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Federal Register / Vol. 86, No. 229 / Thursday, December 2, 2021 / Rules and Regulations
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Regarding the contention that the CSAPR Update, which covered the 2008
8-hour ozone NAAQS, will not be sufficient to bring areas into attainment of the 2008 or 2015 8-hour ozone NAAQS, this is not relevant to the analysis in support of this action.
Whether downwind states may or may not reach attainment of the 2015 8-hour ozone NAAQS with the assistance of the upwind state emissions reductions resulting from the CSAPR Update is not determinative of whether Florida, Georgia, North Carolina, and South Carolina have Good Neighbor obligations for the 2015 8-hour ozone NAAQS pursuant to the CAA. At issue is whether Florida, Georgia, North Carolina, and South Carolina will significantly contribute to downwind nonattainment or interfere with maintenance of the 2015 8-hour ozone NAAQS in any other state. The updated information presented in the SNPRM
made clear that they will not, and no party commented on that updated information.
Comment 2: Several commenters call into question certain assumptions used in EPAs 2023 air quality modeling described in the March 2018
memorandum. A number of commenters contend that EPAs modeling was flawed because it relied on unenforceable emissions limitations, including assumptions that power plants equipped with selective catalytic reduction SCR controls would emit at or below 0.10 pounds per one million British Thermal Units lb/mmBtu beginning in 2017. One commenter contended that many plants emit above that rate. Another commenter asserts that EPA should not approve any prong 1 and 2 SIPs 9 that reflect EPAs flawed data showing attainment by 2023.
Response 2: As discussed previously and in the SNPRM, EPA is relying on updated modeling and analysis based on the 2021 analytic year and not the 2023 air quality modeling described in the March 2018 memorandum.
However, EPA disagrees that its assessment of air quality and contributions at step 1 and 2 of the fourstep interstate transport framework is flawed because it relies on unenforceable emission assumptions for electric generating units EGUs or that those assumptions are otherwise unrealistic. As an initial matter, in this context it is appropriate for EPA to 9 Section 110a2DiI requires SIPs to contain adequate provisions that prohibit any source or other types of emissions activity in one state from contributing significantly to nonattainment of the NAAQS in another state prong 1 and from interfering with maintenance of the NAAQS in another state prong 2.

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focus on actual EGU emission projections, rather than modeling only enforceable limits sometimes referred to as allowable emissions. EPA has previously explained that its analysis at steps 1 and 2 of the four-step interstate transport framework is appropriately focused on a projection of actual air quality concentrations and upwind-state contributions. As EPA explained in the final CSAPR Close-out, this approach to conducting future-year modeling in the Good Neighbor analysis to identify downwind air quality problems and linked states is consistent with the use of current measured data in the designations process under section 107
of the CAA. See 83 FR 65878, 65887
88 December 21, 2018.10 In both cases, the purpose is to determine whether there is an actual air quality problem that needs to be further addressed in the designations context, whether an area is in nonattainment of a NAAQS;
in the Good Neighbor context, whether there are expected future air quality problems i.e., downwind nonattainment or maintenance receptors and upwind state contribution to these downwind nonattainment or maintenance receptors that require further analysis at steps 3
and 4. EPAs future-year air quality projections reflect a variety of factors, including current emissions data, onthe-books control measures, economic market influences, and meteorology.
Like the factors that affect measured ozone concentrations used in the designations process, not all of the factors influencing EPAs modeling projections are or can be subject to enforceable limitations on emissions or ozone concentrations. However, EPA
believes that consideration of these factors contributes to a reasonable estimate of anticipated future ozone concentrations and contributions at steps 1 and 2 of the four-step interstate transport framework. In short, EPAs consideration of these factorseven when not based on or amendable to enforceable limits or controlsin its future-year modeling projections used at steps 1 and 2 of the Good Neighbor analysis is reasonable. See 83 FR at 65888 December 21, 2018. Only where such analysis indicates an upwind-state linkage under projected conditions does further analysis proceed at steps 3 and 4 of the four-step interstate transport framework to determine what enforceable emissions limits should be required in the linked upwind state.
EPAs air quality modeling and analysis 10 The CSAPR Close-out was vacated on grounds unrelated to this issue. See New York v. EPA, 781
F. Appx. 4 D.C. Cir. 2019.

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is designed to reflect what downwind air quality problems will exist in the relevant analytic year, and the assumptions used are based on realistic projections of source emissions.
In response to the commenters contention that EPA should not model using the 0.1 lb/mmBtu emission rate assumption for EGUs because it is not enforceable and some units emit higher than this rate, this concern is addressed by the updates contained in the updated 2023 modeling used to derive EPAs 2021 air quality analysis for this final action. Specifically, as noted in the SNPRM, EPA is relying on updated Integrated Planning Model IPM
modeling for its EGU projection in the updated analysis for this final action.
Additionally, EPA has modeled a range of scenarios reflecting alternative EGU
assumptionseach resulting in the same finding made in this action.11
Although EPA disagrees with these comments regarding the modeling approach it took at the original proposal with respect to projecting EGU
emissions,12 the Agency made updates to incorporate the latest modeling and data, which address the concerns expressed by the commenters. The December 30, 2019 NPRM rule relied on air quality modeling analysis and data released in 2018 that showed results from analytic work completed in 2017
prior to the completion of the first year of CSAPR Update compliance.13 As explained in the modeling TSD
referenced in the July 19, 2021 SNPRM, EPA started with the latest historical data at that time 2016 and assumed that, on average, SCR-controlled coal units would operate at 0.1 lb/mmBtu if not already doing so reflecting the fleets response on average to the CSAPR Update that would begin in 2017.14 In this final action, EPAs future year air quality projections are informed by actual compliance data from 2019, which allows EPA to rely less on compliance assumptions and more on actual data from the past three years in evaluating likely EGU
emissions in 2021. EPA estimated future 11 See the Ozone Air Quality Assessment Tool AQAT spreadsheet and the Ozone Policy Analysis TSD located in the docket for this action for details about these scenarios, emissions, and air quality estimates.
12 As explained further in this rule, the analysis supporting the December 30, 2019 proposal overestimated EGU emissions.
13 See March 2018 memorandum, located in the docket for this action.
14 Technical Support Document TSD Additional Updates to Emissions Inventories for the Version 6.3, 2011 Emissions Modeling Platform for the Year 2023, available at https www.epa.gov/sites/
production/files/2017-11/documents/2011v6.3_
2023en_update_emismod_tsd_oct2017.pdf.

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