## Martin Lake Generating Station

Tatum, Texas

Evaluation of Compliance wi th the 1-hour NAAQS for SO 2



## September 11, 2015

Conducted by:

Steven Klafka, P.E., BCEE

Wingra Engineering, S.C.

Madison, WisconsinEvaluation of Compliance with the 1-hour NAAQS for SO 2 September 11, 2015 Page 2

1. Introduction

Wingra Engineering, S.C. was hi red by the Sierra Club to conduc t an air modeling impact analysis to help USEPA, state and local air a gencies identify facilities th at are likely causing exceedences of the 1-hour sulfur dioxide (SO 2 ) national ambient air qualit y standard (NAAQS). This document describes the results and pro cedures for an evaluation conducte d for the Martin Lake Generating Station located in Tatum, Texas. To improve the accuracy of the modeling analysis, it included the H.W. Pirkey Power Plant in Halls ville, Texas. This is an additi onal source of SO 2 emissions located
within 50 kilometers of the Mar tin Lake Generating Station.

The dispersion modeling analysis predicted ambient air concentr ations for comparison with the 1-
hour SO 2 NAAQS. The modeling was performe d using the most recent versi on of AERMOD, AERMET, and AERMINUTE, with data provided to the Sierra Club by regulatory air agencies and through other publicly-available so urces as documented below. The analysis was conducted in
adherence to all available USEP A guidance for evaluating source impacts on attainment of the 1-
hour SO 2 NAAQS via aerial dispersion mode ling, including the AERMOD Imp lementation Guide; USEPA's Applicability of Appendi x W Modeling Guidance for the 1 -hour SO 2 National Ambient Air Quality Standard, August 23, 2010; modeling guidance promul gated by USEPA in Appendix W to 40 CFR Part 51; USEPA’s Ma rch 2011 Modeling Guidance for SO 2 NAAQS Designations; 1 and,
USEPA’s December 2013 SO 2 NAAQS Designations Technical Assistance Document. 2

It was determined that based on m easured actual emissions or cu rrent allowable limits, the Martin Lake Generating Station is estimated to create SO 2 concentrations which exceed the 1-hour NAAQS.

2. Compliance with the 1-hour SO 2 NAAQS

2.1 1-hour SO 2 NAAQS

The 1-hour SO 2 NAAQS takes the form of a t hree-year average of the 99 th percentile of the annual distribution of daily maximum 1- hour concentrations, which cann ot exceed 75 ppb. 3 Compliance
with this standard w as verified using USEPA’s AERMOD air disper sion model, which produces air concentrations in units of μg/m 3 . The 1-hour SO 2 NAAQS of 75 ppb equals 196.2 μg/m 3 , and this is the value used for determining whether modeled impacts exceed t he NAAQS. 4 The 99 th percentile
of the annual distri bution of daily maximum 1-hour concentratio ns corresponds to the fourth-highest

1 http://www.epa.gov/scram001/ so2_modeling_guidance.htm

2 http://www.epa.gov/oaqps001/sulfurdioxide/pdfs/SO2ModelingTAD. pdf

3 USEPA, Applicability of Appendix W Modeling Guidance for the 1- hour SO 2 National Ambient Air Quality Standard, August 23, 2010.

4 The ppb to μg/m 3 conversion is found in the source code to AERMOD v. 14134, sub routine Modules. The conversion calculation is 75/0.3823 = 196.2 μg/m 3

.Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 11, 2015 Page 3

value at each receptor for a given year.

2.2 Modeling Results

Model results for both sources i ncluded in the analysis of SO 2 are summarized in Table 1. Results are provided for each source alone, and for both sources combin ed.

Modeling results for Martin Lak e Generating Station are summari zed in Table 1. It was determined
that based on either current all owable emissions or measured ac tual emissions, the Martin Lake Generating Station is estim ated to create downwind SO 2 concentrations which exceed the 1-hour NAAQS.

More specifically, the modeling results presented in Table 1, s how exceedences of the NAAQS by the plant’s allowable and actua l emissions. “Allowable” is the peak emission rate from each unit as approved by the current air quali ty operation permit for the fa cility. “Actual” are the measured emissions for each hour between January 1, 2012 and December 31 , 2014 as taken from USEPA Air Markets Program Data

. 5

Air quality impacts in Texas are based on a background concentr ation of 7.8 μg/m 3 . This is the 2011-13 design value for El Paso, Tex as - the lowest measured b ackground concentration in the
state. This is the most recen tly available design value. See S ection 5 for further discussion of the background concentrations used for this analysis.

Table 1 - SO 2 Modeling Results for Martin Lake Generating Station Modeling Analysis

Emission Rates Averaging Period 99 th Percentile 1-hour Daily Maximum (μg/m 3 ) Complies with NAAQS? Impact Background Total NAAQS

Allowable Martin Lake 679.6 7.8 687.4 196.2 No

Actual 339.8 7.8 347.6 196.2 No

Allowable Pirkey 187.5 7.8 195.3 196.2 No

Actual 40.9 7.8 48.7 196.2 Yes

Allowable Both 682.8 7.8 690.6 196.2 No

Actual 339.9 7.8 347.7 196.2 No

5 http://ampd.epa.gov/ampd/Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 11, 2015 Page 4

The emissions used for the mode ling analysis are summarized in Table 2.

Table 2 - Modeled SO 2 Emissions from Martin Lake Generating Station 6

Stack

ID Unit
ID Allowable Emissions 30-day Average (lbs/hr) S01 Unit 1 9,516.0 S02 Unit 2 9,516.0 S03 Unit 3 9,516.0 Martin Lake Total 28,548.0 Pirkey Unit 1 8,652.0 Both Stations Total 37,200.0

Based on the modeling results, Table 3 provides the necessary e mission reductions from current allowable rates necessary to ach ieve compliance with the 1-hour NAAQS.

Table 3 - Required Emission Reductions from Cu rrent Allowable Limits to Comply with the 1-

hour NAAQS for SO 2 Acceptable Impact (NAAQS - Background) 99th Percentile 1-hour Daily Max (μg/m 3 ) Required Total Facility Reduction Based on Allowable Emissions (%) Required Total Facility Emission Rate (lbs/hr) Required Total Facility 1-hour Average Emission Rate

(lbs/mmbtu)

188.4 72% 7,877.0 0.33

Predicted exceedences of the 1-hour NAAQS for SO 2 based on allowable emissions from both sources extend throughout the reg ion to a maximum distance of 4 6 kilometers.

Figure 1 shows the extent of NAA QS violations based on allowabl e emissions from both sources.

Figure 2 shows the extent of NAA QS violations based on actual h ourly emissions from both sources.

2.3 Conservative Modeling Assumptions

A dispersion modeling analysis requires the selection of numero us parameters which affect the predicted concentrations. For the enclosed analysis, several pa rameters were selected which underpredict facility impacts.

6 Martin Lake allowable emissions a re taken from Federal Operati ng Permit, No. RL-0020-K, May 19, 1999. Pirkey allowable emissions are taken from Federal Operating Permit, No . O31, July 26, 2010. The applicable SO2 emision limitation for both facilities is 1.2 lbs per million BTU.Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 11, 2015 Page 5

Assumptions used in this modeli ng analysis which likely under-e stimate concentrations include the following:

 Allowable emissions are base d on a limitation with an averaging period which is greater than the 1-hour average used for the SO 2 air quality standard. Emissions and impacts during any 1-hour period may be higher than assumed for the modeling analy sis.

 No consideration of facility operation at less than 100% load. Stack parameters such as exit flow rate and temperature are typically lower at less than full load, reducing pollutant dispersion and increasing predic ted air quality impacts.

 No consideration of building or s tructure downwash. These downw ash effects typically increase predicted concentr ations near the facility.

 No evaluation has been conducted t o determine if the stack heig ht exceeds Good Engineering Practice or GEP height. If the st ack height exceeds GEP, the pr edicted concentrations will increase.

 No consideration of off-site sources. These other sources of SO 2 will increase the predicted impacts.

 As noted, air quality impact s are based on a background SO 2 concentration of 7.8 μg/m 3

, which is the lowest measured b ackground concentration in the st ate. Given the proximity of the Martin Lake facility to other sources of SO 2 , the actual background concentration is likely higher.

 No evaluation has been conducted t o determine if the stack heig ht exceeds Good Engineering Practice or GEP height. If the st ack height exceeds GEP, the pr edicted concentrations will increase.Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 11, 2015 Page 6

Figure 1 - Regional View of Impacts Base d on Allowable Emissions from All SourcesEvaluation of Compliance with the 1-hour NAAQS for SO 2 September 11, 2015 Page 7

Figure 2 - Regional View of Impacts Based on Actual Emissions from All Sources for the 2012-14 PeriodEvaluation of Compliance with the 1-hour NAAQS for SO 2 September 11, 2015 Page 8

3. Modeling Methodology

3.1 Air Dispersion Model

The modeling analysis used U SEPA’s AERMOD program, v. 14134. A ERMOD, as available from the Support Center for Regulator y Atmospheric Modeling (SCRAM) website, was used in conjunction with a third-par ty modeling software program, AERMOD View , sold by Lakes
Environmental Software.

3.2 Control Options

The AERMOD model was run with t he following control options:

 1-hour average air concentrations

 Regulatory defaults

 Flagpole receptors

To reflect a representative i nhalation level, a flagpole height of 1.5 meters was used for all modeled receptors. This parameter was added to the receptor file when running AERMAP, as described in
Section 4.4.

An evaluation was conducted to det ermine if the modeled facilit y was located in a rural or urban setting using USEPA’s methodology outlined in Section 7.2.3 of the Guideline on Air Quality
Models. 7 For urban sources, the URBANOPT option is used in conjunction with the urban population from an appropriate ne arby city and a default surfac e roughness of 1.0 meter. Methods
described in Section 4.1 were used t o determine whether rural o r urban dispersion coefficients were appropriate for the modeling analysis.

3.3 Output Options

The AERMOD analysis was based on three years of recent meteorol ogical data. The modeling analyses used one run with three ye ars of sequential meteorolog ical data from 2012-2014. Consistent with USEPA’s Modeling Guidance for SO 2 NAAQS Designations, AER MOD provided a table of fourth-high 1-hour SO 2 impacts concentrations consiste nt with the form of the 1-hour SO 2 NAAQS. 8

Please refer to Table 1 for the modeling results.

7 USEPA, Revision to the Guidelin e on Air Quality Models: Adopti on of a Preferred General Purpose (Flat and Complex Terrain) Dispersion Model and Other Revisions, Appendix W to 40 CFR Part 51, November 9, 2005.

8 USEPA, Area Designations for the 2010 Revised Primary Sulfur Di oxide National Ambient Air Quality Standards, Attachment 3, March 24, 2011, pp. 24-26.Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 11, 2015 Page 9

4. Model Inputs

4.1 Geographical Inputs

The “ground floor” of all air dis persion modeling analyses is e stablishing a coordinate system for identifying the geographical loc ation of emission sources and r eceptors. These geographical
locations are used to determine local characteristics (such as land use and elevation), and also to ascertain source to receptor di stances and relationships.

The Universal Transverse Merca tor (UTM) NAD83 coordinate system was used for identifying the easting (x) and northing (y) coordi nates of the modeled sources and receptors. Stac k locations were obtained from facility permits and prior modeling files provide d by the state regulatory agency. The
stack locations were then veri fied using aerial photographs.

The facility was evaluated to de termine if it should be modeled using the rural o r urban dispersion coefficient option in AERMOD. A GIS was used to determine whet her rural or urban dispersion coefficients apply to a site. L and use within a three-kilomete r radius circle surr ounding the facility was considered. USEPA guidance st ates that urban dispersion coe fficients are used if more than 50%
of the area within 3 kilometers has urban land uses. Otherwise, rural dispersion coefficients are appropriate. 9

USEPA’s AERSURFACE v. 13016 was use d to develop the meteorologi cal data for the modeling analysis. This model was also us ed to evaluate surrounding land use within 3 kilometers. Based on the output from the AERSURFAC E, approximately 6.4% of surroundi ng land use around the modeled facility was of urban l and use types including Type 21 – Low Intensity Residential, Type 22 – High Intensity Residential and Type 23 – Commercial / Indu strial / Transportation.

This is less than the 50% value c onsidered appropriate for the use of urban dispersion coefficients. Based on the AERSURFACE analysis, i t was concluded that the rur al option would be used for the modeling summarized in this re port. Please refer to Section 4. 5.3 for a discussion of the AERSURFACE analysis.

9 USEPA, Revision to the Guidelin e on Air Quality Models: Adopti on of a Preferred General Purpose (Flat and Complex Terrain) Dispersion Model and Other Revisions, Appendix W to 40 CFR Part 51, November 9, 2005, Section 7.2.3.Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 11, 2015 Page 10

4.2 Emission Rates and Source Parameters

The modeling analyses only considered SO 2 emissions from the facilit y. Off-site sources were not
considered. Concentrations were predicted for the scenarios sho wn in Tables 1 and 2:

1) allowable emissions based on t he current permit issued by th e regulatory agency, and

2) actual hourly emissions meas ured each hour between January 1 , 2011 and December 31,
2014 as taken from USEPA Air Markets Program Data

. 10

Stack parameters and emissions use d for the modeling analysis a re summarized in Table 4.

Table 4 – Facility Stack Parameters and Emissions 11

Facility Martin Lake Pirkey

Stack S01 S02 S03 S01 Description Unit 1 Unit 2 Unit 3 Unit 1 X Coord. [m] 352028 352066.8 352107.1 360449 Y Coord. [m] 3570404.46 3570314.64 3570224.87 3592510 Base Elevation [m] 95.18 94.95 94.79 109.43 Release Height [m] 137.77 137.77 137.8 160.02 Gas Exit Temperature [°K] 449.261 449.261 449.261 414.817

Gas Exit Velocity [m/s] 27.249 28.042 28.042 25.769

Inside Diameter [m] 7.01 7.01 7.01 7.62 Allowable Emission Rate [g/s] 1,199 1,199 1,199 1,090

Actual Emission Rate [g/s] - - - -

The above stack parameters and emissions were obtained from reg ulatory agency documents and
databases identified in Secti on 2.2. The analysis was conducted based on 100% operating load using
maximum exhaust flow rates and t emperatures. Operation at less than full capacity loads was not considered. This assumption te nds to under-predict impacts sinc e stack parameters such as exit flow rate and temperature are typically lower at less than full load , reducing pollutant dispersion and increasing predicted air qualit y impacts. Stack location, heigh t and diameter were verified using aerial photographs, and flue gas fl ow rate and temperature were verified using combustion
calculations.

10 http://ampd.epa.gov/ampd/

11 Martin Lake stack parameters obtained from Environ, 2018 Base C aseCAMx Simulation, Texas Haze Evaluation, Appendix A: Stack Parameters of Major Units at the Selected 38 Facilities, September 7, 2013. Stack parameters for the H.W. Pirkey Power Plant were obtained from the U.S. Energy Info rmation Agency, http://www.eia.gov/electricity/data/eia860/, 2013 Form EIA-860 Data - Schedule 6, 'Stack & Flue Data' , 6_2_EnviroEquip_Y2013.xlsxEvaluation of Compliance with the 1-hour NAAQS for SO 2 September 11, 2015 Page 11

4.3 Building Dimensions and GEP

No building dimensions or prior dow nwash evaluations were avail able. Therefore this modeling analysis did not address the e ffects of downwash and this may u nder-predict impacts.

4.4 Receptors

For Martin Lake Generating Station, three receptor grids were e mployed:

1. A 100-meter Cartesian receptor gr id centered on Martin Lake Gen erating Station and extending out 5 kilometers.

2. A 500-meter Cartesian receptor gr id centered on Martin Lake Gen erating Station and extending out 10 kilometers.
3. A 1,000-meter Cartesian receptor grid centered on Martin Lake G enerating Station and extending out 50 kilometers. 50 kilome ters is the maximum dista nce accepted by USEPA for the use of the AERMOD dispersion model. 12

A flagpole height of 1.5 meters w as used for all these receptor s.
Elevations from stacks and recep tors were obtained from Nationa l Elevation Dataset (NED) GeoTiff data. GeoTiff is a binary file tha t includes data descriptors a nd geo-referencing information necessary for extract ing terrain elevations. These elevations w ere extracted from 1 arc-second (30 meter) resolution NED files. The U SEPA software program AERMAP v. 11103 is used for these
tasks.

4.5 Meteorological Data

To improve the accuracy of the modeling analysis, recent meteor ological data for the 2012-2014 period were prepared using the U SEPA’s program AERMET which cre ates the model-ready surface and profile data files requir ed by AERMOD. Required data inpu ts to AERMET included surface meteorological measurements, t wice-daily soundings of upper air measurements, and the micrometeorological parameters surface roughness, albedo, and B owen ratio. One-minute ASOS
data were available so USEPA met hods were used to reduce calm a nd missing hours. 13 The USEPA software program AERMINUTE v. 14237 is used for these tasks.

This section discusses how the meteorological data was prepared for use in the 1-hour SO 2 NAAQS

12 USEPA, Revision to the Guideline on Air Quality Models: Adopti on of a Preferred General Purpose (Flat and Complex Terrain) Dispersion Model and Other Revisions, Appendix W to 40 CFR Part 51, Section A.1.(1), November 9, 2005.

13 USEPA, Area Designations for the 2010 Revised Primary Sulfur D ioxide National Ambient Air Quality Standards, Attachment 3, March 24, 2011, p. 19.Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 11, 2015 Page 12

modeling analyses. The USEPA software program AERMET v. 14134 is used for these tasks.

4.5.1 Surface Meteorology

Surface meteorology was obtained for Longview Texas Regional Ai rport located near the Martin Lake Generating Station. Integrated Surface Hourly (ISH) data f or the 2012-2014 period were
obtained from the National Clima tic Data Center (NCDC). The I SH surface data was processed through AERMET Stage 1, which perf orms data extraction and qual ity control checks.

4.5.2 Upper Air Data

Upper-air data are collected by a “ weather balloon” that is rel eased twice per day at selected
locations. As the balloon is rel eased, it rises through the at mosphere, and radios the data back to the surface. The measuring and transmitting device is known as eit her a radiosonde, or rawindsonde.
Data collected and radioed back i nclude: air pressure, height, temperature, dew point, wind speed, and wind direction. The upper air data were processed through AERMET Stage 1, which performs data extraction and quality control checks.

For Martin Lake Generating S tation, the concurrent 2012-2014 up per air data from twice-daily
radiosonde measurements obtained at the most representative loc ation were used. This location was the Shreveport, Louisiana measurement station. These data are i n Forecast Systems Laboratory (FSL) format and were downloaded in ASCII text format from NOAA ’s FSL website. 14 All reporting levels were downloade d and processed with AERMET.

4.5.3 AERSURFACE

AERSURFACE is a program that ex tracts surface roughness, albedo , and daytime Bowen ratio for an area surrounding a given locatio n. AERSURFACE uses land use and land cover (LULC) data in the U.S. Geological Survey’s 1992 National Land Cover Dataset t o extract the necessary micrometeorological data. LULC data was used for processing me teorological data sets used as input to AERMOD.

AERSURFACE v. 13016 was used to deve lop surface roughness, albe do, and daytime Bowen ratio values in a region surrounding the meteorological data collecti on site. AERSURFACE was used to develop surface roughness in a one kilometer radius surrounding the data collection site. Bowen ratio and albedo was developed for a 10 kilometer by 10 kilomet er area centered on the meteorological data collection si te. These micrometeorological data were processed for seasonal periods using 30-degree sectors . Seasonal moisture conditions w ere considered ave rage with winter

14 Available at: http://esrl.noaa.gov/raobs/Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 11, 2015 Page 13

months having no continuous snow cover.

4.5.4 Data Review

Missing meteorological data were not filled as the data file me t USEPA’s 90% data completeness requirement. 15 The AERMOD output file shows th ere were 0.91% missing data.

To confirm the representativene ss of the airport meteorological data, the surface characteristics of the airport data collection s ite and the modeled source locatio n were compared. Sin ce the Longview Texas Regional Airport is locate d close to Martin Lake Generati ng Station, this meteorological data set was considered appropriate for this modeling analysis. 16 Additionally, this weather station provided high quality surface measurements for the most recent 3-year time, and had similar land use, surface characteristics , terrain features and climate.

5. Background SO 2 Concentrations

Background concentrations were determined consistent with USEPA ’s Modeling Guidance for SO 2 NAAQS Designations. 17, 18 To preserve the form of the 1-hour SO 2 standard, based on the 99 th
percentile of the annual distri bution of daily maximum 1-hour c oncentrations averaged across the number of years modeled, the b ackground fourth-highest daily ma ximum 1-hour SO 2 concentration
was added to the modeled fourth-h ighest daily maximum 1-hour SO 2 concentration. 19 Background
concentrations were based on the 2011-13 design value measured by the ambient monitors located in

Texas. 20

6. Reporting

All files from the programs used for this modeling analysis are available to regulatory agencies. These include analyses prepared w ith AERSURFACE, AERMET, AERMAP , and AERMOD.

15 USEPA, Meteorological Monitoring Guidance for Regulatory Modeli ng Applications, EPA-454/R-99-05, February 2000, Section 5.3.2, pp. 5-4 to 5-5.

16 USEPA, AERMOD Implementation Guide, March 19, 2009, pp. 3-4.

17 USEPA, Area Designations for the 2010 Revised Primary Sulfur D ioxide National Ambient Air Quality Standards, Attachment 3, March 24, 2011, pp. 20-23.

18 USEPA, SO 2 NAAQS Designations Modeling Te chnical Assistance Document, Dec . 2013, section 8.1, pp 27-28.

19 USEPA, Applicability of Appendix W Modeling Guidance for the 1- hour SO 2 National Ambient Air Quality Standard, August 23, 2010, p. 3.

20 http://www.epa.gov/airtrends/values.html