UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8 1595Wynkoop 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"Subjectto" 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: OnJune 19, 2006, EPA received a letter from the MontanaDepartment ofEnvironmental Quality that stated it was withdrawing its efforts to meetthe 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 wouldbe conducting modeling to determine which sources in Montana are "subjectto" the Best Available Retrofit Technology (BART) requirements inthe RHR as part of our effortto address the requirements ofthat rule. Since it was determined that PPL MontanaColstrip Units 1& 2 (Colstrip) was BART eligible, we informed you that Colstrip would be included inthe modeling and asked youto certify the datathat wouldbe used for this modeling.
EPA Region 8, withthe assistance ofthe Western Regional AirPartnership (WRAP), has now completedthe visibility modeling for determining those Montana sources subject to BART. Based onthe modeling, EPA Region 8 has determined that your facility is subjectto 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 ifa source is subject to BART, including the specifics onhowthe 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 Yto 40 CFRPart 51. EPA Region 8's visibility modeling also generally followed the protocol outlined in the document "Draft CaipuffBARTModeling Protocol for Federal Mandatory Class 1Areas" (MontanaDepartment ofEnvironmental Quality, September2006). An electronic copy ofthis protocol is located onEPA 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 subjectto BART, including the use ofdispersion modeling to determine whether an individual source may be reasonably anticipated to cause orcontribute to any visibility impairment in any Class I area. When dispersion modeling is used, part ofthe process ofdetermining whether a source is subject to BART is the selection ofa deciview threshold against which to measure the visibility impact ofa source. Forits analysis ofMontana sources, EPA Region 8has established athreshold of 0.5 deciviews as the appropriate thresholdbased onthe number and distribution ofsources impacting Class I areas in and around Montana. Ifdispersion modelingpredicts that a source will have visibility impacts of0.5 deciviews or more at a Class I area on the 98th percentile of values, EPA Region 8 considers that source to be subjectto BART. Further information regarding this approach to determining whether a source is subjectto BART canbe 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 of0.5 deciviews. Since Colstrip exceeds the 0.5 deciview threshold, and thus may reasonably be anticipated to cause or contribute to visibility impairment in one ormore ClassI areas, EPA Region 8has concludedthat Colstrip is subjectto 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 ofthe plant. More detailed modeling results, includingthe electronic CALPUFF/CALMET files, are available onthe WRAP website at http://pah.cert.ucr.edu/agm/308/bart.shtml.
Because Colstrip is subjectto BART, EPA Region 8 is requesting that Colstrip conduct a BART engineering analysis onthe emission units specified on the enclosed spreadsheet and submitthe analysis to our office. One oftherequirements 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 ofcontinuous emissions reduction and corresponding emission limits for each visibility impairing pollutantthat is emitted by the Colstrip facility. The CleanAirAct and the RHRrequire that BARTbe 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 ofcompliance, any pollutioncontrol 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 ofthe Regional Haze FIP for Montana, EPA Region 8 is intending to follow its BART Guidelines from 40 CFRPart 51, Appendix Y. The BART Guidelines are a statement ofEPA's thinking on how bestto meetthe requirements ofBART in the CAA and RHR. Thus, in conducting the Colstrip BART engineering analysis, you will need to follow the five­3 step BART analysis process identified in Appendix Y, section IV.D, in orderto identify an appropriate BART emission limit. The five steps are:

• Identify all available retrofit control technologies • Eliminate technically-infeasible options • Evaluate the control effectiveness ofremaining 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 onthe above analysis, you will then identify what you believe is BART for your facility. You will need to provide ajustificationfor adopting the technology and the emission limits that you select as the best level ofcontrol, including anexplanation ofhow the BART factors (costs ofcompliance, 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 overthe 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 documentationto EPA Region 8, we will review the BART analysis and will notify you ofourpreliminary BART determination. We will provide an opportunity for youto respond to ourpreliminary BART determination before making a final determination. Our final determination will be,included as part ofourRegional Haze FIP for Montana, which will be adopted through notice and comment rulemaking.
In orderto meet regulatory schedules and coordinate with other states, EPA Region 8 is requesting that you submit your BART analysis to ouroffices 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 youmay have onthe RHR, the BART Guidelines, orthe BART analysis. We will assist you in any way we can and look forward to working with you. Ifyou choose notto perform or are unable to perform an engineering analysis for Colstrip, EPA will perform the BART engineering analysis. Ifyou will not be performing and submitting the BART analysis, we ask that you contact us within 30 days from the date ofthis letter so that we may begin the process ofdeveloping the analysis.4 Colstrip may assert abusiness confidentiality claim covering part or all ofthe informationrequested by this letter, in the manner described at 40 CFR 2.203(b). Ifno 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 bymeans ofthe procedures, set forth at 40 CFRPart 2, Subpart B.
Once again, we look forward to working with you. Ifyou have any questions regarding the modeling results, please contact Kevin Golden ofmy staffat (303) 312-6442. Forquestions related to development ofthe BART analysis, please contact Laurel Dygowski at (303) 312­ 6144. Sincerely,

Stephen S. Tuber Assistant Regional Administrator Office ofPartnerships and Regulatory Assistance Enclosure



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Printed on Recycled PaperSummaryofCalpuffModeling 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 > 0.5 dv (km) 2001 2002 2003 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