### Draft Technical Support Document (TSD)
Montana Area Designations For the 2010 

### S02Primary National Ambient Air Quality Standard

Summary
Pursuant to section 107(d) ofthe Clean Air Act (CAA) , EPA must initially designate areas as either

"unclassifiable ", " attainment", or " nonattainment" for the 2010 1-hour sulfur dioxide (S02 ) primary national ambient air quality standard (NAAQS). The CAA defines a nonattainment area as one that does not meet the NAAQS or that contributes to poor air quality in a nearby area that does not meet the NAAQS. Areas that cannot be classified based on available information as meeting or not meeting the NAAQS will be deferred. Table 1 below identifies the counties or portions ofcounties (or areas of Indian country) in Montana that EPA intends to designate " nonattainment" based on monitored violations.


### Tabl 1 N tt

. e 

# . ona ammentArea D" f f< M 

### t es1gna Ions or on ana Montana's Recommended EPA ' s Intended Designation Area Designation of Counties ofCounties Yellowstone County Yellowstone County: Unclassifiable Nonattainment excluding Crow Tribe of Montana 

### Background
On June 2, 2010, EPA revised the primary S02NAAQS (75 FR 35520, June 22 , 2010) by establishing a new 1-hour standard at a level of75 parts per billion (ppb) which is attained when the 3-year average of the 99 1 h percentile ofthe daily maximum 1-hour average concentration at each monitor in an area does not exceed 7 5 ppb. EPA has determined that this is the level necessary to provide protection ofpublic 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 S02
. The Agency is revoking the two prior primary standards of 140 ppb evaluated over 24-hours, and 30 ppb evaluated over an entire year because the standards will not add additional public health protection given a 1-hour standard at 7 5 ppb. Accordingly, EPA is not designating areas in this process on the basis of either ofthese two prior primary standards. Similarly, the secondary standard for S02has not been revised, so EPA is not designating areas in this process on the basis ofthe secondary standard.


### EPA's S02 Designation Approach
Section 1 07(d) ofthe CAA requires that not later than 1 year after promulgation of a new or revised NAAQS , state Governors must submit their recommendations for designations and boundaries to EPA. This deadline was in June 2011. Section 1 07(d) also requires EPA to provide a notification to states of no less than 120-days prior to promulgating an initial area designation that is a modification of a state ' s recommendation. EPA has reviewed the State's recommendations and has notified the State through aletter signed by the Regional Administrator on February 6, 2013, of any intended modifications. [While language in section 107 specifically addresses states, we intend to follow the same process for tribes, pursuant to section 301(d) ofthe CAA and Tribal Authority Rule (40 CFR Part 49). Therefore, we intend to designate areas oflndian country, in consultation with the tribes, on the same schedule as state designations.] If a State or Tribe did not submit designation recommendations, EPA will promulgate the designations that it deems appropriate. If a state or Tribe disagrees with EPA's intended area designations, they have an opportunity to demonstrate why any proposed modification is inappropriate.
The Crow Tribe ofMontana's area of Indian country is located adjacent to the intended Yellowstone county nonattainment area. This area ofIndian country does not contain any sources that are contributing to the violating monitor in Yellowstone County. Therefore, EPA intends to exclude Crow Tribe ofMontana's area of Indian country from the Yellowstone County nonattainment area and defer designations for the area ofIndian country. Designations guidance was issued by EPA through a March 24, 2011 , memorandum from Stephen D. Page, Director, U.S. EPA, Office ofAir Quality Planning and Standards, to Air Division Directors , U.S. EPA Regions 1-X. This memorandum identifies factors EPA intends to evaluate in determining boundaries for areas designated nonattainment. These 5 factors include: 1) Air quality data; 2) Emissions and emissions-related data (location of sources and potential contribution to ambient S02 concentrations); 3) Meteorology (weather/transport patterns); 4) Geography/topography (mountain ranges or other air basin boundaries); and 5) Jurisdictional boundaries (e.g., counties, air districts , preexisting nonattainment areas, reservations, metropolitan planning organization), among any other information deemed relevant to establishing appropriate area designations and boundaries for the 1-hour S02 NAAQS.
The

. March 24, 2011, memo recommended that area boundaries be defaulted to the county boundary unless additional provided informationjustifies a larger or smaller boundary than that ofthe county. EPA believes it is appropriate to evaluate each potential area on a case-by-case basis, and to recognize that area-specific analyses conducted by states , tribes and/or EPA may support a different boundary than
a default county boundary.

In this TSD , EPA discusses its review and technical analysis ofthe recommendations submitted by the states and/or tribes for designations ofthe 1-hour so2 standard and any modifications from these recommendations. Definition of important terms used in this document: 1) 

### Designated "nonattainment" area
- an area which EPA has determined, based on a state recommendation and/or on the technical analysis included in this document, has violated the 2010 so2 NAAQS , based on the most recent three years of air quality monitoring data, or contributes to a violation in a nearby area. 2) 

### Recommended nonattainment area- an area a State or Tribe has recommended to EPA be designated as nonattainment.

23) Violating monitor- an ambient air monitor meeting all methods, quality assurance and citing criteria and requirements whose valid design value exceeds 75 ppb, as described in Appendix T of40 CFR part 50. 4) 2010 

### 802 NAAQS- 75 ppb, national ambient air quality standard for S02promulgated in 2010. Based on the 3-year average ofthe 99 1 h percentile ofthe annual distribution ofdaily maximum 1-hour average concentrations 5) Design Value
- a statistic that describes the air quality status ofa given area relative to the level of theNAAQS.
Nonattainment Designations
Technical analysis for Yellowstone County
Introduction
This technical analysis for Yellowstone County identifies the whole county with a monitor that violates the 2010 S02NAAQS and evaluates nearby counties for contributions to S02 concentrations in the area. EPA has evaluated Yellowstone County and nearby counties based on the weight ofevidence ofthe factors recommended in the March 24, 2011 EPA guidance. Figure 1, below, is a map ofthe area analyzed showing the locations and design values of air quality monitors in the area, and the counties surrounding any violating air quality monitors.

3

### Figure 1. 

### Map of the Analyzed Area with Design Values at the Monitoring Sites.

Musselshell Gol den V a lley

Carbon 

### Yellowstone County, MT

Rosebud

Big Horn Legend

- EPA proposes whole county as nonattainment · EPA proposes partial county as nonattainment

- Counties proposed as a different S02 nonattainment area



## + Mon itor violating 2010 S02 NAAQS (2009-2011 ) 

## + Mon itor attaining 2010 S02 NAAQS ( 2009-20 11) 

### BIIJ EPA'S inten ded S02 nonattainment area A

reas of Indian country

- N a tiona l highway W

a ter body S02 em ission s ource (NE I 2008v2

.0 ) • 100

- 1 ,000 tons/year 0 1 ,000 or more ton s/year

0 5 1 0 20 Miles I I I I I I I I I

From Figure 1 above, all ofthe facilities that emit S02 are located within the Southern part of Yellowstone County. These facilities are located within the Laurel/Billings area. The major S02 emitting industries in the Billings area are the ConocoPhillips and ExxonMobil Petroleum Refineries; Western Sugar Company (sugarbeet processing plant) ; PPL Montana, LLC

- J.E. Corette (PPL

- Corette) coal-fired electrical generating station; Montana Sulphur Chemical Company (MSCC) (gas processing plant, sulfur recovery and sulfur products) ; and Yellowstone Energy Limited Partnership (YELP) (petroleum coke-fired electrical/steam co-generation facility
.) The major S02 emitting industry in the Laurel area is the Cenex Harvest States , Inc. (CHS) Petroleum Refinery. Although Laurel and Billings are 15 miles apart, the industries in Billings have some impact on the air quality in Laurel and the industry in Laurel has some impact on the air quality in Billings.
On May 27 , 2011 , Richard Opper, Director ofMontana' s Department ofEnvironmental Quality, recommended that Yellowstone County be designated as " unclassifiable" for the 2010 S02NAAQS based primarily on a Consent Decree between ExxonMobil and EPA Region 8. The State discusses an emission increase from 2009 to 201 0 being a direct result ofExxonMobil ' s performance under an S02 additive testing schedule pursuant to an EPA consent decree

. The State believes that consideration of 2010 monitoring data for initial designation purposes is inappropriate. Montana further states that they believe EPA should initially designate Yellowstone County as " unclassifiable" until such time as representative data is available. Montana discusses using , in lieu ofusing 2010 data, either 2009 , 2011 , and 2012 data or 2011-2013 data to determine a design value for comparisons to the NAAQS

. Letter

4and supporting analysis from Mr. Opper, to James B. Martin, Regional Administrator, USEPA, Region 8 (May 27 , 2011) is on file with EPA Region 8 Air Program Unit. Additionally, Montana discusses implementation offuture regulations. These include: the EPA Refinery Initiative and Associated Consent Decrees, Utility MACT Implementation, Existing FIP Implementation, Regional Haze/BART Implementation, Boiler Maximum Achievable Control Technology (MACT) Implementation, New Source Performance Standards (NSPS)- 40 CFR 60 Subpart Ja, and EPA Flare Initiative. These will be discussed below.
Based on EPA's technical analysis ofthe State ' s TSD described below and based on this analysis EPA is intending to designate one county in Montana as nonattainment. For the 2010 S02NAAQS, Yellowstone County will be designated as a nonattainment area, based upon currently available information. This county is listed above in Table 1.


### Detailed Assessment
Air Quality Data
The Air Quality data factor considers S02 air quality monitoring data, including the design values (in ppb) calculated for all air quality monitors in the Yellowstone County and the surrounding area. The factor considered monitoring data for the 2008-2010 period.
The Director' s recommendation was based on data from the Coburn Road (Monitor ID: 30-111-0066) , a Federal Equivalent Method (FEM) monitor located in Yellowstone County. The Coburn Road monitor is classified as a State and Local Air Monitoring Station (SLAMS).
The majority ofthe monitored data in Table 2, below, was provided by the State in their recommendation letter and TSD. The table shows a summary ofmonitored NAAQS exceedances by quarter during the 2008-2010 time period. The EPA extended the table to include 2011 exceedances. The majority ofexceedances occurred during the third and fourth calendar quarters ofthe 2008-2011 monitoring period.

5

### Table 2. Coburn Road SLAMS Monitored NAAQS Exceedances 2008-2011 Calendar Year Calendar Quarter Number ofExceedances (> 

### 75 ppb) 1 0 2008 2 1 3 2 4 3 

### 2008 Total Exceedances 6 1 1 2009 2 0 3 2 4 0 

### 2009 Total Exceedances 3 1 1 2010 2 0 3 4 4 4 

### 2010 Total Exceedances 9 1 0 2011 2 0 3 0 4 4 

### 2011 Total Exceedances 3 

### 2008-2011 Total Exceedances 21
The State provided Table 3, below, in their recommendation letter and TSD. The EPA extended the table to include 2011 1-hour daily maximums. The table shows 1-hour daily maximum S02values and these values were used to calculate the annual 99th percentile. The annual 99th percentile is highlighted in the table for each ofthe years 2008 through 2011.
The average ofthe 99th percentiles for 2008-2010 is 84 ppb and the average for 2009-2011 is 79 ppb. The averages are presented in Table 4 and show that using either ofthese time periods results in a violation ofthe 2010 S02NAAQS at Coburn Road SLAMS. The data supports EPA ' s decision of designating Yellowstone County as a nonattainment area. The three year average 99t hpercentile for 2006 through 2008 and 2007 through 2009 are included in Table 4 and provide the perspective that that 1-hour S02values have been generally consistent in the Billings area since 2008.
The State discussed with EPA that the increased S02values in 2010 may have been the result ofcontrol measures taken at the ExxonMobil refinery. In 2010, the refinery installed and tested a S02reducing catalyst. Testing the catalyst resulted in a briefperiod ofhigher S02emissions than expected while the equipment under went the tests. The State pointed out that it was a temporary situation and that the catalyst is now operating correctly. Lower S02emissions at ExxonMobil are now the result ofthe equipment operating correctly.

6The State asked EPA to delay its decision ofnonattainment status for the Billings area until more monitoring data could be collected while the catalyst was operating correctly. However, additional exceedances occurred during 2011 after ExxonMobil had implemented the catalyst controls and the catalyst was working correctly. As a result, EPA was not persuaded by the State's request. The NAAQS violations at the Coburn Road monitor after the installation ofthe catalyst supported EPA's preliminary decision to designate the area as nonattainment. The exceedances at the Coburn Road monitor appear to be a result ofemissions from all facilities in the Billings/Laurel area, notjust ExxonMobil.
Table3. C b o urn 

### R dSLAMS1 H oa
- our D "I M any ax1mum SO VI 2 a ues 

### 2008-2011. 2008 2009 2010 2011 Date ppb Date ppb Date 

### _ppb Date ppb 8/24 119 9/22 107 7/8 111 9/5 142 10/28 112 2/5 83 12/24 101 9111 113 10/27 95 9/25 83 7/9 92 10/30 85 6/14 

### 89* 1/20 

### 72* 2/10 

### 91* 9/30 

### 74* 10/1 77 8/12 69 10/22 89 11120 66'
The 2006

-2008,2007-2009,2008-2010, and 2009-2011 S02NAAQS design values for Yellowstone County are shown in Table 4.
Table 4. Air Quality Data for Nonattainment Designations in Montana County State Monitor Monitor S02 Design S02 Design S02 Design S02 Design Recommended Name& Location Value, Value, Value, Value, Nonattainment? System 10 2006-2008 2007-2009 2008-2010 2009-2011 (ppb) (ppb) (ppb) (ppb) Yellowstone No Coburn \12 mile south 73 73 84 79 County, Road, of 1-94 Montana 30-1 I 1-0066 Interchange on Coburn Road
Since Yellowstone County shows a violation ofthe 2010 S02 NAAQS; reviews ofthe surrounding counties were also undertaken and completed. The adjacent counties to Yellowstone County are: Musselshell, Rosebud, Treasure, Big Hom, Carbon, Stillwater, and Golden Valley. Ofthese seven adjacent counties, only Rosebud County had a regulatory industrial S02 monitor. There were no exceedances found at the S02 monitor in Rosebud. Additionally, due to the geography/topography of the surrounding area around the Billings/Laurel area where the violating monitor is located, there is only
a very small possibility ofemissions from the facilities in Rosebud County reaching the Coburn Road SLAMS monitor (see geographical/topographical section for discussion on geography and topography ofBillings/Laurel area). The EPA also reviewed the five factors found in the March 24,2011 guidance, for each ofthe seven counties and finds that it is appropriate to not designate any ofthese counties as nonattainment related to the violating monitor in Yellowstone County.

7

### Figure 2. Map ofMajor Potential Sources of 802 

### in Montana (Ref.: Montana Recommendation Letter and TSD.**Mon~SUII:hur** n Conecof'tlillps EnonMotliJ**PPLMon~** corh.
C HS Inc



## Major Potential Sources of 502

Major 502 Source Affected County



### Emissions andEmissions-Related Data 

## in Montana ·**== ========;** 

Evidence of S02 emissions sources in the vicinity of a violating monitor is an important factor for determining whether a nearby area is contributing to a monitored violation

. For this factor, EPA evaluated county level emissions data for 

## so2 and any growth in 

## so2 emitting activities since the date represented by those emissions data.
Emissions
In Table 5 below, EPA calculated the average emissions in tpy for each source for the periods 2006- 2008 , 2007-2009 , 2008-2010 and 2009-2011.

8

### Table 5. Billings/Laurel Area S02 

### Average Emissions. (Ref.: Montana's May 27, 2011 

### Recommendation Letter & 

### TSD)
County Facility Facility Location
PPL Montana 30 I Charlene St.

- Corette P

.O

. Box 30495 Billings , MT 59107 ExxonMobil 700 Exxonmobil Rd, Billings, MT 59101 *YELP 2215N. Frontage Rd. Billings, MT Yellowstone 59101-7303 * *MSCC 627 Exxonmobil County , Rd. Billings, MT Montana 59101 * ** CHS 803 

### us Highway 212 S. Laurel , MT 59044 Western Sugar 3020 State Ave

. Billings, MT 59101 ConocoPhilips 40 I S. 23ra St. Billings , MT 59101 *Yellowstone Energy Ltmtted Partnership (YELP) **Montana Sulphur & Chemical Company (MSCC) ***Cenex Harvest States, Inc (CHS) 2006-2008 2007-2009 S02 Average S02 Average

Emissions Emissions (tons/yr) (tons/yr) 3,307 3 ,076

2,203 1,458

1,645 1,750

1,282 1,390

404 309

122 139

201 169 2008-2010 2009-2011 S02 Average S02 Average

Emissions Emissions (tons/yr) (tons/yr) 2 ,663 2,411

1,617 1,287

1,823 1,995

1,421 1,623

241 227

123 104

103 86

In Table 6 below, Montana provided information on total emissions of S02 (given in tons per year) that were from 2008 through 2011 for sources in Yellowstone County (Billings/Laurel area). Represented in the table are ExxonMobil ' s emissions for 2008,2009 , 2010, and 2011 which are 1,765 ; 696; 2,389; and 775 tons/year, respectively

. This table shows that 2009 emissions for ExxonMobil were low compared to emissions in 2008 and 2010.

9

### Table 6. Billings/Laurel Area 802 

### Emissions (Ref.: Montana's May 27, 2011 

### Recommendation Letter & 

### TSD) Facility County Facility Location PPL Montana 30 I Charlene St.

- Corette P.O

. Box 30495 Billings, MT 59107 ExxonMobil 700 Exxonmobil

. Rd , Billings, MT 59101 *YELP 2215 N

. Frontage Rd. Billings, MT Yellowstone 59101-7303

County, **MSCC 627 Exxonmobil Rd. Billings, MT Montana 59101 ***CHS 803 

## us Highway 2 12 S. Laurel , MT 59044 Western Sugar 3020 State Ave

. Billings, MT 59101 ConocoPhilips 40 I S. 23ra St. Billings, MT 59101 *Yellowstone Energy Limited Partnership (YELP) **Montana Sulphur & Chemical Company (MSCC) ***Cenex Harvest States, Inc (CHS) 2oos 

## so2 20o9 

## so2 Emissions Emissions (tons/yr) (tons/yr) 2 ,929 2,788

1,765 696

1,590 2,062

1,320 1,559

268 231

138 133

108 127 2010 

## so2 2011 

## so2 Total 

## S02 Emissions Emissions Emissions (tons/yr) (tons/yr) (tons) 2,271 2, 174 10, 162

2,389 775 5 ,625

1,816 2, 106 7 ,574

1,3 83 1,927 6, 189

225 226 950

98 80 449

73 57 365

In Table 7 below, the State provided total S02 emissions (given in tons per year) for the years 2008, 2009 , and 201 0 and total emissions for all three years combined for sources within Yellowstone County emitting (or anticipated to contribute) greater than 100 tons per year ofS02 according to the State's emissions inventories for 2008,2009 , and

- 2010. EPA provided total S02 emissions (given in tons per year) for 2011 and added the emissions to the total the State provided in their TSD

. From these data, and from Figure 3, the 2009 emissions, and in addition 2011 data, appear to be low compared to past emissions and 2010. This is in contrast to what the State concluded, which is that the abnormal year was 2010 and that the monitored data from 2010 was inappropriate to use for initial designations. However, from the emissions and monitored data provided by the State in their TSD and as stated above, the 2010 emissions appear representative ofnormal emissions and thus the 2010 monitored data is appropriate to use for initial designations.

10

### Table 7. Billings/Laurel Area Combined Industrial S02 Emissions (Ref.: Montana Recommendation Letter & 

### TSDJ Emissions Year Total S02 Emissions (tons/year) 2008 8,11 8 2009 7,595 2010 8,254 2011 7,345 

### Total Emissions 2008-2011 31,312 

### tons
The State additionally concluded that performance testing for catalysts at ExxonMobil was the primary issue for the 1,700 ton/year increase from 696 tons/year in 2009 to 2,389 tons/year in 2010. Though when the emissions for ExxonMobil are shown in extended years, from 2008 through 2011, the 2008 and 2010 years are more representative ofnormal emissions and the 2009 , and possibly 2011 , emissions appear low (Table 6). Figure 3 shows historical S02 emissions for industries in the Billings/Laurel area using continuous emissions monitor (CEMs) data. In Figure 3 it shows a general decrease in emissions from ExxonMobil from 1995 through 2011. The 2009 data in Figure 3, from ExxonMobil is low compared to the last 15 years of CEMs data. Additionally, other facilities show almost uniform emissions from 2000 to 2010, which could have an impact on monitored data and possible exceedances in the 2008-2010 and 2009-2011 data sets. 

### Figure 3. Historical S02Emissions for Billings/Laurel Industries using CEMS data.

HISTORICAL S02 EMISSIONS 16000 Billings-Laurel Industries

14000

0::: 12000**MSCC** <( w 

### >- 10000

.... Q) a. (/) 8000 

### z 0 1- ..J 6000 <( 1- 0 1- 4000

2000

0

11In the Air Quality Data section ofthis TSD , ExxonMobil installation ofa catalyst was discussed. In Figure 4, below, the 2010 S02 CEMs data is shown for the ExxonMobil refinery. Specifically, the figure shows the daily S02 emissions (in lbs/day) and the days where catalyst testing occurred. The highlight ofpurple is the timeframe when the first catalyst was tested, the green highlight is representative ofthe second catalyst testing, and blue shows the third and last catalyst tested. Days when exceedances were monitored ofthe 75 ppb standard are shown as the red lines in the figure

. This graph represents the relationship between the exceedances and the catalyst testing at ExxonMobil. Even when the new catalysts were being tested, the exceedances occurred towards the end ofthe testing phase when it appears the company had broken in the catalyst and dialed in the conditions , which were the best for S02 control. From this observation the exceedances occurred during the lower, controlled emissions rates that were achieved by the catalysts. ExxonMobil indicated in a memo that they intended to go with the catalyst represented by the green highlighted area in the graph. So even with the new catalyst, emission conditions at the facility will exist that can result in NAAQS exceedances. While the new controls at the refinery will result in a reduction of S02 , it appears that others sources contribute to the exceedances in addition to the refinery and must be addressed to bring the area into attainment. Figure 4
. CEMS S0 2 Data for ExxonMobil with Overlay ofExceedances in 2010 and Catalyst Testin
. 30000

25000



## > 

# "' "'C 20000 

# ' (/) 

## .c
(/) 

### c: 0 15000


# ·- (/) (/) 

# E w 10000 N 

### 0 V)

### ~ 5000

0**~**

## ~ i**~** 

# M

# ~.**~·~** Ia 

# f' • 

# ' I

I

# ~ - Cat 1 Testing 

# rtf· - cat 2 Testing

- Cat 3 Testing

- NonAttainment Days

- 502 Emissions

12The State mentions that the Clean Air Act does not expect states to revise SIPs when federal requirements in the consent decree interfere with attainment ofthe NAAQS (42 USC §7410(a)(3)(C)). EPA believes that from Figure 4 above that the S02 reduction catalyst testing did not interfere with attainment ofthe 2010 S02 NAAQS since most ofthe exceedances were found when ExxonMobil had the catalysts working at their optimal capacity. Therefore, EPA believes that the CAA 42 USC §7410(a)(3)(C), does not apply to this instance. Additionally, the State discusses 40 CFR 52.21 (b)(48)(iii), which provides a definition of "Baseline actual emissions " with the inclusion ofthe following sentence: "The Administrator shall allow the use of a different time period upon a determination that it is more representative ofnormal source operation." From the figures and tables presented in this TSD EPA believes that the 2009-2011 time period is representative ofnormal emissions.
From Figure 1, above, the map shows S02 emission sources in Yellowstone County and their relation to the air quality monitors. In addition, it shows EPA' s recommendation ofthe entire county of Yellowstone being the nonattainment area, which is circled in gray with a distance scale. EPA is recommending the entire county of Yellowstone as the nonattainment area due to the March 24, 2011 guidance, which discusses that area boundaries be defaulted to the county boundary unless provided informationjustifies a larger or smaller boundary than that ofthe county.
Emissions Controls
The emissions data used by EPA in this technical analysis and provided in Table 6 represent emissions levels, taking into account any control strategies implemented on stationary sources in Yellowstone County up to and including 2008. Additionally, ExxonMobil will have SOz reducing catalysts implemented in 2011. EPA has received additional information on emissions reductions resulting from controls put into place after 2008 for ExxonMobil for their consent decree. These controls will be a S02 reducing catalyst that had the largest reduction in SOz. The addition ofthis S02 reducing catalyst could possibly lower the SOz monitored values at Coburn Road but due to the fact that since implementation ofthe catalyst in 2011 and Coburn Road monitor is still monitoring exceedances there seems to be a need for additional controls for facilities in the Billings/Laurel area. Meteorology (weather/transportpatterns)
For this factor, EPA considered meteorological data from the Billings Airport for six years (2006-2011). This data consisted ofwind direction and wind speed which corresponded with the exceedance at Coburn Road monitor. Meteorology data is shown in the wind rose in the docket and Tables 8, 9, 10, and 11. The data may provide evidence ofthe potential for S02 emissions sources located upwind ofa violating monitor to contribute to ambient S02 levels at the violation location. Billings and Laurel are situated in the Yellowstone River Valley, which runs from the southwest to northeast. Wind roses for the area reflect the valley orientation with southwest winds being the most common.

13According to the available data from the Billings International Airport, it appears that the exceedances shown in Tables 8, 9, 10, and 11 are primarily driven from emissions blown from the southwest, the predominate wind direction. Exceedances follow the trend as well, occurring mostly when the wind is blowing from the southwest. It should be noted that the Billings Airport is located on the opposite side ofthe valley as the Coburn Road Monitor, but both are on the northeast side ofBillings and located above the valley floor. Additionally, ExxonMobil is located northeast ofthe Coburn Road Monitor and the Airport while the other facilities are located to the southwest ofthe monitor.


### Table 8 . 2008 Exceedances (from AQS) with Wind Direction and Wind Speed. Date and Time Value Wind Direction Wind Speed (Military) (ppb) (degrees) (Meters/s) 8/24 1:00 119 127 0

.9 10/28 8:00 112 240 7.8 10/27 1:00 95 119 0.8 6/ 14 6:00 89 238 4.8 10/01 8:00 77 243 5.3


### Table 9 . 2009 Design Values (from AQS) with Wind Direction and Wind Speed. Date and Time Value Wind Direction Wind Speed (Military) (ppb) (degrees) (Meters/s) 9/22 9:00 107 Poor Quality 3 .0 Assurance Results 2/5 2:00 83 240 8.8 9/25 9:00 83 Poor Quality 4.1 Assurance Results 1/20 5:00 72 238 12


### Table 10. 2010 Exceedances (from AQS) with Wind Direction and Wind Speed. Date and Time Value Wind Direction Wind Speed (Military) (ppb)**(degree~_** 

### (Meters/s) 2/10 4:00 91 Poor Quality 7

.2 Assurance Results 7/8 6:00 111 Machine 3.7 Malfunction 7/9 6:00 92 Machine 4.2 Malfunction 9/28 8:00 83 235 5.9 10/3 9:00 87 242 4.8 10/22 9:00 89 241 5.0 12/21 9:00 86 232 3.0 12/24 9:00 101 242 5.4

14Table 11. 2011 Exceedances (from AQS) with Wind Direction and Wind Speed. Date and Time Value Wind Direction Wind Speed (Military) (ppb) (degrees) (Meters/s)

9/5 8:00 142 248 14.2 9/11 7:00 113 242 12.7 10/30 85 238.6 12.1 Geography/Topography (mountain ranges or other air basin boundaries)
The dominant topographical feature to influence airflow in the Billings and Laurel areas is the Yeqowstone River Valley. The terrain in the vicinity ofBillings and Laurel is upland bench which is steeply cut by the Yellowstone River and its tributaries. The bench lies at an elevation of4,000 feet while the valley in Billings is approximately 3,000 feet above sea level and Laurel is approximately 3,300 feet above sea level. A constriction in the Yellowstone Valley occurs between central Billings and the Lockwood area located to the east. The valley is generally 3 or 4 miles wide but narrows to a little over a mile wide at the constriction. Nearby terrain, such as the Sacrifice Cliffto the southeast of Billings and the Rimrocks to the north, rises abruptly and is often higher than the tallest smoke stack. Laurel is located within the Yellowstone Valley approximately 15 miles southwest ofBillings. The valley near Laurel is 3 or 4 miles wide. Nearby
· terrain to the northwest and southeast ofLaurel rises abruptly and is often higher than the tallest smoke stack.
The geography/topography ofthe area has the possibility to restrict air flow and cause stagnation of an air mass. However, from Tables 8, 9, and 10 above, they show that even though the terrain signifies that there could be stagnation ofair flow and inversion ofthe air mass, the wind speed does not stagnate and shows that there is continuous movement. However, this should not be interpreted to signify that the Billings/Laurel area has no inversion or stagnation occurrences. Jurisdictional Boundaries
Yellowstone County has a nonattainment area for the 1971 24-hour primary S02 NAAQS at 0.14 ppm. This area is found within the Laurel area and the area is a 2 km radius around CHS. From the information presented above the Laurel nonattainment area could possibly be contributing to the exceedances and ultimately the violation at the Coburn Road SLAMS Monitor. Additionally, the information above shows that the industries in the Billings area are possibly contributing to the exceedances and the violation at the Coburn Road SLAMS Monitor. Since the Billings area is not included in the nonattainment area for the 1971 24-hour primary S02 NAAQS, EPA is recommending the entire county of Yellowstone be designated as the nonattainment area due to the March 24, 2011 guidance which discusses that area boundaries be defaulted to the county boundary unless provided informationjustifies a larger or smaller boundary than that ofthe county.
Other Relevant Information
Montana submitted in their recommendation letter and TSD a discussion ofcurrently implemented S02 reducing requirements and future rules for implementation that the State believes will help reduce S02 further. These include: EPA Refinery Initiative and Associated Consent Decrees; Utility MACT Implementation; Existing Federal Implementation Plan (FIP) Implementation; Regional Haze/Best

15Available Retrofit Technology (BART) Implementation; Boiler Maximum Achievable Control Technology (MACT) Implementation; New Source Performance Standards (NSPS)

- 40 CFR 60, Subpart Ja; and EPA's Flare Initiative.
Montana' s discussion on the EPA Refinery Initiative and Associated Consent Decree includes the S02 reduction additives in the fluidized catalytic cracker unit (FCCU) , the treatment of sour water stripper overhead gas, enhanced flare gas recovery, and elimination ofroutine and continuous flaring of sour gas. The S02reduction additives in the FCCU are discussed more fully in the previous sections and the 2008-2010 data appears representative ofnormal emissions. Additionally, the 2011 data is continuing to show exceedances and pos· sibly will show a violation ofthe 2010 S02NAAQS after the data is QA/QC. The treatment of sour water stripper overhead gas became effective in October 2009 and the S02 reductions from this treatment is representative in the 2008-2010 time period and also in the 2011 data, which still shows a violation at the Coburn Road monitor. For the enhanced flare gas recovery and elimination ofroutine and continuous Haring of sour gas, they became effective in September 2010 and the so2reductions from these enhancements are representative in the 2008-2010 time period, and also in the 2011 data, which still shows a violation ofthe 2010 S02NAAQS. Since the 2009-2011 design value still shows a violation ofthe 2010 S02NAAQS , Yellowstone County should be designated as a nonattainment area and the use ofany other time periods are irrelevant.
For the utility MACT implementation, the State discusses that the rule was finalized in February 16, 2012, and the options that subject facilities may choose from for meeting compliance. Since a facility is allowed to choose a · control strategy that may not reduce S02emissions, it is most appropriate to consider so2reductions in this initial designation process
. The existing FIP has not been implemented due to ongoing litigation

. Though the FIP has not been implemented, the State discusses aspects ofthe FIP as if it has been. One ofthese is that MSCC installed (in 2008) duplicate/redundant SuperClaus

### TM to allow either unit to carry on tail gas processing tasks while the other is out of service. Since this unit was installed in 2008 the S02emissions reduction should already be realized and thus the 2008-2010 time period is representative ofnormal emissions. Additionally, Lockwood, MSCC , and ExxonMobil worked together to bring about a functional enhanced flare recovery system serving the refinery flare system and using the MSCC facilities for gas treating. This project became operational in 2010.
For EPA ' s Regional Haze Program/BART implementation, Montana is required to develop a program to assure reasonable progress toward meeting the national goal ofprotecting, and preventing, visibility impairment in mandatory Class I areas. Montana declined to submit a Regional Haze State Implementation Plan; and thus , EPA developed a FIP for Montana' s Regional Haze Program. As BART controls for S02were not required for any sources in Billings, EPA believes it is premature to use this as a basis on so2emissions reductions for the initial designations process
. Montana discusses in their TSD the Boiler MACT Implementation, which was finalized and published as 40 CFR 63 , Subpart DDDDD in the Federal Register on March 21 , 2011. On May 18 , 2011 , EPA published an indefinite delay ofthe implementation ofthe major source Boiler MACT rules. Since this rule has not been implemented and is on an indefinite delay, reductions in S02emissions cannot be properly quantified for the initial 1-hour S02designations. When or ifimplemented, the Boiler MACT rule could have possible so2reductions , but the reductions for so2 are expected to be minimal for this

16rule and for this area. Additionally, even ifthe rule were to be implemented in the near future , S02 reductions would not have a significant impact on the attainment status ofthe area.
The New Source Performance Standards (NSPS)

- 40 CFR Part 60 , subpart Ja gives a new set of regulations that includes new standards and requirements for new, modified, reconstructed FCCUs , fluid coking units, process heaters , and flares. Since this NSPS regulation is only for new, modified, or reconstructed sources, this regulation would not apply to the facilities in the Billings/Laurel area. With the implementation ofthis regulation, there will be no reduction in so2 emissions unless the facilities modify or reconstruct.
The National Flare Initiative is an enforcement initiative. The EPA assumes all facilities to be in compliance with state, local, and federal regulations until shown otherwise, and assumes no emission reductions can be counted on to occur through this initiative.
The regulatory actions stated in Montana' s recommendation letter and TSD will have little impact on reducing S02 emissions at the violating Coburn Road monitor.
Conclusion
EPA has reviewed the information above and is determining that it is appropriate to designate the counties listed in Table 1 as " nonattainment" for the 2010 S02NAAQS.
After considering the factors described above, EPA is determining that it is appropriate to designate Yellowstone County as a nonattainment area for the 2010 S02NAAQS , also found in Table 1.
The air quality monitor in Yellowstone County shows a violation ofthe 2010 S02NAAQS , based on 2009-2011 air quality data. The nearby counties ofMusselshell, Rosebud, Treasure, Big Hom, Carbon, Stillwater, and Golden Valley, do not contribute to the violations of Coburn Road SLAMS monitor in Yellowstone County, and thus will not be included in the nonattainment area. The EPA is deferring designations on these and all other areas in Montana. Based on the consideration ofall the relevant and available information, as described above, the boundaries described herein encompass the entire area that does not meet (or that contributes to ambient air quality in a nearby area that does not meet) the 2010 S02NAAQS. Additionally, while the new controls at the ExxonMobil refinery will result in a reduction of S02 , others
sources contribute to the exceedances, in addition to the refinery, and these sources must be addressed to bring the area into attainment.

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