## 2010 Primary Sulfur Dioxide (SO 2 

## )

National Ambient Air Quality Standard (NAAQS)
Technical Analyses and Information Supporting the Designation Recommendation for Oklahoma

Introduction and Summary

Air Quality Division

Oklahoma Department of Environmental Quality

September 1 8 , 20151

Introduction , Summary, and State Recommendation
In 2010, the U.S. Environmental Protection Agency (EPA) promulgated a new National Ambient Air Quality Standard (NAAQS) for sulfur dioxide (SO 2 ) of 75 parts per billion (ppb) on a 1

- hour average. In response , Governor Mary Fallin submitted a letter dated May 27, 2011 providing the State of Oklahoma’s recommendations for designations under the new NAAQS. The State recommended a designation of unclassifiable for Muskogee and Tulsa counties, and attainment for all the other 75 counties within t he state. EPA identified areas of the U.S. with monitored violations of the 2010 SO 2 NAAQS , designated those areas as nonattainment in July 2013 , and deferred designations for remaining areas . No areas in Oklahoma were included in the July 2013 designation s. On March 2, 2015, the U.S. District Court for the Northern District of California entered a federal consent decree between EPA and Sierra Club (SC) and Natural Resources Defense Council (NRDC) , which resolved litigation over the deadline for EPA’s comp letion of designations. The court order established that EPA must complete designations in three additional rounds. The first round of designations must be completed by July 2, 2016, and must be made for 1) areas that have newly monitored violations of the 2010 SO 2 standard and 2) areas that contain any stationary source that according to the EPA’s Air Markets Database either emitted more than 16,000 tons of SO 2 in 2012 or emitted more than 2,600 tons of SO 2 and had an emission rate of at least 0.45 lbs SO 2 /MM BTU in 2012 and that has not been announced for retirement (as of March 2, 2015).
In a letter dated March 20, 2015 to Scott Thompson, Executive Director, Oklahoma Department of Environmental Quality (DEQ) , EPA A cting Assistant Administrator Janet McCabe identified three a ff ected electric power plant sources in Oklahoma that meet the criteria for designation by July 2, 2016 : Western Farmers Electric Cooperative (WFEC) Hugo Generating Station in Choctaw County , Oklahoma Gas and Electric (OG & E) Sooner Generating Station in Noble County , and OG & E Muskogee Generating Station in Muskogee County

. EPA stated that the most recent information available would be used in making designations and boundary decisions for these areas in Oklahoma
, and provided an opportunity for Oklahoma to submit an updated recommendation and supporting information to inform the designations for the affected areas. Any updated recommendation and supporting information was to be submitted to EPA by September 18, 2 015 , and was to conform to the “Updated Guidance for Area Designation for the 2010 Primary Sulfur Dioxide National Ambient Air Quality Standard , March 20, 2015 .”
On August 17, 2015 Governor Fallin sent a letter to EPA recommending designations of unclassif iable for Muskogee County and attainment for Noble and Choctaw Counties for the July 2, 2016 designations. Th at recommendation is based on supporting information contained within this package.2

General O verview of Impact Analysis Approach and M odeling M ethodology DEQ evaluated pertinent source

- oriented monitoring data and conducted air dispersion modeling for the three affected facilities to determine impacts, and to inform the State’s recommendations for the 2010 1

- hour SO 2 NAAQS designations.

Ambient impacts of SO 2 are largely source

- oriented
, meaning the highest concentrations will be exhibited in close proximity to the emitting sources. The 2010 1

- hour SO 2 NAAQS replaced the existing annual and 24

- hour standards ( 140 ppb and 30 ppb, respectively) with a one

- hour standard of 75 ppb. This substantial change to the form of the standard indicat ed more focus on short

- term exposure to high levels of SO 2 . These facts, as well as limited state and federal resources, have led to EPA’s “hybrid” approach to attainment designation s

– relying on modeling to overcome limitations of the SO 2 monitoring network.
40 CFR Part 51, Appendix W, Guideline on Air Quality Models, recommends the use of AMS/EPA Regulatory Model (AERMOD), citing the dispersion model's capabi lity to address multiple sources, both rural and urban areas, flat and complex terrain, and surface and elevated emission release points. The enclosed “Modeling Compliance with the 1

- Hour SO 2 NAAQS” (“Modeling Report”) describes the significant effort DEQ has expended to determine, obtain and refine the data required to complete the modeling analysis. Due to the unique nature of utilizing model predictions as a surrogate to monitored air qual ity data, model inputs were chosen in a manner that best reflects actual conditions.

The 2010 1

- hour SO 2 NAAQS is attained when the three

- year average of the 99 th percentile of the daily maximum one

- hour average does not exceed 75 ppb (or 196.4 μg/m 3 ) 1

. The “design value” used to compare to the 75 ppb standard is calculated as the three

- year average of the highest fourth highest (H4H) SO 2 value for a particular monitor or modeling receptor. A ttainment of the standard would be demonstrated if the modeled cumulative impact of the affected sources and other contributing nearby sources added to the background concentration is less than 75 ppb. The 2012

- 2014 monitoring design value (9.6 μg/m 3 ) from the monitor (ID 40

- 109

- 1037) in Oklahoma County was used as a background concentration for the modeling analyses , since it is the only SO 2 monitor located in Oklahoma that is not directly impacted by a large SO 2 emission source. For each affected facility/area, the Modeling Report describes the determination of the appropriate modeling domain
, receptor grid, meteorological and terrain data, ambient monitored background concentrations, and emissions from other contributing nearby sources. Actual source emissions data were gathered or calculated for the years 2012

- 2014. Hourly emissions data from the affected sources were taken from continuous emissions monitoring systems (CEMS) when available. If CEMS data were unavailable, the emissions were calculated using throughputs and

1 For all ambient measurements/projections, EPA ref erence conditions are used in converting between ppb and μg/m 3 ( see 40 CFR §50.3 )

.3

operational data. F ederal ly enforceab le requirements will result in significant SO 2 emissions reductions from the OG&E Sooner and Muskogee Stations within the next five years. As described in more detail below, m odeling was also performed using alternate operating scenarios
to project the impact of these changes on ambient air quality . Oklahoma DEQ primarily utilized meteorological data from Oklahoma Mesonet sites in combination with data from the National Climatic Data Center's (NCDC) Integrated Surface Hourly Database (ISHD) to gene rate more representative surface meteorological conditions

. For the Muskogee area, only data from the ISHD was utilized. The OG&E Muskogee facility section below, along with the additional documents
, discuss es questions regarding meteorological data repr esentativeness
, effects of complex terrain, and other issues f or the Muskogee area

. The following additional reports have been prepared and included to support modeling report’s conclusions:

1. Comparison of Modeled and Monitored SO 2 Concentrations in Muskogee, Oklahoma 2. Effects of Terrain on Wind Flow in Muskogee, Oklahoma 3. Source

- Oriented SO 2 Monitoring Placement for the Area of Muskogee, Oklahoma

– Modeling Analysis Report
A description of the three affected electric generating stat ions and modeling analysis and results for each are described

. Choctaw County WFEC Hugo Generating Station The WFEC

– Hugo Generating Station in Choctaw County is located t hree miles w est of Ft. Towson on US

- 70 , 12 miles east of Hugo , Oklahoma

.
The coal

- fired complex at the Hugo p ower p lant consists of one main boiler with a maximum heat input of 184 million British thermal units per hour ( MMB TU /hr) and a n auxiliary boiler unit . The main boiler has a capacity of 446 m ega w att s (MW) electrical outp ut and primarily combusts sub

- bituminous coal to produce steam used to generate electric power (SIC 4911)

. The flue gas is exhausted through a single 500 foot stack. An a uxiliary unit is used as backup during turnaround periods
, and is fueled exclusively b y No. 2 fuel oil. The Hugo power plant was constructed in 1978 as authorized by Permit Number PSD

- OK

- 053 and has no SO 2 controls installed

. The Hugo plant is operating under permit number 2008

- 337

- TVR (M

- 1) , which limits SO 2 emission s t o 1.2 lbs /MMBTU, 4,591.8 lbs/hr, and 16,404.1 tons per year.
There is no ambient monitoring site in close proximity to the WFEC Hugo Generating Station

. T he facility’s SO 2 emissions would not be expected to have a significant impact on the Muskogee monitoring site (40

- 101

- 0167) , which is the Oklahoma monitoring site located closest to the Hugo p lant

. DEQ performed m odeling to confirm the State’s recommended designation of attainment with the new SO 2 standard for the areas affected by the Hugo p lant emissions

. The modeling utilized actual emissions data for years 2012 through 2014 obtained from EPA’s Clean Air Markets Database (CAMD)

. The modeling demonstrate d compliance with the 2010 1

- hour SO 2 NAAQS of 75 ppb for the areas surrounding the WFEC Hugo Generating Station
, with a three

- year4

average of the H4H daily maximum impact s of 4 5 ppb (118.2 μg/m 3 )

. ( See M odeling R eport , Section 7.1)
Noble County

– OG&E Sooner Generating Station The OG&E Sooner Generating Station in Noble County is located 19 miles North of Stillwater on US

- 177 , six miles east of Red Rock
, Oklahoma. The Sooner Generating Station is a coal

fired steam boiler electric generation facility consist ing of two units that use sub

- bituminous low

- sulfur Wyoming coal as the primary fuel and No. 2 fuel oil as a start

- up fuel . Neither boiler is designed to operate on oil continuously.
Both Units 1 and 2 can potentially combust approximately 300 tons per hour of coal to produce 3.8 million pounds per hour of steam each. Both boilers were design ed with a maximum heat input of 5,116 MM B TU / hr and a nominal 550 MW electrical output. Flue gas is exhausted through two 500

- foot stacks. The Sooner plant currently operates under AQ Permit Number 2010

- 338

- TVR2 (M

- 2), which limits SO 2 emission s to 1.2 lbs/MMBTU fo r Units 1 and 2. However , under the Regional Haze Program, the Sooner plant is required to meet limits that represent Best Available Retrofit Technology (BART) to control SO 2 emissions from Units 1 and 2. OG&E Sooner Generating Station is subject to a Fe deral Implementation Plan (FIP) (40 CFR §52.1923), which requires Units 1 and 2 to meet a SO 2 emission limit of 0.06 lb/MMBTU by January 4, 2019. OG&E has committed 2 to meet the federal BART limit by using flue gas desulfurization to control SO 2 emissions from Units 1 and 2.

There is no ambient monitoring site in close proximity to the OG&E Sooner Generating Station

. No violation of the 2010 SO 2 NAAQS has been detected at the Ponca City monitoring site (40

- 071

- 0604) in Kay County, which is the site located closest to the Sooner Plant
, for the last three years of available certified data. The design value for the Ponca City site for t he years 2012 through 2014 is 37 ppb

. DEQ performed modeling to confirm the State’s recommended designation of attainment with the new SO 2 standard for the areas affected by the Sooner p lant emissions

. Since the BART emission reduction s will occur after the court

- ordered deadline for the designation decision , t he air quality analyse s for this facility involved three operating scenarios.

For Scenario 1: Modeled using a ctual emissions data for OG&E Unit 1 & Unit 2 from EPA’s Clean Air Markets Database for years 2012 through 2014.

For Scenario 2: Modeled potential emissions from OG&E Unit 1 using the BART emissi on limit (0.06 lb/MMBTU) and projected actual emissions from OG&E Unit 2 using the 2012 through 2014 three year average of the 99 th percentile emission rate and heat input.

2 See “ OG&E’s Public Statements on Commitments to Meet EPA’s Regional Haze FIP Requirements.”5

For Scenario 3: Modeled p otential emissions from OG&E Unit 1 and Unit 2 using the BART emission li mit (0.06 lb/MMBTU)

.
The model ed three

- year average of the H4H daily maximum impact s for each operating scenario

are:
Scenario 1

- 52 ppb (136.6 μg/m 3 )

Scenario 2

- 62 ppb (161.7 μg/m 3 )

Scenario 3

- 17 ppb (43.5 μg/m 3 )

The modeling review demonstrated compliance with the 2010 1

- hour SO 2 NAAQS of 75 ppb, for the areas surrounding the OG&E Sooner Generating Station , with a three

- year average of the H4H daily maximum impact of 62 ppb (161.7 μg/m 3 ) .( See Modeling R eport , Section 7.3)

Muskogee County

– OG&E Muskogee Generating Station The OG&E Muskogee Generating Station in Muskogee County is located near Muskogee on US

- 62 on the East b ank of the Arkansas River, in Fort Gibson, Oklahoma.
The Muskogee Generating Station is a coal

- fired steam boiler electric generation facility consisting of three units ( Units 4, 5 and 6 ) that use sub

- bituminous low

- sulfur Wyoming coal as the primary fuel and natural gas as a start

- up fuel

. Units 1, 2, and 3, the oldest units, have been

re tired. Units 4, 5, and 6 can each potentially combust approximately 300 tons per hour of coal to produce 3.8 million pounds per hour of steam each. These units each have a nominal capacity of 550 MW electrical output. Units 4 and 5 each have a 350 foot stack, and U nit 6 has a 500 foot stack. The Muskogee plant is operating under AQ Permit Number 2005

- 271

- TVR (M

- 7), which contains SO 2 emission limits of 1.2 lbs/MMBTU for units 4 and 5, and 1.2 lbs/MMBTU and 6,180.0 lbs/ hr for unit 6. However, under the Regional Haze Program, the Muskogee plant is required to meet limits that represent Best Available Retrofit Technology (BART) to control SO 2 emissions from Units 4 and 5. OG&E Muskogee Generating Station is subject to a Federal Implementation Plan (FIP) (40 CFR §52.1923), which requires Units 4 and 5 to meet a SO 2 emission limit of 0.06 lb/MMBTU by January 4, 2019. OG&E has committed 3 to meet the federal BART limit by conversion of Unit 4 and Unit 5 to natural gas

. A sou rce

- oriented SO 2 monitoring site (40

- 101

- 0167) has been operated in close proximity to the OG&E Muskogee Generating Station since 1981 4

. No violation of the 2010 SO 2 NAAQS has been detected at the Muskogee monitoring site
, located 4 km NNW of the facility
, for the last

3 Ibid. 4 See “Source

- Oriented SO 2 Monitoring Placement for the Area of Muskogee, Oklahoma

– Modeling Analysis Report”6

three years of available certified data. The design value for the Muskogee site for 2012 through 20 14 is 49 ppb

. DEQ performed modeling to confirm the State’s recommended designation of unclassifiable for the new SO 2 standard for the areas affected by the Muskogee p lant emissions

. Since the BART emission reductions will occur after the court

- ordered deadline for the designation decision, the air quality analyses for this facility involved three operating scenarios. The future oper ating scenarios were modeled using continuous operation of all the affected emission units.

For Scenario 1: Modeled using a ctual emissions data for OG&E Unit 4, Unit 5, & Unit 6 from EPA’s C lean Air Markets Database for years 2012 through 2014

.
For Scen ario 2: Modeled potential emissions from OG&E Unit 4 using the natural gas fired emission rate of 0.0006 lb/MMBTU (which is lower than the BART emission limit of 0.06 lb/MMBTU)
, and projected actual emissions from OG&E Unit 5 & Unit 6 using the 2013 and 20 14 two

year average of the 99 th percentile emission rate and heat input.

For Scenario 3: Modeled p otential emissions from OG&E Unit 4 and Unit 5
, using the natural gas fired emission rate of 0.0006 lb /MMBTU (which is lower than the BART emission limit of 0.06 lb/MMBTU) and projected actual emissions from OG&E Unit 6
, using the 2013 and 2014
two

- year average of the 99 th percentile emission rate and heat input.

The model ed three

- year average of the H4H daily maximum impact s for each operating scenario

are:
Scenario 1

- 85 ppb (223.6 μg/m 3 )

Scenario 2

- 72 ppb (189.5 μg/m 3 )

Scenario 3

- 50 ppb (129.7 μg/m 3 )

T he modeling review demonstrate d compliance with the 2010 1

- hour SO 2 NAAQS of 75 ppb (196.4 μg/m 3 ) for the areas surrounding the OG&E Muskogee Generating Station for Scenario s 2 and 3 . However, the modeling review was not able to demonstrate compliance for Scenario 1

. Under a certain combination of meteorological and operating conditions, a potential violation was modeled for a small area (approximately one quarter

- section )

. ( See Modeling R eport , Section 7.2)
Uncertainty for the Muskogee A rea Modeling and Monitoring
DEQ’s assessment for the Muskogee area reinforces the premise that, although both source

oriented monitoring sites and dispersion modeling are valuable evaluation tools, neither is7

definitive in characterizing ambient air quality conditions for NAAQS desi gnation purposes. Despite the considerable efforts of DEQ and others, much uncertainty remains as to whether there is a potential for a NAAQS violation within a small area during the relatively short window of time before BART is fully implemented. The m odeling analysis for domain ID 36 (Muskogee) raised significant questions regarding representativeness of available meteorological data, effects of complex terrain, and other issues. These questions must be taken into account if modeling is used as a deci sion

- making tool in the attainment status designation process for the areas surrounding the OG&E Muskogee Generating Station

. This is particularly important since a designation of “nonattain ment” is unlikely to have a practical effect on air quality before the implementation of “on

- the

- books” requirements that will soon remove the concern.
While under Scenario 1, modeling indicated the re is a small area near the OG&E Muskogee Generating Station with potential impacts greater than the 2010 1

- hour SO 2 NAAQS, under Scenarios 2 and 3 the modeling demonstrate s compliance with the 2010 1

- hour SO 2 NAAQS

. The federally enforceable BART reductions reflected in Scenarios 2 and 3 are to be obtained on or before January 4, 2019. The last three years of certified monitoring data indicate compliance with the standard. Based on the Monitor vs

. Model Report 5 , DEQ determined that terrain effects on wind direction and speed in the area surrounding the modeling domain were not adequately characterized by the a vailable meteorological data. The modeling results did not correlate well with monitored values; therefore, there is uncertainty regarding the modeling results.

The modeling of the OG & E Muskogee area was first performed using the Porter M e sonet site for meteorological data. Those modeling results provided insight as to how sensitive the model was to topographic features near the plant, which explain in part why the SO 2 concentrations predicted by the model do not reflect the lower concentrations recorded at the monitor for the same time period

. See the separate DEQ report 6 on e ffects of t errain on w ind s peeds for more information. For the final modeling analysis, t he nearest National Weather Service meteorological site available (KMKO) was used. KMKO is located 13 kilometers SSW of the OG&E Muskogee Generating Station

. T he result s of the final modeling analysis show that the hourly modeling outputs do not correlate well with the actual hourly impacts recorded at the monitor (40

- 101

- 0167)

. The lack of correlation is a result of how the model attempts to replicate atmospheric stability (See Model v s. Monitor Report 7 )

. Modeling for t he area surrounding the OG & E Muskogee Generating Station , using the described meteorological data, c an demonstrate attainment by assuming BART emission reductions that

are federally enforceable , but are not required to be fully implemented until after EPA’s court

ordered deadline for final designation action

.

5 “ Comparison of Modeled and Monitored SO 2 Concentrations In Muskogee, Oklahoma” 6 “Effects of Terrain on Wind Speeds in and near Muskogee, Oklahoma” 7 Comparison, op cit.8

Conclusion
Choctaw County, including the area surrounding WFEC Hugo Generating Station, should be designated as “ attainment ” for 2010 1

- hour SO 2 NAAQS, based on the modeling results and no available monitoring data indicating a contrary conclusion. Noble County, inc luding the area surrounding OG&E Sooner Generating Station, should be designated as “attainment” for 2010 1

- hour SO 2 NAAQS, based on monitoring data and modeling results. Muskogee County, including
t he area surrounding OG & E Muskogee Generating Station, should be desi gnated as

“ unclassifiable ” or “unclassifiable/attainment” based on the current monitoring data , which indicates compliance with the standard
, and other important consider ations. OG&E Muskogee Generating Station is already under legal obligat ion to make SO 2 reductions that would essentially remove all concerns over a potential violation of the 2010 SO 2 NAAQS

. Also, additional questions regarding meteorological data representativeness and the ability of the model to accurately determine the atmospheric stability cast doubt over whether a significant potential for such a violation even exists under current operations and conditions

.