UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8 1595Wynkoop 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: OnJune 19, 2006, EPA received a letterfrom the Montana Department ofEnvironmental Qualitythat stated it was withdrawing its efforts to meet the requirements ofthe Regional Haze Rule (RHR) specified at 40 CFR51.308. OnSeptember 27, 2006, EPA Region 8 sent a letter notifying you thatwe would be conducting modeling to determine which sources in Montana are "subjectto" the BestAvailable Retrofit Technology (BART) requirements in the RHRas part of our effort to address the requirements ofthat rule. Since it was determined thatPPL 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 completedthe visibility modeling for determining those Montana sources subjectto BART. Based onthe modeling, EPA Region 8 has determined that your facility is subjectto BART. Accordingly, we are requestingthat 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 ifa source is subjectto BART, including the specifics on how the modeling should be performed, set out in the final RHR and EPA's "Guidelines for BestAvailable Retrofit Technology Determinations" (BART Guidelines). See 70 FR 39104, July 6, 2005. The BART Guidelines can be found at Appendix Y to 40 CFRPart 51. EPA Region 8's visibility modeling also generally followed the protocol outlined in the document "Draft CalpuffBARTModeling Protocol for Federal Mandatory Class 1Areas" (Montana Department ofEnvironmental Quality, September 2006). An electronic copy ofthisprotocol 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 detennining whether a source is subject to BART, including the use ofdispersion modeling to detennine whether an individual source may be reasonably anticipated to cause orcontribute to any visibility impainnent in any Class I area. When dispersion modeling is used, part ofthe process ofdetennining whether a source is subject to BARTis the selection ofa deciview threshold against which to measure the visibility impact ofa source. For its analysis ofMontana sources, EPA Region 8 has established a threshold of 0.5 deciviews as the appropriate threshold based onthe number and distribution ofsources impacting Class I areas in and around Montana. Ifdispersion modeling predictsthat a source will have visibility impacts of0.5 deciviews ormore at a Class I area onthe 98th percentile of values, EPA Region 8 considers that source to be subjectto BART. Further infonnation regarding this approach to detennining whether a source is subjectto BART canbe found in section lILA ofthe 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 of0.5 deciviews. Since Corette exceeds the 0.5 deciview threshold, andthus may reasonably be anticipated to cause orcontributeto visibility impainnent in one ormore Class I areas, EPA Region 8 has concludedthat Corette is subjectto BART. A summary ofthe BART modelingresults 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 CALPUFFICALMETfiles, are available onthe WRAP website at http://pah.cert.ucr.edulaqml308Ibart.shtml. Because Corette is subjectto BART, EPA Region 8 is requesting that Corette conduct a BARTengineering analysis onthe emissionunits specified onthe enclosed spreadsheet and submitthe 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 BARTanalysis will be used to identify the best system ofcontinuousemissions reduction and corresponding emission limits for each visibility impairing pollutantthat is emitted by the Corette facility. The Clean Air Act andthe 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 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 ofthe 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-step3 BART analysis process identified in Appendix Y, section IV.D, inorderto identify an appropriate BART emission limit. The five steps are:

• Identify all available retrofit control technologies • Eliminate technically-infeasible options • Evaluatethe control effectiveness ofremaining control technologies • Evaluate impacts and document the results • Evaluate visibility impacts Foreach 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 BARTfor your facility. You will need to provide ajustificationfor adopting the technology and the emission limits that you select as the best level ofcontrol, including an explanation ofhowthe 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 optionoverthe others. Your BART analysis should include proposed emission limits for each BART-eligible unit at your facility and for each pollutant subject to BART. ForCorette we have identified sulfur dioxide, nitrogen oxides, and particulate matter as the pollutants that need to be analyzed. Once you submitthe BART analysis and related documentation to EPARegion 8, we will review the BART analysis and will notify you ofourpreliminary BARTdetermination. We will provide an opportunity for you to 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 meetregulatory schedules and coordinate with other states, EPARegion 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 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 not to perform or are unable to perform an engineering analysis for Corette, EPA will performthe 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. Corette may assert a business confidentiality claim covering part or all ofthe information requested by this letter, inthe manner described at 40 CFR 2.203(b). Ifno such claim4 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 onlyto the extent, and by means ofthe procedures, set forth at 40 CFRPart 2, Subpart B. Once again, we look forward to working withyou. Ifyouhave 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, 

### Carol 

## l.**C~mpbe"** Stephen S. Tuber Assistant Regional Administrator Office ofPartnerships and Regulatory Assistance Enclosure



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Printed on Recycled PaperSummary ofCalpuffModelingResults 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 > 0.5 dv (km) 2001 2002 2003 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 ofthe 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