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Federal Register / Vol. 86, No. 208 / Monday, November 1, 2021 / Rules and Regulations
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AMS, in its RACT II determinations, considered the prior source-specific RACT requirements and, where more stringent, retained those prior RACT
requirements as part of its new RACT
determinations. In the NPRM, EPA
proposed to find that all the proposed revisions to previously SIP-approved RACT requirements would result in equivalent or additional reductions of NOX and/or VOC emissions. The proposed revisions should not interfere with any applicable requirements concerning attainment of the NAAQS, reasonable further progress, or other applicable requirements under section 110l of the CAA.
Other specific requirements of the 2008 8-hour ozone NAAQS case-by-case RACT determinations and alternative NOX emissions limits and the rationale for EPAs proposed action are explained more thoroughly in the NPRM, and its associated technical support document TSD, and will not be restated here.
III. EPAs Response to Comments Received EPA received comments from three commenters on the February 9, 2021
NPRM. 86 FR 8743. 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 2008 8hour 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 1-hour 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 NAAQS 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

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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 and allow for comment on any such modeling information or other information utilized in the demonstration that the NAAQS will be protected.5
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 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. For subject sources located in Philadelphia, the City of Philadelphias AMS is the government agency responsible for making such determinations.
As required by Pennsylvanias RACT
II regulations, AMS then conducted, for sources seeking a CbC determination, an analysis examining what air pollution controls were available for those individual sources to determine the lowest emissions 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 For sources seeking an alternative NOX emissions limit, AMS
reviewed the NOX averaging plan to determine that the alternative NOX
emissions limits demonstrated that the emissions under the averaging plan were equivalent to emissions as if the individual sources were operating in accordance with the applicable presumptive limit.
5 This summary of the comment includes supplemental information provided by the commenter in a similar comment to EPAs proposed rulemaking in EPAR03OAR20200597.
6 40 CFR 52.2020d1.
7 84 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.

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Through its source-specific RACT II
determinations, AMS has established NOX and VOC limits and requirements for various sources that either reaffirm existing emissions limits or makes the limits more stringent. PADEP, on behalf of AMS, 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 nine facilities in Philadelphia County. 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 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. For these reasons, EPA
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 RACT II 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
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