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Federal Register / Vol. 86, No. 122 / Tuesday, June 29, 2021 / Proposed Rules
additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit https www.epa.gov/dockets/
commenting-epa-dockets.

lotter on DSK11XQN23PROD with PROPOSALS1

II. Have the requirements for approval of a SIP revision been met?
The State submission has met the public notice requirements for SIP
submissions in accordance with 40 CFR
51.102. The submission also satisfied the completeness criteria of 40 CFR part 51, appendix V. The State provided public notice on the December 2017 SIP
submittal from July 31, 2017 to September 7, 2017 and held a public hearing on August 31, 2017. The State received and addressed nineteen combined comments from a total of five sources. The State revised the maintenance plan based on public comment prior to submitting to the EPA.
On April 9, 2021, Missouri submitted a supplement to the SIP revision to the EPA consisting of an addendum to the Consent Agreement between Ameren and Missouri. The Consent Agreement addendum incorporates monitoring, reporting and recordkeeping requirements needed to make the emissions limits contained in the Consent Agreement practically enforceable. Missouri held a public hearing for this SIP supplement on January 28, 2021 and made the supplement available for public review and comment from December 28, 2020
through February 4, 2021. Missouri received supportive comments from Ameren.
In addition, as explained above and in more detail in the technical support document which is included in the docket for this action, the revision meets the substantive SIP requirements of the CAA, including section 110 and implementing regulations.
III. What is the background for the EPAs proposed actions?
On June 2, 2010, the EPA revised the primary SO2 NAAQS, establishing a new 1-hour standard of 75 parts per billion ppb.1 Under the EPAs regulations at 40 CFR part 50, the 2010
1-hour SO2 NAAQS is met at a monitoring site when the 3-year average of the annual 99th percentile of daily maximum 1-hour average concentrations is less than or equal to 75 ppb based on the rounding convention in 40 CFR part 50, appendix T.2 Ambient air quality monitoring data
for the 3-year period must meet a data completeness requirement. A year meets data completeness requirements when all four quarters are complete, and a quarter is complete when at least 75
percent of the sampling days for each quarter have complete data. A sampling day has complete data if 75 percent of the hourly concentration values, including State-flagged data affected by exceptional events which have been approved for exclusion by the Administrator, are reported.3
Upon promulgation of a new or revised NAAQS, the CAA requires the EPA to designate as nonattainment any area that does not meet or that contributes to ambient air quality in a nearby area that does not meet the NAAQS.4 On August 5, 2013, the EPA
designated a portion of Jefferson County, Missouri, as nonattainment for the 2010 1-hour primary SO2 NAAQS, effective October 4, 2013.5 The designation was based on 20082010
monitoring data in Herculaneum, Missouri, which monitored violations of the standard see section III of this document for additional monitoring information. This action established an attainment date five years after the effective date for the areas designated as nonattainment for the 2010 SO2 NAAQS
i.e., by October 4, 2018. The State was also required to submit a SIP for the Jefferson County SO2 nonattainment area to the EPA that meets the requirements of CAA sections 110, 172c and 191192 within 18 months following the October 4, 2013, effective date of designation i.e., by April 4, 2015. The State of Missouri submitted the Nonattainment Area Plan for the 2010 1-Hour Sulfur Dioxide National Ambient Air Quality Standard Jefferson County Sulfur Dioxide Nonattainment Area on June 5, 2015, and subsequently withdrew the plan on March 30, 2018, following several intervening steps discussed later in this section.
On February 2, 2016, the State submitted a request asking the EPA to determine that the Jefferson County SO2
nonattainment area attained the 2010 1hour primary SO2 NAAQS per the EPAs Clean Data Policy. The clean data policy represents the EPAs interpretation that certain planning-related requirements of part D of the Act, such as the attainment demonstration, reasonably available control measures RACM, and reasonable further progress RFP, are suspended for areas that are in fact 3 40

CFR part 50, appendix T, section 3b.
section 107d1Ai.
5 78 FR 47191 August 5, 2013, codified at 40
CFR 81.326.
4 CAA

1 See 2 See
75 FR 35520.
40 CFR 50.17.

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attaining the NAAQS. A determination of attainment, or clean data determination, does not constitute a formal redesignation to attainment. If the EPA subsequently determines that an area is no longer attaining the standard, those requirements that were suspended by the clean data determination are once again due.
On June 23, 2017, the EPA published a notice of proposed rulemaking to approve the States request for a clean data determination. The proposal was based on 20142016 monitoring data the Mott Street monitor design value dv was 23 parts per billion ppband modeling data a mix of 20132015
actual and allowable emissions.6 7 After considering public comments received, the EPA published a Notice of Final Rulemaking NFRM approving the States request for a clean data determination in the Federal Register on September 13, 2017.8
On December 27, 2017, the State submitted a request for redesignation of the Jefferson County SO2 nonattainment area to attainment and a SIP revision containing a 10-year maintenance plan for the area. On May 15, 2018, the State submitted a clarifying letter that Appendix A containing the emissions inventory for the area and Appendix B
containing a Consent Agreement for certain sources in the area of the SIP
submittal should be considered part of the SIP revision request. On February 7, 2019, and February 25, 2019, the State submitted supplemental modeling information to the EPA. On April 9, 2021, the State submitted an addendum to the Consent Agreement which contains the emissions limits and monitoring, reporting, and recordkeeping requirements needed to determine compliance with the emissions limits for the covered sources.
This proposal document discusses the EPAs review of the redesignation request, the maintenance plan including Consent Agreement and addendum, and the supplemental information and provides support for the EPAs proposed approval of the request to redesignate the area to attainment and for proposed approval of the 10-year maintenance plan.
Additional analysis of the redesignation request, 10-year maintenance plan, Consent Agreement and addendum, and supplemental modeling information is 6 See
82 FR 28605.
State or Local Air Monitoring Station SLAMS was moved from Main Street to Mott Street in 2011 with EPA approval. The Mott Street SLAMS location was selected to characterize source specific both SO2 and lead emissions from the Doe Run Herculaneum primary lead smelter.
8 See 82 FR 42945.
7 The
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