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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 designate areas as either 

“nonattainment,” “attainment,” or “unclassifiable” 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 in Iowa that EPA is initially

designating “nonattainment” based on monitored violations. EPA is not yet prepared to designate other 

areas in Iowa, and will address those other areas and their sources in a future final designations action.

Table 1. Nonattainment Area Designations for Iowa

County Name

Iowa Recommended

Designation of

Areas/Counties

EPA’s 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 met at an 

ambient air quality monitoring site when the 3-year average of the annual (99th percentile) of the

daily maximum 1-hour average concentrations do not exceed 75 ppb, as determined in accordance 

with Appendix T of 40 CFR part 50. 40 CFR 50.17(a)-(b). 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 provides that not later than 1 year after promulgation of a new or revised 

NAAQS, state Governors may 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 

Commissioner through a letter signed by the Regional Administrator of any intended modifications. If

a state does not submit designation recommendations, EPA will promulgate the designations that it 
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deems appropriate. If a state disagrees with EPA’s intended area designations, it has 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 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

State of Iowa 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, based on the most recent three years of air quality monitoring data, or contributes to a

violation in a nearby area.

2) Recommended nonattainment area – an area that a state or tribal government has recommended to 

EPA to 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 notified the Governor of Iowa (in the 120 day letter) of its 

intention to designate the entire county of Muscatine, Iowa as nonattainment (Table 1). In response to 

EPA’s 120-day letter explaining our intention of designating Muscatine County, Iowa as nonattainment, 

the Iowa Department of Natural Resources (IDNR) prepared and submitted a technical analysis rebutting 

our presumptive county-wide nonattainment boundary. This technical analysis examined several factors, 

including monitoring data, meteorological data, proximity and magnitude of emissions. As a component 

of the technical analysis, IDNR provided a windrose analysis of exceedance days that included the 

violating monitor at Musser Park and 2 additional SO2 monitors in the area. This windrose analysis 

identifies several SO2 sources in Muscatine County that contribute to the violating monitor at Musser Park. 

In addition to the daily windrose analysis, IDNR submitted hourly monitoring and wind direction 

information identifying the predominant SO2 source(s) causing the violation at the Musser Park monitor

and locating them to the south, within a revised nonattainment boundary IDNR proposed that EPA adopt.

Finally, although EPA is not relying upon it at this time, IDNR provided dispersion modeling that it 

believes would help inform the extent of the nonattainment boundary and included all major sources 

surrounding the Musser Park monitor along with a conservative background value. Upon reviewing the 

analysis provided by IDNR, EPA finds that a smaller than county-wide boundary is appropriate and that 

the boundary recommended by IDNR includes those sources that are appropriate to initially identify as 

contributing to the violation observed at the monitor. Therefore, EPA is finalizing the nonattainment 

boundary for Muscatine, Iowa proposed by IDNR. This boundary is based on violations observed at the 

Musser Park monitor and a design value established over the years 2009 and 2011. EPA is not yet 

reaching a conclusion concerning areas, and their sources, that are outside of the finalized nonattainment 

boundary, and will address these areas in a future final designations action.

Upon receipt of IDNRs recommendation and technical analysis supporting a smaller nonattainment 

boundary than proposed by EPA in our 120-day letter, we analyzed IDNR’s submission and integrated its

analysis, apart from IDNRs dispersion modeling, into the five factor analysis we prepared for Muscatine 

County in our 120-day letter. The five factor analysis prepared for the 120-day letter included a review of:

1. Air Quality Data

2. Emissions and Emissions Related Data

3. Meteorology

4. Geography and Topology

5. Jurisdictional Boundaries

This technical support document also includes an additional review of other relevant information supplied 

by the IDNR in its submission that contribute to the five factors analysis found in a later section. 
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Nonattainment Designations

Technical analysis for Muscatine County, Iowa

Introduction

This technical analysis for Muscatine County, Iowa identifies a portion of the county with a monitor

(AQS ID 191390020) that violates the 2010 SO2 NAAQS based on 2009-2011 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, EPA 

guidance.

Figure 1 is a map of the area in Iowa that EPA is initially designating 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 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 significant sources of SO2 in the greater Muscatine Co. area.

Figure 2: Muscatine County Showing SO2 Monitor and Sources of SO2
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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. At that time, the State provided no further information or analysis 

supporting its attainment recommendations other than the monitored values for the years 2008 through 

2010.

On February 6, 2013, EPA sent a letter to the Governor of Iowa notifying the State of our intention of 

designating all of Muscatine County, Iowa as the presumptive nonattainment boundary, and initiating the 

required 120-day minimum period for state review prior to EPA issuing a final designation. EPA’s 

proposal was based upon available monitoring data for the 3-year period of the monitor’s operation 

spanning years 2009 through 2011 indicating a violation at the Musser Park monitor, and the application 

of 40 CFR Part 50 Appendix T 3(d) to replace missing data during this 3-year period and allow for the 

calculation of a valid design value. 

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, even though the monitor was 

in place and operating for over the minimum necessary 3-year period, data from the Musser Park monitor

in Muscatine, Iowa 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 3-year period of time which we are using to evaluate compliance with the

NAAQS, even though the monitor had been in place and operating for well over the minimum 

necessary 3 years. The completeness criteria specified in Appendix T of 40 CFR Part 50 require 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 covering a monitor’s 3 years of operation.

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 that the ambient SO2 concentration in Muscatine, Iowa was 

significantly above the 2010 SO2 1-hr primary NAAQS. In fact, in evaluating whether to apply the
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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 daily concentration of SO2 in the ambient 

air for the period of malfunction). This approach resulted in a design value 127 ppb (when calculated for

the three year period of the monitor’s operation beginning on January 1, 2009 and ending on December

31, 2011), which exceeds the NAAQS by 150%, and demonstrates that the monitor is for that 3-year 

period recording a violation of the 1-hr standard.

In response to our proposed designation, IDNR prepared comments to our proposal recommending that 

EPA finalize a revised boundary that did not include the entire county. In this analysis, the state reviewed 

the impact at the monitor of sources emitting SO2 in and around all of Muscatine County, and found that

establishing a nonattainment boundary for the entire county was not warranted. IDNR has instead 

recommended that the EPA finalize a boundary that is approximately 1/3 the size of our proposed 

boundary. In this TSD, EPA discusses its review and technical analysis of the recommendations 

submitted by the State of Iowa for designations of the 1-hour SO2 standard and any modifications from 

these recommendations.

Detailed Assessment

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 2009 - 2011. This factor considers the SO2 air quality monitoring

data (found in EPA’s Air Trends website at http://www.epa.gov/airtrends/values.html), including the

design values (in ppb) calculated for all air quality monitors in Muscatine County and the surrounding

area based on data for the 2009-2011 period.

EPA’s final nonattainment boundary for Muscatine County, Iowa 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,

2009-2011

(ppb)

Muscatine No Musser Park 191390020 Muscatine, IA 127*

Clinton No Chancy Park 190450019 Clinton 21

Linn No 500 

11TH 191130040 Cedar Rapids 28

Polk No Public Health

Building

191530030 Des Moines 3

Scott No Jefferson

School 191630015 Davenport 13

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.
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The Musser Park monitor in Muscatine, Iowa shows a violation of the 2010 SO2 NAAQS. Due to the 

violating monitor, EPA must determine an appropriate boundary for the area surrounding the 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 significant change in SO2 emitting activities 

since the date represented by those emissions data.

Emissions

EPA relied on verified emissions data currently available in the 2008 National Emissions Inventory

(NEI) emissions database (NEI2008V3.0). Generally, the point source inventory found in the database

represents the bulk of the SO2 emissions in Region 7.

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

counties in and around Muscatine County, including sources emitting greater than 100 tons per year of

SO2 according to the 2008 NEI. The two Iowa counties adjacent to Muscatine County with sources 

within 50 kilometers and emitting greater than 100 tons per year are found in Louisa County, Iowa, 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 County is Lafarge North America Cement Kiln 

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

At the time of proposal, EPA was uncertain over the contribution or direct impact specific sources had 

on the violating monitor; however, windrose analysis (discussed in more detail later) provided by IDNR 

supports that emissions from Grain Processing Corporation (GPC), Muscatine Power and Water 

(MPW), and Monsanto Company are contributing to the violations recorded by the monitor.
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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

26,479

Central Iowa Power – Fair

Station 7,068

Muscatine Power and

Water 3160

Monsanto Company 520

SSAB Iowa Inc 374

Gerdau Ameristeel US 80

Louisa MidAmerican – 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

County and surrounding areas 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 

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.

In response to EPA’s 120-day letter and technical support document, IDNR notified EPA of the following 
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changes that have occurred at the GPC facility. The following sources were removed: EP-103.0, EP104.0, EP-542.0, and EP-543.0. The stack height for EP195.0 was increased to 66.5 feet. Two new 

sources were added (EP-546.0 and EP-548.0). And, the emissions from EP-551.0 were changed from 

internally-venting to a point source.

Central Iowa Power Coop – Fair Station (CIPCO)

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

East-Northeast of the violating monitor. CIPCO’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.

In response to EPA’s 120-day letter and technical support document, IDNR notified EPA that CIPCO is 

currently scheduled to cease operation in September of 2013. However, because EPA is not aware of an 

enforceable agreement that requires CIPCO to cease operation, CIPCO must be included in any analysis 

regarding its impact on the area exceeding the SO2 NAAQS.

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 subpart 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.

La Farge – North American

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

preheater/precalciner/kiln/raw mill system (EP-0466-0) located approximately 31 kilometers EastNortheast of the violating monitor in Muscatine, Iowa 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 
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with any SO2 controls.

Due to EPA not including any portion of Fort Scott County, Iowa in the nonattainment area we proposed 

in our 120-day letter, the Lafarge facility was not included in the analysis submitted by IDNR in 

response to EPA’s proposal. We note that the Lafarge facility is east of the violating monitor, and that 

IDNR’s windrose analysis does not indicate that sources east of the monitor are contributing violation at 

the Musser Park monitor. Based on this, we are not yet prepared to conclude that the emissions from the 

Lafarge facility contribute to the monitored violation or to other possible violations. In a subsequent 

round of designations we will make final designations decisions for areas (and their sources), like Fort 

Scott County, that are not currently included in the nonattainment area designation addressed in this 

TSD. 

MidAmerican Energy Company – Louisa Generating Station (MidAmerican or LGS)

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

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

located in Muscatine County, Iowa. 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. 

EPA’s proposed default nonattainment boundary did not include the LGS facility in neighboring Louisa 

County, however IDNR’s analysis included an evaluation of the LGS facility for its contribution at the 

violating monitor. The LGS facility is located south of the violating monitor, which is the general 

direction of the sources implicated by IDNR’s windrose analysis as causing or contributing to the 

violations detected at the Musser Park monitor. However, as our 120-day letter to Iowa did not address 

this source, we are not yet prepared to conclude that the emissions from the LGS facility contribute to the 

monitored violation or to other possible violations, and we will make final designations decisions for 

areas and sources outside Muscatine County in a subsequent round of designations.

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
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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 

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. 

Based on its location and distance to the east of the violating monitor at Musser Park, IDNR’s windrose 

analysis does not indicate that the SSAB facility is causing or contributing to the violating Musser Park 

monitor. Based on this, we are not yet prepared to conclude that the emissions from the SSAB facility 

contribute to the monitored violation or to other possible violations. In a subsequent round of 

designations we will make final designations decisions for areas and sources not currently included in 

the nonattainment area designation addressed in this TSD.

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.

Based on its location and distance to the north of the violating monitor at Musser Park, IDNR’s 

windrose analysis does not indicate that the Gerdau facility is causing or contributing to the violating

Musser Mark monitor. Based on this, we are not yet prepared to conclude that the emissions from the 

Gerdau facility contribute to the monitored violation or to other possible violations. In a subsequent 

round of designations we will make final designations decisions for areas and sources not currently 

included in the nonattainment area designation addressed in this TSD.
13

Meteorology (weather/transport patterns)

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.

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 the additional 

information submitted by IDNR that contained windrose analysis on exceedance days.

IDNR provided a windrose analysis on exceedance days for three SO2 monitors in the Muscatine area.

This analysis is found in Figure 3. Because the Musser Park monitor represents the design value 

monitor, the EPA focused on the windrose associated with this monitor, and notes that the majority of 

the exceedances are from sources located south of the monitor. This windrose analysis provides

supporting information to not include in this initial round of designations several SO2 sources found in 

the northern and eastern portion of Muscatine County, including SSAB, Gerdau Ameristeel, and CIPCO, 

as the wind does not come from the direction of these sources during monitored exceedances at the 

Musser Park monitor. In addition to the daily windrose analysis, IDNR submitted hourly monitoring 

and wind direction information, Figure 4, demonstrating that the predominant SO2 source(s) impacting 

the Musser monitor were located to the south.

EPA finds that the IDNR windrose and meteorological analysis supports a smaller initial boundary that 

includes the Muscatine County sources that EPA has sufficient information to conclude are contributing 

to the violations at the Musser Park monitor. EPA is not yet reaching a conclusion concerning areas and 

sources not included in the initial nonattainment boundary, and will address these areas and their sources 

in a future final designations action.
14

Figure 3. IDNR Windroses on observed exceedance days (2010-2012).
15

Figure 4. IDNR analysis of hourly winds paired with hourly SO2 concentrations at Musser Park.

Increased Southerly Wind Speeds Winds Shifted from East to South

Wind Direction: North Wind Direction: East
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Geography/Topography (mountain ranges or other air basin boundaries)

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.

Muscatine County, Iowa 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. Iowa. The existence of the river channel through and across 

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

located in Muscatine, Iowa.

Jurisdictional Boundaries

Once the geographic area associated with the area violating the SO2 standard and the nearby areas

contributing to violations is determined, we consider 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.

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

nonattainment boundary. The revised boundary recommended by IDNR encompasses the area that 

includes the sources within Muscatine County that we are now prepared to conclude are contributing 

to exceedances observed at the monitor, as well as the area IDNR’s analysis shows is exceeding the 

NAAQS. IDNR’s recommendation is also consistent with jurisdictional (township) boundaries of 

the area. Areas and sources that we are not yet prepared to conclude are contributing to the 

monitored violation are not included in this initial nonattainment area. The legal description is as 

follows in Table 4.
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Table 4. Legal Description of Iowa DNR Proposed Nonattainment Area.

Township Sections

T77N R3W (Lake township) 1-3, 10-15, 22-27, 34-36

T76N R3W (Seventy-six township) 1-3, 10-15, 22-27, 34-36

T77N R2W (Bloomington township) All

T76N R2W (Fruitland township) All

T77N R1W (Sweetland township) All except 1, 12, 13, 24, 25, 36

Other Relevant Information

To support its revised boundary proposal, IDNR also conducted refined dispersion modeling. We are not 

relying upon the specific results of this modeling to support our final initial designation, but provide the 

following discussion for informational purposes. IDNR performed two types of modeling – a culpability 

test to assess which sources contributed to the exceedances observed at the Musser Park monitor, and a 

full grid analysis to evaluate the extent of the predicted exceedances surrounding the Musser Park 

monitor.

The full grid analysis modeling performed by IDNR was centered on the Musser Park monitor and 

extended out to cover EPA’s presumptive county-wide nonattainment boundary. The modeling analysis 

performed by IDNR utilized actual emission rates from 2009 through 2010 for the following sources: 

Grain Processing Corporation (GPC); Muscatine Power and Water (MPW); Monsanto; MidAmerican 

Energy (Louisa Generating Station); and Central Iowa Power Corporation (CIPCO). IDNR used a default 

background concentration typically used for modeling conducted in the new source review program

permit applications. The results of the modeling analysis predict that exceedances of the 1-hr 2010 SO2

NAAQS extend over an area substantially smaller than the presumptive county-wide boundary proposed 

by EPA. This revised area includes 3 of the 6 SO2 emissions sources that were included in EPA’s 

original county-wide presumptive boundary, and is consistent with IDNR’s contribution conclusions from 

its windrose analysis for those sources. Figure 5 contains the results of the IDNR modeling showing the 

extent of the predicted exceedances and its proposed nonattainment boundary within Muscatine County.

EPA is not prepared to conclude on the basis of IDNR’s refined dispersion modeling, that sources or areas 

excluded based upon IDNR’s modeling are or are not contributing to violations of the SO2 NAAQS. 

EPA is not yet reaching a conclusion concerning areas excluded from the initial nonattainment boundary 

and will address these areas in a future final designations action.
18

Figure 5. IDNR Proposed Nonattainment Boundary (highlighted in green)

Conclusion

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

2009-2011 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 technical analysis prepared and submitted by IDNR to respond 

to EPA’s preliminary nonattainment area proposal presents a reasonable and technically supported 

alternative initial nonattainment boundary. IDNR’s technical analysis examined several factors, 

including monitoring data, meteorological data, and proximity and magnitude of emissions.

Additionally, IDNR demonstrated through windrose analysis which sources are known to be impacting 

the violating monitor and should be included in the nonattainment area. The windrose analysis also 

provided supporting information to exclude from the initial nonattainment area several SO2 sources, 
19

which will be further analyzed in subsequent designations actions, in the northern and eastern portion of 

Muscatine County, including Gerdau Steel, SSAB and CIPCO.

EPA finds the windrose analysis performed by IDNR supports a smaller initial boundary, excluding 

those sources within Muscatine County that we are not yet prepared to conclude are contributing to the 

violating monitor on days exceeding the standard. Based upon the consideration of all relevant and 

available information, as described above, EPA is finalizing the initial SO2 nonattainment area boundary 

proposed by IDNR that is described in Table 4 above.