1

Technical Support Document

New York

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.

New York submitted updated recommendations on September 18, 2015, ahead of a July 2, 2016, 

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

New York’s recommendations and identifies the counties or portions of counties in New York

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: New York’s Recommended and EPA’s Intended Designations

Area New York’s

Recommended 

Area Definition

New York’s 

Recommended 

Designation

EPA’s Intended 

Area Definition

EPA’s Intended 

Designation 

Erie -

Niagara, NY

Erie County, 

Niagara County, 

Cattaraugus 

County

Attainment Erie County, 

Niagara County

Unclassifiable/

Attainment

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 

two prior primary standards of 140 ppb evaluated over 24 hours, and 30 ppb evaluated over an 
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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 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 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 

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 

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 

 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.
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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 I-X. 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.

For the State of New York, 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 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 New York’s updated 

recommendations for the 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: 

 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, 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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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 Erie - Niagara, NY Area

Introduction

The Erie-Niagara area contains two stationary sources 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 pounds of SO2 per one million British 

thermal units (lbs SO2/mmBTU). As of March 2, 2015, these stationary sources had not met the 

specific requirements for being “announced for retirement.” Specifically, the Huntley Generating

Station emitted 2,716 tons of SO2 in 2012, and had an emissions rate of 0.70 lbs SO2/mmBTU.

In addition, the Somerset Generating Station emitted 5,653 tons of SO2 in 2012, and had an 

emissions rate of 0.53 lbs SO2/mmBTU. Pursuant to the March 2, 2015 court-ordered schedule, 

the EPA must designate the area surrounding these facilities by July 2, 2016.

In its submission, New York recommended that the area surrounding the Huntley and Somerset 

Generating Stations, specifically the entirety of Erie, Niagara, and Cattaraugus Counties, 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, 

the EPA does not agree entirely with the State’s recommendation for the area, and intends to 

designate only Erie and Niagara Counties as unclassifiable/attainment.

The Huntley Generating Station is located in the northwestern portion of Erie County 10.5 km 

north-northwest of Buffalo, NY. The plant is on the shore of the Niagara River in the Town of 

Tonawanda, NY and can be seen in Figure 1 below. In addition, the Somerset Generating 

Station is located in Niagara County approximately 35 miles north-northeast of Buffalo, NY and 

50 miles west-northwest of Rochester, NY. The plant is on the south shore of Lake Ontario and 

can be seen in Figure 2. Also included in the figures are nearby emitters of SO2, the State’s 

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

unclassifiable/attainment designation for the area.
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Figure 1: The Huntley Generating Station, Erie County, New York
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Figure 2: The Somerset Generating Station, Niagara County, New York

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

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

the factors for evaluation contained in the EPA’s March 20, 2015 guidance, as appropriate.
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Detailed Assessment for Huntley Generating Station

Air Quality Data

This factor considers the SO2 air quality monitoring data in the area surrounding Huntley 

Generating Station. The facility is located in Erie County, and the State included monitoring data 

from the Air Quality Systems monitor (Tonawanda - Brookside Terrace (or Tonawanda II) -

monitor id - 360291014) closest to the facility in its recommendation. This monitor is located at

192 Brookside Terrace West, Buffalo, NY, in Erie County, and is approximately 3.2 km away 

from Huntley Generating Station. Data collected at this monitor indicates that SO2

concentrations are well below the SO2 NAAQS and have been trending downward. In addition, 

these data have been quality assured and are valid for comparison to the NAAQS. A summary of 

historical design values (DV) in ppb in is listed below in Table 2.

Table 2: Available Air Quality Data for the Area Closest to Huntley Generating Station

County Air Quality 

Systems 

(AQS) 

Monitor ID

Monitor 

Location

Distance to 

Huntley 

Generating 

Station

’10 – ’12 DV

(ppb)

’11 – ’13 DV

(ppb)

’12 – ’14 DV

(ppb)

Erie 36-029-1014 192 Brookside 

Terrace West, 

Buffalo NY

3.2 km 29 25 22

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 State used AERMOD version 14134, and a discussion of the individual components 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.
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The State came to this conclusion by examining the land-use within 3 km of the facility. They 

analyzed the meteorological data using the AERSURFACE pre-processor. AERSURFACE uses 

land cover data from the National Land Cover Data (NCLD) 1992 database to determine the 

surface roughness, albedo, and Bowen ratio.

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 Huntley Generating 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 area surrounding the Huntley Generating Station in the Erie - Niagara, NY area, the State

used only ambient monitoring data along with the Huntley Generating Station modeling results 

since the ambient monitoring data, to a large degree, reflect the contributions from the other 

sources in the area.

- 100 m spacing from the source to 2km

- 250 m spacing from 2 km to 5 km

- 500 m spacing from 5 km to 10 km

- 1000 m spacing from 10 km to 20 km

Receptors were placed on 36 radials 10 degrees apart and the grid was centered on the emission 

source. Receptors within the Huntley fence line were eliminated and special receptor were 

placed along the fence line at every 25 m. The grid contained a total of 1369 receptors. While 

the EPA believes that with increasing distance, spatial resolution may diminish while using a 

polar grid (as opposed to Cartesian), since the maximum concentration from the facility was 

close in and was well below the NAAQS, we feel that this is acceptable.

Figure 3, included in the State’s recommendation, shows the State’s chosen area of analysis

surrounding the Huntley Generating Station, as well as receptor grid for the area of analysis.
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Figure 3: Huntley 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. 

Modeling Parameter: Source Characterization 

The State characterized the source(s) 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. The AERMOD component BPIPPRIME was used to assist in addressing

building downwash. 
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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 continuous emissions monitoring systems (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 State only included ambient monitoring data along with the Huntley 

Generating Station for this analysis. In its recommendation, New York stated that because 

ambient monitored air quality data in the area already to a large degree reflect the contribution of 

Huntley and nearby sources to the SO2 concentration, it was not necessary to include emissions 

from sources other than Huntley in the modeling. All of the available monitor data was used in 

calculating the seasonal/hourly background values, including the time periods when the nearby 

sources were impacting the monitor. As such, the modeled concentrations, which include 

seasonal/hourly 99th percentile background, can be expected to be highly conservative. Actual 

emissions data obtained from temporally variable rates for Huntley Generating Station between 

2012 and 2014 are summarized in Table 3 below. 

Table 3: Actual SO2 Emissions between 2012 and 2014 from Facilities in the Erie - Niagara, NY

Area of Analysis

Facility Name

SO2 Emissions (tons per year)

2012 2013 2014

Huntley Generating Station 2,716 3,218 3,192
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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 Erie - Niagara, NY area of analysis, surface and upper air data were obtained from the 

Buffalo Niagara International Airport, approximately 16.5 km to the southeast, and were 

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

The State used AERSURFACE version 13016 using data from the Buffalo Niagara International 

Airport (located at 685258.87E, 4756637.93N) to estimate the surface characteristics of the area 

of analysis. The State estimated values for 360 degrees out to 1 km at a seasonal temporal 

resolution for average conditions. The State 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 Figure 4 below, included in the State’s recommendation, the location of 

the Buffalo Niagara International Airport station is shown relative to the Huntley Generating 

Station area of analysis.
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Figure 4: Huntley Generating Station Area of Analysis and the Buffalo Niagara International 

Airport

As part of its recommendation, the State provided the 3-year surface wind rose for the Buffalo 

Niagara International Airport. In Figure 5, the frequency and magnitude of wind speed and 

direction are defined in terms of from where the wind is blowing. While the figure shows winds 

from all directions, the predominant wind direction is from the southwest.
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Figure 5: Buffalo Niagara International Airport Cumulative Annual Wind Rose (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 followed the methodology and settings presented in EPA’s Guideline 

on Air Quality Models (40 CFR Appendix W) and DEC’s Air Modeling Procedures as outlined 

in DAR-10 / NYSDEC Guidelines on Dispersion Modeling Procedures for Air Quality Impact 

Analysis, modified by the SO2 NAAQS Designations Modeling Technical Assistance Document 

(Modeling TAD), where applicable, 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 
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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 State set a minimum threshold of 0.5 meters per 

second in processing meteorological data for use in AERMOD. This approach is consistent with 

a March 2013 EPA memo titled, “Use of ASOS meteorological data in AERMOD dispersion 

Modeling.” 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. 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

USGS 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 Huntley Generating

Station area of analysis, the State chose this second approach. The hourly SO2 data from the 

Tonawanda II monitor for the period 2012 – 2014 were processed to obtain 3-year averages of 

the 99th percentile concentrations by season and hour-of-day. The background concentrations for 

this area of analysis varied by wind direction and wind speed and were incorporated into the final 

AERMOD results. New York acknowledges that the modeled concentrations can be expected to 

be highly conservative but should not have a major impact on the final design value.

Summary of Modeling Results

The AERMOD modeling parameters for the Huntley Generating Station area of analysis are 

summarized below in Table 4.

Table 4: AERMOD Modeling Parameters for the Huntley Generating Station Area of Analysis

Huntley Generating Station Area of Analysis

AERMOD Version 14134

Dispersion Characteristics Rural
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Modeled Sources 1

Modeled Stacks 1

Modeled Structures 6

Modeled Fencelines 1

Total receptors 1,369

Emissions Type Actual

Emissions Years 2012-2014 

Meteorology Years 2012-2014

Surface Meteorology Station

Buffalo Niagara International 

Airport

Upper Air Meteorology Station

Buffalo Niagara International 

Airport

Methodology for Calculating 

Background SO2 Concentration Temporal Varying

Calculated Background SO2

Concentration

1.30ppb – 4.49ppb depending 

on WD and WS

The results presented below in Table 5 show the magnitude and geographic location of the 

highest predicted modeled concentration based on actual emissions.

Table 5: Maximum Predicted 99th Percentile 1-Hour SO2

Concentration in the Huntley Generating Station Area of Analysis Based on 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 668784.63E 4759614.9N 142.3 196.5*

*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 142.3 μg/m3, or 54.3 ppb. This modeled concentration 

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

facilities.

Figure 6 below was included as part of the State’s recommendation and shows the modeled 

impact of Huntley Generating Station on the 1-hr SO2 design value in the area.
17

Figure 6: Modeled impact of Huntley Generating Station on 1-hour SO2 Design Value
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Detailed Assessment for Somerset Generating Station

Air Quality Data

This factor considers the SO2 air quality monitoring data in the area surrounding Somerset 

Generating Station. The facility is located in Niagara County, and the State included monitoring 

data from the Air Quality Systems monitor (Niagara Falls) - monitor id -360632008) closest to 

the facility in its recommendation. This monitor shut down in 2013 and was located at Frontier 

Avenue and 55th Street, Niagara Falls, NY. New York used data from 2010 – 2012 in their 

modeling since that was the period with the most recent SO2 background data for their modeling 

analysis. The more urban setting of the monitor as compared to the facility as well as the data 

being a year older when trends had been coming down for SO2 made this a conservative choice 

of representative background data. This monitor was approximately 45 km away from Somerset 

Generating Station. Data collected at this monitor indicates that SO2 concentrations are well 

below the SO2 NAAQS and have been trending downward. In addition, this data has been 

quality assured and are valid for comparison to the NAAQS. The State intended all available 

data collected at this monitor to support and corroborate air dispersion modeling results; the 

discussion of these modeled results follows in Table 6 below.

Table 6: Available Air Quality Data for the Area Closest to Somerset Generating Station.

County Air Quality 

Systems 

(AQS) 

Monitor ID

Monitor 

Location

Distance to 

Somerset

Generating Station

’10 – ’12 DV

(ppb)

’11 – ’13 DV

(ppb)

’12 – ’14 DV

(ppb)

Niagara 36-063-2008 Frontier Ave 

at 55th Street, 

Niagara 

Falls, NY

45 km 14 * *

* - Monitor shut down at end of 2012

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
19

The State used AERMOD version 14134, and a discussion of the individual components 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.

The State came to this conclusion by examining the land-use within 3 km of the facility. They 

analyzed the meteorological data using the AERSURFACE pre-processor. AERSURFACE uses 

land cover data from the National Land Cover Data (NCLD) 1992 database to determine the 

surface roughness, albedo, and Bowen ratio.

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 Somerset Generating 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 area surrounding the Somerset Generating Station in the Erie - Niagara, NY area, the 

State used only ambient monitoring data along with the Somerset Generating Station modeling 

results since the ambient monitoring data, to a large degree, reflect the contributions from the 

other sources in the area.

- 100 m spacing from the source to 2km

- 250 m spacing from 2 km to 5 km

- 500 m spacing from 5 km to 10 km

- 1000 m spacing from 10 km to 20 km

Receptors were placed on 36 radials 10 degrees apart and the grid was centered on the emission 

source. Receptors within the Somerset fence line were eliminated as non-ambient and special 

receptors were placed along the fence line at every 50 m. The grid contained a total of 1723 

receptors. While the EPA believes that with increasing distance, spatial resolution may diminish 

while using a polar grid (as opposed to Cartesian), since the maximum concentration from the 

facility was close in and was well below the NAAQS, we feel that this is acceptable.

Figure 7, included in the State’s recommendation, shows the State’s chosen area of analysis

surrounding the Somerset Generating Station, as well as the receptor grid for the area of analysis.
20

Figure 7: Somerset 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 to record ambient 

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

document.

Modeling Parameter: Source Characterization

The State characterized the source(s) 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, 
21

location, and diameter. 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 

PTE or allowable) emissions rate.

The EPA believes that continuous emissions monitoring systems (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 State only included ambient monitoring data along with the Somerset 

Generating Station for this analysis. New York said that since monitor data in the area already to 

a large degree reflect the contribution of Somerset and nearby sources to the SO2 concentration, 

it was not necessary to include emissions from sources other than Somerset in the modeling. All 

of the available monitor data was used in calculating the seasonal/hourly background values, 

including the time periods when the nearby sources were impacting the monitor. As such, the 

modeled concentrations, which include seasonal/hourly 99th percentile background, can be 

expected to be highly conservative. Actual emissions data obtained from temporally variable 

rates for Somerset Generating Station between 2012 and 2014 are summarized in Table 7 below.

Table 7: Actual SO2 Emissions between 2012 and 2014 from Facilities in the Erie - Niagara, NY

Area of Analysis
22

Facility Name

SO2 Emissions (tons per year)

2012 2013 2014

Somerset Generating Station 5,653 5,723 4,817

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. However, as mentioned above, New York 

used 2010 – 2012 meteorological data since the nearest monitor had shut down in 2013 and this 

data set would be more conservative. 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 NWS stations, site-specific or onsite data, and other sources such as 

universities, FAA, and military stations.

For the Erie - Niagara, NY area of analysis, surface and upper air data were obtained from the 

Buffalo Niagara International Airport, approximately 40 km to the southwest, and were selected 

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

The State used AERSURFACE version 13016 using data from the Buffalo Niagara International 

Airport (located at 685258.87E, 4756637.93N) to estimate the surface characteristics of the area 

of analysis. The State estimated values for 360 degrees out to 1 km at a seasonal temporal 

resolution for average conditions. The State 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 Figure 8 below, included in the State’s recommendation, the location of 

the Buffalo Niagara International Airport station is shown relative to the Somerset Generating 

Station area of analysis.
23

Figure 8: Somerset Generating Station Area of Analysis and the Buffalo Niagara International 

Airport
24

As part of its recommendation, the State provided the 3-year surface wind rose for the Buffalo 

Niagara International Airport. In Figure 9, the frequency and magnitude of wind speed and 

direction are defined in terms of from where the wind is blowing. While the figure shows winds 

from all directions, the predominant wind direction is from the southwest.

Figure 9: Buffalo Niagara International Airport Cumulative Annual Wind Rose (2011 – 2013)

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 followed the methodology and settings presented EPA’s Guideline on 

Air Quality Models (40 CFR Appendix W) and DEC’s Air Modeling Procedures as outlined in 

DAR-10 / NYSDEC Guidelines on Dispersion Modeling Procedures for Air Quality Impact 

Analysis, modified by the SO2 NAAQS Designations Modeling Technical Assistance Document 
25

(Modeling TAD), where applicable, 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 State 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. 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 

USGS 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 Somerset Generating

Station area of analysis, the State chose this second approach. The hourly SO2 data from the 

Niagara Falls monitor for the period 2010 – 2012 were processed to obtain 3-year averages of the 

99th percentile concentrations by season and hour-of-day. The background concentrations for 

this area of analysis varied by wind direction and wind speed and were incorporated into the final 

AERMOD results. New York acknowledges that the modeled concentrations can be expected to 

be highly conservative but should not have a major impact on the final design value.

Summary of Modeling Results
26

The AERMOD modeling parameters for the Somerset Generating Station area of analysis are 

summarized below in Table 8.

Table 8: AERMOD Modeling Parameters for the Somerset Generating Station Area of Analysis

Somerset Generating Station Area of Analysis

AERMOD Version 14134

Dispersion Characteristics Rural

Modeled Sources 1

Modeled Stacks 1

Modeled Structures 18

Modeled Fencelines 1

Total receptors 1,723

Emissions Type Actual

Emissions Years 2011-2013

Meteorology Years 2011-2013*

Surface Meteorology Station

Buffalo Niagara International 

Airport

Upper Air Meteorology Station

Buffalo Niagara International 

Airport

Methodology for Calculating 

Background SO2 Concentration Temporal Varying

Calculated Background SO2

Concentration

4ppb – 10ppb depending on

WD and WS

* NY processed 5 years of surface and upper air met data but were truncated

to dates that fit the hourly emissions records (Jan. 1, 2011 to Dec. 31 2013).

The results presented below in Table 9 show the magnitude and geographic location of the 

highest predicted modeled concentration based on actual emissions.

Table 9: Maximum Predicted 99th Percentile 1-Hour SO2

Concentration in the Somerset Generating Station Area of Analysis Based on 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 694120.63E 4803304.06N 111.7 196.5*

*Equivalent to the 2010 SO2 NAAQS set at 75 ppb
27

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

within the chosen modeling domain is 111.7 μg/m3, or 42.6 ppb. This modeled concentration 

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

facilities.

Figure 10 below was included as part of the State’s recommendation and shows the modeled 

impact of Somerset Generating Station on the 1-hr SO2 design value in the area.

Figure 10: Modeled impact of Somerset Generating Station on 1-hour SO2 Design Value

Jurisdictional Boundaries for Erie - Niagara, NY area:

Once the geographic area of analysis associated with the Huntley Generating Station and the 

Somerset Generating System are determined, existing jurisdictional boundaries are considered 
28

for the purpose of informing our intended unclassifiable/attainment area, specifically with 

respect to clearly defined legal boundaries.

In its recommendation to EPA, New York used the boundaries of the Buffalo-Cheektowaga, NY 

Combined Statistical Area (CSA) as the starting point for their analysis. This was based on the 

high degree of economic and social integration between the core population nucleus, and the 

adjacent communities in the metropolitan statistical areas (MSA) that make up the CSA. New 

York also noted that EPA has historically used the CSA as a starting point for considering 

designation recommendations.

The Buffalo-Cheektowaga, NY CSA is comprised of the Buffalo-Cheektowaga-Niagara Falls, 

NY MSA (Erie and Niagara Counties), and the Olean, NY MSA (Cattaraugus County).

EPA believes that it is currently premature to include counties in the July 2016 designation that 

did not meet the established criteria in the court's order for being designated in the first round 

due July 2, 2016, especially if impacts to that county from neighboring sources have not been 

evaluated. New York did not evaluate the impact to Cattaraugus County from nearby areas in its 

updated recommendation.

For Niagara and Erie Counties, EPA believes that a full county designation (rather than a partial 

county designation) of unclassifiable/attainment is appropriate as explained below. Figure 11 

below shows a map of the area showing stationary sources emitting 100 tpy of SO2 or more, 

ambient air quality monitors, and county boundaries.

Figure 11: Area map of stationary sources, ambient air quality monitors, and county boundaries 

in western New York
29

Niagara County

As previously discussed, the air dispersion modeling results for Somerset performed by New 

York indicate that the entire area of analysis attains the 2010 SO2 NAAQS; therefore, the EPA 

believes that it is unlikely for emissions from Somerset to cause or contribute to a violation of 

the NAAQS in Niagara County or any neighboring county. There are 3 other sources within 

Niagara County that emit 100 tpy or more of SO2. These facilities are Globe Metallurgical, 

Niagara Generating Station, and Covanta Niagara. Their emissions are below the DRR threshold 

of 2,000 tpy when considered alone or when considered a single source, i.e., a cluster, and the 

EPA believes that our assessment of these sources and their emissions as described below 

support the notion that the entirety of Niagara County is attaining the NAAQS, and that no 

sources in Niagara County are causing or contributing to a violation of the NAAQS in a 

neighboring county. 

According to 2014 data provided by the State, the largest of these sources, Globe Metallurgical

emitted 573 tons of SO2, while Niagara Generating Station’s emissions were 244 tons of SO2 and 

Covanta Niagara’s emissions were 225 tons of SO2. All of these sources are located in the 

Niagara Falls metropolitan area. The emissions from Globe Metallurgical have been decreasing 

since 2012 while the Niagara Generating Station and Covanta Niagara emissions have been 

increasing since 2012. However, the Niagara Generating Station and Covanta Niagara emissions 

are less than half of the Globe Metallurgical emissions.
30

The Niagara Falls air monitor (AQS Site ID 36-063-2008), which was used by New York in its 

modeling for Somerset to represent background data as discussed previously, and whose 

historical monitoring data is presented earlier in this document, is in close proximity (within 5 

km) to these 3 facilities. Historical data collected at this monitor indicate that SO2 concentrations 

were well below the SO2 NAAQS and were trending downward. The most recent design value, 

based on data collected between 2010 and 2012 was 14 ppb (the monitor shut down at the end of 

2012). Due to the location of the monitor in relation to the facilities and prevailing wind patterns, 

it is unknown whether this monitor was deployed in order to capture the maximum impacts from 

any of the 3 facilities. However, based on the decreasing emissions from the facilities over time, 

the available historical ambient air quality data, and the distance to the nearest New York county 

border of approximately 15 - 20 km, the EPA does not believe that the potential impacts from 

these facilities extend into any neighboring county in New York.

Other nearby sources that could potentially impact Niagara County are Huntley Generating 

Station, and Tonawanda Coke, which are in Erie County. As previously discussed, the modeled 

impact from Huntley Generating Station, which emitted over 3,000 tons of SO2 in 2014 is well 

below the NAAQS, and is located on the southeastern border of the facility's property. 

Tonawanda Coke’s emissions were 400 tpy in 2013, according to State emissions data, and are 

below the DRR threshold. The Brookside Terrace ambient air quality air monitor (AQS Site ID 

36-029-1014), which is approximately 3.2 kilometers north of both facilities, and just south of 

the Niagara County/Erie County border, has monitored concentrations well below the NAAQS.

As discussed previously in this document, the design values at this monitor have decreased over 

time, and the most recently available design value based on data collected between 2012 and 

2014 was 22 ppb. Due to the prevailing wind patterns in the area, the EPA believes that this 

design value captures the maximum impacts from both Huntley Generating Station and 

Tonawanda Coke at the monitor location. Therefore, even in the absence of State modeling 

results which account for emissions from Towanada Coke, the EPA does not believe that the area 

encompassing the border between Niagara County and Erie County in the vicinity of the 

Brookside Terrace monitor are experiencing violations of the NAAQS due to the combined 

emissions from Huntley Generating Station and Towanada Coke.

Erie County

As previously discussed, the air dispersion modeling results for Huntley Generating Station 

performed by New York indicate that the entire area of analysis attains the 2010 SO2 NAAQS; in 

conjunction with ambient air quality data collected at the Brookside Terrace monitor (AQS Site 

ID 36-029-1014) which account for emissions from both Huntley Generating Station and nearby 

Towanada Coke, the EPA believes that it is unlikely for emissions from either of these facilities 

to cause or contribute to a violation of the NAAQS in Erie County, or any neighboring county. 

There is one other source in Erie County emitting 100 tpy or greater of SO2. PVS Chemical is 

located less than 20km from Huntley Generating Station and Towanada Coke, and the facility’s 

2013 SO2 emissions were 139 tons according to State emissions data. The EPA believes that our 
31

assessment of this source and its emissions as described below supports the notion that the 

entirety of Erie County is attaining the NAAQS, and that no sources in Erie County are causing 

or contributing to a violation of the NAAQS in a neighboring county.

The ambient air quality monitor at 185 Dingens Street in Buffalo (AQS Site ID 36-029-0005) is 

located in close proximity, i.e., approximately 2.5 km, to PVS Chemical. The design values have 

trended downwards in recent years, and the most recent design value based on data collected 

between 2012 and 2014 was 10 ppb. Because this monitor is located in an area that captures the 

general area where maximum SO2 impacts from PVS Chemical are expected, the EPA believes 

that emissions from the facility are not expected to violate or contribute to a violation of the 2010 

SO2 NAAQS in any area of Erie County or a neighboring county.

The only other facility that might impact Erie County is the Dunkirk Steam Generating Station in 

neighboring Chautauqua County. Dunkirk Steam Generating Station is approximately 20 km 

southwest of the Erie County border. According to the EPA’s 2014 Clean Air Markets database, 

the facility’s SO2 emissions were 951 tons. The New York State air monitor in the town of 

Dunkirk (AQS Site ID 36-013-0006, Wright Drive, Dunkirk, NY) is in close proximity, i.e., 2.5 

km to the Dunkirk Generating Station, and has monitored concentrations well below the SO2

NAAQS. Design values have trended downwards, and the most recent design value based on 

data collected between 2012 and 2014 was 18 ppb. Because this monitor is located in an area 

that captures the general area where maximum SO2 impacts from Dunkirk Generating Station are 

expected, the EPA does not believe that emissions from Dunkirk Generating Station are causing 

or contributing to a violation of the 2010 SO2 NAAQS in Erie County. The EPA would like to 

clarify that this assessment applies only to Dunkirk Steam Generating Station’s potential impacts 

on Erie County, and is not intended to inform air quality characterization within Chautauqua 

County.

Evaluating all current information, the EPA does not believe that there are any stationary sources 

in any other neighboring county that cause or contribute to a violation of the 2010 SO2 NAAQS 

in Erie County or Niagara County. As discussed above, the impacts from sources in Erie County 

and Niagara County are expected to attain the NAAQS with an adequate margin of safety, and 

furthermore, are not expected to cause or contribute to a violation of the NAAQS in any 

neighboring county in New York. As a result, the EPA believes that our intended 

unclassifiable/attainment area, consisting of Niagara County and Erie County in New York 

State, are comprised of clearly defined legal boundaries, and we find these boundaries to be a 

suitably clear basis for defining our intended unclassifiable/attainment area. As previously noted, 

New York has not evaluated the impact to Cattaraugus County from nearby areas in its 

recommendation, and in conjunction with the fact that Cattaraugus County does not contain any 

areas meeting the conditions requiring designation by July 2, 2016, the EPA is not proposing to 

designate any portion of Cattaraugus County at this time.

Other Relevant Information
32

The EPA did not receive any additional relevant information with respect to the two sources in 

New York State impacted by the July 2, 2016 court-ordered deadline.

Conclusion

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

available relevant information, the EPA intends to designate the Erie - Niagara, NY area as 

unclassifiable/attainment for the 2010 SO2 NAAQS. Specifically, the boundaries are comprised 

of Niagara County and Erie County in New York State. This decision was made based on all 

available information, including historical ambient air quality monitoring, air dispersion 

modeling results performed by the State, and other supporting materials found in the State’s 

updated recommendation.

At this time, our intended designations for the State only apply to the area presented in this 

technical support document. Consistent with the conditions in the March 2, 2015 court-ordered 

schedule, the EPA will evaluate and designate all remaining undesignated areas in New York by 

either December 31, 2017, or December 31, 2020.