UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8 1595 Wynkoop Street DENVER, CO 80202-1129 Phone 800-227-8917 http://VNN1.epa.gov/region08



## JAN 2 82008 Ref: 8P-AR

James Parker Manager

- Compliance Services PPL Montana

- Colstrip P.O. Box 38 Colstrip, MT59323

Re: BestAvailableRetrofit Technology (BART) Assessment Colstrip GeneratingStation

Dear Mr. Parker:

On February 28, 2007, EPA Region 8 sent a letterto PPL Montana

- Colstrip (PPL) that providedthe results ofour "subjectto" modeling for Best Available Retrofit Technology (BART) and**requ~sted** that Colstrip perform a BARTanalysis for Units 1&2 and submit it to EPA Region 8. On August 8, 2007, Colstrip submitted a BART analysis to EPA that was performed by TRC. We would like to thank you for submitting the BART analysis and recognizethe effortthat has gone into developing this document.

We have completed our initial review oftheAugust 8,2007 submittal and have determined thatthere is additional information and analysis needed from Colstrip in order for us to complete ourreview. Following are EPA Region 8's comments on the analysis. In addition,

we are attaching a copy ofcomments on the BART analysis for Colstrip Units 1&2 submittedto EPA on November 5, 2007 from the National Park Service

.. Visibility Improvement and Impacts
Throughoutyour analysis, you state thatthe amount ofvisibility improvementresulting from a reduction in emissions, based onyour currentBART analysis, would not be discernible and therefore additional controls are notjustified. The visibility improvement for S02, NOx, and PM in your analysis are all below 1.0 deciviews, and this is used as a reason not to implement

more stringent control measures. EPA disagrees with your assertion. EPA states in the preamble to its BART Guidelines that, "Eventhough the visibility improvement from an individual source may notbe perceptible, it should still be considered in setting BARTbecause the contributionto haze may be significantrelative to other source contributions in the Class I areas." (see 70 FR 39129, July 6, 2005). Visibility modeling showsthat for Class I areas in Montana, and in particularU.L. Bend National Wildlife Refuge, Colstrip Units 1&2 have the largest impact of any single stationary source in Montana.Failing to consider less-than-perceptible contributions to visibility impainnentwould

.ignore the Clean Air Act's (CAA) intentto have BARTrequirements apply to sources that

contribute to, as well as cause, such impainnent (see 70 FR 39129, July 5,2006). The BART Guidelines indicate that for purposes ofdetennining which sources are subjectto BART, "A single source that is responsible for a 1.0 deciview change or more should be consideredto "cause" visibility impainnent; a source that causes less than a 1.0 deciview change may still contribute to visibility impainnent and thus be subjectto BART." (see 70 FR 39161, July 5, 2006). The BART Guidelines further state that "As a general matter, any threshold that you use for detennining whether a source "contributes" to visibility impainnent should not be higherthan 0.5 deciviews" (see 70 FR 39161, July 5,2006). Given that EPA has said that sources are subject to BARTbased on a contributionthreshold ofno greater than 0.5 deciviews, it would be inconsistentto automatically rule out additional controls where the improvement in visibility may be less than 1.0 deciview oreven 0.5 deciviews. The Colstrip BART analysis shows that a 0.5 or greater deciview reduction is achievable for bothNOx and S02 as individual pollutants at

one Class I area, D.L. Bend, and demonstrates that with reductions inNOx and S02 combined, there is the potential for a 1.0 deciview or more improvement.

General Comments

1. PPL's analysis is based on adding control technology to meet wmtit tenns "best demonstrated technology." PPL assumes recently updatedNSPS emission limits for particulates, S02, and NOx represent best demonstrated technology and does nottake into accountthe highest efficiency many ofthese control technologies are capable of achieving. However, the BARTGuidelines statethat "It is not ourintent to require analysis ofeachpossible level ofefficiency for a control technique as such an analysis would result in a large number ofoptions. It is important, however, that in analyzing the technology youtake intoaccountthe most stringent emission control level that the technology is capable ofachieving. You should consider recent regulatory decisions and perfonnance data 

### (e.g., manufacturer's data, engineering estimates and the experience of other sources) when identifying an emissions perfonnance level or levels to evaluate." (see 70 FR 39166, July 6,2005). Throughoutyour analysis, youhave not evaluated control technologies with the most stringent emission control level, resulting in inflated calculated cost effectiveness values. PPL needs to redo the analysis forcontrol technologies using the most stringent emissioncontrol level thatthe technology is capable ofachieving. Specific examples ofthis include: PPL should re-evaluate the costs and benefits ofreducing S02 based on a higher removal efficiency. For S02, PPL only estimates a 91% removal efficiency with additional control technology, but inthe EPA Control Cost Manual, EPA states that most absorbers have removal efficiencies in excess of90%, and packed tower absorbers have removal efficiencies as high as 99.9% ("EPA AirPollution Control CostManual", Sixth ed., EPA-452-02-001, January 2002, Section 5.2, Chapter 1, pg 1-3).

- The BART analysis assumedthat the addition ofselective non-catalytic reduction (SNCR) to separated overfire air (SOFA) couldreduce NOx emissions by about 11% over SOFA. However, EPA estimates that SNCRcan reduce NOx by40%­
250% for a boilerthis size (EPA 2002, Section 4.2, Chapter 1, pg 1-3). PPL should re-evaluate SNCR at these higher efficiencies. PPL has assumed that the addition ofselective catalytic reduction (SCR) would reduce NOx, by 17% to 0.15 lb/MMbtu. However, EPA estimates that SCRcan reduce NOx, by 70%

- 90%+ for aboilerthis size (EPA 2002, Section 4.2, Chapter 2, pg 2-3). IfSCR is capable ofreducing emissions below PPL's target, then the amount ofthe reductions and consequent visibility improvements will increase. PPL should re-evaluate SCR at these higher efficiencies.

2. The cost analysis for the control technologies included in the analysis does not contain the properdocumentation to support the costs contained in the appendices. The BART Guidelines state that "Once the control technology alternatives and achievable emissions performance levels have been identified, you then develop estimates ofcapital and annual costs. The basis forequipmentcostestimates also should be documented, either with data supplied by an equipment vendor 

### (i.e., budget estimates orbids) orby a referenced source (such as the OAQPS 

### Control CostManual, Fifth Edition, February 1996, EPA 453/B-96­ 00 1). In order to maintain and improve consistency, cost estimates should be based on the OAQPS 

### Control CostManual, where possible." (see 70 FR 39166, July 6,2005). PPL needs to provide the proper documentation to support the costs used in the analysis. Please note that the "QAQPS Control CostManual", Fifth Edition, referenced above has been replaced by the "EPA AirPollution Control Cost Manual", Sixth Edition, January 2002.

3. There is a discrepancy between the emission rates discussed in the text and those presented in tables 4

...7 and 4-9. For example, the texton page 4-19 discusses reaching 0.18 lb/MMBtu ofNOx through the application ofSOFA, howevertable 4-9 shows that the application ofSOFA would achieve only 0.23/0.27 lb/MMBtu. Itappears that the loweremission numbers in the textreflect 24-hour averaging times, while those in the table reflect 30-day rolling averages. Since the EPNWRAP modeling that was conducted to determine that Colstrip is subject-to-BART was based on 24-hour actual emission rates, we believe that modeling conducted to show the visibility improvement from applying controls should also be based on 24-hour averages. In addition to the modeling thathas been provided, PPL needs to remodel the control measures based on 24-hour averages.



### S02 Emissions and Controls

4. The analysis used 11 years for the remaining useful life for all ofthe control technologies. However, the typical useful life ofthese control technologies is expected to be 15 years based on information from the EPA Control CostManual (EPA 2002, Section 5.2, Chapter 1, pg. 1-28). The boilers are expectedto have a useful life beyond 20 years, and therefore do not have any effect on the useful life determinations. PPL needs to reanalyze the annualized costs for the control technologies using fifteen years as provided in the EPA Control Cost Manual.

35. In your BART analysis, you did not analyze 

### any fuel switching options for S02 control. Fuel substitutionto lowerthe fuel sulfur content can be a very cost effective means for reducing S02 emissions and should be analyzed. The analysis does state that coal cleaning would notresult in sulfurreductions; howeverthere are no calculations or documentation that supports this. PPL needs to provide an analysis for fuel switching options and provide an analysis to show what emission reductions coal cleaning would result in.

6. In the portion ofthe analysis pertaining to energy impacts, you state that cost estimates

are based onexperience from Colstrip Units 3&4. PPL needs to provide additional information and documentationto explain howittranslated the energy impacts at Units 3&4 to Units 1&2.

7. The BART Guidelines indicate thatEGUs with pre-existing post-combustion controls achieving removal efficiencies ofat least 50% should consider upgrades to the current scrubbers. PPL currently has pre-existing post-combustion controls with venturi wet scrubbers achieving at least 50% control efficiency. In the BART analysis, PPL only considers the addition oflimeto the scrubbers as a possible upgrade. The BART Guidelines provide additional information on what upgrades and improvements sources should considerto existing wet scrubbers. The Guidelines state "Forthose BARTeligible EGUs withpreexisting post-combustion S02 controls achieving removal efficiencies ofat least 50 percent, your BART determination should considercost effective scrubber upgrades designed to improve the system's overall S02removal efficiency. There are numerous scrubberenhancements available to upgrade the average removal efficiencies ofall types ofexisting scrubber systems. We recommend that as you evaluate the definition of"upgrade", youevaluate options that not only improve the design removal efficiency ofthe scrubber vesselitself, but also consider upgrades that can improve the overall S02removal efficiency ofthe scrubber system. Increasing a scrubber system's reliability, and conversely decreasing itsdowntime, by way ofoptimizing' operationprocedures, improving maintenance practices, adjusting scrubber chemistry, and increasing auxiliary equipmentredundancy, are all ways toimprove average S02 removal efficiencies. We recommend that as you evaluate theperformance ofexisting wet scrubber systems, you consider some ofthe following upgrades,in no particular order, as potential scrubberupgrades thathave been proven in the industry as cost effective means to increase overall S02removal ofwet systems: (a) Elimination of Bypass Reheat; (b) Installation ofLiquid Distribution Rings; (c) Installation ofPerforated Trays; (d) Use ofOrganic Acid Additives; (e) Improve orUpgrade Scrubber Auxiliary System Equipment; (f) Redesign Spray Header orNozzle Configuration." (see 70 FR 39171, July 6, 2005). PPL needs to provide an analysis for upgrades to the current scrubbers that includes the upgrades suggested by the BART Guidelines and any other improvements to this control equipment that may be appropriate.

4NOx Emissions and Controls

8. The analysis used 11 years for the remaining usefullif<;: for all ofthe control technologies. However, the typical useful life ofthese control technologies is expected to be 20 years based OJ;l information from the EPA Control CostManual (EPA 2002, Section4.2, Chapter 1, pg. 1-39). The boilers are expectedto have a useful life beyond 20 years, and therefore do nothave any effect on the useful life determinations. PPL needs to reanalyze the annualized costs for the control technologies using twenty years as provided in the EPA Control Cost Manual.

9. You state in the BART analysis that the newNOxNSPS level is belowthe presumptive BART level and therefore was not analyzed. The BART Guidelines require an analysis ofa level ofcontrol equivalentto NSPS, even ifit is belowthe presumptive limits. Specifically,the BART Guidelines state that "Where a NSPS exists for a source category (which is the case for most ofthe categories affected by BART), you should include a level ofcontrol equivalent to the NSPS as one ofthe control options. The NSPS standards

are codified in 40 CFRpart 60. We note that there are situations where NSPS standards do not require the most stringent level ofavailable control for all sources within a category. Forexample,postcombustionNOx controls (the most stringent controls for stationary gas turbines) are notrequired under subpart GG ofthe NSPS for Stationary Gas Turbines. However, such controls must still be considered available technologiesforthe BART selectionprocess." (see 70 FR 39164). PPL needs to provide an analysis for NOx that is equivalentto the currentNSPS.

.
10. In your analysis for adding Separated Overfire Air (SOFA), you state that you based CCEt estimates onrecent upgrades to the burners in Units 3&4. PPL needs to provide additional information and documentation to explain how it translated the costs ofadding SOFA at Units 3&4to Unitsl&2.

11. Units 1&2, currently controlled by 10w-NOx burners (LNB), are subjectto the presumptive limits in the BARTGuidelines, which are .15 Ib/MMbtu for tangential-fired, sub-bituminous fired boilers. The BART Guidelines state "MostEGUs can meetthese presumptiveNOx limits through the use ofcurrent combustion control technology, i.e. the careful control ofcombustion air and 10w-NOx burners. Forunits that cannotmeet these limits using suchtechnologies, you should consider whether advanced combustion control technologies such as rotating opposed fire air should be used to meetthese limits." (see 70 FR 39172, July 6,2005). In addition to the analysis for SOFA,:SNCR, and SCR, PPL should analyze newcontrol technologies than can achieve higher control levels than LNB and SOFA. Some ofthe technologies PPL should analyze include advanced separated overfire air (ASOFA), rich reagent injection (RRI), and rotating overfire air (ROFA).

12. Table A4-8(a) contains an error. The value for uncontrolled annual emissions is 5,166.50 tpy, which should be 5,616 tpy, as it is in Table A4-8(b) and Table A4-8(c). The


### 5incorrect value was carried forward in the cost effectiveness calculations. PPL needs to revise Table A4-8(a) and well as any cost effectiveness calculations that are affected by this.

Particulate Matter Emissions and Controls

13. On page 4-10 ofthe BART analysis, you state that"Wet scrubbers are currently operating to control particulate and S02 emiss.ions on Colstrip Units 1&2. While enhancements to particulate collection efficiency are potentially possible, the filterable emission rates of 0.047 and 0.058 lblMMBtu, as determined from stacktesting, are already very low and indicative ofexcellent control efficiency for this technology. Furthermore, enhancement ofthe wet scrubbers would not be expected to result in additional particulate removal. Accordingly, ESP and FF controls were the applicable and available control technologies to enhance the already 98% particulate control efficiency ofthe Colstrip Units 1&2 boilers." PPL needs to provide an analysis or information for the basis ofthe statement that 98% control efficiency can not be enhancedto perform better.

14. The PPL PM10 BART analysis assumes thatthe lowest emissionrate achievable by either a fabric filter (baghouse) or an Electrostatic Precipitator (ESP) is 0.015 lb/MMBtu. However, EPA has proposed that the Desert Rock power plant will meet a filterable PM10 limit of0.010 lblMMBtu (see Desert Rock Energy Center Proposed Permit, AZP 04-01, http://www.epa.gov/region09/air/pemit/deserocdesert-rock-proposed-permit.pd). PPL should re-evaluate the costs and benefits ofreducing PM10 to the level that EPA has said represents BestAvailable Control Technology usingtechniques developed in the EPA Control CostManual.

In orderto move forward with the BARTprocess, we ask that you submitthe requested information and analysis to our office within thirty days from the date ofthis letter.

Once again, we would like to thank you for submitting the BART analysis and acknowledge the work that has gone into preparing this analysis. Ifyou have any questions, please contact Laurel Dygowski at (303) 312-6144.

I f'.**§ince.ry~** .

# //~~

# ~Videtich, Director. Air.and Radiation Program



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