## Rockport Plant

Rockport, Indiana

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



## September 16, 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 16, 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). This doc ument describes the results and procedures for an evaluation conducted for the Rockport Plan t located in Rockport, Indiana.

To ensure the modeling analysis reflected the cumulative concen tration of SO 2 emissions, it included
emissions from the followi ng additional sources of SO 2 emissions located within 50 kilometers of the Rockport Plant:

 Warrick Power Plant – Newburgh, Indiana

 Elmer Smith Station – Owensboro, Kentucky

 Coleman Station – Hawesville, Kentucky

 ALCOA Inc. – Warrick Ope rations – Newburgh, Indiana

 Century Aluminum Sebree LLC – Robards, Kentucky

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

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

2 http://www.epa.gov/oaqps001/sulfurdioxide/pdfs/SO2ModelingTAD. pdfEvaluation of Compliance with the 1-hour NAAQS for SO 2 September 16, 2015 Page 3

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

2.2 Modeling Results

Modeling results for Rockport Pl ant and the othe r five faciliti es are summarized in Table 1. Results are provided for each source alone, and for all sources combine d.It was determined that based on
either current allowable emissi ons or measured actual emissions , the Rockport Plant 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 exceedances 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” for the four power plants are the measured emissi ons for each hour between January 1, 2012 and December 31, 2014 as
taken from USEPA Air Markets Program Data

. 5 For the two industrial sour ces, actual emissions are an annual average of the actual emissions reported to the state agencies.

In addition, the emissions from t he other five facilities signi ficantly contribute to the ambient SO 2 concentration in the area impacted by Rockport Plant.

Air quality impacts in India na are based on a background concen tration of 47.1 μg/m 3 . This is the 2011-13 design value for Vanderburgh County, Indiana - the lowe st measured background
concentration in the state. This is the most recently availabl e design value. See S ection 5 for further discussion of the background concen trations used for this analy sis.

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

. 5 http://ampd.epa.gov/ampd/Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 16, 2015 Page 4

Table 1 - SO 2 Modeling Results for Rockport Plant Modeling Analysis

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

Allowable Rockport Plant 217.8 47.1 264.9 196.2 No

Actual 103.6 47.1 150.7 196.2 Yes

Allowable Warrick Plant 2,219.1 47.1 2,266.2 196.2 No

Actual 91.6 47.1 138.7 196.2 Yes

Allowable Elmer Smith Station 1,230.6 47.1 1,277.7 196.2 No

Actual 130.6 47.1 177.7 196.2 Yes

Allowable Coleman Station 1,057.7 47.1 1,104.8 196.2 No

Actual 204.5 47.1 251.6 196.2 No

Actual ALCOA 613.3 47.1 660.4 196.2 No

Actual Century 571.3 47.1 618.4 196.2 No

Allowable Power Plants 2,419.0 47.1 2,466.1 196.2 No

Actual All Facilities 613.6 47.1 660.7 196.2 NoEvaluation of Compliance with the 1-hour NAAQS for SO 2 September 16, 2015 Page 5

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

Table 2 - Modeled SO 2 Emissions 6

Stack

ID Unit
ID Allowable Emissions (lbs/hr) Actual Emissions (lbs/hr)

C01 Unit 1 8,138.0 2012-14 CEM
Unit 2 8,138.0 2012-14 CEM
Unit 3 8,247.2 2012-14 CEM
Coleman Subtotal 24,523.2 2012-14 CEM

ES01 Unit 1 9,042.0 2012-14 CEM
Unit 2 15,398.4 2012-14 CEM
Elmer Smith Subtotal 24,440.4 2012-14 CEM

R01 Unit 1 14,848.8 2012-14 CEM
Unit 2 14,848.8 2012-14 CEM
Rockport Subtotal 29,697.6 2012-14 CEM

W01 Unit 1 8,119.8 2012-14 CEM
Unit 2 8,119.8 2012-14 CEM
Unit 3 8,119.8 2012-14 CEM
W04 Unit 4 15,115.4 2012-14 CEM
Warrick Subtotal 39,474.8 2012-14 CEM

A102 Ring Furnace - 22.3

A161 Potline 2 - 152.4

A162 Potline 3 - 162.1

A163 Potline 4 - 162.9

A164 Potline 5 - 163.7

A165 Potline 6 - 135.7

ALCOA Subtotal - 799.1

SB01 Boiler House #1 - 367.9

SB02 Boiler House #2 - 399.6

SB12 Residue Boiler #530AB - 5.3

SABIC Subtotal - 772.8

C01A Potline #1 Roofs - 123.0

6 Rockport allowable emissions are based on Indiana DEM, Title V - Renewal, 147-29841-00020, August 15, 2014. Warrick allowable emissions were taken from IDEM, Part 70 Opera ting Permit Renewal, Operation Permit No. T173- 35059-00002, November 13, 2014. Elmer Smith allowable emisison s were taken from Kentucky DEP, Air Quality Permit No. V-11-055, October 29, 2012. Coleman allowable emissi ons were taken from Kentuck DEP, Air Quality Permit No. V-08-019 R3, November 10, 2008, Revised September 19 , 2011. ALCOA actual emissions for 2014 provided by IDEM - Email, J. Koch to S. Klafka, Request for Det ailed Emissions Summary Reports, August 13, 2015. Hourly rate is an annual average. Century Aluminum actual emiss ions for 2013 taken from KDEP, Acknowledgment Checklist for 2013 Emissions Data, July 16, 2014.Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 16, 2015 Page 6

C01B Potline #1 Scrubbers - 123.0

C02A Potline #2 Roofs - 123.0

C02B Potline #2 Scrubbers - 123.0

C03A Potline #3 Roofs - 123.0

C03B Potline #3 Scrubbers - 123.0

C04A Furnace Baked Anodes - 123.0

C04B Furnace Gas Burners - 123.0 Century Aluminum Subtotal - 984.0
All Facilities - 118,136.0 -

Based on the modeling results, Table 3 provides the emission re ductions from current allowable rates necessary to achieve com pliance with the 1-hour NAAQS. T his assumes a one-hour averaging period for the emission rate and that the emission rate is bind ing 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 wer e not evaluated. During these periods, decreased gas velocities and temperatures may lead to greater ambient impacts at ground level. Further, the hypothetic al emission limitation in Table 3 would allow Rockport Plant to consume the entire NAAQS, leav ing little to no room for any oth er source of SO 2 in the area. No margin of safety has been incl uded in the hypothetical emission limitation.

Table 3 - Required Emission Reductions from Rockport Plant 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)

149.1 94% 1,830.5 0.07

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 all sources.

Figure 2 shows the extent of NAA QS violations based on actual h ourly emissions from all 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.Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 16, 2015 Page 7

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.

 Except for the five additional facilities, no consideration of off-site sources. Any other offsite sources of SO 2 will increase the predicted impacts.Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 16, 2015 Page 8

Figure 1 - Regional View of Impacts Du e to Allowable Emissions from All SourcesEvaluation of Compliance with the 1-hour NAAQS for SO 2 September 16, 2015 Page 9

Figure 2 - Regional View of Impacts Du e to Actual Emissions from All SourcesEvaluation of Compliance with the 1-hour NAAQS for SO 2 September 16, 2015 Page 10

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 16, 2015 Page 11

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. Stack 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. 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 0.7% 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 16, 2015 Page 12

4.2 Emission Rates and Source Parameters

The modeling analysis considered SO2 emissions from the Rockpor t, and five additional facilities.
Other off-site sources were not c onsidered. Concentrations were predicted 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 for th e power plants were measured e ach hour between January 1, 2012 and December 31, 2014 as taken from USEPA Air Markets Program Data

. 10 Actual hourly emissions for ALCOA and Century Aluminum were the annual average developed
from the actual annual emissions r eported to the state agencies

.

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

10 http://ampd.epa.gov/ampd/Evaluation of Compliance with the 1-hour NAAQS for SO2September 16, 2015Page 13Table 4 – Facility Stack Parameters and Emissions11FacilityRockport Coleman Elmer Smith WarrickStackR01 C01 ES01 W01 W04DescriptionUnits 1 and 2 Units 1, 2 and 3 Units 1 and 2 Units 1, 2 and 3 Unit 4X Coord. [m]496744 518199 494741 470747 470708Y Coord. [m]4197574 4201625 4183109 4196346 4196369Base Elevation [m]120.34 121.78 124.97 121.3 120.42Release Height [m]316.38 137.16 128.02 116.13 152.4Gas Exit Temperature [°K]430.372 329.261 327.594 328.706 328.706Gas Exit Velocity [m/s]40.06 13.939 16.088 16.457 16.618Inside Diameter [m]12.954 9.083 7.65 7.132 5.944Allowable Emission Rate [g/s]3,742 3,090 3,079 3,069 1,905Actual Emission Rate [g/s] - - - - -11Power plant stack parameters taken from USEIA, 2012 Form EIA-860 Data - Schedule 6, 'Stack & Flue Data', http://www.eia.gov/electricity/data/eia860/. ALCOAactual emissions for 2014 and stack parameters provided by IDEM- Email, J. Koch to S. Klafka, Request for Detailed EmissionsSummary Reports, August 13, 2015.Hourly rate is an annual average.Century Aluminum actual emissions for 2013 taken from KDEP, Acknowledgment Checklist for 2013 Emissions Data, July 16, 2014.Hourly rate is an annual average. Century Aluminum stack parameters provided by KDEP – Email, J. Griffith to S. Klafka, FOIA for Stack Parameters for CenturyAluminum – Rogards, KY, August 19, 2015.Evaluation of Compliance with the 1-hour NAAQS for SO2September 16, 2015Page 14Facility ALCOA Inc. –Warrick OperationsStack A102 A161 A162 A163 A164 A165Description Ring Furnace POTLINE 2POTLINE 3 POTLINE 4 POTLINE5 POTLINE 6X Coord. [m] 470710 470710 470710 470710 470710 470710Y Coord. [m] 4196858 4196858 4196858 4196858 4196858 4196858Base Elevation [m] 119.17 119.17 119.17 119.17 119.17 119.17Release Height [m] 28.96 14.94 60.66 60.66 14.94 14.94Gas Exit Temperature [°K] 351.333 355.222 343 343 350.222 370.222Gas Exit Velocity [m/s] 43.855 49.655 31.653 31.653 69.519 81.266Inside Diameter [m] 1.173 0.61 6.096 6.096 0.61 0.61Actual Emission Rate [g/s] 2.814 19.2 20.43 20.52 20.62 17.1Facility Century AluminumStack C01A C01B C02A C02B C03A C03B C04A C04BDescriptionPotline #1RoofsPotline #1ScrubbersPotline #2RoofsPotline #2ScrubbersPotline #3RoofsPotline #3ScrubbersFurnaceAnodesFurnace GasBurnersX Coord. [m] 455873 455816 455805 455749 455704 455648 456075 456075Y Coord. [m] 4167897 4167833 4167957 4167893 4168047 4167984 4168059 4168059Base Elevation [m] 140.93 139.39 140.2 135.07 140.41 140.69 144.41 144.41Release Height [m] 24.57 24.57 24.57 24.57 31.98 31.98 21.34 21.34Gas Exit Temperature [°K] 389.817 389.817 389.817 389.817 389.817 389.817 347.039 347.039Gas Exit Velocity [m/s] 16.255 16.255 16.255 16.255 13.6 13.6 11.982 11.982Inside Diameter [m] 1.219 1.219 1.219 1.219 3.438 3.438 1.289 1.289Actual Emission Rate [g/s] 15.5 15.5 15.5 15.5 15.5 15.5 15.5 15.5Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 16, 2015 Page 15

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.

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 Rockport Plant, three receptor grids were employed:

1. A 100-meter Cartesian receptor grid centered on Rockport Plant and extending out 5
kilometers.

2. A 500-meter Cartesian receptor grid centered on Rockport Plant and extending out 10
kilometers.
3. A 1,000-meter Cartesian receptor grid centered on Rockport Plan t and extending out 50 kilometers. 50 kilometers is the maximum distance accepted by U SEPA 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

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.Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 16, 2015 Page 16

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

4.5.1 Surface Meteorology

Surface meteorology was obtained for Evansville Regional Airpor t located near the Rockport Plant. Integrated Surface Hourly (ISH) data for the 2012-2014 period w ere obtained from the National Climatic Data Center (NCDC). T he ISH surface data was process ed through AERMET Stage 1, which performs data extraction a nd quality 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 Rockport Plant, the concurrent 2012-2014 upper air data fro m twice-daily radiosonde
measurements obtained at the most representative location were used. This location was the Lincoln, Illinois measurement st ation. These data are in Foreca st Systems Laboratory (FSL) format
and were downloaded in ASCII textformat from NOAA’s FSL websit e. 14 All reporting levels were downloaded 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

13 USEPA, Area Designations for the 2010 Revised Primary Sulfur D ioxide National Ambient Air Quality Standards, Attachment 3, March 24, 2011, p. 19.

14 Available at: http://esrl.noaa.gov/raobs/Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 16, 2015 Page 17

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 months having 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 0.75% 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. Since the Evansville Regional Airport is located close to Rockport Plant, this meteo rological data set was considered appropriate for this modeling analysis. 16 This weather station pr ovided high quality surface measurements for the most recent 3-year time, and had similar l and use, surface characteristics,
terrain features and climate. Fin ally, the meteorological data from the selected surface and upper air stations were recommended by the Indiana Department of Environm ental Management for modeling
facilities locate d in Spencer County. 17

5. Background SO 2 Concentrations

Background concentrations were determined consistent with USEPA ’s Modeling Guidance for SO 2 NAAQS Designations. 18, 19 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. 20 Background
concentrations were based on the 2011-13 design value measured by the ambient monitors located in

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 Indiana DEM, Air Dispersion Me teorological Data, http://www.in .gov/idem/airquality/2376.htm

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

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

20 USEPA, Applicability of Appendix W Modeling Guidance for the 1- hour SO 2 National Ambient Air Quality Standard, August 23, 2010, p. 3.Evaluation of Compliance with the 1-hour NAAQS for SO 2 September 16, 2015 Page 18

Indiana. 21

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.

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