## Attachment B

TCEQ Analys es

Contents:

Part 1: Summary of TCEQ’s Analyses

Part 2: TCEQ’s Modeling Analyses

A. The June 5, 2015 Modeling Analysis of Sulfur Dioxide for Coleto Creek Power, LP

– Coleto Creek Power Station (RN100226919)

B. The June 5, 2015 Modeling Analysis of Sulfur Dioxide for Southwestern Public Service Company – Tolk Station Power Plant (RN100224534 )

C. The June 5, 2015 Modeling Analysis of Sulfur Dioxide for Major Oak Power, LLC – Twin Oaks (RN100226570)

### Attachment B, Part 1:
Summary of TCEQ’s Analyses

In a letter to the Texas Commission on Environmental Quality ( TCEQ ) dated March 20, 2015,
t he U.S. Environmental Protection Agency ( EPA ) identified 12 power plants to be evaluat ed in order to determine their impacts, if any, on compliance with the 2010 SO 2 National Ambient Air Quality Standard ( NAAQS )

. T he TCEQ evaluated f our of the 12 EPA

- identified Texas sources meeting the consent decree criteria , being large emissions sources not announced for retirement as of March 2015, with 2012 SO 2 emissions greater than 16,000 tons

, or with 2012 emissions greater than 2,600 tons and an average emission rate greater than 0.45 MMBtu

. This attachment identifies the information that the TCEQ considered in its evaluation of the four SO 2 emissions sources , being Sandy Creek Energy Station, located in McLennan County; Coleto Creek Power Station , located in Goliad County; Tolk Generating Station, located in Lamb County; and Twin Oaks Power Station, located in Robertson County

. The TCEQ evaluated Sandy Creek Energy Station based on McLennan County monitoring data, with further support from modeli ng performed by Sandy Creek, as described in Attachment C: Evaluation of the Impact of Sandy Creek Energy Station SO 2 Emissions

. While the TCEQ continues to support the use of ambient air monitoring data as the appropriate information for use in making de signation decisions, the TCEQ modeled three of the four

sources it evaluated. The TCEQ’s analys e s are contained in Attachment B, Part 2: TCEQ’s Modeling Analyses

.

One of the modeled facilities – Coleto Creek Power Station – provided additional information, contained in Attachment D: Information Submitted to the TCEQ by Coleto Creek Power Station

. The TCEQ did not thoroughly evaluate this supplemental information due to time constraints.

The TCEQ’s basis for evaluation and determinations made for each of the four sources are :

EPA Identified Source County Basis for Evaluation Recommended Designation Additional I nfo rmation Submitted by

the Source Sandy Creek Energy Station McLennan Available monitoring data – Waco Mazanec C1037 Attainment See
Attachment C

Coleto Creek Power Station Goliad Modeled maximum concentration 38 parts per billion ( ppb ) Unclassifiable/ Attainment See
Attachment D
Tolk Generating Station Lamb Modeled maximum concentration 64 ppb Unclassifiable/ Attainment None

Twin Oaks Power Station Robertson Modeled maximum concentration 38 ppb Unclassifiable/ Attainment None

The modeling files referenced in Attachment B, Part 2: TCEQ’s Modeling Analyses are available to the EPA from the TCEQ’s secure ftp site ( https://ftps.tceq.texas.gov/ ). The “Help” link on that Web page provides instructions to sign up for an account.

## Attachment B :

TCEQ Analys es

Part 2: TCEQ’s Modeling Analyses

A. The June 5, 2015 Modeling Analysis of Sulfur Dioxide for Coleto Creek Power, LP – Coleto Creek Power Station (RN100226919)

B. The June 5, 2015 Modeling Analysis of Sulfur Dioxide for Southwestern Public Service Company – Tolk Station Power Plant (RN100224534)

C. The June 5, 2015 Modeling Analysis of Sulfur Dioxide for Major Oak Power, LLC – Twin Oaks (RN100226570)