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Draft Technical Support Document (TSD)

Iowa

Area Designations For the 

2010 SO2 Primary National Ambient Air Quality Standard

Summary

Pursuant to section 107(d) of the Clean Air Act (CAA), EPA must initially designate areas as either 

“unclassifiable”, “attainment”, or “nonattainment” for the 2010 1-hour sulfur dioxide (SO2) primary 

national ambient air quality standard (NAAQS). The CAA defines a nonattainment area as one that does 

not meet the NAAQS or that contributes to poor air quality in a nearby area that does not meet the 

NAAQS. Table 1 below identifies the counties or portions of counties (or Indian Country) in Iowa that 

EPA intends to initially designate “nonattainment” based on monitored violations. 

Table 1. Nonattainment Area Designations for Iowa

County Name

Iowa Recommended 

Designation of 

Areas/Counties

EPA’s Intended Designation 

of Areas/Counties

Muscatine Unclassifiable Nonattainment

Background

On June 2, 2010, EPA revised the primary SO2 NAAQS (75 FR 35520, June 22, 2010) by establishing a 

new 1-hour standard at a level of 75 parts per billion (ppb) which is attained when the 3-year average of 

the 99th percentile of the daily maximum 1-hour average concentration at each monitor in an area does 

not exceed 75 ppb. EPA has determined that this is the level necessary to provide protection of public 

health with an adequate margin of safety, especially for children, the elderly and those with asthma. 

These groups are particularly susceptible to the health effects associated with breathing SO2. The 

Agency is revoking the two prior primary standards of 140 ppb evaluated over 24-hours, and 30 ppb 

evaluated over an entire year because the standards will not add additional public health protection given 

a 1-hour standard at 75 ppb. Accordingly, EPA is not designating areas in this process on the basis of 

either of these two prior primary standards. Similarly, the secondary standard for SO2 has not been 

revised, so EPA is not designating areas in this process on the basis of the secondary standard.

EPA’s SO2 Designation Approach

Section 107(d) of the CAA requires that not later than 1 year after promulgation of a new or revised 

NAAQS, state Governors must submit their recommendations for designations and boundaries to EPA. 

This deadline was in June, 2011. Section 107(d) also requires EPA to provide a notification to states of 

no less than 120-days prior to promulgating an initial area designation that is a modification of a state’s 

recommendation. EPA has reviewed the State’s recommendations and has notified the State 
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Commissioner through letter signed by the Regional Administrator of any intended modifications. If a 

State or Indian Country did not submit designation recommendations, EPA will promulgate the 

designations that it deems appropriate. If a state or Indian Country disagrees with EPA’s intended area 

designations, they have an opportunity to demonstrate why any proposed modification is inappropriate.

Designations guidance was issued by EPA through a March 24, 2011, memorandum from Stephen D. 

Page, Director, U.S. EPA, Office of Air Quality Planning and Standards, to Air Division Directors, U.S. 

EPA Regions I-X. This memorandum identifies factors EPA intends to evaluate in determining 

boundaries for areas designated nonattainment. These 5 factors include: 1) Air quality data; 2) 

Emissions and emissions-related data (location of sources and potential contribution to ambient SO2

concentrations); 3) Meteorology (weather/transport patterns); 4) Geography/topography (mountain 

ranges or other air basin boundaries); and 5) Jurisdictional boundaries (e.g., counties, air districts, preexisting nonattainment areas, reservations, metropolitan planning organization), among any other 

information deemed relevant to establishing appropriate area designations and boundaries for the 1-hour 

SO2 NAAQS.

The March 24, 2011, memo recommended that area boundaries be defaulted to the county boundary 

unless additional provided information justifies a larger or smaller boundary than that of the county. 

EPA believes it is appropriate to evaluate each potential area on a case-by-case basis, and to recognize 

that area-specific analyses conducted by states, Indian Country and/or EPA may support a different

boundary than a default county boundary.

In this TSD, EPA discusses its review and technical analysis of the recommendations submitted by the 

states and/or Indian Country for designations of the 1-hour SO2 standard and any modifications from 

these recommendations.

Definition of important terms used in this document:

1) Designated “nonattainment” area – an area which EPA has determined, based on a state 

recommendation and/or on the technical analysis included in this document, has violated the 2010 SO2

NAAQS, or contributes to a violation in a nearby area. 

2) Recommended nonattainment area – an area a State or Indian Country has recommended to EPA 

be designated as nonattainment.

3) Violating monitor – an ambient air monitor meeting all methods, quality assurance and citing criteria 

and requirements whose valid design value exceeds 75 ppb, as described in Appendix T of 40 CFR part 

50.

4) 2010 SO2 NAAQS - 75 ppb, national ambient air quality standard for SO2 promulgated in 2010. 

Based on the 3-year average of the 99th percentile of the annual distribution of daily maximum 1-hour 

average concentrations

5) Design Value – a statistic that describes the air quality status of a given area relative to the level of 

the NAAQS.
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Nonattainment Designations

Introduction

In Iowa’s designation recommendation letter to EPA, dated June 2, 2011, Terry E. Branstad, Governor 

of Iowa, recommended that 5 counties be designated as attainment for the 2010 SO2 NAAQS based on 

monitored air quality data from 2008-2010, with all other counties designated as unclassifiable. 

Based on EPA’s technical analysis, EPA is intending to designate 1 county in the State of Iowa as 

nonattainment (Table 1). 

The 5 factors were used to analyze the nonattainment area for 1-hour SO2 designations:

1. Air quality data. We reviewed SO2 air quality monitoring data from EPA’s Air Trends website 

(see http://www.epa.gov/airtrends/values.html), including the design value calculated for the

monitor in Muscatine County, Iowa for the years 2008 - 2010. A monitor’s design value 

indicates whether that monitor attains a specified air quality standard. The 2010 SO2 NAAQS is

met at a monitoring site when the identified design value is valid and less than or equal to 75 ppb 

as described in Appendix T of 40 CFR Part 50; however, data from the Musser Park monitor in 

Muscatine, IA could not be validated using the standard procedure found in Appendix T because 

a substantial amount of data had been flagged from the years 2008, 2009 and 2010. 

The data was flagged as a result of a malfunction of the internal calibration system of the 

monitor. The malfunction wasn’t detected immediately and the monitor continued to collect data 

for over a year. The malfunction was discovered following performance of a reference 

procedure on the monitor’s SO2 calibration system. Following the reference procedure a 

reference audit was completed which informed IDNR and EPA that the monitor had been 

operating out of specification. Following the audit, EPA and IDNR reviewed the results and 

jointly agreed to: 1) adjust the original recorded values to account for the calibration error; 2) 

certify the adjusted values into the Air Quality System (AQS) database; and, 3) flag the adjusted 

data in the AQS database so it could not be used for regulatory purposes. 

Due to the large amount of flagged data the Musser Park monitor no longer met the minimum 

data completeness criteria for the period of time which we are using to evaluate compliance with 

the NAAQS. The completeness criteria specified in Appendix T of 40 CFR Part 50 requires 3 

years of complete data to establish a design value. A year is complete when all 4 quarters are 

complete. A quarter is complete when 75% of the days are complete. A day is complete when it 

has 75% of its hours. Although Appendix T of 40 CFR Part 50 includes data substitution 

provisions, due to the large amount of missing data from the Musser Park monitor, the data 

substitution provisions were not applicable. However, 40 CFR Part 50 Appendix T 3(d) allows 

the Administrator of EPA to consider other factors, such as consistency and levels of the valid 

concentration measurements that are available for the purpose of establishing a design value. 

The Appendix T 3(d) provision was applied in the Musser Park situation because the valid data 

recorded from the monitor for the number of years preceding and following the malfunction 

included sufficient high hourly measurements to demonstrate the ambient SO2 concentration in 

Muscatine, IA was significantly above the new health-based standard of the 2010 SO2 1-hr 
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primary NAAQS. In fact, in evaluating whether to apply the Appendix T 3(d) provision to the 

Musser Park data, EPA Region 7 took the most conservative approach possible and assumed that 

all the data that was flagged between the dates of August 30, 2008 to September 20, 2010 was 

zero (i.e., the monitor reported a zero 1-hr concentration of SO2 in the ambient air for the period

of malfunction). This approach resulted in a design value 123ppb, which exceeds the NAAQS 

by 150%, and demonstrates that the monitor is recording a violation of the 1-hr standard. 

2. Emissions and emissions-related data We reviewed data from the 2008 National Emissions 

Inventory (NEI), version 2 (NEI2008V2.0), which was the most current version of the national 

inventory available in 2011 when these data were compiled for the designations process, (see 

http://www.epa.gov/ttn/chief/net/2008inventory.html). EPA recognizes that there might be new 

information associated with any changes in emissions that may have occurred after 2008, and

will consider more recent years if available. For example, certain large sources of emissions in 

or near an area may have installed emission controls or otherwise significantly reduced 

emissions since 2008. Two source categories from the 2008 NEI were examined: the point 

source inventory and the nonpoint source inventory. Generally, the point source inventory 

represents the bulk of the SO2 emissions in Region 7.

3. Meteorology We evaluated meteorological data to help determine how weather conditions, 

including wind speed and direction, affect the plume of sources contributing to ambient SO2

concentrations. The National Weather Service maintains surface and upper air monitoring sites 

across the United States. Automated Surface Observing System (ASOS)

(http://www.weather.gov/asos) sites collect hourly averaged wind measurements including wind 

direction and wind speed. 

4. Geography/topography We examined the physical features of the land that might affect the 

distribution of SO2 over an area. River valleys, escarpments, or other physical features may 

affect the distribution of emissions, and may help define boundaries. Satellite images depicting 

river valleys and point sources were constructed and evaluated to determine the effects of the 

topography on point source emissions.

5. Jurisdictional Once the geographic area associated with the area violating the SO2 standard and 

the nearby area contributing to violations were determined, we considered existing jurisdictional 

boundaries for the purposes of providing a clearly defined legal boundary for carrying out the air 

quality planning and enforcement functions for the nonattainment area. If an existing 

jurisdictional boundary is used to help define the nonattainment area, it encompasses all of the 

area that has been identified as meeting the nonattainment definition. These existing boundaries 

may include an existing nonattainment or maintenance area boundary, a county or township 

boundary, a metropolitan area boundary, an air management district, or an urban planning 

boundary established for coordinating business development or transportation activities. Where 

existing jurisdictional boundaries are not adequate to describe the nonattainment area, other 

clearly defined and permanent landmarks or geographic coordinates are used.
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Nonattainment Designations

Technical analysis for Muscatine County, Iowa

Introduction 

This technical analysis for Muscatine County, Iowa identifies the entire county with a monitor (AQS ID 

191390020) that violates the 2010 SO2 NAAQS based on 2008-2010 data, and evaluates nearby counties 

for contributions to SO2 concentrations in the area. EPA has evaluated this county and nearby counties 

based on the weight of evidence of the factors recommended in the March 24, 2011, issued EPA 

guidance. 

Figure 1 is a map of the area in IA that EPA intends to designate nonattainment for the 2010 1-hr SO2

NAAQS including source information and the location of the monitor violating the standard. 

Figure 1. Muscatine County, IA Intended Nonattainment Boundary 
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Figure 2 is a map of the area analyzed showing the location of the air quality monitors in the area, the 

Muscatine County line in red, and large sources of SO2 in the greater Muscatine Co. area.

Figure 2: Muscatine County Showing SO2 Monitor and Sources of SO2

On June 2, 2011 Governor of Iowa, Terry E. Branstad, recommended that 5 counties in Iowa with SO2

monitors reporting ambient concentrations below the 75ppb standard be designated attainment and all 

other areas of the state be designated unclassifiable for the 2010 SO2 NAAQS based on monitored air 

quality data from 2008-2010. The state provided no further information or analysis supporting their

attainment recommendations other than the monitored values for the years 2008 through 2010. 

EPA, based on its technical analysis described below, is intending to designate one county in Iowa as 

nonattainment and to defer classifications for all other counties until a later date. EPA is proposing to 

designate all of Muscatine County, Iowa as nonattainment, based upon currently available information, 

and the application of 40 CFR Part 50 Appendix T 3(d). The county listed for nonattainment is listed 

above in Table 1.
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Detailed Assessment

Air Quality Data 

This factor considers the SO2 air quality monitoring data, including the design values (in ppb) calculated 

for all air quality monitors in Muscatine County and the surrounding area based on data for the 2008-

2010 period.

EPA Region 7’s proposal is based on data from (a) Federal Reference Method (FRM) or Federal 

Equivalent Method (FEM) monitor(s) located in the state. 

The 2011 SO2 NAAQS design values for all counties (containing a monitor) in the State of Iowa and 

surrounding area are shown in Table 2.

Table 2. Air Quality Data for All Monitors in the State of Iowa

County

State

Recommended

Nonattainment?

Monitor Name Monitor Air Quality

System ID

Monitor 

Location

SO2 Design Value,

2008-2010

(ppb)

Muscatine No Musser Park 191390020 Muscatine, IA 123*

Clinton No Chancy Park 190450019 Clinton 30

Linn No Scottish Rite 

Temple 191130031 Cedar Rapids 38

Polk No Public Health 

Building 191530030 Des Moines 3

Scott No Jefferson 

School 191630015 Davenport 10

Van Buren No Lake Sugema 191770006 Keosuaqua 5

* The DV is based on an application of the 40 CFR Part 50 Appendix T 3(d) providing authority for the Administrator to approve the use of an 

incomplete data set to establish a valid DV. 

The Musser Park monitor in Muscatine, IA shows a violation of the 2010 SO2 NAAQS. Therefore, EPA 

must determine the appropriate boundaries for the area surrounding the violating monitor to be 

designated nonattainment, otherwise by default EPA identifies the entire county as the area of 

nonattainment. The absence of a violating monitor alone is not a sufficient reason to eliminate nearby 

counties as candidates for inclusion in a nonattainment area as well. Each area has been evaluated based 

on the weight of evidence of the five factors and other relevant information. 

Emissions and Emissions-Related Data

Evidence of SO2 emissions sources in the vicinity of a violating monitor is an important factor for 

determining whether a nearby area is contributing to a monitored violation. For this factor, EPA 

evaluated county level emissions data for SO2 and any growth in SO2 emitting activities since the date 

represented by those emissions data.
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Emissions

EPA recognizes that there may be important new information on emissions levels for the period after 

2008, and would consider more recent information if available. EPA relied on verified emissions data 

currently available in the 2008 National Emissions Inventory (NEI) emissions database (NEI2008V2.0).

Table 3 shows total emissions of SO2 (given in tons per year) for violating and potentially contributing 

counties in and around the Muscatine County, Iowa including sources emitting greater than 100 tons per 

year of SO2 according to the 2008 NEI. The two IA counties adjacent to Muscatine, Co with sources

within 50 kilometers and emitting greater than 100 tons per year are found in Louisa County, IA, and 

Scott County, IA. The source in Louisa County is an electric generating unit owned and operated by 

MidAmerican Energy (the Louisa Power Station). The other source of SO2 (2,488 tons per year-not 

listed in the table 3 below) located outside of Muscatine Co. is Lafarge North America Cement Kiln in 

Buffalo, IA (Scott County) approximately 31.5 kilometers East-Northeast of the violating monitor. 

Based on the distance of these sources from the violating monitor, and the predominant wind patterns in 

the area at times violations are recorded at the monitor, these sources will not impact the monitor to 

cause a violation.

Table 3. Annual SO2 Emissions 2008

County Facility >80 tpy 

(EIS or State Facility ID) Facility Emissions (tpy)

Total County SO2

Emissions

(tons per year)

Muscatine

Grain Processing 

Corporation 14, 979

Central Iowa Power – Fair 

Station 7,068

Muscatine Power and 

Water 3,458

Monsanto Company 520

SSAB Iowa Inc 374

Gerdau Ameristeel US 80 26,479

Louisa Mid American – Louisa 

Station 2,453 2,453

Scott La Farge North American 2,488 2,488

Area Total 31,420

Emissions Controls

The emissions data used by EPA in this technical analysis and provided in Table 3 represent emissions 

levels taking into account any control strategies implemented on stationary sources in Muscatine and 

Louisa County up to and including the year 2008. EPA has not received any additional information on 

emissions reductions resulting from federally enforceable controls put into place after 2008. Emission 

control information for the sources identified in Table 3 is summarized below.

Grain Processing Corporation (GPC)

GPC processes grain for the production of food and liquor grade ethanol, as well as a variety of grain 

based food products and animal feeds. GPC is located 1.2 kilometers South-Southeast of the violating 

monitor. As part of the grain conversion and production process GPC operates a variety of boilers for 

heating and power production. GPC’s main source of SO2 emissions is emission point #1 (EP-1) which 
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includes boilers 1, 2, 3, 4, 6 and 7. The boilers range in heat input capacity from 105 – 230 MMBtu/hr. 

The boilers are capable of burning coal and natural gas. EP-1 is limited to 3915 lbs of SO2/hr (averaged 

over a 24-hour period) and 6 lb/MMBtu. EP-1 is not equipped with any SO2 control system. EP-1 is 

equipped with an SO2 continuous emission monitor (CEM). GPC operates four germ dryers. The germ 

dryers have the following SO2 emission limits: 13.73 lb/hr (EP-15), 9.20 lb/hr (EP-97), 0.53 lb/hr (EP126) and 500 ppm (EP-178). The germ dryers are not equipped with any SO2 control systems. EP-600 

is capable of burning biogas and natural gas. EP-600 is limited to 4.86 lb SO2/hr. EP-600 is equipped 

with a wet gas scrubber. GPC operates gluten flash dryer #4 (EP-173) which is capable of burning 

biogas. EP-173 has a heat input capacity of 29 MMBtu/hr. EP-173 is limited to no more than 4.5 lb 

SO2/hr. The dryer is equipped with a wet scrubber that is expected to achieve a 91.2% control efficiency 

while burning biogas. GPC operates four natural gas-fired “Power House Boilers” (EP-103, 104, 142

and 153) with heat input capacities that range from 120 – 124 MMBtu/hr. These boilers burn natural 

gas only and have an emission limit of 500 ppm. These units are not equipped with any SO2 control 

system. GPC operates an additional “Power House Boiler” (EP-177) with a heat input capacity of 360 

MMBtu/hr. This unit is limited to 500 ppm and 0.23 lb SO2/hr. This unit is also not equipped with any 

SO2 control system. GPC operates several small natural-gas fired emission units including dryers. 

These units are limited to 500 ppm SO2 and are not equipped with any SO2 control system.

Central Iowa Power Coop – Fair Station (CIPC)

Central Iowa Power Coop (Fair Station) is an electric generating facility that is located 25.4 kilometers 

East-Northeast of the violating monitor. CIPC’s main SO2 emission sources are EP-1 and EP-2.

EP-1 is a 280 MMBtu/hr boiler that is capable of burning coal and natural gas. EP-1 is limited to 6 lb 

SO2/MMBtu. EP-1 is not equipped with any SO2 control system. EP-1 is not equipped with a SO2

CEM. EP-2 is a 477 MMBtu/hr boiler that is capable of burning coal and natural gas. EP-2 is limited to 

6 lb SO2/MMBtu. EP-2 is not equipped with any SO2 control system. EP-2 is equipped with a SO2

CEM. CIPC also operates a small natural gas/diesel boiler and two small emergency generators.

Muscatine Power & Water (MPW)

MPW is a nonprofit public utility offering electric, water, and communications services to the greater 

Muscatine municipal area located 1.9 km South-Southeast of the violating monitor. MPW’s main SO2 

emission sources are electric generating units designated EP-70, EP-80 and EP-90. EP-70 is a 289 

MMBtu/hr boiler that is capable of burning coal and natural gas. EP-70 is limited to 6 lb SO2/MMBtu. 

EP-70 and EP-80 are also limited to a combined 2,772 lb SO2/hr (averaged over a 24-hour calendar day) 

and 12,141 tons SO2/yr. EP-70 is not equipped with any SO2 control system. EP-70 is equipped with a 

SO2 CEM. EP-80 is a 890 MMBtu/hr boiler that is capable of burning coal, natural gas, waste solvent 

(limited), diesel oil (limited) and waste oil (limited). EP-80 is limited to 6 lb SO2/MMBtu. EP-70 and 

EP-80 are also limited to a combined 2,772 lb SO2/hr (averaged over a 24-hour calendar day) and 

12,141 tons SO2/yr. EP-80 is not equipped with any SO2 control system. EP-80 is equipped with a SO2

CEM. EP-90 is a 1,556 MMBtu/hr boiler that is capable of burning coal and natural gas. EP-90 is 

limited to 0.56 lb SO2/MMBtu (averaged over a 24-hr calendar day) and 0.45 lb SO2/MMBtu (averaged 

over a 30-day period). EP-90 is also subject to a 92% reduction in SO2 from the flue gas desulfurization 

system (scrubbers CE-93 and CE-94). EP-90 is also subject to NSPS Da emission limits. As 

mentioned, EP-90 is equipped with two scrubbers (CE-93 and CE-94) that control SO2 emissions. EP90 is equipped with a SO2 CEM. MPW also operates several small diesel and gasoline-powered 

emission units.
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La Farge – North American

Lafarge's cement manufacturing plant located in Buffalo, IA main source of SO2 emissions is the 

preheater/precalciner/kiln/raw mill system (EP 0466-0) located approximately 31 kilometers East of the 

violating monitor in Muscatine, IA The cement processing plant has a capacity of 145.3 tons clinker per 

hour. EP 0466-0 is limited to 4,850 tons SO2/yr and 2,900 lb SO2/hr. EP 0466-0 is equipped with a dry 

absorbent addition system. EP 0466-0 is also equipped with an SO2 continuous emission monitor. 

Lafarge can burn a range of approved materials in the kiln.

Lafarge also has a couple of small fossil-fired emission units including a diesel-fired emergency 

generator and a diesel-fired water pump that are limited to 2.5 lb SO2/MMBtu limit and are not equipped 

with no controls.

MidAmerican Energy Company – Louisa Generating Station (MidAmerican)

MidAmerican Energy Company is a for profit power production company that operates an electric 

generating facility in Louisa County, IA 13.9 kilometers South-Southwest of the violating monitor, 

located in Muscatine County, IA. The Louisa generating station is just south of the Muscatine county 

line with a portion of its property lying across the county line. MidAmerican’s main SO2 emission 

source is EP-1 (Utility Boiler). MidAmerican also operates two auxiliary boilers (EP-2 and EP-3) and 

two emergency generators (EP-4 and EP-5). 

EP-1 is a 8,624 MMBtu/hr boiler that is capable of burning coal, #2 fuel oil and natural gas. EP-1 is 

limited to 0.96 lb SO2/MMBtu (BACT) (averaged over a 30-day period), 1.20 lb SO2/MMBtu (NSPS D) 

while burning solid fossil fuel, and 0.80 lb SO2/MMBtu (NSPS D) while burning liquid fossil fuel. EP-1 

is also limited to 3,450 lb SO2/hr (averaged over a 30-day period). The sulfur content of any coal is 

limited to 2.0 lb/MMBtu or less. EP-1 is equipped with a lime spray dryer flue gas desulfurization 

system (scrubber). EP-1 is equipped with a SO2 CEM. EP-2 and EP-3 are 98 MMBtu/hr boilers that are 

capable of burning natural gas and #2 fuel oil. EP-2 and EP-3 are limited to 98.3 lb SO2/hr each. The 

sulfur content of the fuel oil is limited to 0.5% by weight. EP-2 and EP-3 are not equipped with any SO2

control system. EP-2 and EP-3 are not equipped with an SO2 CEM. EP-4 and EP-5 are 16 MMBtu/hr 

emergency generators that are capable of #2 fuel oil only. EP-4 and EP-5 are limited to 8.4 lb SO2/hr 

each. The sulfur content of the fuel oil is limited to 0.5% by weight. EP-4 and EP-5 are not equipped 

with any SO2 control system. EP-4 and EP-5 are not equipped with an SO2 CEM.

Monsanto Company (Monsanto)

Monsanto is an agricultural services company that produces on-site power and heat at its product 

development facility approximately 9.0 kilometers South-Southwest of the violating monitor, 

Monsanto’s main SO2 emission sources are Boiler #6, #7 and #8. EP-33 (Boiler #6) is a 73 MMBtu/hr 

boiler that is capable of burning fuel oil and natural gas. EP-33 is limited to 36.6 lb SO2/hr. The amount 

of fuel oil EP-33 can combust is dependent on whether EP-45 is burning fuel oil. The sulfur content of 

the fuel oil is limited to 0.5% by weight. EP-33 is not equipped with any SO2 control system. EP-33 is 

not equipped with an SO2 CEM. EP-45 (Boiler #7) is a 124 MMBtu/hr boiler that is capable of burning 

fuel oil and natural gas. EP-45 is limited to 61.4 lb SO2/hr. The amount of fuel oil EP-45 can combust 

is dependent on whether EP-33 is burning fuel oil. The sulfur content of the fuel oil is limited to 0.5% 

by weight. EP-45 is not equipped with any SO2 control system. EP-45 is not equipped with an SO2

CEM. EP-195 (Boiler #8) is a 150 MMBtu/hr boiler that is capable of burning coal, sludge (limited) and 
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seed corn (limited). EP-195 is limited to 292.5 lb SO2/hr and 1.95 lb SO2/MMBtu (averaged over a 3-hr 

period). EP-195 is not equipped with any SO2 control system. EP-195 is equipped with an SO2 CEM.

EP-21 (Boiler #5) is a 73 MMBtu/hr boiler that is capable of natural gas only. EP-21 is limited to 500 

ppm SO2. Monsanto also operates several small natural gas-fired emission units and a small diesel 

emergency generator.

SSAB Iowa, Inc. (SSAB)

SSAB Inc. is a steel manufacturer that is located 21.6 kilometers East-Northeast of the violating 

monitor, SSAB’s main SO2 emission source is EP-1 (EAF/LMF). EP-1 is an electric arc furnace and a 

ladle metallurgy furnace. The electric arc furnace has a capacity of 200 tons of liquid steel/hr. EP-1 is 

limited to 0.70 lb SO2/ton of steel produced and 613.2 tons SO2/yr. EP-1 is not equipped with any SO2

control system. EP-1 is not equipped with an SO2 CEM. SSAB also operates a 371 MMBtu/hr furnace 

(EP-13) that burns natural gas only. EP-13 is limited to 0.52 lb SO2/hr and 2 tons of SO2/yr. SSAB also 

operates several small natural gas and diesel-fired emission units.

Gerdau Ameristeel US, Inc. (Gerdau)

Gerdau Ameristeel is a steel manufacturer that is located 20.5 kilometers North of the violating monitor. 

Gerdau’s main SO2 source is EP-01 (which includes the electric arc furnace). The electric arc furnace 

has a capacity of 90 tons of liquid steel/hr. EP-01 is limited to 70.2 lb SO2/hr and 190 tons SO2/yr. 

There are permit conditions that limit the amount of liquid steel processed, the carbon sources for the 

electric arc furnace and the amount of natural gas combusted. EP-01 is not equipped with any SO2

control system. EP-01 is not equipped with an SO2 CEM. Gerdau also operates a 150 MMBtu/hr Billet 

Reheat Furnace (EP-04). This furnace burns natural gas only. The SO2 emissions are limited to 500 

ppm. Gerdau also operates several small natural gas and diesel-fired emission units.

Meteorology (weather/transport patterns)

Evidence of source-receptor relationships between specific emissions sources and high SO2 values at 

violating monitors is another important factor in determining the appropriate contributing areas and the 

appropriate extent of the nonattainment area boundary. For this factor, EPA considered recent hourly or 

sub-hourly meteorological data from the site nearest to the violating monitor to determine which wind 

vectors might be associated with 1-hour SO2 exceedances. For Muscatine County, IA, the 

meteorological data used in this analysis were based on 2009-2011 data from the National Weather 

Service Station located 11.4 kilometers from the violating monitor. 

Figure 2 lists the frequency of wind direction and wind speed observations associated with the years 

2009 through 2011. The winds in Muscatine, IA over the three year period show a pattern of blowing 

consistently out of the West-Northwest or South-Southeast. Winds from the South-Southeast are in-line 

with SO2 sources located at GPC and Muscatine Power facilities. The GPC facility is the largest source 

of SO2 in Muscatine County and Muscatine Power is the third largest source. Additional SO2 sources in 

neighboring Louisa and Scott County are not close enough to the violating monitor nor are they inline 

with the predominant winds to impact the reading at the monitor on days exceedances are observed. I.e., 

During recorded exceedances at the Muscatine, IA monitor, the winds are coming predominantly from 

the south in a direction from GPC and Muscatine Power and Water.
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Figure 2: Wind Rose Analysis 2009-2011

Geography/Topography (mountain ranges or other air basin boundaries)

Muscatine County, IA does not have any significant geographical or topographical barriers significantly 

limiting air-pollution transport within its air shed; however, Muscatine County rests on the western 

shore of the upper Mississippi river. This factor did not play a significant role in determining the 

nonattainment boundary. The river valley created by the Mississippi River can impact local winds by 

channeling them along the valley north and south, and can serve to limit the impact of a particular 

source on a monitor sited in proximity to the river valley. In the case of Muscatine, as the Mississippi 

River flows south it makes a strong bend to the West across the Eastern edge of the county then abruptly 

turns South again at the City of Muscatine. IA. The existence of the river channel through across the 

Eastern edge of the county is not expected to impact the emissions observed at the violating monitor

located in Muscatine, IA.
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Jurisdictional Boundaries 

EPA reviewed jurisdiction boundary information, including townships, city limits, and a previous SO2

nonattainment boundary. EPA has elected to propose the nonattainment boundary as the Muscatine 

County line, which is the default boundary identified by EPA in its Designation Guidance. 

Other Relevant Information

EPA did not collect additional information relevant to establishing a nonattainment area boundary for 

this area and we believe the information included above is sufficient to satisfactorily establish an 

intended nonattainment area boundary for Muscatine County, IA.

Conclusion

The air quality monitor in Muscatine County shows a violation of the 2010 SO2 NAAQS, based on 

2008-2010 air quality data. As a result Muscatine County or some portion of Muscatine County must be 

designated as nonattainment. Based upon the consideration of all the relevant and available information, 

as described above, EPA believes that the boundaries described herein encompass the entire area of 

Muscatine County, Iowa that does not meet (or that contributes to ambient air quality in the area that 

does not meet) the 2010 SO2 NAAQS.