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Federal Register / Vol. 86, No. 131 / Tuesday, July 13, 2021 / Proposed Rules
monitor in the Greene County Area is 0.064 ppm, which is well below 85% of the 1997 ozone NAAQS.
States can also support the demonstration of continued maintenance by showing stable or improving air quality trends, and 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 DV
increase over one or more consecutive years that has been observed in the area over the past several years. A sum of these two values that does not exceed the level of the 1997 ozone NAAQS may be a good indicator of expected continued attainment. The data in Table 2 of this document show that the largest DV increase at the monitor located in the Greene County Area was 0.002 ppm, which occurred between the 20092011
0.069 ppm and 20102012 0.071 ppm DVs. Adding 0.002 ppm to the DV for the 20172019 period 0.064 ppm results in 0.066 ppm, a sum that is still below the 1997 ozone NAAQS.
The Greene County Area has maintained air quality levels below the 1997 ozone NAAQS since the Area first attained the NAAQS in 2009, and maintained air quality levels at or below 85% of the NAAQS since 2011.15
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 Greene County Area is expected to be 0.0565 ppm.16 Therefore, EPA proposes to determine that future violations of the 1997 ozone NAAQS in the Greene County Area are unlikely.
C. Continued Air Quality Monitoring and Verification of Continued Attainment Once an area has been redesignated to attainment, the state remains obligated to maintain an air quality network in accordance with 40 CFR part 58 to verify the areas attainment status. In the
February 25, 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 Greene County 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 VMT 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 Greene County 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 25, 2020 submittal includes a contingency plan for the Greene County Area. In the event that the fourth highest eight-hour ozone concentrations at a monitor in the Greene County Area exceeds 84 parts per billion ppb equivalent to 0.084
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.17 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 enacted 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 Greene County 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 Greene County Area include, but are not limited to, those summarized in Table 3. If additional emission reductions are necessary, PADEP commits to adopt additional emission reduction measures to attain and maintain the 1997 ozone NAAQS.

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TABLE 3GREENE COUNTY AREA SECOND MAINTENANCE PLAN CONTINGENCY MEASURES
Non-Regulatory Measures Voluntary diesel engine chip reflash installation software to correct the defeat device option on certain heavy-duty diesel engines.
Diesel retrofit including replacement, repowering or alternative fuel use for public or private local onroad or offroad fleets.
15 As explained in EPAs July 16, 2008 notice proposing to redesignate the Greene County Area as attainment for the 1997 ozone NAAQS 73 FR
40813, the 20032005 DV for the Greene County Area was 0.081 ppm.

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16 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-quality-

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17 A violation of the NAAQS occurs when an areas 3-year design value exceeds the NAAQS.

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