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Federal Register / Vol. 86, No. 195 / Wednesday, October 13, 2021 / Proposed Rules
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As discussed in Appendix D of the Indian Wells Second Maintenance Plan, direct PM10 emissions estimates for stationary point sources reflect actual emissions reported to the District in 2017 by owners or operators of industrial point sources in the Indian Wells Valley planning area. Areawide sources, such as consumer products and agricultural burning, occur over a wide geographic area. Emissions for these categories are estimated by both CARB
and the District using various models and methodologies.
Emissions from on-road mobile sources, which include passenger vehicles, buses, and trucks, were estimated using outputs from CARBs EMFAC2017 model.33 These emissions were calculated by applying EMFAC2017 emissions factors to the transportation activity data provided by the Kern Council of Governments KCOG from their 2018 Regional Transportation Plan/2019 Federal Transportation Improvement Program 2018 RTP/2019 FTIP.34 KCOG is the metropolitan planning organization representing Kern County and the 11
incorporated cities within Kern County.
Emissions from off-road mobile sources e.g., cargo handling equipment, pleasure craft, recreational vehicles, and locomotives were estimated using a suite of category-specific models or, where a new model was not available, the OFFROAD2007 model. Many of the newer models were developed to support recent regulations, including inuse off-road equipment.
Based on the estimates for the year 2017 in Table 3, areawide and off-road mobile sources account for a majority approximately 96 percent of total PM10
emissions in the Indian Wells Valley planning area.35 Fugitive windblown dust and unpaved road dust account for a majority of the areawide emissions 54
percent and 17 percent, respectively, whereas aircraft account for a majority 33 EMFAC is short for EMission FACtor. The EPA
approved EMFAC2017 for SIP development and transportation conformity purposes in California on August 15, 2019. 84 FR 41717. EMFAC2017 was the most recently approved version of the EMFAC
model that was available at the time of preparation of the Indian Wells Second Maintenance Plan.
34 The Kern Council of Governments Board of Directors adopted the 2018 RTP/2019 FTIP on August 16, 2018.
35 Indian Wells Second Maintenance Plan, Appendix C.

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of the off-road mobile source emissions 98 percent.
The EPA considers the selection of the 2017 base year inventory to be appropriate given that it is the most recent emissions inventory associated with the triennial reporting schedule required under the Air Emissions Reporting Requirements rule. Moreover, preparation of an annual average daily inventory, as opposed to a seasonal or episodic inventory, is appropriate given that elevated PM10 concentrations in the Indian Wells Valley do not exhibit a clear seasonal or episodic pattern. Based on our review of the documentation provided with the plan, we find that the 2017 emissions inventory for direct PM10 is based on reasonable assumptions and methodologies, and that the inventory is comprehensive, current, accurate, and consistent with applicable CAA provisions and the Calcagni Memo.
B. Maintenance Demonstration Section 175Aa of the CAA requires that the maintenance plan provide for the maintenance of the national primary ambient air quality standard for such air pollutant in the area concerned for at least 10 years after the redesignation. A
state may generally demonstrate maintenance of the NAAQS by either showing that future emissions of a pollutant or its precursors will not exceed the level of the attainment inventory, or by conducting modeling that shows that the future mix of sources and emissions rates will not cause a violation of the NAAQS.36
Projected emissions inventories for future years must account for, among other things, the ongoing effects of economic growth and adopted emissions control requirements, and the inventories are expected to be the best available representation of future emissions. The plan submission should include documentation explaining how the state calculated the emissions data for the base year and projected inventories.
The Indian Wells Second Maintenance Plan demonstrates continued maintenance of the PM10
NAAQS by projecting the direct PM10
emissions in the area through 2025 and showing that future emissions of PM10
36 Calcagni
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will not exceed the level of the attainment inventory. As discussed in section IV.A, the Plan includes emissions inventories representing actual emissions in 2013 the final year of the first maintenance period through 2017 the Plans base year inventory, and projected emissions for 2018
through 2025 the final year of the second maintenance period for sources in the Indian Wells Valley planning area.37
Projected inventories are derived by applying expected growth trends for each source category and are based on data that reflect historical trends, current conditions, and recent economic and demographic forecasts with expected emissions reductions resulting from adopted control measures to the base year inventory. For the Indian Wells Second Maintenance Plan, emissions projections for 2018 through 2025 were generated by applying growth and control profiles to the 2017 base year inventory. Growth forecasts for most point and areawide sources were developed by CARB. Mobile sources were forecast using total vehicle miles traveled projections provided by KCOG.
Off-road sources were forecast using various growth surrogates as shown in Table 7 of Appendix D of the Plan.
Appendix D documents the methods and assumptions used to develop the emissions projections upon which the maintenance demonstration relies and presents the detailed source-categoryspecific estimates for each of the analysis years.
Table 4 presents a summary of the Indian Wells Second Maintenance Plans estimates of direct PM10
emissions in an interim year 2020 and the horizon year 2025 along with the corresponding emissions estimates for the year 2013 the final year of the first maintenance period and the 2017 base year. For simplicity, Table 4 shows emissions for just one of the interim years i.e., 2020 between the base year and the horizon year, but as discussed above, the Plan provides emissions estimates for each year from 2013
through 2025.38
37 Indian Wells Second Maintenance Plan, sections IV.B and IV.D, and Appendix D.
38 Id. at Table 2 and Table 3.

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