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Federal Register / Vol. 86, No. 152 / Wednesday, August 11, 2021 / Proposed Rules
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contains a statistical demonstration states can use to show that areas are meeting certain air quality criteria with a high degree of probability and therefore will maintain the standard 10
years into the future. By providing this statistical demonstration, the EPA can consider the maintenance demonstration requirement of the CAA
to be satisfied for the moderate PM10
nonattainment area meeting this air quality criteria. If the tests described in section IV of the LMP Option memo are met, the EPA will treat that as a demonstration that the area will maintain the NAAQS. Consequently, it follows that future year emission inventories for these areas, and some of the standard analyses to determine transportation conformity with the SIP
are no longer necessary.
To qualify for the LMP Option, a State must demonstrate the area meets the following criteria. First, the area should have attained the PM10 NAAQS.
Second, the most recent five years of air quality data at all monitors in the area, called the 24-hour average design value, should be at or below 98 micrograms per cubic meter mg/m3. Third, the State should expect only limited growth in on-road motor vehicle PM10 emissions and should have passed a motor vehicle regional emissions analysis test. Lastly, the LMP Option Memo identifies core provisions that must be included in all limited maintenance plans. These provisions include an attainment year emissions inventory, assurance of continued operation of an EPAapproved air quality monitoring network, and contingency provisions.
B. Conformity Under the Limited Maintenance Plan Option The transportation conformity rule and the general conformity rule set forth in the Code of Federal Regulations CFR at 40 CFR parts 51 and 93 apply to nonattainment areas and maintenance areas covered by an approved maintenance plan. Under either conformity rule, an acceptable method of demonstrating that a Federal action conforms to the applicable SIP is to demonstrate that expected emissions from the planned action are consistent with the emissions budget for the area.
While the EPAs LMP option does not exempt an area from the need to affirm conformity, it explains that the area may demonstrate conformity without conforming to an emissions budget.
Under the LMP option, emissions budgets are treated as essentially not limited maintenance plan and can be found at https www.epa.gov/sites/production/files/201606/documents/2001lmp-pm10.pdf.

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constraining for the length of the maintenance period because it is unreasonable to expect that the qualifying areas would experience so much growth in that period that a violation of the PM10 NAAQS would result. For transportation conformity purposes, the EPA would conclude that emissions in these areas need not be capped for the maintenance period and therefore a regional emissions analysis would not be required. Similarly, Federal actions subject to the general conformity rule could be considered to satisfy the budget test specified in 40
CFR 93.158 a5iA for the same reasons that the budgets are essentially considered to be unlimited.
While areas with maintenance plans approved under the LMP option are not subject to the budget test see 40 CFR
93.109e, the areas remain subject to the other transportation conformity requirements of 40 CFR part 93, subpart A. Thus, the metropolitan planning organization MPO in the area or the state must document and ensure that:
a. Transportation plans and projects provide for timely implementation of SIP transportation control measures TCMs in accordance with 40 CFR
93.113;
b. transportation plans and projects comply with the fiscal constraint element as set forth in 40 CFR 93.108;
c. the MPOs interagency consultation procedures meet the applicable requirements of 40 CFR 93.105;
d. conformity of transportation plans is determined no less frequently than every four years, and conformity of plan amendments and transportation projects is demonstrated in accordance with the timing requirements specified in 40 CFR
93.104;
e. the latest planning assumptions and emissions model are used as set forth in 40 CFR 93.110 and 40 CFR 93.111;
f. projects do not cause or contribute to any new localized carbon monoxide or particulate matter violations, in accordance with procedures specified in 40 CFR 93.123; and g. project sponsors and/or operators provide written commitments as specified in 40 CFR 93.125.
If the EPA approves the second 10year LMP, the Mendenhall Valley maintenance area will continue to be exempt from performing a regional emissions analysis but must meet project-level conformity analyses as well as the transportation conformity criteria described above.

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III. Review of the States Submittal A. Qualifying for the Limited Maintenance Plan Option As discussed in Section II.A. of this preamble, the LMP Option Memo outlines the requirements for an area to qualify for an LMP. First, the area should be attaining the PM10 NAAQS.
The PM10 NAAQS is attained when the expected number of days per calendar year with a 24-hour average concentration above 150 mg/m3 is equal to or less than one 40 CFR 50.6. We have evaluated the most recent ambient air quality data for the 24-hour PM10
NAAQS and determined that the Mendenhall Valley area continues to attain the NAAQS with zero annual exceedances for the period 2018 through 2020. Table 1 of this preamble shows the Mendenhall Valley area has not exceeded the standard of 150 mg/m3 for the 24-hour maximum PM10
concentrations measured at the Floyd Dryden monitoring site from 20102020.

TABLE 1FLOYD DRYDEN 24-HOUR
MAXIMUM PM10 CONCENTRATIONS
20102020
Year
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020

24-Hr max g/m3
30
24
26
33
38
21
34
30
24
64
35

Number of days exceeding NAAQS
0 0
0 0
0 0
0 0
0 0
0

Second, the 24-hour average design value for the most recent five years of monitoring data must be at or below the critical design value of 98 mg/m3 for the PM10 NAAQS. The critical design value is a margin of safety in which an area has a one in ten probability of exceeding the NAAQS. The 5-year average design value for Mendenhall Valley, based on PM10 monitoring data from 2014
through 2018, is 49 mg/m3. In addition, the EPA calculated the 5-year average design value for the Mendenhall Valley based on PM10 monitoring data from 2016 through 2020 and found the most conservative average design value estimate to be 62 mg/m3, which is below the critical design value of 98 mg/m3.
The EPAs attainment and average design value evaluation used to determine if the area qualifies for the LMP option is included in the docket
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