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Federal Register / Vol. 86, No. 25 / Tuesday, February 9, 2021 / Proposed Rules Area is 0.062 ppm, which is below 85%
of the 1997 ozone NAAQS.
Additionally, states can support the demonstration of continued maintenance by showing stable or improving air quality trends. According to EPAs 2018 Resource Document, several kinds of analyses can be performed by states wishing to make such a showing. One approach is to take the most recent DV at a monitor located in the area and add the maximum design value increase over one or more consecutive years that has been observed in the area over the past several years. A sum that does not exceed the level of the 1997 ozone NAAQS may be a good indicator of expected continued attainment. As shown in Table 2 of this document, the largest increase in DVs at the monitor located in the Erie Area was 0.004 ppm, which occurred between the 20092011
0.072 ppm and 20102012 0.076 ppm DVs. Adding 0.004 ppm to the DV for the 20172019 period 0.062 ppm results in 0.066 ppm, a sum that is still below the 1997 ozone NAAQS.
The Erie Area has maintained air quality levels well below the 1997
ozone NAAQS since the area first attained the NAAQS in 2006.14
Additional supporting information that the area is expected to continue to maintain the standard can be found in projections of future year DVs that EPA
recently completed to assist states with the development of interstate transport SIPs for the 2015 8-hour ozone NAAQS.
Those projections, made for the year 2023, show that the DV at the monitor located in the Erie Area is expected to be 0.0611 ppm.15 Therefore, EPA
proposes to determine that future violations of the 1997 ozone NAAQS in the Erie Area are unlikely.
C. Continued Air Quality Monitoring and Verification of Continued Attainment
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Once an area has been redesignated to attainment, the state remains obligated to maintain an air quality network in 14 As explained in EPAs July 25, 2007 document proposing to redesignate the Erie Area as attainment for the 1997 ozone NAAQS 72 FR 40776, the 20042006 DV for the Erie Area was 0.079 ppm.
15 See U.S. EPA, Air Quality Modeling Technical Support Document for the Updated 2023 Projected Ozone Design Values, Office of Air Quality Planning and Standards, dated June 2018, available at https www.epa.gov/airmarkets/air-qualitymodeling-technical-support-document-updated2023-projected-ozone-design.

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accordance with 40 CFR part 58, in order to verify the areas attainment status. In the February 27, 2020
submittal, PADEP commits to continue to operate their air monitoring network in accordance with 40 CFR part 58.
PADEP also commits to track the attainment status of the Erie Area for the 1997 ozone NAAQS through the review of air quality and emissions data during the second maintenance period. This includes an annual evaluation of vehicles miles traveled and stationary source emissions data compared to the assumptions included in the LMP.
PADEP also states that it will evaluate the periodic i.e., every three years emission inventories prepared under EPAs Air Emission Reporting Requirements 40 CFR part 51, subpart A. Based on these evaluations, PADEP
will consider whether any further emission control measures should be implemented for the Erie Area. EPA has analyzed the commitments in PADEPs submittal and is proposing to determine that they meet the requirements for continued air quality monitoring and verification of continued attainment.
D. Contingency Plan The contingency plan provisions are designed to promptly correct or prevent a violation of the NAAQS that might occur after redesignation of an area to attainment. Section 175A of the CAA
requires that a maintenance plan include such contingency measures as EPA deems necessary to assure that the state will promptly correct a violation of the NAAQS that occurs after redesignation. The maintenance plan should identify the contingency measures to be adopted, a schedule and procedure for adoption and implementation of the contingency measures, and a time limit for action by the state. The state should also identify specific indicators to be used to determine when the contingency measures need to be adopted and implemented. The maintenance plan must require that the state will implement all pollution control measures that were contained in the SIP
before redesignation of the area to attainment. See section 175Ad of the CAA.
PADEPs February 27, 2020 submittal includes a contingency plan for the Erie Area. In the event that the fourth highest eight-hour ozone concentrations at a monitor in the Erie Area exceeds 0.084

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ppm for two consecutive years, but prior to an actual violation of the NAAQS, PADEP will evaluate whether additional local emission control measures should be implemented that may prevent a violation of the NAAQS.16 After analyzing the conditions causing the excessive ozone levels, evaluating the effectiveness of potential corrective measures, and considering the potential effects of Federal, state, and local measures that have been adopted but not yet implemented, PADEP will begin the process of implementing selected measures so that they can be implemented as expeditiously as practicable following a violation of the NAAQS. In the event of a violation, PADEP commits to adopting additional emission reduction measures as expeditiously as practicable in accordance with the schedule included in the contingency plan as well as the CAA and applicable Pennsylvania statutory requirements.
PADEP will use the following criteria when considering additional emission reduction measures to adopt to address a violation of the 1997 ozone NAAQS in the Erie Area: 1 Air quality analysis indicating the nature of the violation, including the cause, location, and source; 2 emission reduction potential, including extent to which emission generating sources occur in the nonattainment area; 3 timeliness of implementation in terms of the potential to return the area to attainment as expeditiously as practicable; and 4
costs, equity, and cost-effectiveness. The measures PADEP would consider pursuing for adoption in the Erie Area include, but are not limited to, those summarized in Table 3 of this document. If additional emission reductions are necessary, PADEP
commits to adopt additional emission reduction measures to attain and maintain the 1997 ozone NAAQS. The contingency plan includes schedules for the adoption and implementation of both non-regulatory and regulatory contingency measures, including schedules for adopting potential land use planning strategies not listed in Table 3 of this document, which are summarized in Tables 4 and 5
respectively.
16 A violation of the NAAQS occurs when an areas 3-year design value exceeds the NAAQS.

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