::;<1.::;-1**~'U<;** ExxonMobil 

## DEC

- 32007 Refining & Supply Company 700 ExxonMobil Road PO Box 1163 Billings, Montana 59103-1163 406 657 5380Telephone 4066575374 Facsimile 

## EJf(onMobil Refining& 

## Supply

November29,2007

Callie A. Videtich, Director Airand Radiation Program USEPA Region VIII 1595Wynkoop Street Denver, CO 80202-1129 Re: Exxon Mobil Corporation Billings Refinery Response to EPA's "Results of "Subject to Visibility Modeling for BART" Dear Ms. Videtich: This letter serves as Exxon Mobil Corporation Billings Refinery's (ExxonMobil) response to EPA Region 8's letter referenced above, received by ExxonMobil on October 29, 2007. The letter was addressed to Bruce Brodie, Refinery Manager, Exxon Mobil Refining and Supply Company (ExxonMobil) in Billings, MT. The EPA letter addresses dispersion modeling results that were performed forthe BestAvailable RetrofitTechnology (BART) requirements to meetthe Regional Haze Rule (RHR) specified in 40 CFR 51.308(e). ExxonMobil received verbal confirmation to extend the date ofour response to November29,2007. Briefly, EPA's letter suggested that a short-term mass emission limit from the combustion of sour water stripper overhead (SWSOH) in the Fluid Catalytic Cracking Unit Carbon Monoxide Boiler (FCCUCOB) should be established (through the proposed Federal Implementation Plan [see 71 FR 39259, et al.l) in order to create a "synthetic minor" status. Such a designation would, according to the letter, avoid BART. You requested whether such an approach was acceptableto ExxonMobil. ExxonMobil does not agree with this approach for several reasons outlined in Attachment 2 to this letter. However, ExxonMobil has determined that EPA's proposed approach is unnecessary in the base case. We are submitting new modeling results performed by our modeling contractor. The results ofadditional dispersion modeling based on actual emissions from 2001, 2002, and 2003, consistent with the BART Guideline, indicates ExxonMobil is not subject to BART, having a modeled deciview impact below the 0.5 threshold. Those results, by themselves, negate the need forany emission limitation on the FCCUCOB as the model shows visibility impact less than the threshold values contained in the BART protocols. Attachment 1 to this letterexplains this direct resolution to the issue you have raised.We would be pleased to discuss this matter further with you at your convenience. We believe that the attachment is self-explanatory and resolves the concerns raised by your letter. In support of ExxonMobil's conclusions, enclosed are three CD-ROMs with copies of the CALPUFF inputfiles and CALPOSToutputfiles. Sincerely,

# ~/fL/ Ron J. Kuhler Environmental and Safety Section Supervisor

Enclosures (2 Attachments and 3 CDs)

cc: Kevin Golden, EPA Region VIII Laurel Dygowski, EPA Region VIII CERTIFIED MAIL

## ATTACHMENT 1 Response to 

### EPA Region 

### 8 Letter Regarding "Subjectto"BARTandEmission Limits

November29, 2007


### Background
In general terms, a facility (or a portion ofa facility) is BART-eligible if it meets certain emissions and construction or re-construction criteria. 1 The facility (or portion of a facility) is "subjectto"2 a BART analysis ifthe constructed or reconstructed units "cause or contribute,,3 to visibility impairment at any of the 156 "mandatory Class I Federal 4 Areas

.. . On September27, 2006, EPA sent a letterto ExxonMobil seeking to certifythe emitting units and emissions data that would be used in the modeling. In a letter dated October 17,2006,we provided a listofemitting unitsthatwe believe are "BART-eligible"sources in accordance with Section II of the "Guideline for BART Determinations Under the Regional Haze Rule" (herein referred to as the "Guideline") found in 40 CFR 51, AppendixY.
The October 17, 2006 response departed slightly from the Guideline and from the Montana "Modeling Protocol For Federal Mandatory Class I Areas"s. Those two documents require that the emission rate used in the dispersion modeling be the "24_ hour average actual emission rate from the highest emitting day ofthe meteorological period, unlessthis rate reflects periods ofstart-up, shutdown, ormalfunction."6 

### Issue Although the Regional Haze Rules (RHRf and Guideline suggest the use of "actual" emission rates, ExxonMobil found it inconsistent to use "actuals" data in the face of requirements that have since prohibited or will prohibit the emission rates observed during the modeling-year periods (years: 2001, 2002 and 2003). ExxonMobil believed

1 Furtherdescription is available in 40 CFR51, AppendixY, Section II.
2As described in 40 CFR 51, AppendixY, Section 111.1. 3 Ibid.
4 Defined in 40 CFR301. 5 http://www.epa.gov/Region8/air/pdf/MontanaBARTProtocoI0906.pdf. 640CFR51, Appendix Y, Section 111.A.3. 740CFR51.308.that the new potential emission rates that would be imposed by United States, etal. v. ExxonMobil Corporation, etal. (Consent Decree) would be a more realistic estimate of emissions than the 2001-2003 actual emissions. The result would be a higherquality of modelingwith more realistic results reflecting the Consent Decree requirements. As a result, ExxonMobil requested and EPA agreed to model the lower emission rate constrained by the Consent Decree.8 The modeling results demonstrated ExxonMobil's impact on all Class I areas to be less than the 98th percentile threshold value (0.5 deciviews). Since the values are less than 0.5 deciviews, EPA concludes that ExxonMobil must not be "subjectto" further BART review.
It appears from the EPA's letter, however, that EPA has made an assumption that the 0.5 deciview modeling results were achieved only because a lower emission rate constrained by the Consent Decree was used in the model. Expressed another way, EPA seems to have assumed that ExxonMobil would be "subject to" BART had the higher "actual" emission rates been used in the model (as outlined by the modeling protocol EPA used in this exercise9). As a result of this assumption, EPA then argues that it is necessaryto establish a "synthetic minor" emission limitto avoid BART. 1O
We have tested this assumption using refined estimates of past actual emissions with new modeling. This new dispersion modeling, discussed below, has demonstrated that regardless ofthe emission rates used in the model, the conclusion remains the same. The results indicate modeled values below 0.5 deciviews regardless ofConsent Decree or"actual" emission rates. 

### Resolution
The dispersion modeling was rerun using the "actual" emission rates as outlined in the Montana modeling protocol.11 If the results of dispersion modeling indicate deciview impacts less than 0.5, a facility is not "subject to" BART since it would fail to meet the 98th percentile threshold requirements found in the modeling protocols. 12 This methodology is identical to emission rates and results of all of the BART-eligible sources in Montana and Region 8.
For reference, Table 1 provides a summary ofthe emission rates at issue. The table showsthe emission rates thatwere used in previous (EPA) modeling demonstrations as well as the emission rates used forthis (ExxonMobil) analysis.

8 See 3'd paragraph ofOctober29,2007 letterfrom EPAto ExxonMobil.
9 http://www.epa.gov/Region8/air/pdf/MontanaBARTProtocoI0906.pdf.
10 See last paragraph ofpage 2 ofOctober29, 2006 letterfrom EPAto ExxonMobil.
11 EPA agreed that it would usethe Montana modeling protocol as its methodologyforconducting the BART modeling "subjectto" analysis. This is furtherconfirmed via the modeling results presented bythe UniversityofCalifornia Riverside (on behalfof EPA) and the accompanying summarydocument:**~2ttP:/**/pah.cert.ucr.edu/aqm/308/bartlcalpuff/summary/MT _summary

_v5_May30_2007.doc. http://pah.cert.ucr.edu/aqm/308/bartIWRAP_RMC_BART_Protocol_Aug15_2006.pdfand http://www.epa.gov/Region8/air/pdf/MontanaBARTProtocoI0906.pdf.Bison Engineering, Inc., on behalfof ExxonMobil, has revisited the dispersion modeling. The model input files used by EPA (via University of California Riverside) were retrieved. The emission rates in the original modeling were replaced with the 2001, 2002,2003 "actual" emission rate13 forthe facility (see Table 1above). The model was then re-run using the "actual" emission rates, while holding constant all other inputdata. The results ofthe modeling are summarized in Table 2. The table demonstrates that even with the use ofthese higher emission rates, the results at the 98th percentile are well belowthe 0.5threshold value. 

### Conclusion
Given that the model has now been executed using actual emiSSion rates that are consistent with all other BART-eligible sources throughoutthe region, we conclude that ExxonMobil is not "subject to" a BART analysis since the modeling results are consistent regardless of the emission rate inputs. Also, consistent with other U.S. facilities, there is nojustification orregulatory basis fora "synthetic minor" limit.

13 Emission rates arecontained in the02/03/06 letterfrom ExxonMobil to Montana Departmentof Environmental Quality.Table 1: SummaryofEmission Rates

Emission Rates Used Submitted on October 17, 2006to EPA1 Actual Maximum Emissions During 2001, 2002, &2003 (on dateshown)2 NOx S02 PM 10 8/16/01 2/27/01 10/5/02 Emission Unit tpy (Ibs/dav) tpy (Ibs/day) tpy (Ibs/day) NOx Ibs/dav S02 Ibs/day PM 10 Ibs/day Fluid Cat Cracking CO Boiler 113 (619) 46 (252) 6 (32.9) 1,780 10,291 379 Fluid Coker CO Boiler 184 (1008) 14 (76.7) 5 (27.4) 1,030 7 1 Crude/Vacuum/F-2 236 (1293) 31 (170) 10 (54.8) 1,076 11 37 HF #2/3

- F-3X 25 (137) 3 (16.4) 1 (5.5) 72 2 4 HF #2/3

- F-5 20 (110) 3 (16.4) 1 (5.5) 103 4 2 Hydrogen Plant/F-551 76 (416) 12 (65.8) 5 (27.4) 403 5 17 Hydrocracker/F651 25 (137) 3 (16.4) 1 (5.5) 146 2 6 Powerformer/F-700 251 (1375) 10 (54.8) 4 (21.9) 845 3 12 Flare 23 (126) 219 (1200) 7 (38.4) 19 0.1 4 Tank Heater/F-10 2 (11.0) 0 (0) 0 (0) 2 0.01 0.1 Boiler House/B-8 145 (795) 13 (71.2) 5 (27.4) 0 0 25 Notes: 1. Emission rates submitted to EPAon October 17, 2006, were provided in tons/year. 2. Emission rates submitted to MDEQ on February3, 2006, were provided in Ibs/day.Table2: CALPUFF Modeling Results

Source

## =ExxonMobii Billings Refinery 99th 98th Percentile by Minimum Max 98th 98th3-yr Class IArea1 vear(dv Distance Delta-dv Delta-dv Delta-dv Average

(km) # Days (dv) noab >0.5dv 2002 2003 (dv) (dv) 2001 (dv) NorthAbsarokaWilderness 0.27 0.19 0.22 yell 143 0.24 0.19 0.58 0.32 2 Yellowstone NP 0.17 0.14 0.15 wash 0.14 150 0.43 0.19 0.15 0 WashakieWilderness 0.16 ulbe 176 0.14 0.22 0.12 0.32 0.22 0.16 0 0.31 teto UL Bend 0.31 187 0.38 0.23 0.10 0.44 0.30 10 0.07 gamo Teton Wilderness 0.10 0.05 0.17 0.06 205 0.11 0.08 0 Gates ofthe MountainsWA 0.07 0.13 redr 0.11 0.22 277 0.74 0.22 0.14 2 0.05 Notes: Red Rock Lakes 0.03 0.09 0.04 282 0.24 0.05 0 0.09
1. Class Iareas arethose onlywithin 300 km ofthe Billings Refinery.

## ATTACHMENT2 Response to EPA Region 8 

### Letter Regarding "Subjectto"BARTandEmission Limits

November29,2007 

### Objectionsto EPA Proposal
The analysis in Attachment 1 responds to EPA's request and negates a need for a "synthetic minor" emission rate. This resolution notwithstanding, ExxonMobil would like to take this opportunity to outline a few of its additional objections regarding EPA's proposal. If you find it necessary, we would be pleased to discuss these concerns in more detail in thefuture.
No RegulatoryBasis for USynthetic MinorStatus"underRHR
A BART-eligible source would be required to conduct a BART control technology analysis only if it is determined to "cause orcontribute" to visibility impairment at one of the 156 Federal Class I areas. The Guideline provides a methodology regarding how that determination is to be made. In summary, the BART-eligible source is subject to BART if dispersion modeling demonstrates that "actual" emission rates in the model yield an impact greaterthan 0.5 deciviews.14 The key point is thatthe "actual" emission rate, not the potential to emit (PTE) rate, is the defining model input value that determines "cause or contribute." The "actual" rate, therefore, is not a regulatoryimposed "not-to-exceed" limit. Thetriggering event is based on historical past actuals.
ExxonMobil originally proposed the use of a PTE rate for the BART modeling as a conservative estimate of emissions. EPA agreed that this approach was a reasonable one. This conservative approach, however, does notjustify the imposition of a future limit on PTE based on a concern that ExxonMobil might increase emissions in the future. A source determined not to be subject to BART based on actual emissions would not be required to take a limit underthe BART applicability requirements. EPA cannot create and apply a new requirementwithouta rulemaking.
ExxonMobil also has some elemental concerns with EPA's use of this term in the context of "subject to" BART analyses. While the term has a clear meaning in the permitting program, it has no meaning in the Regional Haze Rule (RHR). The term synthetic minor really refers to limiting one's emissions in orderto avoid an applicability determination.That is notthe case here.

14 It is understood thatthis is a guideline and that details in AppendixY provide various options. However, EPA hastaken a position thatthe 0.5 deciviewvalue is appropriate in Montanaforthis and other BARTeligiblefacilities.For BART, there are (in simplistic terms) two tests that would cause a facility to be "subject to,,15 a BART review. The first is that the facility must meet an emissions threshold, date requirement and source category. [This first test is usually known as a test for "BART-eligible."] The second is that the facility (or portion of a facility) must "cause or contribute" to a visibility impairment. [This test is usually referred to as a "subject to" BART analysis.] For ExxonMobil's case, it is clearthat the refinery meets the BART-eligible firsttest. It is onlythe second "subjectto" testthat could have been in question. For synthetic minorpurposes, as thatterm is widely used in the air pollution field, it only has meaning for the first test. One could become a "synthetic minor" source within the meaning of BART if and only ifthe facility were to agree to an emission rate less than 250tons peryear (the BARTthreshold for "BART-eligible" sources). Sincethat is clearly notthe case here, the term has no meaning. Start-up, Shutdown andMalfunction Emission Limits
EPA proposed that an emission limit be established that "would not be subject to exceptions during startup, showdown, and malfunction periods.,,16 This is wholly inconsistentwith the BARTguidelines.
As noted earlier, the issue for ExxonMobil is one of "subject to" BART, rather than BART-eligible. The instructions provided in the Guideline for conducting the "subjectto" analysis states that those emission rates do not include periods of startup, shutdown and malfunctions.17

EPA has, on the other hand, proposed a limit that includes those periods of startup, shutdown and malfunction emissions. This is at direct odds with the instructions in the Guideline. The EPA letter states that this limit (including startup shutdown and malfunctions) is necessary for enforcement purposes for synthetic minor emissions. This is notthe case. The issue here does not relate to limiting emissions for regulatory applicability purposes (BART-eligible). The issue is whether the facility, excluding startup, shutdown and malfunctions, causes or contributes to visibility impairment. The Guideline clearly instructs the states (and EPA) to usethis methodology. To require thatthese emissions be included in the "subjectto" analysis is inconsistentwith the Guideline instructions.
As a general matter, ExxonMobil objects to EPA's proposal to apply limits during startup, shutdown, and malfunction, as set forth in EPA's proposed Federal

15Theterm "subjectto" is in referenceto the Subject Line in the 10/29/97 letteras well as howthatterm is discussed, and found in quotes, in 40 CFR51, AppendixY, Section III. 16 Page2, last paragraph, EPA 10/29/07 letterto ExxonMobil. 1740 CFR51, AppendixY, Section III.A.3.Implementation Plan (FIP) for S02 in the Laurel/Billings area. ExxonMobil hereby incorporates its November2,2006 commentson the proposed FIP by reference. CEMandFlowMonitor
Because the above analysis confirms ExxonMobil is not "subjectto" BART, the need for a CEMS is no longer applicable. As EPA correctly noted, underthe Consent Decree, either a CEM or alternative monitoring plan is required for the SWSOH gas consistent with the NSPS

### J requirements.