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Federal Register / Vol. 86, No. 195 / Wednesday, October 13, 2021 / Proposed Rules
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TABLE 4INDIAN WELLS PM10 EMISSIONS INVENTORY, 2013, 2017, 2020, AND 2025
Annual average, tpd Source category
Subcategory
Stationary Point Sources

Fuel Combustion
Waste Disposal
Cleaning & Surface Coatings
Industrial Processes
Miscellaneous Processes
On-Road Motor Vehicles
Off-Road Motor Vehicles

0.018
0.000
0.000
0.009
1.424
0.051
1.228

0.031
0.002
0.001
0.019
1.199
0.039
1.172

0.027
0.002
0.001
0.020
1.193
0.037
1.167

0.018
0.002
0.001
0.021
1.262
0.036
1.161

All Stationary, Sources.

2.679

2.462

2.446

2.501

Areawide Sources
Mobile Sources
Total

2013

Areawide,
and
Mobile
2017

2020

2025

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Source: Indian Wells Second Maintenance Plan, Table 2 and Table 3.
Totals may not add up due to rounding.

The emissions estimates in the Plan predict a gradual change in direct PM10
emissions within the Indian Wells Valley planning area over time, with slight decreases in certain categories e.g., fuel combustion, on-road motor vehicles, off-road motor vehicles nearly offsetting slight increases in certain other source categories i.e., industrial processes, miscellaneous processes relative to the 2017 base year emissions.
By 2025, overall direct PM10 emissions are estimated to be approximately 0.039
tpd 1.6 percent higher than in the 2017
base year. However, despite the expected growth in the area, the Plans projected PM10 emissions through 2025
are approximately 0.178 tpd 6.6
percent lower than emissions in 2013, the final year of the first maintenance period and a year in which there were no recorded exceedances of the PM10
NAAQS.
Based on our review, we find that the projected emissions inventories for direct PM10 for years 2018 through 2025
are based on reasonable methods, growth factors, and assumptions, and are based on the most current and accurate information available to CARB
and EKAPCD at the time the Plan and its inventories were being developed.
Given that the projections of direct PM10
emissions show future emissions increases through 2025 are within 1.6
percent of those in 2017 and below those in 2013 both of which reflect attainment conditions, we find that the Indian Wells Second Maintenance Plan provides an adequate basis to demonstrate maintenance of the PM10
NAAQS within the Indian Wells Valley planning area through 2025. Lastly, we find that by providing emissions projections through 2025, the Plan demonstrates maintenance of the PM10
NAAQS for more than 10 years after the expiration of the first 10-year maintenance plan i.e., 2023 in
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accordance with section 175Ab of the CAA.
C. Verification of Continued Attainment Once an area has been redesignated, the state should continue to operate an appropriate air quality monitoring network, in accordance with 40 CFR
part 58, to verify the attainment status of the area.39 Data collected by the monitoring network are also needed to implement the contingency provisions of the maintenance plan.
As discussed in section I.B, EKAPCD
monitors ambient concentrations of PM10 in the Indian Wells Valley planning area at the Ridgecrest monitoring station. In section V.A
Tracking of the Indian Wells Second Maintenance Plan, the District commits to continue to operate and maintain a PM10 air quality monitor in Ridgecrest in accordance with 40 CFR part 58. We find that the Indian Wells Second Maintenance Plan contains adequate provisions for continued ambient PM10
monitoring to verify continued attainment through the maintenance period.
The EPA also recommends that the state verify continued attainment through methods in addition to the ambient air monitoring program, e.g., through periodic review of the factors used in development of the attainment inventory to show no significant change.40 In the Indian Wells Second Maintenance Plan, EKAPCD commits to perform periodic reviews of the air monitoring data and emissions inventory, to review the inputs and assumptions used to develop the emissions inventory on an annual basis, and, if the District finds that these inputs have changed significantly, to request that CARB update the existing inventory and to compare the revised 39 Calcagni
Memo, 11.

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D. Contingency Provisions Section 175Ad of the CAA requires that maintenance plans include contingency provisions, as the EPA
deems necessary, to promptly correct any violations of the NAAQS that occur after redesignation of the area. Such provisions must include a requirement that the state will implement all measures with respect to the control of the relevant air pollutants that were contained in the SIP for the area before redesignation of the area as an attainment area. These contingency provisions are distinguished from contingency measures required for nonattainment areas under CAA section 172c9 in that they are not required to be fully adopted measures that will take effect without further action by the state for the maintenance plan to be approved. However, the contingency provisions of a maintenance plan are considered to be an enforceable part of the SIP and should ensure that contingency measures are adopted expeditiously once they are triggered.
The maintenance plan should clearly identify the measures to be adopted, include a schedule and procedure for adoption and implementation of the measures, and contain a specific timeline for action by the state. In addition, the state should identify the specific indicators or triggers that will 41 Indian Wells Second Maintenance Plan, section VI Subsequent Maintenance Plan Revisions.

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inventory with the inventories in the Indian Wells Second Maintenance Plan.41 We find that the Districts commitment to verify continued attainment of the PM10 NAAQS through continued ambient air monitoring and annual review of the inputs and assumptions used to develop the emissions inventories in the Indian Wells Second Maintenance Plan are acceptable.

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