## TCEQ Interoffice Memorandum To: David Brymer, Director Air Quality Division From: ¥-Daniel Menendez, Team Leader Air Dispersion Modeling Team (ADMT) Air Permits Division Date: June 5, 2015 Subject: Mocleling Analysis ofSulfur Dioxide for Major Oak Power, LLC -Twin Oaks (RN100226570) 1. Project Identification Information OnMarch 2, 2015, the U.S. District Court for theNorthern District ofCalifornia accepted as an enforceable order an agreementbetweenthe Environmental Protection Agency (EPA) and Sierra Club aod Natural Resources Defense Council to resolve litigation concerning the deadline for completing !-hour

## so2 designations. OnMarch 20, 2015, the EPA notified the Texas Commission onEnvironmental Quality (TCEQ) ofTexas powerplant sources that meet the criteria established inthe court's order. In addition, the letter advised thatthe EPA will use the most recent available information when making designation and boundary decisions. The EPA requested updatedrecommendations aod supporting information by September 18, 2015. Due to time aod resource constraints, the TCEQ conducted limited refined screening modelingto support attainment designations near selected sources. 2. Modeling Results Thepredicted maximum ground level concentration (GLCmax) is 84 [.Lg/m3

, aod this represents a three-year average ofthe high, fourth high (or 991 h percentile) maximun1 daily !-hour concentrations. The location ofthe GLCmax is approximately 1300 meters from the two modeled stacks to the north. Table !liststhe location ofthe predicted GLCmax. The locationis inthe Universal Traosverse Mercator (UTM) Zone 

### 14 North, North American Datum of 1983 (NAD83) coordinate system.

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## TCEQ Interoffice Memorandum

719635 Background concentrations for S02 were obtained from the EPA Aerometric Information Retrieval System (AIRS) monitor 483091037located at 4472 Mazanec Road, Waco McLennm1 County. The tln·ee-ycar average (2012-2014) ofthe 99'11percentile ofthe annual distribution ofthe maximum daily 1-hour concentrations was used for the !-hour value. The monitor is located approximately 70 kilometers north-northwest ofthe site, which is inthe direction ofthe predominMtwind flow for the region. TCEQ emissions inventory datafrom 2013 were reviewed Md there were not any emissions ofS02 reported within 20 kilometers ofthe Twin Oaks site. ]1Jere are approximately 360 tons of S02emissions from sources located within 20kilometers ofthemonitor site. The use of this monitor is reasonable given the location ofthe monitor Mdthe magnitude of emissions nearthemonitor site relative to the Twin Oaks site. Thenearest source, located approximately 21 kilometers away, to the Twin Oaks site is the Oak Grove Stemn Electric Station. In2013, the Oak Grove Steam Electric Station reported 6950 tons ofS02. Although this source would be unlikely lo cause a significm1t concentration gradient inthe vicinity ofthe Twin Oaks site, itwas included inthe modeling sincethere are no sources near the monitor with a similar magnitude of reported emissions. 

### 3. Model Used and Modeling Techniques AERMOD (Version 14134) was used in a refined screening mode. Forrefined screening, National Weather Service (NWS) meteorological raw input data are used with generalized surface characteristics ofthe application site. 

### A. Land Use A land use/land cover analysis was performed using AERSURFACE consistent with guidance given inthe AERMOD Implementation Guide (March 19, 2009). The recommended input data, the National Land Cover Data 1992 archives (NLCD92), were used for this Malysis. The AERSURFACE analysis conducted ofthe area surroundingthe Twin Oaks site resulted in a calculated albedo of0.17 a calculated Bowen ratio of0.70, and a calculated surfacerotJghness length of0.043 meters. These values were used to develop the meteorological data set for this analysis. Texas Commission on Environmental Quality Page 2 of4

## TCEQ Interoffice Memorandum

Terrain elevations within the modeling domain were determined using AERMAP (Version Ill03). The input data used for this analysis were National Elevation Data (NED) seamless data obtained from the United States Geological Survey (USGS). B. Meteorological Data Meteorological data for years 2012-2014 were used in the analysis. Raw surface and upper air meteorological data were processed using AERMET (Version 14134). Surface Station and ID: College Station, TX (Station#: 3904) Upper Air Station and ID: Fort Worth, TX (Station#: 3990) Meteorological Dataset: 2012-2014 Profile Base Elevation: Ioo·meters These meteorological stations are the nearest stations to the Twin Oaks site and are representative to use given that there are no significant terrain barriers between the site and the meteorological stations. C. Receptor Grid The receptor grid used in the modeling analysis consisted ofreceptors with 100 meter spacing along the fence line outto one kilometer, receptors with 500 meter spacing outto five kilometers, and receptors with one kilometer spacing outto 50 kilometers. Thepurpose ofthe receptor grid was to determine representative maximum ground-level concentrations. D. Building Wake Effects (Downwash) Input data to BPIP-Prime (Version 04274) were developed from a plot plan submitted dming previous permitting actions. The building locations were validated by ADMTusing aerial photography. 4. Modeling Emissions Inventory Source locations were validated by ADMT using aerial photography. The emission source coordinates are in the UTM Zone 14 North, NAD83 coordinate system.

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## TCEQ Interoffice Memorandum

-------------------------------------- Table 2. On-Property Point Source Parameter Information

1-1 Ul 719731.92 3442182.39 103.63 437.98 24.57 3.8 2-1 U2 719768.86 3442220.88 103.63 451.32 23.16 3.8 An hourly emissions file (TwinOaks_OakGrove_emissions.txt) for years 2012-2014 was developed for the modeling analysis. The emissions data were obtained from the EPA's Acid Rain Program database. The modeled emission rates represent the actual !-hour average emission rates reported for the two modeled stacks. As in section 2, the TCEQ emissions inventory data from 2013 were reviewed to determine ifany nearby sources should be modeled. Thenearest source, the Oak Grove Steam Electric Station, is located within approximately 21 kilometers and reported 6950 tons ofS02 in 2013. The emissions datafor the Oak Grove Steam Electric Station were obtained from the EPA's Acid RainProgram database and included inthe hourly emissions file. The modeled emissionrates represent the actuall-hour average emission rates reported for the Oak Grove SteamElectric Station. With respect to any additional nearby sources ofS02, Twin Oaks is a relatively isolated source. TCEQ emissions inventory data :from 2013 were reviewed and the next closest sources are located approximately 29-35 kilometers east ofthe site with a total of69 tons ofS02 emissions. Giventhe distance and magnitude ofemissions, these sources would notbe expected to cause significant concentration gradients inthe vicinity ofTwin Oaks and are represented inthe modeling viamonitored background concentrations. 

### 5. Modeling Files Listing

CLLFWD2012_2014.SFC AERMET surface output file CLLFWD2012_2014.PFL AERMET profile output file Twin oaks 2012-2014.DTA AERMOD input file Twin oaks 2012-20!4.GRF AERMOD plot file Twin_oaks_2012-2014.LST AERMOD output file Twin oaks 2012-20!4.SUM AERMOD summary file TwinOaks_OakGrove _emissions.txt Hourly emissions file bpip.PIP BPIP-PR!ME input file bpip.SO BPIP-PRIME output file bpip.SUM BPIP-PRIME summary file Texas Cmnmission on Environmental Quality Page4 of4