# 2010 **1**

**- Hour**  **Sulfur Dioxide**  **Standard**

**Designation Recommendations** 

**Technical Support**  **Document**

**Iowa Department**  **of Natural**  **Resources**

**Environmental Services**  **Division**

**Air Quality**  **Bureau**

**7900 Hickman**  **Rd Suite**  **1**

**Windsor Heights,**  **IA 50324** 

**December 2**  **3 , 2015** 2 

## i. **Executive Summary** 

The State of Iowa is providing to the U.S. Environmental Protection Agency (EPA) updated designation

recommendations for the 2010 1

- hour sulfur dioxide ( SO 2 ) N ational A mbient A ir Q uality S tandard

(NAAQS)

. The updated designations recommendations address three areas in the state that contain the

following sources :

• IPL

- Burlington Generating station (located in Des Moines County)

• IPL

- Ottumwa Generating Station (located in Wapello County)

• MidAmerican Energy Company

- George Neal South facility (located in Woodbury County)

These three facilities are identified because EPA determined they meet criteria specified in the March 2,

2015

, federal Consent Decree between EPA and plaintiffs Sierra Club and Natural Resources Defense

Council

. The federal Consent Decree establishes deadlines for finalizing three new rounds of area

designations under the 2010 1

- hour SO 2 NAAQS (75 FR 35520; June 22, 2010)

. For the first new round

the C onsent D ecree requires that by June 2, 2016, EPA must sign for publication in the Federal Register

designation s for areas which contain ( in simple and incomplete te rms) any power plant that in 2012

emitted more than 2,600 tons of SO 2 and had an SO 2 emission rate of 0.45 lb/MMBtu or more and had

not announced any units for retirement.

One round of designations for the 1

- hour SO 2 NAAQS was completed in 2013 . At that time EPA only

issued nonattainment designations and most areas in the U.S. were left undesignated for the 1

- hour SO 2 NAAQS. Although states were required to submit initial designation recommendations to EPA in 2011

, those recommendations have largely not been acted upon and may no longer be appropriate . EPA is

now providing states with an opportunity to update their designation recommendations for the first

new round of SO 2 designations required by the Consent Decree . EPA is requesting any updated

recommendations and supporting informati on by September 18, 2015

.

Revised Designation Recommendations

The State is revising the unclassifiable designation recommendations submitted to EPA on June 2, 2011,

for the three counties in Iowa that contain the identified sources

. The revised 1

- hour SO 2 designations

recommendations are based on air dispersion modeling results

.

Burlington Generating station is a power plant operated by Interstate Power and Light (IPL), a subsidiary

of Alliant Energy. The facility is located in Des Moines County in far southeast Iowa. The State of Iowa is

recommending that all of Des Moines County be designated attainment.

Ottumwa Generating station is a power plant operated by IPL

. The facility is located in Wapello County

in southeast Iowa. The State of Iowa is recommending that all of Wapello County be designated

attainment.

George Neal South is a power plant operated by MidAmerican Energy Company. The facility is located in

Woodbury County in northwest Iowa. The State of Iowa is recommending that all of Woodbury County

be designated attainment.3 

## Table of Contents

i. Executive Summary

................................ ................................ ................................ ............................... 2

1. Background

................................ ................................ ................................ ................................ ........... 4

2. Affected Sources and Revised Recommendations Summary

................................ ............................... 6

3. IPL

– Burlington Generating Station

................................ ................................ ................................ ...... 7

3.1. Source Characterization and Emission Rates

................................ ................................ ................ 7

3.2. Nearby Sources of SO 2

................................ ................................ ................................ .................. 8

3.3. Dispersion Model

................................ ................................ ................................ ........................ 13

3.4. R eceptor Grid

................................ ................................ ................................ .............................. 13

3.5. Meteorological Data

................................ ................................ ................................ ................... 14

3.6. Background Concentration

................................ ................................ ................................ ......... 15

3.7. Modeling Results

................................ ................................ ................................ ......................... 15

3.8. D esignation Recommendation

................................ ................................ ................................ ... 16

4. IPL

– Ottumwa Generating Station

................................ ................................ ................................ ..... 17

4.1. Source Characterization and Emission Rates

................................ ................................ .............. 17

4.2. Nearby Sources of SO 2

................................ ................................ ................................ ................ 18

4.3. Dispersion Model

................................ ................................ ................................ ........................ 19

4.4. Receptor Grid

................................ ................................ ................................ .............................. 20

4.5. Meteorological Data

................................ ................................ ................................ ................... 21

4.6. Background Concentration

................................ ................................ ................................ ......... 22

4.7. Modeling Results

................................ ................................ ................................ ......................... 22

4.8. Designation Recommendation

................................ ................................ ................................ ... 23

5. MidAmerican

– George Neal South

................................ ................................ ................................ .... 24

5.1. Source Characterization and Emission Rates

................................ ................................ .............. 24

5.2. Nearby Sources of SO 2

................................ ................................ ................................ ................ 26

5.3. Dispersion Model

................................ ................................ ................................ ........................ 27

5.4. Receptor Grid

................................ ................................ ................................ .............................. 27

5.5. Meteo rological Data

................................ ................................ ................................ ................... 28

5.6. Background Concentration

................................ ................................ ................................ ......... 29

5.7. Modeling Results

................................ ................................ ................................ ......................... 29

5.8. Designation Recommendation

................................ ................................ ................................ ... 304 

## 1. **Background**

On June 2, 2010, the U.S. Environmental Protection Agency ( EPA ) signed a final rule revising the SO 2

National Ambient Air Quality Standards (NAAQS)

. EPA established a new 1

- hour (hr) SO 2 primary NAAQS

of 75 parts per billion (ppb), based on the three

- year average of the annual 99 th percentile of daily 1

-

hour maximum concentrations. The NAAQS revision was published in the Federal register on June 22,

2010 ( 75 FR 35520).

Whenever EPA r evises a NAAQS the C lean Air Act (CAA) requires EPA to designate areas as "attainment"

(meeting), "nonattainment" (not meeting), or "unclassifiable" (insufficient data). Compared to other

criteria pollutants EPA has chosen a different approach to determine an area ’ s attainment status for the

1

- h r SO 2 NAAQS. Unlike other criteria pollutants SO 2 is almost exclusively emitted by point sources and

“[d]ue to the generally localized impacts of SO 2 , [EPA has] not historically considered monitoring alone

to be an adequate, nor the most appropriate, tool to identify all maximum concentrations of SO 2 ” (75 FR

35520). Instead of using only monitoring data to assess compliance with the 1

- h r SO 2 NAAQS

, which

would require a prohibitively expensive SO 2 monitoring network, EPA is supporting a hybrid approach to

the designations process

, allowing the use of either modeling or monitoring data

.

In the March 20, 2015

, document, “ Updated Guidance for Area Designations for the 2010 Primary Sulfur

Dioxide National Ambient Air Quality Standard ,” EPA defines area designation categories for this

standard as follows:

• Nonattainment: An area that the EPA has determined violates the 2010 1

- hr SO 2 NAAQS, based

on the most recent three years of ambient air quality monitoring data or an appropriate

modeling analysis, or that EPA has determined contributes to a violation in a nearby area.

• Attainment: An area that the EPA has determined meets the 2010 1

- hr SO 2 NAAQS and does

not contribute to a violation of the NAAQS in a nearby area based on either: 1 ) the most recent

three years of ambient air quality monitoring data from a monitoring network in an area that is

sufficient to be compared to the NAAQS per EPA interpretations in the Monitoring Tech nical

Assistance Document

, 1 or 2 ) an appropriate modeling analysis.

• Unclassifiable: An area where the EPA cannot determine

, based on available information

, whether the area is or is not meeting the 2010 1

- hr SO 2 NAAQS and whether the area

contributes to a violation in a nearby area.

EPA is prom ulgating designations under the 1

- hr SO 2 standard for areas throughout the nation in

multiple phases. In the initial round completed in 2013 EPA designated 29 areas in 16 states as

nonattainment based on available monitoring data (78 FR 47191

, August 5, 2013 ). That action included

a nonattainment designation for a portion of Muscatine County

. However, no other areas in Iowa have

yet been designated for the 1

- hr SO 2 NAAQS

, and most areas across the U.S

. remain undesignated . To

address that deficiency t hree additional rounds of designations are required by a Consent Decree

entered in federal court on March 2, 2015, between EPA and the plaintiffs Sierra Club and Natural

Reso urces Defense Council.

1 http://www.epa.gov/airquality/sulfurdioxide/pd fs/SO2MonitoringTAD.pdf5 The first new round of designations required by the Consent Decree must be completed (meaning the

designations must be signed for publication in the Federal Register) within sixteen months of the court’s

entry of the Consent Decree

, which is by July 2, 2016. By that date EPA must have signed for publication

in the Federal Register designations for areas that contain sources meeting specific criteria identified in

the Consent Decree. The Consent Decree criteria include emissions related thresholds affecting sources

that report emissions and other data to EPA’s Clean Air Markets Division (CAMD). In Iowa only e lectric

g enerating u nits (EGUs) , more commonly known as power plants, report data to CAMD. The EGUs

subject to the first new round of Consent Decree designations are those that (in simple and incomplete

terms) h ad not announced any units for retirement and had

, according to the data in EPA’s Air Markets

Database :

• more than 16,000 tons of SO 2 emissions in 2012 ; or

• more than 2,600 tons of SO 2 emissions in 2012 and an annual average emission rate of at least

0.45 lbs SO 2 /MMB tu

.

The second and third rounds of designations required by the Consent Decree must be completed by

December 31, 2017

, and December 31, 2020

. The designations completed under tho se deadlines are

expected to be made pursuant to EPA’s final Data Requirements Rule (DRR)

, published in the Federal

Register on August 21, 2015 ( 80 FR 51051 )

. The DRR does not directly govern the first new round of

Consent Decree designations.

In a letter to the State of Iowa dated March 20, 2015

, EPA notes their responsibility to issue designations

by June 2, 2016, and their intent to use the latest available information when making designations and

boundary determ inations. States may update or submit new designations recommendations to EPA

before (or around) September 18, 2015. EPA’s March 20, 2015 “ Updated Guidance for Area

Designations for the 2010 Primary Sulfur Dioxide National Ambient Air Quality Standard ” l ists five factors

to be considered when developing boundary designation recommendations:

• Monitoring/Modeling data

• Emissions information, including growth, controls, and regional emission reductions

• Meteorology

• Topography

• Jurisdictional boundaries

The fir st factor listed provides for the consideration of modeling or monitoring data as a means of

evaluating air quality. In December 2013 EPA released draft technical assistance documents t hat aid in

the technical aspects of evaluating air quality using eithe r modeling or monitoring approaches for

designation purposes. The other factors are summarized within EPA’s Ma r ch 20, 2015, guidance

document, although d ispersion modeling is capable of addressing several of the factors simultaneously.

The S tate has evaluated EPA’s SO 2 designations guidance and is providing updated designation

recommendations developed using methods consistent with current guidance. This document provides

a discussion and technical justification of the boundary recommendatio ns for the three areas in Iowa

affected by the first new round of designations required under the federal Consent Decree

.6 

## 2. **Affected Sources and**  **Revised Recommendations**  **Summary**

According to EPA’s March 20, 2015

, letter to the Iowa DNR

, three EGUs in Iowa me e t the Consent

Decree criteria. The se facilities are listed in Table 2

- 1 and shown in Figure 2

- 1

.

Table 2

- 1

. F acilities in Iowa subject to the first new round of Consent Decree designations.

Facility Name (Owner) Facility ID County 2012 SO 2

Emissions (tons) † 2012 SO 2 Rate

(lb/MMBtu) †

Burlington Generating Station (Alliant/IPL) 29

- 01

- 013 Des Moines 4,697 0.672

Ottumwa Generating Station (Alliant/IPL) 90

- 07

- 001 Wapello 11,985 0.666

George Neal South (MidAmerican) 97

- 04

- 010 Woodbury 14,273 0.638

† The 2012 e missions and emission rate data are from EPA’s Clean Air Markets Division.

Figure 2

- 1

. L ocations of the 3 facilities affected by the first new round of C onsent D ecree designations.

The S tate is revising the unclassifiable designation recommendations submitted to EPA on June 2, 2011,

and is now recommending that each of the three counties (Des Moines, Wapello, and Woodbury) that

contain an identified source be designated at tainment. The u pdated designation recommendations are

based on dispersion modeling results (discussed below) conducted in accordance with EPA’s most recent

modeling Technical Assistant Document. 2

2 While an SO 2 monitor is located in Woodbury County, it is not sited to assess the maximum 1

- hr impacts from

George Neal South and has not been in operation long enough to produce a (three

- year) design value. No ambient

SO 2 monito rs are located in either Des Moines or Wapello counties.7 

## 3. **IPL**

**– Burlington**  **Generating Station** 

Burlington Generating Station is a c oal

- fired electric generating facility located in Des Moines County

,

Iowa

, (see Figure 3

- 1 ) and is operated by Interstate Power and Light (IPL), a subsidiary of Alliant Energy.

There are no ambient SO 2 monitors near Burlington Generating Station that can be relied upon to

characte rize the air quality around the source. Instead, d ispersion modeling was conducted. Based on

the DNR’s technical review of this facility a n attainment recommendation for all of Des Moines County is

appropriate

.

Figure 3

- 1

. Location of IPL’s Burlington Generating Station. Counties in Iowa are shaded slightly.



### 3.1. **Source Characterization**  **and Emission**  **Rates**

The SO 2 emission sources at Burlington Generating Station are a coal

- fired main boiler, a natural gas

fired auxiliary boiler for heating, and four natural gas combustion turbines

. The emergency generator is

an intermittent emission source that will be excluded in this modeling analysis pur suant to Section 5.4 of

EPA’s draft “ SO 2 NAAQS Designations Modeling Technical Assistance Document ” ( T AD ), dated December

2013

.

The SO 2 emission rates used in the modeling analysis are summarized in Table 3

- 1

. The emission rates

reflect a mix of existing limits and actual hourly emission s

.8 Table 3

- 1

. Burlington Generating Station m odeled SO 2 e mission r ates

.

Model

ID SO 2 Emission Points Rated

Capacity

(MMBtu/hr) SO 2 Limit Notes Modeling

Emission

Rate

(lb/hr)

EP01 C ombustion T urbine #1 (NG) 288 1.8 lb/hr Existing Limit 1.8

EP02 C ombustion T urbine #2 (NG) 288 1.8 lb/hr Existing Limit 1.8

EP03 C ombustion T urbine #3 (NG) 288 1.8 lb/hr Existing Limit 1.8

EP04 C ombustion T urbine #4 (NG) 288 1.8 lb/hr Existing Limit 1.8

EP16 † Auxiliary (Aux.) Boiler (NG) 15 500 ppm Conservative

Limit 0.9

EP17 Main Boiler (Coal) 2077 1.0 lb/MMBtu Actual

Emissions Varies

Hourly ‡

† The existing potential emission rate for the auxiliary boiler, EP16, is 0.009 lb/hr. The modeled emission rate

however is conservatively higher as it reflects an earlier proposal to establish a new limit for this unit. Given the

modeling results (discu ssed below) there was no need to remodel this unit using the existing lower limit.

‡ The SO 2 emission rate for the main boiler, EP17, is based on actual reported CEMS data provided by IPL for the

period 2012

- 2014.

Table 3

- 2 s ummarizes the stack characteristics used in the 1

- h r SO 2 modeling demonstration. T he

actual stack height was modeled for the main boiler stack (EP17) since the good engineering practice

( GEP ) stack height was higher than the actual stack height.

Table 3

- 2

. Burlington Generating Station p oint s ource e xhaust c haracteristics

.

Model

ID UTM

Easting

(m) UTM

Northing

(m) Base

Elevation

(m) Stack

Height

(m) Stack

Diameter

(m) Exhaust

Temperature

(K) Exhaust

Velocity

(m/s)

EP01 658898.2 4511791.1 161.05 11.28 3.08 788.7 24.56

EP02 658907.1 4511790.0 161.28 11.28 3.08 788.7 24.56

EP03 658916.8 4511788.9 161.65 11.28 3.08 788.7 24.56

EP04 658925.8 4511787.8 162.01 11.28 3.08 788.7 24.56

EP16 658985.4 4511701.9 162.1 52.36 0.59 533.2 10.17

EP17 659014.6 4511681.0 161.91 93.27 3.58 477.6 34.98



### 3.2. **Nearby Sources**  **of SO**  **2**

The SO 2 emission levels from all facilities within 10 km were evaluated to determine if additional sources

of SO 2 should be included in the modeling analysis. Table 3

- 3 summarizes the sources within 10 km of

Burlington Generating Station an d their recent SO 2 emissions. Any source that would contribute a

significant portion of the total SO 2 emissions in the area was identified to be included in the modeling

analysis. The total average emissions for the area were 4

, 098.5 t ons per year (t py )

, of which Burlington

Generating Station is the primary contributor. All other sources combined only contribute 0.005%.

Therefore no other sources within 10 km were included in the modeling analysis.9 Table 3

- 3

. Facilities within 10 km of Burlington Generating Station.

SO 2 Emissions (tpy) ‡

Facility Name Address 2012 2013 2014 Most Recent

(or a verage)

Cessford Construction

Company

- Burlington 3808 Old H wy 61

Burlington, IA 52601 - - - 0.09

IPL

- Burlington Agency Street

Combustion Turbines 3320 Agency St

. Burlington, IA 52601 0 0 0 0

Lamont Limited 1530 Bluff Rd

. Burlington, IA 52601 - - - 0

Champion Spark Plug 3009 Sylvania Dr

. Burlington, IA 52601 - - - NA

Riley Paint Company 860 Washington St

. Burlington, IA 52601 - - - 0

Great River Medical Center 1221 S Gear Ave

.

West Burlington, IA

52655 - - - 0

Ideal Ready Mix Co Inc

. - d ba

Burlington Ready Mix 520 S. Main St

. Burlington, IA 52601 - - - 0

Ideal Ready Mix Co Inc

. - Burlington Block 3810 HWY 61

Burlington, IA 52601 - - - 0

PPG Industries Inc

. 3700 Division St

. Burlington, IA 52601 - - - 0

Dresser

- rand Company 1106 W ashington S t.

Burlington, IA 52601 - - - 0.01

Burlington High School 421 Terrance

Burlington, IA 52601 - - - 0

ADM / Growmark

- Burlington 701 Cash St

. Burlington, IA 52601 - - - 0

Exide Technologies

- Burlington 3400 West Ave

. Burlington, IA 52601 - - - 0

Burlington Basket Company 922 Bluff Rd

. Burlington, IA 52601 - - - 0

Simpson Security Papers 3355 Agency St

. Burlington, IA 52601 - - - 0

Burlington Wilbert Vault 2845 Mount Pleasant St

. Burlington, IA 52601 - - - 0

Flint Cliffs Manufacturing

Corp. 1600 Bluff Road

Burlington, IA 52601 - - - 0

Qwest Communications Dba

Century Link

- Burlington 421 Columbia St

. Burlington, IA 52601 - - - NA

General Electric

- Consumer

& Industrial Division 510 E Agency Road

West Burlington, IA

52655 - - - 0.08

Borghi USA 402 W est D ivision S t.

West Burlington, IA

52655 - - - NA10 Modern Welding Co Of Iowa

Inc

. 2818 Mount Pleasant St

. Burlington, IA 52601 - - - 0

Summer Street Animal Clinic 6457 Summer St

. Burlington, IA 52601 - - - NA

Burlington Generating

Station 4282 Sullivan Slough Rd

. Burlington, IA 52601 4697.1 3940.9 3657 4098.3

(avg)

Olympic Foundry Inc

. 2825 Mount Pleasant

Burlington, IA 52601 - - - NA

Winegard Company 3000 Kirkwood St.

Burlington, IA 52601 - - - NA

OMG Midwest Dba Cessford

Const Co. 121ST AVE and HWY 61 S

Burlington, IA 52601 - - - 0

CNH America LLC

. 1 930 Des Moines Ave.

Burlington, IA 52601 0.05 0.01 0.06 0.04

(avg)

Total Average Emissions 4,098.5

‡ Major sources report emissions every year while minor sources report at most once every three years. If the

latest available inventory for a minor source predates 2012 then the facility’s emissions are listed only in the

“Most Recent” column. The “Most Recent” column also includes the 3

- year average emission rates for major

sources.

In addition, a search was performed for major sources of SO 2 within 10

- 20 km. One fac ility was

identified for additional review during this search, Iowa Army Ammunition Plant. This facility had a

maximum SO 2 emission rate of 753.26 tpy during the three

- year period 2012

- 2014. The SO 2 emissions

from this facility are attributable to a pair of coal

- fired boilers venting through a common stack. The

facility is unique in that it has a very large property, which places the coal boilers far from ambient air

(see Figure 3

- 2 ). The nearest ambient air is 1.9 km to the north of the boiler stack, which restricts the

largest concentration gradients to the property. A screening analysis was performed for the Iowa Army

Ammunition Plant to determine if it would need to be included in the IPL

- Burlington modeling analysis.

The screening modeling consisted of a single point source (EP 500

- 139

- 1) with the parameters listed in

Table 3

- 4

.11 Figure 3

- 2

. Iowa Army Ammunition P lant overview. Their f ence line is shown in green.

Table 3

- 4 . Iowa Army Ammunition Plant boiler point source characteristics.

Emission units: Two (2) Zurn boilers

Emissions: 753.26 tpy (171.98 lbs/hr), based on maximum reported emissions from 2012

- 2014

Stack Height: 150 ft

Discharge type: Vertical/unobstructed

Diameter: 108 in

Temperature: 403 degrees F

Flow rate: 78,690 scfm (128,162 acfm)

Two iterations of the modeling were conducted. The first assuming no downwash, and the second using

conservative estimates of the building dimensions based on recent aerial photography (see Figure 3

- 3

and Figure 3

- 4 ). The maximum results of these two analyses were the same, indicating that building

do wnwash is not an important factor in determining the maximum concentration from the boiler stack.

Both analyses were evaluated using meteorological inputs from the nearby Burlington airport for the

period 2012

- 2014. Actual terrain elevations were used ba sed on the National Elevation Dataset (NED).12 Figure 3

- 3

. Iowa Army Ammunition Plant b oiler.

Figure 3

- 4

. Iowa Army Ammunition P l ant m odel i nput (Facing SW).13 Given the size of the facility’s property it is likely that the maximum concentration from the boiler

actually occurs on their property (the nearest fence line to the boiler stack is 1.9 km away). Therefore,

receptors were only placed along the fenc e line of the facility to determine the location and magnitude

of the maximum concentration.

The highest

- fourth

- highest predicted concentration averaged over three years was 21.29 μg/m 3 . This

value is far below the standard (196 μg/m 3 ) and the cumulative result remain s below the standard if it is

conservat ively added to the total results from Burlington Generating Station and background (discussed

below)

.

The State of Illinois was also contacted to determine if there were any facilities that would need t o be

included from that state. No such sources were identified.



### 3.3. **D ispersion**  **M odel** 

The EPA recommended American Meteorological Society (AMS)/EPA Regulatory Model (AERMOD) was

used to perform the analysis. The most current version (Version 1 5181 ) of AERMOD available at the

time of the analysis was used with regulatory default options as recommended in the EPA Guideline on

Air Quality Models. The following supporting pre

- processing programs for AERMOD were also used:

• BPIP

- Prime (Version 04274)

• AERMET (Vers ion 14134)

• AERMAP (Version 11103)

AERMOD is a steady

- state plume model that simulates air dispersion based on planetary boundary layer

turbulence structure and scaling concepts, including treatment of both surface and elevated sources,

and both simple and complex terrain

. This model is recommended for short

- range (< 50 kilometers

[km]) dispersion from the source

. The model incorporates the Plume Rise Model Enhancement (PRIME)

algorithm for modeling building downwash

. AERMOD is designed to accept input data prepared by two

specific pre

- processor programs, AERMET and AERMAP

. AERMOD was run with the following options:

• Regulatory default options

• Direction

- specific building downwash characterized by BPIP

- PRIME

• Actual receptor elevations and hill height scal es obtained from AERMAP

• SO 2 pollutant keyword



### 3.4. **Receptor Grid** 

Receptors were sited outside of the fence line boundary of the Burlington Generating Station. Receptor

placement grid spacing was:

• 50 meters along the facility fence line

• 50 meters from the fence line to 0.5 km

• 100 meters extending from 0.5 km to 1.5 km

• 250 meters extending from 1.5 km to 3 km

• 500 meters extending from 3 km to 5 km14 Consistent with Section 4.2 of the TAD

, receptors were not placed on water bodies within the gridded

area

. This would include removing receptors on the adjacent Mississippi River. Figure 3

- 5 shows the

receptor grid for the modeling analysis.

Figure 3

- 5 . Dispersion modeling r eceptor g rid surrounding Burlington Generating Station.

Interpolated terrain elevations were input to the model using United States Geological Survey (USGS)

National Elevation Dataset (NED) data for Des Moines County in North American Datum 1983 (NAD83).

All receptors were assigned a terrain height and hill height using the terrain preprocessor AERMAP.



### 3.5. **Meteorological Data** 

Hourly meteorological data for the dispersion modeling analysis was preprocessed with the AERMET

program by the Iowa DNR

. The surface data was collected from the Burlington (KBRL) station with

upper air data from the Davenport NWS station (KDVN) for calendar years 2012 through 2014

. Based on

the results from a representivity study conducted by the Iowa DNR, 3 t hese meteorological data are

considered representative of the conditions near the Burlington Generating Station. Figure 3

- 6 shows

the 2012

- 2014 3

- year wind rose for the KBRL station.

3 The " 2005

- 2009 AERMOD Met Data Technical Support Document ” available at:

http:// www.iowadnr.gov/InsideDNR/RegulatoryAir/Modeling/DispersionModeling/MeteorologicalData.aspx15 Figure 3

- 6 . Burlington (KBR L ) 3

- year wind rose (2012

- 2014).



### 3.6. **Background Concentration** 

A 1

- h r SO 2 background concentration of 32 μ g/m 3 was added to the model design value for comparison

to the NAAQS. This background concentration was proposed in the submitted model ing protocol and

subsequently approved by the DNR and was derived using a multiple

- monitor average of design

concentrations from 2009

- 2011 data.

The model design value was used in conjunction with the conservative background concentration for

comparison to the NAAQS. For SO 2 , consistent with EPA guidance, the receptor with the highest 3

- year

average of the 99th percentile maximum daily 1

- hr modeled concentration was added to the

background concentration identified above. AERMOD internally calculates the 3

- year average of the

99 th percentile 1

- hr concentration at each receptor using the SO 2 pollutant keyword.



### 3.7. **Modeling Results** 

Following the AERMOD dispersion modeling app roach described above, Table 3

- 5 summarizes the

AERMOD output model design value, background concentration, and total concentration for comparison

to the 1

- hr SO 2 NAAQS. The maximum concentration of 92.9 μg/m 3 is less than the 1

- hr SO 2 NAAQS

. Adding 21.29 μ g/m 3 to the cumulative modeling results, to conservatively represent the Iowa Army

Ammunition Plant, still yields a total concentration ( 114.2 μ g/m 3 ) which meets the 1

- hr SO 2 NAAQS.

Table 3

- 5

. Model p redicted concentration ( μ g/m 3 ) for the Burlington Generation Station analysis.

Model Design

Value Background

Concentration Total

Concentration 1

- Hour SO 2

NAAQS Above NAAQS?

60.9 32 92.9 196 No16 

### 3.8. **Designation Recommendation**

The Burlington Generating Station will not cause or contribute to a modeled violation of the 1

- hr SO 2

NAAQS. Within Des Moines County there are two additional major (Title V) stationary source s (see

Figure 3

- 7 ) not previously discussed : Big River Resources West Burlington, LLC ; and Un ited States

Gypsum Co

. – Sperry . For calendar year 2014

, Big River Resources reported 68 tons of SO 2 emissions,

wh ile US Gypsum reported less than 1 ton. The 68 tpy emission rate represents only 3.4% of the 2,000

tpy threshold finalized in the Data Requirements Rule ( 80 FR 51051 ; August 21, 2015). There is one

additional major source within 20 km of Des Moines Count y’s borders, Natural Gas Pipeline Co

. o f

America

- Station 204 . The 2014 SO 2 emissions reported for thi s fa cility were less than 1 ton, which will

not affect the attainment status of the area.

Figure 3

- 7

. Major sources in and within 20 km ( as indicated by the red circle ) of Des Moines County.

Minor sources in the area do not emit a significant quantity of SO 2 and are adequately represented by

the background concentration included in the cumulative modeling results. No sources within Des

Moines County or within 20 km of the county’s border are expected to cause or contribute to a violation

of the 1

- hr SO 2 NAAQ S. Based on the technical review completed for this area all of Des Moines County

should be designated attainment for the 1

- hr SO 2 NAAQS.17 

## 4. **IPL**

**– Ottumwa**  **Generating Station** 

O ttumwa Generating Station is a coal

- fired electric generating facility located in Wapello County, Iowa

, (see Figure 4

- 1 ) and is operated by Interstate Power and Light (IPL), a subsidiary of Alliant Energy

. There

are no ambient SO 2 monitors near Ottumwa Generating Station that can be relied upon to characterize

the air quality around the source. Instead, dispersion modeling was conducted. Based on the DNR’s

technical review of this facility an attainment recommendation for all of Wapello County is appropriate.

Figure 4

- 1

. Location of IPL’s Ottumwa Generating Station. (All Counties shown are in Iowa.)



### 4.1. **Source Characterization**  **and Emission**  **Rates**

The SO 2 emission sources at Ottumwa Generating Station are a coal

- fired main boiler and a fuel oil

- fired

auxiliary boiler for house heating. The emergency generator is an intermittent emission source that will

be excluded in this modeling analysis pursuant to Section 5.4 of EPA’ s draft “ SO 2 NAAQS Designations

Modeling Technical Assistance Document ” (TAD ), dated December 2013.

The SO 2 emission rates used in the modeling analysis are summarized in Table 4

- 1

. The emission rates

reflect a mix of existing limits and actual hourly emissions

.18 Table 4

- 1

. Ottumwa Generating Station m odeled SO 2 e mission r ates

.

Model

ID SO 2 Emission

Points Rated

Capacity

(MMBtu/hr) SO 2 Limit Notes Modeling

Emission

Rate (lb/hr)

EP1 Main Boiler 8669 0.2 lb/MMBtu Actual Emissions Varies

Hourly ‡

EP67 Plant Heat

Boiler 77.413 0.10143 lb/MMBtu Existing Oper ating

Limit, 0.1% sulfur 7.852

‡ The SO 2 emission rate for the main boiler, EP1, is based on actual reported CEMS data provided by IPL for the

period 2012

- 2014.

Table 4

- 2 summarizes the stack characteristic s used in the 1

- hr SO 2 modeling demonstration. T he GEP

stack height was conservatively modeled for the main boiler stack (EP1) even though the GEP stack

height was lower than the actual stack height

.

Table 4

- 2

. Ottumwa Generating Station p oint s ource e xhaust c haracteristics

.

Model

ID UTM

Easting

(m) UTM

Northing

(m) Base

Elevation

(m) Stack Height

(m) Stack

Diameter

(m) Exhaust

Temperature

(K) Exhaust

Velocity

(m/s)

EP1 537387.3 4549481.6 208.12 152.5 7.62 344.3 29.39

EP67 537421.6 4549359 197.9 66.75 1.22 477.6 1.74



### 4.2. **Nearby Sources**  **of SO**  **2**

The SO 2 emission levels from all facilities within 10 km were evaluated to determine if additional sources

of SO 2 should be included in the modeling analysis. Table 4

- 3 summarizes the sources within 10 km of

Ottumwa Generating Station and their recent SO 2 emissions

. Any source that would contribute a

significant portion of the total SO 2 emissions in the area was identified to be included in the modeling

analysis. The total average emissions for the area were 13,105 .0 tpy, of which Ottumwa Generating

Station is the primary contributor at 87 .3 % and Cargill , Inc.

– Eddyville (Cargill) a secondary contributor

at 12.7 %

. All other sources combined only contribute 0.005%. Based on this information both Ottumwa

Generating Station and Cargill should be included in the analysis.

A fter further investigation it was determined that Cargill will no longer contribute a significant amount

of SO 2 emissions to the area. Cargill recently had two new natural gas

- fired boilers permitted to replace

the three existing coal

- fired boilers that currently acco unt for approximately 94% of the potential SO 2

emissions from the plant. This change from the three coal

- fired boilers to the two natural gas

- fired

boilers will result in over a 99% reduction in SO 2 emissions from Cargill’s boilers

. When the transition

from coal to gas is complete in the fall of 2015, the quantity of SO 2 emissions from Cargill

, in

combination with the six other facilities found within the 10 km radius of the Ottumwa Generating

Station

, will be approximately 1% of the total emissions from Ottumwa Generating Station

. These low

levels of SO 2 emissions should be adequately represented in the background concentration. Therefore

no other sources within 10 km were included in the modeling analysis.

In addition, a search was performed for major sources of SO 2 within 10

- 20 km. One additional facility

was identified during this search , John Deere Ottumwa Works

. For calendar year 2014 John Deere19 reported less than 1 ton of SO 2 emissions, therefore , only Ottumwa Generating Station was include d in

this modeling analysis.

Table 4

- 3

. Facilities within 10 km of Ottumwa Generating Station

.

SO 2 Emissions (tpy) ‡

Facility Name Address 2012 2013 2014 Most Recent

(or a verage)

Ajinomoto Heartland

Inc. 1 Heartland Dr.

Eddyville, IA 52553 0.61 0.65 0.49 0 .58

Cargill Inc.

- Eddyville 1 Cargill Dr.

Eddyville, IA 52553 1,626.5 1,771.6 1,576.5 1,658.2

The American Bottling

Company 14955 Truman Street

Ottumwa, IA 52501 - - - 0.02

Ideal Ready Mix Co Inc.

- Eddyville 17535 Monroe Wapello

Rd.

Eddyville, IA 52553 - - - 0.00

Chamness Technology

Inc. 24820 160th St.

Eddyville, IA 52553 - - - 0.03

Al

- jon Inc. 15075 Al

- Jon Ave.

Ottumwa, IA 52501 - - - 0.00

Ottumwa Generating

Station

- Alliant Energy 20775 Power Plant Rd.

Ottumwa, IA 52501 11,985.0 13,125.8 9,227.4 11,446.1

Wacker Chemical

Corporation 1 Wacker Dr.

Eddyville, IA 52553 0.07 0.07 0.08 0 .07

Total Average Emissions 13,105 .0

‡ Major sources report emissions every year while minor sources report at most once every three years. If the

latest available inventory for a minor source predates 2012 then the facility’s emissions are listed only in the

“Most Recent” column. The “Most Recent” column also includes the 3

- year average emission rates for major

sources.



### 4.3. **Dispersion Model** 

The EPA recommended American Meteorological Society (AMS)/EPA Regulatory Model (AERMOD) was

used to perform the analysis. The most current version (Version 1 5181 ) of AERMOD available at the

time of the analysis was used with regulatory default options as recommended in the EPA Guideline on

Air Quality Models. The following supporting pre

- processing programs for AERMOD were also used:

• BPIP

- Prime (Version 04274)

• AERMET (Version 14134)

• AERMAP (Version 11103)

AERMOD is a steady

- state plume model that simulates air dispersion based on planetary boundary layer

turbulence structure and scaling concepts, including treatment of both surface and elevated sources,

and both simple and complex terrain

. This model is recommended for short

- range (< 50 kilometers

[km]) dispersion from the source

. The model incorporates the Plume Rise Model Enhancement (PRIME)

algorithm for modeling building downwash

. AERMOD is designed to accept input data prepared by two

specific pre

- processor pr ograms, AERMET and AERMAP

. AERMOD was run with the following options:20 • Regulatory default options

• Direction

- specific building downwash characterized by BPIP

- PRIME

• Actual receptor elevations and hill height scales obtained from AERMAP

• SO 2 pollutant keyword



### 4.4. **Receptor Grid** 

Receptors were sited outside of the fence line boundary of the Ottumwa Generating Station. Figure 4

- 2

shows the receptor grid for the modeling analysis. Receptor placement grid spacing was:

• 50 meters along the facility fence line

• 50 meters from the fence line to 0.5 km

• 100 meters extending from 0.5 km to 1.5 km

• 250 meters extending from 1.5 km to 3 km

• 50 0 meters extending from 3 km to 5 km21 Figure 4

- 2 . Dispersion modeling r eceptor g rid surrounding Ottumwa Generating Station.

Interpolated terrain elevations were input to the model using United States Geological Survey (USGS)

National Elevation Dataset (NED) data for Wapello County in North American Datum 1983 (NAD83). All

receptors were assigned a terrain height and hill height using the terrain preprocessor AERMAP.



### 4.5. **Meteorological Data** 

Hourly meteor ological data for the dispersion modeling analysis was preprocessed with the AERMET

program by the Iowa DNR

. The surface data was collected from the Ottumwa (KOTM) station with

upper air data from the Davenport NWS station (KDVN) for calendar years 2012 through 2014

. Based on

the results from a representivity study conducted by the Iowa DNR, 4 t hese meteorological data are

4 The " 2005

- 2009 AERMOD Met Data Technical Support Document ” available at:

http://www.iowadnr.gov/InsideDNR/RegulatoryAir/Modeling/DispersionModeling/MeteorologicalData.aspx22 considered representative of the conditions near the Ottumwa Generating Station

. Figure 4

- 3 shows the

2012

- 2014 3

- year wind rose for the KOTM station.

Figure 4

- 3

. Ottumwa ( KOTM ) 3

- year wind rose (2012

- 2014).



### 4.6. **Background Concentration** 

A 1

- hr SO 2 background concentration of 32 μ g/m 3 was added to the model design value for comparison

to the NAAQS. This background concentration was proposed in the submitted modeling protocol and

subsequently approved by the DNR and was deriv ed using a multiple

- monitor average of design

concentrations from 2009

- 2011 data.

The model design value was used in conjunction with the conservative background concentration for

comparison to the NAAQS

. For SO 2 , consistent with EPA guidance, the receptor with the highest 3

- year

average of the 99 th percentile maximum daily 1

- hr modeled concentration was added to the background

concentration identified above

. AERMOD internally calculates the 3

- year average of the 99 th percentile

1

- hr concentration at each receptor using the SO 2 pollutant keyword.



### 4.7. **Modeling Results** 

Following the AERMOD dispersion modeling approach described above, Table 4

- 4 summarizes the

AERMOD output model design value, background concentration, and total concentration for comparison

to the 1

- hr SO 2 NAAQS. The maximum concentration of 139.4 μg/m 3 is less than the 1

- hr SO 2 NAAQS.

Table 4

- 4

. Model predicted concentration ( μ g/m 3 ) for the Ottumwa Generation Station analysis.

Model Design

Value Background

Concentration Total

Concentration 1

- Hour SO 2

NAAQS Above NAAQS?

107.4 32 139.4 196 No23 

### 4.8. **Designation Recommendation**

The Ottumwa Generating Station will not cause or contribute to a modeled violation of the 1

- hr SO 2

NAAQS. All major sources within Wapello County were previously discussed

. There are three major

(Title V) stationary source s (see Figure 4

- 4 ) within 20 km of Wapello County’s borders not previously

discussed : Fairfield Casting, LLC; ANR Pipeline Co

- Birmingham Compressor; and Clow Valve Company

. These three fac ili ties emitted a combined 11.5 tons of SO 2 in 2014, wi th the largest source emitting 8.5

tons, which is less than 0.5% of the 2,000 tpy threshold finalized in the Data Requirements Rule.

Figure 4

- 4 . Major sources in and within 20 km ( c rudely indicted by the red outline ) of Wapello County.

Minor sources in the area do not emit a significant quantity of SO 2 and are adequately represented by

the background concentration included in the cumulative modeling results. No sources within Wapello

County or within 20 km of the county’s border are expected to cause or contribute to a violation of the

1

- hr SO 2 NAAQS. Based on the technical review completed for this area all of Wapello County should be

designated attainment for the 1

- hr SO 2 NAAQS.24 

## 5. **MidAmerican**

**– George**  **Neal South** 

George Neal South is a coal

- fired electric generating facility located in Woodbury Count y, Iowa

, (see

Figure 5

- 1 ) and is operated by MidAmerican Energy Company (MidAmerican)

. While there is an ambient

SO 2 monitor (ID 19

- 193

- 0020 ) in Woodbury County it is sited near the George Neal North facility

. George Neal North is also operated by MidAmerican and is classified as a coal

- fired electric generating

facility

. The George Neal North monitor began operation in July 2012 and three calendar years of a data

are not yet available to compute a design value

. As an alternative

, d ispersion modeling was conducted

to characterize air quality for the area. Based on the DNR’s technical review of this facility an

attainment recommendation for all of Woodbury County is appropriate.

Figure 5

- 1

. Location of MidAmerican’s George Neal facilities . Counties in Iowa are shaded slightly.



### 5.1. **Source Characterization**  **and Emission**  **Rates**

The MidAmerican George Neal South and George Neal North f acilities include a number of emission

units that emit SO 2

. All emission units modeled in AERMOD were characterized as point sources. Small

sources of SO 2 , such as emergency generators and comfort heating, were not included in the analysis.

The emission units were modeled at their maximum potential SO 2 hourly emission rate, except George

Neal South Unit 4 and George Neal North Unit 3

. The paragraphs below summarize the development of

the emission factors for these units

. Table 4

- 1 summarizes the emission rate modeled for each emission

unit and Table 4

- 2 summarizes the stack characteristics used in the 1

- hr SO 2 modeling demonstration.25 Table 5

- 1 . George Neal South and George Neal North modeled SO 2 emission rates. 5

Model ID SO 2 Emission Points Modeling Emission

Rate (lb/hr)

EP3 George Neal South Unit 4 3,396.7

EP001 George Neal North Unit 1 0.8018

EP002 George Neal North Unit 2 1.812

EP003 George Neal North Unit 3 2,707.5

EP301 George Neal North Unit 3 Auxiliary Boiler 0.03

Table 5

- 2

. George Neal South and George Neal North point source exhaust characteristics.

Model

ID UTM

Easting

(m) UTM

Northing

(m) Base

Elevation

(m) Stack

Height

(m) Stack

Diameter

(m) Exhaust

Temperature

(K) Exhaust

Velocity

(m/s)

EP3 222828.6 4688308.0 327.40 142.95 7.85 355.37 25.54

EP001 221572.3 4691127.5 327.61 68.58 2.87 433.15 39.47

EP002 221601.0 4691046.0 327.85 91.44 4.65 416.48 31.83

EP003 221397.6 4691272.0 322.34 121.92 6.10 355.37 28.40

EP301 221531.9 4691230.5 322.87 15.24 0.86 466.48 12.31

In 2014 George Neal South Unit 4 and George Neal North Unit 3 installed SO 2 s crubbers; the

corresponding permitted emission limit with scrubber technology is based on a 30

- day rolling average of

2,760 lb/hr and 2,200 lb/hr for George Neal South Unit 4 and George Neal North Unit 3, respectively. An

evaluation of the current 30

- day rolling permit limits for both emission units was conducted to develop

an hourly emission rate which would preserve the variability of the hour

- to

- hour emission profile with

scrubber controls, yet be conservative to protect the ambient air quality standard for the attainment

demonstration. This approach relies on the EPA Guidance for 1

- Hour SO2 Nonattainment Area [State

Implementation Plan] Submissions me morandum. Based on that guidance a review of continuous

emissions monitoring system ( CEM S) data for similar MidAmerican units with similar control technology

was conducted to assist in establishing an appropriate emission rate for this modeling . Surrogate units

must be used since George Neal South Unit 4 and George Neal North Unit 3 do not have 3

- years of

corresponding SO 2 CEMS data after installation of the scrubber controls.

Walter Scott, Jr. Energy Center Unit 3 and Louisa Generating Station are coal

- fired boilers similar to

George Neal South Unit 4 and George Neal North Unit 3. Walter Scott, Jr. Energy Center Unit 3 and

Louisa Generating Station have CEMS data available that reflects scrubber operation

. The EPA guidance

allows an evaluation of the data to determine a corresponding ratio to apply to the 30

- day limits

. The

steps below outline the approach:

1. Collect 5

- years of suitable hourly CEMS data

.

2. Calculate the 99 th percentile 1

- hr emission rate , over the 5

- year period

.

5 Emission rates modeled for George Neal Nor th Unit 1 and George Neal North Unit 2 reflect potential emissions

with natural gas. These units are required to cease utilization of coal as a fuel by April 16, 2016, per a consent

agreement between MidAmerican and the Sierra Club.

The George Neal North Auxiliary Boiler wa s under construction at the time of modeling. This unit is scheduled

to become operational in the fall of 2015. The modeled emission rate represents emissions at maximum design

capacity while using natural gas fuel, as permitted.26 3. Calculate the 99 th percentile 30

- day rolling average, over the 5

- year period.

4. Calculate the ratio of the 99 th p ercentile 30

- day rolling average from Step 3 to the 99 th percentile 1

-

hr value calculated from Step 2.

5. Apply that calculated ratio to the similar unit 30

- day rolling limit that does not have corresponding

CEMS data to back

- calculate the corresponding hourly emission rate to model (the permitted 30

- day

r olling limit divided by the calculated ratio).

Based on the procedure outlined above, the ratios at Walter Scott, Jr. Energy Center Unit 3 and Louisa

Generating Station are ~ 0.817 and ~ 0.80 8

, respectively

. The average of the two ratio s, 0.8125 5

, was

divided into the 30

- day rolling limits for the George Neal South Unit 4 and George Neal North Unit 3 to

compute the hourly SO 2 emission rate s used in the modeling analysis (and shown in Table 5

- 1 )

.



### 5.2. **Nearby Sources**  **of SO**  **2**

The SO 2 emission levels from all facilities within 10 km were evaluated to determine if additional sources

of SO 2 should be included in the modeling analysis. Table 5

- 3 summarizes the sources within 10 km of

George Neal South. Any source that would contribute a significant portion of the total SO 2 emissions in

the area was identified to be included in the modeling analysis. The total average emissions for the area

were 21,967.4 tpy, of which George Neal South is the primary contributor at 62.5% and George Neal

North a secondary contributor at 37.5%. All other sources combined only contribute 0.009%. Therefore

both George Neal South and George Neal North were included in the modeling analysis but no other

sources within 10 km were included.

In addition, a search was performed for major sources of SO 2 within 10

- 20 km. One additional facility

was identified during this search, Sioux City Brick and Tile. This facility had a maximum SO 2 emission

rate of 89.26 tpy during the three

- year period 2012

- 2014 and an average of 73.97 tpy. When this

average is added to the total average emissions from all sources within 10 km of George Neal South this

accounts for only 0.3% of the total emissions in the area. For this reason, and the fact that it is 12 km

away, Sioux City Brick and Tile was screened out of the modeling analysis.

The State of Nebraska was also contacted to determine if there were any facilities that would need to be

included from that state. No such sources were identified.

Table 5

- 3

. Facilities within 10 km of George Neal South.

SO 2 Emissions (tpy) ‡

Facility Name Address 2012 2013 2014 Most Recent

(or a verage)

MidAmerican

- Neal

South 2761 Port Neal Rd.

Salix, IA 51052 14,272.8 20,099.4 6,813.3 13728.5

MidAmerican

- Neal

North Energy Center 1151 260th St.

Sergeant Bluff, IA 51054 9788 8421.2 6501.2 8,236.8

CF Industries

- Port Neal

Complex 1182 260th St.

Sergeant Bluff, IA 51054 2.56 1.41 1.3 1.76

Gelita USA Sioux City 2445 Port Neal Rd.

Sergeant Bluff, IA 51054 0.18

- - -

Ag Processing, Inc.

-

Sergeant Bluff 2735 Port Neal Rd.

Sergeant Bluff, IA 51054 0.18 0.14 0.08 0.1327 Sabre Industries Towers

And Poles 7101 Southbridge Dr.

Sioux City, IA 51111 - 0.01

- -

Nutra

- Flo Company

- Sergeant Bluff: Nulex 2717 Port Neal Rd.

Sergeant Bluff, IA 51054 - - - 0

Total Average Emissions 21,967.4

‡ Major sources report emissions every year while minor sources report at most once every three years. If the

latest available inventory for a minor source predates 2012 then the facility’s emissions are listed only in the

“Most Recent” column. The “Most Recent” column also includes the 3

- year average emission rates for major

sources.



### 5.3. **Dispersion Model** 

The EPA recommended American Meteorological Society (AMS)/EPA Regulatory Model (AERMOD) was

used to perform the analysis. The most current version (Version 14134) of AERMOD available at the

time of the analysis was used with regulatory default options as recommended in the EPA Guideline on

Air Quality Models. The following supporting pre

- processing programs for AERMOD were also used:

• BPIP

- Prime (Version 04274)

• AERMET (Version 14134)

• AERMAP (Version 11103)

AERMOD is a steady

- state plume model that simulates air dispersion based on planetary boundary layer

turbulence structure and scaling concepts, including treatment of both surface and elevated sources,

and both simple and complex terrain

. This model is recommended for short

- range (< 50 kilometers

[km]) dispersion from the source

. The model incorporates the Plume Rise Model Enhancement (PRIME)

algorithm fo r modeling building downwash

. AERMOD is designed to accept input data prepared by two

specific pre

- processor programs, AERMET and AERMAP

. AERMOD was run with the following options:

• Regulatory default options

• Direction

- specific building downwash characterized by BPIP

- PRIME

• Actual receptor elevations and hill height scales obtained from AERMAP

• SO 2 pollutant keyword



### 5.4. **Receptor Grid** 

Receptors were sited outside of the fence line boundary of the George Neal South and George Neal

North facilities

. Receptor placement grid spacing was:

• 50 meters along the facility fence line

• 50 meters from the fence line to 0.5 km

• 100 meters extending from 0.5 km to 1.5 km

• 250 meters extending from 1.5 km to 3 km

• 500 meters extending from 3 km to 5 km

Consistent with Section 4.2 of EPA’s TAD

, receptors were not placed on water bodies within the gridded

area. This would include removing receptors on the adjacent Missouri River. Figure 5

- 2 shows the

receptor grid for the modeling analysis.28 Figure 5

- 2 . Dispersion modeling r eceptor g rid surrounding George Neal South.

Interpolat ed terrain elevations were input to the model using United States Geological Survey (USGS)

National Elevation Dataset (NED) data for Woodbury County in North American Datum 1983 (NAD83).

All receptors were assigned a terrain height and hill height using the terrain preprocessor AERMAP.



### 5.5. **Meteorological Data** 

Hourly meteorological data for the dispersion modeling analysis was preprocessed with the AERMET

program by the Iowa DNR

. The surface data was collected from the Sioux City (KSUX) station with upper

air data from the Omaha NWS station (KOMA) for calendar years 2012 through 2014

. Based on the29 results from a representivity study conducted by the Iowa DNR, 6 t hese meteorological data are

considered representative of the conditions near the George Neal South and George Neal North

facilities. Figure 5

- 3 shows the 2012

- 2014 3

- year wind rose for the KSUX station.

Figure 5

- 3

. Sioux City (KSUX) 3

- year wind rose (2012

- 2014).



### 5.6. **Background Concentration** 

The statewide default 1

- hr SO 2 background concentration of 32 μ g/m 3 was added to the model design

value for comparison to the NAAQS. The background c oncentration was derived using a multiple

monitor average of design concentrations from 2009

- 2011 data.

The model design value was used in conjunction with the conservative background concentration for

comparison to the NAAQS

. For SO 2 , consistent with EPA guidance, the receptor with the highest 3

- year

average of the 99 th percentile maximum daily 1

- hr modeled concentration was added to the background

concentration identified above

. AERMOD internally calculates the 3

- year average of the 99 th percentile

1

- hr concentration at each receptor using the SO 2 pollutant keyword.



### 5.7. **Modeling Results** 

Following the AERMOD dispersion modeling approach described above, Table 5

- 4 summarizes the

AERMOD output model design value, background concentration, and total concentration for comparison

to the 1

- hr SO 2 NAAQS. The maximum concentration of 194.8 μg/m 3 is less than the 1

- hr SO 2 NAAQS.

6 T he " 2005

- 2009 AERMOD Met Data Technical Support Document ” available at:

http://www.iowadnr.gov/InsideDNR/RegulatoryAir/Modeling/DispersionM odeling/MeteorologicalData.aspx30 Table 5

- 4

. Model predicted concentration ( μ g/m 3 ) for the George Neal South analysis.

Model Design

Value Background

Concentration Total

Concentration 1

- Hour SO 2

NAAQS Above NAAQS?

162.8 32 194.8 196 No



### 5.8. **Designation Recommendation**

T he George Neal South and George Neal North facilities will not cause or contribute to a modeled

violation of the 1

- hr SO 2 NAAQS

. Within Woodbury County there is one additional ma jor (Title V)

stationary source (see Figure 5

- 4 ) no t previously discussed , Cargill Inc.

– Sioux City. For calendar year

2014

, Cargill reported l ess than 1 ton of SO 2 emi ssions , which will no t affect the attainment status of the

area. The re is one additional major source within 20 km of Woodbury County’s border s , Prairie Sun

Foods (previously Plymouth Energy , LLC ). Again

, the 2014 SO 2 emissions from th is facility w ere less than

1 ton

.

Figure 5

- 4 . Major sources in and within 20 km (as indicated by the red circle) of Woodbury County.

Minor sources in the area do not emit a significant quantity of SO 2 and are adequately represented by

the background concentration inclu ded in the cumulative modeling results. No sources within

Woodbury County or within 20 km of the county’s border are expected to cause or contribute to a

violation of the 1

- hr SO 2 NAAQS. Based on the technical review compl eted for this area all off

Woodbury County should be designated attainment for the 1

- hr SO 2 NAAQS.