Draft Technical Support Document (TSD) 

Montana 

Area Designations For the 

2010 S02 Primary 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 of counties (or areas of 

Indian country) in Montana that EPA intends to designate "nonattainment" based on monitored 

violations. 

Tabl e 1 N . ona tt ammen . tA rea D" es1gna f Ions f< or M on t ana 

Montana's Recommended EPA's Intended Designation 

Area Designation of Counties of Counties 

Yellowstone County 

Yellowstone County: Unclassifiable N onattainment 

excluding Crow Tribe of 

Montana 

Background 

On June 2, 2010, EPA revised the primary S02 NAAQS (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 991h percentile of the 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 of 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 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 of these two prior primary standards. Similarly, the secondary standard for S02 has not been 

revised, so EPA is not designating areas in this process on the basis of the secondary standard. 

EPA's S02 Designation Approach 

Section 1 07( d) of the 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 a 
letter 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 of Montana's area of Indian country is located adjacent to the intended Yellowstone 

county nonattainment area. This area of Indian country does not contain any sources that are 

contributing to the violating monitor in Yellowstone County. Therefore, EPA intends to exclude Crow 

Tribe of Montana's area of Indian country from the Yellowstone County nonattainment area and defer 

designations for the area of Indian country. 

Designations guidance was issued by EPA through a March 24, 2011 , memorandum from Stephen D. 

Page, Director, U.S. EPA, Office of Air Quality Planning and Standards, to Air Division Directors, U.S. 

EPA Regions 1-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 information justifies a larger or smaller boundary than that of the 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 of the recommendations submitted by the 

states and/or tribes for designations of the 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. 

2 
3) 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 of 40 CFR part 

50. 

4) 2010 802 NAAQS- 75 ppb, national ambient air quality standard for S02 promulgated in 2010. 

Based on the 3-year average of the 991

h percentile of the annual distribution of daily maximum 1-hour 

average concentrations 

5) Design Value - a statistic that describes the air quality status of a 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 S02 NAAQS and evaluates nearby counties for contributions to S02 concentrations in the area. 

EPA has evaluated Yellowstone County and nearby counties based on the weight of evidence of the 

factors recommended in the March 24, 2011 EPA guidance. 

Figure 1, below, is a map of the 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 

Golden Valley 

Carbon 

Yellowstone County, MT 

Rosebud 

Big Horn 

Legend 

- EPA proposes whole county as non attainment · 

EPA proposes partial county as nonattainment 

- Counties proposed as a different S02 nonattainment area 

+ Monitor violating 2010 S02 NAAQS (2009-2011) 

+ Monitor attaining 2010 S02 NAAQS (2009-2011) 

BIIJ EPA'S intended S02 nonattainment area 

Areas of Indian country 

- National highway 

Water body 

S02 emission source (NEI 2008v2.0) 

• 100 - 1,000 tons/year 

0 1 ,000 or more tons/year 

0 5 10 20 Miles 

I I I I I I I I I 

From Figure 1 above, all of the 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 of Montana's Department of Environmental Quality, 

recommended that Yellowstone County be designated as "unclassifiable" for the 2010 S02 NAAQS 

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 of ExxonMobil' 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 of using 2010 data, either 2009, 2011 , 

and 2012 data or 2011-2013 data to determine a design value for comparisons to the NAAQS. Letter 

4 
and supporting analysis from Mr. Opper, to James B. Martin, Regional Administrator, USEP A, Region 8 

(May 27, 2011) is on file with EPA Region 8 Air Program Unit. 

Additionally, Montana discusses implementation of future 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 S02 NAAQS, 

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 of the monitored data in Table 2, below, was provided by the State in their 

recommendation letter and TSD. The table shows a summary of monitored NAAQS exceedances by 

quarter during the 2008-2010 time period. The EPA extended the table to include 2011 exceedances. 

The majority of exceedances occurred during the third and fourth calendar quarters of the 2008-2011 

monitoring period. 

5 
Table 2. Coburn Road SLAMS Monitored NAAQS Exceedances 2008-2011 

Calendar Year Calendar Quarter Number of Exceedances 

(> 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 S02 values and 

these values were used to calculate the annual 99th percentile. The annual 99th percentile is highlighted 

in the table for each of the 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 of these time periods results in a 

violation of the 2010 S02 NAAQS at Coburn Road SLAMS. The data supports EPA's decision of 

designating Yellowstone County as a nonattainment area. The three year average 99th percentile for 

2006 through 2008 and 2007 through 2009 are included in Table 4 and provide the perspective that that 

1-hour S02 values have been generally consistent in the Billings area since 2008. 

The State discussed with EPA that the increased S02 values in 2010 may have been the result of control 

measures taken at the ExxonMobil refinery. In 2010, the refinery installed and tested a S02 reducing 

catalyst. Testing the catalyst resulted in a brief period ofhigher S02 emissions 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 S02 emissions at ExxonMobil are now the result of the 

equipment operating correctly. 

6 
The State asked EPA to delay its decision of nonattainment 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 of the catalyst supported EPA's 

preliminary decision to designate the area as nonattainment. The exceedances at the Coburn Road 

monitor appear to be a result of emissions from all facilities in the Billings/Laurel area, not just 

ExxonMobil. 

Table3. C o b urn R oa dSLAMS1 -H our D any "I M ax1mum SO 2 VI 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 S02 NAAQS 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 of emissions 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 of the seven counties and finds that it is appropriate to not designate any of these counties as 

nonattainment related to the violating monitor in Yellowstone County. 

7 
Figure 2. Map of Major Potential Sources of 802 in Montana (Ref.: Montana Recommendation 

Letter and TSD. 

Mon~SUII:hur 

n Conecof'tlillps EnonMotliJ 

PPLMon~ corh. 

CHS Inc 

Major Potential Sources of 502 

Major 502 Source 

Affected County 

Emissions and Emissions-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 

Exxon Mobil 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 

1,383 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 of normal 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 of normal 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 S02 Emissions for Billings/Laurel Industries using CEMS data. 

HISTORICAL S02 EMISSIONS 

16000 Billings-Laurel Industries 

14000 

0::: 12000 MSCC 

<( 

w 

>- 10000 .... 

Q) 

a. 

(/) 

z 8000 

0 

1-

..J 

<( 6000 

1-

0 

1- 4000 

2000 

0 

11 
In the Air Quality Data section of this TSD, ExxonMobil installation of a 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 of purple is the time frame when the first catalyst was tested, the green highlight is 

representative of the second catalyst testing, and blue shows the third and last catalyst tested. Days 

when exceedances were monitored of the 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 of the 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 

12 
The State mentions that the Clean Air Act does not expect states to revise SIPs when federal 

requirements in the consent decree interfere with attainment of the 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 of the 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 of the following sentence: "The Administrator shall allow the use of 

a different time period upon a determination that it is more representative of normal source operation." 

From the figures and tables presented in this TSD EPA believes that the 2009-2011 time period is 

representative of normal 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 of the 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 

information justifies a larger or smaller boundary than that of the 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 of this S02 reducing catalyst could 

possibly lower the SOz monitored values at Coburn Road but due to the fact that since implementation 

of the 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/transport patterns) 

For this factor, EPA considered meteorological data from the Billings Airport for six years (2006-2011). 

This data consisted of wind 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 of the potential for S02 emissions sources located upwind of a 

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. 

13 
According 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 

of the valley as the Coburn Road Monitor, but both are on the northeast side of Billings and located 

above the valley floor. Additionally, ExxonMobil is located northeast of the Coburn Road Monitor and 

the Airport while the other facilities are located to the southwest of the 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 

14 
Table 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 of Billings and Laurel is upland bench which is 

steeply cut by the Yellowstone River and its tributaries. The bench lies at an elevation of 4,000 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 Cliff to 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 of Billings. The 

valley near Laurel is 3 or 4 miles wide. Nearby ·terrain to the northwest and southeast of Laurel rises 

abruptly and is often higher than the tallest smoke stack. 

The geography/topography of the 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 of air flow and inversion of the 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 

information justifies a larger or smaller boundary than that of the county. 

Other Relevant Information 

Montana submitted in their recommendation letter and TSD a discussion of currently 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 

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Available 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 of routine and continuous flaring of sour gas. 

The S02 reduction additives in the FCCU are discussed more fully in the previous sections and the 

2008-2010 data appears representative of normal emissions. Additionally, the 2011 data is continuing to 

show exceedances and pos·sibly will show a violation of the 2010 S02 NAAQS 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 of routine and continuous Haring of sour gas, they became effective in September 2010 and 

the so2 reductions from these enhancements are representative in the 2008-2010 time period, and also in 

the 2011 data, which still shows a violation of the 2010 S02 NAAQS. Since the 2009-2011 design value 

still shows a violation of the 2010 S02 NAAQS, Yellowstone County should be designated as a 

nonattainment area and the use of any 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 S02 emissions, it is most appropriate to 

consider so2 reductions 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 of the FIP as if it has been. One of these 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 S02 emissions reduction 

should already be realized and thus the 2008-2010 time period is representative of normal 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 of protecting, 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 S02 were not required for any sources in Billings, EPA believes it is premature to use this as 

a basis on so2 emissions 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 of the implementation of the major source Boiler MACT rules. Since this 

rule has not been implemented and is on an indefinite delay, reductions in S02 emissions cannot be 

properly quantified for the initial 1-hour S02 designations. When or if implemented, the Boiler MACT 

rule could have possible so2 reductions, but the reductions for so2 are expected to be minimal for this 

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rule and for this area. Additionally, even if the rule were to be implemented in the near future, S02 

reductions would not have a significant impact on the attainment status of the 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 of this 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 S02 NAAQS. 

After considering the factors described above, EPA is determining that it is appropriate to designate 

Yellowstone County as a nonattainment area for the 2010 S02 NAAQS, also found in Table 1. 

The air quality monitor in Yellowstone County shows a violation of the 2010 S02 NAAQS, based on 

2009-2011 air quality data. The nearby counties of Musselshell, 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 of all 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 S02 NAAQS. 

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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