Determination of Attainment by the Attainment Date for the 2010 1-Hour Primary Sulfur Dioxide National Ambient Air Quality Standard; Texas; Freestone-Anderson and Titus Counties

SUPPLEMENTARY INFORMATION:

Throughout this document “we,” “us,” or “our” mean the EPA.

I. Background

A. The 2010 1-Hour Primary SO ₂ NAAQS

Under section 109 of the CAA, the EPA has established primary and secondary NAAQS for certain pervasive air pollutants (referred to as “criteria pollutants”) and conducts periodic reviews of the NAAQS to determine whether they should be revised or whether new NAAQS should be established. The primary NAAQS represent ambient air quality standards that the EPA has determined are requisite to protect the public health, while the secondary NAAQS represent ambient air quality standards that the EPA has determined are requisite to protect the public welfare from any known or anticipated adverse effects associated with the presence of such an air pollutant in the ambient air.

Under the CAA, the EPA must establish a NAAQS for SO₂, which is primarily released to the atmosphere through the burning of fossil fuels by power plants and other industrial facilities. SO₂ is also emitted from industrial processes including metal extraction from ore and heavy equipment that burns fuel with a high sulfur content. Short-term exposure to SO₂ can damage the human respiratory system and increase breathing difficulties. Small children and people with respiratory conditions, such as asthma, are more sensitive to the effects of SO₂ . Sulfur oxides at high concentrations in ambient air can also react with compounds to form small particulates (fine particulate matter or PM_2.5) that can penetrate deeply into the lungs and cause acute health problems and/or chronic diseases. The EPA first established primary SO₂ standards in 1971 at 140 parts per billion (ppb) over a 24-hour averaging period and at 30 ppb over an annual averaging period.

On June 22, 2010, the EPA published in the Federal Register a strengthened, primary 1-hour SO₂ NAAQS, establishing a new standard at a level of 75 ppb, based on the 3-year average of the annual 99th percentile of daily maximum 1-hour average concentrations of SO₂ . The revised SO₂ NAAQS provides increased protection of public health. Along with revision of the SO₂ NAAQS, EPA revoked the 1971 primary annual and 24-hour SO₂ standards for most areas of the country following area designations under the new NAAQS.

B. Designations, Classifications, and Attainment Dates for the 2010 SO ₂ NAAQS

Following promulgation of a new or revised NAAQS, the EPA is required to designate all areas of the country as either “attainment,” “nonattainment,” or “unclassifiable,” pursuant to CAA section 107(d)(1). On August 5, 2013, the EPA finalized its first round of designations for the 2010 1-hour primary SO₂ NAAQS. In that 2013 action, the EPA designated 29 areas in 16 states as nonattainment for the 2010 1-hour primary SO₂ NAAQS based on air quality monitoring data. Following the first round of designations, EPA entered into a March 2, 2015, Consent Decree which required the EPA to complete the remaining area designations by three specific deadlines according to a court-ordered schedule. On July 12, 2016, the EPA finalized its second round of initial designations under the 2010 1-hour primary SO₂ NAAQS, designating an additional four areas as nonattainment, effective September 12, 2016. On December 13, 2016 (effective January 12, 2017), EPA finalized a supplement to the July 12, 2016, second round final action, designating three more areas in Texas as nonattainment for the 2010 1-hour primary SO₂ NAAQS. Included in that supplement to the second round of designations was one area in Freestone and Anderson Counties and one area in Titus County. These designations were based on consideration of the data available at the time of designations, including air quality modeling. Pursuant to section 192(a) of the CAA, the attainment dates for the Freestone-Anderson and Titus NAAs were both no later than 5 years after the effective date of initial designation, or January 12, 2022.

CAA section 191(a) requires states that contain an area designated nonattainment for the 2010 1-hour primary SO₂ NAAQS to develop and submit a nonattainment area (NAA) State Implementation Plan (SIP) to the EPA within 18 months of the effective date of an area's designation as nonattainment ( i.e., by July 12, 2018). For SO_2, a NAA SIP (also referred to as an attainment plan) must meet the requirements of CAA sections 110 and 172(c), and 191-192, and provide for attainment of the NAAQS by the applicable statutory attainment date, or no later than 5 years from the effective date of designation ( i.e., by January 12, 2022).

When a NAA is attaining the 2010 1-hour primary SO₂ NAAQS based on the most recent available data, the EPA may issue a Clean Data Determination (CDD), suspending certain NAA planning requirements. The EPA issued a CDD for the Freestone-Anderson and Titus NAAs based on available monitoring data, emissions data, and air quality modeling via a final rule published on May 14, 2021 (effective June 14, 2021). A CDD does not alter the nonattainment designations for these areas. For the EPA to redesignate these areas to attainment, the state must submit, and the EPA must approve, a redesignation request for these NAAs that meets the requirements of CAA section 107(d)(3). On March 3, 2022, Texas submitted a request to EPA to redesignate the Freestone-Anderson and Titus NAAs to attainment for the 2010 1-hour SO₂ NAAQS, and accompanying maintenance plans for the two areas. EPA is currently reviewing Texas' redesignation submission.

C. EPA Determination of Attainment by the Attainment Date

Section 179(c)(1) of the CAA requires the EPA to determine whether a NAA attained an applicable standard by the applicable statutory attainment date based on the area's air quality as of the attainment date. The EPA is to issue this determination within 6 months of the attainment date. Thus, the EPA had a mandatory duty under CAA section 179(c) to determine by July 12, 2022, whether the NAAs attained the NAAQS by the statutory attainment date. With this action, the EPA proposes to determine, in accordance with CAA section 179(c), that the Freestone-Anderson and Titus NAAs attained the 2010 1-hour primary SO₂ NAAQS by the January 12, 2022, statutory attainment date.

A determination of whether an area's air quality meets applicable standards is generally based upon the most recent 3 years of complete, quality-assured data gathered at established state and local air monitoring stations (SLAMS) in a NAA and entered into the EPA's Air Quality System (AQS) database, along with other available information. Data from ambient air monitors operated by state and local agencies in compliance with the EPA monitoring requirements must be submitted to AQS. Monitoring agencies annually certify that these data are accurate to the best of their knowledge. All data are reviewed to determine the area's air quality status in accordance with 40 CFR part 50, appendix T (for SO₂). In general, for SO₂ the EPA does not rely exclusively on monitoring data to determine whether the NAAQS is met unless it has been demonstrated that the monitors were appropriately sited to record expected maximum ambient concentrations of SO₂ in an area. As such, monitoring data can be supplemented with other relevant information, including dispersion modeling and emissions inventories, for determining attainment.

The attainment date for the Freestone-Anderson and Titus NAAs was January 12, 2022. For an area where monitoring data alone is used in the determination of attainment, the 3-year design value for the calendar years preceding the attainment date is typically used ( e.g., the design value for January 2019-December 2021 is the appropriate design value for an attainment date of January 12, 2022). In this case for the Freestone-Anderson and Titus NAAs, however, to demonstrate attainment EPA is relying on a combination of monitoring data, past modeling from the designation action and discussed in the May 2021 CDD, primary source shutdowns, and recent emissions data.

II. The EPA's Proposed Determination

A. Area Characterization

The Freestone-Anderson NAA in Texas is bound by the following Universal Traverse Mercator (UTM) coordinates encompassed by the following rectangular area vertices in UTM zone 14 with datum NAD83:

(1) vertices—UTM Easting (m) 766752.69, UTM Northing (m) 3536333.0,

(2) vertices—UTM Easting (m) 784752.69, UTM Northing (m) 3536333.0,

(3) vertices—UTM Easting (m) 784752.69, UTM Northing (m) 3512333.0,

(4) vertices—UTM Easting (m) 766752.69, UTM Northing (m) 3512333.0.

The Titus NAA in Texas is bound by the following UTM coordinates encompassed by the following rectangular area vertices in UTM zone 15 with datum NAD83:

(1) vertices—UTM Easting (m) 304329.030, UTM Northing (m) 3666971.0,

(2) vertices—UTM Easting (m) 311629.030, UTM Northing (m) 3666971.0,

(3) vertices—UTM Easting (m) 311629.03, UTM Northing (m) 3661870.5,

(4) vertices—UTM Easting (m) 304329.03, UTM Northing (m) 3661870.5.

At the time of these area designations, EPA relied on modeling that indicated that the Big Brown Steam Electric Station in Freestone County and the Monticello Steam Electric Station in Titus County were the key contributors to the modeled 2010 SO₂ NAAQS violations in these rural areas. These two coal-fired power plants were responsible for contributing almost, if not equal to, 100 percent of the SO₂ impacts on the maximum modeled concentrations in each respective area. Therefore, EPA only included these two principal sources within these area boundaries when designating these areas.

Shortly after EPA published these nonattainment designation boundaries, Luminant announced plans to retire the Monticello Steam Electric Station (October 6, 2017) and the Big Brown Steam Electric Station (October 13, 2017), and to close both facilities at the beginning of 2018. Luminant permanently retired the Big Brown electric generating units 1 and 2 on February 12, 2018, and the TCEQ voided the operating permit for these units on August 3, 2018. The TCEQ voided most individual NSR permits for Big Brown units 1 and 2 on March 28, 2018, and the remaining NSR authorizations were voided on June 30, 2020. On April 18, 2021, the Big Brown facility was permanently demolished. Luminant permanently retired the Monticello electric generating units 1, 2, and 3 on December 31, 2017, and the TCEQ voided the operating permit for these units on August 29, 2018. The TCEQ voided most individual NSR permits for Monticello units 1, 2, and 3 on February 14, 2018, and the remaining NSR authorizations were voided on July 14, 2020. On July 1, 2021, the Monticello facility was permanently demolished. Thus, a key factor in our determination that these two areas attained the 2010 SO₂ standard is the retirement of these two facilities since they were the only principal sources within these area boundaries when these areas were designated as nonattainment.

B. Evaluation of SO ₂ Monitoring Data

On October 30, 2017, Texas deployed a special purpose SO₂ monitor in Freestone County, Texas near the Big Brown Steam Electric facility at the Fairfield Farm to Market (FM) 2570 Ward Ranch site. This special purpose monitor (Air Quality System (AQS) ID 48-161-1084) was specifically established to collect information about the SO₂ ambient air concentrations impacted by emissions from the Big Brown Electric Station. Though the Big Brown Steam Electric Station shut down in February 2018, Texas continues to operate the monitor. In review of the available data at the time of the CDD request, data from the Big Brown monitor demonstrated a marked improvement in air quality in the NAA due to the permanent retirement of the source. CAA section 179(c) requires EPA's determination of whether the area attained by the attainment date to be based on the area's air quality as of the attainment date. Therefore, for the attainment date of January 12, 2022, the 3-year period of 2019 through 2021 is the relevant time period for evaluation in fulfilling the Agency's obligation under CAA section 179(c). The 2019-2021 design value for the Big Brown monitor was 5 ppb (7 percent of the standard), compared to the standard of 75 ppb. The more recent 2020-2022 design value for the Big Brown monitor was 7 ppb (9 percent of the standard). The Freestone County monitor's 1-hour SO₂ design values have never violated the 2010 1-hour primary SO₂ NAAQS for the periods following the source shutdown. The EPA is proposing to find that this monitoring data supports the determination that the Freestone-Anderson NAA has been in attainment since the Big Brown Steam Electric Station retired in 2018.

For the Titus County NAA, Texas did not install a monitor that had been planned near the Monticello Steam Electric Station once the retirement of the facility was announced for 2017. However, monitoring data from the Welsh monitor (AQS ID 48-449-1078), (the Cookville FM 4855 monitor) also located in Titus County, Texas approximately 16 km to the east of the NAA surrounding the Monticello Steam Electric Station, was evaluated to provide corroborating evidence that the source shutdowns have resulted in attainment. The Welsh Monitor began operating in January 2017. The Welsh monitor was located at the Cookville FM 4855 site by Texas to characterize the SO₂ concentrations from the Welsh Power Plant. The Welsh plant was not included in the Titus NAA because it was not identified as a contributing source to the modeled SO₂ NAAQS violation in the Titus NAA. Although the Welsh plant was not identified as a contributing source to the Titus NAA, it is the only other major SO₂ producing plant in Titus County now that the Monticello Steam Electric Station has retired, and its SO₂ emissions and resulting SO₂ concentrations are accounted for with this monitor. And, moreover, the Welsh monitor which was sited to capture the impacts of this lone remaining source is recording SO₂ concentrations well below the level of the NAAQS. The 2019-2021 design value at the Welsh monitor is 19 ppb, 25 percent of the 1-hour SO₂ NAAQS standard. The 2020-2022 design value is 14 ppb, 19 percent of the standard. As explained in the CDD final action, these values represent an upper limit for the estimated design value for the Titus County NAA since the Welsh monitor includes the impacts from the nearby Welsh Power Plant. Concentrations within the Titus NAA, farther from the Welsh plant, would be expected to be lower since there are no other large sources nearby. The EPA is proposing to find that the monitoring data from the Welsh monitor in Titus County support the conclusion that the Titus NAA attained the 2010 1-hour SO₂ NAAQS by the January 12, 2022, statutory attainment date.

C. Evaluation of SO ₂ Modeling Data

In 2016, Sierra Club and Vistra Energy submitted modeling data for the most recent 3 years (2013-2015) at that time. This modeling provided the basis for the two nonattainment designations as discussed earlier. In our CDD, we evaluated this modeling to determine if there was any possibility these areas would still be in nonattainment after the plant shutdowns. Our analysis of the maximum impacts around Big Brown and around Monticello found that these plants were responsible for almost 100 percent of the impacts on the maximum ambient SO₂ concentration. EPA's boundaries for the NAAs encompassed the areas shown to be in violation of the standard based on the 2013-2015 emissions and the principal sources that contributed to the violation in each area ( i.e., Big Brown and Monticello). Both facilities no longer emit any SO₂ due to permanent shutdowns. Big Brown has emitted zero emissions since the second quarter of 2018 and Monticello has emitted zero emissions since the first quarter of 2018. The only emissions explicitly modeled were those from Big Brown and Monticello; the contributions from all other sources were represented in the model by an estimate of the background concentration. This is a technique in modeling to address smaller or more distant source contributions by examining monitoring data thought to be representative. In the modeling evaluated for designations, these contributions were estimated to be small, 2 ppb for both areas (much less than the 75 ppb standard). Consistent with our analysis in the CDD, we do not believe that new modeling is required to determine attainment of the standard by the attainment date. Because the emissions from the Big Brown and Monticello facilities for the 2019-2021 period are zero and their modeled concentrations would also be zero, the total concentration within the nonattainment area would be modeled as equal to the contribution from all other sources, or background. In other words, the modeled design value, if remodeled, would be small and equal to the concentrations from all other sources as represented by the background concentration.

D. Evaluation of SO ₂ Emissions Data

Although the initial designation modeling showed that Big Brown and Monticello Steam Electric Stations contributed nearly 100 percent of the point source emissions in their nonattainment areas, and those sources have shutdown, the EPA also evaluated total County-wide emissions to consider any point sources that are within the Counties. The EPA evaluated annual SO₂ point source emission trends for sources within each County for 2012, and 2017 through 2022.

Table 1 shows that Big Brown emitted nearly 100 percent of the total point source emissions within Freestone and Anderson Counties until after its retirement in 2018. The total SO₂ point source emissions have been 100 tons per year (tpy) or less each year from 2019 to 2022. A flare from Mosbacher Energy Company is responsible for the majority of those remaining annual SO₂ emissions (ranging from 28 to 86 tpy) with the rest coming from Freestone Energy Center (ranging from 12 to 16 tpy) and other various combined sources emitting less than 1 tpy each.