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

.epa.gov/region08 

## FEB - 4 2008
Ref: 8P-AR James Parker Manager

- Compliance Services PPL Montana, LLC 303 N. Broadway, Suite 400 Billings, MT 591 01 Re: BestAvailable Retrofit Technology (BART) AssessmentJ

### E. Corette Generating Station
Dear Mr. Parker: On February 28,2007, EPA Region 8 sent a letter to PPL Montana- Corette (PPL) that providedthe results ofour "subjectto" modeling for Best Available Retrofit Technology (BART) and requested that PPL perform a BART analysis for Corette Generating Station (Corette) and submit it to EPA Region 8. OnAugust 10,2007,PPL submitted a BART analysis to EPA that was performed by TRC. We would like to thankyou for submitting the BART analysis and recognize the effort thathas gone into developing this document. We have completed our initial review ofthe August 10,2007 submittal and have determined thatthere is additional information and analysis needed from PPL in order for us to complete our review on Corette. Following are EPA Region 8's comments onthe analysis. In addition, we are attaching a copy ofcomments onthe BART analysis for Corette submittedto EPA onNovember 8, 2007 from the U.S. Fish and Wildlife Service. Visibility Improvement and Impacts Throughoutyour analysis, you state thatthe amount ofvisibility improvementresulting 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 notto 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 significant relative to other source contributions in the Class I areas." (see 70 FR 39129, July 6, 2005). Visibility modeling shows that for numerous Class I areas in Montana, Corette is one ofthe larger stationary source contributors to visibility impairment.In addition, failing to consider less-than-perceptible contributions to visibility impairment would ignore the Clean AirAct's (CAA) intentto have BARTrequirements apply to sources that contributeto, 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 thatis responsible for a 1.0 deciview change or more should be consideredto "cause" visibility impairment; a source that causes less than a 1.0 deciview change may still c;ontribute 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 you use for determining whether a source "contributes" to visibility impairment should notbe higherthan 0.5 deciviews" (see 70 FR 39161, July 5,2006). Giventhat EPAhas said that sources are subject to BARTbased on a contribution threshold ofno greater than 0.5 deciviews, itwould be inconsistentto automatically rule out additional controls where the improvement invisibility may be less than 1.0 deciview or even 0.5 deciviews. General Comments
1. PPL's analysis is based on adding controltechnology to meetwhat itterms "best demonstratedtechnology." PPL assumes recently updated NSPS emission limits for particulates, S02, and NOxrepresentbest**demonstrat~d** technology and does nottake into accountthe highest efficiency many ofthese control technologies are capable of achieving. However, the BARTGuidelines state that "It is notourintentto 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 into accountthe most stringent emission control level thatthe technology is capable ofachieving. You should considerrecentregulatory decisions and performance data (e.g., manufacturer's data, engineering estimates and the experience of other sources) when identifying an emissionsperformance level or levels to evaluate." (see 70 FR 39166, July 6, 2005). Throughoutyour analysis, you have not evaluated control technologies withthe 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' ofachieving. Specific examples ofthis include: PPL should reevaluate the costs and benefits ofreducing S02based on a higher removal efficiency. For S02, PPL only estimates a maximum 75%removal efficiency with additional control technology, butin the EPA Control Cost Manual, EPA states thatmost absorbers haveremoval efficiencies in excess of 90% and packed tower absorbers have removal efficiencies as high as 99.9% ("EPA Air Pollution Control CostManual" Sixthed., EPA-452-02-001, January 2002, Section 5.2, Chapter 1, pg 1-3). The BART analysis assumed thatthe addition ofSNCRto SOFAcould reduce NOx emissions by about 19%. However, EPA estimates that SNCRcanreduce NOxby 40%-50% for a boilerthis size (EPA 2002, Section 4.2, Chapter 1, pg 1­ 3). 

### ppL should re-evaluate SNCRatthese higher efficiencies.

2

### PPL has assumed thatthe addition ofSCRwould reduce NOx by 52% to 0.15 lb/MMbtu. However, EPA estimates that SCRcanreduce NOx by 70%-90+% for a boilerthis size (EPA 2002, Section 4.2, Chapter 2, pg 2-3). IfSCRis capable of reducing emissions belowPPL's target, then the amount ofthe reductions and consequent visibility improvements will increase. PPL should re-evaluate SCRat these higher efficiencies. 2. The cost analysis for the control technologies included inthe analysis does not containthe 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 for equipment cost estimates also should be documented, eitherwith data supplied by an equipmentvendor (i.e.,nbudget estimates orbids) orby a referenced source (such as the OAQPS Control CostManual, Fifth Edition, February 1996, EPA 453/B-96-00l). In orderto maintain and improve consistency, costestimates should be based on the OAQPS Control Cost Manual, where possible." (see 70 FR 39166, July 6,2005). PPLneedsto provide the proper documentation to support the costs used in the analysis. Please note that the "OAQPS 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 betweenthe emission rates discussed in the text and those presented in tables 4-9 and 4-12. Forexample, the text onpage 4-20 discusses reaching 0.18 lb/MMBtu ofNOx through the application ofSOFA, however table 4-12 shows that the application ofSOFA would achieve only 0.21lb/MMBtu. Itappears 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 EPAfWRAP 

### modeling that was conductedto**de~ermine** 

### that Corette is subject-to-BART was based on 24-hour actual emission rates, we believe that modeling conductedto showthe 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. 

### S02Emissions and Controls 

### 4. The analysis used 11 years for the remaining useful life forall 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 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.

. 5. The capital cost for the S02 control equipment was done using the "Air Pollution Control Technology Fact Sheet, Flue Gas Desulfurization (FGD) -Wet, Spray Dry, and Dry Scrubbers" (EPA-452/F-03-034). This document is meant to provide information and 3estimated costranges for using various FGD technologies, and is not intended to be used for cost analyses. The cost analysis for the control technologies based onthe EPA Fact Sheet has resulted in capital equipmentcost estimates that are high in comparisonto other estimates. As an example, the capital equipment costs were estimatedto be $24,300,000 for the 25% dry injection option and $243,000,000 for each ofthe 70% dry injection and wet scrubber options: The lime injection equipmentcost supplied in the Colstrip Generating Station BART analysis was only $1,500,000. PPL needs to use the EPA Control CostManual to re-evaluate the costs and benefits ofreducing S02from the boiler.
6. Inyour BART analysis, you did not analyze any fuel switching options for 502 control. Fuel substitutionto lowerthe fuel sulfur content canbe a very cost effective means for reducing S02 emissions and should be analyzed. The analysis does state that coal cleaning would not result in sulfurreductions; however there are no calculations or documentation that supportthis. PPL needs to provide an analysis for fuel switching options and provide an analysis to showwhat emission reductions coal cleaning would result in. NOx Emissions and Controls
7. The analysis used 11 years for the remaining useful life for all ofthe control technologies. However, the typical useful life ofthese control technologies is expectedto be 20 years based oninformation from the EPA Control Cost Manual (EPA 2002, Section 4.2, Chapter 1, pg. 1-39). The boilers are expectedto have a useful life beyond 20 years, and therefore do nothave 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 CostManual. 8. You state in the BART analysis that the newNOx NSPS level is belowthe presumptive BART level and therefore was not analyzed. The BART Guidelines require an analysis ofa level ofcontrol equivalent to NSPS, evenifit 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 equivalentto 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. For example, postcombustionNOx controls (the most stringent controls for stationary gas turbines) are not required under subpart GG ofthe NSPS for Stationary Gas Turbines. However, such controls must still be considered available technologies for the BART selectionprocess." (see 70 FR 39164). PPL needs to provide an analysis for NOx that is equivalentto the currentNSPS. 9. The emitting unit at Corette is a tangential-fired, sub-bituminous boiler. PPL analyzed SOFA, SNCR, and SCRfor this unit. The BART Guidelines state "Most EGUs can meet these presumptiveNOx limits through the use ofcurrent combustion control technology, 4i.e. the careful control ofcombustion air and 10w-NOx burners. Forunits that cannot meetthese limits using such technologies, you should consider whether advanced combustion control technologies such as rotating opposed fire air shouldbe 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). These technologies meet the requirements for consideration as part ofthe BART analysis. Particulate Matter Emissions and Controls 10. The uncontrolled emissionrate for the boiler used inthe cost effectiveness calculations is based onthe stacktestresults from the electrostatic precipitator (ESP) outlet. Therefore, the cost effectiveness calculations for BART are in conjunction withthe currently installed ESP. This approachprovides unrealistic and inflated cost effectiveness values for applying BART. The cost effectiveness calculations should be based onthe actual uncontrolled emission rates (i.e., inlet emission rates before the ESP). PPL needs to reanalyze the cost effectiveness calculations based onuncontrolled emissionrates. 11. PPL did notprovide any designparameters for the existing PM control technologies, which include an ESP and fabric filters (FF). 

### Itis possible thatBARTfor PM for these two sources could include additional controls and/or increased performance ofthe existing technologies. The BART Guidelines state that "Foremission units subjectto BARTreview, there will oftenbe control measures or devices already inplace. For such emission units, it is importantto include control options that involve improvements to existing controls and not to limitthe control options only to those measures that involve a complete replacement ofcontrol devices" (see 70 FR 39164, July 6, 2005). PPL needs to submitthe design parameter information for the current PM controls and analyze the possibility ofadditional controls and increased performance ofthe existing equipment. 12. The PPL PMI0 BART analysis assumes thatthe lowest emissionrate achievable by either

# aFF (baghouse) or an ESP is 0.015 Ib/MMBtu. However, EPAhas proposed that the Desert Rockpowerplantwill meet a filterable PMI0 limit of0.010 Ib/MMBtu (see Desert RockEnergy CenterProposed Permit, AZP 04-0I, http://www.epa.gov/region09/air/permitJdesertrockidesert-rock-proposed-permit.pdt). PPL should re-evaluate the costs andbenefits ofreducing PM10 to the level that EPAhas said represents Best Available Control Technology using techniques developed inthe EPA Control CostManual.

5In orderto move forward with the BARTprocess, we ask that you 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. Ifyouhave any questions, please contact Laurel Dygowski at (303) 312-6144.

## Sm~e~ely,

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### 6

# United States Departmentofthe Interior
FISH ANDWILDLIFE SERVICE National Wildlife Refuge System Branch ofAirQuality 7333 W. Jefferson Ave., Suite 375 IN REPLY REFERTO: Lakewood, CO 80235-2017 FWS/ANWS-AR-AQ November 8, 2007
Laurel Dygowski Air Quality Planning & Management Unit US EPA Region 8 1595 Wynkoop Street Denver, CO R0202·-1·;:9 RE: Comments on the Corette Generating Station Best Available Retrofit Technology (BART) Assessment, Billings, Montana

## /~ Dear Ms.**D~owskI:** I am sending these draft comments on the Corette Generating Station BART determination at this time withthe understanding that ourfinal comments. willbe incQrp,orated within our overall review onreasonableprogress ofthe**M~ritana.Regio1}al** ijaze.Federallmplementation Plan near the end**ofthe:60~1ay** cOlnmen(period,··· ",..

. . . .**~,:** "fhefacility

## IS owned and operated by PPLM6titana, LLC(PPL),which includes one Electric Generating Unit (EGU), in Billings, MT. The plant is located within 300km ofseven Class I areas: North Absaroka Wilderness Area, Yellowstone National Park, Washakie Wilderness Area,

. UL Bend National Wildlife Refuge, Teton Wilderness Area, Gates ofthe Mountains Wilderness

Area, and Red Ruck Lakes.
The boiler is tangentially-fired using Powder River Basin sub-bituminous.coal (0.3% weight

.percent sulfur) and is rated at 154 MW. The boiler is equipped with 8n electrostatic precipitator (ESP) to control emissions ofparticulate matter (PM), and low NOx burners (LNB) and close coupled over-fire airto limitthe formation ofnitrogen oxides (NOx). Visibility Improvement Comments
We believe that it is appropriate to consider boththe degree ofvisibility improvement in a given Class I area as well as theaggregate effects of**improvi~g** visibility acro.ss <),11 ofthe Class 

### Jareas a'ffected: For the PPL/Corette BART-eligible unit, the base case'shows the greatest impactto visibility at any single Class I areais 0.645 deciviews (dv) at UL Bend Wildlife Area. Impacts to vrsibility 'are'shown for each'ofthe seven Class I areas analyzed**.~n** .the BARTreport, and for three oftheise, impacts are at or ab()vethe 0.5 dv BART screening threshoid. The collective

. impacts and potential improvements should be addressed by the BART determination. 

## TAKE**PRIDE·~ INAMERICA~** PPL analyzed several pote11.tial BART options to project the visibility improvement that would be realized in each case. The largest, single improvement was 0.238 dv using wet scrubbing for S02 control. PPL concluded on page 5-2 that, ifthe amount ofvisibility improvement resulting from a reduction in emissions is 0.238 dv, it is not discernable, and therefore the cost ofachieving the improvement is notjustified. EPA states in the preamble to its BART Guidelines that, "Even though the visibility improvement from an individual source may not be perceptible, I it sho.uld still be considered in setting BARTbecause the contributionto haze may be significantrelative to other source contributions in the Class I areas. Thus, we disagree thatthe degree of improvement should be contingentupon perceptibility. Failing to consider less-than-perceptible contributions to visibility impairmentwould ignore the CAA's intentto have BART requirements apply to sources that contribute to, as well as cause, such impairment.,,2 

### General Cost-Effectiveness Comments
EPA'sBART guidelines state, "The basis for equipment cost estimates also should be documented, either with data supplied by an equipment vendor (i.e., budgetestimates orbids) or by a referenced source (such as the OAQPS Control Cost Manual). In orderto maintain and improve consistency, cost estimates should be based on the OAQPS Control Cost Manual, where possible. The Control Cost Manual addresses most control technologies in sufficient detail for a BART analysis. The cost analysis should also take into account any site-specific design or other conditions identified above that affect the cost ofaparticular BART technology option.',3 While PPL used the Cost Manual in many cases, it used a 1988 EPRI study for the PM control equipment cost that was not provided and may well be out ofdate, or provided no supporting documentation at all. In addition, the capital cost for the S02 control equipment was done using the "AirPollution Control Technology Fact Sheet, Flue Gas Desulfurization (FGD)

- Wet, Spray Dry, and Dry Scrubbers" (EPA-452/F-03-034). This document is meant to provide information and estimated cost ranges for using various FGD technologies, and is not intendedto be used for cost analyses. The analysis used the OAQPS control cost method to calculate the annualized cost for the control technology, The equations and assumptions used to calculate the annualized cost are reasonable except for the equipment life. The analysis used a useful life of 11 years for all ofthe control technologies, which corresponds to a capital recovery factor of0.1334. The typical useful life of these control technologies are expected to be 20 years, which would reduce the capital recovery factor to 0.09439. The boiler is expected to have a useful life beyond 20 years, and therefore do not have any effect on the useful life determinations.

EPA's threshold ofperceptibility is 0.5 dv. 2 See Federal Register at 70 FR 39129, July 6, 2005; middle column 3 See 40 eFR Part 51, Appendix Y, Section IV.DA.a.5. The U.S. Environmental Protection Agency finalized it's BART Guidelines on June 15,2005, and published the preamble and final rule text in the Federal Register on July 6, 2005. The rulemaking action added Appendix Y to Part 51, titled "Guidelines for BART Determinations Under the Regional Haze Rule." The section ofthe Appendix referenced above appears in the Federal Register at 70 FR 39166, July 6, 2005. 2 IWe are also concerned withthe way in which the incremental cost analysis was used. According to EPA'sBART Guidelines, "You should considenhe incremental costeffectiveness in combination withthe average cost effectiveness when considering whether to eliminate a control option

.... "4 "You should exercise caution notto misuse these [average and incremental cost effectiveness] techniques

... [but considerthem in situations where an option shows]

...slightly greater emission reductions

..."s Reviewing agencies are quite familiar with the concept oftotal average cost and expectto see costs in the $2,000

- $12,000 perton range. However, incremental costs are rarely estimated'and evaluated, so the much higher numbers that result appear quite high at first glance. Forthis reason, rigid use ofincremental cost effectiveness will always result in the choice ofthe cheapest option ifcarried to the extreme. Forexample, ifonly incremental costs were used to evaluate PM controls, it is likely that all controls more expensive than a multiple cyclone would be rejected. To use incremental costs properly, they must be compared to incremental costs for similar situations.
In addition, in situations where a facility's emissions affect visibility at multiple Class I areas, consideration should be given to the control cost compared to the aggregate visibility improvement projected (i.e., cost/total dvreduction, or some other method).

PPL considered five approaches for reducing S02 emissions: coal pre-treatment, alkali wet scrubbing, limestone scrubbing with forced oxidation, spray dryer absorption, and dry injection. The analysis did not provide any fuel switching options. The evaluation used a S02 emission rate of0.46 IblMMBtu as the base case for the cost analyses. This base case S02 emission rate was obtained from averaging the facility's CEM data for the Years 2001-2003. The facility notes that the boiler already combusts a low-sulfur coal.
PPL eliminated the coal pre-treatment approach because the coal is already low-sulfur and gasification ofthe coal would require a complete change in the operation. The analysis did not distinguish between the other control teclmologies and instead presented cost evaluations for dry injection and wet scrubbing approaches. The dry injection options were performed using a 25% S02reduction and a 70% S02reduction. The wet scrubbing option was performed at an emission reduction at 70% S02reduction. The 25% S02 reduction option was performed because the facility believed thatthis reduction level does not impact the PM emission rate. The cost analysis for the control technologies uses an EPA Fact Sheet to support the equipment costs contained in the appendices. The capital equipment costs were estimated to be $24,300,000

4 See 40 eFR Part 5I, Appendix Y, Section IV.DA.e.J., also appearing in the Federal Register at 70 FR 39167, July 6,2005.

5 See 40 CFR Part 51, Appendix Y, Section IV.DA.e.5., also appearing in the Federal Register at 70 FR 39168, July 6, 2005,
6 The presumptive S02 limit for similar boilers is 0.15 Ib/mmBtu. 3for the 25% dry injection option and $243,000,000 for each ofthe 70% dry injection and wet scrubber options. Both ofthese capital equipment"cost estimates are extremely high in comparison to other estimates. As an example, the lime injection equipment cost supplied in the Colstrip Generating Station BART analysis was only $1,500,000. PPL should re-evaluate the costs and benefits ofreducing S02 using techniques developed in the OAQPS Control Cost Manual.?

. The PPL BART analysis states that coal cleaning would not result in sulfurreductions; however there are no calculations or documentation that supports this.

The Corette facility is currently equipped with Low NOxBurners (LNB) and Close Coupled Over-Fire Air to reduce emissions ofNOx. PPL considered 4 approaches for reducing NOx emissions: boiler tuning, separated over-fire air (SOFA), selective non-catalytic reduction (SNCR), and selective catalytic reduction (SCR). PPL stated that each ofthese control options were feasible and proceeded to estimate the cost effectiveness ofeach ofthe options. No options for fuel switching (i.e., natural gas, fuel oil) were presented in the analysis. PPL evaluated the costs effectiveness ofeach ofthese options using cost data from the World Bank for the SOFA option and the OAQPS Cost Manual for the SNCR and SCRoptions. The boiler tuning cost was not referenced, but appears that it may be based on past cost informationJor the boilers.
PPL estimated the emission reductions for the boiler tuning and the SOFA options using typical NOx reductions using these technologies. The cost effectiveness for these options are $147per ton ofNOxreduced for the boilertuning option, and $914 perton ofNOx reduced for the SOFA option. These values are reasonable in comparisonto other control costcalculations. The SNCR and SCRcost effectiveness options were calculated based on achieving an NSPS emission rate of0.16 Ib/MMBtu for SNCRand 0.15 Ib/MMBtu for SCR from the current emission rate of0.26 Ib/MMBtu. This translates to only 38.5% reduction efficiency for SNCR and 42.3% reduction efficiency for SCR. EPA states that SCR is capable ofachieving 90-99% reduction in NOx emissions from ·similar units. Therefore the cost effectiveness value of$4,354 per ton ofNOxremoved for SCR is biased high in comparisonto other SCR application costs. We believe that PPL should re-evaluate the cost effectiveness and visibility improvementsfrom applying SCRto the boiler. PPL's cost analysis is based upon several significant errors and misrepresentations: • PPL has assumedthat addition ofSNCRto SOFA could reduce NOxemissions by about 19%. However, EPA estimates that SNCR can reduce NOxby 40%

- 50% for a boiler this size. 9 PPL should re-evaluate SNCR at these higher efficiencies.

7 PPL should alsojustify using an eleven year equipment life instead ofthe 15 years assumed by the OAQPS Control Cost Manual. 8 The presumptive NOx limit for similarboilers is 0.15 Ib/mmBtu. 9 OAQPS Cost Manual, p 1-3 and EPA CostTool for Corette 4• PPL concluded thatthe $1,723/ton cost ofSNCR is notjustifiable. However, in the preamble to its BART Guidelines, EPA states, "The limits provided were chosen at levels that approximately75 percent ofthe units could achieve with cun-ent combustion control technology. The costs ofsuch controls in most cases range fromjust over $100 to $1000 per ton.,,10 This range ofproposed control costs includes addition ofSOFA at Corette. Application ofEPA's Cost Tool model to Corette predicts that 40% NOxreductions can be achieved for $826

- $1016 per ton. • PPL has assumed that addition ofSCRwould reduce NOxby 52%to 0.15 Ib/mmBtu. However, EPA estimates that SCR can reduce NOxby'70% to 90% or more for a boiler this size. 11 IfSCR is capable ofreducing emissions below PPL's target, then the amount ofthe reductions and consequent visibility improvements will increase. PPL should reevaluate SCR at these higher efficiencies. 12 Technical Feasihility ofROFA: In the preamble to its BART Guidelines, EPA states "For those units that cannot meet the presumptive limits using cun-ent combustion control technology, states should carefully considerthe use ofadvanced combustion controls such as Rotating Over-Fire Air (ROFA) in their BART determinations." 13 PPL did not consider ROFA, and provided no reason why this technology could not be transferred14 froin similar, but smaller applications, such as at MN Power's Taconite Harbor facility where it will install Mobotec multi-pollutant control technology on each ofthree 75 MW boilers to reduce S02 (by 65% to 0.24 lb/mmBtu) and NOx (by 64% to 0.14 lb/mmBtu). PMIO 

### BART
PPL considered 4 approaches at Corette for reducing filterable particulate emissions; fabric filter (baghouse), electrostatic precipitator, mechanical collectors (i.e., cyclones), wet scrubbers. PPL eliminated mechanical collectors and wet scrubbers because they are unable to achieve the high efficiencies to reach the 0.015 lb/MMBtll NSPS emission rate. The use ofa mechanical collector in conjunction with the existing ESP should achieve a significant reduction in PM emissions from the boiler with relatively little cost. However, this scenario was not researched in this analysis. '111e wet scrubber was analyzed as a control option for S02, but not for PM. No options for fuel switching (i.e., natural gas, fuel oil) were presented in the analysis. Also there was no discussion on remodeling the current ESP to increase the PMremoval efficiency. The uncontrolled emission rate for the boilerused in the cost effectiveness calculations are based on the stack test results from the ESP outlet. Therefore, the cost effectiveness calculations for

10 See 70 FR 39135, July 6, 2005, first column. 11 OAQPS Cost Manual, p2-3 and EPA Cost Tool for Corette 12 No reason is given in the BART analysis for setting this target. However, EPA has proposed that the Desert Rock power plant meet a 24-hour average NOx limit of0.06 lb/mmBtu. IJ See 70 FR 39135, July 6, 2005; middle columnbelow tables. 14See 40 CFR Part 51, Appendix Y, Section IV.D.2., also appearing in the Federal Register at 70 FR 39165, July 6, 2005, which says: "Deployment ofthe control technology on a new orexisting source with similar gas stream characteristics is generally a sufficient basis for concludingthe technology is technically feasible barring a demonstration to the contrary as described below." 5BARTare in conjunction with the currently installed ESP. We believe this approach provides unrealistic and inf1ated cost effectiveness values for applying BART. The cost effectiveness calculations should be based on the actual uncontrolled emission rates (i.e., inlet emission rates before the ESP). No information on the PMremoval efficiency ofthe currently installed ESP was provided in the analysis.
The PPL BART analyses assume thatthe lowest emission rate achievable by 

### either a fabric filter (baghouse) or an ESP is 0.015 Ib/mmBtu. Datafrom EPA has shownthatthese technologies are able to achieve lower emissionrates than theNSPS level. For example, the**De~ert** Rock power plant will meet a filterable PMIO limit of0.010 Ib/mmBtu. We believe that PPL should reevaluate the costs and benefits ofreducing PMto the level that EPA has said represents Best Available Control Technology usingtechniques developed in the OAQPS Control Cost Manual.'s Equipment cost values for the ESP and FF are based on cost data from the Air Pollution Engineering Manual developed by the Air 

### &Waste ManagementAssociation. The capital costs were obtained using $60/kW for the ESP and $50/kWfor the FF and are based on a collection efficiency of99%. These capital cost values seem high in comparison to other cost evaluations for these technologies.
Conclusions & Recommendations

• PPL should recognize that control equipment can achieve varying degrees ofcontrol based upon how it is designed and operated, and use the 

### highest level ofcontrol feasible in its analyses. • Impacts upon all affected Class I areas should be considered collectively. Therefore, the relative cost-effectiveness ofcontrol strategies should be compared on a cost/deciview improvement basis. • The costs ofadding SOFA and SNCRare economically feasible and produce relatively high visibility benefits. • PPL should re-evaluate application ofROFA. • PPL should evaluatemeeting a lower filterable PMlo limit using the highest degree of control for the ESP and FF. • PPL should use a useful life of20 years for calculating aJillual cost ofthe control equipment rather than the 11 yeaJ's used in the BART assessment. • Because of.I.E. Corette Power Plant's geographic location and its impacts to visibility at multiple Class I areas, the Federal ImplementationPlan's Reasonable Progress analysis may benefit from revisiting the options for controls at this facility.
We look forward to working with EPA and PPL as this process advances. We believe that good communication and sharing ofinformation will help expedite this process, and suggestthat you

15 PPL should also justify using an eleven year equipment life instead ofthe twenty years assumed by the OAQPS Control Cost Manual. 6contact Tim Allen (Tim_Allen@fws.gov at (303) 914-3802) ofmy staffifyou have any questions or comments. Sincerely.

# yj~cz 

# yLiveD
Sandra Silva, Chief Branch ofAir Quality

cc: Richard Coleman, Regional Chief National Wildlife Refuge System FWS-MountainPrairie Region Denver Federal Center P.O. Box 25486 Denver, CO 80225
Barron Crawford, Project Leader ULBend National Wildlife Refuge P.O. Box 110 Airport Road Lewistown, MT 59457
Ann Mebane USDA

- U.S. Forest Service
Bruce Polkowsky National Park Service

- Air Resources Division

7·