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Federal Register / Vol. 86, No. 195 / Wednesday, October 13, 2021 / Proposed Rules concentration above the standard referred to as an exceedance,7
averaged over three years, is equal to or less than one. The expected number of exceedances averaged over a three-year period at any given monitor is known as the PM10 design value. The PM10 design value for the area is the highest design value within the nonattainment area.8
Generally, the EPA determines whether an areas air quality is meeting the PM10 NAAQS based on the most recent complete,9 quality-assured, and certified data measured at established state and local air monitoring stations SLAMS in the nonattainment area and entered into the EPA Air Quality System AQS database. Data from air monitoring sites operated by state, local, or tribal agencies in compliance with the EPAs monitoring requirements must be submitted to AQS. These monitoring agencies annually certify that these data are accurate to the best of their knowledge. Accordingly, the EPA relies primarily on data in AQS
when determining the attainment status of an area.10 All valid data are reviewed to determine the areas air quality status in accordance with 40 CFR part 50, appendix K.

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B. The Indian Wells Valley PM10
Planning Area Under section 107 of the CAA, the EPA is required to designate all areas of the country as attainment, nonattainment, or unclassifiable for each of the NAAQS. In response to an area designation of nonattainment, states are required to adopt and submit SIP revisions that, among other things, provide for attainment of the NAAQS
within such area. Once a nonattainment area attains the NAAQS and meets certain other prerequisites, the state may 7 An exceedance is defined as a daily value that is above the level of the 24-hour standard i.e., 150
mg/m3 after rounding to the nearest 10 mg/m3 i.e., values ending in five or greater are to be rounded up. Thus, a recorded value of 154 mg/m3 would not be an exceedance because it would be rounded to 150 mg/m3. A recorded value of 155 mg/m3 would be an exceedance because it would be rounded to 160 mg/m3. 40 CFR part 50, Appendix K, section 1.0.
8 40 CFR 50.6 and 40 CFR part 50, appendix K.
The comparison with the allowable expected exceedance rate of one per year is made in terms of a number rounded to the nearest tenth fractional values equal to or greater than 0.05 are to be rounded up; e.g., an exceedance rate of 1.05 would be rounded to 1.1, which is the lowest rate for nonattainment. 40 CFR part 50, appendix K, section 2.1b.
9 For PM , a complete year of air quality data 10
includes all four calendar quarters with each quarter containing a minimum of 75 percent of the scheduled PM10 sampling days. 40 CFR part 50, Appendix K, section 2.3a.
10 40 CFR 50.6; 40 CFR part 50, appendix J; 40
CFR part 53; and 40 CFR part 58, appendices A, C, D, and E.

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request that the EPA redesignate the area to attainment.
Through its enactment of the CAA
Amendments of 1990, Congress designated certain areas of the country as nonattainment areas for the PM10
NAAQS. The Searles Valley planning area was one of the areas designated as nonattainment.11 In 1991, the EPA
classified the Searles Valley planning area, as a Moderate PM10
nonattainment area.12
The Searles Valley planning area included three subregions Coso Junction, Indian Wells Valley, and Trona under the planning jurisdiction of different air pollution control agencies. On August 6, 2002, the EPA
changed the boundaries of the Searles Valley PM10 nonattainment area by dividing this area into three separate, newly created PM10 nonattainment areas, including the Indian Wells Valley planning area.13 The Indian Wells Valley planning area is under the planning jurisdiction of the Eastern Kern Air Pollution Control District EKAPCD or District. The planning area boundaries include the portion of Kern County contained within the United States Geological Survey Hydrologic Unit 108090205.14 It covers approximately 300 square miles and is populated by about 30,000 persons, with only one community of significant size, Ridgecrest.
On May 7, 2003, the EPA determined that the Indian Wells Valley planning area had attained the 24-hour PM10
NAAQS.15 The determination was based on complete, quality-assured, and certified ambient air monitoring data that showed the area monitored attainment of the PM10 NAAQS during 19992001.16 Based on the determination, the EPA finalized approval of the maintenance plan and redesignated the Indian Wells Valley planning area to attainment, effective June 6, 2003.17
EKAPCD is a monitoring organization within the California Air Resources Board CARB Primary Quality Assurance Organization. EKAPCD
operates the PM10 monitoring network in the Indian Wells Valley area. CARB
submits annual monitoring network plans to the EPA that cover monitors operated by EKAPCD. These network plans describe the monitoring network 11 CAA section 107d4Bi and 52 FR 29383
August 7, 1987.
12 56 FR 56694 November 6, 1991.
13 67 FR 50805.
14 For the definition of the Indian Wells Valley planning area, see 40 CFR 81.305.
15 68 FR 24368.
16 67 FR 77196 December 17, 2002.
17 68 FR 24368.

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operated by EKAPCD within the Indian Wells Valley area and discuss the status of the air monitoring network, as required under 40 CFR 58.10. The EPA
regularly reviews these annual plans for compliance with the applicable reporting requirements in 40 CFR part 58. With respect to PM10, the EPA has found that CARBs network plans meet the applicable reporting requirements for the area under 40 CFR part 58, appendix D.18 EKAPCD and CARB
annually certify that the data they submit to AQS are complete and quality-assured.19
EKAPCD operates one PM10 SLAMS
monitoring site, Ridgecrest AQS ID: 06
0290018, within the Indian Wells Valley PM10 planning area.20 The monitor is located at the northeast corner of Sydnor Avenue and Primavera Street in Ridgecrest, California 21 see Figure 8 in the Indian Wells Second Maintenance Plan and was sited to monitor the highest concentration in the area at a neighborhood scale. SLAMS
monitors produce data comparable to the NAAQS, and therefore the monitor must be an approved federal reference method, federal equivalent method FEM, or approved regional method.
The Ridgecrest monitor measures hourly PM10 concentrations on a daily, yearround basis using a method that has been designated as an FEM by the EPA.
Table 1 shows the maximum monitored 24-hour PM10 concentrations at the Ridgecrest monitoring site for 20022020. The table reflects that values for the Indian Wells Valley area are typically well below the PM10
NAAQS of 150 mg/m3.

18 For example, see letter dated November 5, 2020, from Gwen Yoshimura, Manager, Air Quality Analysis Office, EPA Region IX, to Ravi Ramalingam, Chief, Consumer Products and Air Quality Assessment Branch, Air Quality Planning and Science Division, CARB.
19 For example, see letter dated June 21, 2021, from Sylvia Vanderspek, Chief, Air Quality Planning Branch, CARB, to Gwen Yoshimura, Manager, Air Quality Analysis Office, EPA Region 9.
20 The EPA approved the relocation of the Ridgecrest monitor from the California Ave 06
0290015 site to the Ward Ave site 060290018
on June 27, 2018. See letter dated June 27, 2018, from Gwen Yoshimura, Manager, Air Quality Analysis Office, Air Division, EPA Region IX, to Glen E. Stephens, P.E., Air Pollution Control Officer, EKAPCD.
21 Monitoring site address is 2051 Ward Ave., Ridgecrest, CA 93555.

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