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Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules
docket. Do not submit electronically any information you consider to be Confidential Business Information CBI
or other information whose disclosure is restricted by statute. Multimedia submissions audio, video, etc. must be accompanied by a written comment.
The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission i.e., on the web, cloud, or other file sharing system. For additional submission methods, or if you need assistance in a language other than English or if you are a person with disabilities who needs a reasonable accommodation at no cost to you, please contact the person identified in the FOR
FURTHER INFORMATION CONTACT section.
For the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit https www.epa.gov/dockets/
commenting-epa-dockets. If you need assistance in a language other than English or if you are a person with disabilities who needs a reasonable accommodation at no cost to you, please contact the person identified in the FOR
FURTHER INFORMATION CONTACT section.
FOR FURTHER INFORMATION CONTACT: Jerry Wamsley, Air Planning Office ARD2, EPA Region IX, 75 Hawthorne Street, San Francisco, CA 94105, 415 947
4111, or by email at wamsley.jerry@
epa.gov.
SUPPLEMENTARY INFORMATION:
Throughout this document, we, us, and our refer to the EPA.

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Table of Contents I. Regulatory Context A. PM10 Standard, Area Designations, and SIPs B. CAA and Regulatory Requirements for Moderate PM10 Nonattainment Area SIPs II. Submissions From the State of Arizona To Address 1987 PM10 Standard Requirements in the West Pinal County Nonattainment Area A. Summary of State Submissions B. CAA Procedural Requirements for Adoption and Submission of SIP
Revisions III. Evaluation of the West Pinal County PM10
Plan A. Emissions Inventories B. PM10 Precursors C. Reasonably Available Control Measures Demonstration D. Attainment Demonstration E. Reasonable Further Progress Demonstration F. Contingency Measures G. Motor Vehicle Emissions Budgets for Transportation Conformity IV. Proposed Action
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V. Statutory and Executive Order Reviews
I. Regulatory Context A. PM10 Standard, Area Designations, and SIPs The EPA sets the National Ambient Air Quality Standard NAAQS for certain ambient air pollutants at levels required to protect human health and the environment. Particulate matter with an aerodynamic diameter less than or equal to a nominal ten micrometers, or PM10, is one of these ambient air pollutants for which the EPA has established health-based standards. On July 1, 1987, the EPA promulgated two primary standards for PM10: A 24-hour standard of 150 micrograms per cubic meter mg/m3; and an annual PM10
standard of 50 mg/m3. The EPA also promulgated secondary PM10 standards that were identical to the primary standards.1 Because they are identical, we refer to the primary and secondary standards using the singular term, NAAQS. Effective December 18, 2006, EPA revoked the annual PM10 NAAQS
but retained the 24-hour PM10 NAAQS.2
An area attains the 24-hour PM10
NAAQS when the expected number of days per calendar year with a 24-hour concentration in excess of 150
micrograms per cubic meter mg/m3
referred to herein as an exceedance, is equal to or less than one as determined in accordance with 40 CFR
part 50, appendix K.3 Conversely, a violation of the PM10 NAAQS occurs when the number of expected annual exceedances of the 24-hour NAAQS is greater than one.
Most of Pinal County, Arizona, including what is now the West Pinal County PM10 nonattainment area, was included in the rest of state area, which was designated unclassifiable for the 24-hour PM10 NAAQS by operation of law upon enactment of the CAA, consistent with section 107d4Biii. Until recently, this area in Arizona remained designated unclassifiable for the 1987 24-hour PM10 NAAQS. The CAA, under section 107d3, authorizes the EPA to revise the designation of, or redesignate, areas or portions thereof based on air quality data, planning and control considerations, or any other air-qualityrelated considerations that the EPA
deems appropriate.
On October 14, 2009, under CAA
section 107d3A, the EPA notified the Governor of Arizona and four tribal leaders whose areas of Indian country 1 52

FR 24634 July 1, 1987.
FR 61144 October 17, 2006.
3 See 40 CFR 50.6 and 40 CFR part 50, appendix K.
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are located entirely, or in part, within Pinal County that the designation for Pinal County, and any nearby areas that may be contributing to the monitored violations in Pinal County, should be revised.4 Our decision to initiate the redesignation process was due to ambient data for 20062008 from PM10
monitoring sites within the County showing widespread, frequent, and in some instances, severe, violations of the PM10 standard.
Effective July 2, 2012, the EPA
designated a portion of state lands in Pinal County, Arizona West Pinal County as nonattainment for the 1987
PM10 NAAQS based on monitoring data from 20062008.5 West Pinal County is located in central Arizona, southeast of the Phoenix metropolitan area and northwest of the city of Tucson. Pinal County covers 5,365 square miles and has two distinct western and eastern regions with different characteristics relevant to pollution formation. The West Pinal County PM10 nonattainment area is located within the western region, characterized by low desert valleys and an arid climate. The eastern region is mountainous, with elevations up to 6,441 feet.
As a result of the nonattainment designation, EPA classified West Pinal County as a Moderate PM10
nonattainment area. Consequently, by January 2, 2014, Arizona was required to submit a nonattainment plan SIP
revision for the 24-hour PM10 NAAQS
meeting relevant CAA requirements.
The State submitted a SIP revision intended to meet these requirements on December 21, 2015, and this 2015 West Pinal Moderate PM10 Nonattainment Area SIP is the subject of this proposed action. For a PM10 nonattainment area classified as Moderate, section 188c of the CAA provides that the Moderate area attainment date is as expeditiously as practicable, but no later than the end of the sixth calendar year after the areas designation as nonattainment. Consequently, the applicable attainment date for the West Pinal County area, designated nonattainment in 2012, was as expeditiously as practicable, but no later than December 31, 2018.
CAA section 188b2 requires the EPA to determine whether a state has 4 Letter from Laura Yoshii, Acting Regional Administrator to Governor Jan Brewer dated October 14, 2009. The EPA notified the tribal leaders of the Ak-Chin Indian Community, Gila River Indian Community, San Carlos Apache Tribe by letters dated December 30, 2009, and Tohono Oodham Nation by letter dated September 21, 2010.
5 77 FR 32024 May 31, 2012. The precise boundaries for the West Pinal County nonattainment area are described in 40 CFR 81.303.

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