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Federal Register / Vol. 86, No. 138 / Thursday, July 22, 2021 / Proposed Rules
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prong 4 visibility transport provisions for the 2015 Ozone NAAQS, as the state is not contributing significantly to nonattainment or maintenance issues in any other state.
In summary, Oklahoma relied on the following points to support its conclusion that Oklahoma meets the prong 4 visibility transport provision for the 2015 Ozone NAAQS: 1 The modeling and technical analysis in the States interstate transport SIP revision as to prongs 1 and 2 under section 110a2DiI purportedly demonstrating that Oklahoma does not significantly contribute to nonattainment or maintenance in another state for the 2015 Ozone NAAQS; 2 the fact that ozone formed from ozone precursor emissions is not believed to contribute significantly to visibility impairment; and 3
Oklahomas 2010 Regional Haze SIP, which Oklahoma says demonstrates that PM2.5 emissions from Oklahoma do not interfere with any other states measures to protect visibility.
On December 1, 2020, EPA sent a letter to ODEQ requesting clarification on how the Oklahoma SIP satisfies the prong 4 interstate visibility transport requirement with respect to the 2015
Ozone NAAQS.17 In a letter dated January 5, 2021, ODEQ pointed out that EPA approved the NOX BART
determinations in the 2010 Oklahoma Regional Haze SIP and also clarified that the SIP addressed NOX and VOC
emissions, which are ozone precursors, using an approach that is consistent with what was anticipated under the CENRAP process for the first regional haze planning period.18 In the letter, ODEQ noted that Sections VII and IX of the 2010 Oklahoma Regional Haze SIP
explain that the SIP requires NOX
reductions resulting from BART and other program requirements, as well as other factors, that are consistent with what was anticipated under the CENRAP consultation process for regional haze SIP development for the first planning period. In the letter, ODEQ further noted that Section VIII of the 2010 Oklahoma Regional Haze SIP
17 Letter from Michael Feldman, Chief, SO and 2
Regional Haze Section, U.S. Environmental Protection Agency, Region 6, to Melanie Foster, Manager, Rules & Planning Section, Air Quality Division, Oklahoma Department of Environmental Quality, December 1, 2020. A copy of this letter is included in the docket associated with this proposed rulemaking.
18 Letter from Kendal Stegmann, Director, Air Quality Division, Oklahoma Department of Environmental Quality, to Michael Feldman, Chief, SO2 and Regional Haze Section, U.S. Environmental Protection Agency, Region 6 January 5, 2021. A
copy of this letter is included in the docket associated with this proposed rulemaking.

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explains that the CENRAP modeling used to project the visibility impacts in 2018 as a result of growth and control of emissions from the baseline for Class I areas in CENRAP states included emission adjustments made by ODEQ to reflect presumptive BART controls for the OG&E Sooner Plant, the OG&E
Muskogee Plant, and the AEP/PSO
Northeastern Plant. For NOX emissions, this presumptive control level is equivalent to 0.15 lb/MMBtu for NOX
BART and is consistent with the NOX
emission limits required by the 2010
Oklahoma Regional Haze SIP for subject-to-BART units at these three power plants.
In the January 5, 2021 letter, ODEQ
also explains that the 2010 Oklahoma Regional Haze SIP did not include additional control requirements to address VOC emissions under regional haze for the first planning period. In the letter, ODEQ points to Section VIA of the 2010 Oklahoma Regional Haze SIP, which explains that ODEQ determined that the visibility impairing pollutants in Oklahoma include SO2, NOX, PM10, and PM2.5, while CENRAP modeling showed that anthropogenic VOCs do not significantly impair visibility at the Wichita Mountains. ODEQ also notes that Section IXE4 of the 2010
Oklahoma Regional Haze SIP explains that the emissions inventory associated with the SIP assigns most emissions of VOCs to biogenic sources, which ODEQ
considers to be natural and therefore uncontrollable. ODEQ explains that Section IXE4 of the 2010 Oklahoma Regional Haze SIP noted that a minority of VOC emissions in Oklahoma originate from area, industrial, point, and mobile sources, and that most of these sources already employ controls under various federal mandates. The 2010 Oklahoma Regional Haze SIP
explained that considering the small and uncertain contribution of anthropogenic sources of VOC to visibility impairment at the Wichita Mountains, ODEQ did not find further VOC controls reasonable. In the letter, ODEQ explains that these determinations similarly apply to the approach taken in the 2010 Oklahoma Regional Haze SIP regarding potential VOC-related impacts of and remedies for visibility impairment at other states Class I areas, and that this approach is consistent with what was anticipated under the CERNAP process for the first regional haze planning period. Further, ODEQ notes that Section VIII of the 2010 Oklahoma Regional Haze SIP
presented model output data that demonstrates that Oklahoma emissions are projected to impair visibility only
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insignificantly at all Class I areas in other states, and ODEQ therefore concluded that additional emission reduction action was not needed to protect other Class I areas, including for NOX and VOC as ozone precursors.
Thus, ODEQ clarifies in the letter that the EPA-approved portion of the 2010
Oklahoma Regional Haze SIP addressed NOX and VOC emissions using an approach that is consistent with what was anticipated in the CENRAP process for the first regional haze planning period and ODEQ states that it believes that, considering the clarifications in the January 5, 2021 letter, and as certified in the October 25, 2018 submittal, the Oklahoma SIP satisfies the interstate visibility transport CAA requirement of section 110a2DiII with respect to the 2015 Ozone NAAQS.
III. The EPAs Evaluation Our 2013 i-SIP guidance addresses the requirements for prong 4 and lays out two ways in which a states infrastructure SIP submittal may satisfy these requirements.19 The first method is through a states confirmation in its infrastructure SIP submittal that it has a fully approved regional haze SIP in place. As previously discussed, EPA
promulgated a partial approval and partial disapproval of the 2010
Oklahoma Regional Haze SIP in 2011
because the SO2 BART determinations for the OG&E Sooner Units 1 and 2, the OG&E Muskogee Units 4 and 5, and the AEP/PSO Northeastern Units 3 and 4
did not comply with our regional haze regulations under 40 CFR 51.308e, and EPA concurrently promulgated a FIP to address these deficiencies.20 On June 20, 2013, Oklahoma submitted a SIP
revision to address this deficiency with respect to the AEP/PSO Northeastern Units 3 and 4, and the FIP with respect to these two units was withdrawn on March 7, 2014.21 However, the FIP
remains in place with SO2 BART
requirements for the OG&E Sooner Units 1 and 2 and the OG&E Muskogee Units 4 and 5. Therefore, Oklahoma cannot rely on a fully approved Regional Haze SIP as the basis for meeting its prong 4
visibility transport obligations for the 2010 SO2, 2012 PM2.5, and the 2015
Ozone NAAQS.
In the absence of a fully approved Regional Haze SIP, the second method provided by the 2013 i-SIP guidance to meet prong 4 requirements is a demonstration that emissions within a states jurisdiction do not interfere with 19 See
2013 i-SIP Guidance at 3235.
FR 81728.
21 79 FR 12954.
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