1

Technical Support Document

Ohio

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.

Ohio submitted updated recommendations on September 16, 2015, ahead of a July 2, 2016, 

deadline for EPA to designate certain areas established by the U.S. District Court for the 

Northern District of California. This deadline is the first of three deadlines established by the 

court for EPA to complete area designations for the 2010 SO2 NAAQS. Table 1 below lists 

Ohio’s recommendations and identifies the counties or portions of counties in Ohio that 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, and other evidence and supporting 

information. 

Table 1: Ohio’s Recommended and EPA’s Intended Designations

Area

Ohio’s 

Recommended 

Area Definition

Ohio’s 

Recommended 

Designation

EPA’s Intended 

Area Definition

EPA’s 

Intended 

Designation 

Clermont 

County, Ohio

Clermont County, 

excluding Pierce 

Township

Attainment

Same as State’s 

Recommendation

Unclassifiable/ 

Attainment

Gallia

County, Ohio

Gallia County

and

In Meigs County: 

Bedford, 

Columbia, 

Rutland, Salem, 

Salisbury, and 

Scipio Townships

Attainment

Same as State’s 

Recommendation Unclassifiable

Background
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On June 3, 2010, 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. 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 

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, 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 EPA is also not 

currently designating areas on the basis of the secondary standard.

General Approach and Schedule

Section 107(d) of the Clean Air Act 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 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, EPA will promulgate 

the designations that it deems appropriate. If a state disagrees with EPA’s intended designations, 

it is given an opportunity within the 120 day period to demonstrate why any proposed 

modification is inappropriate.

On August 5, 2013, 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, 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 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 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 EPA to complete the area designations 

according to the court-ordered schedule.

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

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

 

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 EPA approves a SIP providing for attainment of the 2010 NAAQS. Clermont, 

Gallia, and Meigs Counties are not subject to these exceptions. 
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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 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 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. 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 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 I-X. This memorandum supersedes earlier designation 

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

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

guidance also contains the factors 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, EPA

released its most recent versions of documents titled, “SO2 NAAQS Designations Modeling 

Technical Assistance Document” (Modeling TAD) and “SO2 NAAQS Designations SourceOriented Monitoring Technical Assistance Document” (Monitoring TAD) in December 2013.

Based on ambient air quality data collected between 2012 and 2014, no violations of the 2010 

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

 

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

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

certified data for 2015, the analyses of applicable areas for 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 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 EPA to complete 
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sources in the state meeting the emissions criteria of the consent decree for which EPA must 

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

its review and technical analysis of Ohio’s updated recommendations for the areas that we must 

designate. EPA also discusses any intended modifications from the state’s recommendations

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 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. 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 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 EPA has determined to have 

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

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 EPA

designate as attainment. 

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

designate as nonattainment. 

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

designate as unclassifiable.

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

that 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. 

 

the designation. Instead, we may designate the area and all other previously undesignated areas in the state on a 

schedule consistent with the prescribed timing of the court order, i.e., by December 31, 2017, or December 31, 2020. 
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Technical Analysis for the Clermont County, Ohio Area

Introduction

Clermont County, Ohio contains a stationary source that according to 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 pounds of SO2 per one million British 

thermal units (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 W.H. 

Zimmer Generating Station (Zimmer) emitted 11,975 tons of SO2, and had an emissions rate of 

0.53 lbs SO2/MMBTU. Pursuant to the March 2, 2015 court-ordered schedule, EPA must 

designate the area surrounding the facility by July 2, 2016.

In its submission, Ohio recommended that the area surrounding Zimmer, specifically all 

townships in Clermont County with the exception of Pierce Township3, 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. After careful 

review of the state’s assessment, supporting documentation, and all available data, EPA agrees

that the area is attaining the standard, and intends to designate Clermont County (excluding 

Pierce Township) as unclassifiable/attainment. 

As seen in Figure 1 below, Zimmer is located in Moscow, along the Ohio River along the 

southern border of Clermont County. Clermont County is in southwest Ohio, near Cincinnati. 

Also included in the figure are nearby emitters of SO2 and EPA’s intended designation for the 

area.

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

 

3 Pierce Township, Clermont County, Ohio was designated nonattainment for the 2010 SO2 NAAQS on 

August 5, 2013 (78 FR 47191). This township included a major source (Beckjord Generating Stations) that

subsequently shut down. Ohio has addressed this township separately, notably by submitting a redesignation request

on August 11, 2015 for this township, and EPA will be addressing this township separately as well.
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The discussion and analysis that follows below will reference the state’s use of the Modeling 

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

factors for evaluation contained in EPA’s March 20, 2015 guidance, as appropriate.

Detailed Assessment

Model Selection and Modeling Components

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 
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- 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 state used AERMOD version 15181, the most recent regulatory version of the model, and a 

discussion of the individual components will be referenced in the corresponding discussion that 

follows, as appropriate.

Modeling Parameter: Rural or Urban Dispersion

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

evaluating the dispersion environment within 3 kilometers (km) of the facility. According to 

EPA’s Guideline on Air Quality Models, rural dispersion coefficients are to be used 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 this area is urban, urban dispersion coefficients should be used in the 

modeling analysis. Using this recommended approach, the state determined that less than 50

percent of the land area within 3 km of Zimmer is industrial, commercial, or dense residential, 

which indicates that the area is primarily rural. Therefore, the state determined that it was most 

appropriate to run the model in rural mode. 

Modeling Parameter: Area of Analysis (Receptor Grid)

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

surrounding Zimmer 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. As 

AERMOD is recommended for use within 50 km of a given emission source, the state 

conservatively determined that 50 km was an appropriate distance 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. For the Clermont County area, 

the state considered fifteen other emitters of SO2 within 50 km of Zimmer. The state found that 

none of the sources within 50 km were close enough or large enough to cause a significant 

concentration gradient in the vicinity of Zimmer. The grid receptor spacing for the area of 

analysis chosen by the state is as follows:

- 50 meter spacing on the fenceline

- 50 meter spacing to 3 km from the stacks 

- 100 meter spacing to 5 km

- 500 meter spacing to 10 km

- 1000 meter spacing to 25 km from the facility

- 1000 meter spacing covering the northern portion of Clermont County
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- A discrete receptor was placed at the background monitor location.

The receptor network contained 37,702 receptors. For the purposes of this designation effort, the 

Modeling TAD states that the receptor grid need not include receptors in areas where it would 

not be feasible to place a monitor and record ambient air impacts, such as bodies of water. In the 

Clermont County analysis, receptors were not placed on the Ohio River or within facility 

fencelines in the receptor grid. The receptor grid covered the entirety of Clermont County, a 

portion of Brown and Hamilton Counties in Ohio, and a portion of Campbell, Pendleton, and 

Bracken Counties in Kentucky.

Figure 2 below shows the area surrounding the Zimmer plant in southern Clermont County and 

some of the Hamilton County source locations. The location of the surface NWS station is 

shown in this figure, in northern Boone County, Kentucky, northwest of Zimmer.

Figure 2: Clermont County, Ohio Area of Analysis 

Figure 3, included in the state’s recommendation, shows the receptor grid for the area of 

analysis. In Figure 3, the area outlined in blue to the northwest of the fine receptor grid is the 

Campbell-Clermont SO2 nonattainment area, which includes Pierce Township in Clermont 

County, Ohio, and a portion of Campbell County, Kentucky. Ohio has submitted a request to 

redesignate the area to attainment. 
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Figure 3: Receptor Grid for the Clermont County, Ohio Area of Analysis

Modeling Parameter: Emissions

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. The Modeling TAD highly encourages the use of the 

most detailed throughput, operating schedule and emissions information available. Variable 

emissions, temperature, and flow data can be modeled using AERMOD’s hourly varying 

emissions keyword HOUREMIS or variable emission factor keyword EMISFACT. EPA

believes that continuous emissions monitoring systems (CEMS) data provide valuable historical 

emissions information, when it is available, and that these data are available for many electric 

generating units. However, the TAD does provide for the flexibility of using allowable 

emissions in the form of a federally enforceable limit on the emissions rate (referred to as PTE or 

allowable emissions).
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In certain instances, it may be advantageous or simpler to use PTE rates in designations 

modeling analyses. 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 designations-related 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 state considered fifteen other SO2 sources of varying size, located 

within 50 km of Zimmer. See Table 2. The state chose that distance to ensure a thorough 

facility search, out to the maximum distance for which AERMOD is considered to be applicable.

However, none of these SO2 sources were determined by the state to have the potential to cause 

significant concentration gradient impacts within the area of analysis. 

Table 2: Actual SO2 Emissions for 2012 – 2014 from Facilities in the Clermont County, Ohio

Area of Analysis

Facility Name

Distance

from 

Zimmer 

(km)

Actual SO2 Emissions 

(tons per year)

2012 2013 2014

W.H. Zimmer Generating Station -- 11,975 18,457 13,498

Duke Energy Ohio, Beckjord Station 

(stopped operating 10/2014) 14.9 67,069 51,900 32,603A

Miami Fort Power Station, Hamilton 

Co OH (Unit 6 closed 6/2015) 57.1 26,407 31,844 28,479

DTE ST. Bernard, LLC, Hamilton Co 

OH 41.6 1,666

Rock-Tenn Converting, Hamilton Co 

OH 36.1 179

Duke Energy Kentucky, East Bend 

Station, Boone Co KYA 54.5 1,497 2,198 2,103

Spurlock Station, Mason Co KY B 40.9 5,131 4,469 4,689

Carmeuse Lime Pendleton Co KY C, E 3.1 614 524 655

Griffin Industries, Pendleton Co KY C 21.4 101

KAO Brands N/A 92

Mill Creek WWTP N/A 20

University of Cincinnati N/A 14

TSS Aviation N/A 10

Emery Oleochemicals N/A 1

Caraustar Mill N/A 0.1
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Emerald Performance N/A 0.05

Total Emissions From All Facilities in 

the State’s Area of Analysis 114,776D 111,475D 84,110

A Beckjord Station closed its coal-fired units in October 2014 and no longer emits SO2. Therefore its 2012-2014 emissions were 

not included in the Zimmer modeling analysis.

B Emissions from EPA’s Air Markets Database. Other 2014 data from Ohio’s Fee Emission Reports.

C Emissions from 2008 NEI.

D Totals assume 2014 emissions for facilities without reported 2012 or 2013 data.

E See text.

The Walter C. Beckjord power plant (Beckjord) was not included in the modeling because it shut 

down its coal-fired units in October 2014, and the closure is permanent and enforceable. Its 

current SO2 emissions are zero. Therefore, while it would have been contributing significantly to 

local SO2 concentrations in the time period Ohio modeled (2012-2014), Beckjord’s historical 

emissions do not represent current (or future) conditions, and therefore are not relevant for 

determining the appropriate SO2 designation for the remainder of Clermont County. The Miami 

Fort Power Station (Miami Fort) permanently stopped using its Unit 6 in June 2015. Although 

the plant’s other SO2 emitting units still operate, preliminary 2015 data from EPA’s Air Markets 

Database shows that Miami Fort emitted 14,239 tons per year (tpy) in 2015, which is about half 

of its 2014 emissions. Miami Fort is 57 km from Zimmer and 43 km from the nearest border of 

Clermont County. With similar SO2 emissions to Miami Fort’s, the Zimmer plant’s modeled 

impacts were less than 100 μg/m3further than 5 km from the source. This suggests that Miami 

Fort’s impacts are likely to be well below the NAAQS in Clermont County. In addition, the 

prevailing winds in the area, as measured at Cincinnati/Northern Kentucky Airport, blow 

primarily from the south-southwest, which would not bring Miami Fort’s emissions into 

Clermont County. Ohio determined that given its location, Miami Fort is unlikely to provide a 

significant concentration gradient near Zimmer or anywhere within Clermont County. DTE St. 

Bernard, LLC in Hamilton County and the remaining emission sources in Hamilton County 

would be similarly affected by the prevailing south-southwest winds, and given their distance 

from the Clermont County border and from Zimmer, they are not expected to cause or contribute 

to an exceedance of the 2010 SO2 NAAQS in Clermont County. The background concentration 

is expected to account for their impacts in the Zimmer analysis. The two Kentucky power plants 

are located 40 to 54 km from Zimmer, and they have relatively low emissions, so they are not 

expected to provide significant concentration gradient in Clermont County. Their emissions are 

expected to be accounted for by the background concentration.

Carmeuse Lime, in Pendleton, KY, was not discussed in Ohio’s September 16, 2015 

recommendation submittal. Ohio EPA staff informed EPA on November 17, 2015, that they had 

been unable to obtain modeling input information from Kentucky in time to include it in the 

Clermont County analysis. Ohio has previously modeled a similar, but larger, Carmeuse facility 

in Ohio, which had approximately 7 times the SO2 emissions of the Pendleton, KY facility. By 

extrapolating from that analysis, Ohio concluded that the Pendleton, KY facility would be 

unlikely to cause or contribute to modeled concentrations over the standard either in its own 

vicinity or in Clermont County, nor would the facility have caused or contributed to a modeled 

exceedance of the NAAQS near Zimmer, had it been included in the Clermont County modeling 

analysis. Ohio believes that the impacts of the Pendleton facility in Clermont County are 

adequately covered by the background concentration. EPA agrees that the emissions from this 
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source are sufficiently small and sufficiently distant from Zimmer and other locations in 

Clermont County that it may reasonably be accounted for as part of the background 

concentration and judged not to cause air quality significantly different than that found in Ohio’s 

modeling.

Modeling Parameter: Source Characterization

The state characterized Zimmer in accordance with the best practices outlined in the Modeling 

TAD. Specifically, the state used actual stack heights in conjunction with hourly actual 

emissions, stack temperatures, and stack exit velocities. The state also adequately characterized 

the source’s 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.

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 

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 Clermont County area of analysis, surface meteorology from Cincinnati/Northern 

Kentucky Airport in Covington, Kentucky, 43 km northwest of Zimmer, and coincident upper air 

observations from Wilmington, Ohio 74 km to the northeast, were selected as best representative 

of meteorological conditions within the area of analysis. 

The state used AERSURFACE version 13016 to estimate the surface characteristics of the area 

of analysis. The state developed surface characteristics for 12 spatial sectors at a seasonal

temporal resolution at the Cincinnati NWS site. These surface characteristics are the albedo (the 

fraction of solar energy reflected from the earth back into space), the Bowen ratio (representing 

the ratio of sensible heat flux to latent heat flux at the ground level), and the surface roughness

(representing the influence of ground features such as buildings and vegetation on surface wind 

flow). 

As part of its recommendation, the state provided the 3-year surface wind rose for Cincinnati, 

Ohio. In Figure 4, the frequency and magnitude of wind speed and direction are defined in terms 

of from where the wind is blowing. Winds at the Cincinnati airport are predominantly from the 

southwest.
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Figure 4: Cincinnati, Ohio Cumulative Annual Wind Rose for Years 2012 – 2014

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 state used AERSURFACE to determine appropriate surface characteristics, 

and followed EPA guidance in the processing of the raw meteorological data into an AERMODready format. Ohio processed the Cincinnati NWS surface meteorological data using the 

AERMINUTE preprocessor, which uses one-minute meteorological observations to provide the 
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most complete and accurate hourly-averaged surface wind data. Then Ohio used AERMET to 

combine surface and upper air data into input files required by the AERMOD model. 

Modeling Parameter: Geography and Terrain

The terrain in the area of analysis is hilly, along the Ohio River valley. The AERMAP terrain 

program within AERMOD was used to specify elevations for all the receptors. The source of the

elevation data incorporated into the model is from the USGS National Elevation Dataset. 

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 Clermont County area of 

analysis, the state chose to use the SO2 monitor in northern Campbell County, Kentucky (21-

037-3002). This monitor, which is located approximately 28 km northwest of Zimmer, is the 

nearest representative SO2 monitor. This monitor is considered to be well representative of other 

SO2 sources in the Cincinnati area. It was also impacted by emissions from Beckjord, until the 

facility permanently shut down its coal-fired boilers in October 2014. For such situations, the 

Modeling TAD recommends determining background concentrations based on a data set that 

excludes “concentrations when the source in question is impacting the monitor.” Ohio analyzed 

hourly concentrations at this monitor and correlated the data with wind direction data from the 

Cincinnati NWS site, processed with AERMINUTE, for January 2012 through February 2015. 

The data was also correlated with hourly emissions from Beckjord and Zimmer. For the full 

dataset, maximum concentrations at the monitor appeared to be primarily due to Beckjord. Ohio 

also analyzed a dataset of the 10,321 hours when Beckjord’s SO2 emissions were zero. No 

exceedances of the standard occurred during these hours, and the maximum monitored 

concentrations for this time period came from the west and southwest of the monitor. Ohio 

determined that a background concentration taken from this data set would account well for any 

currently operating SO2 sources which currently affect the Clermont County area. In addition, 

the background is still conservative because it was likely impacted by the emissions of Unit 6 at 

the Miami Fort power plant east of Cincinnati, which was operating during 2012-2014, but shut 

down in June 2015, reducing SO2 emissions by over 18,000 tons per year. The background 

concentration which Ohio used for the Clermont County analysis was determined by the state to 

be the 99th percentile of the values for which Beckjord had zero emissions and the monitor value 

was nonzero. The resulting value was 28.8 micrograms per cubic meter (μg/m3), or 11 ppb.

4

This value was incorporated into the final AERMOD results and is expected to account for the 

impacts of sources not included in the Clermont County analysis. 

 

4 The conversion factor for SO2 (at the standard conditions applied in the ambient SO2 reference 

method) is 1ppb = approximately 2.62μg/m3.
15

Since the SO2 air quality standard reflects the 99th percentile among daily maximum 

concentrations, the common means of determining a single, “first tier” background value is to 

determine the 99th percentile among daily maximum background concentrations, i.e. the 99th

percentile among a set of daily maximum values in a data set that includes only values that are 

representative of background concentrations. The common means of determining hourly 

background concentrations is to determine the 99th percentile among 24 sets of values reflective 

of background concentrations, where each data set is for a single hour. The average of these 24 

hourly 99th percentile background concentrations would be approximately the same as the 99th

percentile among the full data set. In this sense, Ohio has applied a single, “first tier” 

background concentration, but Ohio has determined a level that corresponds approximately to 

the average of the levels they would have determined had they evaluated hourly background 

concentrations. In addition, by excluding hours when the monitor recorded zero ppb, Ohio has 

determined a somewhat conservative approach in determining 99th percentile values. Therefore, 

Ohio has applied a reasonable background concentration in its analysis, consistent with the 

recommendations of the Modeling TAD.

Summary of Modeling Results

The AERMOD modeling parameters for the Clermont County area of analysis are summarized 

below in Table 3

Table 3: AERMOD Modeling Parameters for the Clermont County, Ohio Area of Analysis

Clermont County, Ohio Area of Analysis

AERMOD Version 15181 

Dispersion Characteristics Rural 

Modeled Sources 1

Modeled Stacks 2

Modeled Structures 24

Modeled Fencelines 1

Total receptors 37,702

Emissions Type Actual, temporally varying

Emissions Years 2012-2014

Meteorology Years 2012-2014 

Surface Meteorology Station

Cincinnati/Northern Kentucky

Airport

Upper Air Meteorology Station Wilmington, Ohio

Methodology for Calculating 

Background SO2 Concentration

99th percentile of monitored hours 

without influence from now-closed 

neighboring power plant

Calculated Background SO2

Concentration 11 ppb/ 28.8 μg/m3
16

The results presented below in Table 4 show the magnitude and geographic location of the 

highest predicted modeled concentration based on actual emissions from Zimmer and 

background concentrations.

Table 4: Maximum Predicted 99th Percentile 1-Hour SO2

Concentration in the Clermont County, Ohio Area of Analysis Based on Actual Emissions

Averaging Period Data Period

Receptor Location SO2 Concentration (μg/m3

)

UTM E UTM N

Modeled (including 

background) NAAQS

99th Percentile 

1-Hour Average 2012-2014 741200 4306850 147.0 196.4*

*Equivalent to the 2010 SO2 NAAQS set at 75 ppb

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

within the chosen modeling domain is 147.0 μg/m3, or 56.1 ppb. This modeled concentration 

included the background concentration of SO2. Figure 5 below was included as part of the state’s 

recommendation, and indicates that the predicted value occurred just to the north of Zimmer.

Figure 5: Maximum Predicted 99th Percentile 1-Hour SO2 Concentrations in the 

Clermont County, Ohio Area of Analysis Based on Actual Emissions
17

Jurisdictional Boundaries:

Once the geographic area of analysis associated with Zimmer was determined, existing 

jurisdictional boundaries were considered for the purpose of informing our intended designated 

area, specifically with respect to clearly defined legal boundaries. Ohio recommended 

designating all of Clermont County attainment, with the exception of Pierce Township. Pierce 

Township was designated nonattainment on August 15, 2013. The recommended attainment 

area for Clermont County consists of the following townships: Batavia, Franklin, Goshen, 

Jackson, Miami, Monroe, Ohio, Stonelick, Tate, Union, Washington, Wayne, and Williamsburg. 

This area has clearly defined legal boundaries, and we find this boundary to be a suitably clear 

basis for defining our intended unclassifiable/attainment area.

Ohio’s modeling demonstrated that actual emissions from the Zimmer facility, in addition to 

background SO2, would not cause or contribute to a violation of the 2010 SO2 NAAQS in 

Clermont County. There are other SO2-emitting sources located in the Cincinnati area in 

Hamilton County, which borders Clermont County to the west. Ohio did not model these 

additional sources to explicitly demonstrate attainment near Clermont County’s border with 

Hamilton County, but EPA believes that the Hamilton County sources are not likely to cause 

NAAQS violations in Clermont County. The largest SO2 source in Hamilton County is the 

Miami Fort Generating Station, but this source, in western Hamilton County, is located about 40

km from the Clermont County border, and almost 60 km from Zimmer, and therefore is unlikely 

to have a significant concentration gradient in Clermont County. The next largest source in 

Hamilton County is DTE St. Bernard, which emitted 1,666 tpy in 2014. With its moderate 

emissions and its location approximately 10 km from the western Clermont County border, it is 

not expected to cause or contribute to a violation of the NAAQS in Clermont County. The

remaining SO2-emitting facilities in Hamilton County emit less than 200 tpy and are all 10-20 

km from the Clermont County border. Although EPA expects further air quality characterization 

of the SO2 sources in the Hamilton County area which exceed the DRR threshold of 2,000 tpy, 

these sources are sufficiently distant, generally 40-50 km from the Clermont County border, that 

they can be presumed not to be causing or contributing to violations of the NAAQS in Clermont 

County. In addition, the background monitor Ohio is using for the Clermont County analysis is 

located near Hamilton County and is expected to be influenced by emissions from Hamilton 

County SO2 sources.

Other Relevant Information

On September 16, 2015, the Sierra Club submitted a modeling analysis for the area surrounding 

Zimmer. This analysis indicated a violation of the NAAQS. In a November 17, 2015 letter to 

EPA, Ohio commented that the Sierra Club analysis used incomplete and incorrect hourly 

emissions and stack parameter information for Zimmer, and emissions data which was more 

conservative than the Modeling TAD requires for two additional modeled sources. These errors 

can have significant effect on model estimates, rendering the Sierra Club modeling a less reliable 

analysis of air quality in the area than the state’s analysis. The Sierra Club analysis did not 

provide information refuting the appropriateness of Ohio’s analysis of Zimmer and Clermont 

County for this round of SO2 designations, and EPA does not find that the Sierra Club analysis 
18

has provided compelling information to designate Clermont County as nonattainment rather than 

applying the unclassifiable/attainment designation supported by Ohio’s analysis.

Conclusion

After careful evaluation of the state’s recommendation and supporting information, as well as all 

available relevant information, EPA intends to designate Ohio’s recommended townships in 

Clermont County, Ohio as unclassifiable/attainment for the 2010 SO2 NAAQS. 

EPA does not believe that the designation of Clermont County outside of Pierce Township for 

the 2010 SO2 NAAQS is affected by the fact that Pierce Township, Clermont County, is 

currently designated nonattainment for the 2010 SO2 NAAQS. Pierce Township’s designation in 

August 2013 was based on a NAAQS violation recorded in Campbell County, Kentucky, for the 

time period 2009-2011. The Beckjord plant was presumed to be the primary contributor to this 

violation, based on the plant’s location, emissions level, and local wind trajectory analyses. The 

Beckjord plant shut down its coal-fired boilers as of October 2014. On August 11, 2015, Ohio 

formally requested that EPA redesignate Pierce Township to attainment of the 2010 SO2

NAAQS, based on the Beckjord plant’s shutdown and the improvement in monitored air quality 

demonstrated at the monitor. As Ohio recommended, EPA will address Pierce Township 

through a separate process that focuses on Ohio’s request for redesignating that Township to 

attainment. EPA is not in this separate designation pre-judging that future action, which will be 

based on the agency’s review of that administrative record.

At this time, our intended designations for the state only apply to this area and the other areas 

presented in this technical support document. Consistent with the conditions in the March 2, 

2015 court-ordered schedule, EPA will evaluate and designate all remaining undesignated areas 

in Ohio by either December 31, 2017, or December 31, 2020. 
19

Technical Analysis for the Gallia County, Ohio Area

Introduction

Gallia County in southern Ohio contains a stationary source that according to 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 General James M. Gavin Power Plant (Gavin) emitted 

31,269 tons of SO2, and its emissions rate was 0.36 lbs SO2/MMBTU. Pursuant to the March 2, 

2015 court-ordered schedule, EPA must designate the area surrounding the facility by July 2, 

2016.

In its submission, Ohio recommended that the area surrounding Gavin, specifically Gallia 

County and a portion of Meigs County which contains the SO2 monitor, 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. After careful 

review of the state’s assessment, supporting documentation, and all available data, EPA finds 

that due to a discrepancy in the state’s analysis, the area cannot be designated attainment at this 

time, but the evidence does not fully support a designation of nonattainment. Therefore, EPA 

intends to designate Gallia County and a portion of Meigs County as unclassifiable. 

As seen in Figure 6 below, Gavin and the nearby Kyger Creek Station are both located south of 

the village of Cheshire along the Ohio River in northeast Gallia County. The Gavin facility is 

located approximately 17 km northeast of the county seat of Gallipolis. Also included in the 

figure are nearby emitters of SO2, and the boundaries of the state’s recommended area.

Figure 6. EPA’s intended designation for Gallia County, Ohio 
20

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

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

factors for evaluation contained in EPA’s March 20, 2015 guidance, as appropriate.

Detailed Assessment

Monitored Data

There are five SO2 monitors in the Gallia County area. These monitors and their design values 

(DV) are listed in Table 5. The Meigs County monitor is located to the northeast of Gavin and 

Kyger Creek. The other monitors, which were sited to capture impacts from other large SO2

sources, are located approximately 70 km southeast of Gavin and Kyger Creek. The Meigs 

County monitor was sited to represent impacts from Gavin and Kyger Creek. Its 2012-2014 

design value is 30 ppb, well below the 2010 SO2 NAAQS. Ohio cited this data as evidence that 

Gallia County is currently attaining the 2010 SO2 NAAQS, given the current impacts of Gavin 

and Kyger Creek, along with the low SO2 concentrations coming into Gallia County from 

Lawrence and Scioto Counties with the prevailing winds from the southwest. While this monitor 
21

appears not to be located where maximum concentrations would be expected, so that the 

monitoring data do not provide convincing evidence as to the attainment status of the area, the 

monitored data do provide some support for the state’s conclusion that the area is attaining the 

standard.

Table 5: Design Values at Monitors Near Gavin Facility

Monitor ID County 2012-2014 DV (ppb) Distance from Gavin 

(km)

39-105-0003 Meigs 30 13

39-087-0012 Lawrence 17 67

39-145-0013 Scioto 9 72

39-145-0020 Scioto 27 71

39-145-0022 Scioto 19 73

Model Selection and Modeling Components

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

In its modeling study to support the Gallia County recommended designation, the state used 

AERMOD version 15181, the most recent regulatory version of the model. A discussion of the 

individual components, most notably a discussion of two beta options used in Ohio’s analysis,

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

Modeling Parameter: Rural or Urban Dispersion

When performing the modeling for the area of analysis, the state determined that it was most 

appropriate to run the model in rural mode. Although Ohio did not conduct a formal Auer 

analysis of the area, clearly less than 50 percent of the land use near the two large sources in 

Gallia County is industrial, commercial, or dense residential.

Modeling Parameter: Area of Analysis (Receptor Grid)
22

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

surrounding Gavin 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 Gallia

County area, the state considered other emitters of SO2 within 50 km of Gavin. The state 

determined that this was an appropriate conservative 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. The grid receptor spacing 

for the area of analysis chosen by the state is as follows:

- 50 meter spacing along fencelines and to 2 km from the stacks 

- 250 meter spacing to 8 km

- 500 meter spacing to 15 km

- 1000 meter spacing to 25 km

- 2000 meter spacing to 50 km

- Included receptor at monitor location

The receptor network contained 34,225 receptors. For the purposes of this designation effort, the 

Modeling TAD states that the receptor grid need not include receptors in areas where it would 

not be feasible to place a monitor and record ambient air impacts, such as bodies of water. Ohio 

did not seek to identify areas where it might be infeasible to place a monitor, and instead 

conservatively placed receptors according to the above array without respect to feasibility of 

monitoring.

Figure 7. Gallia County area of analysis.
23

Figure 8, included in the state’s recommendation, shows the state’s receptor grid for the area of 

analysis.

. 
24

Figure 8: Receptor Grid for the Gallia County, Ohio Area of Analysis

Modeling Parameter: Source Characterization

The state characterized the sources within the area of analysis in accordance with the best 

practices outlined in the Modeling TAD. Specifically, the state used actual stack heights in 

conjunction with actual emissions. The state also adequately characterized the source’s 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.

Modeling Parameter: Emissions 

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. The Modeling TAD highly encourages the use of the

most detailed throughput, operating schedule and emissions information available. Variable 

emissions, temperature, and flow data can be modeled using AERMOD’s hourly varying 

emissions keyword HOUREMIS or variable emission factor keyword EMISFACT. EPA

believes that continuous emissions monitoring systems (CEMS) data provide valuable historical 

emissions information, when it is available, and that these data are available for many electric 

generating units. However, the TAD does provide for the flexibility of using allowable 

emissions in the form of a federally enforceable limit on the emissions rate (referred to as PTE or 

allowable emissions rate.
25

As previously noted, the state evaluated other SO2 sources located within 50 km of the area of 

analysis. The Phillip Sporn power station and the Mountaineer power station in Mason County, 

WV are located approximately 17 km from Gavin. The Sporn station closed in June 2015. The 

predominant winds from the southwest, as measured at Huntington, WV, would disperse the 

emissions of the Mountaineer plant toward the eastern portion of Meigs County (not included in 

Ohio’s designation recommendation). There are no other significant sources of SO2 in or near 

Gallia and Meigs Counties. Only Gavin and Kyger Creek were determined by the state to have 

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

facilities in the area of analysis and their most recently available annual actual SO2 are 

summarized below. 

Table 6: Actual SO2 Emissions Between 2012 – 2014 from Facilities in the Gallia County, Ohio 

Area of Analysis

Facility Name

Distance 

from 

Gavin 

(km)

Actual SO2 Emissions 

(tons per year)

2012 2013 2014

AEP General James M. Gavin Plant -- 31,269A 27,852 36,872

AEP Kyger Creek Station 2.5 4,989 9,434 13,748

Appalachian Power Mountaineer Plant 

(Mason Co WV) 16.7 1,151 2,903 4,411

Appalachian Power Phillip Sporn Plant 

(Mason Co WV) closed 6/2015 17.2 8,078 9,032 10,650

Felman Productions-New Haven (Mason 

Co WV)B 17.2 534

Total Emissions From All Facilities in the 

State’s Area of Analysis 46,021C 49,755C 66,215

A Emissions from EPA’s Air Markets Database. Other 2014 data from Ohio’s Fee Emission Reports.

B Emissions from 2011 NEI.

C Assumes 534 tons per year from Felman Productions

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 

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.
26

For the Gallia County area of analysis, surface meteorology from the Huntington Tri-State 

Airport in West Virginia, located 65 km south-southeast of Gavin, and coincident upper air 

observations from the NWS station in Pittsburgh, Pennsylvania, 235 km to the northeast, were 

selected as best representative of meteorological conditions within the area of analysis. 

The state used AERSURFACE version 13016 to estimate the surface characteristics of the area 

of analysis. The state developed surface characteristics for 12 spatial sectors at a monthly 

temporal resolution at the Huntington NWS site. These surface characteristics are the albedo (the 

fraction of solar energy reflected from the earth back into space), the Bowen ratio (representing 

the ratio of sensible heat flux to latent heat flux at the ground level), and the surface roughness 

(representing the influence of ground features such as buildings and vegetation on surface wind 

flow).

As part of its recommendation, the state provided the 3-year surface wind rose for Huntington, 

WV. In Figure 9, the frequency and magnitude of wind speed and direction are defined in terms 

of from where the wind is blowing. The winds at Huntington are most frequently from the 

southwest.

Figure 9: Huntington, WV Cumulative Annual Wind Rose for Years 2012 – 2014
27

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 state used AERSURFACE to determine appropriate surface characteristics, 

and followed EPA guidance in the processing of the raw meteorological data into an AERMOD-
28

ready format. Ohio processed the Huntington NWS surface meteorological data using the 

AERMINUTE preprocessor, which uses one-minute meteorological observations to provide the 

most complete and accurate hourly-averaged surface wind data. Then Ohio used AERMET to 

combine surface and upper air data into input files required by the AERMOD model. 

In the Gallia County modeling, Ohio used two AERMET/AERMOD beta options, which are not 

yet part of the regulatory default option in AERMOD: Adjusted U-star, and LOWWIND3. 

These options adjust AERMOD’s performance during low wind speed conditions. Using these 

options for a regulatory application currently requires EPA approval. Ohio provided a model 

performance analysis to support their decision to apply the options. 

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 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 EPA’s Modeling Clearinghouse, EPA Regional Offices may 

approve the use of these beta options for regulatory applications as an alternative model. 

However, Ohio performed air dispersion modeling intended to characterize air quality as a result 

of SO2 emissions from Gavin and Kyger Creek without prior consultation with and approval 

from an EPA Regional Office, and therefore has not met the applicable regulatory requirements 

contained in Appendix W, Section 3.2.2. As a result, EPA does not believe that the air quality 

modeling results obtained from the use of these beta options can be used as a reliable indicator of 

attainment status in Gallia County until appropriate alternative model approval is granted or 

these beta options are promulgated as regulatory options in AERMOD through EPA rulemaking. 

Specific to LOWWIND3, this beta option currently has only one reasonable pathway for 

appropriate EPA Regional Office approval with EPA’s Model Clearinghouse concurrence. This 

pathway, specifically contained as condition number 2 in Appendix W, Section 3.2.2(b), is one 

in which an application-specific statistical performance evaluation is conducted. In an 

application-specific statistical performance evaluation, air quality modeling for the particular 

type of facility in question would have to be evaluated against representative air quality monitors 

that are appropriately sited for the given application. However, LOWWIND 3 at this time has not 

yet fully received scientific peer-review (i.e., criterion “i” for condition number 3 of Appendix 

W, Section 3.2.2(e)), and so this option must meet a more rigorous test for its approval as an 

alternative model. Through a proposed rulemaking to revise Appendix W and promulgate new 

regulatory options in AERMOD, we have received a number of public comments specific to the 

LOWWIND3 beta options and are working to complete our review of those comments and then 

to finalize appropriate action on the LOWWIND3 option with the necessary peer-reviewed 

journal articles as part of final Appendix W rulemaking package. Due to the potential changes 

that may occur prior to finalization of the Appendix W rulemaking package, in conjunction with 

the fact that, at this time, LOWWIND 3 has not been demonstrated to have statistically improved 

performance over that of the regulatory default version of AERMOD for the particular type of 

facility or has not yet fully received scientific peer-review, EPA does not believe that the air 
29

quality modeling results obtained from the use of this beta option can be used at this time as a 

reliable indicator of attainment status in Gallia County.

Modeling Parameter: Geography and Terrain

The terrain in the area of analysis is hilly, along the Ohio River valley. The AERMAP terrain 

program within AERMOD was used to specify elevations for all the receptors. The source of the 

elevation data incorporated into the model is from the USGS National Elevation Dataset. 

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 Gallia County analysis, 

the state chose to use 2012-2014 data from the monitor at Pomeroy in Meigs County (39-105-

0003) as background. This monitor, which is located 15 km north-northeast of Gavin, is the 

nearest representative SO2 monitor. The State eliminated all hours in which the winds came from 

the 30 degree sector influenced by Gavin and Kyger Creek, then took the 3-year average of the 

99th percentile of each year’s hourly distribution. The background concentration for the Gallia

County analysis was determined by the state to be 26.2 micrograms per cubic meter (μg/m3), or 

10 ppb.5 This value was incorporated into the final AERMOD results. 

Since the SO2 air quality standard reflects the 99th percentile among daily maximum 

concentrations, the common means of determining a single, “first tier” background value is to 

determine the 99th percentile among daily maximum background concentrations, i.e. the 99th

percentile among a set of daily maximum values in a data set that includes only values that are 

representative of background concentrations. The common means of determining hourly 

background concentrations is to determine the 99th percentile among 24 sets of values reflective 

of background concentrations, where each data set is for a single hour. The average of these 24 

hourly 99th percentile background concentrations would be approximately the same as the 99th

percentile among the full data set. In this sense, Ohio has applied a single, “first tier” 

background concentration, but Ohio has determined a level that corresponds approximately to 

the average of the levels they would have determined had they evaluated hourly background 

concentrations. Therefore, Ohio has applied a reasonable background concentration in its 

analysis, consistent with the recommendations of the modeling TAD.

Summary of Modeling Results

 

5 The conversion factor for SO2 (at the standard conditions applied in the ambient SO2 reference 

method) is 1ppb = approximately 2.62μg/m3.
30

The AERMOD modeling parameters for the Gallia County analysis are summarized below in 

Table 7

Table 7: AERMOD Modeling Parameters for the Gallia County, Ohio Area of Analysis

Gallia County, Ohio Area of Analysis

AERMOD Version 15181 

Dispersion Characteristics Rural 

Modeled Sources 2

Modeled Stacks 4

Modeled Structures 47

Modeled Fencelines 2

Total receptors 34,225 

Emissions Type Actual hourly

Emissions Years 2012-2014

Meteorology Years 2012-2014 

Surface Meteorology Station Huntington, WV

Upper Air Meteorology Station Pittsburgh, PA

Methodology for Calculating 

Background SO2 Concentration

99th percentile with large facility 

emissions omitted

Calculated Background SO2

Concentration 10 ppb/ 26.2 μg/m3

The results presented below in Table 8 show the magnitude and geographic location of the 

highest predicted modeled concentration based on actual emissions from Gavin, Kyger Creek, 

and background concentrations.

Table 8: Maximum Predicted 99th Percentile 1-Hour SO2

Concentration in the Gallia County, Ohio Area of Analysis Based on Actual Emissions

Averaging Period Data Period

Receptor Location SO2 Concentration (μg/m3

)

UTM E UTM N

Modeled (including 

background) NAAQS

99th Percentile 

1-Hour Average 2012-2014 400900 4306700 188.3 196.5*

*Equivalent to the 2010 SO2 NAAQS set at 75 ppb

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

within the chosen modeling domain is 188.3 μg/m3, or 71.9 ppb. This modeled concentration 

included the background concentration, and is based on actual emissions from the nearby 

facilities. Figure 10 below was included as part of the state’s recommendation, and indicates that 

the predicted value occurred 1200 meters from the Kyger Creek fenceline.
31

Figure 10: Maximum Predicted 99th Percentile 1-Hour SO2 Concentrations in the 

Gallia County, Ohio Area of Analysis Based on Actual Emissions

Other Relevant Information

On September 16, 2015, the Sierra Club submitted a modeling analysis for the area surrounding 

Gavin. This analysis indicated a violation of the NAAQS. In a November 17, 2015 letter to 

EPA, Ohio commented that the Sierra Club analysis used an inaccurate stack configuration for 

Kyger Creek, with incorrect hourly emissions and stack parameter information for both Gavin 

and Kyger Creek. An additional source was modeled with overly conservative emissions data. 

These errors have the potential to cause significant misrepresentations of the impacts of these 

sources, such that EPA does not consider the Sierra Club’s modeling to provide a reliable 

assessment of whether the area is violation the NAAQS. As noted above, EPA also does not 

consider Ohio’s analysis to be a reliable assessment of concentrations in the area. Since the 

deficiencies in the two analyses are different, the Sierra Club analysis does not provide a reliable 

indication, even in combination with the state’s analysis, as to whether the area is attaining the 

NAAQS. 

Jurisdictional Boundaries:
32

Once the geographic area of analysis associated with Gavin and Kyger Creek is determined, 

existing jurisdictional boundaries are considered for the purpose of informing our intended 

designated area, specifically with respect to clearly defined legal boundaries. 

Ohio recommended an attainment designation for all of Gallia County and the western half of 

Meigs County, which includes Bedford, Columbia, Rutland, Salem, Salisbury, and Scipio 

Townships. This area has clearly defined legal boundaries, and we find this boundary to be a 

suitably clear basis for defining our intended designated area.

Ohio’s modeling demonstrated that the Gavin and Kyger Creek facilities would not cause or 

contribute to a violation of the 2010 SO2 NAAQS in Gallia or Meigs Counties. There are other 

SO2-emitting sources in Mason County, West Virginia, to the east of Gavin and Kyger Creek. 

Ohio did not model these sources, as they were considered to be too distant, given their moderate 

emission levels, to have a significant contribution in the vicinity of Gavin. They are closest to the 

eastern half of Meigs County, and it is expected that their impacts would be most significant in 

that area, based on their location and the prevailing southwest winds. There are several sources 

with SO2 emissions between 1000 and 3000 tpy in counties neighboring Gallia and Meigs 

County: one in Athens County (1,338 tpy, 14.5 km from the Meigs County border; two in 

Washington County (2,993 tpy, 15 km from the Meigs County border, and 2,593 tpy, 21 km 

from the Meigs County border); and one in Jackson County West Virginia (2,636 tpy, 25 km 

from the Meigs County border). Due to their distance from the Meigs County border, these 

facilities are not expected to cause or contribute to violations of the NAAQS within Meigs 

County. The impacts of these sources are reasonably considered to be represented as part of the

background concentration included in the analysis.

Due to the use of the AERMOD beta option LOWWIND3, which cannot be approved at this 

time, EPA does not find Ohio’s modeled analysis demonstrating attainment in the Gallia County 

area to be a reliable assessment of whether the area is attaining the standard. While EPA also 

received an independent modeling analysis from Sierra Club demonstrating nonattainment, EPA 

finds that this analysis contained incorrect source and plume data and emission inputs which 

were more conservative than the Modeling TAD recommends. Therefore, EPA finds that this 

modeling analysis also does not provide a reliable basis on which to determine EPA’s 

designation for this area. Therefore, EPA intends to designate the area recommended by Ohio as 

unclassifiable. EPA believes that our intended unclassifiable area, consisting of Gallia County 

and the western half of Meigs County, has clearly defined legal boundaries, and we find this 

boundary to be a suitably clear basis for defining our intended unclassifiable area.

Conclusion

Because the Ohio modeling analysis used a draft model option which cannot be approved by 

EPA at this time, EPA has determined that the state’s recommended designation of attainment 

does not provide a reliable assessment of whether the area is attaining the NAAQS. While a 

monitor that is 13 km from Gavin indicates attainment at its location, this monitor provides little 

basis for determining whether areas closer to the major facilities in this area are attaining the 

NAAQS. EPA has also determined that evidence of nonattainment demonstrated by Sierra Club 

is unreliable as a result of mischaracterization of source and stack gas characteristics and overly 
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conservative eimission input values. Therefore, EPA does not find that a reliable basis exists for 

designating the area either as attainment or nonattainment. Instead, after careful evaluation of 

available relevant information, EPA intends to designate Gallia County and Bedford, Columbia, 

Rutland, Salem, Salisbury, and Scipio Townships in Meigs County as unclassifiable for the 2010 

SO2 NAAQS. 

At this time, our intended designations for the state only apply to this area and the other areas 

presented in this technical support document. Consistent with the conditions in the March 2, 

2015 court-ordered schedule, EPA will evaluate and designate all remaining undesignated areas 

in Ohio by either December 31, 2017, or December 31, 2020.