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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8 1595Wynkoop Street DENVER, CO 80202-1129 Phone 800-227-8917 http://www.epa.gov/region08 

## FEB 2 82007 Ref: 8P-AR
Joe Scheeler Ash Grove Cement Company 100 Highway 518 Clancy, MT 59634-9701
Re: Results of"Subjectto" Visibility Modeling for BestAvailable Retrofit Technology (BART) and Request to Conduct a BART Analysis for BART-Eligible Units at Ash Grove Cement Company
Dear Mr. Scheeler:
On June 19,2006, EPA received a letter from the Montana Department ofEnvironmental 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 youthat we would be conducting modeling to determine which sources in Montanaare "subjectto" 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 Ash Grove Cement Company (Ash Grove) was BART eligible, we informed youthat Ash Grove would be included in the modeling and asked youto 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 BARTAnalysis for Ash Grove within 90 days ofthis letter, as explained below.
In modeling Ash Grove'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 inthe final RHR and EPA's "Guidelines for Best Available Retrofit TechnologyDeterminations" (BART Guidelines). See 70 FR 39104, July 6, 2005. The BART Guidelines canbe found at Appendix Y to 40 CFR Part 51. EPA Region 8'svisibility modeling also generally followed the protocol outlined in the document "Draft CaipuffBARTModeling Protocol for Federal Mandatory Class 1Areas" (Montana Department ofEnvironmental Quality, September 2006). 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 subject to BART, including the use ofdispersion modeling to determine whether an individual source may be reasonably anticipatedto cause or contribute to any visibility impairment in any Class I area. When dispersion modeling is used, part oftheprocess ofdetermining whether a source is subject to BART is 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 predicts that a source will have visibility impacts of0.5 deciviews or more at a Class I area onthe 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 sectionlILA ofthe BART Guidelines.
ForAsh Grove, the modeling results show a maximum 98th percentile impact within a Class I area of2.70 deciviews, which exceeds the threshold of0.5 deciviews. Since Ash Grove exceeds the 0.5 deciview threshold, and thus may reasonably be anticipated to cause orcontribute to visibility impairment in one ormore Class I areas, EPA Region 8has concludedthat Ash Grove is subjectto BART.
A summary ofthe BARTmodeling results is enclosed. The enclosure provides a summary ofthe 98th percentile predictions for the three years modeled for Ash Grove at all federal Class I areas in the vicinity ofthe plant. More detailed modeling results, including the electronic CALPUFFICALMET files, are available onthe WRAP website at http://pah.cert.ucr.edu/agrn/308/bart.shtml.
Because Ash Grove is subjectto BART, EPA Region 8 is requesting that Ash Grove conduct a BARTengineering analysis on the emissionunits specified onthe enclosed spreadsheet and submitthe analysis to ouroffice. One oftherequirements ofthe RHR is that each regional haze implementationplancontainenforceable emission limits for eligible stationary sources based on BART. The BARTanalysis will be used to identify the best system ofcontinuous emissions reduction and corresponding emission limits for each visibility impairing pollutantthat is emittedby the Ash Grove facility. The CleanAir Act and the RHR require that BARTbe established on a case-by-case basis taking into account the available retrofit control options, the costs ofcompliance, 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 ofimprovement in visibility which may reasonably be anticipated to result from the use ofthe technology.
Forpurposes oftheRegional Haze FIP for Montana, EPA Region 8 is intending to follow its BARTGuidelines from 40 CFRPart 51, Appendix Y. The BART Guidelines are a statement ofEPA's thinking onhow best to meet the requirements ofBARTin the CAA and RHR. Thus, in conducting the Ash Grove BARTengineering analysis, you will need to follow the five-step3 BART analysisprocess 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
Foreach ofthese five steps, the BART Guidelines provide detailed guidance for producing an acceptable BART analysis. In addition, yourBART 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 ajustification for 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 eachpollutant subject to BART. ForAsh Grove Cement we have identified sulfur dioxide, nitrogen oxides, and particulate matter as the pollutants that needto be analyzed.
Once you submitthe 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 determinationbefore making a final determination. Ourfinal determination will be included as part ofour Regional 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 submityour 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 onthe RHR, the BART Guidelines, orthe BARTanalysis. We will assist you in any way we can and look fornard to working with you.
Ifyou choose not to performor are unable to perform an engineering analysis forAsh Grove, EPA will perform the BARTengineering analysis. Ifyou will notbe performing and submitting the BART analysis, we ask that you contact us within 30 days from the date ofthis letter so that we may beginthe process ofdeveloping the analysis.
Ash Grove may assert a business confidentiality claim covering part or all ofthe information requested by this letter, in the manner described at 40 CFR2.203(b). Ifno such4 claim accompanies the information when it is received by EPA, EPA may make the information available to the public without further notice to Ash Grove. Information subjectto a business confidentiality claim will be disclosed by EPA only to the extent, and by means 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. For questions related to development ofthe BART analysis, please contact Laurel Dygowski at (303) 312­ 6144. Sincerely,**~~rol** 

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



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