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Federal Register / Vol. 86, No. 167 / Wednesday, September 1, 2021 / Rules and Regulations
the NAAQS, reasonable further progress, or other applicable requirements under section 110l of the CAA.
Other specific requirements of Pennsylvanias 1997 and 2008 8-hour ozone NAAQS case-by-case RACT
determinations and alternative NOX
emissions limits and the rationale for EPAs proposed action were explained in the NPRM, and its associated technical support document TSD, and will not be restated here.

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III. Public Comments and EPA
Responses EPA received comments from four commenters on the February 11, 2021
NPRM. 86 FR 9031. A summary of the comments and EPAs response are discussed in this section. A copy of the comments can be found in the docket for this rule action.
Comment 1: The commenter claims that EPA cannot approve the proposed Pennsylvania RACT II case-by-case CbC determinations under the 1997
and 2008 8-hour ozone NAAQS because the CAA section 110l analysis is inadequate. In particular, the commenter focuses on the proposed NOX limitations and whether they will cause or contribute to violations of the 2010 1-hour NOX NAAQS. The 2010 1hour NAAQS is for oxides of nitrogen, as measured by nitrogen dioxide NO2.
The commenter argues that under CAA
section 110k1a and 40 CFR part 51, Appendix V, 2.2d, a state must demonstrate that the NAAQSs are protected if a SIP is to be approved and that Pennsylvania has not made an adequate demonstration under section 110l related to the potential impact of these RACT determinations on the 2010
1-hour NOX NAAQS. The commenter then suggests that EPA is unable to approve Pennsylvanias CbC RACT II
determinations unless such a demonstration has been made, even though the rules reduce NOX emissions.
The commenter highlights their concern by including results from air dispersion modeling of NOX emissions from the Bighorn well pad in Colorado that they claim shows the potential impact of NOX emissions on 1-hour NOX NAAQS
violations. The commenter states that EPA must undertake a modeling analysis to determine if the proposed CbC RACT II determinations will cause or contribute to 2010 1-hour NOX
NAAQS violations. The commenter indicates that EPA must repropose this action including any such modeling information or other information utilized in the demonstration that the NAAQS will be protected.

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Response 1: As described in the proposed rulemaking, Pennsylvania was required through implementation of the 1997 and 2008 8-hour ozone NAAQS to determine RACT II requirements for major NOX and VOC emitting sources within the Commonwealth. PADEP had previously established CbC RACT
requirements under the 1979 1-hour ozone NAAQS.6 PADEP finalized its overall RACT II program, which included presumptive RACT for certain sources, and it was conditionally approved by EPA.7 As part of the EPAs conditional approval, PADEP was required to complete source-specific CbC RACT II determinations for subject NOX or VOC sources that could not meet the presumptive requirements or for which a presumptive limit did not exist. As required by its regulations, PADEP then conducted a RACT II CbC
analysis examining what air pollution controls are available for those individual sources to determine the lowest emission limit that a particular source is capable of meeting by the application of control technology that is reasonably available considering technologically and economic feasibility.8
Through its RACT II CbC
determinations, PADEP has established NOX and VOC limits and requirements for various sources that either reaffirm existing emission limits or makes the limits more stringent. PADEP submitted those determinations to EPA as bundled packages of individual SIP revisions.
EPA is now approving the RACT II CbC
SIP revisions for individual NOX and VOC sources at eight facilities. For the reasons explained below, EPA
concludes that the arguments presented by the commenter do not prohibit approval of these SIP revisions.
CAA section 110l prohibits EPA
from approving a SIP revision if the revision would interfere with any applicable requirement concerning attainment and reasonable further progress . . . or any other applicable requirement of this chapter. 42 U.S.C.
7410l. While EPA interprets section 110l as applying to all NAAQS that are in effect, including those for which a relevant SIP submission may not have been made, the level of rigor needed for any CAA section 110l demonstration will vary depending on the nature and circumstances of the revision. For 6 40

CFR 52.2020d1.
FR 20274 May 9, 2019.
8 See December 9, 1976 memorandum from Roger Strelow, Assistant Administrator for Air and Waste Management, to Regional Administrators, Guidance for Determining Acceptability of SIP
Regulations in Non-Attainment Areas, and 44 FR
53762 September 17, 1979.
7 84

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example, an in-depth section 110l analysis is more appropriate where there is a reasonable expectation that an existing SIP standard is being weakened or that there will be a net emissions increase because of approval of the SIP
revision under consideration. However, here, the Pennsylvania CbC RACT II SIP
revisions are either retaining an existing standard or establishing a more stringent one. EPA, for these reasons, did not include a detailed section 110l analysis at the proposal stage. Since the commenter raised the issue, EPA is responding in this final action by explaining why its approval is consistent with section 110l.
In circumstances where an existing SIP standard is being weakened or a net emissions increase is expected, there are two generally recognized paths for satisfying CAA section 110l. First, a state may demonstrate through an air quality modeling analysis that the revision will not interfere with the attainment of the NAAQS, reasonable further progress, or any other applicable requirement. This is the approach the commenter claims is required for the Pennsylvania CbC SIP revisions.
Second, a state may substitute equivalent or greater emissions reductions to compensate for any change to a plan to ensure actual emissions to the air are not increased and thus preserve status quo air quality.
A showing that the substitute measures preserve status quo air quality is generally sufficient to demonstrate noninterference through this alternative approach. Courts have upheld EPAs approval of a SIP revision based on a states use of substitute measures.
Kentucky Resources Council, Inc. v.
EPA, 467 F.3d 986 6th Cir. 2006 and Indiana v. EPA, 796 F. 3d 803 7th Cir.
2015.
Both the Kentucky Resources and Indiana cases involved circumstances where a state sought to revise provisions within its SIP related to its vehicle emissions testing program. In both situations, the petitioners were concerned with increased emissions that might occur due to the changes to the testing program. The state in each case justified its SIP revision, in part, by demonstrating that it had substitute emission reductions that would fully compensate for the expected emissions increase caused by the modifications to the testing program. The court in each case upheld EPAs interpretation of section 110l, which allows states to substitute equivalent emissions reductions to compensate for any change to a plan to ensure actual emissions to the air are not increased and thus preserve status quo air quality.

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