# Washington

# University in 

# St.lDuis SCHOOL OF LAW Interdisciplinary Environmenta l 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 ofthe Sierra Club, we submit the attached modeling report prepared by Wingra Engineering regarding the S0 2 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 Schoo l of Law One Brookings Drive - CB 1120 St. Louis, MO 63130 314
- 935-5837 (phone); 314-935-5171 (fax) milip ele@ wu s tl.edu Attorneys for the Sierra C lub
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 S0 2 

## September 3, 2015

Co11ducted by: 

### Steve11 Klajka, P.E., 

### BCEE

Wi11gra E11gi11eeri11g, S.C. Madiso11, Wisco11si11Evaluation 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 ca u sing exceedances of the 1-hour su lfur dioxide (S02) national ambient air quality standard (NAAQS). This document describe s the results and procedures for an evaluation conducted for the Sib ley 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 di spersion modeling analy s is predicted ambient air concentrations for comparison with the 1
- hour S02 NAAQS. The modeling was performed using the most recent version ofAERMOD, AERMET, and AERMINUTE, with data pro vided to Sierra C lu b by regulatory air agencies or obtained through other publicly

- avai lable sources as documented be low. The analys is was conducted 

### in adherence to all available USEP A guidance for evaluating source impacts on attainment of the 1 -hour S02 NAA QS vi a aerial dispersion modeling, including the AERMOD Imp lementation Guide; USEPA's Applicability of Appendix W Model in g Guidance for the 1-hour S02 National Ambient Air Quality Standard, August 23, 2010; mode ling guidance promulgated by USEPA in Appendix W to 40 CFR Part 51; USEPA's March 201 1 Mode ling Guidance for S02 NAAQS D es ignations; 1 and USEPA's December 2013 S02 NAAQS De s ignations Technical Assi s tance Document. 2 

### 2. Complia nc e with the 1-hour S0 2 

### NAAQS 2.1 1-hour S0 2 

### NAAQS The 1-hour S02 NAAQS takes the form of a three-year average ofthe 99th-percentile ofthe annual di stribution 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 di spersion 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 / s o2
_ modeling

_ guidance.htm 2 http: //www.epa.gov/oaqpsOO 1 /s ulfurdioxide/pdfs/S02ModelingT AD.pdf 3 US EPA , Applicability of Appendix W Modeling Guidance for the 1-hour S0 2 Natio nal Ambient Air Quality Standard, August 23, 20 I0.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 S0 2 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 S0 2 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 concentrat ion 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/m 3

. 5 http: //ampd.epa.gov/ ampd/Evaluation of Compliance with the /
- hour NAAQS for SOz September 3, 2015 Page4 Table 1 - S02 Modeling R es ult s

for Sibley Generating Station Modeling Analys i s Averaging 99th Percentile 1-hour Daily Maximum (Jlg/rn 3) Emission Rates P er iod L mpact Backgro und To tal NAAQS Allowable Sibley 1 , 197. 1 23.5 1 ,220.6 196.2

Actua l B oiler 70 47.8 23.5 71.3 196.2 Allowable Sibley 1,4 11.9 23.5 1,435.4 196.2 Boilers Actua l 50,60 & 70 50.8 23.5 7 4. 3 196.2 Allowab le 379.7 23.5 403.2 196.2 Hawthorne Actua l 23.5 23.5 47 . 0 196.2 Allowable Nearman 126.3 23.5 149 .8 196.2

Actual C reek 8 1.4 23.5 104.9 196.2 A llowab le 1,614.5 23.5 1 ,638 .0 196 .2 Veo lia Actual 407.6 23.5 431.1 196 .2 All owab le All With 1 ,706.5 23.5 1 ,73 0.0 19 6.2 S ib ley Actual Boiler 70 41 1. 7 23.5 435.2 196.2 Allowab le Al l With 1 ,73 9.0 23.5 1 ,762.5 196.2 Sibley Actual B o ilers 411.7 23.5 435.2 196.2 50, 60 & 70 Complies with NAAQS ? No Yes No Yes No Ye s Yes Yes No No No No No NoEvaluation of Comp liance with the 1
-hour NAAQS for S02 Sep temb e r 3, 2015 Page5 The emiss ions u sed for the modeling analysis are summa rized in Table 2. 

### Table 2 -Modeled S02 

### Emissions 6 Stack Unit

ID ID Boiler 50 SOl Boiler 60 Boiler 70 Sibley Subtotal

HOI U nit 5A Hawthorne Subtotal N Ol 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 con servative aspects of this modeling protocol, it is extremely likely that this limit is too high to protect the NAAQS. For examp le , startup or s hutdown periods were not evaluated. During these periods , decreased gas ve locities 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 S0 2 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 wer e taken from Misso uri DNR, Part 70 Permit to Operate, No. OP2013-0024, July 12, 2013. Nearman Creek all owable emiss ions were taken from Kansas , Air Emission Source Class I Op e ratin g Permit, ID 209000 8, March 24, 2004 . Veolia allowab le emissions were taken from Missouri DNR, Part 70 Permit to Operate, No. OP2012-050, No. OP2012-050, March 4, 2013 .Evaluation of Complian ce with the 1
- hour NAAQSfor S0 2 Se

ptember 3, 2015 Page6 

### Table 3 -Required Emission Reductions from Sib ley Generating Stationfor Compliance with the 1-hourNAAQS 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 ofthe 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 emiss ions 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 po llutant 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 considerat ion of off
- s ite sources. Any other off
- site sources of S02 will increase the predicted impacts. 

### 2.4 Compar i son 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 MonitorEvaluation of Complian ce with th e 1
- hour NAAQS for S02 Septembe r 3 , 2015 Page 7 #72 90950034 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.t g/m 3

. Bas ed on actual hourly emissions from the Sibley plant and other regional sources, the modeling analy s is predicted a concentration near the monitor location of382 . 5 J.t g/m3 • Minus the assumed background of23 .5 J.tg/m3 the predicted impact due to regional S0 2 sources is 359 J.tg/m3

. Since the predicted and actual measured desi gn values are in close agreement, this comparison supports the accuracy ofthe modeling res ults presented in this report.

7 http: //www.epa.gov/airtrends/pdfs/ S02

_ De s ign Values_ 20 1220 l4_FINAL_ 8 _3_l 5.xlsxEvaluation of Compliance with th e 1-hour NAAQS for S0 1 September 3 , 2015 Page8

1-hour average S02 concentrations ( u g per c u bic mete r )- A ll colo red areas exceed the NAAQS. 196 4 00 600 800 1000 Figur e 1
- R e gional V iew of Impa ct s Bas ed on A llowable Emi ss ion s from A ll SourcesEvaluatio n of Co mplian ce with th e 1
- hour NAAQS for SO z Se

p tem ber 3, 2015 Page 9
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10COOO 1 - hour average S02 concentrations ( ug p er cubic me ter) - All colored areas exceed the NAAQS
. 1 9 6 300 400 

### Figure 2 -R egional View of Impacts Based on Actual Emi ssions from A ll Sources 

### • I I )

J0!.000Evaluation of Complianc e with the 1
-hour NAAQS for S0 1 Se

ptember 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 mode l 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 analy ses used one run with three years of sequential meteorological data from 2012-2014. Consistent with USEPA's Modeling Guidance for S0 2NAAQS Designations, AERMOD provided a table of fourth-high 1-hour S02 impacts concentrations consistent with the form of the 1-hour S0 2 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 T errain) 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 , Attachme nt 3 , March 24 , 2011, pp. 24-26 .Evaluation of Complia n ce with the 1-hour NAAQS for S02 Se

pt

ember 3, 2015 Page 11 

### 4. Model Inputs 4.1 Geographical Inputs The "ground floor" of all air dispersion modeling analyses is establishing a coordina te system for ident ifying the geographical location of emission sources and receptors. These geographical locations are u sed to determine local characteristics (such as land u se and elevation), and also to ascertain source to receptor distances and relationships. The Universal Tran sverse Mercator (UTM) NAD83 coordinate system was used for identifying the easting (x) and northing (y) coordinate s of the modeled sources and receptors . Stack loc ations 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 mode led using the rural or urban di spersion coefficient option in AERMOD. A Ge ographic Information System (GIS) was used to determine whether rural or urban disper sion coefficients app ly to a s ite. Land use within a three-kilometer radius circle surrounding the facility was con s idered. USEPA guidance states that urban di sper sion coefficients are used ifmore than 50% of the area within 3 kilometers h as urban land u ses. Otherwise, rural dispersion coefficients are appropriate. 10 USEPA's AERSURFACE v . 13016 was used to develop the meteorological data for the modeling analysis. This mode l was also used to evaluate surrounding land use within 3 kilometers. Base d on the output from the AERSURFACE, 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 u se of urban dispersion coefficients. Based on the AERSURF ACE analysis, it was concluded that the rural option would be u sed for the modeling summarized in this report. Please refer to Section 4.5.3 for a di scu ss ion of the AERSURFACE analysis.

10 USEPA, Revision to the Guideline on Air Quality Models: Adoption of a Preferred General Purpose (Flat and Comp lex Terrain) D ispersion Model and Other Revisions, Appendix W to 40 CFR Part 51 , November 9 , 2005 , Section 7.2.3 .Evaluation of Compliance w ith the 1-hour NAAQSfor S02 September 3, 2015 Page 12 

### 4.2 E mission Rates and Source Parameters The modeling analysis cons idered 

### SOz emissions from the Sibley, Hawthorne , Nearman Creek and Veolia power pl ants. Other of f
- s ite sources were not considered . Concentrations were predicted fo r the scenarios shown in Tables 1 and 2: 1) allowable emissions based on the current p ermit issued by the regulatory agency, and 2) ac tual hourly emi ssions for Sibley , Hawthorne and Ne arman Creek were measured each hour between January I, 2012 and D ecember 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 Veol ia

Stack SOl S03 H O I NO ! VOl De sc ription 50,60 and 70 Boiler 7 0 Unit SA Unit I 6 and 8 X Coord . [m] 397718 3977 1 8 372264 353388 363375 Y Coord. [m] 4337279 4337279 4332322 4337135 4330433 Base Elevation [m] 221.13 221.13 22 6 .0 6 229.41 234.12 Release Height [m] 213.36 2 13. 36 1 82 . 88 121.92 85.95 Gas Ex it 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

Ins ide Di ameter [m] 4.115 4. 1 15 6.462 6.096 5.105 Allowab le Emissio n Rate [g/s] 6,011 4 ,609 1 ,36 0 367 . 9 886 . 8

Actual Emiss ion Rate [g/s] 

### - - 

## - - 223.9 The above s tack parameters and emiss ions were obtained from regulatory agency documents and databases ident ified in Section 2.2. The analysis was conduct ed based on 100% operating load u s in g maximum exha u st flow rates and tem p eratures. Operation at less than full capacity loads was not considered. Thi s assump tion under-predi cts impacts since stack parameters s uch as exit flow rate and temp erature are lower at less than full load , reducing pollutant dispersion and increas ing predicted air quality imp acts . Stack loc ation , height and diameter were verified u sing aerial photographs, and flue gas flow rate and t emperature were verified u s ing 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 D etailed Data , Schedule 6, Stack & F lue Data, http: //www.eia.gov/ electricitv / data/eia923 / . Veo lia stack parameters obtained from Missouri DNR, Em iss ion s Inventory Questionnaire for 2014.Evaluation of Compliance with th e !
-hour NAAQSfor S0 1 Se

pt

embe r 3 , 2015 Pa ge 13 

### 4.3 Building Dimensions No building dimensions or prior downwash evaluations were available. Therefore this modeling analysis did not address the effects ofdownwash and this may under-predict impacts. 

### 4.4 Receptors For Sib ley Generating Station, three receptor grids were employed: l. A 1 00-meter Cartesian receptor grid centered on Sib ley 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 1,0 00-met er Cartesia n 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 di spersion model. 13 A flagpole height of 1.5 meters was used for all these receptors. Elevations from s tacks and receptors were obtained from National Elevation Dataset (NED) GeoTiff data. GeoTiff is a binary file th at includes data de scriptors 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 u sed 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 u sing 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 micrometeoro 1ogical parameters surface roughness, albedo, and Bowen ratio. One-minute ASOS data were available so USEPA me thods were used to reduce calm and missing hours. 14 The USEPA software program AERMINUTE v. 14237 is u sed for these tasks. This section discu sses how the meteorological data was prepared for u se in the 1-hour S0 2 NAAQS

13 USEPA , Revision to the Guideline on Air Quality Model s : Adoption of a Preferred General Purpose (Flat and Co mplex Terrain) Dispersion Model and Other Revisions , Appendix W to 40 CFR Part 51 , S ection A.l.(l), November 9 , 2 005. 14 USEPA, Area Designations for the 2 010 Revised Primary Sulfur Dioxide National Ambient Air Quality Standards, Attachment 3, March 24,201 1, p. 19 .Evaluation of Compliance with th e 1
-hour NAAQS for S0 2 Se

ptember 3 , 2015 Page 14 modeling analyses. The USEPA software program AERMET v. 14134 is used for these tasks. 

### 4.5.1 S urfa ce Mete orolo gy Surface meteorology was obtained for Kansas City Downtown Airport located near the Sibley Generating Station. Integrated Surface Hourly (ISH) data for the 20 1 2-2014 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 Upp er Air 

### D ata Upper
- air data are collected by a "weather balloon" that is re leased twice per day at selected locations. As the balloon is released, it rises through the atmosphere, and rad ios the data back to the s urface. 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 contro l checks. For Sibley Generating Station, the concurrent 20 1 2-20 1 4 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.FACE is a program that extracts surface roughness, albedo, and daytime Bowen ratio for an area surrounding a given location. AERSURFACE 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 d aytime Bowen ratio va lues in a region surrounding the meteorological data co llection site. AERSURFACE was used to develop surface roughness in a one kilometer radius surrounding the data co llection site. Bowen ratio and albedo was developed for a I 0 kilometer by 10 ki lometer area centered on the meteorological data collect ion s ite. These micrometeorologica l data were processed for seasonal periods using 30-degree s ectors. Seasonal moisture conditions were considered average with winter

15 Availab le at: http: //esrl.noaa.gov/raobs/Evaluation of Compliance with tlze !-hour NAAQSfo r S02 Septemb er 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 provi ded 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 S0 2 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 S0 2 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. The se include analyses prepared with AERSURFACE, AERMET , AERMAP, and AERMOD .

16 USEPA, Meteorological Monitoring Guidance for Regulatory Modeling Applications, EPA-454/R-99-05, February 2000, Sectio n 5.3.2 , pp . 5-4 to 5-5 . 17 USEPA , AERMOD Impl e mentation Guide , March 19,2009, pp. 3-4. 18 US EPA , Area Designations for the 2 010 Revised Primary Sulfur Di oxide National Ambient Air Quality S tandards , Attachment 3, March 24, 2011, pp. 20-23. 19 USEPA, S02 NAAQS D es ignations Modeling Technical Assistance Document, D ec. 2013, section 8.1 , pp 27-28. 20 US EPA , Applicability of Appendix W Modeling Guidance for the 1-hour S 0 2 National Ambient Air Quality Standard, August 23, 2010, p. 3. 21 http: //www.epa.gov/ airtrends/values.html