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Federal Register / Vol. 86, No. 30 / Wednesday, February 17, 2021 / Proposed Rules D. Fully Approved Maintenance Plan CAA section 107d3Eiv requires that, for a NAA to be redesignated to attainment, EPA must fully approve a maintenance plan which meets the requirements of CAA section 175A. The plan must demonstrate continued attainment of the relevant NAAQS in the area for at least 10 years after our approval of the redesignation. Eight years after our approval of a redesignation, the State must submit a revised maintenance plan demonstrating attainment for the 10
years following the initial 10-year period. The maintenance plan must also contain a contingency plan to ensure prompt correction of any violation of the NAAQS. See CAA sections 175Ab and d. The Calcagni Memo provides additional guidance on the content of a maintenance plan, stating that a maintenance plan should include the following elements: 1 An attainment emissions inventory; 2 a maintenance demonstration showing attainment for 10 years following redesignation; 3 a commitment to maintain the existing monitoring network; 4 verification of continued attainment; and 5 a contingency plan to prevent or correct future violations of the NAAQS. The following paragraphs describe how each of these elements is addressed in Idahos maintenance plan.
1. Attainment Inventory As discussed in the General Preamble see 57 FR 13498, April 16, 1992 and
the Calcagni Memo, PM2.5 maintenance plans should include an attainment emission inventory to identify the level of emissions in the area which is sufficient to maintain the NAAQS.
The maintenance plan attainment year inventory should include the emissions during the time period associated with the monitoring data showing attainment.13 For the Logan, UT-ID PM2.5 NAA, IDEQ determined attainment using air quality data from 2015, 2016, and 2017, the design value period relied upon for the EPAs Determination of Attainment 83 FR
52983, October 19, 2018. The State therefore used 2017 to calculate its base year attainment inventory, which aligned with the 2017 National Emissions Inventory NEI data available for point, area, on-road mobile, and nonroad mobile sources. IDEQ then projected the 2017 base year inventory to both a horizon year a future year at least 10 years from the approval date of the maintenance plan of 2031 and an interim year of 2026.
The NEI is compiled at the county level, so the State first calculated the 2017 emissions inventories for Franklin County, and then apportioned these county-wide inventories to the portion of Franklin County included in the Logan, UT-ID NAA.14 IDEQ projected mobile source emissions using the latest version of EPAs Motor Vehicle Emissions Simulator MOVES model MOVES2014b. IDEQ used apportioned 2017 NEI data for the on-road mobile
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source emissions, and used MOVES2014b model defaults for the nonroad portion of the model, because the State has not yet developed input files for that version of the model.15 To best represent emissions that occur on days when the ambient concentrations of PM2.5 are of concern, the MOVES
meteorological inputs were based on an average episodic day representing conditions present during wintertime stagnation events leading to high levels of ambient PM2.5 in the Logan UT-ID
PM2.5 NAA.16 IDEQ ran MOVES2014b to calculate on-road and nonroad mobile source emissions on an average episodic winter day for Franklin County for January 2017, 2026 and 2031. Area source emissions were apportioned from 2017 NEI data for individual categories, which were projected for the 2026 and 2031 inventories based on an average annual growth rate. No point sources were listed in the base year or projected future inventories. More detailed descriptions of the 2017 base year inventory and the 2026 and 2031
projected inventories can be found in section 4 and Appendix A of Idahos September 13, 2019 submittal, in the docket for this action.
For each of these source categories, the pollutants that were inventoried include: PM2.5, sulfur dioxide SO2, NOX, VOC, and ammonia NH3.
Summary of emission figures from 2017
base year and the projected inventories are provided in Table 3 of this document.

TABLE 3IDAHO PORTION OF THE LOGAN, UT-ID PM2.5 NAA; ACTUAL EMISSIONS FROM 2017 AND PROJECTED
EMISSIONS FOR 2026 AND 2031

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Pounds per average episodic winter day PM2.5
filterable
Year
Source category
PM2.5
condensable
2017
2017
2017

Area
Mobile
Nonroad

9.72

208.8
127.3
42.5

338.8
957.7
286.6

28.3
1.9
0.8

1,626.5
901.2
1,189.1

868.6
13.8
0.7

2017
2026
2026
2026

Total
Area
Mobile
Nonroad

9.72
9.88

378.5
222.4
109.4
31.2

1,583
363.5
421.8
302.8

31
28.6
2.0
0.8

3,716.8
2,061.1
533.1
776.4

883.1
872.1
12.5
0.7

2026
2031
2031
2031

Total
Area
Mobile
Nonroad

9.88
9.97

363
230
110.5
29.8

1088.1
377.2
297.3
306.7

31.4
28.8
2 0.8

3,370.6
2,302.6
396.3
732.5

885.3
874
13.2
0.7

2031

Total

9.97

370.4

981.2

31.6

3,431.4

887.9

Projected change %

2.5

2.2

38

2

7.70

0.5

13 See
Calcagni Memo at 8.
Appendix A of Idahos September 13, 2019
submittal for the apportionment methodology.
14 See
VerDate Sep<11>2014

16:07 Feb 16, 2021

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NOX

15 With the exception of paved road dust emissions, which IDEQ calculated using AP42
guidance.
16 An episodic day was defined as any day from November through March during which the daily average PM2.5 concentration in Franklin County was
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SO2

VOC

NH3

above 35 mg/m3. A total of 62 days were identified that met these criteria at the Logan-Cache Airport weather station from 2013 through 2017. The hourly meteorological data from these 62 days were then averaged to create the final average episodic day inputs.

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