Btyan W. Shaw, Ph.D., P.E., Chairman 

Toby Baker, Commissioner 

Jon Nierrnann, Commissioner 

Richard A. Hyde, P .E., Executive Director 

TEXAS COMMISSION ON ENVIRONMENTAL QUALITY 

Mr. Erik M. Snyder 

Protecting Texas by Reducing and Preventing Pollution 

November 30, 2015 

Environmental Protection Agency, Region 6 

1445 Ross Avenue 

Suite 1200 

Mail Code: 6PD 

Dallas, TX 75202-2733 

Dear Mr. Snyder: 

Thank you for holding a conference call on November 6, 2015 to discuss modeling 

performed by the Texas Commission on Environmental Quality (TCEQ) in support of our 

September 18, 2015 updated recommendation regarding designations for the 2010 Sulfur 

Dioxide (S02) National Ambient Air Quality Standard (NAAQS). 

In our discussions, you requested supplemental modeling to evaluate the sensitivity of 

A,ERMOD to changes in meteorological files based on the location used to determine 

surface characteristics. The modeling submitted by the 'l'CEQ on September 18, 2015 used 

AERSURFACE to calculate generalized surface characteristics of the areas surrounding the 

emission sources. The resulting meteorological input data was considered to be 

adequately representative for the project site and modeling domain, and to satisfy the 

intent of section 7.2: Surface Characteristics and Representativeness of the S02 Modeling 

Technical Assistance Document. 

Although the TCEQ does not agree that characteristics of a meteorological tower must be 

used, supplemental modeling was performed for the Twin Oaks, Coleto Creek, and Tolk 

facilities to resolve the United States Environmental Protection Agency's (EPA) concerns 

about the representativeness of the meteorological data used in our analyses. The 

supplemental modeling was performed using the same model setup as the modeling 

analysis submitted to the EPA on September 18, 2015, except that in developing the 

meteorological data, AERSURF ACE-calculated surface characteristics at the 

meteorological tower location were used instead of AERSURFACE-calculated surface 

characteristics at the project site. The most recent versions of AERMOD andAERMET 

(version 15181) were used in the modeling exercises. 

Table 1: Surface Characteristic Comparison and Table 2: AERMOD Predicted Maximum 

Ground Level Concentrations (GLCmax) compare the TCEQ's modeling results using 

meteorological data developed using AERSURFACE-calculated surface characteristics at 

the project site to the supplemental modeling results using data developed using 

AERSURF ACE-calculated surface characteristics at the meteorological tower location. 

P.O. Box 13087 • Austin, Texas 78711-3087 • 512-239-1000 • tceq.texas.gov 

How is our customer service? tceq.texas.govjcustomersurvey 
Mr. Erik M. Snyder 

Page 2 

November 30, 2015 

Twin Oaks 0.17 

Coleta 0.17 Creek 

Talk 0.18 

Table 1: Surface Characteristic Comparison 

0.70 0.043 0.17 0.67 0.069 

0.68 o.os8 0.17 0.78 o.os8 

0.79 0.122 0.18 0.61 0.090 

Table 2: AERMOD Predicted Maximum Ground Level Concentrations (GLCmax) 

Twin Oaks 84 83 

Coleta 84 85 Creek 

Talk 150 158 

represents average 99th maximum 

concentrations. 

As shown in Table 2, the changes to the GLCmax are minimal between the two modeling 

demonstrations. As a result, the overall conclusions from the previous modeling are not 

changed, and all three locations are predicted to be in compliance with the 2010 one-hour 

S02NAAQS. 

Thank you for the opportunity to provide this supplemental information to clarify the 

modeling information provided by the TCEQ in support of designations recommended by 

the State of Texas. If you would like copies of the modeling files or have specific questions 

about the modeling, please contact Daniel Menendez at 512-239-1537 or 

Daniel.Menendez@tc~texas.gov. Otherwise, please contact me at 512-239-1295 or at 

Steve.Hagle@tceq.texas.go.Y,_or David Brymer, Director of the Air Quality Division, at 512-

239-1725 or at DavidJ.ITymer@tceq.texas.gov, with any questions. 

Sincerely, 

Steve 

~~ Hagle, P.E., Deputy Director 

Office of Air 

Texas Commission on Environmental Quality