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

Toby Baker, Commissioner 

Jon Niermann, Commissioner 

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

TEXAS COMMISSION ON ENVIRONMENTAL QUALITY 

Protecting Texas by Reducing and Preventing Pollution 

November 17, 2015 

Mr. Guy Donaldson 

Air Planning Section Chief 

Environmental Protection Agency, Region 6 

Fountain Place 12th Floor, Suite 1200 

1445 Ross Avenue 

Dallas, Texas 75202-2733 

Dear Mr. Donaldson: 

Thank you for your letter of October 20, 2015 informing the Texas Commission on 

Environmental Quality (TCEQ) that the United States Environmental Protection Agency 

(EPA) has received information from the Sierra Club (SC) regarding the air quality near 

five Texas power plants relative to the 2010 Sulfur Dioxide (S02) National Ambient Air 

Quality Standard (NAAQS). Since the areas where these facilities are located are among 

those slated for designation by July 2, 2016, the TCEQ appreciates that the EPA is 

reviewing all relevant information received in preparation for its proposed designations. 

It is good to hear that the information provided by the TCEQ on September 18, 2015 will 

be helpful, and we appreciate the opportunity to review and respond to the SC's 

information submittal. 

The TCEQ's Air Permits Division reviewed the SC modeling and analyses for W A Parish 

Electric Generating Station, Limestone Electric Generating Station, Big Brown Steam 

Electric Station, Martin Lake Electrical Station, and Monticello Steam Electric Station. 

We did not perform an exhaustive review ofthe SC's submittal. However, we did find 

several issues, both with the modeling conducted and with the conclusions drawn. 

Several items of concern that are common to all five of the modeling analyses were 

identified. Some of the techniqlles used in the SC analyses are not consistent with the 

EPA's S02 NAAQS Designations Modeling Technical Assistance Document (TAD). 

Further, there are statements contained in the modeling reports that lack supporting 

justification. Therefore, the TCEQ does not agree with the SC's modeling results or 

conclusions. 

The issues common across the provided SC modeling included: meteorological data 

used, use of inappropriate receptor locations and heights, and lack of downwash 

parameters. For the meteorological data processing with AERMET, the option to not 

randomize wind directions was selected. According to the EPA's Guideline on Air 

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

How is our customer service? tccq.texas.gov/customersurvey 

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Mr. Guy Donaldson 

Page 2 

Quality Models (GAQM), wind data from the National Weather Service should be 

randomized in order to ensure a lack of bias in wind direction assignments made in the 

modeling. In addition, data from receptor locations on-property and over adjacent 

bodies of water (lakes) are included in the modeling analyses. The S02 TAD notes that 

receptors can be ignored or not placed in areas where it is not feasible to place a monitor 

(water bodies, etc.). On-property locations are not considered to be representative of 

ambient air concentrations and these areas should be excluded from the receptor grid. 

Flagpole receptor heights, which are noted to be unnecessary in the SOz Modeling TAD, 

were used in the modeling analyses. The GAQM does not specify that receptors should 

be placed at any level other than at ground level for comparison to the NAAQS. Also, 

building downwash effects are not considered in the modeling analyses. The reports 

note that down wash effects typically increase predicted concentrations near a facility, 

but this is not always the case, particularly when the source-to-receptor distance is 

great. Section 2.3 of each of the modeling reports includes a number of assumptions 

used in the modeling analyses (bulleted list) and notes that these assumptions likely 

contribute to under-estimation of the predicted concentrations. However, neither those 

assumptions nor the conclusions drawn from them are supported. 

The attached document contains commentmy and details resulting from our review of 

the modeling analyses and discusses items unique to each of the five power plants. After 

reviewing the SC modeling and related information, the TCEQ maintains that the 

designations recommended on September 18, 2015 are the most accurate 

characterizations of air quality that can be made with the information available, 

particularly clue to the lack of S02 air quality monitoring data available for counties 

where the subject power plants are located. These counties- Fort Bend, Limestone, 

Freestone, Rusk, and Titus - all remain unmonitored, and the unclassifiable/ attainment 

designation recommended for each remains unchanged. 

Thank you for the opportunity to contribute to your evaluation of the materials 

submitted by the Sierra Club. Please contact me at 512-239-1295 or at 

Steve.Hagle@tceq.texas.gov, or David Brymer, Director of the Air Quality Division, at 

512-239-1725 or at David.Brymer@tceq.texas.gov, with any questions. 

Sincerely, 

_£±=--~-

Steve Hagle, P.E., Deputy D~ector Office of Air 

Texas Commission on Environmental Quality 

Enclosure 
Attachment- TCEQ Review of Sierra Club Modeling Analysis 

The Air Permits Division reviewed modeling conducted by the Sierra Club (SC) for the 

following power plants: W A Parish Electric Generating Station, Limestone Electric 

Generating Station, Big Brown Steam Electric Station, Martin Lake Electrical Station, and 

Monticello Steam Electric Station. Below is a discussion of items that are unique to the 

individual modeling analysis for each of these five power plants. 

W A Parish Electric Generating Station 

The hourly emission rate file utilized in the modeling analysis for the W A Parish Electric 

Generating Station was inappropriately developed. The last column on the hourly emission 

rate file provides stack diameters, instead of the exit velocities as specified in section 2.7.2 of 

theAERMOD User's Guide. As a result there are significant discrepancies with model inputs 

leading to overly conservative model predictions. 

Table 2 of the modeling report includes information on the allowable emissions data used in 

the modeling analysis. It is not clear what these emissions data represent, and they appear to 

be much greater than previous permitting information and other emissions inventory data. 

In the modeling, receptors were placed on-property and over adjacent bodies of water. The 

location of the GLCmax is located on-property and over water; this is not consistent with the 

S02 Modeling TAD guidance. 

The modeling analysis includes emissions from Rhodia Inc., an off-property source. The 

report notes, "In addition, the emissions from Rhodia Inc., significantly contribute to the 

ambient S02 concentration in the area impacted by W A Parish Electric Generating Station." 

However, the report does not contain sufficient information to support this statement. 

Limestone Electric Generating Station 

Table 2 of the modeling report for the Limestone Generating Station includes information on 

the allowable emissions data used in the modeling analysis. It is not clear what these 

emissions data represent, and they appear to be much greater than previous permitting 

information and other emissions inventmy data. 

The modeling analysis includes emissions from several off-property sources - Big Brown 

Steam Electric Station, Oak Grove Power Station, and the Twin Oaks Electric Services facility. 

However, the Twin Oaks facility is located approximately 56 kilometers from the Limestone 

Electric Generating Station. This is beyond the 50 kilometer "useful distance" for reasonable 

estimations of off-property concentrations associated with AERMOD. 

The modeling report notes, "In addition, the emissions from Big Brown Steam Electric 

Station, Oak Grove Power Station, and the Twin Oaks Electric Services significantly contribute 

to the ambient S02 concentration in the area impacted by Limestone Electric Generating 

Station." However, the report does not contain sufficient information to support this 

statement. 

The predicted concentrations reported in Table 1 of the modeling report for "Limestone" and 

"All Plants" are reported as the high, second high (H2H) fourth highest daily maximum 1-hour 

results averaged over three years. The appropriate metric should be the high, first high (H1H) 

fourth highest daily maximum 1-hour results averaged over three years. 
Big Brown Steam Electric Station 

The modeling analysis for the Big Brown Steam Electric Station was conducted with only one 

year of meteorological data. Even though three years of meteorological data were processed 

with AERMET, the start and end keywords were used within AERMOD to limit the length of 

period to one year. 

Table 2 of the modeling report includes information on the allowable emissions data used in 

the modeling analysis. It is not clear what these emissions data represent, and they appear to 

be much greater than previous permitting information and other emissions inventory data. 

In the modeling, receptors were placed on-property and over adjacent bodies of water. The 

location of the GLCmax is located on-property, which is not consistent with the S02 Modeling 

TAD guidance. 

The modeling analysis includes emissions from the Limestone Electric Generating Station, an 

off-property source. The report notes, "In addition, the emissions from Limestone Electric 

Generating Station significantly contribute to the ambient S02 concentration in the area 

impacted by Big Brown Steam Electric Station," However, the report does not contain 

sufficient information to support this statement. 

Martin Lake Electrical Station 

The modeled exit temperature for each of the sources included in the modeling analysis for 

the Martin Lake Electrical Station is not consistent with other source inventory information. 

Monticello Steam Electric Station 

The modeling analysis for Monticello Steam Electric Station was conducted with only one year 

··- ~·-- - ---ofmeteorological-dat~e-Even-though-three years-of-meteorological-data were-processed with· 

AERMET, the start and end keywords were used within AERMOD to limit the length of period 

to one year. 

The modeled actual emission rates for source ID M01 are not consistent with the EPA's Air 

Markets Program Data for certain hours of the three-year period (2012-2014). In addition, 

the modeled exit temperature for source ID M01 is not consistent with other source inventory 

information. 

Table 2 of the modeling report includes information on the allowable emissions data used in 

the modeling analysis. It is not clear what these emissions data represent, and they appear to 

be much greater than previous permitting information and other emissions inventory data. 

In the modeling, receptors were placed on-property and over adjacent bodies of water. The 

location of the GLCmax is located on-property, which is not consistent the S02 Modeling TAD 

guidance. 

The modeling analysis included emissions from the Welsh Power Plant, an off-property 

source. The report notes, "In addition, the emissions from Welsh Power Plant significantly 

contribute to the ambient S02 concentration in the area impacted by Monticello Steam 

Electric Station." However, the report does not contain sufficient information to suppo1t this 

statement. Furtber, the modeled exit velocity for each of the Welsh Power Plant sources is not 

consistent with other source inventory information.