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



## JAN 2 8 2008 Ref: 8P-AR

James Parker Manager

- Compliance Services PPL Montana

- Colstrip P.O. Box 38 Colstrip, MT 59323

Re: BestAvailable Retrofit Technology (BART) Assessment Colstrip GeneratingStation



### DearMr. Parker:

OnFebruary 28, 2007, EPA Region 8 sent a letterto PPL Montana

- Colstrip (PPL) that provided the results ofour "subjectto" modeling for Best Available Retrofit Technology (BART) and**requ~sted** 

### that Colstrip perform a BART analysis for Units 1&2 and submit it to EPA Region 8. On August 8, 2007, Colstrip submitted a BART analysis to EPA that wasperformed by TRC. We would like to thank you for submitting the BART analysis and recognizethe effort that has gone into developing this document.

We have completed our initial review oftheAugust 8, 2007 submittal and have determined that there is additional information and analysis needed from Colstrip in 

### order for us to complete our review. Following are EPA Region 8's comments onthe analysis. In addition,

we are attaching a copy ofcomments onthe BART analysis for Colstrip Units 1&2 submitted to EPA on November 5,2007 from the National Park Service.'
Visibility Improvement and Impacts
Throughout your analysis, you state that the amount ofvisibility improvement resulting from a reduction in emissions, based on your current BART 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 withyour assertion. EPA states in the preamble to its BART Guidelines that, "Even though the visibility improvement from an individual source may not be perceptible, it should still be considered in setting BARTbecause the contribution to haze may be significantrelative to other source contributions in the Class I areas." (see 70 FR 39129, July 6, 2005). Visibility modeling shows that for Class I areas in Montana, and in particular 

## u.L. BendNational 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 impairmentwould

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

contribute to, as well as cause, such impairment (see 70 FR 39129, July 5,2006). The BART Guidelines indicate that for purposes ofdetermining which sources are subjectto BART, "A single source that is responsible for a 1.0 deciview change ormore should be considered to "cause" visibility impairment; a source that causes less than a 1.0 deciview change may still contribute to visibility impairment 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 youuse for determining whether a source "contributes" to visibility impairment should notbe higherthan 0.5 deciviews" (see 70 FR 39161, July 5,2006). Given that EPA has saidthat sources are subject to BART based on a contribution threshold ofno greaterthan 0.5 deciviews, it would be inconsistentto automatically rule outadditional controls where the improvement in visibility may be less than 1.0 deciview or even 0.5 deciviews. The Colstrip BART analysis shows that a 0.5 or greater deciviewreduction is achievable for bothNOx and S02 as individual pollutants at

one Class I area, D.L. Bend, and demonstrates that with reductions in NOx 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 what it terms "best demonstrated technology." PPL assumes recently updatedNSPS emission limits for particulates, S02, andNOxrepresent best demonstrated technology and does nottake into
account the highest efficiency many ofthese control technologies arecapable of achieving. However, the BART Guidelines state that "It is not our intentto require analysis ofeachpossible level ofefficiency for a control technique as such an analysis would result in a large number ofoptions. Itis important, however, that in analyzing the technology youtake into accountthe most stringentemission control level thatthe technology is capable ofachieving. You should consider recent regulatory decisions and performance data (e.g., manufacturer's data, engineering estimates and the experience of other sources) when identifying anemissions performance level orlevels to evaluate." (see 70 FR 39166, July 6,2005). Throughout your 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 fotcontrol 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 in the 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% ("EPAAir Pollution Control Cost Manual", Sixth ed., EPA-452-02-001, January 2002, Section 5.2, Chapter l,pg 1-3). The BART analysis assumedthat the addition ofselective non-catalytic reduction (SNCR) to separated overfire air (SOFA) could reduce NOx emissions by about 11% over SOFA. However, EPA estimates that SNCRcanreduce NOx by40%

­ 250% for a boilerthis size (EPA 2002, Section4.2, Chapter 1, pg 1-3). PPL should re-evaluate SNCR atthese higher efficiencies. PPL has assumed that the addition ofselective catalytic reduction (SCR) would reduce NOx, by 17%to O.l5lb/MMbtu. However, EPA estimates that SCRcan reduce NOx, by 70%

- 90%+ for a boilerthis size (EPA 2002, Section4.2, Chapter 2, pg 2-3). IfSCRis capable ofreducing emissions below PPL's target, thenthe amount ofthereductions and consequent visibility improvements will increase. PPL should re-evaluate SCRatthese higher efficiencies.

2. The cost analysis for the control technologies included in the analysis does not containthe proper documentation to supportthe costs contained inthe appendices. The BART Guidelines state that "Oncethe control technology alternatives and achievable emissions performance levels have been identified, youthen develop estimates ofcapital and annual costs. The basis for'equipment cost estimates 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 bebased on the OAQPS 

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

3. There is a discrepancy betweenthe emissionrates discussed in the text and those presented in tables**4~** 7 and 4-9. For example, the text onpage 4-19 discusses reaching 0.18 Ib/MMBtu ofNOx through the application ofSOFA, howevertable 4-9 shows that the application ofSOFA would achieve only 0.23/0.27 Ib/MMBtu. 

### It appears that the lower emission numbers in the text reflect 24-hour averaging times, while those in the table reflect 30-day rolling averages. Sincethe EPAlWRAP modeling that was conducted to determine that Colstrip is subject-to-BART was based on 24-hour actual emission rates, we believethat modeling conducted to show the visibility improvement from applying controls should also be based on24-hour averages. In addition to the modeling that has beenprovided, PPL needs to remodel the control measures based on 24-hour averages.



### 802 Emissions and Controls

4. The analysis used 11 years for the remaining useful life for all ofthecontrol technologies. However, the typical useful life ofthese control technologies is expected to be 15 years based on information from the EPA Control Cost Manual (EPA 2002, Section 5.2, Chapter 1, pg. 1-28). The boilers are expected to have a useful life beyond 20 years, and therefore do not have any effect onthe 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.

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### 5. In your BART analysis, you did not analyze any 

### fuel switching options for S02 control. Fuel substitution to lower the 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 sulfur reductions; however there are no calculations or documentation that supports this. PPL needs to provide an analysis for fuel**swit~hing** 

### options and provide an analysis to show what emissionreductions coal cleaning would result in.

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

are based on experience from Colstrip Units 3&4. PPL needs to provide additional information and documentation to explain how it translated the energy impacts at Units 3&4 to Units 1&2.

7. The BART Guidelines indicate that EGUs with pre-existing post-combustion controls achieving removal efficiencies ofat least 50% should considerupgrades 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 oflime to the scrubbers as apossible upgrade. The BART Guidelines provide additional informationon what upgrades and improvements sources should consider to existing wet scrubbers. The Guidelines state "For those BARTeligible EGUs with preexisting post-combustion S02 controls achieving removal efficiencies ofat least 50 percent, your BART determination should consider cost 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 vessel.itself, but also consider upgrades that can improve the overall S02removal efficiency ofthe scrubber system. Increasing a scrubber system's reliability, and conversely decreasing its downtime, by way ofoptimizing

. operationprocedures, improving maintenance practices, adjusting scrubber chemistry, and increasing auxiliary equipmentredundancy, are all ways to improve 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 that have beenproven in the industry as cost effective means to increase overall S02removal ofwet systems: (a) Elimination of Bypass Reheat; (b) Installation ofLiquid DistributionRings; (c) Installation ofPerforated Trays; (d) Use ofOrganic Acid Additives; (e) Improve or

### Vpgrade ScrubberAuxiliary System Equipment; 

## (0 Redesign Spray Header or Nozzle 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 equipmentthat may be appropriate.

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### NOx 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 Cost Manual (EPA 2002, Section4.2, Chapter 1, pg. 1-39). The boilers are expected to have a useful life beyond 20 years, and therefore do not have any effect onthe useful life determinations. PPL needs to reanalyze the annualized costs for the control technologies using twenty years as provided inthe EPA Control Cost Manual.

9. You state inthe 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 aNSPS exists for a source category (which is the case for most ofthe categories affected by BART), you should include a level ofcontrol equivalentto theNSPS as one ofthe control options. The NSPS standards

are codified in40 CFRpart 60. We note thatthere are situations where NSPS standards do notrequire the most stringent level ofavailable control for all sources within a category. Forexample, postcornbustionNOx 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 technologies for the BART selection process." (see 70 FR 39164). PPL needs to provide an analysis for NOx that is equivalentto the currentNSPS.

.

10. Inyour analysis for adding Separated Overfire Air (SOFA), you state that youbased ccst estimates onrecentupgrades to the burners in Units 3&4. PPL needs to provide additional information and documentation to explain how it translated the costs ofadding SOFA atUnits 3&4 to Units 1&2.

11. Units 1&2, currently controlled by 10w-NOx burners (LNB), are subjectto the presumptive limits inthe BARTGuidelines, which are .15 Ib/MMbtu for tangential-fired, sub-bituminous fired boilers. The BARTGuidelines state "Most EGUs can meetthese presumptive NOx limits through the use ofcurrent combustion control technology, i.e. the careful control ofcombustion air and 10w-NOx burners. For units that cannot meet 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 

### itis in Table A4-8(b) and Table A4-8(c). The

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### incorrect 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 BARTanalysis, you state that "Wet scrubbers are currently operating to control particulate and S02**emis~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 IbIMMBtu, as determined from stack testing, 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 orinformation for the basis ofthe statement that 98% control efficiency can not be enhanced to perform better.

14. The PPL PMIO BART analysis assumes that the lowest emission rate achievable by either a fabric filter (baghouse) or an Electrostatic Precipitator (ESP) is 0.015 Ib/MMBtu. However, EPA has proposed thatthe Desert Rock powerplant will meet a filterable PM10 limit of0.010 Ib/MMBtu (see Desert Rock Energy CenterProposedPermit, 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 Cost Manual.

In orderto move forward with the BARTprocess, we ask thatyou submit the 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 

### 1',**.Since~**

# /'~~

# ~Videtich, Director. Air.and Radiation Program

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