the

24-hour SO2 standard and one 3-hour “violation” in 1985.

Based on monitored emissions, SO2 levels remained relatively constant throughout the 1980s, decreasing slightly in

1983-86, then rising again in 1989. 

In 1990, the City of Billings (“Billings” or the “City”) hired

a contractor to perform dispersion modeling for the Billings

area. The Montana Department of Health and Environmental

Sciences (“MDHES”) reviewed the contractor’s report, which

indicated “potential violations of federal SO2 standards at

both actual and allowable emissions levels” and predicted

“high concentrations in areas where ambient monitoring had

not been conducted.” One year later, Yellowstone Energy

Limited Partnership performed dispersion modeling for its

permit application and similarly identified potential violations

of national SO2 standards in the Billings area. 

Citing these studies, the EPA advised MDHES in 1992 that

its SIP might be inadequate and in need of revision. MDHES

in turn notified the City that the emissions from industrial process units were not adequately regulated by the existing SIP.

It also noted that “current monitoring sites are not at the highest predicted locations, nor could we locate enough monitors

to provide the spatial coverage represented in the model.” A

revised SIP, it noted, would ease permitting of new industries

in the Billings/Laurel area. 

The EPA then issued a formal SIP Call in 1993, finding the

existing SIP “substantially inadequate” to attain and maintain

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NAAQS and asking MDHES to submit revisions within eighteen months; the EPA noted that the SIP Call was “a preliminary step in an ongoing process” and “not subject to judicial

review.” Notice of the SIP Call was published August 4,

1993. 58 Fed. Reg. at 41,430.

MDHES thereafter developed a protocol for the SIP revisions that incorporated EPA-approved models. MDHES submitted various revisions of the SIP to the EPA in 1996, 1997,

1998, and 2000. 67 Fed. Reg. at 22,171, 22,175.

In 1999, the EPA proposed action on the SIP revisions, 64

Fed. Reg. at 40, 791, and took final actions on the SIP on May

2, 2002 (67 Fed. Reg. 22,168) and May 22, 2003 (68 Fed.

Reg. 27, 908), approving most of the SIP, but disapproving a

number of specific items affecting Montana Sulphur, including (1) the attainment demonstration due to issues with emission limits, inappropriate stack height credit, and lack of

submitted emission limits on flares; (2) the emission limits for

Montana Sulphur’s Sulfur Recovery Unit 100-meter stack and

the stack height credit supporting those limits; and (3) the

emission limits for Montana Sulphur’s 30-meter and auxiliary

vent stacks.

Montana Sulphur petitioned for review of the EPA’s May

2, 2002 SIP action. That case, No. 02-71657, was stayed

pending the EPA’s promulgation of a FIP to remedy the SIP.

In 2006, the EPA published its proposed FIP. 71 Fed. Reg.

39,259 (July 12, 2006). Montana Sulphur and others commented on that proposal. In 2008, the EPA promulgated its

final FIP. 73 Fed. Reg. at 21,418. In case No. 08-72642, Montana Sulphur challenges, among other things, the timeliness of

the FIP, the limits on flares, and the feasibility of flare monitoring technology required by the FIP. Neither the State of

Montana nor any party other than Montana Sulphur has challenged the SIP Call or the EPA’s SIP or FIP actions.

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STANDARDS OF REVIEW

When reviewing the EPA’s decision regarding a SIP or its

promulgation of a FIP:

[T]he court may reverse any such action found to be

—(A) arbitrary, capricious, an abuse of discretion, or

otherwise not in accordance with law; (B) contrary

to constitutional right, power, privilege, or immunity; (C) in excess of statutory jurisdiction, authority,

or limitations or short of statutory right . . . .

42 U.S.C. § 7607(d)(9)(A)-(C). We afford Chevron2 deference to issues of statutory construction; if the statute is ambiguous, we ask whether the agency’s answer is based on a

permissible construction of the statute. MacClarence v. EPA,

596 F.3d 1123, 1130 (9th Cir. 2010). 

We also give deference to an agency’s interpretation of its

own regulations, Wickland Oil Terminals v. Asarco, 792 F.2d

887, 891-92 (9th Cir. 1986), and to the evaluation of complex

scientific data within its area of expertise, Envtl. Def. Ctr.,

Inc. v. EPA, 344 F.3d 832, 869 (9th Cir. 2003). However, we

do not simply rubber stamp an agency’s decision, but “must

carefully review the record to ensure that agency decisions are

founded on a reasoned evaluation of the relevant factors.”

Vigil v. Leavitt, 381 F.3d 826, 833 (9th Cir. 2004) (citation

omitted).

2Chevron U.S.A., Inc. v. Natural Res. Def. Council, Inc., 467 U.S. 837,

842-43 (1984). Agency actions which have gone through notice and comment are typically reviewed for Chevron deference, see United States v.

Mead Corp., 533 U.S. 218, 230 (2001), but those which have not are still

afforded Skidmore deference, which focuses on whether the agency has

taken a position that has the “power to persuade,” see Skidmore v. Swift

& Co., 323 U.S. 134, 140 (1944). 

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DISCUSSION

I. The SIP Call

A. Justiciability 

[1] One of Montana Sulphur’s primary arguments concerns

the EPA’s authority to make the SIP Call in the first place,

because, in its view, the existing SIP was not substantially

inadequate because there were no monitored violations of

NAAQS in the area, only predicted violations based on computer modeling. This issue, however, raises a number of

threshold justiciability concerns. The SIP Call is not a final

agency action and did not impose any specific obligations on

Montana Sulphur. The SIP Call was only an “act of limited

consequence preliminary to other events anticipated by the

[Clean Air] Act.” Illinois v. EPA, 621 F.2d 259, 261 (7th Cir.

1980). As the Sixth Circuit has elaborated:

[T]he issuance of notice of deficiency and the

request for a revised SIP is not final agency action

subject to judicial review. It in no way alters the

obligations of the parties in either a practical or legal

sense. It is impossible to anticipate which of the

many available alternative strategies the State and

the EPA will pursue. . . . Until the State responds to

the EPA’s request for revision, and the EPA’s subsequent actions become real rather than merely speculative, no legally cognizable harm has been visited.

Greater Cincinnati Chamber of Commerce v. EPA, 879 F.2d

1379, 1383 (6th Cir. 1989).

[2] Thus, the EPA is correct to the extent it argues that at

the time of the SIP Call there was no final agency action, see

Bennett v. Spear, 520 U.S. 154, 177-78 (1997), the issue was

not yet ripe, see Abbott Labs. v. Gardner, 387 U.S. 136, 148-

49 (1967), and Montana Sulphur had not suffered an “actual

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or imminent” as opposed to a “conjectural or hypothetical”

injury that would suffice for standing, see Friends of the

Earth, Inc. v. Laidlaw Envtl. Servs. (TOC), Inc., 528 U.S. 167,

180 (2000); see also Bova v. City of Medford, 564 F.3d 1093,

1095-96 (9th Cir. 2009) (noting how ripeness and the injury

prong of standing are interrelated). 

[3] This does not, however, mean that the alleged problems

with the SIP Call are forever beyond challenge. Montana Sulphur filed its petition for review after the EPA both made the

SIP Call and issued its partial approval/partial disapproval of

the SIP. There is no dispute that the SIP disapproval was a

final agency action and that Montana Sulphur has standing to

challenge this action. 

[4] The EPA’s 2002 disapproval, in turn, is necessarily

predicated on the validity of the initial SIP Call and the modeling assumptions made therein, which Montana Sulphur also

seeks to challenge. Compare 58 Fed. Reg. at 41,430 with 67

Fed. Reg. at 22,173, 22,183-22,189. Because Montana Sulphur’s claim that the EPA exceeded its statutory authority by

issuing the SIP Call in the first place would necessarily invalidate the 2002 SIP disapproval as well, its challenge to the SIP

Call may be brought at this time. See Virginia v. EPA, 108

F.3d 1397, 1414 (D.C. Cir. 1997), as modified, 116 F.3d 499

(D.C. Cir. 1997) (striking down a SIP Call which was based

on a final agency rule that exceeded the EPA’s authority

under the Clean Air Act); see also Greater Cincinnati, 879

F.2d at 1382 (holding claim regarding SIP Call was premature

“[u]ntil the State responds to the EPA’s request for revision,

and the EPA’s subsequent actions become real rather than

merely speculative”) (emphasis added).

B. Merits

[5] Although Montana Sulphur has standing to challenge

the underlying SIP Call as part of its challenge to the final

agency disapproval in 2002, we conclude that the EPA did not

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exceed its authority under the Clean Air Act by issuing the

SIP Call. The EPA lacks authority to issue a SIP Call unless

the SIP is “substantially inadequate.” 42 U.S.C.

§ 7410(a)(2)(H), (k)(5). The thrust of Montana Sulphur’s

argument is that the SIP Call was improper because the Montana SIP was not “substantially inadequate to attain or maintain” the SO2 NAAQS, and did satisfy all of the statutory

criteria of 42 U.S.C. § 7410(a)(2). 

[6] Montana Sulphur contends that the EPA could not

properly rely on predicted violations of NAAQS that were

modeled in the Billings/Laurel area, because the EPA did not

provide any reason to believe that there was an actual, monitored SO2 violation in any location in the Billings area. Specifically, Montana Sulphur argues that the EPA’s reliance on

dispersion modeling “provides an unrealistic picture of reality

because it assumes that every single facility is always emitting as much pollution as it can possibly emit during every

hour of the modeling run” and under “worst case” weather

conditions. 

[7] Contrary to Montana Sulphur’s contentions, the EPA

did not ignore actual SO2 monitoring data when it issued the

SIP Call. Rather, the EPA expressly addressed these results

and explained their shortcomings. In its Technical Support

Document (“TSD”), which explained the rationale for the call,

the EPA explained that it was “not practical, given the number and complexity of sulfur dioxide sources, to install a sufficient number of monitors to provide the spatial coverage

provided by air quality dispersion models.” In fact, much of

the data collected prior to the call (throughout the 1970s and

’80s) came from a monitoring network of just three to four

sites in the Billings and Laurel area. The EPA further

explained that the existing monitors were not located in areas

of maximum concentration, and that areas “with the most

severe exceedances according to the studies have never been

monitored—or were once monitored but no longer.” 

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The EPA further addressed Montana Sulphur’s complaint

when it partially disapproved the SIP in 2002:

Monitoring is not more accurate than computer modeling, except for determining ambient concentrations

under real-time conditions at a discrete location.

Monitoring is limited in time as well as space. Monitoring can only measure pollutant concentrations as

they occur; it cannot predict future concentrations

when emission levels and meteorological conditions

may differ from present conditions. Computer modeling, on the other hand, can analyze all possible

conditions to predict concentrations that may not

have occurred yet but could occur in the future.

67 Fed. Reg. at 22,185. See Northern Plains Res. Council v.

EPA, 645 F.2d 1349, 1362-63 (9th Cir. 1981) (reliance on

model without validation arbitrary only if “EPA ignored reliable data that so undermined the EPA model projections . . .

that reliance on the model was irrational”); Republic Steel

Corp. v. Costle, 621 F.2d 797, 805 (6th Cir. 1980) (approving

use of modeling to predict future violations and incorporating

“worst-case” assumptions regarding weather and full-capacity

operations of pollutant sources).

[8] As the EPA also points out, the Clean Air Act

expressly recognizes modeling as an appropriate regulatory

tool. 42 U.S.C. § 7410(a)(2)(K)(i) requires SIPs to provide for

“the performance of such air quality modeling as the Administrator may prescribe for the purpose of predicting the effect

on ambient air quality of any emissions of any air pollutant

for which the Administrator has established a national ambient air quality standard.” 

[9] Montana Sulphur argues that the 1990 amendments to

the Clean Air Act indicate a Congressional intent to eliminate

the use of modeling. Section 7501(2) formerly defined a

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tored data or which is calculated by air quality modeling (or

other methods determined by the Administrator to be reliable)

to exceed any [NAAQS].” In 1990, Congress deleted both the

references to monitored data and air quality modeling, replacing them with a cross-reference to air quality designations in

§ 7407(d). Montana Sulphur would have a better argument if

Congress had deleted the reference to modeling and left the

reference to monitored data intact, but that is not what happened. In any event, the legislative history underlying the

1990 amendment clarifies that the EPA may rely on any

“sound data” that is available, and that “where appropriate

and necessary, the Agency may rely on modeling or on statistical extrapolation.” S. Rep. No. 101-228, at 15 (1989). 

[10] Although the available evidence did not point unambiguously in any one direction, the EPA had plausible reasons

for concern in 1993 about attainment given the proximity

between Laurel (a nonattainment area) and Billings, the limitations of the existing monitoring methods, the indications

from the modeling studies available, and the gravity of the

health issues that SO2 NAAQS seek to prevent. The EPA

therefore did not act arbitrarily or capriciously by relying on

predictive modeling to make the SIP Call in 1993.3

3Montana Sulphur also contends that the EPA had no statutory authority

to demand a new attainment demonstration from the State of Montana

because the relevant area was not officially designated as a “nonattainment

area.” In its view, the EPA may only require attainment demonstrations

when they are needed to assure that nonattainment areas will attain the

NAAQS, and that the EPA should have first sought to re-designate the

Billings area to “nonattainment” via the statutory process. 42 U.S.C.

§ 7407(d)(3). 

However, § 7410(a)(1) requires states to submit SIPs that provide for

the maintenance of NAAQS regardless of whether a nonattainment area

has been designated; similarly, the EPA’s authority to declare a SIP “substantially inadequate” to attain or maintain NAAQS does not hinge on an

area’s designation. 42 U.S.C. § 7410(k)(5). We have already determined

that the EPA did not exceed its authority by making the SIP Call, and it

necessarily follows that a new attainment demonstration is a logical and

lawful part of responding to the SIP Call. 

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II. 2002 Partial Disapprovals of Montana Revised SIP

[11] Montana Sulphur next challenges several aspects of

the 2002 partial EPA disapproval of the revised SIP. 

A. Stack Height Credits

[12] One of the most vigorously contested issues in this

protracted dispute is whether the EPA’s computation of stack

height was irrational. Montana Sulphur has a 100-meter high

flue stack which was constructed after the 1993 SIP Call.

Under EPA regulations, the EPA concluded the appropriate

credit for that stack should be only 65 meters, and that the

State of Montana’s modeling assumptions using a greater

stack height were therefore invalid. 67 Fed. Reg. at 22,209-

22,238.

[13] The basic concern with stack height is this: a pollution

source can lower ground-level, measured concentrations of

pollution by raising the height of its stack and dispersing the

pollution further into the atmosphere. Concerned that such a

dispersion technique does not actually reduce the amount of

pollution but merely spreads it around, Congress adopted 42

U.S.C. § 7423 to regulate the use of tall stacks. See Sierra

Club v. EPA, 719 F.2d 436, 441 (D.C. Cir. 1983) (discussing

legislative history). Rather than completely prohibiting the

use of tall stacks, which do prevent some harmful downwash

of pollutants near the source, the statute and regulations seek

to strike a balance between elevating stack height to disperse

pollution away from a source and preventing relocation of

pollution from one site to others. 

Finally, we note that the burden of producing a new attainment demonstration fell solely on the State of Montana’s shoulders, and the State did

not object. It is unclear how Montana Sulphur was injured by the attainment demonstration itself, as opposed to the specific disapprovals of the

revised SIP which are discussed below. 

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[14] The formulas thus restrict a source from receiving

credit for stack height that is higher than a Good Engineering

Practice (“GEP”) figure. The applicable federal statutory provisions provide that emission limitations under an implementation plan “shall not be affected in any manner by . . . so

much of the stack height of any source as exceeds good engineering practice (as determined under regulations to be promulgated by the [EPA.].” 42 U.S.C. § 7423(a)(1). GEP is “the

height necessary to ensure that emissions from the stack do

not result in excessive concentrations of any air pollution in

the immediate vicinity of the source as a result of atmospheric

downwash, eddies, and wakes which may be created by the

source itself, nearby structures or nearby terrain obstacles.” 42

U.S.C. § 7423(c). 

[15] The EPA regulations provide three possible options

for calculating GEP stack height, and allow use of the greatest

resulting number: (1) 65 meters (“de minimis” height); (2) the

height calculated using one of two formulas (“formula

height”), or (3) the height demonstrated using fluid modeling

or field study (“above-formula” height). 40 C.F.R.

§ 51.100(ii). In the SIP, Montana had approved a modeling

demonstration for Montana Sulphur’s 100-meter stack under

Option 3, and concluded the creditable stack height was 97.5

meters. However, the EPA rejected Montana’s calculations

and maintains that the de minimis 65 meters is the proper

stack height figure. Montana Sulphur disagrees with several

steps in the process which led the EPA to this conclusion.4

4Montana Sulphur does not directly challenge the calculation of “formula height” because Montana and the EPA addressed the stack height

under Option 3 in the SIP. However, it does assert in passing that the only

formula height in the record is 97.5 meters. This assumes that an 8-footwide, 310-foot-tall cylindrical steel structure which supports the flue stack

can be considered a “nearby structure” under the regulations. The EPA,

however, rejected this position. 67 Fed. Reg. at 22,223-22,229. Because

the opening brief contains no argument as to why this determination

regarding the support stack is arbitrary or capricious, we deem the issue

waived. Harger v. Dept. of Labor, 569 F.3d 898, 904 n.9 (9th Cir. 2009).

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1. New Source Performance Standards (“NSPS”)

[16] The EPA rejected Montana’s fluid modeling calculation of GEP stack height because, even though it used NSPS

for the modeling, the SIP did not actually require Montana

Sulphur to meet the NSPS emission rate. 67 Fed. Reg. at

22,209. Montana Sulphur concedes that NSPS may be used

for modeling purposes, but contends that NSPS cannot be

used as a substantive emissions limit, noting that the EPA regulations themselves state that the “allowable emission rate to

be used in making demonstrations under this part shall be prescribed by the [NSPS] that is applicable to the source category

. . . .” 40 C.F.R. § 51.100(kk)(1) (emphasis added). 

[17] The EPA’s interpretation of its own regulation, however, is not unreasonable. The EPA explains that “allowable

emissions” is a term of art it uses to denote an enforceable

emission limit, not a mere assumed emission rate that may be

disregarded later. The EPA claims it has always interpreted

this language to require ongoing compliance with the NSPS,

and notes that the term is used elsewhere in the stack height

regulations as a substantive limit. 67 Fed. Reg. at 22,210. 

The EPA further points out that § 51.100(kk)(1) allows a

source to demonstrate that the NSPS emission rate is “infeasible,” and that there would be no reason to include this provision if the NSPS rate were a mere assumption in fluid

modeling that need never actually be met. 67 Fed. Reg. at

22,212. We must review the provision as a whole and, where

Even if we were to consider the issue, the EPA has fully and persuasively

explained why the stack support structure is properly considered part of

the stack itself, rather than a nearby structure. 67 Fed. Reg. at 22,223-

22,229. 

Without inclusion of the support structure, the formula height is 47.8

meters. 73 Fed. Reg. at 21,446. Thus, Montana Sulphur could achieve

greater stack height option only through Option 1 de minimus height or

Option 3 above-formula modeling. 

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possible, effectuate every word. See Boise Cascade Corp. v.

EPA, 942 F.2d 1427, 1432 (9th Cir. 1991).

The EPA’s interpretation is also consistent with the views

expressed in the preamble to the EPA stack height regulations, which states that the applicable section “has been

revised . . . to specify that an emission rate equivalent to

NSPS must be met before a source may conduct fluid modeling to justify stack height credit in excess of that permitted by

the GEP formulae.” 50 Fed. Reg. 27,892, 27,898 (July 8,

1985) (emphasis added); see Las Vegas v. FAA, 570 F.3d

1109, 1117 (9th Cir. 2009) (if regulation is ambiguous, “we

consult the preamble of the final rule as evidence of context

or intent of the agency promulgating the regulations”). 

Our conclusion is also consistent with that of the D.C. Circuit, which addressed the issue of stack height and the use of

NSPS and concluded that the EPA has the discretion to

impose NSPS requirements in the “above formula” context.

Natural Res. Def. Council, Inc. v. Thomas, 838 F.2d 1224,

1241 (D.C. Cir. 1988). The court noted that above-formula

credit should be granted with the “utmost caution” and that

the selection of the NSPS baseline was consistent with this

admonition. Id. (internal quotation marks omitted).

[18] In light of the foregoing, we conclude it was neither

arbitrary nor capricious for the EPA to require the SIP to

include NSPS limits consistent with the modeling demonstration.5

5To the extent Montana Sulphur argues it was treated differently from

the ExxonMobil refinery because that source was not required to comply

with NSPS rates in modeling or in reality, the EPA explains that the different treatment was because ExxonMobil performed fluid modeling to

obtain credit for a within-formula stack height credit, not an aboveformula stack height credit. 67 Fed. Reg. 22,215-22,216. NSPS are applied

by EPA only in cases involving modeling to obtain credit for aboveformula stack height credit. 67 Fed. Reg. at 22,215; see also Thomas, 838

F.2d at 1238-41; id. at 1232 (noting regulation’s preference for withinformula stacks). 

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2. Ambient Air Quality Standards

[19] In calculating stack height credit, the regulations only

permit a source to use stack height that is necessary to avoid

an exceedance of “an ambient air quality standard.” 40 C.F.R.

§ 51.100(kk)(1). Therefore, lower exceedance standards can

be used to justify a higher “stack height credit.” A source

seeking to justify a higher stack will seek to establish that the

downwash pollution effects of the stack are “excessive.” In

such cases, a higher stack—which redistributes pollution over

a wider area—is justified in order to prevent excessive local

pollution effects. Thus, it matters whether NAAQS, versus

more stringent state standards, control in calculating “excessive” local concentrations.

[20] Montana Sulphur argues that Montana’s emission

rates (“MAAQS”) properly could be used as benchmarks for

ambient air quality under § 51.100(kk)(1), because the regulation refers only to “an ambient air quality standard” whereas

the regulations elsewhere describe “primary,” “secondary,”

and “national” standards. 40 C.F.R. § 51.100(kk)(1) (emphasis added); 40 C.F.R. § 51.100(c), (d), (e). The EPA, however,

insists that national standards, not Montana’s state-only

annual SO2 standard, should apply to the determination of

what is an “excessive” concentration of SO2 that exceeds an

“ambient air quality standard” under these regulations. 

[21] The regulation is ambiguous because it does not specifically identify which “ambient air quality standard” exceedances may be used to support the stack height. The preamble

to the regulation, however, frequently refers to the use of

NAAQS in addressing above-formula stack height and supports the EPA’s interpretation that national standards should

provide the benchmark. 50 Fed. Reg. at 27,898-27,899; see

Las Vegas, 570 F.3d at 1117-18.

Again, the EPA’s interpretation of its own regulation is reasonable. Using NAAQS versus the MAAQS as the applicable

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benchmarks for the exceedance analysis comports with the

purposes of 42 U.S.C. § 7423: using NAAQS prevents states

from setting standards that might enable local industry to justify above-formula stack height credits that do not meet

national standards, and better assures that the EPA will fulfill

its obligations. See Sierra Club, 719 F.2d at 450 (EPA must

make certain “the standard it derives in fact fairly approximates the stack height level needed to protect local health and

welfare; in doing so, moreover, it should err on the side of

reducing stack height, in keeping with Congress’s command

that credit for stack heights above [formula] height be granted

with ‘utmost caution’ ”).

3. Conclusion

[22] The applicable statutory provisions leave room for

interpretation, and the applicable stack height regulations lend

support to the EPA’s determinations on these complex points.

We defer to the agency’s judgment in these technical matters,

and conclude the EPA did not act arbitrarily or capriciously

by rejecting Montana’s stack height credit calculation.

B. Flare Emissions

[23] The EPA also disapproved the revised Montana SIP

in part because it failed to include any numerical emissions

limits on flares. “Flaring” is a practice that provides for equipment to immediately release gases to a device (a flare) for

incineration. It is used in emergencies (malfunctions) and

some routine circumstances, such as startup, shutdowns and

maintenance (collectively, “SSM”).

Montana included an emission rate assumption for each

flare in its attainment demonstration, assuming limitations of

150 pounds of SO2 per 3-hour period.6 However, in its

6Although Montana Sulphur suggests the selection of these figures was

itself random and arbitrary, the record indicates that the rates included in

this modeling were the product of discussion and investigation and based

on area refineries’ run estimates. 

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revised SIP, Montana imposed instead a work practice standard during SSM that required “best practices” be used to

minimize flaring, and eliminated any numerical emission limitations on flares. Montana concluded it was technically infeasible to regulate flares through numerical limits, but agreed

with the EPA “that the SIP is incomplete without enforceable

emission limitations applicable to flares, and that such limitations should correspond to the emission rates used in the

attainment demonstrations.”

[24] Disapproval of the SIP was not arbitrary or capricious

in these circumstances. Under the EPA’s regulations, a proposed SIP “must demonstrate that the measures, rules, and

regulations contained in it are adequate to provide for the

timely attainment and maintenance of the national standard

that it implements.” 40 C.F.R. § 51.112(a); see also Hall v.

EPA, 273 F.3d 1146, 1158 n.8 (9th Cir. 2001) (“An ‘attainment demonstration’ is a formal demonstration . . . that the

pollution control measures contained in an implementation

plan are adequate to provide for the timely attainment and

maintenance of NAAQS.”). Here, Montana demonstrated the

control strategies contained in the SIP plus a 150 lb/3-hour

limit on flares would attain the NAAQS. The SIP itself, however, was missing the second part of the equation. Although

Montana Sulphur contends flaring is not a significant source

of SO2 emissions, the EPA points to modeling evidence that

the flare emissions likely were significant (219

tons/year/source)—well above the 100 tons/year threshold

that can trigger major source permitting requirements. 67 Fed.

Reg. at 22,182. Flare emissions can affect attainment, and

limits on them reasonably can be required, particularly where

the state has relied on such limits to demonstrate attainment.

See Michigan Dep’t of Envtl. Quality v. Browner, 230 F.3d

181 (6th Cir. 2000) (holding EPA properly disapproved Michigan SIP revision that permitted automatic exemption for

source that violates emissions standards if violation results

from SSM and meets other standards).

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Note that at this point, we consider only whether the EPA

acted rationally in disapproving the SIP for failing to include

emission limitations that were otherwise part of the state’s

attainment demonstration. We discuss in further detail below,

in the context of the FIP, whether the EPA can rationally limit

flaring during SSM periods.

C. Auxiliary Vent Stacks and 30-Meter Stack

[25] The last set of challenged SIP disapprovals involves

Montana Sulphur’s five auxiliary vent stacks and its 30-meter

stack. The SIP included a SO2 limit of 12 lbs/3- hour period

for these stacks. The EPA disapproved the limit because it did

not restrict the sulfur content of the fuel burned, and because

the SIP lacked a monitoring method that would make the limit

practically enforceable. 67 Fed. Reg. at 22,170.

Montana Sulphur argues that the limit was not required

because the emissions from these stacks are too small to have

any practical effect on air quality; thus, it claims, monitoring

methods to assure that the limit is met are unnecessary. While

the EPA cannot require a state to adopt a particular control

measure, see Virginia, 108 F.3d at 1407-08, the EPA has the

power to assure that a SIP will achieve NAAQS, 42 U.S.C.

§ 7410(a)(2), and the Clean Air Act prohibits it from approving a SIP that would interfere with attainment, see Browner,

230 F.3d at 185. 

[26] The State of Montana included the limit in its SIP as

a control strategy. The EPA is thus not requiring Montana to

adopt a particular control measure, but requiring Montana to

include a monitoring method only where it relies upon such

limits in its SIP for an attainment demonstration, which in

turn was designed to assure that it achieved NAAQS. Thus,

it was reasonable for the EPA to insist that the limit be

enforceable. See also Pennsylvania v. EPA, 932 F.2d 269, 272

(3d Cir. 1991) (“[S]tandards cannot be maintained unless the

measures taken to achieve them are enforceable.”).

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III. The FIP

A. Timeliness

[27] Montana Sulphur argues that the EPA lost its authority to promulgate a FIP when it failed to act within two years,

as set forth in 42 U.S.C. § 7410(c).7 Section 7410(c)(1)(B)

indicates that the EPA “shall promulgate a Federal implementation plan at any time within 2 years after” disapproval or

partial disapproval of a SIP. While this is certainly an “explicit deadline,” as opposed to a more general requirement

such as “after reasonable notice and public hearings,” see generally General Motors Corp. v. United States, 496 U.S. 530

(1990), it does not follow that the agency loses authority to

act if it fails to meet that deadline. Rather, the Supreme Court

has declined to treat a statutory requirement that an agency

“ ‘shall’ act within a specified time, without more, as a jurisdictional limit precluding action later.” Barnhart v. Peabody

Coal Co., 537 U.S. 149, 158 (2003). “When, as here, there are

less drastic remedies available for failure to meet a statutory

deadline, courts should not assume that Congress intended the

agency to lose its power to act.” Brock v. Pierce Cty., 476

U.S. 253, 260 (1986). 

[28] As the Court noted in General Motors Corp., the

Clean Air Act provides remedies for EPA inaction, including

a suit to compel agency action or a request for reduction or

elimination of penalties during any period of unreasonable

agency delay. 496 U.S. at 542 n.4 (citing 42 U.S.C.

§§ 7604(a)(2) & 7413(b)). We hold that in the absence of any

Congressional indication otherwise, the failure to act within

7Although the EPA argues Montana Sulphur has waived this argument,

we find Montana Sulphur sufficiently preserved the issue during the comments on the FIP proposal, where Montana Sulphur noted that the EPA

failed to promulgate a FIP within two years, claimed that the EPA had “clear[ly] disregard[ed]” its requirement to do so, and asserted that numerous

circumstances had changed, including modeling technology and cleanup,

rendering the current action arbitrary and capricious. 

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two years does not utterly deprive the EPA of authority to

promulgate the FIP. See Nat’l Petrochemical & Refiners

Ass’n. v. EPA, 630 F.3d 145, 155-56 (D.C. Cir. 2010). 

B. Limits on Flares during SSM

[29] Montana Sulphur contends that the EPA acted arbitrarily and capriciously by imposing numerical limits on flaring emissions during periods of unusual operations such as

SSM. The FIP requires that emissions not exceed 150 lbs/3

hrs and also provides an affirmative defense to penalties for

emissions that are beyond the company’s control, such as during unusual events like SSM. See 73 Fed. Reg. at 21,431-

21,437 (addressing comments to FIP); 73 Fed. Reg. at 21,459

(flare requirements); 73 Fed. Reg. at 21,464-21,465 (affirmative defense). 

Montana Sulphur argues that: a numerical limit on flaring

emissions is infeasible and violations will assuredly occur, see

Bunker Hill Co. v. EPA, 572 F.2d 1286 (9th Cir. 1977); the

EPA is acting inconsistently with its history of exempting

flaring during SSM; the 150 lb./3-hour figure is based on

unsupported state modeling; no deference should be given to

the EPA’s internal excess emissions policy (the “EEP”)8; and

enforcement discretion cannot compensate for infeasible

requirements, see Marathon Oil Co. v. EPA, 564 F.2d 1253

(9th Cir. 1977).

[30] In turn, the EPA responds that it must provide for

attainment of NAAQS at all times so a total exemption for

SSM during flaring is inadequate, see Sierra Club v. EPA,

551 F.3d 1019 (D.C. Cir. 2008); it is reasonable to encourage

minimizing flare emissions, whether they are routine or during SSM; the numerical requirements are generally consistent

8EPA, Sept. 20, 1999, State Implementation Plans: Policy Regarding

Excess Emissions During Malfunctions, Startup and Shutdown (the “EEP”

or the “Herman Memorandum”). 

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with longstanding internal policies such as the EEP, see Ariz.

Public Serv. Co. v. EPA, 562 F.3d 1116, 1129 (10th Cir.

2009); and the FIP provides relief for truly unavoidable emissions with an affirmative defense to penalties, 73 Fed. Reg. at

21,464-21,465. 

Although not always consistently employed, as early as

1983, the EPA adopted a policy requiring continuous compliance with the Clean Air Act requirements but acknowledging

that some leeway might be necessary for unusual events such

as SSM.9 In 1999, the EPA’s EEP identified several SIPs that

did not comply with its policy and urged regions to review for

compliance; this later memo also clarified that while outright

exemptions for SSM were not acceptable, states could adopt

an affirmative defense to penalties for unforeseeable and

unavoidable exceedances, although noting that this may not

be appropriate for SO2 emissions where attainment problems

are caused by one or only a few sources. 

The FIP here contains such an affirmative defense, and the

EPA indicates that other regulatory agencies, including the

State of Colorado and Maricopa County, Arizona, have

adopted similar criteria. 73 Fed. Reg. at 21,432. The EPA

explains that although including the defense in the FIP is a

slight deviation from the EEP (because in the Billings/Laurel

area one or more sources may have the potential to cause an

exceedance of the SO2 limits),10 experience since the time the

EEP was issued led the agency to conclude that the elements

of the affirmative defense provide “a very significant incentive for facilities to do all they can to comply with their emission limits” and that this approach—numerical limits plus the

9EPA, February 15, 1983, Policy on Excess Emissions During Startup,

Shutdown, Maintenance and Malfunction. 

10We note, therefore, that to the extent the EPA is being inconsistent

with its prior policy, it actually enures to Montana Sulphur’s benefit by

providing an affirmative defense to penalties where the 1999 memo suggests one should not be provided. 

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affirmative defense—“appropriately and reasonably addresses

industry concerns” regarding safety. 73 Fed. Reg. at 21,435.

[31] Other circuits have endorsed the EPA’s position that

the Clean Air Act requires continuous compliance, including

during SSM. The Sixth Circuit rejected a challenge to the

EPA’s disapproval of a Michigan SIP which had provided an

automatic exemption from emission limits during SSM. Mich.

Dep’t of Envtl. Quality v. Browner, 230 F.3d 181 (6th Cir.

2000). The Sixth Circuit deferred to the EPA’s interpretation

of the Clean Air Act that broad exclusions from compliance

with emissions limitations during SSM could jeopardize

ambient air quality and upheld the SIP disapproval. Id. at 185;

see also Ariz. Public Serv. Co., 562 F.3d at 1127, 1129

(rejecting challenge to EPA’s “refusal to exempt excess emissions caused by malfunctions,” and concluding that the policy

“is a reasonable interpretation of the Clean Air Act” because

“excess emissions resulting from malfunctions are violations

of the Clean Air Act, for such emissions can interfere with

attainment of the national air standards” ).

In fact, when the EPA attempted to be more lax under

another section of the Clean Air Act by permitting good work

practices for emissions during SSM events rather than imposing numerical emission limits, the D.C. Circuit concluded that

the “SSM exemption violates the [Clean Air Act’s] requirement that some section 112 standard apply continuously,” and

vacated the exemption. Sierra Club, 551 F.3d at 1028. 

[32] Montana Sulphur also contends that the actual numerical limits imposed by the EPA are arbitrary, going beyond

what is necessary to satisfy the NAAQS, claiming the EPA

simply “seized upon” and accepted Montana’s decision to

impose a 150 lb/3-hour limitation on flares. However, in

response to a similar comment, the EPA explained in its final

rule:

Emission inputs to the model were established using

criteria contained in 40 CFR part 51, Appendix W,

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Section 8. The emission limits set by the modeling

analysis are based on emission rates that would just

meet the NAAQS. They are not based on “arbitrary

limits” that go “far beyond protecting the NAAQS”.

For example, with the limits we are establishing and

the SIP limits we approved, our modeling resulted in

a high value of 354 μg/m which would exactly meet

the 24-hour SO2 NAAQS of 365 μg/m when background concentrations of 11 μg/m are considered.

73 Fed. Reg. at 21,439 (emphasis added).

Finally, the EPA acknowledges that violations are likely

inevitable, but relies on the provision of an affirmative

defense to compensate for the infeasibility problem. Montana

Sulphur claims that the possibility of “enforcement discretion” is insufficient to require compliance with an infeasible

limitation. However, here the EPA does not rely on enforcement discretion alone, but specifically promulgates an affirmative defense in the FIP, which clearly defines the

requirements to avoid penalties.

Although Montana Sulphur argues that there is no rational

basis to limit the affirmative defense to penalties and that the

defense should extend to injunctive relief as well, the EPA

persuasively explains that “[t]here could be instances in which

malfunctions are unavoidable based on current plant layout

and operating parameters but in which some form of corrective action would still be appropriate” and that “it is reasonable to retain the authority to seek injunctive relief for all

exceedances of emission limits so that we remain able to protect the NAAQS, regardless of source ‘culpability’ for any

specific exceedance.” 73 Fed. Reg. at 21,435-21,437. 

[33] In sum, we conclude that the EPA reasonably interpreted the Clean Air Act to require continuous limits on emissions and that the actual numerical limits imposed by the FIP

are neither arbitrary nor capricious.

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C. Flare Monitoring Technology

[34] Montana Sulphur further argues that the EPA acted

arbitrarily and capriciously by requiring implementation of

flare monitoring technology that does not exist. It contends

that it is technically infeasible to monitor low rates of flow to

flares during routine operations, and that the required “total

sulfur” monitors exist only in pilot testing. 

[35] However, Montana Sulphur repeats its objections to

the initially proposed FIP without addressing the modifications the EPA made in the final FIP to accommodate these

concerns. With respect to the concern that flare flow monitors

cannot monitor accurately at low flow velocities (under 1.0

fps), the EPA responded that: (1) it had based the requirement

on what it saw was achievable in vendor literature and

required in at least two other areas, 73 Fed. Reg. at 21,425;

(2) it modified the accuracy requirement from +/- 5% to +/-

20% when dealing with low flows between 0.1 and 1 fps, 73

Fed. Reg. at 21,426; and (3) it implemented a secondary

means for companies to determine whether flow is reaching

the flare when the flow monitor indicates low flow, 73 Fed.

Reg. at 21,426. 

[36] With respect to the total sulfur monitors, Montana

Sulphur is correct that these monitors appear to have primarily been in pilot testing at the time of the FIP, though the EPA

does identify two sources where analyzers are on lines leading

to refinery flares, and did revise the FIP to give industry a full

year to install the monitors. 73 Fed. Reg. at 21,427-21,428.

Moreover, the EPA also revised the final FIP to allow other

methods to determine total sulfur concentration, including

“grab” or “integrated” sampling. 73 Fed. Reg. at 21,429.

Thus, the availability of total sulfur concentration monitoring

is something of a red herring since the company can use an

alternate means to measure sulfur. 40 C.F.R. § 52.1392(h)(3).

Montana Sulphur does not point to any evidence in the record

that grab sampling is technically infeasible.

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D. Variable versus Fixed Emission Limits

[37] Montana Sulphur contends that the EPA acted arbitrarily and capriciously when it granted variable emission limits to a nearby power plant and the ExxonMobil refinery, but

imposed fixed emission limits on it instead. In Montana’s SIP,

the state used a variable emissions limit for all three sources,

which involved a computer dispersion model that required

Montana to run 1,320 modeling scenarios. 73 Fed. Reg. at

21,444. However, as discussed above, in that modeling, Montana had improperly calculated the stack height credit for

Montana Sulphur’s primary 100-meter stack (see section

II.A., supra). Because the EPA disapproved the SIP’s use of

the stack height credit in the modeling calculation, it was left

with no fixed or variable emissions limit for Montana Sulphur; thus, it needed to fill this gap with the FIP. 67 Fed. Reg.

at 22,170, 22,206. 

The EPA explained that it considered fixed emissions limits

to be easier to model, monitor and enforce, 71 Fed. Reg. at

39,268, and that this was the type of limit used at virtually

every other source in the country (with the exception of the

other two Montana sources). 73 Fed. Reg. at 21,444-21,445.

The EPA also notes that based on past reporting data, it

appeared Montana Sulphur would be able to attain the fixed

limit without the need for any additional pollution controls. 71

Fed. Reg. at 39,268. 

[38] Because the EPA would have primary enforcement

responsibility regarding the FIP and the Montana Sulphur

emissions, it chose what it perceived as a simpler method.

Although the EPA approved Montana’s use of the variable

limits with respect to the other two sources, the emission limits at play there did not involve improper stack calculations,

and, in addition, the State was primarily responsible for ensuring the other sources’ compliance with the variable limits.

Montana Sulphur does not point to any other source in which

the EPA itself imposed variable limits in a FIP. Moreover, the

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EPA expressed reservations about the State’s use of the variable limits as to the other sources; it indicated it would be

monitoring the situation closely and might reconsider its

approval of those conditions if doubts arose about the accuracy of the monitoring and/or reporting under that system. 67

Fed. Reg. at 22,207.

[39] Thus, contrary to Montana Sulphur’s argument, this is

not a case where the EPA “depart[ed], sub silentio, from its

usual rules of decision to reach a different, unexplained result

in a single case.” See Western States Petroleum Ass’n v. EPA,

87 F.3d 280, 284 (9th Cir. 1996) (quotation marks omitted).

Rather, it offered a reasonable explanation for why it selected

a different type of emissions limit than the State had chosen,

and, in fact, explained that fixed emissions limits are the norm

and the preferred method. 73 Fed. Reg. at 21,444-21,445. 

E. Auxiliary Stacks/30-Meter Stack

[40] Montana Sulfur next argues that the EPA acted arbitrarily and capriciously by imposing emission limits and monitoring requirements regarding Montana Sulphur’s auxiliary

stacks and 30-meter stack. Montana Sulphur argues that the

requirements are unnecessary to comply with the NAAQS

because the emissions are extremely small and have no practical effect on NAAQS.11 It also contends that the “worst case

scenario” calculation by the EPA ignores reality because

Montana Sulphur cannot vent all five boilers to the auxiliary

stacks and still operate its plant.

As discussed above, the EPA partially disapproved Montana’s limitations on the auxiliary stacks and the 30-meter

stack because there was no restriction on the sulfur content of

11These general arguments about the necessity of regulating these small

stacks overlap with Montana Sulphur’s objections to the SIP Call and partial disapproval of the SIP and, to the extent they do, are governed by the

discussion in Sections I and II above. 

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the fuel when exhausting through these stacks and because the

SIP lacked a monitoring method to make the mass emission

limits practically enforceable. 67 Fed. Reg. at 22,170. The FIP

adopted the same mass emission limits that the state had

imposed in the SIP—12 lbs/3 hours—and added monitoring

requirements to ensure compliance with the limits. 73 Fed.

Reg. at 21,451-21,452. 

As for the arbitrariness of the actual limits and monitoring

requirements, it was reasonable for the EPA to use the state’s

original emission limitations for consistency because they

were a piece of the state’s overall control strategy supporting

attainment. The EPA further points out that (1) the final FIP

was revised to allow Montana Sulphur to use its existing

“length-of-stain detector tubes” for monitoring rather than

requiring the portable analyzers suggested in the initial proposal, 73 Fed. Reg. at 21,446 (noting that the final FIP was

similar to the state operating permit requirements that already

applied to Montana Sulphur); and (2) the final FIP increased

the concentration limits on the fuel burned in the units from

100 ppm/3 hours to 160 ppm/3 hours to accommodate Montana Sulphur’s concern that it was too restrictive, noting that

modeling using 160 ppm for up to three hours would still

meet attainment requirements (but not if emissions were at

this level for the entire day) and that evidence indicated Montana Sulphur should already be within these limits in light of

the SIP’s requirement of burning only “low sulfur” gas and

the fuel gas scrubbing technology it uses. 73 Fed. Reg. at

21,446-47. 

The EPA also explains that its modeling assumption that all

units were venting to the stacks, whether this would ever happen, was a way of simplifying monitoring and compliance for

Montana Sulphur. Under this model, Montana Sulphur needed

only to measure H2S ppm concentration (using its existing

monitoring device) to determine compliance, whereas direct

compliance per boiler stack would either require additional

monitoring equipment or methods or be unreliable due to

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potential variation in boiler use and venting practices. 73 Fed.

Reg. at 21,446-21,447 & 21,452. The EPA sums up its decision in its final FIP:

We believe additional monitoring equipment would

need to be installed, or additional monitoring would

need to be performed, at greater expense to [Montana Sulphur], to achieve adequate method to determine direct compliance with the mass emission

limits. The concentration limits we are imposing are

reasonable, can be monitored at reasonable cost, and

will ensure protection of the NAAQS. 

73 Fed. Reg. at 21,447. 

[41] Thus, the specific emission limits and monitoring

requirements imposed by the FIP, based on revised emission

models and that allow Montana Sulphur to use existing technology, were not arbitrary or unreasonable.

F. Proper Stack Height Credit

[42] This issue is addressed in Section II.A above, regarding the 2002 SIP disapproval. Because we previously concluded that the EPA properly rejected Montana’s calculated

stack height credit in the SIP and that it was proper to use the

65-meter de minimis figure instead, see 40 C.F.R. § 51.118,

we likewise hold here that the EPA did not act arbitrarily in

using that figure in the FIP.12

12We further note that, in its 2006 comments to the proposed FIP, Montana Sulphur merely summarized and reiterated its objections from the SIP

disapproval process and the EPA incorporated by reference the reasons it

had already articulated for rejecting those arguments. 73 Fed. Reg. at

21,445; 67 Fed. Reg. at 22,223-22,229; see also 73 Fed. Reg. at 21,446

(“We have not received any new information to indicate formula height

should be higher than 47.8 meters, nor have we received a valid demonstration for above-formula stack height credit.”). Although Montana SulMONTANA SULPHUR & CHEMICAL CO. v. EPA 461

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G. Emission Limits from Consent Decrees

[43] Montana Sulphur claims the EPA acted arbitrarily and

capriciously because the FIP did not take into account the

reduced emission limits resulting from certain consent decrees

and Montana air quality permit changes entered into between

sources such as ExxonMobil, CHS Refineries, and the State

of Montana. Montana Sulphur contends it was irrational for

the EPA to ignore the effects of these consent decrees, which

were entered into after the 2002 SIP disapproval but before

the 2006-2008 FIP. 

The EPA offered three justifications for declining to consider the emission reductions that resulted or will result from

those consent decrees and permit changes. First, it noted that

Montana did not actually make any revisions to the SIP to

address the flaws in that document, and, having disapproved

portions of the SIP, the EPA was required to fill those gaps.

73 Fed. Reg. at 21,421. Second, the EPA noted that even

though federally enforceable, some of the state permits can be

revised without EPA approval and the consent decrees have

a “limited lifespan”; it opined that stationary source emission

limits necessary to demonstrate attainment must be included

in the FIP or approved SIP so that changes to those limits may

only be made with its approval. Id. Finally, the EPA

explained that the emission limits within the consent decrees

and permit actions do not contain limits that are consistent

with the averaging times of the NAAQS, specifically the 3-

hour and calendar-day averaging periods. 73 Fed. Reg. at

21,422. For example, the CHS permit and decree impose ppm

limits for 7-day and 365-day rolling averages instead of mass

phur criticizes the EPA for failing to respond to its additional comments

and data, the EPA points out that these comments were not presented to

the EPA until March of 2008, many months after the comment process

had closed and only a few weeks before the final FIP was issued. Thus,

the EPA was not required to consider these untimely comments. See Bd.

of Regents of Univ. of Wash. v. EPA, 86 F.3d 1214, 1222 (D.C. Cir. 1996).

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pound limits per 3-hour and calendar-day periods. Id. The

EPA pointed out that “[n]one of the commenters has suggested these limits be converted to FIP mass limits that would

apply over a 3-hour averaging period, and the State has not

submitted a SIP revision with such limits.” Id.

[44] In light of the specific procedures in place for SIP

approval or disapproval and the responsibility of the EPA to

promulgate a FIP when the state plan is inadequate in some

respect, we conclude the EPA’s position is justified. The EPA

correctly reads 42 U.S.C. § 7410(a)(2) as requiring states to

include enforceable emission limits and other control measures in the plan itself. Whatever requirements may exist in

the consent decrees and construction permits (which may or

may not be equivalent to the requirements of the FIP, since

they are measured by different means over a different time

frame), they are not part of the underlying SIP and the EPA

here has authority to fill the gaps in the portions of the SIP it

had previously disapproved. 

H. Outdated Modeling Methodology

[45] Finally, Montana Sulphur argues that the EPA acted

arbitrarily and capriciously because it used outdated modeling

in the FIP. In the FIP, the EPA used the Industrial Source

Complex (“ISC”) model, which was the preferred model at

the time Montana proposed its SIP. In 2005, the EPA revised

its Guideline on Air Quality Models and recommended use of

a new dispersion model—AERMOD. 70 Fed. Reg. 68,218

(Nov. 9, 2005). However, the rule grandfathered ISC models

for one year (through Nov. 8, 2006), and indicated that during

that time AERMOD could, but was not required to, be substituted for ISC for appropriate applications.13 The EPA proposed the FIP in July 2006, within the one-year transition

period.

13In addition, even after the one-year transition period, applications of

ISC with approved protocols were still acceptable under the regulations.

70 Fed. Reg. at 68,226. 

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In issuing the final FIP in April 2008, the EPA further

defended its choice to stick with the ISC dispersion model:

The commenter is correct that a newer model is

now available. For new SIPs, we would require

states to use EPA’s most recent model. However,

this is a unique situation. The State developed the

Billings/Laurel SO2 SIP using the ISC model, which

was current at that time, and we approved various

source-specific emission limits in the SIP based on

the State’s modeling effort. The purpose of this FIP

is to fill gaps in the approved SIP. We are not intending or required to re-do the entire SIP. . . .

We note that MDEQ tested the performance of the

ISC model when the Billings/Laurel SO2 SIP was

being developed, and the results showed that the

model performance exceeded the performance

criteria for models of this type. . . . 

We also note that ISC remained an accepted EPA

model at the time we proposed our FIP, and it is reasonable to finalize the FIP based on the same model.

Switching models after our proposal would have

required us to re-propose the FIP and would have

delayed the FIP further.

73 Fed. Reg. at 21,437-21,438. 

[46] The EPA’s continued use of the ISC model was not

arbitrary or capricious. The model was properly employed at

both the time of the state SIP and the proposed FIP. The FIP

did not replace the entire SIP, but only the limited portions the

EPA had disapproved; because use of a different model could

have yielded results that did not comport with the remainder

of the SIP, it was not arbitrary or capricious for the EPA to

continue with the existing model despite some later technological improvements.

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CONCLUSION

[47] For the foregoing reasons, we conclude the EPA did

not act arbitrarily or capriciously or abuse its discretion by

making the SIP Call, disapproving portions of the revised SIP,

or promulgating the requirements set forth in the FIP. We

therefore deny the petition for review in both 02-71657 and

08-72642. 

PETITIONS DENIED.

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