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Federal Register / Vol. 86, No. 152 / Wednesday, August 11, 2021 / Proposed Rules
for this action. The EPA reviewed the data and methodology provided by the State and the most recent 5-year average design value and finds that the Mendenhall Valley areas 5-year average design value is below the critical design value of 98 mg/m3 outlined in the LMP
Option Memo. Therefore, the EPA finds that the Mendenhall Valley area meets the design value criteria outlined in the LMP Option Memo.
Third, the area must meet the motor vehicle regional emissions analysis test described in the LMP Option Memo.
The State submitted an analysis showing that growth in on-road mobile PM10 emissions sources was minimal and would not threaten the assumption of maintenance that underlies the LMP
policy. Using the EPAs methodology, the State calculated total projected growth in on-road motor vehicle PM10
emissions through 2033 the end of the maintenance planning period for the Mendenhall Valley area. This calculation is derived using Attachment B of the EPAs LMP Option Memo, where the projected percentage increase in vehicle miles traveled over the next ten years VMTpi is multiplied by the on-road mobile portion of the attainment year inventory DVmv, including re-entrained road dust. This test is met when VMTpi DVmv plus the design value for the most recent five years of quality assured data is below the margin of safety MOS for the relevant PM10 standard in mg/m3 for a given area. This MOS value can be 98
mg/m3 or a site-specific value computed from data collected at the site of interest using methods outlined in Attachment A of the LMP Option Memo. The 24hour average design value of 49 mg/m3
was used to compute a MOS selected for the Floyd Dryden monitoring site in Mendenhall Valley of 50.2 mg/m3, which is below the MOS value of 98 mg/m3.
See the Mendenhall Valley LMP, Section III.D.3.4 and associated appendix, placed in the docket for this action, for details of this computation.
The EPA reviewed the calculations in the States LMP submittal and concurs with the determination that the area meets the motor vehicle regional emissions analysis test.
As described above, the Mendenhall Valley PM10 maintenance area meets the qualification criteria set forth in the LMP Option Memo and accordingly qualifies for the LMP option. To ensure these requirements continue to be met, the State commits to evaluate monitoring data annually to ensure the area continues to qualify for the LMP
option. However, if after performing the annual recalculation of the areas average design value in a given year, the
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State determines that the area no longer qualifies for the LMP, the State will take action to attempt to reduce PM10
concentrations enough for the area to requalify for the LMP. One possible approach the State could take is to implement a contingency measure found in its SIP. See Section III.D.3.9 of the States submittal, placed in the docket for this action, for a description of the contingency measures.
B. Attainment Inventory Pursuant to the LMP Option Memo, the States submission should include an emissions inventory, which can be used to demonstrate attainment of the relevant NAAQS. The inventory should represent emissions during the same five-year period associated with air quality data used to determine whether the area meets the applicability requirements of the LMP option. The State should review its inventory every three years to ensure emissions growth is incorporated in the inventory if necessary.
Alaskas Mendenhall Valley PM10
LMP includes an emissions inventory, with a base year of 2017. The assumptions, methods and computations used to generate the 2017
emissions inventory are described in detail in Appendix III.D.3.6 of the Mendenhall Valley LMP submittal in the docket for this action. The 2017 base year represents the most recent emissions inventory data available, is representative of the level of emissions during a period of time used to calculate the area is attaining the NAAQS, and is consistent with the data used to determine applicability of the LMP
option i.e., having no violations of the NAAQS during the five-year period used to calculate the design value.
Like the first 10-year LMP, four main source categories were inventoried for the second 10-year LMP. These include 1 On-Road; 2 Non-Road; 3 Area Sources; and 4 Point Sources. The same assumptions and methods used to develop the first 10-year LMP were used to develop the 2017 base year PM10
emissions inventory for the second 10year LMP. The analysis of the emissions inventory for the second 10-year LMP
indicates that that the PM10 emissions in the maintenance area declined by about 78% between 2004 and 2017 and shows paved roads remain the most significant source of fugitive emissions in the maintenance area. Fugitive dust from paved roads accounted for 46.2% of the overall inventory; fugitive dust from unpaved roads accounted for 0.53%;
and emissions from wood burning accounted for 8.4% of the overall inventory.

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Efforts by the City and Borough of Juneau and the State to pave sections of unpaved roads and sweeping and sanding mitigation programs in the Valley, as well as the woodsmoke control program, have led to significant reduction in PM10 emissions. In accordance with the LMP Option Memo, all controls relied on to demonstrate attainment and continued maintenance will remain in place, and ADEC asserts that no additional control measures are necessary to maintain the NAAQS.
The submittal meets the EPA
guidance for purposes of an attainment emissions inventory, and the emissions inventory data supports the States conclusions that the existing control measures will continue to protect and maintain the PM10 NAAQS.
C. Air Quality Monitoring Network Once an area is redesignated, the state must continue to operate an appropriate air monitoring network in accordance with 40 CFR part 58 to verify the attainment status of the area. From 1986
until the present, Alaska has operated a PM10 monitor at the Floyd Dryden Middle School in the Mendenhall Valley NAA. The Floyd Dryden monitor was sited and maintained in accordance with Federal siting and design criteria in 40 CFR part 58, and in consultation with the EPA Region 10. On June 26, 2020, ADEC submitted the 2020 Annual Monitoring Network Plan, which the EPA approved on January 25, 2021.
ADECs network plan and the EPAs approval letter are included in the docket for this action.
The State commits to continued operation of at least one EPA-approved PM10 monitoring site in the Mendenhall Valley maintenance area through the end of the maintenance planning period, 2033, and will continue to operate the monitor consistent with the EPA-approved ADEC annual network plan in order to meet the EPA
requirements at 40 CFR part 58.
D. Verification of Continued Attainment The level of the PM10 NAAQS is 150
mg/m3, 24-hour average concentration.
The 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. As stated in Section III.D of this preamble, ADEC commits to continue to operate a regulatory monitoring network in accordance with 40 CFR part 58. In addition, ADEC commits to verifying continued attainment of the PM10
standard through the maintenance plan period with the operation of an appropriate PM10 monitoring network.

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