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Federal Register / Vol. 86, No. 99 / Tuesday, May 25, 2021 / Rules and Regulations
CONTACT section to schedule your inspection. The Regional Offices official hours of business are Monday through Friday 8:30 a.m. to 4:30 p.m., excluding Federal holidays.
FOR FURTHER INFORMATION CONTACT:
Evan Adams, Air Regulatory Management Section, Air Planning and Implementation Branch, Air and Radiation Division, U.S. Environmental Protection Agency, Region 4, 61 Forsyth Street SW, Atlanta, Georgia 303038960.
Mr. Adams can be reached by telephone at 404 5629009 or via electronic mail at adams.evan@epa.gov.
SUPPLEMENTARY INFORMATION:

I. Background
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The Clean Air Act CAA or Act establishes a process for air quality management through the establishment and implementation of the national ambient air quality standards NAAQS.
On June 2, 2010, EPA revised the primary SO2 NAAQS, establishing a new 1-hour SO2 standard of 75 parts per billion ppb. See 75 FR 35520 June 22, 2010.1 After the promulgation of a new or revised NAAQS, EPA is required to designate all areas of the country, pursuant to section 107d12 of the CAA. For the 2010 1-hour SO2 NAAQS, designations were based on EPAs application of the nationwide analytical approach to, and technical assessment of, the weight of evidence for each area, including but not limited to available air quality monitoring data and air quality modeling results. In advance of designating the Sumner County Area, EPA issued updated designations guidance through a March 20, 2015, memorandum from Stephen D. Page, Director, U.S. EPA, Office of Air Quality Planning and Standards, to Air Division Directors, U.S. EPA Regions 110, titled Updated Guidance for Area Designations for the 2010 Primary Sulfur Dioxide National Ambient Air Quality Standard, which contains the factors that EPA evaluated in determining the appropriate designations and associated boundaries when designating the Sumner County Area, including: 1 Air quality characterization via ambient monitoring or dispersion modeling results; 2
emissions-related data; 3 meteorology;
4 geography and topography; and 5
jurisdictional boundaries.2 3 The 1 On February 25, 2019 effective April 17, 2019, based on a review of the full body of currently available scientific evidence and exposure/risk information, EPA issued a decision to retain the existing NAAQS for SO2. See 84 FR 9866.
2 The 2015 memorandum is available at https
www.epa.gov/sites/production/files/2016-04/
documents/20150320so2designations.pdf.

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guidance also references EPAs nonbinding Monitoring Technical Assistance Document Monitoring TAD
and Modeling Technical Assistance Document Modeling TAD,4 which contain scientifically sound recommendations on how air agencies should conduct such monitoring or modeling.
EPA completed the first set of initial area designations for the 2010 1-hour SO2 NAAQS in 2013 Round 1.
Pursuant to a March 2, 2015, consent decree and court-ordered schedule,5
EPA finalized a second set of initial area designations for the 2010 1-hour SO2
NAAQS in 2016 Round 2. The March 2, 2015, consent decree identified the following emissions criteria such that EPA must designate, in Round 2, an area surrounding any stationary source which had: a Annual emissions in 2012 exceeding 16,000 tons of SO2, or b both an annual average emissions rate of at least 0.45 pounds of SO2 per one million British thermal units, according to EPAs Clean Air Markets Division Database, and annual emissions of at least 2,600 tons of SO2
in 2012. Sumner County, Tennessee, contained one source, Tennessee Valley Authority TVA Gallatin Fossil Plant TVA Gallatin, that met these Round 2
criteria. EPA evaluated the Area, using the five factors identified previously, during the Round 2 designations. TVA
Gallatin is a large Electric Generating Unit located in north central Tennessee in the southern portion of Sumner County, approximately five kilometers km southeast of the center of Gallatin, Tennessee. The facility was included in the list of facilities to be designated pursuant to the March 2, 2015, Consent Decree.6 7
3 This designation guidance has since been superseded by a July 22, 2016, designation guidance memorandum from Stephen D. Page, Director, U.S.
EPA, Office of Air Quality Planning and Standards, to Regional Air Division Directors, U.S. EPA
Regions 110. The 2016 memorandum is available at https www.epa.gov/sites/production/files/201607/documents/areadesign.pdf.
4 Sulfur Dioxide SO National Ambient Air 2
Quality Standards Designations Modeling Technical Assistance Document, August 2016 draft, available at https www.epa.gov/sites/production/files/201606/documents/so2modelingtad.pdf. Note, EPA
released earlier drafts of this document in May 2013
and February 2016.
5 See Sierra Club et. al. v. McCarthy, Civil Action No. 3:13cv3953SI N.D. Cal., and 79 FR 31325
June 2, 2014.
6 TVA Gallatin was also subject to EPAs 2015
Data Requirements Rule DRR for the 2010 SO2 1hour NAAQS. See https www.epa.gov/sites/
production/files/2016-06/documents/tn.pdf for Tennessees letter dated January 15, 2016, with the Data Requirements Rule DRR source list.
7 In accordance with the DRR, 40 CFR part 51, subpart BB, through a letter dated June 7, 2016, Tennessee notified EPA that the State chose to
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EPAs March 20, 2015, guidance specified the designation category definitions to be used in the Round 2
designations.8 EPA was unable to determine whether the Sumner County Area met the definition of a nonattainment area or the definition of an attainment area based on the available information at the time of the Round 2 designations. As a result, EPA
designated the Sumner County Area as unclassifiable in the Round 2
designations published on July 12, 2016.9 The boundary for this designation was the jurisdictional boundary of Sumner County.10
In support of this final redesignation action, EPA evaluated new modeling for the Sumner County Area provided by Tennessee and developed a new technical support document TSD.11
On September 29, 2020, Tennessee submitted a request for EPA to redesignate the Sumner County Area to attainment/unclassifiable for the 2010 1hour primary SO2 NAAQS based on air quality dispersion modeling showing that the Area is in compliance with the 2010 1-hour primary SO2 NAAQS.12 13 14
characterize peak 1-hour SO2 concentrations for TVA Gallatin using air quality dispersion modeling.
8 Specifically, EPA defined a nonattainment area as an area that EPA has determined violates the 2010 1-hour SO2 NAAQS based on the most recent three years of ambient air quality monitoring data or an appropriate modeling analysis, or that EPA
has determined contributes to a violation in a nearby area; and defined an attainment area as an area that EPA has determined meets the 2010 1hour SO2 NAAQS and does not contribute to a violation of the NAAQS in a nearby area based on either: a The most recent 3 years of ambient air quality monitoring data from a monitoring network in an area that is sufficient to be compared to the NAAQS per EPA interpretations in the Monitoring TAD, or b an appropriate modeling analysis.
9 See 81 FR 45039 July 12, 2016, codified at 40
CFR 81.343.
10 Detailed rationale, analyses, and other information supporting EPAs original Round 2
designation for this Area can be found in the intended and final Round 2 designations TSD for Tennessee. This document, along with all other supporting materials for the original 2010 1-hour SO2 NAAQS designation for Sumner County, can be found on EPAs SO2 designations website. EPA SO2
designations website can be found at https
www.epa.gov/sulfur-dioxide-designations.
11 The TSD for this proposed action is included in the docket.
12 The demonstration of attainment through air quality dispersion modeling requires an area to review and report annual SO2 emissions pursuant to DRR ongoing verification at 40 CFR 51.1205b.
In its September 29, 2020, redesignation request letter, Tennessee also requested to terminate the section 51.1205b annual reporting requirement because the modeling analyses demonstrated a value of at least 50 percent below the 2010 1-hour SO2 NAAQS at all receptors. EPA will address the annual reporting termination request in a separate action which has no bearing on the final approval of the redesignation.
13 See letter signed by Michelle Owenby, Director of TDECs Division of Air Pollution Control, September 29, 2020, requesting that EPA

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