Washington University in St.lDuis 

SCHOOL OF LAW 

Interdisciplinary Environmental Clinic 

September 3, 2015 

Ms. Wendy Vit 

Chief, Air Quality Planning Section 

Air Pollution Control Program 

Missouri Department ofNatural Resources 

P.O. Box 176 

Jefferson City, MO 65102-0176 

Via email to apcpsip@dnr.mo.gov 

Re: 2010 1-Hour Sulfur Dioxide Standard, Proposed Options for Area Boundary 

Recommendations, July 2016 Designations 

Dear Ms. Vit: 

On behalf of the Sierra Club, we submit the attached modeling report prepared by Wingra 

Engineering regarding the S02 designation for the Sibley power plant. This report documents 

that the area around Sibley should be designated nonattainment based on the most recent actual 

emissions. 

Sincerely yours, 

Maxine I. Lipeles, Director 

Interdisciplinary Environmental Clinic 

Washington University School of Law 

One Brookings Drive - CB 1120 

St. Louis, MO 63130 

314-935-5837 (phone); 314-935-5171 (fax) 

milipele@wustl.edu 

Attorneys for the Sierra Club 

Cc: Rebecca Weber, Director, Air & Waste Management Division, EPA Region 7 

Chief, Air Planning & Development Branch, EPA Region 7 

Kyra Moore, Director, Air Pollution Control Program, DNR 

Campus Box 1120, One Brookings Drive, St Louis, MO 63130-4899 

(314) 935-7238, FAX: (314) 935-5171; www.law.wustl.edu 
Sibley Generating Station 

Sibley, Missouri 

Evaluation of Compliance with the 1-hour NAAQS for S02 

September 3, 2015 

Co11ducted by: 

Steve11 Klajka, P.E., BCEE 

Wi11gra E11gi11eeri11g, S.C. 

Madiso11, Wisco11si11 
Evaluation of Compliance with the 1-hour NAAQSfor S02 

September 3. 2015 

Page2 

1. Introduction 

Wingra Engineering, S.C. was hired by Sierra Club to conduct an air modeling impact analysis to 

help the U.S. Environmental Protection Agency (USEPA) and state and local air agencies identify 

facilities that are likely causing exceedances of the 1-hour sulfur dioxide (S02) national ambient air 

quality standard (NAAQS). This document describes the results and procedures for an evaluation 

conducted for the Sibley Generating Station located in Sibley, Missouri. 

To ensure the modeling analysis reflected the cumulative concentration of S02 emissions, it included 

emissions from the following additional sources of so2 emissions located within 50 kilometers of 

the Sibley Generating Station: 

• Hawthorne Generating Station- Kansas City, Missouri 

• Veolia Energy- Kansas City- Kansas City, Missouri 

• Nearman Creek Power Station- Kansas City, Kansas 

The dispersion modeling analysis predicted ambient air concentrations for comparison with the 1-

hour S02 NAAQS. The modeling was performed using the most recent version of AERMOD, 

AERMET, and AERMINUTE, with data provided to Sierra Club by regulatory air agencies or 

obtained through other publicly-available sources 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 S02 NAAQS via aerial dispersion modeling, including the AERMOD 

Implementation Guide; USEPA's Applicability of Appendix W Modeling Guidance for the 1-hour 

S02 National Ambient Air Quality Standard, August 23, 2010; modeling guidance promulgated by 

USEPA in Appendix W to 40 CFR Part 51; USEPA's March 201 1 Modeling Guidance for S02 

NAAQS Designations; 1 and USEPA's December 2013 S02 NAAQS Designations Technical 

Assistance Document.2 

2. Compliance with the 1-hour S02 NAAQS 

2.1 1-hour S02 NAAQS 

The 1-hour S02 NAAQS takes the form of a three-year average ofthe 99th-percentile ofthe annual 

distribution of daily maximum 1-hour concentrations, which cannot exceed 75 parts per billion 

(ppb).3 Compliance with this standard was verified using USEPA's AERMOD air dispersion model, 

which produces air concentrations in units of ~g/m . The l-hour S02 NAAQS of75 ppb equals 

1 http://www.epa.gov/scramOO I /so2 _ modeling_guidance.htm 2 http://www.epa.gov/oaqpsOO 1/sulfurdioxide/pdfs/S02ModelingT AD.pdf 

3 US EPA, Applicability of Appendix W Modeling Guidance for the 1-hour S02 National Ambient Air Quality Standard, 

August 23, 20 I 0. 
Evaluation of Compliance with the 1-hour NAAQS for S02 

September 3, 2015 

Page3 

196.2 Jlg/m3

, and this is the value used for determining whether modeled impacts exceed the 

NAAQS.4 The 99th-percentile of the annual distribution of daily maximum 1-hour concentrations 

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

2.2 Modeling Results 

Model results for all sources included in the S02 analysis are summarized in Table 1. Results are 

provided for each source alone, and for all sources combined. 

Modeling results for Sibley Generating Station and the other three power plants are summarized in 

Table 1. It was determined that based on either current allowable emissions or measured actual 

emissions, the Sibley Generating Station is estimated to create downwind S02 concentrations which 

exceed the 1-hour NAAQS. 

More specifically, the modeling results presented in Table 1, show exceedances of the NAAQS by 

the plant's allowable and actual emissions. "Allowable" is the peak emission rate from each unit as 

approved by the current air quality operation permit for the facility. "Actual" are the measured 

emissions for each hour between January 1, 2012 and December 31,2014 as taken from USEPAAir 

Markets Program Data.5 

In addition, the emissions from the Hawthorne, Nearman Creek and Veolia plants significantly 

contribute to the ambient S02 concentration in the area impacted by Sibley Generating Station. 

Air quality impacts in Missouri are based on a background concentration of23.5 Jlg/m3

. This is the 

2011-13 design value for Monroe County, Missouri- the lowest measured background 

concentration in the state. This is the most recently available design value. See Section 5 for further 

discussion of the background concentrations used for this analysis. 

4 The ppb to J.Lg/m3 conversion is found in the source code to AERMOD v. 14134, subroutine Modules. The conversion 

calculation is 75/0.3823 = 196.2 llg/m3

. 5 http://ampd.epa.gov/ampd/ 
Evaluation of Compliance with the /-hour NAAQS for SOz 

September 3, 2015 

Page4 

Table 1 - S02 Modeling Results for Sibley Generating Station Modeling Analysis 

Averaging 99th Percentile 1-hour Daily Maximum (Jlg/rn3

) 

Emission Rates Period Lmpact Background Total NAAQS 

Allowable Sibley 1,197. 1 23.5 1,220.6 196.2 

Actual Boiler 70 47.8 23.5 71.3 196.2 

Allowable Sibley 1,411.9 23.5 1,435.4 196.2 

Boilers 

Actual 50,60 & 70 50.8 23.5 74.3 196.2 

Allowable 379.7 23.5 403.2 196.2 

Hawthorne 

Actual 23.5 23.5 47.0 196.2 

Allowable Nearman 126.3 23.5 149.8 196.2 

Actual Creek 81.4 23.5 104.9 196.2 

Allowable 1,614.5 23.5 1,638.0 196.2 

Veolia 

Actual 407.6 23.5 431.1 196.2 

Allowable All With 1,706.5 23.5 1,730.0 196.2 

Sibley 

Actual Boiler 70 41 1.7 23.5 435.2 196.2 

Allowable All With 1,739.0 23.5 1,762.5 196.2 Sibley 

Actual Boilers 411.7 23.5 435.2 196.2 50, 60 & 70 

Complies with 

NAAQS? 

No 

Yes 

No 

Yes 

No 

Yes 

Yes 

Yes 

No 

No 

No 

No 

No 

No 
Evaluation of Compliance with the 1-hour NAAQS for S02 

September 3, 2015 

Page5 

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

Table 2 -Modeled S02 Emissions 6 

Stack Unit 

ID ID 

Boiler 50 

SOl Boiler 60 

Boiler 70 

Sibley Subtotal 

HOI Unit 5A 

Hawthorne Subtotal 

NOl Unit 1 

Nearman Creek Subtotal 

V02 Boiler 6 

Boiler 8 

Veolia Subtotal 

Facility Total 

Allowable Emissions 

(lbslhr) 

5,486.4 

5,645.7 

36,576.9 

47,709.0 

10,792.0 

10,792.0 

2,919.7 

2,919.7 

3,434.3 

3,604.0 

7,038.2 

68,459.0 

Based on the modeling results, Table 3 provides the emission reductions from current allowable 

rates necessary to achieve compliance with the 1-hour NAAQS. This assumes a one-hour averaging 

period for the emission rate and that the emission rate is binding at all times. However, given the 

conservative aspects of this modeling protocol, it is extremely likely that this limit is too high to 

protect the NAAQS. For example, startup or shutdown periods were not evaluated. During these 

periods, decreased gas velocities and temperatures may lead to greater ambient impacts at ground 

level. Further, the hypothetical emission limitation in Table 3 would allow Sibley Generating 

Station to consume the entire NAAQS, leaving little to no room for any other source of S02 in the 

area. No margin of safety has been included in the hypothetical emission limitation. 

6 Sibley allowable emissions were taken from Missouri DNR, Part 70 Permit to Operate, No. OP2006-063, August 31, 

2006. Hawthorne allowable emissions were taken from Missouri DNR, Part 70 Permit to Operate, No. OP2013-0024, 

July 12, 2013. Nearman Creek allowable emissions were taken from Kansas, Air Emission Source Class I Operating 

Permit, ID 2090008, March 24, 2004. Veolia allowable emissions were taken from Missouri DNR, Part 70 Permit to 

Operate, No. OP2012-050, No. OP2012-050, March 4, 2013. 
Evaluation of Compliance with the 1-hour NAAQSfor S02 

September 3, 2015 

Page6 

Table 3 -Required Emission Reductions from Sibley Generating Station for Compliance with the 

1-hour NAAQS for S02 

Acceptable Impact Required Required Required 

(NAAQS - Background) Total Facility Total Facility Total Facility 

99th Percentile Reduction Based on Emission Rate 1-hour Average 

1-hour Daily Max Allowable Emissions (lbslhr) Emission Rate 

(J.tg/m3) (%) (lbs/mmbtu) 

172.7 90% 4,738.0 0.89 

Predicted exceedances of the 1-hour NAAQS for S02 based on allowable emissions extend 

throughout the region to a maximum distance of 50 kilometers. 

Figure 1 shows the extent ofNAAQS violations based on allowable emissions from all sources. 

Figure 2 shows the extent ofNAAQS violations based on actual hourly emissions from all sources. 

2.3 Conservative Modeling Assumptions 

A dispersion modeling analysis requires the selection of numerous parameters which affect the 

predicted concentrations. For the enclosed analysis, several parameters were selected which underpredict facility impacts. 

Assumptions used in this modeling analysis which likely under-estimate concentrations include the 

following: 

• Allowable emissions are based on a Limitation with an averaging period which is greater than 

the 1-hour average used for the S02 air quality standard. Emissions and impacts during any 

1-hour period may be higher than assumed for the modeling analysis. 

• 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 predicted air quality impacts. 

• No consideration of building or structure downwash. These downwash effects typically 

increase predicted concentrations near the facility. 

• Except for the Hawthorne, Nearman Creek and Veolia plants, no consideration of off-site 

sources. Any other off-site sources of S02 will increase the predicted impacts. 

2.4 Comparison with Existing Ambient Monitoring 

An ambient monitor for S02 is operated approximately 1.2 km or 0.7 miles southeast ofVeolia 

Energy. The USEPA database for ambient monitoring measurements identifies Monitor 
Evaluation of Compliance with the 1-hour NAAQS for S02 

September 3, 2015 

Page 7 

#7290950034 as the TROOST: 724 Troost (Rear), Kansas City, MO 64106 monitor.7 The 2012-14 

design value measured at this monitor was 150 ppb or 392.4 J.tg/m3

. 

Based on actual hourly emissions from the Sibley plant and other regional sources, the modeling 

analysis predicted a concentration near the monitor location of382.5 J.tg/m3

• Minus the assumed 

background of23.5 J.tg/m3 the predicted impact due to regional S02 sources is 359 J.tg/m3

. Since the 

predicted and actual measured design values are in close agreement, this comparison supports the 

accuracy of the modeling results presented in this report. 

7 http://www.epa.gov/airtrends/pdfs/S02_Design Values_20 1220 l4_FINAL_ 8 _3 _l 5.xlsx 
Evaluation of Compliance with the 1 -hour NAAQS for S01 

September 3, 2015 

Page8 

1-hour average S02 concentrations (ug per cubic meter)- All colored areas exceed the NAAQS. 

196 400 600 800 1000 

Figure 1 - Regional View of Impacts Based on Allowable Emissions from All Sources 
Evaluation of Compliance with the 1-hour NAAQS for SOz 

September 3, 2015 

Page 9 

Sibley Generating Station 

l , : I , 

-~· . -... \,.• 

'·: "'" ) .. 

·----... 

'• ... ,. ... 

370000 37~0 ~e.oooo 3$1003 

UTM EaSl(m) 

.· 

....... 

"' .. _.- .. ···-· 

.. 

, 

! 

; 

I 

\ 

J 

I 

10COOO 

1-hour average S02 concentrations (ug per cubic meter) - All colored areas exceed the NAAQS. 

196 300 400 

Figure 2 -Regional View of Impacts Based on Actual Emissions from All Sources 

I • 

I 

) 

J0!.000 
Evaluation of Compliance with the 1-hour NAAQS for S01 

September 3, 2015 

Page 10 

3. Modeling Methodology 

3.1 Air Dispersion Model 

The modeling analysis used USEPA's AERMOD program, v. 14134. AERMOD, as available from 

the Support Center for Regulatory Atmospheric Modeling (SCRAM) website, was used in 

conjunction with a third-party modeling software program, AERMOD View, sold by Lakes 

Environmental Software. 

3.2 Control Options 

The AERMOD model was run with the following control options: 

• 1-hour average air concentrations 

• Regulatory defaults 

• Flagpole receptors 

To reflect a representative inhalation 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 determine if the modeled facility 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 nearby city and a default surface roughness of 1.0 meter. Methods 

described in Section 4.1 were used to determine whether rural or urban dispersion coefficients were 

appropriate for the modeling analysis. 

3.3 Output Options 

The AERMOD analysis was based on three years of recent meteorological data. The modeling 

analyses used one run with three years of sequential meteorological data from 2012-2014. Consistent 

with USEPA's Modeling Guidance for S02 NAAQS Designations, AERMOD provided a table of 

fourth-high 1-hour S02 impacts concentrations consistent with the form of the 1-hour S02 NAAQS.9 

Please refer to Table 1 for the modeling results. 

8 US EPA, Revision to the Guideline on Air Quality Models: Adoption 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 US EPA, Area Designations for the 2010 Revised Primary Sulfur Dioxide National Ambient Air Quality Standards, 

Attachment 3, March 24, 2011, pp. 24-26. 
Evaluation of Compliance with the 1-hour NAAQS for S02 

September 3, 2015 

Page 11 

4. Model Inputs 

4.1 Geographical Inputs 

The "ground floor" of all air dispersion modeling analyses is establishing a coordinate system for 

identifying the geographical location of emission sources and receptors. These geographical 

locations are used to determine local characteristics (such as land use and elevation), and also to 

ascertain source to receptor distances and relationships. 

The Universal Transverse Mercator (UTM) NAD83 coordinate system was used for identifying the 

easting (x) and northing (y) coordinates of the modeled sources and receptors. Stack locations were 

obtained from facility pennits and prior modeling files provided by the state regulatory agency. The 

stack locations were then verified using aerial photographs. 

The facility was evaluated to determine if it should be modeled using the rural or urban dispersion 

coefficient option in AERMOD. A Geographic Information System (GIS) was used to determine 

whether rural or urban dispersion coefficients apply to a site. Land use within a three-kilometer 

radius circle surrounding the facility was considered. USEP A guidance states that urban dispersion 

coefficients are used if more than 50% of the area within 3 kilometers has urban land uses. 

Otherwise, rural dispersion coefficients are appropriate. 10 

USEPA's AERSURFACE v. 13016 was used to develop the meteorological data for the modeling 

analysis. This model was also used to evaluate surrounding land use within 3 kilometers. Based on 

the output from the AERSURF ACE, approximately 1.5% of surrounding land use around the 

modeled facility was of urban land use types including Type 21 - Low Intensity Residential, Type 

22 - High Intensity Residential and Type 23 - Commercial I Industrial I Transportation. 

This is less than the 50% value considered appropriate for the use of urban dispersion coefficients. 

Based on the AERSURF ACE analysis, it was concluded that the rural option would be used for the 

modeling summarized in this report. Please refer to Section 4.5.3 for a discussion of the 

AERSURF ACE analysis. 

10 US EPA, Revision to the Guideline on Air Quality Models: Adoption 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 NAAQSfor S02 

September 3, 2015 

Page 12 

4.2 Emission Rates and Source Parameters 

The modeling analysis considered SOz emissions from the Sibley, Hawthorne, Nearman Creek and 

V eolia power plants. Other off-site sources were not considered. Concentrations were predicted for 

the scenarios shown in Tables 1 and 2: 

1) allowable emissions based on the current permit issued by the regulatory agency, and 

2) actual hourly emissions for Sibley, Hawthorne and Nearman Creek were measured each 

hour between January I, 2012 and December 31,2014 as taken from USEPAAir Markets 

Program Data. 11 Actual emissions for Veolia were the annual average based on the 

emissions inventory report for 2014. 

Stack parameters and emissions used for the modeling analysis are summarized in Table 4. 

Table 4- Facility Stack Parameters and Emissions 12 

Facility Sibley Hawthorn Neannan Veolia 

Stack SOl S03 HOI NO! VOl 

Description 50,60 and 70 Boiler 70 Unit SA Unit I 6 and 8 

X Coord. [m] 397718 397718 372264 353388 363375 

Y Coord. [m] 4337279 4337279 4332322 4337135 4330433 

Base Elevation [m] 221.13 221.13 226.06 229.41 234.12 

Release Height [m] 213.36 213.36 182.88 121.92 85.95 

Gas Exit Temperature [°K] 422.039 422.039 338.706 410.928 395.928 

Gas Exit Velocity [ m/s] 37.087 28.43 27.344 13.373 1.798 

Inside Diameter [m] 4.115 4. 115 6.462 6.096 5.105 

Allowable Emission Rate [g/s] 6,011 4,609 1,360 367.9 886.8 

Actual Emission Rate [g/s] - - - - 223.9 

The above stack parameters and emissions were obtained from regulatory agency documents and 

databases identified in Section 2.2. The analysis was conducted based on 100% operating load using 

maximum exhaust flow rates and temperatures. Operation at less than full capacity loads was not 

considered. This assumption under-predicts impacts since stack parameters such as exit flow rate and 

temperature are lower at less than full load, reducing pollutant dispersion and increasing predicted 

air quality impacts. Stack location, height and diameter were verified using aerial photographs, and 

flue gas flow rate and temperature were verified using combustion calculations. 

11 http://ampd.epa.gov/ampd/ 12 Sibley, Hawthorne and Neannan Creek stack parameters obtained from U.S. Energy Information Administration, 

Form EIA-923 Detailed Data, Schedule 6, Stack & Flue Data, http://www.eia.gov/electricitv/data/eia923/. Veolia stack 

parameters obtained from Missouri DNR, Emissions Inventory Questionnaire for 2014. 
Evaluation of Compliance with the !-hour NAAQSfor S01 

September 3, 2015 

Page 13 

4.3 Building Dimensions 

No building dimensions or prior downwash evaluations were available. Therefore this modeling 

analysis did not address the effects of downwash and this may under-predict impacts. 

4.4 Receptors 

For Sibley Generating Station, three receptor grids were employed: 

l. A 1 00-meter Cartesian receptor grid centered on Sibley Generating Station and extending out 

5 kilometers. 

2. A 500-meter Cartesian receptor grid centered on Sibley Generating Station and extending out 

l 0 kilometers. 

3. A 1 ,000-meter Cartesian receptor grid centered on Sibley Generating Station and extending 

out 50 kilometers. 50 kilometers is the maximum distance accepted by USEPA for the use of 

the AERMOD dispersion model. 13 

A flagpole height of 1.5 meters was used for all these receptors. 

Elevations from stacks and receptors were obtained from National Elevation Dataset (NED) GeoTiff 

data. GeoTiff is a binary file that includes data descriptors and geo-referencing information 

necessary for extracting terrain elevations. These elevations were extracted from l arc-second (30 

meter) resolution NED files. The US EPA software program AERMAP v. Ill 03 is used for these 

tasks. 

4.5 Meteorological Data 

To improve the accuracy of the modeling analysis, recent meteorological data for the 2012-2014 

period were prepared using the USEPA's program AERMET which creates the model-ready surface 

and profile data files required by AERMOD. Required data inputs to AERMET included surface 

meteorological measurements, twice-daily soundings of upper air measurements, and the 

micrometeoro1ogical parameters surface roughness, albedo, and Bowen ratio. One-minute ASOS 

data were available so USEPA methods were used to reduce calm and 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 S02 NAAQS 

13 USEPA, Revision to the Guideline on Air Quality Models: Adoption of a Preferred General Purpose (Flat and 

Complex Terrain) Dispersion Model and Other Revisions, Appendix W to 40 CFR Part 51 , Section A.l.(l), November 9, 

2005. 

14 USEPA, Area Designations for the 2010 Revised Primary Sulfur Dioxide National Ambient Air Quality Standards, 

Attachment 3, March 24,201 1, p. 19. 
Evaluation of Compliance with the 1-hour NAAQS for S02 

September 3, 2015 

Page 14 

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

4.5.1 Surface Meteorology 

Surface meteorology was obtained for Kansas City Downtown Airport located near the Sibley 

Generating Station. Integrated Surface Hourly (ISH) data for the 2012-2014 period were obtained 

from the National Climatic Data Center (NCDC). The ISH surface data was processed through 

AERMET Stage 1, which performs data extraction and quality control checks. 

4.5.2 Upper Air Data 

Upper-air data are collected by a "weather balloon" that is released twice per day at selected 

locations. As the balloon is released, it rises through the atmosphere, and radios the data back to the 

surface. The measuring and transmitting device is known as either a radiosonde, or rawindsonde. 

Data collected and radioed back include: 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 Sibley Generating Station, the concurrent 2012-20 14 upper air data from twice-daily radiosonde 

measurements obtained at the most representative location were used. This location was the Topeka, 

Kansas measurement station. These data are in Forecast Systems Laboratory (FSL) format and were 

downloaded in ASCII text format from NOAA's FSL website. 15 All reporting levels were 

downloaded and processed with AERMET. 

4.5.3 AERSURF ACE 

AERSUR.F ACE is a program that extracts surface roughness, albedo, and daytime Bowen ratio for 

an area surrounding a given location. AERSURF ACE uses land use and land cover (LULC) data in 

the U.S. Geological Survey's 1992 National Land Cover Dataset to extract the necessary 

micrometeoro1ogical data. LULC data was used for processing meteorological data sets used as 

input to AERMOD. 

AERSURFACE v. 13016 was used to develop surface roughness, albedo, and daytime Bowen ratio 

values in a region surrounding the meteorological data collection site. AERSURF ACE was used to 

develop surface roughness in a one kilometer radius surrounding the data collection site. Bowen 

ratio and albedo was developed for a I 0 kilometer by 10 kilometer area centered on the 

meteorological data collection site. These micrometeorological data were processed for seasonal 

periods using 30-degree sectors. Seasonal moisture conditions were considered average with winter 

15 Available at: http://esrl.noaa.gov/raobs/ 
Evaluation of Compliance with tlze !-hour NAAQSfor S02 

September 3, 2015 

Page 15 

months having continuous snow cover. 

4.5.4 Data Review 

Missing meteorological data were not filled as the data file met USEPA's 90% data completeness 

requirement. 16 The AERMOD output file shows there were 0.31% missing data. 

To confirm the representativeness of the airport meteorological data, the surface characteristics of 

the airport data collection site and the modeled source location were compared. Since the Kansas 

City Downtown Airport is located close to Sibley Generating Station, this meteorological data set 

was considered appropriate for this modeling analysis. 17 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 S02 Concentrations 

Background concentrations were determined consistent with USEPA's Modeling Guidance for S02 

NAAQS Designations. 18

• 

19 To preserve the form of the 1-hour S02 standard, based on the 99th 

percentile of the annual distribution of daily maximum 1-hour concentrations averaged across the 

number of years modeled, the background fourth-highest daily maximum 1-hour so2 concentration 

was added to the modeled fourth-highest daily maximum 1-hour S02 concentration.20 Background 

concentrations were based on the 2011-13 design value measured by the ambient monitors located in 

Missouri? 1 

6. Reporting 

All files from the programs used for this modeling analysis are available to regulatory agencies. 

These include analyses prepared with AERSURF ACE, AERMET, AERMAP, and AERMOD. 

16 USEPA, Meteorological Monitoring Guidance for Regulatory Modeling Applications, EPA-454/R-99-05, February 

2000, Section 5.3.2, pp. 5-4 to 5-5. 17 USEPA, AERMOD Implementation Guide, March 19,2009, pp. 3-4. 18 USEPA, Area Designations for the 2010 Revised Primary Sulfur Dioxide National Ambient Air Quality Standards, 

Attachment 3, March 24, 2011, pp. 20-23. 19 USEPA, S02 NAAQS Designations Modeling Technical Assistance Document, Dec. 2013, section 8.1, pp 27-28. 

20 US EPA, Applicability of Appendix W Modeling Guidance for the 1-hour S0 2 National Ambient Air Quality Standard, 

August 23, 2010, p. 3. 

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