UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
 

REGION 8
 

1595 Wynkoop Street 

DENVER, CO 80202-1129 

Phone 800-227-8917 

http://www.epa.gov/region08 

JUN 222007 

Ref: 8P-AR 

Mr. Larry Zink 

Montana Sulphur & Chemical Company 

P.O. Box 31118 

Billings, MT 59107 

Re:	 Results of "Subject to" Visibility Modeling for Best Available Retrofit Technology 

(BART) 

Dear Mr. Zink: 

On June 19, 2006, EPA received a letter from the Montana Department of Environmental 

Quality that stated it was withdrawing its efforts to meet the requirements of the Regional Haze 

Rule (RHR) specified at 40 CFR 51.308. On September 27, 2006, EPA Region 8 sent a letter 

notifying you that we would be conducting modeling to determine which sources in Montana are 

"subject to" the Best Available Retrofit Technology (BART) requirements in the RHR as part of 

our effort to address the requirements ofthat rule. Since it was determined that Montana Sulphur 

& Chemical Company (MSCC) was BART eligible, we informed you that MSCC would be 

included in the modeling and asked you to certify the data that would be used for this modeling. 

EPA Region 8, with the assistance of the Western Regional Air Partnership (WRAP), has 

now completed the visibility modeling for determining those Montana sources subject to BART. 

Based on the modeling, EPA Region 8 believes that your facility is not subject to BART. 

In modeling MSCC's visibility impacts, EPA Region 8 followed the approach for 

detem1ining if a source is subject to BART, including the specifics on how the modeling should 

be perfom1ed, set out in the final RHR and EPA's "Guidelines for Best Available Retrofit 

Technology Determinations" (BART Guidelines). See 70 FR 39104, July 6, 2005. The BART 

Guidelines can be found at Appendix Y to 40 CFR Part 51. EPA Region 8's visibility modeling 

also generally followed the protocol outlined in the document "Draft CaipuffBART Modeling 

Protocol for Federal Mandatory Class 1 Areas" (Montana Department ofEnvironmental Quality, 

September 2006). An electronic copy of this protocol is located on EPA Region 8's website at 

http://www.epa.gov/region8/air/mtre£!ionalhaze.html. Where necessary, we made slight 

variations to the protocol, such as instances where meteorological data was not available for a 

certain site. 

States (or EPA) have several options for determining whether a source is subject to 

BART, including the use of dispersion modeling to determine whether an individual source may 

be reasonably anticipated to cause or contribute to any visibility impairment in any Class I area. 
2
 

When dispersion modeling is used, part of the process of detennining whether a source is subject 

to BART is the selection of a deciview threshold against which to measure the visibility impact 

of a source. For its analysis of Montana sources, EPA Region 8 has established a threshold of 

0.5 deciviews as the appropriate threshold based on the number and distribution of sources 

impacting Class I areas in and around Montana. If dispersion modeling predicts that a source 

will have visibility impacts of 0.5 deciviews or more at a Class I area on the 98th percentile of 

values, EPA Region 8 considers that source to be subject to BART. Further information 

regarding this approach to determining whether a source is subject to BART can be found in 

section lILA of the BART Guidelines. 

For MSCC, the modeling results show a maximum 98th percentile impact within a Class I 

area of .30 deciviews, which does not exceed the threshold of 0.5 deciviews. Since MSCC does 

not exceed the 0.5 deciview threshold, EPA Region 8 believes that MSCC is not subject to 

BART. 

A summary of the BART modeling results is enclosed. The enclosure provides a 

summary ofthe 98th percentile predictions for the three years modeled for MSCC at all federal 

Class I a~eas in the vicinity of the plant. More detailed modeling results, including the electronic 

CALPUFF/CALMET files, are available on the WRAP website at 

http://pah.cert.ucr.edulaqrnl308Ibart.shtml. 

While the modeling results indicate that MSCC is not subject to the BART requirements 

of the RHR, it is possible that emission controls at MSCC will be needed in order to meet the 

requirements for reasonable progress and the long-tenn strategy (see 40 CFR 51.308(d)( 1) and 40 

CFR 51.308(d)(3)). In order to address reasonable progress and the long-term strategy 

requirements, EPA Region 8 plans on analyzing contributions from BART sources, point sources 

not subject to BART, area sources, and fire. 

We appreciate your cooperation in providing us with the information necessary to 

conduct this analysis. If you have any questions regarding the modeling results, please contact 

Kevin Golden of my staff at (303) 312-6442. For questions related to development of the 

regional haze Federal Implementation Plan, please contact Laurel Dygowski at (303) 312-6144. 

Sincerely, 

Stephen S. Tuber 

Assistant Regional Administrator 

Office of Partnerships and Regulatory Assistance 

Enclosure 

@Printed on Recycled Paper 
I Source = Montana Sulfur: SOx = 3,259 TPY; NOx = 13 TPY 

Minimum Max 991n 981n 98th 

Class I Area Distance Delta-dv Delta-dv Delta-dv # Days 98th Percentile by Year 3-Year 

(km) (dv) (dv) (dv) > 0.5 dv 2001 2002 2003 Average I 

noab I North Absaroka Wilderness 143 0.51 0.29 0.20 1 0.19 0.22 0.20 0.21 

yell Yellowstone NP 151 0.34 0.20 0.16 0 0.14 0.17 0.15 0.15 

wash Washakie Wilderness 176 0.32 0.18 0.13 0 0.13 0.16 0.10 0.13 

ulbe UL Bend 187 0.75 0.37 0.28 6 0.30 0.23 0.30 0.28 

teto Teton Wilderness 205 0.18 0.09 0.07 0 0.05 0.08 0.06 0.06 

gamo I Gates of the Mountains WA 278 0.69 0.20 0.12 1 0.12 0.19 0.07 0.13 

redr Red Rock Lakes 282 0.24 0.09 0.05 0 0.04 0.09 0.04 0.06