## Marion Generating Station

Marion, Illinois

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

## August 9, 2015

Conducted by:

Steven Klafka, P.E., BCEE

Wingra Engineering, S.C.

Madison, WisconsinEvaluation of Compliance with the 1-hour NAAQS for SO 2 August 9, 2015 Page 2

1. Introduction

Wingra Engineering, S.C. was hi red by Sierra Club to conduct an air modeling impact analysis to help the U.S. Environmental Prot ection Agency (USEPA), state an d local air agencies identify facilities that are likely causing exceedances of the 1-hour su lfur dioxide (SO 2 ) National Ambient Air Quality Standard (NAAQS). T his document describes the resu lts and procedures for an evaluation conducted for the Mari on Generating Station located in Marion, Illinois.

To ensure the modeling analysis reflected the cumulative concen tration of SO 2 emissions, it included the emissions from the Joppa S team Electric Station in Joppa, I llinois, an additional source of SO 2 emissions located within 50 kilome ters of the Marion 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 Sierra Club by reg ulatory air agencies or obtained through other publicly-a vailable sources as documented below. The analysis was conducted in adherence to all ava ilable USEPA guidance for eval uating source impacts on attainment of the 1-hour SO 2 NAAQS via aerial dispersion m odeling, including the AERMOD Implementation Guide; USEPA's A pplicability of Appendix W Model ing Guidance for the 1-hour SO 2 National Ambient Air Qual ity Standard, August 23, 2010; modeli ng guidance promulgated by USEPA in Appendix W to 40 CFR Part 51; USEPA’s March 2011 Model ing Guidance for SO 2 NAAQS Designations; 1 and, USEPA’s December 2013 SO 2 NAAQS Designations Technical Assistance Document. 2

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 parts per billion (ppb). 3 Compliance with this standar d was verified using USEPA’s AERM OD air dispersion model, which produces air concentr ations 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 im pacts exceed the NAAQS. 4 The 99 th -percentile of the annual dist ribution of daily maximum 1-hour concentrations

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 August 9, 2015 Page 3

corresponds to the fourth-highest value at each receptor for a given year.

2.2 Modeling Results

Model results for all sources inc luded in the analysis of SO 2 are summarized in Table 1. Results are provided for each source alone , and for both sources combined.

Modeling results for Marion Gen erating Station and Joppa Steam Electric Station are summarized in Table 1. It was determined that based on either current allowab le emissions or measured actual emissions, the Marion Generating S tation is estimated to create downwind SO 2 concentrations which exceed the 1-hour NAAQS.

More specifically, the modeling results presented in Table 1, s how the plant’s allowable and actual emissions cause exceedances of the NAAQS. “Allowable” is the pe ak emission rate from each unit as approved by the current air qua lity operation permit for the facility. “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

In addition, the Joppa Steam Elect ric Station’s emissions signi ficantly contribute to the ambient SO 2 concentrations in the area imp acted by the Marion Generating St ation.

Air quality impacts in Illi nois are based on a background conce ntration of 20.9 μg/m 3 . This is the 2011-13 design value for LaSalle, Illinois - the lowest measure d background 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.

5 http://ampd.epa.gov/ampd/Evaluation of Compliance with the 1-hour NAAQS for SO 2 August 9, 2015 Page 4

Table 1 - SO 2 Modeling Results for Marion Generating Station Modeling Analysis

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

Allowable Marion 311.4 20.9 332.3 196.2 No

Actual 267.9 20.9 288.8 196.2 No

Allowable Joppa 1,085.2 20.9 1,106.1 196.2 No

Actual 146.4 20.9 167.3 196.2 Yes 6

Allowable Both 1,086.2 20.9 1,107.1 196.2 No

Actual 268.0 20.9 288.9 196.2 No

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

Table 2 - Modeled SO 2 Emissions 7

Stack

ID Unit ID Allowable Emissions 1-hour Average (lbs/hr) M01 Unit 123 1,680.0 M02 Unit 4 2,040.0 Marion Total 3,720.0

J01 Boiler 1 6,144.0 Boiler 2 6,144.0 Subtotal 12,288.0

J02 Boiler 3 6,144.0 Boiler 4 6,144.0 Subtotal 12,288.0

J03 Boiler 5 6,144.0 Boiler 6 6,144.0 Subtotal 12,288.0

6 For this modeling analysis, the Joppa Steam Electric Station d id not have a predicted exceedance of the NAAQS based on its actual hourly SO2 emissions. This was due to the fact th at the modeling receptor grid was centered on the Marion Generating Station and did not identify the maximum impacts due to Joppa emissions. A modeling analysis with the receptor grid centered on Joppa predicted exceedances of the NA AQS based on its actual hourly emissions. Refer to the modeling report, Joppa Steam Electric Station, Joppa, Illinois, Evaluation of Compliance with the 1-hour NAAQS for SO 2 , July 30, 2015.

7 For Marion, allowable emissions are taken from Operating Permi t for ID No. 199856AAC issued September 29, 2005 by Illinois EPA. Allowable SO2 emissions for all units are base d on the current limitation of 1.2 lbs/mmbtu. For Joppa, allowable emissions from Units 1-6 are limited to 36,865 lbs/hr . Operating Permit for ID No. 127855AAC issued September 29, 2005 by Illinois EPA.Evaluation of Compliance with the 1-hour NAAQS for SO 2 August 9, 2015 Page 5

Joppa Total 36,864.0 Both Stations Total 40,584.0

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. This estimate is based on the impact of all sources, but a ssumes that only the Marion Gen erating Station achieves the reductions necessary to comply with the NAAQS.

This assumes a one-hour averagi ng period for the emission rate, and that the emission rate is binding at all times. However, it is e xtremely likely that this limit is too high to protect the NAAQS, given the conservative aspects of thi s modeling protocol. For example , startup or shutdown periods were not evaluated. During these peri ods, decreased gas velocities a nd temperatures may lead to greater ambient impacts at ground level . Further, the hypothetical emi ssion limitation i n Table 3 would allow Marion Generating Station to consume the entire NAAQS, le aving little to no room for any other source of SO 2 in the area. No consideration has been given to other sources aside from the Joppa Steam Electric Station, a nd no margin of safety has been included in the hypothetical emission limitation.

Table 3 - Required Emission Reductions from the Marion Generating Station for Compliance
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)

175.3 84% 600.4 0.19

Predicted exceedances of the 1-hour NAAQS for SO 2 based on allowable emissions extend throughout the region to a maxim um distance of 50 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.

Assumptions used in this modeli ng analysis which likely under-e stimate concentrations include the following:Evaluation of Compliance with the 1-hour NAAQS for SO 2 August 9, 2015 Page 6

 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.

 Except for Joppa Steam Electri c Station, there was no considera tion of off-site sources. These other sources of SO 2 will increase the predicted impacts.Evaluation of Compliance with the 1-hour NAAQS for SO 2 August 9, 2015 Page 7

Figure 1 - Regional View of Impacts Base d on Allowable Emissions from all SourcesEvaluation of Compliance with the 1-hour NAAQS for SO 2 August 9, 2015 Page 8

Figure 2 - Regional View of Impacts Base d on Actual Emission s from All SourcesEvaluation of Compliance with the 1-hour NAAQS for SO 2 August 9, 2015 Page 9

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. 8 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. 9

Please refer to Table 1 for the modeling results.

8 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.
9 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 August 9, 2015 Page 10

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 Geographic Information System (GIS) was used to determine whether rural or urban dispersi on coefficients apply to a site. Land use within a three-kilometer radius circle surrounding the f acility was considered. USEPA gu idance states that urban dispersion coefficients are used if more t han 50% of the area within 3 kil ometers has urban land uses. Otherwise, rural dispersion c oefficients are appropriate. 10

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 0.03% of surround ing 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.

10 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, No vember 9, 2005, Section 7.2.3.Evaluation of Compliance with the 1-hour NAAQS for SO 2 August 9, 2015 Page 11

4.2 Emission Rates and Source Parameters

The modeling analyses only considered SO 2 emissions from the Marion and Joppa facilities. Other off-site sources were not consider ed. Concentrations were predi cted for the scenarios shown 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 , 2012 and December 31, 2014 as taken from USEPA Air Markets Program Data

. 11

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

Table 4 – Facility Stack Parameters and Emissions 12

Facility Joppa Marion

Stack J01 J02 J03 M01 M04 Description Boilers 1 and 2 Boile rs 3 and 4 Boilers 5 and 6 Uni ts 123 Unit 4 X Coord. [m] 335066 335110 335154 327697 327601 Y Coord. [m] 4119613 4119719 4119837 4165367 4165325 Base Elevation [m] 104.52 105.48 106.31 157.58 157.39 Release Height [m] 124.15 124.15 124.15 60.96 121.92 Gas Exit Temperature [°K] 427.594 427.594 427.594 444.261 327.0 39

Gas Exit Velocity [m/s] 25. 938 25.938 25.938 15.285 19.878

Inside Diameter [m] 5.486 5.486 5.486 3.688 4.572 Allowable Emission Rate [g/s] 1,548 1,548 1,548 211.7 257

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 atends to under-p redict impacts since stack pa rameters such as exit flow rate and temperature are typically lower at less than fu ll load, reducin g pollutant dispersion and increasing predicted air quality impacts. S tack location, height and diame ter were verified using aerial photographs, and flue gas flow rat e and temperature were verifi ed using combustion calculations.

11 http://ampd.epa.gov/ampd/

12 Joppa stack parameters were obtained from the Illinois EPA mode ling file "massac_allowables.txt" for the Marion Steam Generating Station. The actual stack height of 550 feet w as reduced to 407.33 feet. This is the Good Engineering Practice or GEP height allowed in the facility operating permit . Marion stack parameters were obtained from the U.S. Energy Information Agency, http://www.eia.gov/electricity/data/ eia860/, 2013 Form EIA-860 Data - Schedule 6, 'Stack & Flue Data' , 6_2_EnviroEquip_Y2013.xlsx.Evaluation of Compliance with the 1-hour NAAQS for SO 2 August 9, 2015 Page 12

4.3 Building Dimensions

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 Marion Generating Station, three receptor grids were employ ed:

1. A 100-meter Cartesian receptor grid centered on Marion Generati ng Station and extending out 5 kilometers.
2. A 500-meter Cartesian receptor grid centered on Marion Generati ng Station and extending out 10 kilometers. 3. A 1,000-meter Cartesian receptor grid centered on Marion Genera ting Station and extending out 50 kilometers. 50 kilometers is t he maximum distance accept ed by USEPA for the use of the AERMOD dispersion model. 13

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. 14 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

13 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.
14 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 August 9, 2015 Page 13

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

4.5.1 Surface Meteorology

Surface meteorology was obtained for Paducah Barkley Regional A irport located near the Marion Generating Station. Integrated S urface Hourly (ISH) data for th e 2012-2014 period were obtained from the National Climatic Data Center (NCDC). The ISH surfac e data was processed through AERMET Stage 1, which performs data extraction and quality cont rol 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 Marion Generating Stati on, the concurrent 2012-2014 upper a ir data from twice-daily radiosonde measurements obtained at the most representative loc ation were used. This location was the Nashville, Tennessee measur ement station. These data are in Forecast Systems Laboratory (FSL) format and were downloaded in ASC II text format from NOAA’s FSL website. 15 All reporting levels were downloaded a nd 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.

15 Available at: http://esrl.noaa.gov/raobs/Evaluation of Compliance with the 1-hour NAAQS for SO 2 August 9, 2015 Page 14

4.5.4 Data Review

Missing meteorological data were not filled as the data file me t USEPA’s 90% data completeness requirement. 16 The AERMOD output file shows th ere were 0.91% missing data.

To confirm the representativene ss of the airport meteorological data, Illinois EPA staff were contacted to determine the mete orological data collection stati on most suitable for the Marion Generating Station. 17 They recommended the use of data f rom the Paducah Barkley Regi onal Airport for the surface measur ements and Nashville, Tennessee for the upper air measurements. Illinois EPA staff provided AER SURFACE output files to assist w ith processing of the most recent surface and upper air measurements. In addition, the surface c haracteristics of the airport data collection site and the modeled s ource location were compared. Since the Paducah Barkley Regional Airport is located close to Mar ion Generating Station with simi lar rural surroundings, this meteorological data set was consid ered appropriate for this mod eling analysis. 18

5. Background SO 2 Concentrations

Background concentrations were determined consistent with USEPA ’s Modeling Guidance for SO 2 NAAQS Designations. 19,20 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. 21 Background concentrations were based on the 2011-13 design value measured by the ambient monitors located in Illinois. 22

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.

16 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.
17 Email Correspondence, M. Will – Illinois EPA to S. Klafka – Wi ngra Engineering, S.C., Request for IEPA Dispersion Modeling Meteorology, May 20, 2015.
18 USEPA, AERMOD Implementation Guide, March 19, 2009, pp. 3-4.
19 USEPA, Area Designations for the 2010 Revised Primary Sulfur D ioxide National Ambient Air Quality Standards, Attachment 3, March 24, 2011, pp. 20-23.
20 USEPA, SO 2 NAAQS Designations Modeling Te chnical Assistance Document, Dec . 2013, section 8.1, pp 27-28.

21 USEPA, Applicability of Appendix W Modeling Guidance for the 1- hour SO 2 National Ambient Air Quality Standard, August 23, 2010, p. 3.
22 http://www.epa.gov/airtrends/values.html