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 andPreventing Pollution

November 17, 2015

Mr. Guy Donaldson Air Planning Section Chief Environmental ProtectionAgency, Region 6 Fountain Place 12th Floor, Suite 1200 1445 Ross Avenue Dallas, Texas 75202-2733 Dear Mr. Donaldson:
Thankyou for yourletter ofOctober 20, 2015 informing the Texas Commission on Environmental Quality (TCEQ) that the United States Environmental ProtectionAgency (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 slatedfor designation by July 2, 2016, the TCEQ appreciates that the EPA is reviewing all relevant information received in preparation for its proposed designations. Itis goodto hear thatthe information providedbythe TCEQ on September 18, 2015 will behelpful, and we appreciatethe opportunity to review and respondto the SC's information submittal.
The TCEQ's Air Permits Division reviewed the SC modeling and analyses for W AParish 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 andwiththe conclusions drawn. Several items ofconcern that are common to all five ofthe modeling analyses were identified. Some ofthe techniqlles usedin the SC analyses are not consistent with the EPA's S02NAAQSDesignationsModeling TechnicalAssistanceDocument (TAD). Further, there are statements contained in the modeling reports that lack supporting justification. Therefore, theTCEQ does not agree with the SC's modeling results or conclusions.
The issues common across the provided SC modeling included: meteorological data used, use ofinappropriate receptor locations andheights, and lack ofdownwash parameters. For the meteorological dataprocessing with AERMET, the option to not randomize wind directions was selected. According to the EPA's Guideline onAir

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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### QualityModels (GAQM), wind datafrom the National Weather Service shouldbe randomized in order to ensure a lack ofbias in wind direction assignments made in the modeling. In addition, datafrom receptor locations on-property and over adjacent bodies ofwater (lakes) are includedinthe modeling analyses. The S02 TAD notes that receptors canbe ignored or notplacedin areas where itis notfeasible toplace a monitor (waterbodies, etc.). On-propertylocations are not considered tobe representative of ambient air concentrations and these areas shouldbe excludedfrom 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 anylevel other than at groundlevel for comparison to the NAAQS. Also, building downwash effects are not considered in the modeling analyses. The reports note that downwash 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 ofthe modeling reports includes a number ofassumptions usedin the modeling analyses (bulleted list) and notes thatthese assumptions likely contribute to under-estimation ofthe predicted concentrations. However, neither those assumptions northe 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 ofthe five power plants. After reviewing the SC modeling andrelated information, theTCEQ maintains thatthe designations recommended on September 18, 2015 are the most accurate characterizations ofair quality that can be made with the information available, particularly clue to the lack of S02 air quality monitoring data available for counties wherethe subject power plants are located. These counties- Fort Bend, Limestone, Freestone, Rusk, andTitus

- all remain unmonitored, andthe unclassifiable/attainment designation recommendedfor each remains unchanged.
Thankyou for the opportunityto contribute to your evaluation ofthe materials submittedbythe Sierra Club. Please contact me at 512-239-1295 or at Steve.Hagle@tceq.texas.gov, or David Brymer, Director ofthe 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 ofAir Texas Commission on Environmental Quality
EnclosureAttachment- TCEQ Review ofSierra Club ModelingAnalysis
The Air Permits Division reviewed modeling conductedbythe 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 ofitems that are unique to the individual modeling analysis for each ofthese five power plants.
W A Parish Electric Generating Station The hourly emission rate file utilized in the modeling analysis for theW A Parish Electric Generating Station was inappropriately developed. The last column onthehourly emission rate file provides stack diameters, instead ofthe 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 ofthe modeling report includes information on the allowable emissions data used in the modeling analysis. Itis not clear what these emissions data represent, andthey appear to be much greater than previous permitting information and other emissions inventory data. Inthe modeling, receptors were placed on-property and over adjacentbodies ofwater. The location ofthe GLCmax is located on-propertyand 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 concentrationin the area impactedbyW A Parish Electric Generating Station." However, the report does not contain sufficient information to support this statement.
Limestone Electric Generating Station Table 2 ofthe modeling report for the Limestone Generating Station includes information on the allowable emissions data used in the modeling analysis. Itis not clear what these emissions data represent, andthey 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, andthe 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 ofoff-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 impactedby Limestone Electric Generating Station." However, the report does not contain sufficient information to support this statement. The predicted concentrations reported in Table 1ofthe 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 shouldbethe 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 conductedwith only one year ofmeteorological data. Even though three years ofmeteorological data were processed withAERMET, the start and endkeywords were usedwithinAERMOD to limit the length of periodto one year. Table 2 ofthe modeling report includes information onthe allowable emissions dataused in the modeling analysis. Itis not clear what these emissions data represent, and they appear to be much greaterthan previous permitting information and other emissions inventory data. Inthe modeling, receptors were placed on-property and over adjacent bodies ofwater. The location ofthe GLCmax is located on-property, which is not consistentwith 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 impactedby Big Brown Steam Electric Station," However, the report does not contain sufficient information to supportthis statement.
Martin Lake Electrical Station The modeled exit temperature for each ofthe sources included in the modeling analysis for the Martin Lake Electrical Station is not consistentwith 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-datawere-processedwith· AERMET, the start and end keywords were used within AERMOD to limit the length ofperiod to oneyear. The modeled actual emission rates for source ID M01 are not consistentwith theEPA's Air Markets Program Data for certain hours ofthe 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 ofthe modeling report includes information onthe allowable emissions data used in the modeling analysis. Itis not clearwhatthese emissions data represent, and they appear to be much greater than previous permitting information and other emissions inventory data. Inthe modeling, receptors were placed on-property and over adjacentbodies ofwater. The location ofthe GLCmax is located on-property, which is not consistent the S02 Modeling TAD guidance. The modeling analysis included emissions from theWelsh 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 impactedby Monticello Steam Electric Station." However, the report does not contain sufficient information to suppo1t this statement. Furtber, the modeled exit velocity for each ofthe Welsh Power Plant sources is not consistent with other source inventory information.