UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

REGION 8
 

1595 Wynkoop Street
 

DENVER, CO 80202-1129
 

Phone 800-227-8917
 

http://www.epa.gov/region08
 

FEB 282007 

Ref: 8P-AR 

James Parker 

PPL Montana - Colstrip 

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 - Colstrip 

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 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 of that rule. Since it was determined that PPL MontanaColstrip Units 1 & 2 (Colstrip) was BART eligible, we informed you that Colstrip 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 Colstrip within 90 days of 

this letter, as explained below. 

In modeling Colstrip'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 CaipuffBART Modeling 

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

September 2006). An electronic copy of this 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. 
2 

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. 

When dispersion modeling is used, part ofthe process of determining 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 ofthe BART Guidelines. 

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

I area of2.99 deciviews, which exceeds the threshold of 0.5 deciviews. Since Colstrip exceeds 

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

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

subject to BART. 

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

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

Class I areas 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.edu/agm/308/bart.shtml. 

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

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

submit the analysis to our office. One ofthe 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 Colstrip 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 ofthe 

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 

of EPA's thinking on how best to meet the requirements of BART in the CAA and RHR. Thus, 

in conducting the Colstrip BART engineering analysis, you will need to follow the five­
3
 

step 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 ofthese 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 ofthe 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 Colstrip 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 a complicated 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 

Colstrip, 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. 
4 

Colstrip 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 accompanies the information when it is received by EPA, EPA may make the information 

available to the public without further notice to Colstrip. Information 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, 

Stephen S. Tuber 

Assistant Regional Administrator 

Office of Partnerships and Regulatory Assistance 

Enclosure 

*Printed on Recycled Paper 
Summary of Calpuff Modeling Results for PPL Colstrip Units 1 and 2 

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

ulbe UL Bend 200 2.99 2.17 2.42 2.53 5.60 3.20 2.42 160 

noab North Absaroka Wilderness 254 1.15 1.55 1.50 1.40 4.22 2.35 1.40 60 

thro Theodore Roosevelt NP 260 2.49 2.09 2.01 2.20 6.69 3.09 2.34 189 

wash Washakie Wilderness 278 0.70 0.87 0.74 0.77 2.27 1.25 0.86 37 

yell Yellowstone NP 281 0.78 0.72 0.81 0.77 3.50 1.34 0.74 41