UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
 

REGION 8
 

1595 Wynkoop Street 

DENVER, CO 80202-1129 

Phone 800-227-8917 

http://www.epa.govlregion08 

FEB 282007 

Ref: 8P-AR 

James Parker 

PPL Montana - Corette 

P.O. Box 38 

Colstrip, MT 59323 

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

(BART) and Request to Conduct a BART Analysis for BART-Eligible Units at PPL 

Montana - Corette 

Dear Mr. Parker: 

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 ofthe 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 PPL Montana ­

Corette (Corette) was BART eligible, we informed you that Corette 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 ofthe 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 has determined that your facility is subject to BART. 

Accordingly, we are requesting that you submit a BART Analysis for Corette within 90 days of 

this letter, as explained below. 

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

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

be performed, 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 CalpuffBART Modeling 

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

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

http://www.epa.gov/region8/air/mtregionalhaze.html. Where necessary, we made slight 

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

certain site. 
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States (or EPA) have several options for detennining whether a source is subject to 

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

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

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 infonnation 

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

section lILA of the BART Guidelines. 

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

area of 1.03 deciviews, which exceeds the threshold of 0.5 deciviews. Since Corette exceeds the 

0.5 deciview threshold, and thus may reasonably be anticipated to cause or contribute to 

visibility impainnent in one or more Class I areas, EPA Region 8 has concluded that Corette is 

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 Corette at all federal 

Class I areas in the vicinity ofthe plant. More detailed modeling results, including the electronic 

CALPUFFICALMET files, are available on the WRAP website at 

http://pah.cert.ucr.edulaqml308Ibart.shtml. 

Because Corette is subject to BART, EPA Region 8 is requesting that Corette conduct a 

BART engineering analysis on the emission units specified on the enclosed spreadsheet and 

submit the analysis to our office. One of the requirements ofthe RHR is that each regional haze 

implementation plan contain enforceable emission limits for eligible stationary sources based on 

BART. The BART analysis will be used to identify the best system of continuous emissions 

reduction and corresponding emission limits for each visibility impairing pollutant that is emitted 

by the Corette facility. The Clean Air Act and the RHR require that BART be established on a 

case-by-case basis taking into account the available retrofit control options, the costs of 

compliance, the energy and non-air quality impacts of compliance, any pollution control 

equipment in use at the source, the remaining useful life ofthe source, and the degree of 

improvement in visibility which may reasonably be anticipated to result from the use of the 

technology. 

For purposes of the Regional Haze FIP for Montana, EPA Region 8 is intending to follow 

its BART Guidelines from 40 CFR Part 51, Appendix Y. The BART Guidelines are a statement 

ofEPA's thinking on how best to meet the requirements ofBART in the CAA and RHR. Thus, 

in conducting the Corette BART engineering analysis, you will need to follow the five-step 
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BART analysis process identified in Appendix Y, section IV.D, in order to identify an 

appropriate BART emission limit. The five steps are: 

• Identify all available retrofit control technologies 

• Eliminate technically-infeasible options 

• Evaluate the control effectiveness of remaining control technologies 

• Evaluate impacts and document the results 

• Evaluate visibility impacts 

For each of these five steps, the BART Guidelines provide detailed guidance for 

producing an acceptable BART analysis. In addition, your BART analysis should follow other 

EPA guidance and policies related to BART. 

Based on the above analysis, you will then identify what you believe is BART for your 

facility. You will need to provide a justification for adopting the technology and the emission 

limits that you select as the best level of control, including an explanation of how the BART 

factors (costs of compliance, energy impacts, non-air quality environmental impacts, remaining 

useful life of the facility, and visibility improvements) were considered (or weighted) in selecting 

one technically feasible control option over the others. 

Your BART analysis should include proposed emission limits for each BART-eligible 

unit at your facility and for each pollutant subject to BART. For Corette we have identified 

sulfur dioxide, nitrogen oxides, and particulate matter as the pollutants that need to be analyzed. 

Once you submit the BART analysis and related documentation to EPA Region 8, we 

will review the BART analysis and will notify you of our preliminary BART determination. We 

will provide an opportunity for you to respond to our preliminary BART determination before 

making a final determination. Our final determination will be included as part of our Regional 

Haze FIP for Montana, which will be adopted through notice and comment rulemaking. 

In order to meet regulatory schedules and coordinate with other states, EPA Region 8 is 

requesting that you submit your BART analysis to our offices within 90 days from the date of 

this letter. We understand this is acomplicated endeavor, and we are available to answer any 

questions that you may have on the RHR, the BART Guidelines, or the BART analysis. We will 

assist you in any way we can and look forward to working with you. 

If you choose not to perform or are unable to perform an engineering analysis for Corette, 

EPA will perform the BART engineering analysis. If you will not be performing and submitting 

the BART analysis, we ask that you contact us within 30 days from the date of this letter so that 

we may begin the process of developing the analysis. 

Corette may assert a business confidentiality claim covering part or all of the information 

requested by this letter, in the manner described at 40 CFR 2.203(b). If no such claim 
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accompanies the infonnation when it is received by EPA, EPA may make the infonnation 

available to the public without further notice to Corette. Infonnation subject to a business 

confidentiality claim will be disclosed by EPA only to the extent, and by means of the 

procedures, set forth at 40 CFR Part 2, Subpart B. 

Once again, we look forward to working with you. 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 BART analysis, please contact Laurel Dygowski at (303) 312­

6144. 

Sincerely, 

Carol l. C~mpbe"

Stephen S. Tuber 

Assistant Regional Administrator 

Office of Partnerships and Regulatory Assistance 

Enclosure 

*Printed on Recycled Paper 
Summary of Calpuff Modeling Results for PPL Montana J.E. Corette Plant 

Class I Area 

Minimum 

Distance 98th Percentile for each Year 

98th 

3 Year 

Average 

Max 

Delta-dv 

(dv) 

99th 

(dv) 

98th 

(dv) 

Days 

(km) 2001 2002 2003 > 0.5 dv

noab North Absaroka Wilderness 137 0.69 0.83 0.62 0.71 1.76 0.96 0.81 47 

yell Yellowstone NP 145 0.49 0.62 0.41 0.51 1.22 0.69 0.51 24 

wash Washakie Wilderness 171 0.49 0.64 0.37 0.50 0.92 0.65 0.51 25 

ulbe UL Bend 192 1.03 0.69 0.91 0.88 2.40 1.26 0.93 58 

teto Teton Wilderness 199 0.14 0.40 0.12 0.22 0.65 0.33 0.23 3 

gamo Gates of the Mountains WA 276 0.36 0.75 0.23 0.45 1.99 0.66 0.36 14 

redr Red Rock Lakes 277 0.11 0.32 0.11 0.18 0.71 0.32 0.17 4