1

Draft Technical Support Document

Kentucky

Area Designations for the 2010 SO2 Primary National Ambient Air Quality Standard

Summary

Pursuant to section 107(d) of the Clean Air Act (CAA), the U.S. Environmental Protection 

Agency (EPA or the Agency) must designate areas as either “unclassifiable,” “attainment,” or 

“nonattainment” for the 2010 one-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 a violation in a nearby area. An attainment area is defined as any 

area other than a nonattainment area that meets the NAAQS. Unclassifiable areas are defined as 

those that cannot be classified on the basis of available information as meeting or not meeting the 

NAAQS.

The Commonwealth of Kentucky (hereafter referred to as “the Commonwealth”) submitted 

updated recommendations on September 16, 2015, ahead of a July 2, 2016, deadline for the EPA 

to designate certain areas. This deadline is the first of three deadlines established by the U.S. 

District Court for the Northern District of California for the EPA to complete area designations 

for the 2010 SO2 NAAQS. Table 1 below lists Kentucky’s recommendations and identifies the 

counties or portions of counties in Kentucky that the EPA intends to designate by July 2, 2016,

based on an assessment and characterization of air quality through ambient air quality data, air 

dispersion modeling, other evidence and supporting information, or a combination of the above. 

Table 1. Kentucky’s Recommended and the EPA’s Intended Designations

Area

Kentucky’s 

Recommended 

Area Definition

Kentucky’s 

Recommended 

Designation

The EPA’s Intended 

Area Definition

The EPA’s Intended 

Designation 

Ohio 

County, KY

Ohio County in 

its entirety Attainment

Same as 

Commonwealth’s 

Recommendation Unclassifiable

Pulaski 

County, KY

Pulaski County

in its entirety Attainment

Same as 

Commonwealth’s 

Recommendation Unclassifiable

Background

On June 3, 2010, the EPA revised the primary (health based) SO2 NAAQS by establishing a new 

one-hour standard at a level of 75 parts per billion (ppb) which is attained when the three-year 

average of the 99th percentile of one-hour daily maximum concentrations does not exceed 75 

ppb. This NAAQS was published in the Federal Register on June 22, 2010 (75 FR 35520) and is 

codified at 40 CFR 50.17. The EPA determined this is the level necessary to protect 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 
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two prior primary standards of 140 ppb evaluated over 24 hours, and 30 ppb evaluated over an 

entire year, codified at 40 CFR 50.4, remain applicable.

1 However, the EPA is not currently 

designating areas on the basis of either of these two primary standards. Similarly, the secondary 

standard for SO2, set at 500 ppb evaluated over 3 hours has not been revised, and the EPA is also 

not currently designating areas on the basis of the secondary standard.

General Approach and Schedule

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

revised NAAQS, state governors must submit their recommendations for designations and 

boundaries to EPA. Section 107(d) also requires the EPA to provide notification to states no less 

than 120 days prior to promulgating an initial area designation that is a modification of a state’s 

recommendation. If a state does not submit designation recommendations, the EPA will 

promulgate the designations that it deems appropriate. If a state or tribe disagrees with the EPA’s 

intended designations, they are given an opportunity within the 120 day period to demonstrate 

why any proposed modification is inappropriate.

On August 5, 2013, the EPA published a final rule establishing air quality designations for 29

areas in the United States for the 2010 SO2 NAAQS, based on recorded air quality monitoring 

data from 2009 - 2011 showing violations of the NAAQS (78 FR 47191). In that rulemaking, the 

EPA committed to address, in separate future actions, the designations for all other areas for 

which the Agency was not yet prepared to issue designations.

Following the initial August 5, 2013 designations, three lawsuits were filed against the EPA in 

different U.S. District Courts, alleging the Agency had failed to perform a nondiscretionary duty 

under the CAA by not designating all portions of the country by the June 2013 deadline. In an 

effort intended to resolve the litigation in one of those cases, plaintiffs Sierra Club and the 

Natural Resources Defense Council and the EPA filed a proposed consent decree with the U.S. 

District Court for the Northern District of California. On March 2, 2015, the court entered the 

consent decree and issued an enforceable order for the EPA to complete the area designations 

according to the court-ordered schedule.

According to the court-ordered schedule, the EPA must complete the remaining designations by 

that contains three specific deadlines. By no later than July 2, 2016 (16 months from the court’s 

order), the EPA must designate two groups of areas: (1) areas that have newly monitored 

violations of the 2010 SO2 NAAQS and (2) areas that contain any stationary sources that had not 

been announced as of March 2, 2015 for retirement and that according to the EPA’s Air Markets 

Database emitted in 2012 either: (i) more than 16,000 tons of SO2 or (ii) more than 2,600 tons of 

SO2 with an annual average emission rate of at least 0.45 pounds of SO2 per one million British 

thermal units (lbs SO2/mmBTU). Specifically, a stationary source with a coal-fired unit that as of 

 

1 40 CFR 50.4(e) provides that the two prior primary NAAQS will no longer apply to an area one year after its 

designation under the 2010 NAAQS, except that for areas designated nonattainment under the prior NAAQS as of 

August 22, 2010, and areas not meeting the requirements of a SIP Call under the prior NAAQS, the prior NAAQS 

will apply until that area submits and the EPA approves a SIP providing for attainment of the 2010 NAAQS. The 

two Kentucky areas are not designated nonattainment under the prior NAAQS nor are they areas not meeting the 

requirements of a SIP Call under the prior NAAQS. 
3

January 1, 2010 had a capacity of over 5 megawatts and otherwise meets the emissions criteria, 

is excluded from the July 2, 2016 deadline if it had announced through a company public 

announcement, public utilities commission filing, consent decree, public legal settlement, final 

state or federal permit filing, or other similar means of communication, by March 2, 2015, that it 

will cease burning coal at that unit. 

The last two deadlines for completing remaining designations are December 31, 2017, and 

December 31, 2020. The EPA has separately promulgated requirements for states and other air 

agencies to provide additional monitoring or modeling information on a timetable consistent with 

these designation deadlines. We expect this information to become available in time to help 

inform these subsequent designations. These requirements were promulgated on August 21, 2015 

(80 FR 51052), in a rule known as the SO2 Data Requirements Rule (DRR). 

 

Updated designations guidance was issued by the EPA through a March 20, 2015 memorandum 

from Stephen D. Page, Director, U.S. EPA, Office of Air Quality Planning and Standards, to Air 

Division Directors, U.S. EPA Regions 1-10. This memorandum supersedes earlier designation 

guidance for the 2010 SO2 NAAQS, issued on March 24, 2011, and it identifies factors that the 

EPA intends to evaluate in determining whether areas are in violation of the 2010 SO2 NAAQS. 

The guidance also contains the factors the EPA intends to evaluate in determining the boundaries 

for all remaining areas in the country, consistent with the court’s order and schedule. These 

factors include: 1) Air quality characterization via ambient monitoring or dispersion modeling 

results; 2) Emissions-related data; 3) Meteorology; 4) Geography and topography; and 5) 

Jurisdictional boundaries. This guidance was supplemented by two technical assistance 

documents intended to assist states and other interested parties in their efforts to characterize air 

quality through air dispersion modeling or ambient air quality monitoring for sources that emit 

SO2. Notably, the EPA released its most recent versions of documents titled, “SO2 NAAQS 

Designations Modeling Technical Assistance Document” (Modeling TAD) and “SO2 NAAQS 

Designations Source-Oriented Monitoring Technical Assistance Document” (Monitoring TAD) 

in December 2013.

Based on ambient air quality data collected between 2012 and 2014, no monitored violations of 

the 2010 SO2 NAAQS have been recorded in any undesignated part of the state.2 However, there 

are two sources in the state meeting the emissions criteria of the consent decree for which the 

EPA must complete designations by July 2, 2016. In this draft technical support document, the 

EPA discusses its review and technical analysis of Kentucky’s updated recommendations for the 

 

2 For designations based on ambient air quality monitoring data that violates the 2010 SO2 NAAQS, the consent 

decree directs the EPA to evaluate data collected between 2013 and 2015. Absent complete, quality assured and 

certified data for 2015, the analyses of applicable areas for the EPA’s intended designations will be informed by data 

collected between 2012 and 2014. States with monitors that have recorded a violation of the 2010 SO2 NAAQS 

during these years have the option of submitting complete, quality assured and certified data for calendar year 2015 

by April 19, 2016 to the EPA for evaluation. If after our review, the ambient air quality data for the area indicates 

that no violation of the NAAQS occurred between 2013 and 2015, the consent decree does not obligate the EPA to 

complete the designation. Instead, the EPA may designate the area and all other previously undesignated areas in the 

state on a schedule consistent with the prescribed timing of the consent decree, i.e., by December 31, 2017, or 

December 31, 2020. 
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areas that we must designate. The EPA also discusses any intended modifications from the 

state’s recommendation based on all available data before us. 

The following are definitions of important terms used in this document: 

1) 2010 SO2 NAAQS – The primary NAAQS for SO2 promulgated in 2010. This NAAQS is 

75 ppb, based on the three year average of the 99th percentile of the annual distribution 

of daily maximum one-hour average concentrations. See 40 CFR 50.17. 

2) Design Value - a statistic computed according to the data handling procedures of the 

NAAQS (in 40 CFR part 50 Appendix T) that, by comparison to the level of the NAAQS, 

indicates whether the area is violating the NAAQS.

3) Designated nonattainment area – an area which the EPA has determined has violated the 

2010 SO2 NAAQS or contributed to a violation in a nearby area. A nonattainment 

designation reflects considerations of state recommendations and all of the information 

discussed in this document. The EPA’s decision is based on all available information 

including the most recent 3 years of air quality monitoring data, available modeling 

analysis, and any other relevant information. 

4) Designated unclassifiable area – an area which the EPA cannot determine based on all 

available information whether or not it meets the 2010 SO2 NAAQS. 

5) Designated unclassifiable/attainment area – an area which the EPA has determined to 

have sufficient evidence to find either is attaining or is likely to be attaining the NAAQS.

The EPA’s decision is based on all available information including the most recent 3 

years of air quality monitoring data, available modeling analysis, and any other relevant 

information. 

6) Modeled violation – a violation based on air dispersion modeling.

7) Recommended attainment area – an area a state or tribe has recommended that the EPA 

designate as attainment. 

8) Recommended nonattainment area – an area a state or tribe has recommended that the 

EPA designate as nonattainment. 

9) Recommended unclassifiable area – an area a state or tribe has recommended that the 

EPA designate as unclassifiable.

10)Recommended unclassifiable/attainment area – an area a state or tribe has recommended 

that the EPA designate as unclassifiable/attainment.

11) Violating monitor – an ambient air monitor meeting all methods, quality assurance and 

siting criteria and requirements whose valid design value exceeds 75 ppb, based on data 

analysis conducted in accordance with Appendix T of 40 CFR part 50. 
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Technical Analysis for the Plant D.B. Wilson – Ohio County Area

Introduction

The Ohio County Area contains a stationary source that according to the EPA’s Air Markets 

Database emitted in 2012 either more than 16,000 tons of SO2 or more than 2,600 tons of SO2

and had an annual average emission rate of at least 0.45 lbs SO2/mmBTU. As of March 2, 2015, 

this stationary source had not met the specific requirements for being “announced for 

retirement.” Specifically, in 2012, the D.B. Wilson Power Plant (Plant Wilson) emitted 7,387

tons of SO2, and had an emissions rate of 0.45 lbs SO2/mmBTU. Pursuant to the March 2, 2015

court-ordered schedule, the EPA must designate the area surrounding the facility by July 2, 2016.

In its submission, the Commonwealth of Kentucky (hereafter referred to as “the 

Commonwealth”) recommended that the area surrounding Plant Wilson, specifically the entirety 

of Ohio County, be designated as attainment based on an assessment and characterization of air 

quality from the facility and other nearby sources which may have a potential impact in the area 

of analysis where maximum concentrations of SO2 are expected. This assessment and 

characterization were performed using air dispersion modeling software, i.e., AERMOD, 

analyzing allowable emissions. The assessment and characterization were originally conducted

by Trinity Consultants and prepared for the Big Rivers Electric Corporation (BREC). The 

Commonwealth then reviewed and submitted the information to the EPA.3

After careful review of the Commonwealth’s assessment, supporting documentation, and all 

available data, the EPA intends to designate Ohio County in its entirety as unclassifiable4

because the EPA does not have necessary information at this time to determine the attainment 

status of the Ohio County Area. Specifically, the future allowable emission limit for Plant 

Wilson used to model attainment for the Ohio County Area has not been established as federallyenforceable5

by the Commonwealth. In order for the EPA to consider the future allowable 

emission limit of 0.85 lbs SO2/mmBTU for Plant Wilson for the designations to be finalized no 

later than July 2, 2016, the Commonwealth will have to ensure that these limits are federallyenforceable (and the EPA has confirmed such) by the time this round of designations is 

complete. Regarding the Plant Wilson future emission limit, if a limit with an averaging time 

 

3 Throughout this document the Commonwealth will be referred to as having assessed air quality in the area because 

the Commonwealth agreed with the BREC’s air quality assessment and characterization of the area of analysis, 

officially submitting the report to the EPA to support their designation recommendation. 

4 Pursuant to the EPA’s April 23, 2014 memorandum entitled “Guidance for the 1-Hour SO2 Nonattainment Area 

SIP Submissions.”

5 Consistent with past interpretations of legal requirements, control measures, emission limits and other curtailments 

need to be installed, operational and federally-enforceable to be considered when informing final designation 

decisions. The mechanisms for establishing federally enforceable emission limits, control measures, or curtailments 

for the purpose of informing SO2 designations include: a source-specific state implementation plan (SIP)-approved 

by the EPA, a minor new source review permit, a title v permit or a consent decree established through Federal civil 

litigation.
6

longer than 1-hour is desired, supporting technical information will also need to include 

explanation, of whether the longer term average limit, that the EPA determines is comparatively 

stringent to a 1-hour limit at the critical emission value, ensures attainment of the SO2 NAAQS.

Also, the EPA needs additional information regarding the operating status of Units 1 and 2 at the 

Tennessee Valley Authority’s (TVA’s) - Paradise Fossil Plant in Muhlenberg County to 

determine if Units 1 and 2 at the source are shut down.

6

If the TVA - Paradise Fossil Plant is not 

shutdown, additional explanation would be necessary as to why these emissions were not 

included in the modeling for this area. If the Commonwealth cannot provide supporting

documentation to confirm the permanent retirement of Units 1 and 2 at the TVA - Paradise Fossil 

Plant, including actual historical emissions for these units in the modeling is an option for 

complete characterization in relation to the proposed Ohio County designation from Kentucky. 

Plant Wilson is located in western Kentucky in the western portion of Ohio County. As seen in 

Figure 1 below, the facility is located approximately 8 kilometer (km) northwest of the center of 

Centertown, KY. Also included in the figure are nearby emitters of SO2, the Commonwealth’s 

recommended area for the attainment designation, and the EPA’s intended 

unclassifiable/attainment designation for the area.

 

6 Emissions for the TVA: Paradise Fossil Plant are important to the characterization of Ohio County because the 

source, while in Muhlenberg County, is immediately across the border from Ohio County. The Commonwealth 

included consideration of emissions from Unit 3 at the TVA: Paradise Fossil Plant in support of their 

recommendation of attainment for Ohio County. 
7

Figure 1. The EPA’s intended designation for Ohio County, Kentucky 

The discussion and analysis that follows below will reference the Commonwealth’s use of the 

Modeling TAD, the EPA’s assessment of the Commonwealth’s modeling in accordance with the 

Modeling TAD, and the factors for evaluation contained in the EPA’s March 20, 2015 guidance, 

as appropriate.

Detailed Assessment

Air Quality Data

This factor considers the SO2 air quality monitoring data in the area surrounding Plant Wilson. 

The facility is located in Ohio County, and the Commonwealth included monitoring data from 

the closest monitors: Baskett Fire House (21-101-0014), Evansville-Buena Vista in Indiana (18-

163-0021), Mammoth Cave National Park (21‐061‐0501), and Owensboro Primary (21-059-

0005), to the facility in its recommendation. The closest monitor is Owensboro Primary, located 

at 716 Pleasant Valley Rd, Owensboro, KY 42303 (37.78077, -87.0753) in Daviess County, and 

is 35 km away from Plant Wilson. Data collected at this monitor is considered indicative of 

population exposure but is not representative of the expected background concentrations in the 
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area surrounding the Plant Wilson. The Baskett Fire House monitor, located at Baskett Fire

Department, 7492 Dr. Hodge Rd, Henderson, KY 42420 (37.8712, -87.46375) is located within 

25 km to several sources to the northwest of Plant Wilson, and the predominant wind direction

indicates that this monitor is reasonably expected to capture the regional effects of these sources. 

Table 2 below summarizes the local monitors and design values from recent years in within 100 

km of Plant Wilson.

Table 2: Historical Ambient Air Quality Data for Nearby Monitors

Monitor AQS ID County

2010–2012 

Design Value 

(μg/m3)

2011–2013 

Design Value 

(μg/m3)

2012–2014 

Design Value 

(μg/m3)

Baskett Fire 

House

21-101-0014 Henderson 65.5 71.5 71.5

EvansvilleBuena Vista18-163-0021 Vanderburgh 47.1 47.1 57.6

Mammoth 

Cave 21-061-0501 Edmonson 31.4 26.2 26.2

Owensboro 

Primary 21-059-005 Daviess 125.7 107.42 112.6

Model Selection and Modeling Components

The EPA’s Modeling TAD notes that for area designations under the 2010 SO2 NAAQS, the 

AERMOD modeling system should be used, unless use of an alternative model can be justified. 

In some instances the recommended model may be a model other than AERMOD, such as the 

BLP model for buoyant line sources. The AERMOD modeling system contains the following 

components:

 AERMOD: the dispersion model

 AERMAP: the terrain processor for AERMOD

 AERMET: the meteorological data processor for AERMOD

 BPIPPRIME: the building input processor 

 AERMINUTE: a pre-processor to AERMET incorporating 1-minute automated surface 

observation system (ASOS) wind data

 AERSURFACE: the surface characteristics processor for AERMET

 AERSCREEN: a screening version of AERMOD

The Commonwealth used AERMOD version 15181, and, as appropriate, a discussion of the 

individual components will be referenced in the corresponding discussion.

Modeling Parameter: Rural or Urban Dispersion

The EPA’s recommended procedure for characterizing an area by prevalent land use is based on 

evaluating the dispersion environment within 3 km of the facility. According to the EPA’s 

modeling guidelines, rural dispersion coefficients are to be used in the dispersion modeling 
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analysis if more than 50 percent of the area within a 3 km radius of the facility is classified as 

rural. Conversely, if more than 50 percent of the area is urban, urban dispersion coefficients 

should be used in the modeling analysis. When performing the modeling for the area of analysis, 

the Commonwealth determined that it was most appropriate to run the model in rural mode. The 

Commonwealth used the Auer’s land use methodology to determine the classification. Land use 

within a 3 km radius of Plant Wilson was examined and quantified. Based on the visual 

inspection of the land use types, the Commonwealth determined that the area is predominantly 

rural by a margin of 99.2 percent and therefore determined that is was most appropriate to run 

the model with rural dispersion coefficients. See Figure 2 below for a depiction of land-use 

around Plant Wilson.

Figure 2. Distribution of Land Use within 3-km of Wilson Station - Source: “Air Dispersion 

Modeling Report Wilson Station SO2 Designations Analysis Revision 1” prepared by Trinity 

Consultants for the Big Rivers Electric Corporation, August 25, 2015.

Modeling Parameter: Area of Analysis (Receptor Grid)

The EPA believes that a reasonable first step towards characterization of air quality in the area 

surrounding Plant Wilson is to determine the extent of the area of analysis, i.e., receptor grid. 

Considerations presented in the Modeling TAD include but are not limited to: the location of the 

SO2 emission sources or facilities considered for modeling; the extent of significant 

concentration gradients of nearby sources; and sufficient receptor coverage and density to 

adequately capture and resolve the model predicted maximum SO2 concentrations. For the Ohio 
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County Area, major sources of SO2 emissions within a 20 km range were considered and larger 

sources within a 20-50 km range that were believed to potentially contribute significant 

concentrations to the area of analysis. The Commonwealth determined that this was the 

appropriate distance in order to adequately characterize air quality from the facility and other 

nearby sources which may have a potential impact in the area of analysis where maximum 

concentrations of SO2 are expected. Sources within these ranges include: Century Aluminum of 

Kentucky, LLC (Hancock County), Reid/Henderson Station II Generating Station and BREC 

Landfill7(Webster County), Owensboro Municipal Utilities - Elmer Smith Station (Daviess 

County), (TVA-Paradise Station, and Green River Generating Station-Kentucky Utilities 

Company (Muhlenberg County).

TVA-Paradise Fossil Plant is approximately 22 km southeast of Plant Wilson, and had SO2

emissions of 19654.55 tpy in 20148. Units 1 and 2 at the facility are scheduled to shut down by 

June 2017, according to an annual report developed by the Energy Information Administration

(EIA)9 which legally requires direct reporting via survey for all energy generating units at or 

greater than 1 megawatt capacity. The TVA website also projects a 2017 date for the retirement 

of Units 1 and 2.10 The modeling report prepared for the Commonwealth presents inconsistent

information, stating that a public announcement indicating TVA-Paradise Fossil Plant Units 1 

and 2 are slated for retirement by April 2016. The Commonwealth decided not to evaluate actual 

emissions from TVA-Paradise Fossil Plant Units 1 and 2 because of their scheduled retirement.

In order for the shutdown to be considered for the designations which must be finalized by July 

2, 2016, the EPA will need confirmation from the Commonwealth that this shutdown is in effect 

prior to final designations.11

Because Unit 3 at TVA-Paradise Fossil Plant is not scheduled for shut down, its hourly 2012-

2014 continuous emissions monitoring systems (CEMS) data from the EPA Air Markets 

Program Data were considered in the modeling analysis for Plant Wilson. However, the unit’s 

temperature and gas exit velocity were not available from this database and were therefore set 

equal to data available in Kentucky’s emissions data archive. 

 

7 Comprised of Reid/Henderson Generating Station. The Big Rivers Electric Corporation landfill is located at 

Reid/Henderson Station II just south of the generating plant and is not a separate source.

8 All 2014 emissions data was accessed via the Emissions Inventory System (EIS) gateway, in which states report 

emissions pursuant to 40 CFR Part 51, Subpart A. The EIS gateway can be accessed via: 

http://www3.epa.gov/ttnchie1/eis/gateway/. 

9 U.S. Energy Information Administration, “Electric Power Monthly with Data for November 2015,” January 2016. 

See http://www.eia.gov/electricity/monthly/pdf/epm.pdf.

10 See, e.g., https://www.tva.com/Energy/Our-Power-System/Fossil-Fuel-Generation/Paradise-Fossil-Plant

11 The EPA is required to characterize the current air quality around Plant Wilson by July 2, 2016, according to the 

terms of the court ordered consent decree. Therefore, unless the Commonwealth can provide documentation that 

Units 1 and 2 are permanently retired by that time to the EPA in advance of the promulgation of final designations, 

the EPA cannot consider the shutdown emissions and instead actual emissions for these units from 2012-2014 

should be accounted for in any modeling to characterize the air quality around the Plant Wilson area of analysis.
11

All units at Green River Generating Station have been retired as of October 2015.12.The 

remaining sources listed above are at least 35 km or more from Plant Wilson which is distant 

enough that their impacts would be significantly reduced in terms of impacts overlapping with 

those of Plant Wilson. The modeling analysis performed and submitted by the Commonwealth 

included only future allowable emissions from Plant Wilson and actual emissions from Unit 3 of 

TVA-Paradise Fossil Plant.

The grid receptor spacing for the area of analysis chosen by the Commonwealth is as follows:

 50-meter intervals along the fence line

 100-meter spaced receptors extending to 3 km from the center of the property and beyond 

the fence line

 250-meter spaced receptors extending from 3 km to 5 km 

 500-meter spaced receptors extending from 5 km to 10 km 

 1,000-meter spaced receptors extending from 10 km to 20 km 

 2,000-meter spaced receptors extending from 20 km to 50 km 

The receptor network contained 6,922 receptors, and the network covered a large area spanning 

50 km in each direction surrounding Plant Wilson, stretching from the southern edge of Indiana 

to the northern edge of Tennessee. 

Figures 3 through 5, included in the Commonwealth’s recommendation, show the 

Commonwealth’s chosen area of analysis surrounding Plant Wilson, as well as receptor grid for 

the area of analysis. Consistent with the Modeling TAD, receptors for the purposes of this 

designation effort were placed only in areas where it would also be feasible to place a monitor

and record ambient air impacts. The impacts of the area’s geography and topography will be 

discussed later within this document.

 

12 The Commonwealth’s modeling report indicated that remaining Units 3 and 4 at Green River Generating station 

were expected to shutdown by April 2016 (based on http://www.coalage.com/news/latest/4152‐green‐river‐coal‐

plant‐will‐remain‐in‐operation‐until‐april‐2016.html#.VckdfflVhBc). However, more recent reports (https://lgeku.com/our-company/community/neighbor-neighbor/green-river-generating-station) indicate remaining Units 3 and 

4 retirement date was September 30, 2015 and the EIA January 2016 Electric Power Monthly report 

(http://www.eia.gov/electricity/monthly/pdf/epm.pdf) tracked Units 3 and 4 as permanently retired effective October 

2015. Furthermore, no emissions were reported to the EPA Air Markets Database beginning in October 2015 for any 

federal programs for which Units 3 and 4 would have been subject.
12

Figure 3: Ohio County Area of Analysis Source: “Air Dispersion Modeling Report Wilson 

Station SO2 Designations Analysis Revision 1” prepared by Trinity Consultants for the Big 

Rivers Electric Corporation, August 25, 2015.
13

Figure 4: Innermost Portion of Modeling Receptor Grid for the Ohio County Area of Analysis -

Source: “Air Dispersion Modeling Report Wilson Station SO2 Designations Analysis Revision 

1” prepared by Trinity Consultants for the Big Rivers Electric Corporation, August 25, 2015.
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Figure 5: Overall Modeling Receptor Grid for Wilson Air Dispersion Modeling Report Wilson 

Station SO2 Designations Analysis Revision 1” prepared by Trinity Consultants for the Big 

Rivers Electric Corporation, August 25, 2015.

Modeling Parameter: Source Characterization

The Commonwealth characterized the sources within the area of analysis in accordance with the 

best practices outlined in the Modeling TAD. Specifically, the Commonwealth followed the 

EPA’s good engineering practices (GEP) policy in conjunction with actual emissions for TVAParadise Fossil Plant Unit 3, and future allowable emissions limits for Plant Wilson. The 

Commonwealth also adequately characterized the source’s building layout and location, as well 
15

as the stack parameters, e.g., exit temperature, exit velocity, location, and diameter. Where 

appropriate, the AERMOD component BPIPPRIME was used to assist in addressing building 

downwash.

Modeling Parameter: Emissions

The EPA’s Modeling TAD notes that for the purposes of modeling to characterize air quality for 

use in designations, the recommended approach is to use the most recent 3 years of actual 

emissions data and concurrent meteorological data. However, the TAD does provide for the 

flexibility of using allowable emissions in the form of the most recently permitted, (referred to as 

potential to emit (PTE) or allowable) emissions rate.

The EPA believes that CEMS data provide acceptable historical emissions information when it is 

available, and that these data are available for many electric generating units. In the absence of 

CEMS data, the EPA’s Modeling TAD highly encourages the use of AERMOD’s hourly varying 

emissions keyword HOUREMIS, or through the use of AERMOD’s variable emissions factors 

keyword EMISFACT. When choosing one of these methods, the EPA believes that detailed 

throughput, operating schedules, and emissions information from the impacted source (s) should 

be used. 

In certain instances, states and other interested parties may find that it is more advantageous or 

simpler to use PTE rates as part of their modeling runs. Specifically, a facility may have recently 

adopted a new federally enforceable emissions limit, been subject to a federally enforceable 

consent decree, or implemented other federally enforceable mechanisms and control 

technologies to limit SO2 emissions to a level that indicates compliance with the NAAQS. These 

new limits or conditions may be used in the application of AERMOD. In these cases, the 

Modeling TAD notes that the existing SO2 emissions inventories used for permitting or SIP 

planning demonstrations should contain the necessary emissions information for designationsrelated modeling. In the event that these short-term emissions are not readily available, they may 

be calculated using the methodology in Table 8-1 of Appendix W to 40 CFR Part 51 titled, 

“Guideline on Air Quality Models.” 

As previously noted, the Commonwealth included Plant Wilson and one other emitter of SO2, 

that is expected to continue operating, i.e., Unit 3 at TVA-Paradise Fossil Plant, within 20-50 km 

in the area of analysis. The Commonwealth considered major sources of SO2 emissions within a 

20 km range and larger sources within a 20-50 km range that were believed to potentially 

contribute significant concentrations to the area of analysis. The Commonwealth selected this 

distance and facilities because it believes that this area of analysis adequately represents the area 

where maximum concentrations of SO2 are expected and adequately includes the sources which 

might contribute to those concentrations. Plant Wilson is the only major SO2 emitting source in 

Ohio County over 100 tpy. Sources the Commonwealth identified within the 20-50 km range 

other than TVA-Paradise Fossil Plant included Century Aluminum of Kentucky, Reid/Henderson 

Station II Generating Station and BREC Landfill, Elmer Smith Station and Green River Station.

TVA-Paradise Fossil Plant in Muhlenberg County is located approximately 22 km southeast of

Plant Wilson, and had SO2 emissions of 1,9654.55 tpy in 2014. Units 1 and 2 at the facility are 
16

scheduled to shut down by June 2017, according to report by the EIA and information from the 

TVA website. However, this information is not consistent with the data for Units 1 and 2 

provided in the modeling report which indicates the units are expected to retire by April 2016. 

Because of the anticipated retirement, the Commonwealth did not evaluate actual emissions from 

TVA-Paradise Fossil Plant Units 1 and 2 nor are the source’s 2012-2014 emissions accounted for 

the in the background concentration selected for the area. Therefore, unless the Commonwealth 

can provide documentation to the EPA in advance of the promulgation of final designations

scheduled for July 2, 2016, that Units 1 and 2 will permanently retire, the EPA may not be able 

to consider these shutdown and believes that actual emissions for these units from 2012-2014 

should be accounted for in any modeling to characterize the air quality around Plant Wilson for 

the Ohio County Area. The EPA is required to characterize the current air quality around Plant 

Wilson by July 2, 2016, according to the terms of the court ordered consent decree. Therefore 

because of the uncertainty of the timing of the permanent shutdown of Units 1 and 2 and the fact 

that 2012-2014 actual historic emissions were not considered in the modeling analysis for Plant 

Wilson, the EPA does not have sufficient information to accurately evaluate the source’s impact 

on the Ohio County Area, and thus intends to designate this area. 

The EPA notes that the Green River Generating Station also in Muhlenberg County is located 

approximately 10 km from Plant Wilson and less than 0.5 km from the Ohio County border. The 

source reported 21976.19 tons of SO2 in 2014 but according to reports from EIA, the last 

remaining Units 3 and 4 were permanently retired in October 201513 resulting in zero potential to 

emit. Green River Station was not explicitly included in the modeling analysis for Plant Wilson 

due to permanent shutdown and zero potential to emit SO2 emissions. However, the source was 

considered in the background concentrations accounting for impacts from nearby sources 

including historic actual emissions. Considering the source’s zero potential to emit and the 

cumulative impacts captured in the background concentrations, the EPA does not have reason to 

believe that emissions from this now non-operational facility are causing or contributing to a 

violation of the SO2 NAAQS in the Ohio County Area.

Other SO2 emitters the Commonwealth assessed within the 20-50 km range that reported SO2

emissions over 100 tpy included: Century Aluminum of Kentucky, LLC (Hancock County), 

Elmer Smith Station (Daviess County), Reid/Henderson Station II Generating Station and BREC 

Landfill (Webster County). These sources were not explicitly included in the modeling analysis 

because they are all located 35 km or greater from Plant Wilson (as well as Ohio County Area)

which the Commonwealth determined to be far enough that impacts from the facility relative to 

Plant Wilson. Therefore, the Commonwealth assessed that these sources would not potentially 

contribute significant concentrations to the area of analysis.

The EPA notes that the BREC’s sources, Green Station (Webster County) and Coleman Station

(Hancock County) and Owensboro Grain Company (Daviess) also reported 2014 emissions over 

100 tpy year. But similar to those sources considered by the Commonwealth, these are also 

 

13 No emissions were reported to the EPA Air Markets Database beginning in October 2015 for any 

federal programs for which Green River Generating Station Units 3 and 4 would have been subject. Also, 

EIA’s US Energy Information Administration “Electric Power Monthly” annual report for January 2016, 

tracked Units 3 and 4 as permanently retired as of October 2015.
17

located over 35 km away from Plant Wilson and Ohio County line. Based on the distance from 

Plant Wilson and Ohio County border (>35 km), the EPA has reason to believe that these sources 

would not cause significant concentration gradients within the area of analysis or Ohio County.

The EPA notes that other sources in counties within the 20-50 km range cumulatively emitted 

less than 100 tpy of SO2 emissions according to 2014 actual emissions. 

For this area of analysis, the Commonwealth opted to use a hybrid approach, where emissions 

from certain facilities are expressed as actual emissions, and those from other facilities are 

expressed as PTE rates. For the following facility in the area of analysis, the Commonwealth

included annual actual SO2 emissions between 2012 and 2014. This information is summarized 

below. 

Table 3: Actual SO2 Emissions Between 2012 – 2014 from Facilities in the Ohio County, 

Kentucky Area of Analysis

Facility Name

SO2 Emissions (tons per year (tpy))

2012 2013 2014

TVA: Paradise Fossil Plant

Unit 3 4,400 2,700 5,000

For Unit 3 at TVA- Paradise Station the Commonwealth used actual emissions from the most 

recent 3-year data set, i.e., 2012 – 2014. These emissions data were obtained from EPA’s Air 

Markets Program Data. Temperature and gas exit velocity were not available and were set equal 

to that in the Kentucky Department of Air Quality’s archive data (CEMS). 

For the following facility in the area of analysis, the Commonwealth has chosen to model the 

facility using a future federally enforceable PTE limit for SO2. The facility in the 

Commonwealth’s area of analysis and its associated PTE rate are summarized below. 

Table 4: SO2 Emissions based on PTE from Facilities in the Ohio County Area of Analysis

Facility Name

SO2 Emissions 

(tpy, based on PTE)

D.B Wilson 

Power Station

TPY value not provided by the Commonwealth, future 

limit is 0.853 lbs SO2/mmBTU

The PTE limit of 0.853 lbs SO2/mmBTU for Plant Wilson was proposed by BREC and modeled 

to show attainment for the 1-hour SO2 NAAQS.

Modeling Parameter: Meteorology and Surface Characteristics

The most recent 3 years of meteorological data (concurrent with the most recent 3 years of 

emissions data) should be used in designations efforts. As noted in the Modeling TAD, the 

selection of data should be based on spatial and climatological (temporal) representativeness. 

The representativeness of the data are based on: 1) the proximity of the meteorological 

monitoring site to the area under consideration, 2) the complexity of terrain, 3) the exposure of 
18

the meteorological site, and 4) the period of time during which data are collected. Sources of 

meteorological data include National Weather Service (NWS) stations, site-specific or onsite 

data, and other sources such as universities, Federal Aviation Administration (FAA), and 

military stations.

For the Ohio County Area of analysis, surface meteorology from the U.S. National Climatic Data 

Center (NCDC) for the Evansville Regional Airport, 76.5 km to the northwest, and coincident 

upper air observations from the nearest U.S. NWS radiosonde equipped station, the Nashville 

International Airport, 151.7 km to the southeast were selected as best representative of 

meteorological conditions within the area of analysis. 

The Commonwealth used AERSURFACE version 13016 using data from the Evansville 

Regional Airport in Evansville, Indiana (located at 38.044, ‐87.521) to estimate the surface 

characteristics of the area of analysis. The Commonwealth estimated values for 12 spatial sectors 

out to 1 km at a seasonal temporal resolution for dry conditions. The Commonwealth also 

estimated values for albedo (the fraction of solar energy reflected from the earth back into 

space), the Bowen ratio (the method generally used to calculate heat lost or heat gained in a 

substance), and the surface roughness (sometimes referred to as “Zo”). In the figure below, 

which was included in the Commonwealth’s recommendation, the location of the Evansville 

Regional Airport is shown relative to the Plant Wilson area of analysis.
19

Figure 6: Plant Wilson Area of Analysis and the Evansville Regional Airport Source: “Air 

Dispersion Modeling Report Wilson Station SO2 Designations Analysis Revision1” prepared by 

Trinity Consultants for the Big Rivers Electric Corporation, August 25, 2015
20

The 3-year surface wind rose for Evansville Regional Airport is depicted in Figure 7. In Figure 7, 

the frequency and magnitude of wind speed and direction are defined in terms of from where the 

wind is blowing. The wind rose indicates that the winds blow predominately from the southsoutheast, at low to mid-level wind speeds of 2.1- 5.7 meters/second. Additionally, winds blow 

from the northeast and northwest a significant amount of time.

Figure 7: Evansville Regional Airport Cumulative Annual Wind Rose for Years 2012 – 2014 

WRPLOT View - Lakes Environmental Software

WIND ROSE PLOT:

2012-2014 Annual Wind Rose

Evansville

Regional Airport (KEVV, WBAN No. 93817)

COMMENTS:

Created by Rick Gillam

EPA Region 4

11/19/15

COMPANY NAME:

MODELER:

DATE:

11/19/2015

PROJECT NO.:

NORTH

SOUTH

WEST EAST

3%

6%

9%

12%

15%

WIND SPEED 

(m/s)

 >= 11.1

 8.8 - 11.1

 5.7 - 8.8

 3.6 - 5.7

 2.1 - 3.6

 0.5 - 2.1

Calms: 2.03%

TOTAL COUNT:

26187 hrs.

CALM WINDS:

2.03%

DATA PERIOD:

Start Date: 1/1/2012 - 00:00

End Date: 12/31/2014 - 22:00

AVG. WIND SPEED:

3.23 m/s

DISPLAY:

 Wind Speed

Direction (blowing from)
21

Meteorological data from the above surface and upper air stations were used in generating 

AERMOD-ready files with the AERMET processor. The output meteorological data created by 

the AERMET processor is suitable for being applied with AERMOD input files for AERMOD 

modeling runs. The Commonwealth followed the methodology and settings presented in standard 

U.S. EPA meteorological processing guidance as outlined in a recent memorandum14 as well as 

other AERMET and associated preprocessor documentation in the processing of the raw 

meteorological data into an AERMOD-ready format, and used AERSURFACE to best represent 

surface characteristics. 

Hourly surface meteorological data records are read by AERMET, and include all the necessary 

elements for data processing. However, wind data taken at hourly intervals may not always 

portray wind conditions for the entire hour, which can be variable in nature. Hourly wind data 

may also be overly prone to indicate calm conditions, which are not modeled by AERMOD. In 

order to better represent actual wind conditions at the meteorological tower, wind data of one 

minute duration was provided from the same instrument tower, but in a different formatted file to 

be processed by a separate preprocessor, AERMINUTE. These data were subsequently 

integrated into the AERMET processing to produce final hourly wind records of AERMODready meteorological data that better estimate actual hourly average conditions and that are less 

prone to over-report calm wind conditions. This allows AERMOD to apply more hours of 

meteorology to modeled inputs, and therefore produce a more complete set of concentration 

estimates. As a guard against excessively high concentrations that could be produced by 

AERMOD in very light wind conditions, the Commonwealth set a minimum threshold of 0.5 

meters per second in processing meteorological data for use in AERMOD. In setting this 

threshold, no wind speeds lower than this value would be used for determining concentrations. 

This threshold was specifically applied to the one minute wind data. 

Modeling Parameter: Geography and Terrain

The terrain in the area of analysis is best described as gently rolling with small hills. To account 

for these terrain changes, the AERMAP terrain program within AERMOD was used to specify 

terrain elevations for all the receptors. The source of the elevation data incorporated into the 

model is from the United States Geological Survey National Elevation Database. 

Modeling Parameter: Background Concentrations of SO2

The Modeling TAD offers two mechanisms for characterizing background concentrations of SO2

that are ultimately added to the modeled design values: 1) a “first tier” approach, based on 

monitored design values, or 2) a temporally varying approach, based on the 99th percentile 

monitored concentrations by hour of day and season or month. For the Ohio County area of 

analysis, the Commonwealth chose the method which uses the 3-year averages of the 99th

percentiles by hour of day (across all seasons). This was chosen based on the review of the 99th

 

14 Fox, Tyler, U.S. Environmental Protection Agency. 2013. “Use of ASOS Meteorological Data in AERMOD 

Dispersion Modeling.” Available Online: 

http://www.epa.gov/ttn/scram/guidance/clarification/20130308_Met_Data_Clarification.pdf
22

percentile hourly values across 2012-2014, which shows a diurnal variation of lowest SO2

concentrations at night and highest in the day. The Baskett Fire House Monitor (Site No. 21-101-

0014) was determined to be the representative background monitor for the area. The Basket 

monitor is classified as a general “population exposure” monitor located about 8-9 km southeast 

of Evansville, Indiana and about 55 km northwest of Plant Wilson. This monitor was determined 

to adequately reflect impacts from the SO2 emissions sources to the northwest of Plant Wilson. 

The ambient SO2 concentrations used as background in the modeling vary from 15 – 50 μg/m3

(see Figure 8 below).

Figure 8: 99th Percentile SO2 Averages by Hour of Day for Baskett Fire House Monitor (21-101-

0014). Source: “Air Dispersion Modeling Report Wilson Station SO2 Designations Analysis 

Revision 1” prepared by Trinity Consultants for the Big Rivers Electric Corporation, August 25, 

2015.
23

Summary of Modeling Results

The AERMOD modeling parameters for the Ohio County Area of analysis provided by the 

Commonwealth are summarized below in Table 5.

Table 5: AERMOD Modeling Parameters for the Ohio County Area of Analysis

Ohio County Area of Analysis

AERMOD Version 15181 

Dispersion Characteristics Rural 

Modeled Sources 2

Modeled Stacks 2

Modeled Structures 8

Modeled Fencelines 1

Total receptors 6,922

Emissions Type PTE

Emissions Years

TBD15/Effective year of new 

limits for PTE

Meteorology Years 2012-2014

Surface Meteorology Station Evansville, Indiana

Upper Air Meteorology Station Nashville, Tennessee

Methodology for Calculating 

Background SO2 Concentration Temporal Varying

Calculated Background SO2

Concentration

Temporally varying between 

15 – 50 μg/m3(see figure 8

above)

The results presented below in Table 6 show the magnitude and geographic location of the 

highest predicted modeled concentration based on PTE emissions from Plant Wilson and actual 

emissions from TVA: Paradise Fossil Plant. 

Table 6: Maximum Predicted 99th Percentile 1-Hour SO2 Concentration in the Ohio County

Area of Analysis Based on PTE and actual emissions. 

Averaging 

Period Data Period

Receptor Location SO2 Concentration (μg/m3)

UTM/Latitude UTM/Longitude

Modeled

(including 

background) NAAQS

99th Percentile 

1-Hour Average [2012-2014] 490583 4144568 186.5 196.5*

 

15 Provided the new modeled allowable limit of 0.85 lb SO2/mmBTU is federally-enforceable by the time that the 

EPA finalizes the designation for this area and, as applicable, includes a longer term average limit that is 

comparatively stringent to a 1-hour limit at the critical emission value.
24

*Equivalent to the 2010 SO2 NAAQS set at 75 ppb

The Commonwealth’s modeling indicates that the predicted 99th percentile 1-hour average 

concentration within the chosen modeling domain is 186.5 μg/m3, or 71.2 ppb. This modeled 

concentration included the background concentration of SO2 of and is based on actual emissions 

from TVA-Paradise Fossil Plant Unit 3, a future allowable limit of 0.85 lbs SO2/mmBTU for 

Plant Wilson, and an assumed zero PTE due to scheduled shutdown of TVA-Paradise Units 1 

and 2. Figure 9 below was included as part of the Commonwealth’s recommendation, and 

indicates that the predicted value occurred approximately 2.3 km west of the Plant Wilson. The 

Commonwealth’s receptor grid is also shown in the figure.
25

Figure 9: Maximum Predicted 99th Percentile 1-Hour SO2 Concentrations in the 

Ohio County Area of Analysis Based on PTE Emissions Source: “Air Dispersion Modeling 

Report Wilson Station SO2 Designations Analysis Revision 1” prepared by Trinity Consultants 

for the Big Rivers Electric Corporation, August 25, 2015 

Regarding Plant Wilson’s modeled future allowable limit the Commonwealth did not provide 

specific information concerning the federal enforceability nor indicate the averaging time and 

how it was derived. Consistent with past interpretations of legal requirements, control measures, 

emission limits and other curtailments need to be installed, operational and federally enforceable 

to be considered when informing final designation decisions. The mechanisms for establishing 

federally enforceable emission limits, control measures, or curtailments for the purpose of 

informing SO2 designations include: a source-specific SIP approved by the EPA, a minor new 

source review permit, a title v permit or a consent decree established through a federal civil 
26

litigation. There was no documentation provided by the Commonwealth on whether the 

averaging time for the future allowable limit is a 1-hour limit or if a longer-term averaging 

period (e.g., 30-day rolling average) was established that is comparatively stringent to a 1-hour 

limit at the critical emission value (pursuant to the EPA’s SO2 Nonattainment Guidance).16

Furthermore, the Commonwealth’s decision to exclude actual emissions from 2012-2014 from 

TVA-Paradise Station Units 1 and 2 was based upon a future retirement of these units which 

questions whether the model configuration accounts for impacts to the area should these 

retirements not occur prior to the final designations scheduled for July 2, 2016. 

The EPA notes inconsistent information on the timing of the retirement of TVA-Paradise Fossil 

Plant Units 1 and 2 (i.e., whether this will occur by April 2016 or June 2017). The EPA is 

required to characterize the current air quality around Plant Wilson by July 2, 2016, according to 

the terms of the court ordered consent decree. Therefore based on the uncertainty on the 

permanent shutdown of Units 1 and 2 and the fact that 2012-2014 actual historic emissions were 

not considered in the modeling analysis for Plant Wilson, the EPA does not have sufficient 

information to consider the source’s impact on the Ohio County Area. Unless the

Commonwealth can provide documentation that Units 1 and 2 will permanently retire in advance 

of the July 2, 2016, designations to the EPA for consideration prior to the promulgation of final 

designations, the EPA cannot consider these shutdowns and instead believes that it is more 

appropriate for the Commonwealth to account for actual emissions for these units from 2012-

2014 in any modeling to characterize the air quality around Plant Wilson for the Ohio County 

Area.

Because Plant Wilson’s future allowable limit is not yet federally-enforceable and there is no 

indication of a 1-hour averaging time or a comparatively stringent longer term averaging period, 

coupled with the uncertainty surrounding the shutdown of TVA Paradise Station Units 1 and 2, 

the EPA intends to designate the Ohio County Area as unclassifiable due to the absence of 

relevant information.

However, if the Commonwealth can: (1) establish Plant Wilson’s new allowable limit of 0.85 lb 

SO2/mmBTU as federally-enforceable(through an appropriate mechanism), by April 19, 2016; 

(2) document the 1-hour averaging time or as applicable, includes a longer term average limit 

that the EPA determines is comparatively stringent to a 1-hour limit at the critical emission value

(pursuant to the SO2 Nonattainment Guidance); (3) confirm and document that TVA-Paradise 

Fossil Plant Units 1 and 2 will be permanently retired for the purposes of validating the modeling 

submitted for the area of analysis and informing final designations scheduled July 2, 2016; (4)

notify the EPA of these conditions in advance of our promulgation of final designations, the EPA 

 

16 See the EPA’s “Guidance for 1-hour SO2 Nonattainment Area SIP Submissions,” dated April 23, 2014 available 

at: http://www3.epa.gov/airquality/sulfurdioxide/pdfs/20140423guidance.pdf. Previous EPA guidance, has 

suggested that averaging times for SIP emission limits should not exceed the averaging time of the applicable 

NAAQS the limit is intended to support attainment(i.e. the averaging time for an emission limit for complying with 

the 1-hour primary SO2 NAAQAS should not exceed 1-hour). (See S02 Guideline Document, U.S. Environmental 

Protection Agency, Office of Air Quality Planning and Standards, Research Triangle Park, N.C. 27711, EPA-452/R94-008, February 1994. (See http://www. epa. govlttnl oarpg/t 1 pgm. htm I). The EPA has established a procedure 

for establishing longer term averaging times (up to 30-days) that is comparatively stringent to a 1-hour limit at the 

critical emission value.
27

may be able to consider a designation of unclassifiable/attainment for the entirety of Ohio 

County. 

Jurisdictional Boundaries:

Once the geographic area of analysis associated with the Plant Wilson, other nearby sources, and 

background concentration is determined, existing jurisdictional boundaries are considered for the 

purpose of informing our intended unclassifiable/attainment area, specifically with respect to 

clearly defined legal boundaries. 

For the Ohio County Area, the Commonwealth considered major sources of SO2 emissions 

within a 20 km range and larger sources within a 20-50 km range that were believed to 

potentially contribute significant concentrations to the area of analysis. The Commonwealth

determined that this was the appropriate distance in order to adequately characterize air quality 

from the facility and other nearby sources which may have a potential impact in the area of 

analysis where maximum concentrations of SO2 from Plant Wilson are expected. 

The surrounding counties captured in Plant Wilson’s area of analysis includes Ohio, Webster 

Henderson, Daviess, and Muhlenberg, none of which have been designated nonattainment for the 

1-hour SO2 NAAQS. Furthermore, none of these counties, with the exception of Daviess County,

have been designated nonattainment for any other NAAQS. Additionally, the large sources 

evaluated within the 20-50 km range additionally included portions of Grayson, Breckinridge, 

Hancock, Henderson, Webster, Hopkins and Butler counties.

TVA-Paradise Fossil Plant in Muhlenberg County is located approximately 22 km southeast of

Plant Wilson, and had SO2 emissions of 1,9654.55 tpy in 2014. Actual emissions data from Unit 

3 at TVA-Paradise Fossil Plant were included in the modeling analysis for the area around Plant 

Wilson. The Commonwealth did not model 2012-2014 actual emissions for Units 1 and 2 but 

rather assumed a zero PTE based upon a future retirement of these units. The EPA notes 

inconsistent information on the timing of the retirement of TVA- Paradise Station Units 1 and 2, 

whether this will occur by April 2016 or June 2017. Therefore, unless the Commonwealth can 

provide documentation to the EPA that Units 1 and 2 have permanently retired in advance of the 

promulgation of final designations, the EPA cannot consider these shutdowns and instead 

believes that the Commonwealth should account for actual emissions for these units from 2012-

2014 in the modeling analysis characterizing the air quality around Plant Wilson for the Ohio 

County Area. 

The Green River Generating Station also in Muhlenberg County is located approximately 10 km 

from Plant Wilson and less than 0.5 km from the Ohio County border. The source reported 

2,1976.19 tons of SO2 in 2014 but according to reports from EIA, the last remaining Units 3 and 

4 were permanently retired in October 201517 resulting in zero PTE. Green River Station was not 

 

17 No emissions were reported to the EPA Air Markets Database beginning in October 2015 for any 

federal programs for which Green River Generating Station Units 3 and 4 would have been subject. Also, 
28

explicitly included in the modeling analysis for Plant Wilson due to permanent shutdown and 

zero potential to emit SO2. However, the source was considered in the background 

concentrations accounting for impacts from nearby sources including historic actual emissions. 

Considering the source’s zero PTE and the cumulative impacts captured in the background 

concentrations, the EPA does not have reason to believe that emissions from this now nonoperational facility are causing or contributing to a violation of the SO2 NAAQS in the Ohio 

County Area.

Other SO2 emitters the Commonwealth assessed within the 20-50 km range that reported SO2

emissions over 100 tpy included: Century Aluminum of Kentucky, LLC (Hancock County)(EPA 

notes this source is just beyond 50 km), Elmer Smith Station (Daviess County), Reid/Henderson 

Station II Generating Station and BREC Landfill (Webster County). These sources were not 

explicitly included in the modeling analysis because they’re all located approximately 35 km or 

greater from Plant Wilson and/or the Ohio County Area which the Commonwealth determined to 

be far enough that impacts from the facility relative to Plant Wilson. Based on the 

Commonwealth’s assessment considering distance from Ohio County Area, the EPA has reason 

to believe these sources would not cause or contribute to a violation of the SO2 NAAQS within 

the Ohio County Area.

The EPA notes that two BREC’s sources Green Station (Webster County) and Coleman Station

(Hancock County) and Owensboro Grain Company (Daviess) also reported 2014 emissions over 

100 tpy year but similar to those sources considered by the Commonwealth are also located over 

35 km away from Plant Wilson and Ohio County Area. Based on the distance from Plant Wilson 

and Ohio County border (>35 km), the EPA has reason to believe that these sources would not 

cause significant concentration gradients within the area of analysis or Ohio County. The EPA 

notes that other sources in counties within the 20-50 km range cumulatively emitted less than 

100 tpy of SO2 emissions according to 2014 actual emissions. 

Any area in Kentucky not designated by July 2, 2016, will be designated by either December 31, 

2017, or December 31, 2020, consistent with the deadlines prescribed in the final consent decree. 

The Commonwealth’s review of other SO2 emitting sources in terms of distance from Plant 

Wilson, potential impacts of other SO2 emitting sources within Ohio County, and scheduled shut 

downs that can be credited for the July 2, 2016, round of designations support the 

Commonwealth’s recommendation to designate the entirety of Ohio County.

The EPA’s observation of the Commonwealth’s review of nearby sources in and outside of Ohio 

County revealed that larger sources are far enough away that their impacts would be significantly 

reduced in terms of its impacts overlapping with those of Plant Wilson. Green River Generating 

Station in Muhlenberg County has permanently retired its remaining Units 3 and 4 as of October

2015, however, there is uncertainty surrounding the shutdown of TVA-Paradise Fossil Plant

Units 1 and 2. Furthermore, because Plant Wilson’s future allowable limit is not yet federally 

enforceable and there is no indication of a 1-hour averaging time or a comparatively stringent

longer term averaging period, the EPA intends to designate the Ohio County Area as 

 

EIA’s US Energy Information Administration “Electric Power Monthly” annual report for January 2016, 

tracked Units 3 and 4 as permanently retired as of October 2015.
29

unclassifiable. The intended unclassifiable designation consisting of Ohio County in its entirety

constitutes a clearly defined legal boundary.

Other Relevant Information

The Commonwealth’s recommended designation of attainment for Ohio County is based on air 

dispersion modeling analysis of a future allowable limit of 0.85 lb SO2/ mmBTU for Plant 

Wilson which is less than the current permitted limit of 1.2 lb SO2/mmBTU. This lower limit 

was proposed by BREC and modeled to show attainment for the 1-hour SO2 NAAQS. 

Consistent with past interpretations of legal requirements, control measures, emission limits and 

other curtailments need to be installed, operational and federally enforceable to be considered 

when informing final designation decisions. The mechanisms for establishing federally 

enforceable emission limits, control measures, or curtailments for the purpose of informing SO2

designations include: a source-specific SIP approved by the EPA, a minor new source review 

permit, a title v permit or a consent decree established through a federal civil litigation.

Therefore, the Commonwealth of Kentucky must ensure this new allowable limit is federally 

enforceable by April 19, 2016 for the purpose of informing final designations and as applicable, 

include a longer term average limit that is comparatively stringent to a 1-hour limit at the critical 

emission value pursuant to the EPA’s April 23, 2014 1-hour SO2 nonattainment guidance.18

Furthermore, the Commonwealth's decision to exclude actual emissions from 2012-2014 from 

Units 1 and 2 and TVA-Paradise Fossil Plant was based upon a future retirement of these units. 

However, the EPA is required to characterize the current air quality around the Plant Wilson 

source by July 2, 2016. The EPA notes conflicting information on the timing of the retirement of 

TVA-Paradise Fossil Plant Units 1 and 2, specifically, whether this will occur by April 2016 or 

June 2017. The Commonwealth and Plant Wilson must ensure that the units will be officially 

retired by April 19, 2016 for the purposes of validating the modeling submitted for the area of 

analysis and informing final designations. 

The EPA received no additional information regarding Plant Wilson or its surrounding area.

Conclusion.

The Commonwealth of Kentucky recommended a designation of attainment for the entirety of

Ohio County based on Plant Wilson’s air dispersion modeling (using AERMOD Model Version 

15181) analysis which considered a future allowable emission limit of 0.85 lb SO2/mmBTU at 

the facility, actual emissions from the TVA-Paradise Station Unit 3 (located just southeast of 

Plant Wilson in Muhlenberg Count) and background concentrations based on rural and natural 

background sources as well as regional impacts from distance large SO2 sources, and assumed 

that TVA-Paradise Units 1 and 2 would be retired. Additional SO2-emitting sources were 

identified within the analysis area, which extended 50 km out from Plant Wilson. But Plant 

Wilson determined that certain sources (i.e., TVA-Paradise Units 1 and 2 and Green River 

 

18 EPA’s “Guidance for 1-hour SO2 Nonattainment Area SIP Submissions,” dated April 23, 2014 available at: 

http://www3.epa.gov/airquality/sulfurdioxide/pdfs/20140423guidance.pdf
30

Station) would be shut down before final designations, and that based on the distance (at least 35 

km) from Plant Wilson and from the boundary of Ohio County (at least 20 km), the impacts from 

remaining sources would be significantly reduced in terms of potential overlap with those from 

Plant Wilson. The areas in other counties surrounding these sources will be designated by one of 

the other deadlines prescribed by the final consent decree, i.e., December 31, 2017, or December 

31, 2020. Based on these factors, Plant Wilson’s modeled 1-hour design value for its 20 km area 

of analysis, covering the entirety of Ohio County, is 186.5 μg/m3

, or 71 ppb. This modeled 

concentration is below the level of the 2010 SO2 NAAQS. Plant Wilson’s modeling parameters, 

assumptions and inputs were in compliance with the Agency’s Modeling TADs after careful 

evaluation of the Commonwealth’s recommendation and supporting information, as well as all 

available relevant information. 

It is unclear in the documentation provided by the Commonwealth whether Plant Wilson’s new 

allowable emission limit will be a 1-hour limit or whether there is some longer-term averaging 

period (e.g., 30-day rolling average) for the limit. As noted above, the EPA has developed SO2

nonattainment implementation guidance which indicates that modeling to determine attainment 

with the 1-hour SO2 NAAQS should use a higher 1-hour “critical value” to account for hourly 

emissions variability in a 30-day rolling average allowable limit. The details for the EPA’s 

recommended procedure for calculating the adjustment factor between the 1-hour critical value 

and an equivalent longer-term average emissions limit are provided in Appendices B and C of 

the EPA’s SO2 Implementation Guidance. The EPA has informed Kentucky that an appropriate 

1-hour critical value should be used in the modeling if the future allowable limit includes an 

averaging period longer than 1-hour. 

The EPA notes conflicting information on the timing of the retirement of TVA-Paradise Fossil 

Plant Units 1 and 2, specifically, whether this will occur by April 2016 or June 2017. Therefore,

it is unclear these units will be officially retired prior to the final promulgation of the July 2, 

2016 designation of the area surrounding Plant Wilson. Consequently, the EPA intends to 

designate the area around Plant Wilson Power Station comprised of Ohio County as 

unclassifiable for the 2010 SO2 NAAQS. 

However, if Plant Wilson’s new allowable limit of 0.85 lbs SO2/mmBTU is federallyenforceable and, as applicable, includes a longer term average limit that the EPA determines is 

comparatively stringent to a 1-hour limit at the critical emission value; and the Commonwealth 

confirms that TVA-Paradise Fossil Plant Units 1 and 2 will be permanently retired prior to the 

July 2, 2016, deadline for designations, and notifies the EPA of these conditions in advance of 

our promulgation of final designations, the EPA anticipates may be able to designate Ohio 

County unclassifiable/attainment. 

Based on all available information, including the reasons discussed above, the EPA is unable at 

this time to determine whether the area is meeting or not meeting the NAAQS. At this time, our 

intended designations for the Commonwealth only applies to this area (Ohio County) and the 

other area (Pulaski County) presented in this technical support document. Consistent with the 

conditions in the March 2, 2015 court-ordered consent decree schedule, the EPA will evaluate 

and designate all remaining undesignated areas in Kentucky by either December 31, 2017, or 

December 31, 2020.
31

Technical Analysis for the Plant Cooper – Pulaski County Area

Introduction

The Pulaski County Area contains a stationary source that according to the EPA’s Air Markets 

Database emitted in 2012 either more than 16,000 tons of SO2 or more than 2,600 tons of SO2

and had an annual average emission rate of at least 0.45 lbs SO2/mmBTU. As of March 2, 2015, 

this stationary source had not met the specific requirements for being “announced for 

retirement.” Specifically, in 2012, the Cooper Power Station emitted 7,428 tons of SO2, and had 

an emissions rate of 1.07 lbs SO2/mmBTU. Pursuant to the March 2, 2015 court-ordered 

schedule, the EPA must designate the area surrounding the facility by July 2, 2016.

In its submission, Kentucky recommended that the area surrounding the Cooper Power Station

(Cooper Station), specifically the entirety of Pulaski County, be designated as attainment based 

on an assessment and characterization of air quality from the facility and other nearby sources 

which may have a potential impact in the area of analysis where maximum concentrations of SO2

are expected. This assessment and characterization was performed using air dispersion modeling 

software, i.e., AERMOD, analyzing actual emissions in part and allowable emissions in part. The 

assessment was originally carried out by Trinity Consultants and prepared for the East Kentucky 

Power Cooperative. The Commonwealth then reviewed and submitted the information to the 

EPA.19

After careful review of the Commonwealth’s assessment, supporting documentation, and all 

available data, the EPA intends to designate the area as unclassifiable. However, if the 

Commonwealth provides notification of the following to the EPA prior to the promulgation of 

the July 2, 2016 designation, the EPA may consider designating the entirety of Pulaski County as 

unclassifiable/attainment, provided that are no outstanding technical issues: 1) assurance that the 

Cooper Station’s new PTE limit of 0.165 lb SO2/mmBTU for Unit 1 is federally-enforceable,

and, as applicable, includes a longer term average limit that the EPA determines is comparatively 

stringent to a 1-hour limit at the critical emission value; 2) the modeling for Units 1 and 2 at the 

facility are matched (e.g., PTE emissions or actual emissions over a common time period); and 

3) the updated modeling shows that the new PTE limit on Unit 1 or modeled actual emissions 

will ensure attainment of the NAAQS.

Cooper Station is located in the southern portion of Pulaski County. As seen in Figure 10 below, 

the facility is located approximately 10 km north of the center of Somerset. The power station is 

located near the Cumberland River, and there is medium to high land use development in the 

surrounding area. Also included in the figure are nearby emitters of SO2, the Commonwealth’s 

recommended area for the attainment designation, and the area the EPA intends to designate as 

unclassifiable.

 

19 Throughout this document the Commonwealth will be referred to as having assessed air quality in the area 

because the Commonwealth agreed with the East Kentucky Power Cooperative’s air quality assessment and 

characterization of the area of analysis, officially submitting the report to the EPA to support their designation 

recommendation.
32

Figure 10. The EPA’s intended designation for Pulaski County, Kentucky

The discussion and analysis that follows below will reference the Commonwealth’s use of the 

Modeling TAD, the EPA’s assessment of the Commonwealth’s modeling in accordance with the 

Modeling TAD, and the factors for evaluation contained in the EPA’s March 20, 2015 guidance, 

as appropriate

Detailed Assessment

Air Quality Data

This factor considers the SO2 air quality monitoring data in the area surrounding Cooper Station. 

The facility is located in Pulaski County, and the Commonwealth included monitoring data from 

the closest monitors: Nicholasville (21‐113‐0001), Lexington (21‐067‐0012), and Mammoth 

Cave National Park (21‐061‐0501), to the facility in its recommendation. The closest monitor is 

Nicholasville, located at KYTC Maintenance Garage, 260 Wilson Drive, Nicholasville, KY 

40356 (37.89147, -84.58825) in Jessamine County, and is 99 km away from Cooper Power 

Station. Data collected at this monitor is considered indicative of population exposure but is not 

representative of the expected background concentrations in the area surrounding the Cooper 
33

Station. The Mammoth Cave monitor, located at Alfred Cook Road, Park City, KY 42160 

(37.131944, -86.14778) is thought to be representative of rural areas with similar influences to 

the air quality around Cooper Station. Table 7 below summarizes the local monitors and design 

values within 150 km of Cooper Station.

Table 7: Historical Ambient Air Quality Data for Nearby Monitors

Monitor AQS ID County

2010–2012 

Design Value 

(μg/m3)

2011–2013 

Design Value 

(μg/m3)

2012–2014 

Design Value 

(μg/m3)

Nicholasville 21-113-0001 Jessamine 68.1 41.9 39.3

Lexington 21-067-0012 Fayette 68.1 44.5 34.0

Mammoth 

Cave 21-061-0501 Edmonson 31.4 26.2 26.2

Model Selection and Modeling Components

The EPA’s Modeling TAD notes that for area designations under the 2010 SO2 NAAQS, the 

AERMOD modeling system should be used, unless use of an alternative model can be justified. 

In some instances the recommended model may be a model other than AERMOD, such as the 

BLP model for buoyant line sources. The AERMOD modeling system contains the following 

components:

 AERMOD: the dispersion model

 AERMAP: the terrain processor for AERMOD

 AERMET: the meteorological data processor for AERMOD

 BPIPPRIME: the building input processor 

 AERMINUTE: a pre-processor to AERMET incorporating 1-minute automated surface 

observation system (ASOS) wind data 

 AERSURFACE: the surface characteristics processor for AERMET

 AERSCREEN: a screening version of AERMOD

The Commonwealth used AERMOD version 15181, and a discussion of the individual 

components will be referenced in the corresponding discussion that follows, as appropriate.

Modeling Parameter: Rural or Urban Dispersion

The EPA’s recommended procedure for characterizing an area by prevalent land use is based on 

evaluating the dispersion environment within 3 km of the facility. According to the EPA’s 

modeling guidelines, rural dispersion coefficients are to be used in the dispersion modeling 

analysis if more than 50 percent of the area within a 3 km radius of the facility is classified as 

rural. Conversely, if more than 50 percent of the area is urban, urban dispersion coefficients 

should be used in the modeling analysis. When performing the modeling for the area of analysis, 

the Commonwealth determined that it was most appropriate to run the model in rural mode. This 

determination was based on an analysis of land use within 3 km of the Cooper Power Station. 

Figure 11 below depicts land use within 3 km of the facility where greens, yellows and browns 
34

are farmland, forests, and grasses, pinks are non-urban developed lands, and red and dark red are 

urban areas. As can be seen in Figure 11, the area is predominantly rural by an overwhelming 

margin. Therefore the Commonwealth determined that is was most appropriate to run the model 

with rural dispersion coefficients

Figure 11. Distribution of Land Use Within 3 km of Cooper Station - Source: “Air Dispersion 

Modeling Report Cooper Station SO2 Designations Analysis Revision 1” prepared by Trinity 

Consultants for the East Kentucky Power Cooperative, September 1, 2015

Modeling Parameter: Area of Analysis (Receptor Grid)

The EPA believes that a reasonable first step towards characterization of air quality in the area 

surrounding the Cooper Station is to determine the extent of the area of analysis, i.e., receptor 

grid. Considerations presented in the Modeling TAD include but are not limited to: the location 

of the SO2 emission sources or facilities considered for modeling; the extent of significant 

concentration gradients of nearby sources; and sufficient receptor coverage and density to 

adequately capture and resolve the model predicted maximum SO2 concentrations. For the 

Pulaski County Area, the Commonwealth has included 1 other emitter of SO2 within 20 km of 

Cooper Station in any direction. For the Pulaski County Area, the Commonwealth evaluated 

offsite SO2 sources within 50 km of the facility in any direction and determined that it was only 

necessary to include one offsite source within 20 km of the facility in order to adequately 

characterize air quality on the vicinity of Cooper Station. This determination was based on the 

actual and potential 2013 emissions at each facility and the distance of each facility from Cooper 

Power Station. Table B-1.2 of the September 1, 2015, modeling report provided to the 
35

Commonwealth via East Kentucky Power Cooperative on September 2, 2015, details this 

screening assessment. The Commonwealth confirmed that a receptor grid extending 20 km in all 

directions from Cooper Station was the appropriate distance in order to adequately characterize 

air quality from the facility and other nearby sources which may have a potential impact in the 

area of analysis where maximum concentrations of SO2 are expected. In addition to Cooper

Station, the only other emitter of SO2 included in the area of analysis is Kingsford Manufacturing 

Company (KMC), located approximately 3 km south of the facility. The grid receptor spacing for 

the area of analysis chosen by the Commonwealth is as follows:

 “Fence Line” receptors at 50 meter (m) spacing along the main fence line for the facility

 100 m spacing out to 3 km

 250 m spacing from 3 km out to 5 km

 500 m spacing from 5 km to 10 km

 1000 m spacing from 10 km to 20 km

The receptor network contained 4,948 receptors, and the network covered the southern twothirds of Pulaski County in Kentucky, extreme northwestern McCreary County in Kentucky, and 

extreme northeastern Wayne County in Kentucky. 

Figures 12 and 13, included in the Commonwealth’s recommendation, show the 

Commonwealth’s chosen area of analysis surrounding the Cooper Station, as well as receptor

grid for the area of analysis.

Consistent with the Modeling TAD, receptors for the purposes of this designation effort were 

placed only in areas where it would also be feasible to place a monitor and record ambient air 

impacts. The impacts of the area’s geography and topography will be discussed later within this 

document.
36

Figure 12: Pulaski County Area of Analysis - Source: “Air Dispersion Modeling Report Cooper

Station SO2 Designations Analysis Revision 1” prepared by Trinity Consultants for the East 

Kentucky Power Cooperative, September 1, 2015
37

Figure 13: Innermost Portion of Modeling Receptor Grid for the Pulaski County Area of 

Analysis - Source: “Air Dispersion Modeling Report Cooper Station SO2 Designations Analysis 

Revision 1” prepared by Trinity Consultants for the East Kentucky Power Cooperative, 

September 1, 2015

Modeling Parameter: Source Characterization

The Commonwealth characterized the sources within the area of analysis in accordance with the 

best practices outlined in the Modeling TAD. Specifically, the Commonwealth used actual stack 

heights in conjunction with future allowable emissions limits for Cooper Station Unit 1 and 

actual emission rates for Cooper Station Unit 2. Units 1 and 2 share a common stack. The actual 

stack height does not exceed the GEP stack height. The Commonwealth also adequately

characterized the sources building layout and location, as well as the stack parameters, e.g., exit 

temperature, exit velocity, location, and diameter. Where appropriate, the AERMOD component 

BPIPPRIME was used to assist in addressing building downwash.
38

Modeling Parameter: Emissions 

The EPA’s Modeling TAD notes that for the purposes of modeling to characterize air quality for 

use in designations, the recommended approach is to use the most recent 3 years of actual 

emissions data and concurrent meteorological data. However, the TAD does provide for the 

flexibility of using allowable emissions in the form of the most recently permitted (referred to as 

PTE or allowable) emissions rate.

The EPA believes that CEMS data provide acceptable historical emissions information, when it 

is available, and that these data are available for many electric generating units. In the absence of 

CEMS data, the EPA’s Modeling TAD highly encourages the use of AERMOD’s hourly varying 

emissions keyword HOUREMIS, or through the use of AERMOD’s variable emissions factors 

keyword EMISFACT. When choosing one of these methods, the EPA believes that detailed 

throughput, operating schedules, and emissions information from the impacted source (s) should 

be used. 

In certain instances, states and other interested parties may find that it is more advantageous or 

simpler to use PTE rates as part of their modeling runs. Specifically, a facility may have recently 

adopted a new federally-enforceable emissions limit, been subject to a federally-enforceable 

consent decree, or implemented other federally-enforceable mechanisms and control 

technologies to limit SO2 emissions to a level that indicates compliance with the NAAQS. These 

new limits or conditions may be used in the application of AERMOD. In these cases, the 

Modeling TAD notes that the existing SO2 emissions inventories used for permitting or SIP 

planning demonstrations should contain the necessary emissions information for designationsrelated modeling. In the event that these short-term emissions are not readily available, they may 

be calculated using the methodology in Table 8-1 of Appendix W to 40 CFR Part 51 titled, 

“Guideline on Air Quality Models.” 

As previously noted, the Commonwealth included Cooper Station and one other emitter of SO2

within the 20 km area of analysis, i.e., KMC. This distance and these facilities were selected 

because the Commonwealth believes that this area of analysis adequately represents the area 

where maximum concentrations of SO2 are expected and adequately includes the sources which 

might contribute to those concentrations. Of the 16 facilities emitting SO2 within 20 km of the 

Cooper Station, only KMC has actual annual SO2 emissions greater than 2.5 tpy (37.97 tpy in 

201420). No other sources beyond 50 km were determined by the Commonwealth to have the 

potential to cause significant concentration gradient impacts within the area of analysis. 

For Cooper Station, the Commonwealth chose a hybrid approach for its analysis. Unit 1 operated 

with a 24-hour emission limit during the years considered, but a project at the facility will tie 

Unit 1 in with an existing dry flue gas desulfurization (DFGD) system for Unit 2 prior to the July 

2, 2016 deadline for characterizing and designating this area. The Commonwealth anticipates 

that both Units 1 and 2 will meet the federally enforceable emission limit currently in place for 

 

20 Unless otherwise noted, all 2014 data was accessed via the Emissions Inventory (EIS) gateway, which states 

report emissions to in accordance with 40 CFR Part 51, Subpart A. The EIS gateway can be accessed via: 

http://www3.epa.gov/ttnchie1/eis/gateway/
39

Unit 2 after the project is complete. Therefore, Unit 1 is modeled at its future allowable emission 

rate21 to reflect the future installation of SO2 emissions controls on that unit. Unit 2 is modeled 

with three years of actual emissions from July 1, 2012, through June 30, 2015 obtained from 

CEMS, reflecting the time for which its DFGD system was operational and its federally 

enforceable emission limit in effect. Actual emissions from July 31, 2012 through June 30, 2014 

for all units (Units 1 and 2) at Cooper Station are summarized in Table 8. 

Table 8: Actual SO2 Emissions Between mid-2012 – mid-2015 from Cooper Station

Facility Name Unit #

SO2 Emissions (tpy)

a

2012b2013 2014 2015c

Cooper Station 

1 1406.25 2812.09 2681.48 566.27

2 1862.96 1791.62 1642.37 682.58

a Data from EPA’s Air Markets Database.

b Beginning July 1, 2012.

c Ending June 30, 2015.

For KMC in the area of analysis, the Commonwealth has chosen to model the facility using the 

most recent federally enforceable PTE limits for SO2. The facilities included in the 

Commonwealth’s area of analysis and their associated PTE rate is shown below. 

Table 9: SO2 Emissions based on PTE from Facilities in the Pulaski County Area of Analysis

Facility Name

SO2 Emissions 

(tpy, based on PTE)

Kingsford 

Manufacturing 

Company 136

All Facilities 136

The PTE limit for Kingsford Manufacturing reflects existing emissions limits.

Modeling Parameter: Meteorology and Surface Characteristics

The most recent 3 years of meteorological data (concurrent with the most recent 3 years of 

emissions data) should be used in designations efforts. As noted in the Modeling TAD, the 

selection of data should be based on spatial and climatological (temporal) representativeness. 

The representativeness of the data are based on: 1) the proximity of the meteorological 

 

21 Cooper Station Unit 1 is undergoing modification to tie-in its exhaust gases into the existing DFGD system 

currently serving Unit 2. This modification is expected to be completed by January 1, 2016. For Cooper Station Unit 

1, the Commonwealth modeled an allowable emission rate of 178 pounds per hour (.165 pounds per million BTU 

(lbs/mmBtu)). This was derived from the existing Title V permit limit of 3.3 pounds SO2 per million BTU (24-hour 

average) by assuming a 95 percent reduction in emissions of SO2 and operating at 1080 mmBtu/hr year round (8,760 

hours). A 95 percent reduction was applied to the existing permit limit because the Commonwealth expects the 

facility to meet a federally enforceable SO2 emission limit of 95% removal efficiency (30-day rolling average) or .1 

lbs SO2 per mmBtu (30-day rolling average) on both Cooper Units once the tie in of Unit 1 into the Unit 2 DFGD is 

complete. The Title V permit is expected to be revised by July 2, 2016 to reflect these limits.
40

monitoring site to the area under consideration, 2) the complexity of terrain, 3) the exposure of 

the meteorological site, and 4) the period of time during which data are collected. Sources of 

meteorological data include NWS stations, site-specific or onsite data, and other sources such as 

universities, FAA, and military stations.

For the Pulaski County Area of analysis, surface meteorology from the NWS station in London, 

Kentucky, 64 km to the east, and coincident upper air observations from the NWS station in 

Nashville, Tennessee, 260 km to the southeast were selected as best representative of 

meteorological conditions within the area of analysis. 

The Commonwealth used AERSURFACE version 15181 using data from the NWS station in 

London, Kentucky (located at Latitude 37.087 North, Longitude 84.077 West) to estimate the 

surface characteristics of the area of analysis. The Commonwealth estimated values for 12 spatial 

sectors out to 1 km at a seasonal temporal resolution for average conditions. The Commonwealth

also estimated values for albedo (the fraction of solar energy reflected from the earth back into 

space), the Bowen ratio (the method generally used to calculate heat lost or heat gained in a 

substance), and the surface roughness (sometimes referred to as “Zo”). In the figure below, the 

location of the London, Kentucky NWS station is shown relative to the Pulaski County Area of 

analysis.
41

Figure 14: Cooper Power Station Area and the Nearby Meteorological Stations - Source: “Air 

Dispersion Modeling Report Cooper Station SO2 Designations Analysis Revision 1” prepared by 

Trinity Consultants for the East Kentucky Power Cooperative, September 1, 2015
42

As part of its recommendation, the Commonwealth provided the 3-year surface wind rose for the 

London-Corbin Airport NWS. In Figure 15, the frequency and magnitude of wind speed and 

direction are defined in terms of from where the wind is blowing. As shown in Figure 15, the 

predominant winds blow from the south at low to mid-level wind speeds of 0.5 to 5.7 

meters/second.

Figure 15: London-Corbin Airport Cumulative Annual Wind Rose from July 2012 – June 2015

Meteorological data from the above surface and upper air stations were used in generating 

AERMOD-ready files with the AERMET processor. The output meteorological data created by 

the AERMET processor is suitable for being applied with AERMOD input files for AERMOD 

modeling runs. The Commonwealth followed the methodology and settings presented in standard 
43

U.S. EPA meteorological processing guidance as outlined in a recent memorandum22 as well as 

other AERMET and associated preprocessor documentation in the processing of the raw 

meteorological data into an AERMOD-ready format, and used AERSURFACE to best represent 

surface characteristics. The Commonwealth selected the beta option ADJ_U* for AERMET. 

The EPA notes that the use of beta options, such as ADJ_U* and LOWWIND3, in AERMOD for 

any regulatory applications requires adherence with Appendix W, Section 3.2.2. This is further 

explained in the EPA’s December 10, 2015 Memorandum titled, “Clarification on the Approval 

Process for Regulatory Application of the AERMOD Modeling System Beta Options.” Among 

other conditions, the use of beta options requires consultation with the appropriate EPA Regional 

Offices. Upon concurrence by the EPA’s Modeling Clearinghouse, the EPA Regional Offices 

may approve the use of these beta options for regulatory applications as an alternative model. 

However, the Commonwealth provided air dispersion modeling intended to characterize air 

quality as a result of SO2 emissions from Cooper Station without prior approval from the EPA 

Region 4, and therefore has not met the applicable regulatory requirements contained in 

Appendix W, Section 3.2.2. As a result, the air quality modeling results obtained from the use of 

these beta options cannot be used as a reliable indicator of attainment status in the Pulaski 

County Area until appropriate alternative model approval is granted or these beta options are 

promulgated as regulatory options in AERMOD through the EPA rulemaking. The modeling 

documentation submitted by the Commonwealth provides information to justify use of the beta 

ADJ_U* option for this application. The EPA Region 4 will work with the EPA’s Model 

Clearinghouse to evaluate the use of beta ADJ_U* prior to the final designation of the area.

Hourly surface meteorological data records are read by AERMET, and include all the necessary 

elements for data processing. However, wind data taken at hourly intervals may not always 

portray wind conditions for the entire hour, which can be variable in nature. Hourly wind data 

may also be overly prone to indicate calm conditions, which are not modeled by AERMOD. In 

order to better represent actual wind conditions at the meteorological tower, wind data of one 

minute duration was provided from the same instrument tower, but in a different formatted file to

be processed by a separate preprocessor, AERMINUTE. These data were subsequently 

integrated into the AERMET processing to produce final hourly wind records of AERMODready meteorological data that better estimate actual hourly average conditions and that are less 

prone to over-report calm wind conditions. This allows AERMOD to apply more hours of 

meteorology to modeled inputs, and therefore produce a more complete set of concentration 

estimates. As a guard against excessively high concentrations that could be produced by 

AERMOD in very light wind conditions, the Commonwealth set a minimum threshold of 0.5 

meters per second in processing meteorological data for use in AERMOD. In setting this 

threshold, no wind speeds lower than this value would be used for determining concentrations. 

This threshold was specifically applied to the one minute wind data. 

 

22 Fox, Tyler, U.S. Environmental Protection Agency. 2013. “Use of ASOS Meteorological Data in AERMOD 

Dispersion Modeling.” Available Online: 

http://www.epa.gov/ttn/scram/guidance/clarification/20130308_Met_Data_Clarification.pdf 
44

Modeling Parameter: Geography and Terrain

The terrain in the area of analysis is best described as complex to hilly. To account for these 

terrain changes, the AERMAP terrain program within AERMOD was used to specify terrain 

elevations for all the receptors. The source of the elevation data incorporated into the model is 

from the United States Geological Survey National Elevation Database. Figure 16 provided in 

the Commonwealth’s recommendation shows a relief map of the terrain within 20 km of the 

Cooper facility.

Figure 16. Relief map of the terrain within 20 km of the Cooper facility - Air Dispersion 

Modeling Report Cooper Station SO2 Designations Analysis Revision 1” prepared by Trinity 

Consultants for the East Kentucky Power Cooperative, September 1, 2015
45

Modeling Parameter: Background Concentrations of SO2

The Modeling TAD offers two mechanisms for characterizing background concentrations of SO2

that are ultimately added to the modeled design values: 1) a “first tier” approach, based on 

monitored design values, or 2) a temporally varying approach, based on the 99

th percentile 

monitored concentrations by hour of day and season or month. For the Pulaski County Area of 

analysis, the Commonwealth chose to use a first tier approach using the 2012-2014 design value 

from the Mammoth Cave National Park ambient SO2 monitoring site located approximately 139 

km west of Cooper Station. Two other nearby monitors, summarized in Table 7, considered for 

this purpose were Nicholasville (99 km from Cooper Station) and Lexington (119 km from 

Cooper Station). These monitors were deemed inappropriate to represent background 

concentrations near Cooper Station due to their local settings and a relative emissions inventory 

that compared SO2 emissions from sources within 20 and 50 km of each monitor and compared 

with those within the same distances from Cooper Station. The Mammoth Cave site has the most 

comparable nearby emissions to Cooper Station. In addition, due to predominant wind patterns in 

the area, the Mammoth Cave site is expected to represent emissions from small sources in the 

Bowling Green-Glasgow combined statistical area (CSA). That CSA has a similar population to 

the Cooper Station. The Mammoth Cave site has a monitoring objective of general/background 

without a specified measurement scale. Due to its background status, this monitor is thought to 

be representative of rural areas with similar influences to the air quality around Cooper Station.

The background concentration for this area of analysis was determined by the Commonwealth to 

be 26.9 μg/m3, or 10.3 ppb,23 and that value was incorporated into the final AERMOD results. 

Summary of Modeling Results

The AERMOD modeling parameters for the Pulaski County Area of analysis are summarized 

below in Table 10.

 

23 The conversion factor for SO2 (at the standard conditions applied in the ambient SO2 reference method) is 1 ppb = 

approximately 2.62 μg/m3.
46

Table 10: AERMOD Modeling Parameters for the Pulaski County Area of Analysis

Cooper Station Area of Analysis

AERMOD Version 15181 

Dispersion Characteristics Rural 

Modeled Sources 2

Modeled Stacks 6

Modeled Structures 11

Modeled Fencelines 1

Total receptors 4,948

Emissions Type Actual & PTE

Emissions Years 7-1-2012 thru 6-30-2015 

Meteorology Years Same as Emissions Years

Surface Meteorology Station London, Kentucky

Upper Air Meteorology Station Nashville, Tennessee 

Methodology for Calculating 

Background SO2 Concentration

1

st tier – Monitored Design 

Value

Calculated Background SO2

Concentration 10.3 ppb or 26.9 μg/m3

The results presented below in Table 11 show the magnitude and geographic location of the 

highest predicted modeled concentration based on modeled emissions.

Table 11: Maximum Predicted 99th Percentile 1-Hour SO2 Concentration in the Pulaski County

Area of Analysis Based on Actual and Expected Future PTE Emissions

Averaging 

Period Data Period

Receptor Location SO2 Concentration (μg/m3)

UTM East UTM North

Modeled 

(including 

background) NAAQS

99th Percentile 

1-Hour Average

7-1-2012-

6-30-2015 714,550 4,098,043 173.1 196.5*

*Equivalent to the 2010 SO2 NAAQS set at 75 ppb

The Commonwealth’s modeling indicates that the predicted 99th percentile 1-hour average 

concentration within the chosen modeling domain is 173.1 μg/m3, or 66.1 ppb. This modeled 

concentration included the background concentration of SO2, and is based on actual and expected 

future PTE emissions from the facilities. This predicted value occurred just northeast of Cooper 

Station, and is graphically represented along with all the other receptors below in Figure 17. 
47

Figure 17: Maximum Predicted 99th Percentile 1-Hour SO2 Concentrations in the Pulaski County 

Area of Analysis Based on Actual and PTE Emissions – Source Air Dispersion Modeling Report 

Cooper Station SO2 Designations Analysis Revision 1” prepared by Trinity Consultants for the 

East Kentucky Power Cooperative, September 1, 2015
48

Jurisdictional Boundaries:

Once the geographic area of analysis associated with the Cooper Station, other nearby sources, 

and background concentration is determined, existing jurisdictional boundaries are considered 

for the purpose of informing our intended unclassifiable area, specifically with respect to clearly 

defined legal boundaries. 

Within the 20 km area of analysis around Cooper Station, 16 SO2 emitting sources were 

identified, all within Pulaski County. Only one source, i.e., KMC, has actual annual emissions 

greater than 2.5 tpy, based on 2013 actual emissions via the Kentucky Emissions Inventory 

System (KYEIS). With the exception of KMC, the cumulative annual SO2 emissions from all 

sources within 20 km of Cooper Station are 8.5 tpy on an actual emissions basis and 40 tpy on a 

potential emissions basis (KYEIS 2013). In comparison to the modeled SO2 emission rates from 

Cooper Station Units 1 and 2, the EPA does not believe that these smaller sources emit SO2 in 

quantities that would significantly alter the modeled concentration of SO2 within the area of 

analysis. Furthermore, the vast majority of these sources are located to the north of Cooper 

Station which is in a low frequency wind sector for wind directions causing transport from the 

regional source locations to the area of highest impacts for Cooper Station.. See Figure 15 above. 

An additional review of 38 sources located between 20 and 50 km from Cooper Station, which 

includes portions of McCleary, Wayne, Russel, Casey, Lincoln, Rockcastle, Laurel, and Whitley 

Counties resulted in only one source with actual SO2 emissions above 5 tpy. Specifically, 

theEKPC Laurel Ridge Landfill-Gas-to-Energy facility (EKPC) has actual annual SO2 emissions

of 36.1 tpy based on the 2013 KYEIS and allowable emissions of 41.3 tpy. EKPC is located 

approximately 45 km east of the Cooper Station, and approximately 19 km from the Pulaski 

County border. The London‐Corbin airport meteorological station wind rose in Figure 15 above

indicates a very low frequency of winds from this direction. Based on the low emissions from 

this facility in conjunction with the distance from the Pulaski County border, the EPA does not 

believe that EKPC’s emissions are causing or contributing to a violation of the NAAQS in 

Pulaski County.

The intended unclassifiable area, consisting of the entirety of Pulaski County constitutes a clearly 

defined legal boundary, and the EPA finds this boundary to be a suitably clear basis for defining 

our intended unclassifiable area.

Other Relevant Information

The EPA has conducted a review of the modeling performed by Trinity Consultants for the East 

Kentucky Power Cooperative and provided by the Commonwealth to support their designation 

recommendation. The EPA’s review has identified a number of unresolved concerns regarding 

the procedures and data used in the modeling which have led to the recommendation of 

unclassifiable for the Pulaski County Area. The following is a brief summary of significant 

issues identified in the EPA’s review of the modeling:

 The EPA’s modeling TAD gives the option of modeling 3-years of actual emissions or

allowable emissions. Cooper Power Station operates two coal-fired boilers with 
49

emissions ducted to a common stack. A scrubber was installed in 2012 and put into 

operation for Unit 2, which has a maximum heat input of 2,089 mmBtu/hr. Emissions 

from Unit 1, which has a maximum heat input of 1,080 mmBtu/hr, are currently in the 

process of being ducted to the same scrubber. Cooper modeled Unit 2 with July 2012-

July 2015 actual emissions combined with new expected future allowable emissions for 

Unit 1, using calculated design stack flow rates and temperatures for the two units 

operating together since they are emitted from a single, common stack. The EPA has 

determined that using a combination of actual and allowable emissions is not appropriate 

since the emissions from the two units are combined and emitted from a common stack. 

The EPA has recommended to the Commonwealth and Cooper Station that the modeling 

be revised to either use the new expected future allowable (PTE) limits from both units, if 

made federally enforceable in time to inform the final designation, or to use actual 

emissions from a common 3-year time period for both units. 

 The EPA’s review of the modeling documentation indicates that Cooper used the 30-day 

rolling average allowable emission limit for Unit 1 directly as the 1-hour emission rate 

input into the AERMOD model. The EPA has developed SO2 nonattainment 

implementation guidance24 which indicates that modeling to determine attainment with 

the 1-hour SO2 NAAQS should use a higher 1-hour “critical value” to account for hourly 

emissions variability in 30-day rolling average allowable limit. The details for the EPA’s 

recommended procedure for calculating the adjustment factor between the 1-hour critical 

value and the equivalent 30-day rolling average emissions limit are provided in 

Appendices B and C of the EPA’s SO2 Implementation Guidance. The EPA has informed 

Kentucky that an appropriate 1-hour critical value must be used if Cooper Station decides 

to revise their modeling to use allowable (PTE) emissions for both units as discussed 

above.

The EPA received no additional information regarding Cooper Station or its surrounding area. 

Conclusion

The Commonwealth of Kentucky recommended a designation of attainment for the entirety of

Pulaski County based on Cooper Station’s air dispersion modeling (using AERMOD Model 

Version 15181) analysis which considered a future allowable emission limit of 0.165 lb

SO2/mmBTU at Unit 1 and actual emissions Unit 2, assuming background concentrations based 

on rural and natural background sources as well as regional impacts from distance large SO2

sources. Additional SO2-emitting sources were identified within the analysis area, which 

extended 50 km out from Cooper Station. But Cooper Station determined that certain sources 

that based on the relatively low emissions for sources within 20 km of Cooper Station (less than 

2.5 tpy) and for sources outside of Pulaski County, between 20 and 50 km from Cooper Station

(less than 5 tpy), the impacts from remaining sources would be significantly reduced in terms of 

potential overlap with those from Cooper Station. The areas in other counties surrounding these 

sources will be designated by one of the other deadlines prescribed by the final consent decree, 

 

24 EPA’s “Guidance for 1-hour SO2 Nonattainment Area SIP Submissions,” dated April 23, 2014 available at: 

http://www3.epa.gov/airquality/sulfurdioxide/pdfs/20140423guidance.pdf
50

i.e., December 31, 2017, or December 31, 2020. Based on these factors, Cooper Station’s

modeled 1-hour design value for its 50 km area of analysis, covering the entirety of Pulaski 

County, is 173.1 μg/m3

, or 66 ppb. This modeled concentration is below the level of the 2010

SO2 NAAQS.

However, it is unclear in the documentation provided by Kentucky and the East Kentucky Power 

Cooperative whether Cooper Station’s new allowable emission limit at Unit 1 will be in place 

and federally-enforceable prior to final designation of the area around Cooper Station. 

Furthermore, as indicated above, the EPA would also need to evaluate the emission limit for its 

applicability for demonstrating compliance with the 1-hour standard due to its identification as a 

30-day rolling average. 

The EPA has determined that if the new PTE limit at Cooper Station’s Unit 1 is federallyenforceable prior to the promulgation of final air quality designations and is consistent with 

guidance on longer-term average limits, Cooper Station’s modeling parameters, assumptions and 

inputs may still not in compliance with the Agency’s Modeling TADs. After careful evaluation 

of the Commonwealth’s recommendation and supporting information, as well as all available 

relevant information, the EPA believes that the modeling for this Area should be updated. 

Specifically, the Commonwealth should provide modeling that uses PTE limits for both Units 1 

and 2, or actual emissions from both units over a common three-year period.

The EPA intends to designate the area around Cooper Station as unclassifiable for the 2010 SO2

NAAQS. Specifically, the boundary is comprised of the entirety of Pulaski County, Kentucky.

However, if the Commonwealth provides notification of the following to the EPA prior to the 

promulgation of the July 2, 2016 designation, the EPA may consider designating the entirety of 

Pulaski County as unclassifiable/attainment, provided that are no outstanding technical issues: 1) 

assurance that the Cooper Station’s new PTE limit of 0.165 lb SO2/mmBTU for Unit 1 is 

federally-enforceable, and, as applicable, includes a longer term average limit that the EPA 

determines is comparatively stringent to a 1-hour limit at the critical emission value; 2) the 

modeling for Units 1 and 2 at the facility are matched (e.g., PTE emissions or actual emissions 

over a common time period); and 3) the updated modeling shows that the new PTE limit on Unit 

1 or modeled actual emissions will ensure attainment of the NAAQS.

Based on all available information, including the reasons discussed above, the EPA is unable at 

this time to determine whether the area is meeting or not meeting the NAAQS. At this time, our 

intended designations for the Commonwealth only apply to this area (Pulaski County) and the 

other area presented in this technical support document (Ohio County). Consistent with the 

conditions in the March 2, 2015, court-ordered schedule, the EPA will evaluate and designate all 

remaining undesignated areas in Kentucky by either December 31, 2017, or December 31, 2020.