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Federal Register / Vol. 86, No. 195 / Wednesday, October 13, 2021 / Proposed Rules measures must include, at a minimum, a requirement that the state will implement all control measures contained in the nonattainment SIP
prior to redesignation.
Section 175Ab of the CAA requires states to submit a subsequent maintenance plan revision second 10year maintenance plan eight years after redesignation. The Act requires only that this second 10-year maintenance plan maintain the applicable NAAQS for 10 years after the expiration of the first 10-year maintenance plan. Beyond these provisions, section 175A of the CAA
does not define the content of a second 10-year maintenance plan.
The primary guidance on maintenance plans and redesignation requests is a September 4, 1992
memorandum from John Calcagni, titled Procedures for Processing Requests to Redesignate Areas to Attainment Calcagni Memo.25 The Calcagni Memo outlines the key elements of a maintenance plan, which include an attainment emissions inventory, maintenance demonstration, monitoring and verification of continued attainment, and a contingency plan.
Maintenance plan submittals are SIP
revisions, and as such, the EPA is obligated under CAA section 110k to approve them or disapprove them depending upon whether they meet the applicable CAA requirements for such plans.

IV. Evaluation of the Indian Wells Second Maintenance Plan A. Emissions Inventories A maintenance plan for the PM10
NAAQS should include an inventory of direct PM10 emissions in the area.26 The inventory should be consistent with the EPAs most recent guidance on emissions inventories for nonattainment areas available at the time; must be comprehensive, including emissions from stationary point sources, area sources, and mobile sources; and must be based on actual emissions during the appropriate season, if applicable.27
The specific PM10 emissions inventory requirements are set forth in the Air Emissions Reporting Requirements rule,28 which requires that emissions inventories report filterable and condensable components, as applicable.29 The EPA has provided additional guidance for developing PM10 emissions inventories in PM10
Emissions Inventory Requirements, EPA454/R94033 September 1994
and Emissions Inventory Guidance for Implementation of Ozone and Particulate Matter National Ambient Air Quality Standards NAAQS and Regional Haze Regulations May 2017.
The Indian Wells Second Maintenance Plan includes inventories for total primary PM10 and for the PM10
precursors NOX, SOX, and ammonia for the years 2013 the final year of the first maintenance period through 2025 the
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final year of the second maintenance period.30 The 2017 emissions inventory represents current emissions and was used to project emissions through 2025, as discussed further in section IV.B of this document. The emissions inventories in the Plan include estimates from all relevant source categories that the Plan divides among fuel combustion, waste disposal, cleaning and surface coatings, industrial processes, miscellaneous processes, onroad motor vehicles, and off-road motor vehicles.31 CARB and the District developed the emissions inventories based on the methods and assumptions presented in detail in Appendix D
IWV Precursor Emission Inventories 20022025.32 The direct PM10 and PM10 precursor emissions are presented in tables 2 and 3 and Appendix D of the Plan, and the specific filterable and condensable components of the direct PM10 emissions estimates are identified in the accompanying document titled Indian Wells Valley Condensable PM10
Emission Inventory. Table 3 provides a summary of the 2017 direct PM10 base year emissions inventory in tons per day tpd for the Indian Wells Valley area.
Because the Indian Wells Second Maintenance Plan depends on direct PM10 emissions to demonstrate compliance, the EPA reviewed those direct PM10 emissions estimates and not the Districts emissions estimates for PM10 precursor emissions.

TABLE 3INDIAN WELLS PM10 BASE YEAR 2017 EMISSIONS INVENTORY
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

0.031
0.002
0.001
0.019
1.199
0.039
1.172

All Stationary, Areawide, and Mobile Sources

2.462

Areawide Sources
Mobile Sources
Total

PM10

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Source: Indian Wells Second Maintenance Plan, Table 3 and Appendix D.
a Emissions inventories are required to include direct PM
10 emissions, separately reported as PM10 filterable and condensable emissions. 40
CFR 51.15a1vii. The accompanying document titled Indian Wells Valley Condensable PM10 Emission Inventory provides this information.
Totals may not add up due to rounding.

25 Memorandum dated September 4, 1992, from John Calcagni, Director, EPA Air Quality Management Division, to Regional Office Air Division Directors, Subject: Procedures for Processing Requests to Redesignate Areas to Attainment.
26 PM
10 precursor emissions should also be included depending upon the contribution of secondary particulate matter to high ambient PM10
concentrations in the area. In this instance, an inventory of PM10 precursor emissions is not required because PM10 precursor controls were not
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relied upon to achieve attainment of the PM10
NAAQS in the Indian Wells Valley planning area nor are they relied upon to demonstrate maintenance of the NAAQS see Indian Wells Second Maintenance Plan, section IV, and 67 FR
77196, 77201 December 17, 2002. While not required, the Indian Wells Second Maintenance Plan includes inventories of NOX, SOX, and ammonia in appendix D IWV Precursor Emission Inventories.
27 CAA section 172c3.

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CFR part 51, subpart A.
CFR 51.15a1vii.
30 Indian Wells Second Maintenance Plan, sections IV.B and IV.D, and Appendix D.
31 Indian Wells Second Maintenance Plan, sections IV.B and IV.D.
32 While Appendix D is titled IWV Precursor Emission Inventories 20022005, the appendix presents the full emissions inventory documentation for direct PM10 in addition to PM10
precursors.
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