1 Technical Support Document (TSD)

Montana Area Designations For the 2010 SO 2 Primary National Ambient Air Quality Standard

Summary

Pursuant to section 107(d) of the Clean Air Act (CA A), EPA must designate areas as either “nonattainment,” “attainment,” or “unclassifiable” for the 2010 1-hour sulfur dioxide (SO 2 ) 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 th e NAAQS. Table 1 below identifies the counties or po rtions of counties in Montana that EPA is designating “nonattainment” based on monitored viol ations. EPA is not yet prepared to designate other areas in Montana, and will address those areas and their sources in a future final designations action

.

Table 1. Nonattainment Area Designations for Monta na Area Montana’s Recommended Designation of Area/County EPA’s Designation of Area/County

Billings, MT Yellowstone County (Partial) Unclassifiable Nonattainment

Background

On June 2, 2010, EPA revised the primary SO 2 NAAQS (75 FR 35520, June 22, 2010) by establishing a new 1-hour standard at a level of 75 parts per bill ion (ppb) which is met at an ambient air quality monitoring site when the 3-year average of the annu al (99 th percentile) of the daily maximum 1-hour average concentrations does not exceed 75 ppb, as d etermined in accordance with Appendix T of 40 CFR part 50. 40 CFR 50.17(a)-(b). EPA has determi ned that this is the level necessary to provide protection of public health with an adequate margin of safety, especially for children, the elderly an d those with asthma. These groups are particularly s usceptible to the health effects associated with breathing SO 2 . The Agency is revoking the two prior primary sta ndards of 140 ppb evaluated over 24 hours, and 30 ppb evaluated over an entire year bec ause the standards will not add additional public health protection given a 1-hour standard at 75 ppb

. 1 Accordingly, EPA is not designating areas in this process on the basis of either of these two prior p rimary standards. Similarly, the secondary standar d for SO 2 has not been revised, so EPA is not designating ar eas in this process on the basis of the secondary standard.

EPA’s SO 2 Designation Approach

1 Generally, the prior SO2 NAAQS will be revoked for areas one year after their designation under the 2 010 NAAQS. However, for certain areas such as the Billings/Lau rel, Montana area, EPA’s rules provide that the pri or NAAQS will continue to apply until that area submits, pursuant to CAA section 191, and EPA approves, an implement ation plan providing for attainment of the 2010 NAAQS. 40 CFR 50.4(e); 75 FR at 35580, n.41.2

Section 107(d) of the CAA provides that not later t han 1 year after promulgation of a new or revised NAAQS, state Governors must submit their recommenda tions for designations and boundaries to EPA. This deadline was in June 2011. Section 107(d) als o requires EPA to provide a notification to states of no less than 120-days prior to promulgating an init ial area designation that is a modification of a st ate’s recommendation. EPA reviewed the State’s recommend ations 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 stat es, we intend to follow the same process for tribal governments, pursuant to section 301(d) of the CAA and Tribal Authority Rule (40 CFR Part 49). If a State or tribal government does not submit designat ion recommendations, EPA will promulgate the designations that it deems appropriate. If a State or tribal government disagrees with EPA’s intended area designations, it has an opportunity to demonst rate why any proposed modification is inappropriate

.

The Crow Tribe of Montana’s Reservation is located adjacent to the Billings, MT nonattainment area that we are initially designating. This area of In dian Country, and the majority of Yellowstone Count y, do not contain SO 2 emissions sources that we are currently prepared, based on monitoring data, to conclude are contributing to the design value at th e violating monitor in Billings. Therefore, EPA is not including the Crow Tribe of Montana’s areas of Indi an Country or the majority of Yellowstone County in the initial Billings nonattainment area. EPA wi ll further address these areas and their sources in a future round of final designations action.

Designations guidance was issued by EPA through a M arch 24, 2011, memorandum from Stephen D. Page, Director, U.S. EPA, Office of Air Quality Pla nning and Standards, to Air Division Directors, U.S

. EPA Regions I-X. This memorandum identifies factor s EPA intends to evaluate in determining boundaries for areas designated nonattainment. The se 5 factors include: 1) air quality data; 2) emissions and emissions-related data (location of s ources and potential contribution to ambient SO 2 concentrations); 3) meteorology (weather/transport patterns); 4) geography/topography (mountain ranges or other air basin boundaries); and 5) juris dictional boundaries (e.g., counties, air districts , preexisting nonattainment areas, reservations, metropo litan planning organizations), among any other information deemed relevant to establishing appropr iate area designations and boundaries for the 1-hou r SO 2 NAAQS.

The March 24, 2011, memo recommended that area boundaries be defaulted to th e 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 pot ential area on a case-by-case basis, and to recogni ze that area-specific analyses conducted by States, tr ibal governments 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 State of Montana for designations of the 1-hour SO 2 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 inc luded in this document, has violated the 2010 SO 23

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 that a State or tribal government has recommen ded to EPA to be designated as nonattainment.

3) Violating monitor – an ambient air monitor meeting all methods, quality assurance and citing criteria and requirements whose valid design value exceeds 7 5 ppb, as described in Appendix T of 40 CFR part 50.

4) 2010 SO 2 NAAQS - 75 ppb, national ambient air quality standard for S O 2 promulgated in 2010. Based on the 3-year average of the 99 th percentile of the annual distribution of daily max imum 1-hour average concentrations

5) Design Value – a statistic that describes the air quality statu s of a given area relative to the level of the NAAQS.

Nonattainment Designations

Introduction

Montana submitted its original recommendations in a letter dated May 27, 2011. Montana recommended an “unclassifiable” designation for all counties in the state including Yellowstone County in that letter. In Montana’s May 27, 2011 letter, it discussed why it believed Yellowstone County should be “unclassifiable” even though a violating monitor is located in the county. Montana conclude d that SO 2 emissions during 2010 were not representative of f uture conditions and that initial designation with consideration of 2010 monitoring data would be inappropriate.

EPA Region 8 sent a “120-day letter” to Montana on February 7, 2013. The 120-day letter indicated EPA’s preliminary decision to designate as nonattai nment Yellowstone County. Montana and the public had 60 days to review the letter and provide EPA wi th information to support any further changes to EPA’s preliminary decision. The comment period off icially closed on April 8, 2013.

Montana reasserted in an April 3, 2013, response le tter that SO 2 emissions in the Billings area during 2010 were not representative of normal or future co nditions and that a designation that used 2010 monitoring data would be inappropriate. Montana ba sed this assertion on catalyst testing conducted at ExxonMobil during 2010. It will be shown later in this TSD that this assertion is incorrect and that 2010 is a representative year and will be included in th e 2009-2011 design value calculation.

The State of Montana also submitted in that April 3 , 2013, letter a five-factor analysis for revising the nonattainment boundary from the default full county that EPA proposed in its February 6, 2013, 120-day letter. In this SO 2 designation for Montana, based on EPA's technical analysis of the State of Montana’s five-factor analysis described below, EPA is finali zing a partial county initial nonattainment area boundary for a portion of Yellowstone County in Mon tana in agreement with Montana’s recommended partial county boundary. EPA is not at this time, however, reaching final designations conclusions fo r4

the remainder of Yellowstone County, and will addre ss it and its source’s in a future final designatio ns action.

Nonattainment Designations

Technical Analysis for Yellowstone County, Montana

Introduction

The EPA reviewed and agrees with the five-factor an alysis that was submitted by the State of Montana for a smaller initial nonattainment area boundary. The EPA also agrees with the physical description of the nonattainment boundary that Montana submitted w ith its analysis. Figure 1 is a map of the area in Yellowstone County that the EPA is initially design ating nonattainment for the 2010 1-hour SO 2 NAAQS, including source information and the locatio n of the monitor violating the standard.

Figure 1. Billings, MT 1-Hour SO 2 Nonattainment Area Boundary

The following technical analysis in this TSD compil es the State of Montana’s and EPA’s information on the five-factor analysis.5

Detailed Assessment

Air Quality Data

The Air Quality Data factor considers SO 2 air quality monitoring data, including the design values (in ppb) calculated for all air quality monitors in the Yellowstone County and the surrounding area. This factor considered monitoring data for the 2008-2011 period.

The State of Montana’s April 3, 2013 response and a nalysis were based on data from the Coburn Road monitor (Monitor ID: 30-111-0066), a Federal Equiva lent Method (FEM) monitor located in Yellowstone County. The Coburn Road monitor is cla ssified as a State and Local Air Monitoring Station (SLAMS). EPA and Montana additionally revi ewed other monitors in the area that were nonregulatory monitors for use in advising on a bounda ry. These included: Johnson Lane, Brickyard, Lockwood (shut down in 2010), Laurel, and Pine Hill s (operated from 1993-2010).

The majority of the monitored data in Table 2 below was provided by the State in its initial May 27, 2011 recommendation letter and TSD. The EPA added 2011 data to the table. The table shows a summary of the monitored NAAQS exceedances by quart er during the 2008-2011 time-period. The majority of exceedances occurred during the third a nd fourth calendar quarters of the 2008-2011 monitoring period.

Table 2. Coburn Road SLAMS Monitored NAAQS Exceeda nces 2008-2011

Calendar Year Calendar Quarter Number of Exceedances (> 75 ppb)

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

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

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

2011 1 0 2 0 3 2 4 1 2011 Total Exceedances 36

2008-2011 Total Exceedances 21

The State provided Table 3 below in its initial rec ommendation letter and TSD. The EPA added the 2011, 1-hour daily maximums. The table shows the C oburn Road monitor’s 1-hour daily maximum SO 2 values, and these values were used to calculate the annual 99 th percentile. The annual 99 th percentile is highlighted in the table for each of the years 2008 through 2011.

Table 3. Coburn Road SLAMS 1-Hour Daily Maximum SO 2 Values 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 9/11 113 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 11/20 66` * 99 th percentile (4 th maximum)

The Coburn Road monitor’s average of the 99 th percentile values for 2008-2010 is 84 ppb and the average for 2009-2011 is 79 ppb. The averages are presented in Table 4. The results for both of these time-periods indicate violations of the 2010 1-hour SO 2 NAAQS at Coburn Road SLAMS. The data supports EPA’s decision of designating a portion of Yellowstone County as a nonattainment area. The three-year average 99 th percentile values for 2006-2008, 2007-2009, 2008-2 010, and 2009-2011 are included in Table 4.

Table 4. Three-Year Average 99 th Percentile Values for Coburn Road Monitor in Monta na County State

Recommended Nonattainment? Monitor

Name & System ID Monitor

Location SO 2 Design

Value, 2006-2008 (ppb) SO 2 Design

Value, 2007-2009 (ppb) SO 2 Design

Value, 2008-2010 (ppb) SO 2 Design

Value, 2009-2011 (ppb) Yellowstone County, Montana No Coburn Road, 30-111-0066 1⁄2 mile south

of I-94 Interchange on Coburn Road 73 73 84 79

The State provided 3-year averages for the monitors , including Coburn Road, in the area as found in Table 5 below and represented in Figure 2. These m onitors, although non-regulatory with the exception of Coburn Road, provide information to support modi fying the initial nonattainment area boundary from the proposed whole county to only a portion of the county. This data indicates that the Coburn Road monitor and the area it represents should be design ated nonattainment.

Table 5. Billings Area SO 2 Regulatory and Non-Regulatory Monitors

3-year Average Design Values for 2009-2011 Monitoring Location 2009-2011

Design Value (ppb) Coburn Road 797 Johnson Lane 71 Brickyard 49 Lockwood* 67 Laurel 58

Italics : Regulatory Monitor *Lockwood monitor suffered irreparable storm damage in 2011

Figure 2. Billings, MT Area SO 2 Major Sources, Historical and Active Monitoring Lo cations

(Ref.: State of Montana’s April 3, 2013, Five-Facto r Analysis)

The State discussed that the increased SO 2 values in 2010 may have been the result of control measures taken at the ExxonMobil refinery. In 2010, the ref inery installed and tested SO 2 reducing catalysts. Testing the catalyst resulted in a brief period of higher SO 2 emissions than expected. The State points out that it was a temporary situation and that the catalyst is now operating correctly resulting in lo wer SO 2 emissions at ExxonMobil. The Meteorology Section that follows on wind patterns will show this to be an inconsequential assertion.

The State asked EPA to delay its decision of nonatt ainment designation for the Billings area until mor e monitoring data could be collected while the cataly st was operating properly. However, additional8

exceedances occurred during 2011 after ExxonMobil h ad fully implemented the catalyst controls. As explained below, EPA was not persuaded by the State ’s request to delay a designation decision for the area impacting the violating monitor, although we d o agree that we are not yet prepared to take final action for the remainder of the County. The NAAQS exceedances, and subsequent 2009-2011 violation, at the Coburn Road monitor supported EPA’s prelimin ary decision to designate the area as nonattainment. The exceedances at the Coburn Road monitor appear to be a result of emissions from PPL’s Corette power plant, which was upwind of the monitor when exceedances were recorded. In the Meteorology section below, EPA discusses the correl ation between wind direction and exceedances/violations.

Since the Coburn Road monitor in Yellowstone County shows a violation of the 2010 1-hour SO 2 NAAQS, reviews of the surrounding counties were als o undertaken. The adjacent counties to Yellowstone County are: Musselshell, Rosebud, Treas ure, Big Horn, Carbon, Stillwater, and Golden Valley. Of these seven adjacent counties, only Ros ebud County had a regulatory SO 2 monitor. There were no exceedances found at the SO 2 monitor in Rosebud. Additionally, due to the geography/topography of the surrounding area around the Billings/Laurel area where the violating monitor is located, it is less likely that emission s from the facilities in Rosebud County are reachin g the Coburn Road SLAMS monitor (see geographical/topogra phical section for discussion on geography and topography of Billings/Laurel area). The EPA also reviewed the five factors found in the March 24, 2011 guidance for each of the seven counties, and i s not yet prepared to conclude that any of these counties’ emissions are contributing to the violati ng monitor in Yellowstone County. In a subsequent round of designations we will make final designations decisions for areas that are not currently included in the initial nonattainment are a designation addressed in this TSD.

Emissions and Emissions-Related Data

Evidence of SO 2 emission sources near a violating monitor is an im portant factor for determining whether a nearby area is contributing to a monitore d violation. For this factor, EPA evaluated county level emissions data for SO 2 and any growth in SO 2 emitting activities since the date represented by those emissions data.

Emissions

The major SO 2 emitting industries in the Billings area are the C onocoPhillips and ExxonMobil Petroleum Refineries; Western Sugar Company (sugarb eet processing plant); PPL Montana, LLC – J.E. Corette (PPL – Corette) coal-fired electrical gener ating station; Montana Sulphur Chemical Company (MSCC) (gas processing plant, sulfur recovery and s ulfur products); and Yellowstone Energy Limited Partnership (YELP) (petroleum coke-fired electrical /steam co-generation facility.) The major SO 2 emitting industry in the Laurel area is the Cenex H arvest States, Inc. (CHS) Petroleum Refinery.

In Table 6 below, EPA calculated the average emissi ons in tons per year for each source for the period s 2006-2008, 2007-2009, 2008-2010 and 2009-2011.9 Table 6. Billings/Laurel Area SO 2 Average Emissions. (Ref.: Montana’s May 27, 2011, Recommendation Lette r & TSD)

County Facility Facility Location 2006-2008

SO 2 Average Emissions (tons/yr) 2007-2009

SO 2 Average Emissions (tons/yr) 2008-2010

SO 2 Average Emissions (tons/yr) 2009-2011

SO 2 Average Emissions (tons/yr)

Yellowstone County, Montana PPL Montana

– Corette 301 Charlene St.

P.O. Box 30495 Billings, MT 59107 3,307 3,076 2,663 2,411

ExxonMobil 700 ExxonMobil

Rd, Billings, MT 59101 2,203 1,458 1,617 1,287

*YELP 2215 N.

Frontage Rd. Billings, MT 59101-7303 1,645 1,750 1,823 1,995

**MSCC 627 ExxonMobil

Rd. Billings, MT 59101 1,282 1,390 1,421 1,623

***CHS 803 US

Highway 212 S. Laurel, MT 59044 404 309 241 227

Western Sugar 3020 State Ave.

Billings, MT 59101 122 139 123 104

ConocoPhilips (Phillips66) 401 S. 23 rd St.

Billings, MT 59101 201 169 103 86

*Yellowstone Energy Limited Partnership (YELP) **Montana Sulphur & Chemical Company (MSCC) ***Cenex Harvest States, Inc (CHS)

In Table 7 below, Montana provided information on t otal emissions of SO 2 (given in tons per year) that were from 2008 through 2011 for sources in Yellowst one County (Billings/Laurel area). This table shows that 2009 emissions for ExxonMobil were low c ompared to years 2008 and 2010.10 Table 7. Billings/Laurel Area SO 2 Emissions (Ref.: Montana’s May 27, 2011, Recommendation Lette r & TSD)

County Facility Facility Location 2008 SO 2

Emissions (tons/yr) 2009 SO 2

Emissions (tons/yr) 2010 SO 2

Emissions (tons/yr) 2011 SO 2

Emissions (tons/yr) Total SO 2

Emissions (tons)

Yellowstone County, Montana PPL Montana

– Corette 301 Charlene St.

P.O. Box 30495 Billings, MT 59107 2,929 2,788 2,271 2,174 10,162

ExxonMobil 700 ExxonMobil

Rd, Billings, MT 59101 1,765 696 2,389 775 5,625

*YELP 2215 N.

Frontage Rd. Billings, MT 59101-7303 1,590 2,062 1,816 2,106 7,574

**MSCC 627 ExxonMobil

Rd. Billings, MT 59101 1,320 1,559 1,383 1,927 6,189

***CHS 803 US

Highway 212 S. Laurel, MT 59044 268 231 225 226 950

Western Sugar 3020 State Ave.

Billings, MT 59101 138 133 98 80 449

ConocoPhilips 401 S. 23 rd St.

Billings, MT 59101 108 127 73 57 365

*Yellowstone Energy Limited Partnership (YELP) **Montana Sulphur & Chemical Company (MSCC) ***Cenex Harvest States, Inc (CHS)

Table 8 below includes data the State provided for total SO 2 emissions (given in tons per year) for the years 2008, 2009, and 2010 and total emissions for all three years combined for sources within Yellowstone County that emit greater than 100 tons per year of SO 2 according to the State’s emissions inventories. In addition, EPA included total SO 2 emissions (provided by Montana in tons per year) f or 2011 in Table 8. From these data in Table 8 and al so in Figure 3 below, which is based on total emissions from each individual source in the area, the 2009 and 2011 emissions appear to be below past emissions levels, while 2010 data appear more repre sentative of emissions. This contrasts the State’s conclusion that 2010 was abnormally high and that t he monitored data from 2010 was inappropriate to use for initial designations. Therefore, from the emissions and monitored data provided by the State in its TSD and as stated above, we find that the 2010 emissions appear to be representative and thus the 2010 monitored data is appropriate to use for initi al designations.11 Table 8. Billings/Laurel Area Combined Industrial SO 2 Emissions (Ref.: Montana Recommendation Letter & TSD) Emissions Year Total SO 2 Emissions (tons/year) 2008 8,118 2009 7,595 2010 8,254 2011 1 7,345 Total Emissions 2008-2011 31,312 tons

1 EPA obtained the 2011 data from Montana for compari son.

The State additionally concluded that performance t esting for catalysts at ExxonMobil was the primary source of the 1,600 tons per year increase from 696 tons per year in 2009 to 2,389 tons per year in 20 10. Figure 3 shows historical SO 2 emissions for industries in the Billings/Laurel ar ea using continuous emissions monitor (CEMs) data provided by the State . Figure 3 indicates a general decrease in emissions from ExxonMobil from 1995 through 2011. Also from Figure 3, the ExxonMobil data for 2009, and possibly for 2011, is low compared to the last 15 years of CEMs data.

Figure 3. Historical SO 2 Emissions for Billings/Laurel Industries Using CEM S Data

In the Air Quality Data section of this TSD, ExxonM obil’s installation of a catalyst was discussed. I n Figure 4, below, the 2010 SO 2 CEMs data is shown for the ExxonMobil refinery. S pecifically, the figure shows the daily SO 2 emissions (in lbs/day) and the days where catalyst testing occurred. The purple, green, and blue highlights in the figure in dicate the first, second, and third catalyst, respe ctively

0 2000 4000 6000 8000 10000 12000 14000 16000TOTAL TONS per YEAR

YEAR HISTORICAL SO2 EMISSIONS Billings-Laurel Industries

PPL/JEC EXXMOB

COP MSCC

W.SUGAR YELP

CENEX12

that ExxonMobil tested. Days when exceedances of t he 75 ppb standard were monitored 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 cata lysts were being tested, the exceedances occurred towards the end of the testing phase when it appear s the company had optimized the operating conditions for maximum SO 2 control efficiency (as shown with the second and t hird catalyst tests in Figure 4). From this observation, the exceedances occurred during the times of relatively low control led SO 2 emissions rates and there does not appear to be a correlation between the catalyst testing and the exceedances. ExxonMobil indicated in a memo that i t intended to select the catalyst represented by th e green highlighted area in the figure. From the fig ure below, even with the new catalyst operating at optimal conditions, NAAQS exceedances occurred with ExxonMobil’s new and lower emissions.

Figure 4. CEMS SO 2 Data for ExxonMobil with Overlay of Exceedances

in 2010 and Catalyst Testing

The State mentions that the Clean Air Act does not expect states to revise SIPs when federal requirements in the consent decree interfere with a ttainment of the NAAQS (42 USC §7410(a)(3)(C)). EPA concludes, based on Figure 4 above, that the SO 2 reduction catalyst testing did not interfere with

0 5000 10000 15000 20000 25000 300001/1/101/16/101/31/102/15/103/2/103/17/104/1/104/16/105/1/105/16/105/31/106/15/106/30/107/15/107/30/108/14/108/29/109/13/109/28/1010/13/1010/28/1011/12/1011/27/1012/12/1012/27/10SO2 Emissions lbs/day Cat 1 Testing

Cat 2 Testing

Cat 3 Testing

NonAttainment Days

SO2 Emissions13

attainment of the 2010 SO 2 NAAQS since most of the exceedances occurred when catalyst operations were optimized at ExxonMobil. Therefore, EPA belie ves that the CAA 42 USC §7410(a)(3)(C), does not apply to this instance.

Additionally, the State discusses 40 CFR 52.21(b)(4 8)(iii), which provides a definition of “Baseline actual emissions” with the inclusion of the followi ng sentence: “The Administrator shall allow the use of a different time period upon a determination that i t is more representative of normal source operation .” From the figures and tables presented in this TSD, EPA finds that the 2009-2011 time-period is representative.

Figure 5 below is a pollution rose for the 2009-201 1 design period, which shows the SO 2 concentrations correlated with wind direction. Since the new cont rols at the refinery will result in a reduction of SO 2 , it appears that the upwind source, PPL’s Corette power plant, is the key contributor to the exceedances, and thus to the 2009-2011 violation of the 1-hour s tandard, and this source will be included in the nonattainment area. Another commenter’s analysis a lso showed that during the period 2009-2011 all concentrations above 75 ppb occurred from the west- southwest wind direction.

Figure 5. Coburn Road SLAMS Pollution Rose for 200 9-2011 (Ref.: State of Montana’s April 3, 2013, Five-Facto r Analysis)

Since the prevailing winds are from the southwest, upwind sources were reviewed for inclusion in this initial nonattainment area designation. These sour ces include: Phillips66, PPL-Corette, Western Sugar

, and CHS. The State provided information in its Apr il 3, 2013, five-factor analysis, which reviewed these sources and their possible role in the exceed ances at Coburn Road monitor. Figure 6 shows the annual emissions for the four major upwind sources during the 2009-2011 design period at Coburn Road monitor, indicating the largest and closest SO 2 source is PPL-Corette.Figure 6 . Major Sources Upwind of the Coburn Road SLAMS

The following Figures 7 and 8, included in show the monitored values at the Coburn Road SLAMS site compared with operating differences of all upwind sources. The figures demonstrate SO 2 concentrations at Coburn Road monitor decreased by nearly 80% when PPL operation.

0 500 1000 1500 2000 2500 3000

2009

231 133 127 2788Annual SO2Emissions (tons/yr) . Major Sources Upwind of the Coburn Road SLAMS

included in the State of Montana’s April 3, 2013 five show the monitored values at the Coburn Road SLAMS site compared with operating differences of all upwind sources. The figures demonstrate a variety of o perating scenarios where the average ambient concentrations at Coburn Road monitor decreased by nearly 80% when PPL

- Corette was not in 2010 2011 218 226 98 80 73 57 2271 2174

14 . Major Sources Upwind of the Coburn Road SLAMS

the State of Montana’s April 3, 2013 five -factor analysis, show the monitored values at the Coburn Road SLAMS site compared with operating differences of all perating scenarios where the average ambient Corette was not in CHS

W. Sugar

Phillips66

PPL

- Corette15 Figure 7. Monitored Hourly Ambient Concentrations at the Coburn Road Monitor for Calendar Year 2010 (Ref.: State of Montana’s April 3, 2013, Five-Facto r Analysis)16 Figure 8. Monitored Hourly Ambient Concentration a t the Coburn Road Monitor for Calendar Year 2011 (Ref.: State of Montana’s April 3, 2013 Five-Factor Analysis)

From Figures 7 and 8 above, we note that monitored exceedances still occurred when Western Sugar was not in operation, and only when PPL-Corette was in operation. Additionally, when both PPLCorette and Western Sugar were off-line and CHS and Phillips66 were on-line, there were no monitored exceedances.

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 spee d, which included periods when exceedances were recorded at Coburn Road monitor. Meteorology data is shown in Tables 9, 10, 11, and 12. These data provide information related to the potential for SO 2 emissions sources located upwind of a violating monitor to contribute to the violation location.

According to the available data from the Billings I nternational Airport, it appears that the exceedanc es shown in Tables 9, 10, 11, and 12 are primarily dri ven by emissions blown from the west-southwest, the predominate wind direction. Exceedances follow the trend as well, occurring mostly when the wind is blowing from the west-southwest. It should be note d that the Billings Airport is located on the oppos ite side of the valley from the Coburn Road Monitor, bu t both are on the northeast side of Billings and located above the valley floor. Additionally, Exxo nMobil, MSCC, and YELP are located northeast of the Coburn Road Monitor and the Airport while PPL, Western Sugar, Phillips66, and CHS facilities are located to the southwest of the monitor. The State of Montana discussed that in 2008 initial catalyst17

testing at ExxonMobil caused the data from that yea r to be unreliable and unrepresentative. However, from Table 9 below, the exceedances and wind direct ion do not correlate with the location of ExxonMobil facility in the northeast. Thus, EPA fi nds that 2008 is a representative year and exceedances were not caused by early catalyst testi ng at ExxonMobil.

Table 9. 2008 Exceedances (from AQS) with Wind Dir ection and Wind Speed Date and Time (Military) Value

(ppb) Wind Direction

(degrees) Wind Speed

(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 10. 2009 Design Values (from AQS) with Wind Direction and Wind Speed

Date and Time (Military) Value

(ppb) Wind Direction

(degrees) Wind Speed

(Meters/s) 9/22 9:00 107 239* 3.0 2/5 2:00 83 240 8.8 9/25 9:00 83 239* 4.1 1/20 5:00 72 238 12 *Poor Quality Assurance Results; Wind Direction fro m MSCC’s April 8, 2013 Five-Factor Analysis

Table 11. 2010 Exceedances (from AQS) with Wind Di rection and Wind Speed Date and Time (Military) Value

(ppb) Wind Direction

(degrees) Wind Speed

(Meters/s) 2/10 4:00 91 202* 7.2 7/8 6:00 111 242** 3.7 7/9 6:00 92 245** 4.2 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 *Poor Quality Assurance Results; Wind direction fro m Brickyard Monitor (Ref.: MSCC’s April 8, 2013 Fiv e-Factor Analysis) **Machine Malfunction; Wind direction from Brickyar d Monitor (Ref.: MSCC’s April 8, 2013 Five-Factor A nalysis)

Table 12. 2011 Exceedances (from AQS) with Wind Di rection and Wind Speed Date and Time (Military) Value

(ppb) Wind Direction

(degrees) Wind Speed

(Meters/s) 9/5 8:00 142 248 14.2 9/11 7:00 113 242 12.7 10/30 85 238.6 12.118

Geography/Topography (mountain ranges or other air basin boundaries)

The dominant topographical feature to influence air flow in the Billings and Laurel areas is the Yellowstone River Valley. The terrain near Billing s and Laurel is upland bench, which is steeply cut by the Yellowstone River and its tributaries. The ben ch lies at an elevation of 4,000 feet while the val ley in Billings is approximately 3,000 feet above sea leve l and Laurel is approximately 3,300 feet above sea level. A constriction in the Yellowstone Valley oc curs 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 wi de at the constriction. Nearby terrain, such as the Sacr ifice Cliff to the southeast of Billings and the Ri mrocks to the north, rises abruptly and is often higher th an the tallest smoke stack. Laurel is located with in 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 so utheast of Laurel rises abruptly and is often highe r than the tallest smoke stack.

The geography/topography of the area has the possib ility to restrict airflow and cause stagnation of a n air mass. However, Tables 9, 10, 11, and 12 above, show that even though the terrain may be a cause o f stagnation of airflow and inversion of the air mass , the wind speed does not stagnate and shows that there is continuous airflow. Additionally, the Sta te of Montana discusses potential daylong stagnatio n events as rare and multi-day events as even rarer. During the winter of 2010-2011, the air shed saw o nly a three-day stagnation episode and only three other individual days when the inversions lasted more th an 24 hours. Outside the winter season, stagnant peri ods that exceed 24 hours are very uncommon. However, inversion or stagnation episodes can occur and this should not be interpreted to signify that the Billings/Laurel area had or will not have any s tagnation occurrences.

Jurisdictional Boundaries

The State of Montana requests, and EPA agrees, that the initial 2010 1-hour SO 2 standard nonattainment area boundary for Yellowstone County should be sign ificantly smaller than the default county boundary. Montana submitted a potential boundary in its April 3, 2013 five-factor analysis, for a nonattainment area based on certain jurisdictional boundaries, wh ich included roads and other permanent features (Sections and Townships).

Conclusion

The air quality monitor in Yellowstone County shows a violation of the 2010 1-hour SO 2 NAAQS, based on 2009-2011 air quality data. EPA is not ye t prepared to conclude that the nearby counties of Musselshell, Rosebud, Treasure, Big Horn, Carbon, S tillwater, and Golden Valley contribute to the recorded violations of Coburn Road SLAMS monitor in Yellowstone County, and thus are not included in the initial nonattainment area but will be furth er addressed in a future final designations action. Based on the consideration of all the relevant and availa ble information, as described above, EPA believes t hat the technical analysis prepared and submitted by th e State of Montana to respond to EPA’s preliminary nonattainment area proposal presents a reasonable a nd technically supported alternative initial nonattainment boundary. The State of Montana’s tec hnical analysis assess the five factors relevant to this monitored violation, including the air quality data, the emission information, the dominate wind19

directions, the topography in the area and the juri sdictional considerations to make their boundary recommendation.

EPA has reviewed the information above and has dete rmined that it is appropriate to initially designat e a portion of Yellowstone County as “nonattainment” fo r the 2010 1-hour SO 2 NAAQS and agrees with the State of Montana’s recommended boundary shown i n Figure 10, and described as:

The proposed NAA originates at the point defined as the southwest corner of Section 11, Township 1S, R ange 26E. From that point the NAA boundary proceeds north alo ng the western section line of Section 11 to the po int of intersection with the midline of Interstate Highway 90. From tha t point the boundary follows the midline of Interst ate Highway 90, across the Yellowstone River, to the point where the highw ay midline intersects the northern boundary of Sect ion 35, Township 1N, Range 26E. From that point the boundary proceeds ea st along the northern section line of Sections 35 a nd 31 to the point where Old US 87/Hardin Road leaves the section line and turns southeast. The boundary follows the midl ine of Old US 87/Hardin Road southeast to the point where the roa d intersects the western boundary of the SE 1⁄4 of th e SE 1⁄4 of Section 31, Township 1N, Range 27E. From that point the boundar y proceeds south along the 1⁄4 section line to the so uthern boundary of Township 1N, then east to the northeast corner of S ection 5, Township 1S, Range 27E. The NAA boundary then proceeds south along the eastern section line of sections 5 and 9 to the southeast corner of Section 9, Townshi p 1S, Range 27E, where it turns west and follows the south section line of Sections 9 and 7, Township 1S, Range 27E; and Sect ions 12 and 11, Township 1S, Range 26E, back to the point of origin

. Areas and sources in Yellowstone County or other co unties in Montana that we are not yet prepared to conclude are contributing to the monitored violatio n or other possible violations are not included in this initial nonattainment area designation. In a subse quent round of designations we will further address such areas and sources and make final designations decisions for areas that are not currently included in the nonattainment area designation addressed in thi s TSD.