UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
 

REGION 8
 

1595 Wynkoop Street 

DENVER, CO 80202-1129 

Phone 800-227-8917 

http://VNN1.epa.gov/region08 

Ref: 8P-AR JAN 2 8 2008

James Parker 

Manager - Compliance Services 

PPL Montana - Colstrip 

P.O. Box 38 

Colstrip, MT 59323 

Re: Best Available Retrofit Technology (BART) Assessment Colstrip Generating Station 

Dear Mr. Parker: 

On February 28, 2007, EPA Region 8 sent a letter to PPL Montana - Colstrip (PPL) that 

provided the results of our "subject to" 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 was performed by TRC. 

We would like to thank you for submitting the BART analysis and recognize the effort that has 

gone into developing this document. 

We have completed our initial review of the August 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 on the analysis. In addition, 

we are attaching a copy of comments on the 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 of visibility improvement resulting 

from a reduction in emissions, based on your current BART analysis, would not be discernible 

and therefore additional controls are not justified. 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, "Even though the visibility improvement from an individual source 

may not be perceptible, it should still be considered in setting BART because the contribution to 

haze may be significant relative 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. 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 impainnent would 

. ignore the Clean Air Act's (CAA) intent to have BART requirements 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 of detennining which sources are subject to BART, "A 

single source that is responsible for a 1.0 deciview change or more should be considered to 

"cause" visibility impainnent; a source that causes less than a 1.0 deciview change may still 

contribute to visibility impainnent and thus be subject to 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 higher than 

0.5 deciviews" (see 70 FR 39161, July 5,2006). Given that EPA has said that sources are subject 

to BART based on a contribution threshold of no greater than 0.5 deciviews, it would be 

inconsistent to automatically rule out additional 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 deciview reduction is achievable for both NOx 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 wmt it tenns "best 

demonstrated technology." PPL assumes recently updated NSPS emission limits for 

particulates, S02, and NOx represent best demonstrated technology and does not take into 

account the highest efficiency many of these control technologies are capable of 

achieving. However, the BART Guidelines state that "It is not our intent to require 

analysis of each possible level of efficiency for a control technique as such an analysis 

would result in a large number of options. It is important, however, that in analyzing the 

technology you take into account the most stringent emission control level that the 

technology is capable of achieving. 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). Throughout your analysis, you have not evaluated 

control technologies with the most stringent emission control level, resulting in inflated 

calculated cost effectiveness values. PPL needs to redo the analysis for control 

technologies using the most stringent emission control level that the technology is 

capable of achieving. Specific examples of this include: 

PPL should re-evaluate the costs and benefits of reducing 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 of 90%, and packed tower 

absorbers have removal efficiencies as high as 99.9% ("EPA Air Pollution 

Control Cost Manual", Sixth ed., EPA-452-02-001, January 2002, Section 5.2, 

Chapter 1, pg 1-3). 

-	 The BART analysis assumed that the addition of selective non-catalytic reduction 

(SNCR) to separated overfire air (SOFA) could reduce NOx emissions by about 

11 % over SOFA. However, EPA estimates that SNCR can reduce NOx by40%­

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50% for a boiler this 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 of selective catalytic reduction (SCR) would 

reduce NOx, by 17% to 0.15 lb/MMbtu. However, EPA estimates that SCR can 

reduce NOx, by 70% - 90%+ for a boiler this size (EPA 2002, Section 4.2, 

Chapter 2, pg 2-3). If SCR is capable of reducing emissions below PPL's target, 

then the amount of the 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 

proper documentation 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 of capital 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 or bids) or by a referenced source 

(such as the OAQPS Control Cost Manual, 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 Cost Manual, 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 Cost Manual", Fifth Edition, referenced above has 

been replaced by the "EPA Air Pollution 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 text on page 4-19 discusses reaching 

0.18 lb/MMBtu ofNOx through the application of SOFA, however table 4-9 shows that 

the application of SOFA would achieve only 0.23/0.27 lb/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. 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 that has 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 of the control technologies. 

However, the typical useful life of these 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 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. 

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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 not result in sulfur reductions; however there 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 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 of at 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 oflime to the scrubbers as a possible upgrade. The BART 

Guidelines provide additional information on 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 of at least 50 percent, your BART determination should consider cost 

effective scrubber upgrades designed to improve the system's overall S02 removal 

efficiency. There are numerous scrubber enhancements available to upgrade the average 

removal efficiencies of all types of existing scrubber systems. We recommend that as you 

evaluate the definition of "upgrade", you evaluate options that not only improve the 

design removal efficiency of the scrubber vessel itself, but also consider upgrades that can 

improve the overall S02 removal efficiency of the scrubber system. Increasing a scrubber 

system's reliability, and conversely decreasing its downtime, by way of optimizing' 

operation procedures, improving maintenance practices, adjusting scrubber chemistry, 

and increasing auxiliary equipment redundancy, are all ways to improve average S02 

removal efficiencies. We recommend that as you evaluate the performance of existing 

wet scrubber systems, you consider some of the following upgrades, in no particular 

order, as potential scrubber upgrades that have been proven in the industry as cost 

effective means to increase overall S02 removal of wet systems: (a) Elimination of 

Bypass Reheat; (b) Installation of Liquid Distribution Rings; (c) Installation of Perforated 

Trays; (d) Use of Organic Acid Additives; (e) Improve or Upgrade Scrubber Auxiliary 

System Equipment; (f) 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 equipment that may be appropriate. 

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NOx Emissions and Controls 

8.	 The analysis used 11 years for the remaining usefullif<;: for all of the control technologies. 

However, the typical useful life of these control technologies is expected to be 20 years 

based OJ;l information from the EPA Control Cost Manual (EPA 2002, Section 4.2, 

Chapter 1, pg. 1-39). The boilers are expected to have a useful life beyond 20 years, and 

therefore do not have any effect 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 new NOx NSPS level is below the presumptive 

BART level and therefore was not analyzed. The BART Guidelines require an analysis 

of a level of control equivalent to NSPS, even if it is below the presumptive limits. 

Specifically, the BART Guidelines state that "Where a NSPS exists for a source category 

(which is the case for most of the categories affected by BART), you should include a 

level of control equivalent to the NSPS as one of the control options. The NSPS standards 

are codified in 40 CFR part 60. We note that there are situations where NSPS standards 

do not require the most stringent level of available control for all sources within a 

category. For example, postcombustion NOx controls (the most stringent controls for 

stationary gas turbines) are not required under subpart GG of the 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 equivalent to the current NSPS. . 

10. In your analysis for adding Separated Overfire Air (SOFA), you state that you based CCEt 

estimates on recent upgrades to the burners in Units 3&4. PPL needs to provide 

additional information and documentation to explain how it translated the costs of adding 

SOFA at Units 3&4 to Unitsl&2. 

11. Units 1&2, currently controlled by 10w-NOx burners (LNB), are subject to the 

presumptive limits in the BARTGuidelines, which are .15 Ib/MMbtu for tangential-fired, 

sub-bituminous fired boilers. The BART Guidelines state "Most EGUs can meet these 

presumptive NOx limits through the use of current combustion control technology, i.e. 

the careful control of combustion air and 10w-NOx burners. For units that cannot meet 

these limits using such technologies, you should consider whether advanced combustion 

control technologies such as rotating opposed fire air should be used to meet these 

limits." (see 70 FR 39172, July 6,2005). In addition to the analysis for SOFA,:SNCR, 

and SCR, PPL should analyze new control 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 

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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 of the 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 stack testing, are already very low and 

indicative of excellent control efficiency for this technology. Furthermore, enhancement 

of the 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 of the Colstrip Units 1&2 

boilers." PPL needs to provide an analysis or information for the basis of the statement 

that 98% control efficiency can not be enhanced to perform better. 

14. The PPL PM10 BART analysis assumes that the lowest emission rate 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 of 0.010 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 Best Available Control Technology using techniques developed in the 

EPA Control Cost Manual. 

In order to move forward with the BART process, we ask that you submit the requested 

information and analysis to our office within thirty days from the date of this 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. If you 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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