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Chapter 10. BEST AVAILABLE RETROFIT 

TECHNOLOGY (BART) EVALUATION

.....................................................

10.5 TASCO BART Determination

10.5.1 History of TASCO BART Process and Overview of Changes

TASCO BART control equipment was initially determined to be the existing baghouse for the 

control of PM emissions, a spray dry flue gas desulfurization (FGD) system for the control of 

SO2 emissions, and a low NOx burner system (LNB) with over-fired air for the control of NOx 

emissions. BART emission limits, a BART alternative to control NOx, and other BART 

requirements were incorporated in Tier II Operating Permit No. T2 2009.0105, which was issued 

on September 7, 2010. On October 12, 2010, TASCO filed a contested case petition seeking 

review of the permit. During negotiations to resolve the contested case, TASCO provided 

additional information concerning the feasibility of SCR and over-fired air control technologies, 

requested revision of the initial BART determinations, and proposed a BART Alternative to the 

Spray Dry FGD control technology. The BART determinations in this document have been 

updated based on the revised BART determinations and the approved BART Alternative. The 

specific revisions to BART and to the BART Alternative, along with the supporting technical 

analyses, regulatory review, and a discussion of the revised permit conditions has been provided 

in Appendix F “Revised TASCO BART Determination” and in the Statement of Basis to the 

reviesed Tier II Operating Permit No. T2 2009.0105, Project 60867, issued December 23, 20ll.

The initial BART determinations made under T2 2009.0105 issued September 7, 2010 have been 

revised based on engineering design information specific to the Riley Boiler retrofit project. A 

summary of the revised BART determinations is provided below.

BART for the control of NOx

 Following the initial BART determination, it was determined that SCR is not 

technically feasible for retrofit on the Riley Boiler. Selective catalytic reduction 

(SCR) is a post-combustion control device that reduces thermal and fuel NOx

emissions with a reagent (generally ammonia or urea) in the presence of a catalyst to 

form water and nitrogen.

 Following the initial BART determination, it was determined that incorporating 

over-fired air as part of a coal-fired low NOx burner system (LNB) is not technically 

feasible for retrofit on the Riley Boiler. Low NOx burners with over-fired air (LNB 

with OFA) utilize fuel and air mixing optimization and/or staged combustion 

techniques to reduce thermal NOx formation.
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 Following the initial BART determination, a coal-fired low NOx burner system 

(LNB) has been determined to be BART for the control of NOx emissions from the 

Riley Boiler. Low NOx burners (without over-fired air) utilize fuel and air mixing 

optimization and/or staged combustion techniques to reduce thermal NOx formation.

 Although considered initially as a BART alternative to the control of NOx emissions, 

the shutdown of three coal-fired pulp dryers has instead been included as part of the 

BART Alternative to the control of SO2 emissions.

BART Alternative to the control of SO2

 The shutdown of three coal-fired pulp dryers and the retrofit of coal-fired low NOx

burner systems (LNB) on two B&W Boilers have been proposed as part of a BART 

Alternative to the control of SO2 emissions from the Riley Boiler. The Pulp Dryer 

shutdowns will eliminate NOx, PM, and SO2 emissions from the pulp dryers, while 

LNB will reduce NOx emissions from the boilers. These controls are predicted to 

result in greater visibility improvement to Class I areas within 300 km of the facility 

than the BART determination for SO2 (Spray Dry FGD), which remains unchanged 

from the initial BART determination.

For spray dry flue gas desulfurization (Spray Dry FGD), the flue gas is introduced into a tower 

and contacts an atomized spray of lime slurry, which absorbs and neutralizes SO2. (TASCO has 

documented concerns regarding the affordability and environmental impacts of Spray Dry FGD; 

however, for the purposes of this BART determination, Spray Dry FGD was considered 

feasible.)

Natural Gas-Fired Operation

 The Riley Boiler was designed to combust coal and/or natural gas fuels. Discussion 

has been provided supporting why BART control equipment and emission limits were 

applied exclusively to the coal-fired operating scenario.

Terminology

BART Terminology

 In this document the initial BART is defined to mean the initial BART determinations 

for PM, SO2, and NOx that were determined under Tier II Operating Permit No.T2-

2009.0105, issued on September 7, 2010.

 In this document the revised BART is defined to mean the BART determination for 

NOx, which is being revised by this permitting action. (The BART for PM and SO2

have not been revised and remain the same as what was determined under Tier II 

Operating Permit No. T2-2009.0105, issued on September 7, 2010.)

BART Alternative Terminology

 In this document the “BART Alternative” scenario is defined to mean the 

combination of BART for PM (Riley Boiler with the existing baghouse), revised 

BART for NOx (Riley Boiler with low NOx burners), and the BART Alternative to 

the control of SO2 (B&W Boilers #1 and #2 with low NOx burners and the three Pulp 

Dryers shut down).
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 In this document the “BART” scenario is defined to mean the combination of BART 

for PM (Riley Boiler with the existing baghouse), revised BART for NOx (Riley 

Boiler with low NOx burners), and BART for SO2 (Riley Boiler with Spray Dry 

FGD), with the addition of the sources affected by the “BART Alternative” scenario: 

B&W Boilers #1 and #2 and three Pulp Dryers in full operation.

 In this document the “Alternative Benchmark” scenario is defined to mean the Riley 

Boiler with the existing baghouse, B&W Boilers #1 and #2, and the three Pulp 

Dryers. This scenario allows comparison of both the “BART” and “BART 

Alternative” scenarios against the same benchmark that includes all of the affected 

sources.

10.5.2 BART Determinations

Background

In accordance with 40 CFR 51.308(e) and IDAPA 58.01.01.668.02.c, Best Available Retrofit 

Technology (BART) means an emission limitation based on the degree of reduction achievable 

through the application of the best system of continuous emission reduction for each pollutant 

which is emitted by an existing stationary facility. The emission limitation must be established, 

on a case-by-case basis, taking into consideration the technology available, the costs of 

compliance, the energy and non-air quality environmental impacts of compliance, any pollution 

control equipment in use or in existence at the source, the remaining useful life of the source, and 

the degree of improvement in visibility which may reasonably be anticipated to result from the 

use of such technology. (These considerations were included in Step 4 of the BART 

determinations.)

The BART analyses and determinations followed the five-step process provided in Guidelines 

for BART Determinations Under the Regional Haze Rule (Appendix Y to Part 51):

1) Identify all retrofit control technologies

2) Eliminate technically infeasible options

3) Evaluate control effectiveness of the remaining control technologies

4) Evaluate the impacts of each remaining control technology (including energy, 

non-air quality environmental, and cost impacts; and the remaining useful life of 

the source)

5) Select BART and determine the degree of visibility improvement

SO2, NOx, and PM emissions were the visibility-impairing pollutants evaluated in the BART 

analyses and determinations. See table 1 below for more information.

Based on CALPUFF air dispersion modeling results, the Riley Boiler was determined to 

contribute to visibility impairment at three Class I areas, including the Eagle Cap Wilderness 

(Oregon), Hells Canyon National Recreation Area (Oregon/Idaho border), and Strawberry 

Mountain Wilderness (Oregon), primarily during the winter time. A single emission source 

which is responsible for a one-half (0.5) deciview change or more in any mandatory Class I 

Federal Area “contributes” to visibility impairment as defined in IDAPA 58.01.01.668.02.b.
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As part of the initial and revised BART determinations, modeling analyses were conducted to 

evaluate visibility impacts at seven Class I areas within a 300 km radius around the Riley Boiler. 

In addition to the three areas listed above, the analyses included Craters of the Moon National 

Monument, Jarbidge Wilderness, Sawtooth Wilderness, and Selway-Bitterroot Wilderness.
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Table 1 BART DETERMINATIONS (a)

(a) This table summarizes each BART determination. The BART determination for NOx has been revised as described 

in this section.

(b) SO2, NOx, and PM emissions were the visibility-impairing pollutants evaluated.

(c) Δdv = delta deciviews; result is based on changes to visibility at the Eagle Cap Wilderness Area.

(d) Because the cost of the enhanced baghouse, dry ESP, and wet ESP options were determined to outweigh the 

improvement, BART was selected based on costs of compliance and the pollution control equipment in use (existing 

baghouse). Specific modeling of each PM control scenario was not analyzed.

(e) The “Base Case” represents continuous coal-fired operation of the Riley Boiler (without controls).

(f) Wet FGD was not determined to be effective due to non-air quality environmental impacts of compliance related to 

wastewater treatment.

(g) SNCR was not considered feasible due to concerns that the flue gas would not have adequate residence time to 

achieve reliable control.

(h) SCR was not considered feasible upstream of the baghouse due to insufficient space necessary to accommodate the 

control device, in addition to concerns regarding catalyst fouling and erosion. SCR was not considered feasible 

downstream of the baghouse due to exhaust gas cooling below the effective operating temperature range of the 

control device.

(i) ULNB was not considered feasible due to concerns that the boiler firebox would not be large enough to 

accommodate the full burner/flame management system required.

Pollutant(b)

Step 1 Step 2 Step 3 Step 5 Step 6

Technologies

Identified

Technically

Feasible

(Yes/No)

Control 

Level

(lb/hr)

Control 

Ranking

Modeled

Impairment

Contribution(c)

Most Effective

(Yes/No)

PM

Wet ESP Yes 12.4 1 --

(d) No(d)

Dry ESP Yes 12.4 1 --

(d) No(d)

Enhanced 

Baghouse Yes 12.4 1 --

(d) No(d)

Existing 

Baghouse Yes 12.4 1 --

(d) Yes

SO2

Wet FGD Yes 26 1 43 No(f)

Spray Dry FGD Yes 104 2 51 Yes

Dry Trona FGD Yes 183 3 58 No

Dry Lime FGD Yes 235 4 66 No

Low Sulfur Coal Yes 444 5 90 No

Base Case(e) Yes 522 6 127 No

NOx

SNCR No(g)-- -- -- --

SCR No(h)-- -- -- --

ULNB No(i)-- -- -- --

LNB/OFA No(j)-- -- -- --

LNB Yes 147 1 60 Yes

Base Case(e) Yes 374 2 127 No
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(j) It was determined that insufficient vertical distance is available between the top burner elevation and the furnace 

nose arch, which is necessary to provide adequate fuel combustion residence time and to accommodate the OFA 

burner/flame management system.

10.5.3 Revisions

The initial BART determinations made under T2-2009.0105 issued September 7 2010 have 

been revised based on engineering design information specific to the Riley Boiler retrofit 

project. A summary of the revised BART determinations is provided below, followed by a 

discussion of the specific changes. Additionally, although not considered a change in the initial 

BART determinations, analysis has been provided for each Riley Boiler fuel operating scenario 

supporting that BART requirements were considered applicable only when firing coal in the 

Riley Boiler.

Infeasibility of SCR

As provided in Table 1, based on the results of an engineering design review of the Riley Boiler 

it has been determined that selective catalytic reduction (SCR) is not technically feasible for 

retrofit on the Riley Boiler. SCR was not considered feasible upstream of the baghouse due to 

insufficient space necessary to accommodate the control device, in addition to concerns 

regarding catalyst fouling and erosion. SCR was not considered feasible downstream of the 

baghouse due to exhaust gas cooling below the effective operating temperature range of the 

control device.

Infeasibility of OFA

As provided in Table 1, based on the results of an engineering design review of the Riley Boiler,

it has been determined that over-fired air (OFA) is not technically feasible for retrofit on the

Riley Boiler. It was determined that insufficient vertical distance is available between the top 

burner elevation and the furnace nose arch, which is necessary to provide adequate fuel 

combustion residence time and to accommodate the OFA burner/flame management system.

As provided in Table 2, LNB is expected to result in the reduction or elimination of 37 days of 

visibility impairment at Eagle Cap Wilderness - the Class I area showing the greatest impact 

from the Riley Boiler - over the baseline case of no NOx controls.

Table 2 NOX BART VISIBILITY IMPROVEMENT

Eagle Cap Wilderness, OR

Delta-deciview impacts greater than contribution threshold (∆dv>0.5)

2003 2004 2005 2003-2005

8

th

highest(a)

Total

days(b)

8

th

highest(a)

Total

days(b)

8

th

highest(a)

Total

days(b)

22nd

highest(c)

Total

days(d)

Base Riley Boiler Scenario 

(wzl10471) 0.721 15 1.086 41 1.109 41 1.086 97

NOx Control Scenario 1 – LNB 

(wzl10496) 0.467 7 0.766 25 0.823 28 0.760 60

(a) The 8th highest delta-deciview impact for the calendar year.

(b) Total number of days in the 1-year period that exceeded 0.5 delta deciviews.

(c) The 22nd highest delta-deciview impact for the 3-year period.

(d) Total number of days in the 3-year period that exceeded 0.5 delta deciviews.
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Modeling of the revised BART was completed using the same protocol as described in Appendix 

F (this protocol was also used in the BART modeling analyses for Tier II Operating Permit 

No.T2-2009.0105, issued on September 7, 2010).

10.5.4 BART Alternative

Revisions

Shutdown of the pulp dryers, in combination with installation and operation of LNB on the 

B&W Boilers, has been proposed as the BART Alternative for the control of SO2 emissions from 

the Riley Boiler.

The “BART Alternative” scenario is expected to achieve greater reasonable progress than the 

“BART” scenario because this scenario results in greater emissions reductions and in greater 

visibility improvements, as described below.

Although this alternative primarily reduces NOx emissions, with some reduction in PM and SO2

emissions also resulting from the pulp dryer shutdowns, the “BART Alternative” scenario is 

expected to result in greater emission reductions in regional haze pollutants (PM, SO2, and NOx) 

than the “BART” scenario, and the visibility improvement at all Class I areas was predicted to be 

greater for the “BART Alternative” scenario – with the reduction or elimination of 41 additional 

days expected when compared to the “BART” scenario. A description of the “BART” and 

“BART Alternative” scenarios that were evaluated is provided in the History and Overview of 

Changes section.

The BART alternative in Tier II Operating Permit No. T2-2009.0101 issued September 7, 2010, 

(which involved shutdown of three pulp dryers in lieu of installing a SCR control technology for 

the control of NOx emissions), is no longer under consideration as initially proposed. Shutdown 

of this equipment has instead been incorporated as part of the new BART Alternative to the 

control of SO2 emissions as described above, in lieu of installing Spray Dry FGD on the Riley 

Boiler.

Emission Reductions

For evaluation of the “BART Alternative” scenario emission reductions, the “BART Alternative”

scenario was compared to the “BART” scenario. The “Alternative Benchmark” scenario is 

included for reference to represent baseline (existing) operating conditions. As provided in the 

tables below, the “BART Alternative” scenario is expected to result in greater emission 

reductions in regional haze pollutants (PM, SO2, and NOx) than the “BART” scenario. Refer to

Appendix F Revised BART Determination for additional information regarding the emission 

reduction estimates. The BART emission reductions are also provided in the tables below.
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Table 3 “BART” EMISSION REDUCTIONS

Pollutant(a) Emission Source

“BART”

Emissions

lb/hr(b)

“Alternative 

Benchmark”

Emissions

lb/hr(c)

Net Emission 

Reductions

lb/hr

Riley Boiler 5.9 12.4 6.5

PM B&W Boilers #1 & #2 56.9 56.9 0.0

North, South, & Center Pulp 

Dryers 92.7 92.7 0.0

Riley Boiler 104.0 522.3 418.3

SO2 B&W Boilers #1 & #2 435.0 435.0 0.0

North, South, & Center Pulp 

Dryers 17.9 17.9 0.0

Riley Boiler 147.0 373.8 226.8

NOx B&W Boilers #1 & #2 227.0 227.0 0.0

North, South, & Center Pulp 

Dryers 191.2 191.2 0.0

Total 1,277.6 1,929.2 651.6

(a) SO2, NOx, and PM emissions were the visibility-impairing pollutants evaluated.

(b) “BART” scenario includes the Riley Boiler with BART for the control of PM (with the existing baghouse), with 

BART for the control of NOx(LNB), and with BART for the control of SO2(Spray Dry FGD); full operation of the 

B&W Boilers (without LNB), and full operation of the three pulp dryers. This control scenario represents BART as 

described in the BART Determinations section.

(c) “Alternative Benchmark” includes the Riley Boiler (with the existing baghouse), full operation of the B&W Boilers

(without LNB), and full operation of the three pulp dryers. Estimated emission reductions attributable to shutdown of 

the pulp dryers were provided in Table 7 of the BART determination submitted February 9, 2009. 
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Table 4 “BART ALTERNATIVE” EMISSION REDUCTIONS

Pollutant(a) Emission Source

“BART 

Alternative”

Emissions

lb/hr(b)

“Alternative 

Benchmark”

Emissions

lb/hr(c)

Net Emission 

Reductions

lb/hr

PM

Riley Boiler 12.4 12.4 0.0

B&W Boilers #1 & #2 56.9 56.9 0.0

North, South, & Center Pulp 

Dryers 0.0 92.7 92.7

SO2

Riley Boiler 522.3 522.3 0.0

B&W Boilers #1 & #2 435.0 435.0 0.0

North, South, & Center Pulp 

Dryers 0.0 17.9 17.9

NOx

Riley Boiler 147.0 373.8 226.8

B&W Boilers #1 & #2 103.0 227.0 124.0

North, South, & Center Pulp 

Dryers 0.0 191.2 191.2

Total 1,276.6 1,929.2 652.6

(a) SO2, NOx, and PM emissions were the visibility-impairing pollutants evaluated.

(b) “BART” scenario includes the Riley Boiler with BART for the control of PM (with the existing baghouse), 

with BART for the control of NOx (LNB), and with BART for the control of SO2 (Spray Dry FGD); full 

operation of the B&W Boilers (without LNB), and full operation of the three pulp dryers. This control 

scenario represents BART as described in the BART Determinations section.

(c) “Alternative Benchmark” includes the Riley Boiler (with the existing baghouse), full operation of the B&W 

Boilers (without LNB), and full operation of the three pulp dryers. Estimated emission reductions attributable 

to shutdown of the pulp dryers were provided in Table 7 of the BART determination submitted February 9, 

2009.

Visibility Improvements

The “BART Alternative” scenario was determined to achieve greater improvement in visibility 

impairment in Class I areas than the “BART” scenario. Refer to Appendix F for additional 

information regarding these modeling scenarios.

Based on CALPUFF modeling, the highest modeled visibility impacts were predicted to occur in 

the Eagle Cap Wilderness Area. The combination of BART for PM, BART for NOx, and the 

BART Alternative to SO2 was predicted to result in a minimum reduction or elimination of 23

days of visibility impairment and an improvement in the 22nd highest visibility impact of 0.101

Table 

5).
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Table 5 “BART ALTERNATIVE” VISIBILITY IMPROVEMENT – EAGLE CAP (a)

Control Scenario

22nd Highest 

Impact

Impairment

Contribution

(b)

“BART”(d)

Riley Boiler w/ Baghouse (“Alternative Benchmark”)

(c)

B&W Boilers #1 & #2 – full operation

North, South, Center Pulp Dryers – full operation

2.201 195

Riley Boiler w/ Baghouse, Spray Dry FGD, LNB (f)

B&W Boilers #1 & #2 – full operation

North, South, Center Pulp Dryers – full operation

1.512 149

Net Visibility Improvement 0.689 46

“BART 

Alternative”(e

)

Riley Boiler w/ Baghouse (“Alternative Benchmark”)

(c)

B&W Boilers #1 & #2 – full operation

North, South, Center Pulp Dryers – full operation

2.201 195

Riley Boiler w/ Baghouse, LNB (f)

B&W Boilers #1 & #2 w/ LNB (f)

North, South, Center Pulp Dryers – shutdown

1.411 126

Net Visibility Improvement 0.790 69

Difference in Improvement 0.101 23

(a) This table compares the modeled visibility impacts for the combined BART determinations and the “BART 

Alternative” to the “Alternative Benchmark” operating scenario. SO2, NOx, and PM emissions were the visibilityimpairing pollutants evaluated.

(b) Δdv = delta deciviews; result is based on changes to visibility at the Eagle Cap Wilderness Area.

(c) “Alternative Benchmark” includes the Riley Boiler (with the existing baghouse), full operation of the B&W Boilers

(without LNB), and full operation of the three pulp dryers. Estimated emission reductions attributable to shutdown of 

the pulp dryers were provided in Table 7 of the BART determination submitted February 9, 2009.

(d) “BART” includes Riley Boiler with BART for the control of PM, NOx, and SO2(with the existing baghouse, LNB, 

and Spray Dry FGD), full operation of the B&W Boilers (without LNB), and full operation of the three coal-firing 

pulp dryers.

(e) “BART Alternative” includes the Riley Boiler with BART for the control of PM (with the existing baghouse) and 

with BART for the control of NOx (LNB), the B&W Boilers with the BART Alternative to the control of SO2(CoalFiring LNB for each boiler), and shutdown of the three coal-firing pulp dryers. This control scenario represents the 

control equipment described in Permit Condition 3.2.

(f) The NOx control efficiency of the Riley Boiler LNBs = 60.7%, and for the B&W Boilers LNBs = 55%.

Similar modeled visibility improvements for the “BART Alternative” scenario were predicted 

across all of the Class I areas evaluated (as summarized in Table 6). On the balance, visibility 

improvement at all Class I areas was predicted to be greater for the “BART Alternative” scenario 

– with the reduction or elimination of 41 additional days expected when compared to the 

“BART” scenario. The single exception was one additional day of visibility impairment and 

22nd highest visibility impact of -0.017 -Bitterroot Wilderness. The modeling 

results also support that the distribution of emissions with respect to the Class I areas evaluated is 

not substantially different than under the “BART” scenario.
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Table 6 “BART ALTERNATIVE” VISIBILITY IMPROVEMENT (a)

Class I Area(a)

“BART”(b) “BART 

Alternative”(c)

Difference in

Improvements(d)

22nd

Highest

Days

>0.5 

22nd

Highest

Days 22nd

Highest

Days

Eagle Cap Wilderness, OR 1.512 149 1.411 126 0.101 23

Craters of the Moon National Monument, ID 0.267 4 0.245 3 0.022 1

Hells Canyon National Recreation Area, ID 1.092 87 1.059 80 0.033 7

Jarbidge Wilderness, NV 0.256 5 0.234 5 0.022 0

Sawtooth Wilderness, ID 0.319 6 0.307 6 0.012 0

Selway-Bitterroot Wilderness, ID 0.281 3 0.298 4 -0.017 -1

Strawberry Mountain Wilderness, OR 1.076 62 0.917 51 0.159 11

Total Number of Days 316 275 41

(a) This table compares the modeled visibility impacts for the combined BART determinations and the “BART 

Alternative” to the “Alternative Benchmark” operating scenario. SO2, NOx, and PM emissions were the visibilityimpairing pollutants evaluated. The Class I areas evaluated were the seven areas within a 300 km radius from the

Riley Boiler SO2, NOx, and PM emissions were the visibility-impairing pollutants evaluated.

(b) “BART” includes Riley Boiler with BART for the control of PM, NOx, and SO2 (with the existing baghouse, LNB, 

and Spray Dry FGD), full operation of the B&W Boilers (without LNB), and full operation of the three coal-firing 

pulp dryers.

(c) “BART Alternative” includes the Riley Boiler with BART for the control of PM (with the existing baghouse) and 

with BART for the control of NOx (LNB), the B&W Boilers with the BART Alternative to the control of SO2

(Coal-Firing LNB for each boiler), and shutdown of the three coal-firing pulp dryers. This control scenario 

represents the control equipment described in Permit Condition 3.2.

(d) Values reported in this column represent the relative difference or improvement of the “BART Alternative” over the 

“BART” control scenario.

10.5.5 Natural Gas-Fired Operation

The Riley Boiler was designed to combust coal and/or natural gas fuels. While the initial BART 

determinations were applicable only to coal combustion, supporting discussion was not provided 

which addressed emissions from natural gas combustion in the Statement of Basis for initial Tier 

II Operating Permit No.T22009.0105. Discussion and supporting information are provided below 

which support the requirement to operate Riley BART control equipment only when firing coal 

in the Riley Boiler. Modeling of fuel operating scenarios was completed using the same protocol 

as described in Appendix F(this protocol was also used in the BART modeling analyses for Tier 

II Operating Permit No.)

Comparing the fuel operating scenarios in the table below, coal combustion resulted in higher 

estimated emissions of visibility-impairing pollutants than natural gas combustion, even when 

taking into account the emissions reductions resulting from BART control equipment.
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Table 7 VISIBILITY-IMPAIRING EMISSIONS BY FUEL

Fuel / Control Scenario

PM

lb/hr(a)

SO2

lb/hr(a)

NOx

lb/hr(a)

Coal-Fired Riley Boiler 12.4 522 374

Coal-Fired Riley Boiler with BART 12.4 104 147

Natural Gas-Fired Riley Boiler 7.7 0.2 99

Comparing the fuel operating scenarios in the tables below, coal combustion also resulted in 

higher predicted visibility impacts than natural gas combustion, even when taking into account 

the emissions reductions resulting from BART control equipment.

Table 8 VISIBILITY IMPACTS BY FUEL – EAGLE CAP (a)

Fuel / Control Scenario

22nd Highest 

Impact

Impairment

Contribution

(b)

Coal-Fired Riley Boiler w/ Baghouse 1.086 97

Coal-Fired Riley Boiler w/ Baghouse,

Spray Dry FGD, LNB 0.343 5

Natural Gas-Fired Riley Boiler 0.166 0

(a) This table summarizes modeled visibility impacts for the Riley Boiler with the existing baghouse and coal-fired, the 

Riley Boiler with BART controls and coal-fired, and for the Riley Boiler natural gas-fired (without controls) 

operating scenarios; detailed technical information can be found in Appendix F Revised TASCO BART 

Determination and Modeling for SO2, NOx, and PM emissions were the visibility-impairing pollutants evaluated.

(b) Δdv = delta deciviews; result is based on changes to visibility at the Eagle Cap Wilderness Area.
Page | 13

Table 9 VISIBILITY IMPACTS FOR NATURAL GAS (a)

Class I Area(a)

Natural Gas

22nd

Highest

Days

Eagle Cap Wilderness, OR 0.166 0

Craters of the Moon National Monument, ID 0.028 0

Hells Canyon National Recreation Area, ID 0.106 0

Jarbidge Wilderness, NV 0.029 0

Sawtooth Wilderness, ID 0.034 0

Selway-Bitterroot Wilderness, ID 0.028 0

Strawberry Mountain Wilderness, OR 0.099 0

Total Number of Days 0

(a) This table summarizes modeled visibility impacts for the Riley Boiler with the existing baghouse and coal fired, the 

Riley Boiler with BART controls and coal fired, and for the Riley Boiler natural gas fired (without controls) operating 

scenarios; detailed technical information can be found in Appendix F Revised TASCO BART Determination and 

Modeling for SO2, NOx, and PM emissions were the visibility-impairing pollutants evaluated.

(b) Δdv = delta deciviews; result is based on changes to visibility at the Eagle Cap Wilderness Area.

As provided, the emissions and modeled visibility impacts when firing 100% natural gas were 

predicted to be significantly lower than when firing coal in the Riley Boiler, even when 

accounting for the use of BART controls. It was therefore considered reasonable to determine the 

“base case” or “no control” options as BART for the control of PM, SO2, and NOx emissions 

when combusting 100% natural gas. As an operational requirement and for compliance 

monitoring purposes, monitoring of average daily feed or firing rate and hours of operation per 

day for each fuel has been required in lieu of complying with explicit BART emission rate limits. 

As a result, operation of the Riley Boiler on 100% natural gas after the BART compliance date 

remains a voluntary “compliance option” in lieu of installing BART and BART Alternative 

control equipment. Operation of BART and BART Alternative control devices is also not 

required (if installed) when Riley Boiler is fired exclusively on natural gas, unless required in 

another permit for other (non-BART) reasons.