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Summary of EPA’s Additional Visibility Improvement Modeling 

EPA performed additional modeling of NOx control scenarios for both BART and 

reasonable progress sources. All Region 8 modeling files are available upon request. Contact 

Laurel Dygowski at dygowski.laurel@epa.gov. For baseline emissions, the BART Guidelines 

recommend that states use the maximum 24-hour average actual emission rate for the 

meteorological period being modeled. The visibility modeling performed by PacifiCorp, and 

subsequently submitted by the state, deviates from this guidance by using the permit limit

emission rates and maximum rated heat input to derive the modeled emission rates instead of the

actual maximum 24-hour average. The visibility modeling performed by Basin Electric, and 

subsequently submitted by the state, also deviates from this guidance by using a baseline hourly emission 

rates derived from actual annual average heat input (MMBtu) and actual annual average emission rates

(lb/MMBtu) from 2001-2003 continuous emissions monitoring (CEM) data. For consistency, EPA’s

additional modeling to ascertain visibility improvements from individual NOx controls used the 

state’s baseline emission rates for the Pacificorp sites and Basin Electric’s Laramie River Station. All 

other aspects of EPA’s additional visibility modeling followed the recommendations made in the BART 

Guidelines.

 The tables beginning on page 4 show the CALPUFF inputs used for each unit modeled. 

EPA’s modeling modified the state of Wyoming’s inputs in order to isolate the impact of 

different NOx control scenarios. As seen in the tables, the NOx emission rates were varied 

across the different scenarios with the other input parameters held constant. For the Pacificorp 

and Basin Electric BART sources, the inputs were derived from the state of Wyoming’s BART 

Application Analyses that can be downloaded from the following website: 

http://deq.state.wy.us/aqd/309(g)%20Attachment%20A_January%202011%20Submittal.asp
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EPA’s modeling utilized the emission and stack parameter CALPUFF inputs from “Post-Control 

Scenario A” in the reports for its Scenarios 1-3 with the only difference between scenarios being 

the emission rate for NOx and, in the SCR scenarios, total sulfate rates were increased to account 

for the additional production that results from SCR controls. EPA’s “New Baseline” is

essentially the state’s “Post-Control Scenario A” but with the NOx emission rate from their 

“Baseline” scenario. Table 1 summarizes the control scenarios from EPA’s additional modeling 

for BART sources.

Table 1- Description of EPA control scenarios for Wyoming’s BART sources

EPA Scenario Description

New Baseline Post-Control Scenario A from state‘s BART Application Analysis with NOx 

emission rate from state’s “Baseline” scenario

Scenario 1 Post-Control Scenario A from state’s BART Application Analysis with NOx 

emission rate that reflects the visibility improvement from LNB/OFA controls.

Scenario 2 Post-Control Scenario A from state’s BART Application Analysis with NOx 

emission rate that reflects the visibility improvement from SNCR controls

Scenario 3 Post-Control Scenario A from state’s BART Application Analysis with NOx 

emission rate that reflects the visibility improvement from SCR controls

EPA also performed additional modeling for Dave Johnston’s Units 1 and 2. These are 

considered reasonable progress sources and were not part of the state’s BART Application 

Analyses. EPA followed a similar approach for modeling these sources as used for the BART 

sources. Permit limit emission rates with heat input were used to derive emission inputs in the 

“New Baseline” scenario. Similar to the BART sources, the only differences in the control

scenarios are the emission rates for NOx and, in the SCR scenario (Scenario 3), total sulfate rates 

were increased to account for the additional production that results from SCR controls. Stack 

parameter data for these sources was obtained from the Western Region Air Partnership’s 

(WRAP) 2002 SMOKE input files. Table 2 summarizes the control scenarios for EPA’s 

reasonable progress source modeling.
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Table 2 – Description of EPA control scenarios for Reasonable Progress sources (Dave 

Johnston Units 1 and 2)

EPA Scenario Description

New Baseline Inputs obtained from facility’s Title V Operating Permit limits

Scenario 0 Same inputs as New Baseline with a NOx emission rate that reflect visibility

improvements from LNB controls

Scenario 1 Same inputs as New Baseline with a NOx emission rate that reflect visibility

improvements from LNB/OFA controls

Scenario 2 Same inputs as New Baseline with a NOx emission rate that reflect visibility

improvements from SNCR controls

Scenario 3 Same inputs as New Baseline with a NOx emission rate that reflect visibility

improvements from SCR controls
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Pacificorp - Dave Johnston Unit 3

New Baseline Scenario 1 Scenario 2 Scenario 3

Hourly Heat Input 

(mmBtu/hour) 2800 2800 2800 2800

Emission

Rates

SO2 (lb/MMBtu) 0.15 0.15 0.15 0.15

Nox (lb/MMBtu) 0.7 0.28 0.19 0.07

Calpuff 

Inputs

SO2 (lb/hr) 420 420 420 420

Total Sulfate (SO4)(lb/hr) 2.5 2.5 2.5 5.1

Nox (lb/hr) 1960 784 532 196

HNO3 0 0 0 0

NO3 0 0 0 0

PM10-2.5 (coarse PM)(lb/hr) 23.9 23.9 23.9 23.9

PM2.5 (lb/hr) 18.1 18.1 18.1 18.1

Stack Height (meters) 152.4 152.4 152.4 152.4

Base Elevation (meters) 1509 1509 1509 1509

Stack Diameter (meters) 4.57 4.57 4.57 4.57

Exit Velocity (meters/second) 25.5 25.5 25.5 25.5

Exit Temperature (Kelvin) 348 348 348 348

Pacificorp - Dave Johnston Unit 4

New Baseline Scenario 1 Scenario 2 Scenario 3

Hourly Heat Input 

(mmBtu/hour) 4100 4100 4100 4100

Emission

Rates

SO2 (lb/MMBtu) 0.15 0.15 0.15 0.15

Nox (lb/MMBtu) 0.4 0.15 0.12 0.07

Calpuff 

Inputs

SO2 (lb/hr) 615 615 615 615

Total Sulfate (SO4)(lb/hr) 3.7 3.7 3.7 7.4

Nox (lb/hr) 1640 615 492 287

HNO3 0 0 0 0

NO3 0 0 0 0

PM10-2.5 (coarse PM)(lb/hr) 35.1 35.1 35.1 35.1

PM2.5 (lb/hr) 26.4 26.4 26.4 26.4

Stack Height (meters) 152 152 152 152

Base Elevation (meters) 1509 1509 1509 1509

Stack Diameter (meters) 5.79 5.79 5.79 5.79

Exit Velocity (meters/second) 25.7 25.7 25.7 25.7

Exit Temperature (Kelvin) 350 350 350 350
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Pacificorp - Jim Bridger Unit 1

New Baseline Scenario 1 Scenario 2 Scenario 3

Hourly Heat Input 

(mmBtu/hour) 6000 6000 6000 6000

Emission

Rates

SO2 (lb/MMBtu) 0.15 0.15 0.15 0.15

Nox (lb/MMBtu) 0.45 0.26 0.2 0.07

Calpuff 

Inputs

SO2 (lb/hr) 900 900 900 900

Total Sulfate (SO4)(lb/hr) 54.1 54.1 54.1 108.1

Nox (lb/hr) 2700 1560 1200 420

HNO3 0 0 0 0

NO3 0 0 0 0

PM10-2.5 (coarse PM)(lb/hr) 77.4 77.4 77.4 77.4

PM2.5 (lb/hr) 102.6 102.6 102.6 102.6

Stack Height (meters) 152 152 152 152

Base Elevation (meters) 2036 2036 2036 2036

Stack Diameter (meters) 7.32 7.32 7.32 7.32

Exit Velocity (meters/second) 24.7 24.7 24.7 24.7

Exit Temperature (Kelvin) 328 328 328 328

Pacificorp - Jim Bridger Unit 2

New Baseline Scenario 1 Scenario 2 Scenario 3

Hourly Heat Input 

(mmBtu/hour) 6000 6000 6000 6000

Emission

Rates

SO2 (lb/MMBtu) 0.15 0.15 0.15 0.15

Nox (lb/MMBtu) 0.24 0.26 0.2 0.07

Calpuff 

Inputs

SO2 (lb/hr) 900 900 900 900

Total Sulfate (SO4)(lb/hr) 54.1 54.1 54.1 108.1

Nox (lb/hr) 1440 1560 1200 420

HNO3 0 0 0 0

NO3 0 0 0 0

PM10-2.5 (coarse PM)(lb/hr) 77.4 77.4 77.4 77.4

PM2.5 (lb/hr) 102.6 102.6 102.6 102.6

Stack Height (meters) 152 152 152 152

Base Elevation (meters) 2036 2036 2036 2036

Stack Diameter (meters) 7.32 7.32 7.32 7.32

Exit Velocity (meters/second) 24.7 24.7 24.7 24.7

Exit Temperature (Kelvin) 328 328 328 328

Pacificorp - Jim Bridger Unit 4
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New Baseline Scenario 1 Scenario 2 Scenario 3

Hourly Heat Input 

(mmBtu/hour) 6000 6000 6000 6000

Emission

Rates

SO2 (lb/MMBtu) 0.15 0.15 0.15 0.15

Nox (lb/MMBtu) 0.45 0.26 0.2 0.07

Calpuff 

Inputs

SO2 (lb/hr) 900 900 900 900

Total Sulfate (SO4)(lb/hr) 54.1 54.1 54.1 108.1

Nox (lb/hr) 2700 1560 1200 420

HNO3 0 0 0 0

NO3 0 0 0 0

PM10-2.5 (coarse PM)(lb/hr) 77.4 77.4 77.4 77.4

PM2.5 (lb/hr) 102.6 102.6 102.6 102.6

Stack Height (meters) 152 152 152 152

Base Elevation (meters) 2033 2033 2033 2033

Stack Diameter (meters) 9.45 9.45 9.45 9.45

Exit Velocity (meters/second) 12.9 12.9 12.9 12.9

Exit Temperature (Kelvin) 322 322 322 322

Pacificorp - Naughton Unit 1

New Baseline Scenario 1 Scenario 2 Scenario 3

Hourly Heat Input 

(mmBtu/hour) 1850 1850 1850 1850

Emission

Rates

SO2 (lb/MMBtu) 0.15 0.15 0.15 0.15

Nox (lb/MMBtu) 0.58 0.26 0.21 0.07

Calpuff 

Inputs

SO2 (lb/hr) 278 278 278 278

Total Sulfate (SO4)(lb/hr) 16.7 16.7 16.7 33.3

Nox (lb/hr) 1073 481 389 130

HNO3 0 0 0 0

NO3 0 0 0 0

PM10-2.5 (coarse PM)(lb/hr) 33.4 33.4 33.4 33.4

PM2.5 (lb/hr) 44.3 44.3 44.3 44.3

Stack Height (meters) 145 145 145 145

Base Elevation (meters) 2115 2115 2115 2115

Stack Diameter (meters) 4.88 4.88 4.88 4.88

Exit Velocity (meters/second) 18.1 18.1 18.1 18.1

Exit Temperature (Kelvin) 323 323 323 323
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Pacificorp - Naughton Unit 2

New Baseline Scenario 1 Scenario 2 Scenario 3

Hourly Heat Input 

(mmBtu/hour) 2400 2400 2400 2400

Emission

Rates

SO2 (lb/MMBtu) 0.15 0.15 0.15 0.15

Nox (lb/MMBtu) 0.54 0.26 0.21 0.07

Calpuff 

Inputs

SO2 (lb/hr) 360 360 360 360

Total Sulfate (SO4)(lb/hr) 21.6 21.6 21.6 43.2

Nox (lb/hr) 1296 624 504 168

HNO3 0 0 0 0

NO3 0 0 0 0

PM10-2.5 (coarse PM)(lb/hr) 55.7 55.7 55.7 55.7

PM2.5 (lb/hr) 73.9 73.9 73.9 73.9

Stack Height (meters) 145 145 145 145

Base Elevation (meters) 2115 2115 2115 2115

Stack Diameter (meters) 5.49 5.49 5.49 5.49

Exit Velocity (meters/second) 18.5 18.5 18.5 18.5

Exit Temperature (Kelvin) 323 323 323 323

Pacificorp - Naughton Unit 3

New Baseline Scenario 1 Scenario 2 Scenario 3

Hourly Heat Input 

(mmBtu/hour) 3700 3700 3700 3700

Emission

Rates

SO2 (lb/MMBtu) 0.22 0.22 0.22 0.22

Nox (lb/MMBtu) 0.45 0.37 0.3 0.07

Calpuff 

Inputs

SO2 (lb/hr) 814 814 814 814

Total Sulfate (SO4)(lb/hr) 33.3 33.3 33.3 66.6

Nox (lb/hr) 1665 1369 1110 259

HNO3 0 0 0 0

NO3 0 0 0 0

PM10-2.5 (coarse PM)(lb/hr) 23.9 23.9 23.9 23.9

PM2.5 (lb/hr) 31.6 31.6 31.6 31.6

Stack Height (meters) 145 145 145 145

Base Elevation (meters) 2113 2113 2113 2113

Stack Diameter (meters) 8.08 8.08 8.08 8.08

Exit Velocity (meters/second) 20.2 20.2 20.2 20.2

Exit Temperature (Kelvin) 322 322 322 322
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Pacificorp – Wyodak

Note: CALPUFF inputs for Pacificorp’s Wyodak facility were inadvertently left out of the original 

“CALPUFF Modeling Summary” file. 

New Baseline Scenario 1 Scenario 2 Scenario 3

Hourly Heat Input 

(mmBtu/hour) 4700 4700 4700 4700

Emission

Rates

SO2 (lb/MMBtu) 0.16 0.16 0.16 0.16

Nox (lb/MMBtu) 0.31 0.23 0.18 0.07

Calpuff 

Inputs

SO2 (lb/hr) 759 759 759 759

Total Sulfate (SO4)(lb/hr) 5.5 5.5 5.5 11.6

Nox (lb/hr) 1457 1081 846 329

HNO3 0 0 0 0

NO3 0 0 0 0

PM10-2.5 (coarse PM)(lb/hr) 70.5 70.5 70.5 70.5

PM2.5 (lb/hr) 40.2 40.2 40.2 40.2

Stack Height (meters) 122 122 122 122

Base Elevation (meters) 1347 1347 1347 1347

Stack Diameter (meters) 6.1 6.1 6.1 6.1

Exit Velocity (meters/second) 23.5 23.5 23.5 23.5

Exit Temperature (Kelvin) 350 350 350 350
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Basin Electric – Laramie River Station Unit 1

New Baseline Scenario 1 Scenario 2 Scenario 3

Hourly Heat Input 

(mmBtu/year) 46814433 46814433 46814433 46814433

Emission

Rates

SO2 (lb/MMBtu) 0.16 0.16 0.16 0.16

Nox (lb/MMBtu) 0.27 0.23 0.12 0.07

Calpuff 

Inputs

SO2 (tpy) 3745 3745 3745 3745

Total Sulfate (SO4)(tpy) 3.06 3.18 3.18 3.18

Nox (tpy) 6320 5384 2809 1639

HNO3 0 0 0 0

NO3 0 0 0 0

PM10-2.5 (coarse PM)(tpy) 0 0 0 0

PM2.5 (tpy) 702 702 702 702

Stack Height (meters) 184.404 184.404 184.404 184.404

Base Elevation (meters) 1348 1348 1348 1348

Stack Diameter (meters) 8.6868 8.6868 8.6868 8.6868

Exit Velocity (meters/second) 21.336 21.336 21.336 21.336

Exit Temperature (Kelvin) 338.7056 338.7056 338.7056 338.7056

Basin Electric – Laramie River Station Unit 2

New Baseline Scenario 1 Scenario 2 Scenario 3

Hourly Heat Input 

(mmBtu/year) 46557738 46557738 46557738 46557738

Emission

Rates

SO2 (lb/MMBtu) 0.16 0.16 0.16 0.16

Nox (lb/MMBtu) 0.27 0.23 0.12 0.07

Calpuff 

Inputs

SO2 (tpy) 3725 3725 3725 3725

Total Sulfate (SO4)(tpy) 2.8 3.25 3.25 3.25

Nox (tpy) 6285 5354 2793 1630

HNO3 0 0 0 0

NO3 0 0 0 0

PM10-2.5 (coarse PM)(tpy) 0 0 0 0

PM2.5 (tpy) 698 698 698 698

Stack Height (meters) 184.404 184.404 184.404 184.404

Base Elevation (meters) 1348 1348 1348 1348

Stack Diameter (meters) 8.6868 8.6868 8.6868 8.6868

Exit Velocity (meters/second) 21.03 21.03 21.03 21.03

Exit Temperature (Kelvin) 338.7056 338.7056 338.7056 338.7056
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Basin Electric – Laramie River Station Unit 3

New Baseline Scenario 1 Scenario 2 Scenario 3

Hourly Heat Input 

(mmBtu/year) 47765529 47765529 47765529 47765529

Emission

Rates

SO2 (lb/MMBtu) 0.17 0.17 0.17 0.17

Nox (lb/MMBtu) 0.27 0.23 0.12 0.07

Calpuff 

Inputs

SO2 (tpy) 4060 4060 4060 4060

Total Sulfate (SO4)(tpy) 0.22 0.22 0.22 0.22

Nox (tpy) 6448 5493 2866 1672

HNO3 0 0 0 0

NO3 0 0 0 0

PM10-2.5 (coarse PM)(tpy) 0 0 0 0

PM2.5 (tpy) 716 716 716 716

Stack Height (meters) 184.404 184.404 184.404 184.404

Base Elevation (meters) 1348 1348 1348 1348

Stack Diameter (meters) 8.6868 8.6868 8.6868 8.6868

Exit Velocity (meters/second) 22.25 22.25 22.25 22.25

Exit Temperature (Kelvin) 352.0 352.0 352.0 352.0
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Reasonable Progress Sources

Dave Johnston Unit 1

New 

Baseline

Scenario 

0

Scenario 

1

Scenario 

2

Scenario 

3

Hourly Heat Input 

(mmBtu/hour) 1350 1350 1350 1350 1350

Emission

Rates

SO2 (lb/MMBtu) 1.2 1.2 1.2 1.2 1.2

Nox (lb/MMBtu) 0.75 0.3675 0.2625 0.45 0.15

Calpuff 

Inputs

SO2 (lb/hr) 1620 1620 1620 1620 0

Total Sulfate (SO4)(lb/hr) 1 1 1 1 2

Nox (lb/hr) 1012.5 496.125 354.375 607.5 202.5

HNO3 0 0 0 0 0

NO3 0 0 0 0 0

PM10-2.5 (coarse PM)(lb/hr) 149.726 149.726 149.726 149.726 149.726

PM2.5 (lb/hr) 198.474 198.474 198.474 198.474 198.474

Stack Height (meters) 152.4 152.4 152.4 152.4 152.4

Base Elevation (meters) 1509 1509 1509 1509 1509

Stack Diameter (meters) 3.35 3.35 3.35 3.35 3.35

Exit Velocity (meters/second) 28.35 28.35 28.35 28.35 28.35

Exit Temperature (Kelvin) 418.15 418.15 418.15 418.15 418.15

Dave Johnston Unit 2

New 

Baseline

Scenario 

0

Scenario 

1

Scenario 

2

Scenario 

3

Hourly Heat Input 

(mmBtu/hour) 1350 1350 1350 1350 1350

Emission

Rates

SO2 (lb/MMBtu) 1.2 1.2 1.2 1.2 1.2

Nox (lb/MMBtu) 0.75 0.3675 0.2625 0.45 0.15

Calpuff 

Inputs

SO2 (lb/hr) 1620 1620 1620 1620 1620

Total Sulfate (SO4)(lb/hr) 1 1 1 1 2

Nox (lb/hr) 1012.5 496.125 354.375 607.5 202.5

HNO3

NO3

PM10-2.5 (coarse PM)(lb/hr) 149.726 149.726 149.726 149.726 149.726

PM2.5 (lb/hr) 198.474 198.474 198.474 198.474 198.474

Stack Height (meters) 152.4 152.4 152.4 152.4 152.4

Base Elevation (meters) 1509 1509 1509 1509 1509

Stack Diameter (meters) 3.35 3.35 3.35 3.35 3.35

Exit Velocity (meters/second) 28.69 28.69 28.69 28.69 28.69

Exit Temperature (Kelvin) 425.93 425.93 425.93 425.93 425.93