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Federal Register / Vol. 86, No. 122 / Tuesday, June 29, 2021 / Proposed Rules modeling, Missouri has demonstrated maintenance by modeling all sources inside of the nonattainment area at their permanent, enforceable, allowable emission rates, nearby sources at their permanent, enforceable, allowable emission rates with actual operating conditions for 20132017, and other sources addressed through the use of a background concentration. The EPA
proposes that the supplemental modeling provided by Missouri demonstrates the standard will be attained and maintained for at least 10
years following redesignation of the area, consistent with the second method outlined in the Calcagni memo by which a State may demonstrate maintenance of the NAAQS. Please see the TSD for details of the modeling inputs, results and the EPAs review of them. The EPA is proposing to approve Missouris maintenance plan including the supplemental modeling and a background concentration revised by the EPA as meeting the maintenance demonstration requirement.

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d. Monitoring Network Missouri has committed to continue operating the appropriate SO2 network in the Jefferson County nonattainment area in accordance with the requirements of 40 CFR part 58, and approved annual monitoring network plans, to verify the attainment status of the area. The State committed to quality assure the data in accordance with 40
CFR part 58 and submit the data to the EPAs air quality system AQS. The maintenance plan, consistent with the States 2019 annual ambient monitoring network plan, indicate that the Mott Street monitor is the only SLAMS or SLAMS like monitor operational in the nonattainment area.29
There are also three industrial source monitors located around Rush Island.30
These monitors are required per the Consent Agreement between Ameren and the State.31 The Consent Agreement required the monitors to start operation by December 2015 and operate 12
consecutive quarters 3 years. The industrial source monitors have also been identified in the States annual ambient monitoring network plans since 2015.32 The Consent Agreement also requires certain responses by Ameren if 29 See Missouris 2019 Ambient Monitoring Network Plan contained in the docket for this action.
30 The industrial monitors are not classified as SLAMS nor as Data Requirements Rule monitors.
31 The Consent Agreement is included as Appendix B of the maintenance plan.
32 The EPA approved the States 2019 Ambient Monitoring Network Plan via letter dated January 8, 2021. Missouris 2019 Plan and the EPAs approval letter are included in the docket for this action.

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elevated monitoring values are recorded at any of the industrial source monitors.
The maintenance plan and Consent Agreement requires Ameren to operate the industrial source monitors for a minimum of 12 consecutive quarters.
The maintenance plan and Consent Agreement do not establish that the monitors must be operated as SLAMSlike monitors which would make them subject to the discontinuation requirements of 40 CFR part 58.33
However, because the EPA is proposing to approve the requirement to operate the industrial source monitors, and that the contingency measures may be triggered by data recorded by these industrial source monitors, as contained in the Consent Agreement, into the SIP, the monitors must operate until the EPA
approves a revision to the SIP to remove the monitoring requirements.
Because the industrial source monitors were not identified by the State as necessary to meet the requirements of the Data Requirements Rule DRR they are not subject to the requirements of 40 CFR 51.1203c.34
The 2018 annual monitoring network plan commits the State to continuing to work with Ameren to collect quality assured SO2 ambient air quality data and meteorological data near the Rush Island power station to provide quantifiable and useful information to supplement the ongoing 1-hour SO2
NAAQS implementation process.
Because there is no regulatory obligation, or commitment from Ameren or the State to operate the industrial source monitors as SLAMS-like or for the duration of the maintenance period, the EPA is proposing to approve that the 33 However, the EPA notes that the industrial source monitors are operated in accordance with an approved industrial source monitoring quality assurance project plan QAPP and quality management plan QMP. The relevant QAPP and QMP documents are included in the docket for this action. The QMP outlines the quality assurance audits to be conducted by Missouri staff to ensure the industrial monitoring data is collected in a manner equivalent to SLAMS and may be used to determine NAAQS compliance. See Missouris 2016
Ambient Monitoring Network Plan contained in the docket for this action for more information.
34 The EPA promulgated the DRR August 21, 2015. The DRR requires air agencies to characterize air quality, either by monitoring or modeling, around sources that emit 2,000 tons per year tpy or more of SO2. The requirement for air quality characterization near a source may be avoided by adopting enforceable emission limits that ensure that the source will not emit more than 2,000 tpy of SO2. On January 15, 2016, the State submitted a final list identifying the sources in the State around which SO2 air quality will be characterized.
Rush Island was not included in the list because it is within the Jefferson County SO2 nonattainment area. Starting in 2016, Missouris annual monitoring network plans state that monitoring around Rush Island is being conducted by agreement between the State and Ameren.

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State is meeting its obligation to continue monitoring in the area, and verify ongoing attainment and maintenance, via operation of the Mott Street SLAMS monitor and that Missouris maintenance plan meets the Monitoring Network requirement.35
However, as previously noted, because the EPA is proposing to approve the Consent Agreement into the SIP, continued operation of the industrial source monitors will be required until the EPA approves a revision to the SIP
to remove the monitoring requirements.36 The available recent monitoring data from these industrial monitors is included in the TSD
associated with this action.
e. Verification of Continued Attainment Each air agency should ensure that it has the legal authority to implement and enforce all measures necessary to attain and maintain the 2010 SO2 NAAQS.
The air agencys submittal should indicate how it will track the progress of the maintenance plan for the area either through air quality monitoring or modeling.37
Missouri has the legal authority to enforce and implement the maintenance plan for the Jefferson County 2010 SO2
nonattainment area. This includes the authority to adopt, implement, and enforce any subsequent emissions control contingency measures determined to be necessary to correct future SO2 attainment problems.38 As noted, the State will track the progress of the maintenance plan by continuing to operate the Mott Street monitor.
Additionally, the State committed to provide future inventory updates to track emissions during the 10-year maintenance period. State Regulation 10
CSR 106.110, Reporting Emission Data, Emission Fees, and Process Information, which is SIP approved requires that all installations with a construction or operating permit report its annual emissions to the State. The methods for calculating and reporting emissions are detailed in each installations applicable permit. The data collected on emissions inventory questionnaires from permitted sources form the basis of the point source emissions inventory that is 35 Any change in the operational status or location of the Mott Street monitor must be approved by the Regional Administrator in accordance with the requirements of 40 CFR part 58.
36 The EPA would also need to approve the monitor changes as part of the States annual monitoring network plan.
37 See 2014 SO Guidance at 6768.
2 38 The EPA last determined that Missouris SIP
was sufficient to meet the requirements of section 110a2Ei of the CAA on March 22, 2018 83
FR 12496.

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