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Federal Register / Vol. 86, No. 52 / Friday, March 19, 2021 / Rules and Regulations move forward with a FIP if the state lacks proper authority.
Response: Although prohibitions on adoption of individual facility limits in state rules is not uncommon, in this situation it resulted in some of the States submitted SIP limits being invalidated under state law, which precludes approval of the attainment demonstration and of those limits. EPA
expects now that Michigan will draft future rules to avoid this prohibition which resulted in invalid limits and make necessary efforts to properly implement the NAAQS. Additionally, EPA is actively working on continued attainment planning efforts for this area, and the result of this SIP disapproval action will be to impose CAA section 179 sanctions if the State does not take necessary steps to correct the deficiencies giving rise to the disapproval. Consequently, in this final action EPA is not prepared to exercise its discretion to issue a CAA section 110k5 SIP Call to Michigan regarding this issue, and notes that the State is already obligated to remedy the deficiencies that would be addressed by any additional SIP Call under section 110k5, which, if issued, would occur under its own separate notice and comment process. In addition, in this final action EPA is not able to additionally promulgate a FIP under CAA section 110c, as that requires its own notice and comment rulemaking process pursuant to CAA section 307d.
Consequently, this final action to partially approve and partially disapprove the submitted SIP does not include any final action under section 110k5 regarding whether to issue a SIP Call, or under section 110c to promulgate a FIP.
Comment: The commenters recommended that EPA not approve the
Trenton Channel permit as SIP
strengthening because the limit is above the plants actual current emissions and, therefore, does not immediately improve air quality. Additionally, the commenters contend that if included, the limits should undergo a robust analysis on how the 30-day average is appropriate to meet the one-hour standard.
Response: EPA disagrees with both points. The permits inclusion into the SIP does improve air quality because it restricts the facilitys potential to emit at higher levels in the future compared to currently allowable levels, even if the facility is not currently emitting at the permits levels or the even higher levels allowed under the current SIP.
Additionally, the 30-day average does not need to be evaluated as to whether it is sufficient to provide attainment under the one-hour NAAQS, because the permit is not currently being approved as part of a strategy to meet that standard. However, if the permit is relied on in future attainment planning efforts, a robust analysis of the 30-day averaging limit and any other limits relied upon in such a future demonstration will be provided. In this action, EPA makes no final judgment on whether the 30-day limit combined with other future possible limits will provide for NAAQS attainment.
Comment: The commenters stated that EPA should not approve the 2012
base year inventory because it does not meet the CAA section 172c3
requirements of being comprehensive, accurate, and current. The commenters attempted to demonstrate this by showing emission increases at two sources when comparing 2012 to 2018 annual emissions.
Response: During the attainment planning and eventual redesignation
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process, three different inventories are considered and approved: Base year, attainment year, and future maintenance year. This action is only approving the base year inventory. Base year inventories are a nonattainment year upon which all future attainment work is based. Regarding the commenters claim that the 2012 inventory is out of date, when Michigan began their attainment planning, 2012 was the most current year with available emissions data. EPA would not expect a base year inventory to be amended because time has passed since the submittal date. The 2018 data would not have been available until 2019 at the earliest, which was three years after the states submittal. EPA disagrees with the commenters second issue, that the 2012
inventory is inaccurate. The commenters examples of 2018
emissions are from the Michigan Air Emissions Reporting System MAERS, publicly available annual emissions data for all major sources in Michigan.
The commenters compared the emissions increase at two sources between 2012 and 2018 to show inaccuracy in the base year inventory.
EPA disagrees that this data proves inaccuracies, but rather demonstrates the variability of emissions over time, generally due to economic factors, i.e.
increased affordability of natural gas lowering emissions and increased manufacturing due to economic demands increasing emissions. When comparing all the sources in the inventory from 2012 to 2018, total emissions have decreased by 82 percent, shown in Table 1 below as tons per year tpy of SO2 emissions.

TABLE 1DETROIT AREA 2012 AND 2018 EMISSIONS COMPARISON
2012
Emissions tpy
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Source
2018
Emissions tpy
River Rouge
Trenton Channel
Monroe
Carmeuse Lime
Severstal Steel
DIG
Marathon
U.S. Steel
EES Coke

8,202.52
22,426.12
49,150.63
699.69
677.12
597.88
137.34
2,874.30
1,900.77

2,118.48
3,114.04
3,854.35
482.79
571.74
820.17
168.39
1,482.91
3,253.76

Total

86,666.37

15,866.63

Emissions inventories are always likely to vary year to year, but that does not deem a previous years inventory
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inaccurate. As an example, Dearborn Industrial Generation DIG, one of the sources pointed out by the commenters
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as increasing emissions between 2012
and 2018, varies greatly year to year.
Looking at data over the most recent 15

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