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Circuit Court Decision on PM2.5 Significant Impact Levels and  

Significant Monitoring Concentration  

Questions and Answers

U.S. Environmental Projection Agency

Office of Air Quality Planning and Standards

March 4, 2013

On January 22, 2013, the United States Court of Appeals for the District of Columbia Circuit

(Court) granted a request from the Environmental Protection Agency (EPA) to vacate and

remand to the EPA the portions of two Prevention of Significant Deterioration (PSD) PM2.5 rules

(40 CFR 51.166 and 40 CFR 52.21) addressing the Significant Impact Levels (SILs) for PM2.5 so

that the EPA could voluntarily correct an error in these provisions. The Court also vacated the

parts of these two PSD rules establishing a PM2.5 Significant Monitoring Concentration (SMC),

finding that the EPA was precluded from using the PM2.5 SMCs to exempt permit applicants

from the statutory requirement to compile preconstruction monitoring data. While the Court’s

holdings are clear, the issuance of the mandate is withheld until seven days after the time to

file a petition for rehearing expires on March 8, 2013, or after a timely petition is denied.1 See

Fed. R. App. P. 41(b). Upon issuance of the mandate, the Court’s decision will become final and

the affected provisions of 40 CFR 51.166 and 52.21 will be vacated.

   

Since the Court’s decision, the EPA has received questions from a number of stakeholders who

implement the PSD permitting program regarding the implications of the Court’s decision in

various contexts. This document is intended to communicate the Court’s decision and the EPA’s

preliminary answers to the most common questions. The EPA is continuing to evaluate the

implications of the Court’s decision and may subsequently refine these answers as necessary.    

At the same time as it is issuing this document, the EPA is also making available for public

comment draft guidance addressing the EPA’s recommendations for completing the air quality

analysis for PM2.5 to support PSD permitting decisions. Portions of that draft guidance reflect

preliminary EPA views on how to complete a PM2.5 air quality impacts analysis in a manner that

is consistent with the January 22 court decision and prior EPA statements. The EPA’s views on

this topic subsequently may be refined based on public comments that are submitted on that

draft guidance. The EPA also intends to develop a proposed rule to address the Court’s

decision.   

                                                           

1 No final decision has been made by the federal government on whether to seek rehearing.
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Given the variability in individual permit applications and the terms of individual state PSD

programs, these preliminary answers may not be applicable in all circumstances. Ultimately, it

is up to individual permitting authorities to determine how best to implement their existing

approved PSD programs in a manner that ensures that their actions on individual PSD permit

applications are consistent with the Court’s decision once it is effective. Moreover, the EPA

advises permitting authorities to immediately align their permitting actions with the decision.

The EPA Regional Offices will also be considering how the decision affects individual state

program approvals that may be pending before the EPA. Accordingly, this document does not

represent a final action with respect to any individual permit application or the EPA’s review of

any individual state implementation plan submission. This document is intended simply to

provide the EPA’s preliminary recommendations for handling situations that the EPA believes

may be common across permit applications and programs.  

I.  Permits

1.  How does the Court’s January 22, 2013 decision vacating the PM2.5 SMC and paragraph (k)(2)

in 40 CFR 52.21 (concerning the implementation of the PM2.5 SILs)  affect pending federal PSD

permits?  

 As a result of the Court’s decision, federal PSD permits issued henceforth by either the

EPA or a delegated state permitting authority pursuant to 40 CFR 52.21 should not rely

on the PM2.5 SMC to allow  applicants to avoid compiling air quality monitoring data for

PM2.5. Accordingly, all applicants requesting a federal PSD permit, including those having

already applied for but have not yet received the permit, should submit ambient PM2.5

monitoring data in accordance with the Clean Air Act requirements whenever either

direct PM2.5 or any PM2.5 precursor is emitted in a significant amount. In lieu of

applicants setting out PM2.5 monitors to collect ambient data, applicants may submit

PM2.5 ambient data collected from existing monitoring networks when the permitting

authority deems such data to be representative of the air quality in the area of concern

for the year preceding receipt of the application. We believe that applicants will

generally be able to rely on existing representative monitoring data to satisfy the

monitoring data requirement.

 In keeping with the Court’s decision vacating paragraph (k)(2), pending permits should

not rely on the PM2.5 SILs alone to demonstrate that the source will not cause or

contribute to a violation of the PM2.5 National Ambient Air Quality Standards (NAAQS) or

increments. Our response to question 3, below, provides more information on this

point.
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2.  How does the Court’s decision vacating paragraph (k)(2) in 40 CFR 51.166 (concerning the

implementation of the PM2.5 SILs) and the PM2.5 SMC affect pending PSD permits issued by

states under EPA‐approved PSD programs?

 Given the clarity of the Court’s decision, states with EPA‐approved PSD programs are

advised to issue PSD permits in a manner consistent with the response to question 3

below concerning the use of PM2.5 SILs, and to not rely on the PM2.5 SMC to allow

applicants to avoid compiling air quality monitoring data for PM2.5 ‐‐ even when their

existing state PSD regulations (whether or not included in an EPA‐approved State

Implementation Plan (SIP)) may still contain the PM2.5 SMC and/or regulatory text

equivalent to the vacated paragraph (k)(2) language for PM2.5 SILs in 40 CFR 51.166.  

3.  May the PM2.5 SILs be used to complete the required PM2.5 air quality analysis in light of the

Court’s decision?

 The EPA does not interpret the Court’s decision to preclude the use of SILs for PM2.5  

entirely but additional care should be taken by permitting authorities in how they apply

those SILs so that the permitting record supports a conclusion that the source will not

cause or contribute to a violation of the PM2.5 NAAQS .   

 PSD permitting authorities have the discretion to select PM2.5 SIL values if the permitting

record provides sufficient justification for the SIL values that are used and the manner in

which they are used to support a permitting decision.

 The PM2.5 SIL values in the EPA’s regulations may continue to be used in some

circumstances if permitting authorities take care to consider background concentrations

prior to using these SIL values in particular ways.  

 Because of the Court’s decision vacating the PM2.5 SMC, all applicants for a federal PSD

permit should include ambient PM2.5 monitoring data as part of the air quality impacts

analysis. If the preconstruction monitoring data shows that the difference between the

PM2.5 NAAQS and the monitored PM2.5 background concentrations in the area is greater

than the EPA’s PM2.5 SIL value, then the EPA believes it would be sufficient in most cases

for permitting authorities to conclude that a proposed source with a PM2.5 impact below

the PM2.5 SIL value will not cause or contribute to a violation of the PM2.5 NAAQS and to

forego a more comprehensive cumulative modeling analysis for PM2.5.  

 As part of a cumulative analysis, the applicant may continue to show that the proposed

source does not contribute to an existing violation of the PM2.5 NAAQS by

demonstrating that the proposed source’s PM2.5 impact does not significantly contribute

to an existing violation of the PM2.5 NAAQS. However, permitting authorities should

consult with the EPA before using any of the SIL values in the EPA’s regulations for this
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purpose (including the PM2.5 SIL value in section 51.165(b)(2), which was not vacated by

the Court).   

4.  How does the Court’s decision on PM2.5 SILs and SMC affect permits already issued?

 The EPA believes that sources with final PSD permits are not likely to be affected by the

Court’s decision, since they were issued in accordance with the rules in effect at that

time.  

5.  In light of the Court’s decision to vacate the PM2.5 SMC, how will the EPA implement the PSD

monitoring requirement, one subsection of which allows sources to be exempt from having to

submit ambient monitoring data for any pollutant for which an SMC is not listed?

 The federal PSD regulations at 40 CFR 52.21(i)(5)(iii) provide the Administrator with

discretionary authority to exempt a proposed source or modification from the PSD

monitoring requirement for a particular pollutant “if the pollutant is not listed in

[paragraph containing the various pollutant SMCs].”  

 In its decision, the Court held that the EPA did not have the authority to use SMCs to

exempt permit applicants from the statutory requirement in the Clean Air Act at section

165(e)(2) that ambient monitoring data for PM2.5 be included in all PSD permit

applications. To ensure that the Court’s decision is not misapplied, we intend not to

exempt sources from the monitoring requirement with respect to PM2.5. A future

rulemaking will propose the necessary changes to ensure that sources will not be

exempted from the monitoring requirement for PM2.5.   

II. State Implementation Plans

1. How does the Court’s decision on PM2.5 SILs and SMC affect the required SIP revisions for

PM2.5?   

 States should avoid including language in their SIP revision that is the same as or has a

similar effect as the paragraph (k)(2) language in 40 CFR 51.166 and 52.21. As a result of

the Court’s decision, the EPA does not believe it can approve the portion of any SIP

submission that is identical, or substantially similar, to the vacated (k)(2) regulatory text,

but the EPA may approve the remainder of the SIP submission where it is appropriate to

do so.  

 Similarly, the SIP should not include the PM2.5 SMC, which the Court’s decision found

inconsistent with the CAA. The EPA does not believe it can approve the portion of the
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SIP that defines the PM2.5 SMC, but it may approve the remainder of the SIP submission

where it is appropriate to do so.  

 Neither the PM2.5 SILs nor the PM2.5 SMC are required elements of the PSD SIP for PM2.5.

Accordingly, States that have already made submissions including either provision are

free to and are encouraged to withdraw those portions of their submissions in light of

the Court’s decision.  

2. How does the Court’s decision affect SIPs that have already been approved for PM2.5?

 The EPA will likely need to consider a rulemaking to remove the vacated provisions from

its PSD regulations at 40 CFR 51.166 and 52.21. The EPA advises states with approved

SIPs containing language that is the same as the PM2.5 SILs and SMC provisions that the

Court determined to be invalid to begin preparations to remove those provisions.

However, if any rehearing or appeal of the court decision is sought, some uncertainty

may remain on this issue until such rehearing or appeal of the Court’s decision is

concluded. Although the Court’s decision is not final until the mandate is issued, the EPA

advises permitting authorities to consider these provisions unlawful and, therefore,

recommends that they not be applied to individual PSD permits even if they remain in

state law or the states’ approved SIPs.   

 States should be advised that permits issued on the basis of these provisions may be

inconsistent with the Clean Air Act and may be difficult to defend in administrative and

judicial challenges. Once the Court’s mandate is issued, the applicable provisions in the

federal PSD regulations will be without legal effect.