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Federal Register / Vol. 86, No. 165 / Monday, August 30, 2021 / Proposed Rules
obligation with respect to the 2015
ozone NAAQS.17

III. EPA Evaluation of Connecticuts Submittal
II. Connecticut Submittal On December 6, 2018, Connecticut submitted a SIP revision addressing the CAA section 110a2DiI interstate transport requirements for the 2015
ozone NAAQS. Connecticut relied on the results of EPAs modeling for the 2015 ozone NAAQS contained in the March 2018 memo to identify downwind nonattainment and maintenance receptors that may be impacted by emissions from sources in Connecticut in the year 2023. These results indicate Connecticuts greatest impact on any potential downwind nonattainment or maintenance receptor would be 0.83 ppb in Suffolk County, New York.18 Based on the March 2018
memo, this was the only nonattainment or maintenance receptor for which Connecticut was projected in 2023 to contribute above the screening threshold of 0.70 ppb one percent of the 2015 ozone NAAQS.
Connecticut noted in its December 2018 good neighbor submittal that EPA
had considered cost-effective only reductions that are available at a cost of less than $1,400 per ton of emissions reduced. Connecticuts emitters are currently required to adopt control measures at costs exceeding $13,000 per ton of NOX. 19 Connecticut states that as it requires this high level of control of ozone precursor emissions, it has exhausted lower-cost emission reduction measures.
As evidence of this, Connecticut points to Regulations of Connecticut Agencies section 22a17422eg and its ozone attainment plan technical support document for the 2008 ozone NAAQS, which was submitted to EPA in August 2017 and documents the States ozone precursor emission reduction measures.
Connecticut concludes that it has met its good neighbor obligations for the 2015 ozone NAAQS because of the existing control measures that are in place.

Connecticuts SIP submission relies on analysis of the year 2023 to show whether it contributes to nonattainment or interferes with maintenance of the 2015 ozone NAAQS in any other state.20
As explained in Section I of this proposal, EPA has conducted an updated analysis for the 2021 analytical year that is being used to evaluate Connecticuts transport SIP submittal.
Significantly, this new analysis shows that, in 2021, Connecticut is not projected to contribute to any potential downwind nonattainment or maintenance receptor, including the monitor in Suffolk County, New York, above the screening threshold of 0.70
ppb one percent of the 2015 ozone NAAQS. While EPA has focused its analysis in this document on the year 2021, modeling data in the record for years 2023 and 2028 confirm that no new linkages to downwind receptors are projected for Connecticut in later years.
This is not surprising as it is consistent with an overall, long-term downward trend in emissions from this state.
As explained in Section I of this document, in consideration of the holdings in Wisconsin and Maryland, EPAs analysis relies on 2021 as the relevant attainment year for evaluating Connecticuts good neighbor obligations with respect to the 2015 ozone NAAQS
using the four-step interstate transport framework. In step 1, we identify locations where the Agency expects there to be nonattainment or maintenance receptors for the 2015 8hour ozone NAAQS in the 2021 analytic year. Where EPAs analysis shows that an area or site does not fall under the definition of a nonattainment or maintenance receptor, that site is excluded from further analysis under EPAs four step interstate transport framework. For areas that are identified as a nonattainment or maintenance receptor in 2021, we proceed to the next step of our four-step framework by identifying the upwind states contribution to those receptors.

17 EPA recognizes that by the time final action is taken with respect to this SIP submission, the 2021
ozone season will be wholly in the past. As discussed below, the available modeling information indicates that our analysis would not change even using 2023 as the analytic year. The 2023 modeling results are included in the Ozone Design Values and Contributions Revised CSAPR
Update.xlsx, included in the docket for this action.
18 EPA notes that the monitoring site ID for Suffolk County, New York is 361030002.
19 EPA notes that the $1,400 ton per year threshold stated by Connecticut is in reference to the cost per ton threshold used in the CSAPR
Update, which was used to evaluate available costeffective EGU controls under the 2008 ozone NAAQS of 0.075 ppm. See 81 FR 74504 October 26, 2016.

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20 We recognize that Connecticut and other states may have been influenced by EPAs 2018 guidance memos issued prior to the Wisconsin and Maryland decisions in making good neighbor submissions that relied on EPAs modeling of 2023. When there are intervening changes in relevant law or legal interpretation of CAA requirements, states are generally free to withdraw, supplement, and/or resubmit their SIP submissions with new analysis in compliance with CAA procedures for SIP
submissions. While Connecticut has not done this, as explained in this section, the independent analysis EPA has conducted at its discretion confirms that the states submission in this instance is ultimately approvable.

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EPAs approach to identifying ozone nonattainment and maintenance receptors in this action is consistent with the approach used in previous transport rulemakings. EPAs approach gives independent consideration to both the contribute significantly to nonattainment and the interfere with maintenance prongs of CAA section 110a2DiI, consistent with the D.C. Circuits direction in North Carolina v. EPA.21
For the purpose of this proposal, EPA
identifies nonattainment receptors as those monitoring sites that are projected to have average design values that exceed the NAAQS and that are also measuring nonattainment based on the most recent monitored design values.
This approach is consistent with prior transport rulemakings, such as CSAPR
Update, where EPA defined nonattainment receptors as those areas that both currently monitor nonattainment and that EPA projects will be in nonattainment in the future analytic year.22
In addition, in this proposal, EPA
identifies a receptor to be a maintenance receptor for purposes of defining interference with maintenance, consistent with the method used in the CSAPR and upheld by the D.C. Circuit in EME Homer City Generation, L.P. v.
EPA, 795 F.3d 118, 136 D.C. Cir.
2015.23 Specifically, monitoring sites with a projected maximum design value in 2021 that exceeds the NAAQS are considered maintenance receptors.
EPAs method of defining these receptors takes into account both measured data and reasonable projections based on modeling analysis.
Recognizing that nonattainment receptors are also, by definition, maintenance receptors, EPA often uses the term maintenance-only to refer to receptors that are not also nonattainment receptors. Consistent with the methodology described above, monitoring sites with a projected maximum design value that exceeds the NAAQS, but with a projected average design value that is below the NAAQS, 21 See North Carolina v. EPA, 531 F.3d 896, 910
11 D.C. Cir. 2008 holding that EPA must give independent significance to each prong of CAA
section 110a2DiI.
22 See 81 FR 74504 October 26, 2016. Revised CSAPR Update also used this approach. See 86 FR
23054 April 30, 2021. This same concept, relying on both current monitoring data and modeling to define nonattainment receptor, was also applied in CAIR. See 70 FR 25241 January 14, 2005; see also North Carolina, 531 F.3d at 91314 affirming as reasonable EPAs approach to defining nonattainment in CAIR.
23 See 76 FR 48208 August 8, 2011. CSAPR
Update and Revised CSAPR Update also used this approach. See 81 FR 74504 October 26, 2016 and 86 FR 23054 April 30, 2021.

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