SUPPLEMENT

Air Quality Modeling Protocol: Utah Regional Haze Federal 

Implementation Plan [November 2015]

May 2016

U.S. Environmental Protection Agency

Region 8

Denver, CO 80202
2

S.1.0 BACKGROUND

In evaluating the Utah’s State Implementation Plan (SIP) revisions and the supporting 

information submitted by the State, EPA Region 8 determined that the analysis conducted for the 

BART Alternatives could not support the analysis of control options for individual BART 

sources under a five factor analysis. As a result, EPA developed separate CALPUFF modeling in 

November 2015 to support the Utah Regional Haze Federal Implementation Plan (UT RH FIP)

and its five factor analysis. The EPA Region 8 modeling conducted in November 2015 assessed

the impacts of the individual BART sources, and assessed the visibility impacts of all of the 

nitrogen oxide (NOx) BART control technologies found to be technologically feasible. The 

details of the modeling performed in November 2015 are discussed in the EPA Region 8 “Air 

Quality Modeling Protocol: Utah Regional Haze Federal Implementation Plan” [dated November 

2015] (hereafter referred to as EPA Region 8 Air Quality Modeling Protocol).

EPA Region 8 decided to supplement the modeling conducted in November 2015 with additional 

analyses. The intent of our supplemental modeling is to determine the combined visibility 

benefits when the selected BART controls are applied to each BART source as a whole. For 

example, we analyzed the benefits when LNB/OFA/SCR is simultaneously applied to both Unit 

1 and Unit 2 at the Hunter BART source (but not the non-BART unit, Unit 3). Similarly, we 

analyzed the visibility benefits when LNB/OFA/SCR is simultaneously applied to both Unit 1 

and Unit 2 at the Huntington BART source. This document describes the additional analyses 

completed by EPA Region 8 and serves as a supplement to the EPA Region 8 Air Quality 

Modeling Protocol.

S.2.0 MODELING APPROACH

This section describes the model assumptions and methodology used in the supplemental 

CALPUFF modeling analysis, including emission sources, control technologies, model 

scenarios, and post-processing methods. In general, the input assumptions used in all of the 

CALPUFF modules (CALMET, CALPUFF, POSTUTIL, and CALPOST) remained the same. 

However, the supplemental analysis used different combinations of selected source units and 

control technologies to predict visibility impacts. The details of the additional analysis are 

described in the subsequent sections.

S.2.1 Emission Sources and Model Scenarios

The sources that EPA Region 8 modeled are listed in Table 1. These include the BART units 

Hunter 1 and 2 and Huntington 1 and 2. It also includes Hunter Unit 3 even though this unit is

not part of the Hunter BART source. This unit was modeled in order to account for the unit’s 

emission contributions when modeling the other units for this source. These sources were still 

considered in the supplemental analysis. 

Table S.1. Emissions Sources Modeled by EPA

Company Name Plant Name Units

PacifiCorp Hunter Plant Boilers #1,2,3 

PacifiCorp Huntington Plant Boilers #1,2
3

The details of the emissions data and model input assumptions are discussed in Appendix B of 

the EPA Region 8 Air Quality Modeling Protocol. Briefly, EPA modeled one baseline scenario 

(referenced as Baseline) for each source and unit listed in Table S.1. EPA also modeled three 

control scenarios for each source and unit listed in Table S.1. To isolate the impact of different 

NOx control technologies, the control scenarios consisted of:

1. Low NOx Burners (LNB) with Separated Over-Fire Air (OFA) (Scenario: LNB/OFA), 

2. LNB and OFA Selective Non-Catalytic Reduction (SNCR) (Scenario: 

LNB/OFA/SNCR), and 

3. LNB and OFA with Selective Non-Catalytic Reduction (SCR) conditions 

(LNB/OFA/SCR).

For this analysis, EPA Region 8 focused on the Baseline and LNB/OFA/SCR scenarios 

previously modeled for the sources and units in Table S.1. As noted above, the source 

parameterizations or input assumptions for these scenarios were not changed in the supplemental 

analysis.

For the November 2015 modeling, EPA Region 8 modeled each unit and scenario separately in 

CALPUFF to isolate the impact of different NOx control technologies for individual BART 

sources under a five factor analysis. As a result, there was not need to redo any of the CALPUFF 

simulations in the supplemental analysis. However, because this analysis focuses on different 

combinations of selected source units and control technologies to predict visibility impacts in 

ammonia-limited conditions, additional POSTUTIL and CALPOST simulations, or postprocessing of the CALPUFF results, were completed for the supplemental analysis. The 

additional post-processing scenarios using the CALPUFF results are described in the following 

section.

S.2.2 Post-Processing

Visibility impacts were calculated from the CALPUFF concentration results using POSTUTIL 

and CALPOST. Similar to the modeling conducted in November 2015, this analysis combines 

multiple units from a single source with the use of POSTUTIL to repartition total nitrate by 

accounting for ammonia-limiting conditions for each model scenario. Aside from changing the 

combination of the CALPUFF output files, the input assumptions and configurations of 

POSTUTIL and CALPOST remained the same. In particular, the supplemental analysis 

continued to assume MNITRATE=1 and constant 1.0 ppb background ammonia concentrations. 

Details of the parameter settings in POSTUTIL and CALPOST are provided in the EPA Region 

8 Air Quality Modeling Protocol Appendix F and Appendix G, respectively. 

A total of three additional model cases, using the sources, units, and control technologies 

outlined above, were considered in the supplemental analysis. In particular, the supplemental 

analysis examined the visibility impacts of excluding and including unit 3 from the Hunter Plant

in the POSTUTIL post-processing. Note that the November 2015 modeling included unit 3 in all 

of the POSTUTIL post-processing for Hunter. The supplemental analysis also explored the 

visibility impacts when assuming that all the BART units had the same control technology in the 

POSTUTIL post-processing. For instance, the CALPUFF data file for the LNB/OFA/SCR 

control scenario for unit 1 of the Huntington Plant was combined with the CALPUFF data file 
4

for the LNB/OFA/SCR control scenario for Huntington unit 2. This is difference from the 

November 2015 modeling because the November 2015 modeling combined the control scenario 

from the unit of interest with the baseline results from the remaining units in the POSTUTIL 

post-processing. The EPA model cases and POSTUTIL modeling combinations are outlined in 

Table S.2. 

 Table S.2. POSTUTIL Modeling Combinations

EPA Model Case EPA Scenario POSTUITL Combination

#1

Baseline #1

Hunter Units

Hunter – Unit 1: Baseline Source Assumptions

Hunter – Unit 2: Baseline Source Assumptions

LNB/OFA and SCR #1

Hunter Units

Hunter – Unit 1: LNB/OFA and SCR Source Assumptions

Hunter – Unit 2: LNB/OFA and SCR Source Assumptions

#2

Baseline #2

Hunter Units

Hunter – Unit 1: Baseline Source Assumptions

Hunter – Unit 2: Baseline Source Assumptions

Hunter – Unit 3: Baseline Source Assumptions

LNB/OFA and SCR #2

Hunter Units

Hunter – Unit 1: LNB/OFA and SCR Source Assumptions

Hunter – Unit 2: LNB/OFA and SCR Source Assumptions

Hunter – Unit 3: LNB/OFA and SCR Source Assumptions

#3

Baseline

Huntington Units

Huntington – Unit 1: Baseline Source Assumptions

Huntington – Unit 2: Baseline Source Assumptions

LNB/OFA and SCR

Huntington Units

Huntington – Unit 1: LNB/OFA and SCR Source Assumptions

Huntington – Unit 2: LNB/OFA and SCR Source Assumptions

S.3.0 PRESENTATION OF RESULTS AND REPORTING

Visibility impacts were tabulated using the output from CALPOST. The visibility impacts are 

reported in Appendix S.A of this supplement. This includes the impacts for each BART source at 

all modeled Class I areas and meteorological years selected for this modeling. The analysis of the 

results are outlined below:

• The 98th percentile value was reported to three decimal places because of the level of 

precision reported by CALPOST. This value was based on the 8th highest day for each 

year. The results are reported for each source, model scenario, Class I area, and model 

year. (see Appendix S.A, Tables S.A.1 to S.A.2)

• The change in visibility based on the 98th percentile deciview change relative to the 20

percent best days natural background conditions. This is based on the difference between 

the baseline and control scenario for the same year. The results are reported for each 

source, model scenario, Class I area, and model year. (see Appendix S.A, Tables S.A.1 to 

S.A.2)

• The maximum change in visibility based on the 98th percentile deciview change relative 

to the 20 percent best days natural background conditions for each source, model 

scenario, and Class I area. This is based on the maximum improvement (i.e., difference 
5

between the baseline and control scenario for the same model year) among the three 

meteorological years at each Class I area. (see Appendix S.A, Tables S.A.3 to S.A.4).

• The number of days with impacts greater than 0.5 and 1.0 Δdv. The results are reported 

for each source, model scenario, Class I area, and model year. (see Appendix S.A, Tables 

S.A.5 to S.A.6).

• The total number of days between 2001 and 2003 with impacts greater than 0.5 and 1.0 

Δdv. The results are reported for each source unit, model scenario, and Class I area. (see 

Appendix S.A, Tables S.A.7 to S.A.8).
6

APPENDIX S.A – VISIBILITY IMPACT RESULTS

Table S.A.1 – Predicted Visibility Impacts for Pacificorp – Hunter Units (EPA Model Cases #1 and #2).

Class I Area Year

EPA Model Case #1 EPA Model Case #2

Baseline #1

(Includes Units 1 & 2 

Excludes Unit 3)

LNB/SOFA/SCR #1

(Includes Units 1 & 2 with SCR

Excludes Unit 3)

Baseline #2

(Includes Units 1 to 3)

LNB/SOFA/SCR #2

(Includes Units 1 & 2 with SCR

Includes Baseline Unit 3)

98th Percentile 

Impact (∆dv)

98th Percentile 

Impact (∆dv)

Visibility 

Improvement (∆dv)

98th Percentile 

Impact (∆dv)

98th Percentile 

Impact (∆dv)

Visibility 

Improvement (∆dv)

Arches NP

2001 3.773 0.854 2.919 4.601 1.981 2.620

2002 3.612 0.959 2.653 4.362 1.895 2.467

2003 2.907 0.701 2.206 3.575 1.577 1.998

Black Canyon NP

2001 0.657 0.153 0.504 0.855 0.318 0.537

2002 0.865 0.289 0.576 1.097 0.481 0.616

2003 0.750 0.181 0.569 0.954 0.398 0.556

Bryce Canyon NP

2001 0.682 0.153 0.529 0.869 0.321 0.548

2002 1.444 0.373 1.071 1.833 0.811 1.022

2003 0.377 0.107 0.270 0.477 0.212 0.265

Canyonlands NP

2001 4.301 1.052 3.249 5.356 2.408 2.948

2002 4.242 1.288 2.954 5.259 2.538 2.721

2003 4.817 1.251 3.566 5.642 2.760 2.882

Capitol Reef NP

2001 3.055 0.675 2.380 3.645 1.702 1.943

2002 3.913 0.958 2.955 4.606 2.171 2.435

2003 3.221 0.813 2.408 3.931 1.805 2.126

Flat Tops 

Wilderness

2001 0.721 0.206 0.515 0.907 0.355 0.552

2002 1.019 0.296 0.723 1.281 0.537 0.744

2003 0.975 0.226 0.749 1.241 0.513 0.728

Grand Canyon NP

2001 0.860 0.201 0.659 1.09 0.474 0.616

2002 1.475 0.348 1.127 1.891 0.730 1.161

2003 0.682 0.168 0.514 0.854 0.351 0.503

Mesa Verde NP

2001 0.965 0.233 0.732 1.208 0.499 0.709

2002 0.860 0.234 0.626 1.08 0.464 0.616

2003 1.053 0.240 0.813 1.327 0.514 0.813

Zion NP

2001 0.763 0.155 0.608 0.963 0.369 0.594

2002 0.755 0.177 0.578 0.957 0.390 0.567

2003 0.180 0.054 0.126 0.223 0.111 0.112
7

Table S.A.2 – Predicted Visibility Impacts for Pacificorp – Huntington Units (EPA Model Case #3).

Class I Area Year

EPA Model Case #3

Baseline LNB/SOFA/SCR

(Includes Units 1 & 2 with SCR)

98th Percentile Impact (∆dv) 98th Percentile Impact (∆dv) Visibility Improvement (∆dv)

Arches NP

2001 3.887 0.848 3.039

2002 2.734 0.867 1.867

2003 3.579 0.936 2.643

Black Canyon NP

2001 0.619 0.172 0.447

2002 0.848 0.282 0.566

2003 0.773 0.196 0.577

Bryce Canyon NP

2001 0.799 0.156 0.643

2002 1.221 0.326 0.895

2003 0.513 0.136 0.377

Canyonlands NP

2001 3.781 1.112 2.669

2002 5.13 1.282 3.848

2003 4.239 1.116 3.123

Capitol Reef NP

2001 2.561 0.558 2.003

2002 3.389 0.986 2.403

2003 2.68 0.636 2.044

Flat Tops Wilderness

2001 0.692 0.230 0.462

2002 0.935 0.302 0.633

2003 0.926 0.216 0.710

Grand Canyon NP

2001 0.996 0.190 0.806

2002 1.107 0.303 0.804

2003 0.767 0.200 0.567

Mesa Verde NP

2001 0.829 0.202 0.627

2002 1.11 0.256 0.854

2003 1.115 0.261 0.854

Zion NP

2001 0.614 0.129 0.485

2002 0.82 0.211 0.609

2003 0.241 0.065 0.176
8

Table S.A.3 – Maximum Predicted Visibility Impacts for Pacificorp – Hunter Units (EPA Model Cases #1 and #2).

Class I Area

EPA Model Case #1 EPA Model Case #2

LNB/SOFA/SCR #1

(Includes Units 1 & 2 with SCR

Excludes Unit 3)

LNB/SOFA/SCR #2

(Includes Units 1 & 2 with SCR

Includes Baseline Unit 3)

Visibility Improvement (∆dv) Visibility Improvement (∆dv)

Arches NP 2.919 2.620

Black Canyon NP 0.576 0.616

Bryce Canyon NP 1.071 1.022

Canyonlands NP 3.566 2.948

Capitol Reef NP 2.955 2.435

Flat Tops Wilderness 0.749 0.744

Grand Canyon NP 1.127 1.161

Mesa Verde NP 0.813 0.813

Zion NP 0.608 0.594

Table S.A.4 – Maximum Predicted Visibility Impacts for Pacificorp – Huntington Units (EPA Model Case #3).

Class I Area

EPA Model Case #3

LNB/SOFA/SCR

(Includes Units 1 & 2 with SCR)

Visibility Improvement (∆dv)

Arches NP 3.039

Black Canyon NP 0.577

Bryce Canyon NP 0.895

Canyonlands NP 3.848

Capitol Reef NP 2.403

Flat Tops Wilderness 0.710

Grand Canyon NP 0.806

Mesa Verde NP 0.854

Zion NP 0.609
9

Table S.A.5 – Predicted Number of Days Greater than 0.5 and 1.0 Δdv for Pacificorp – Hunter Units (EPA Model Cases #1 and #2).

Class I Area Year

EPA Model Case #1 EPA Model Case #2

Baseline #1

(Includes Units 1 & 2 

Excludes Unit 3)

LNB/SOFA/SCR #1

(Includes Units 1 & 2 with SCR

Excludes Unit 3)

Baseline #2

(Includes Units 1 to 3)

LNB/SOFA/SCR #2

(Includes Units 1 & 2 with SCR

Includes Baseline Unit 3)

Number of Days 

∆dv > 0.5

Number of Days 

∆dv > 1.0

Number of Days 

∆dv > 0.5

Number of Days 

∆dv > 1.0

Number of Days 

∆dv > 0.5

Number of Days 

∆dv > 1.0

Number of Days 

∆dv > 0.5

Number of Days 

∆dv > 1.0

Arches NP

2001 71 41 20 5 84 48 44 24

2002 100 56 23 5 117 67 66 25

2003 80 43 17 4 92 55 48 22

Black Canyon 

NP

2001 11 3 0 0 17 4 4 0

2002 23 5 0 0 30 11 5 0

2003 18 5 1 0 21 7 5 1

Bryce Canyon 

NP

2001 13 6 0 0 16 6 6 0

2002 18 9 3 0 21 13 11 5

2003 5 3 1 0 5 3 3 1

Canyonlands 

NP

2001 88 62 25 10 103 70 64 32

2002 122 81 43 10 140 93 90 48

2003 110 65 26 12 116 77 69 31

Capitol Reef 

NP

2001 35 28 13 2 40 30 29 15

2002 63 46 21 7 70 51 49 23

2003 57 32 16 5 65 37 36 17

Flat Tops 

Wilderness

2001 13 4 0 0 16 5 4 1

2002 18 8 1 0 26 13 10 0

2003 30 7 0 0 35 13 8 0

Grand Canyon 

NP

2001 13 7 2 0 16 10 7 4

2002 19 11 5 1 22 15 11 5

2003 9 7 0 0 11 7 7 0

Mesa Verde 

NP

2001 17 7 1 0 23 9 7 3

2002 25 4 0 0 32 12 5 0

2003 22 8 1 0 27 11 9 1

Zion NP

2001 8 4 1 0 11 7 5 1

2002 12 5 3 0 15 5 5 3

2003 3 0 0 0 3 2 0 0
10

Table S.A.6 – Predicted Number of Days Greater than 0.5 and 1.0 Δdv for Pacificorp – Huntington Units (EPA Model Case #3).

Class I Area Year

EPA Model Case #3

Baseline

(Includes Units 1 to 3)

LNB/SOFA/SCR

(Includes Units 1 & 2 with SCR)

Number of Days 

∆dv > 0.5

Number of Days 

∆dv > 1.0

Number of Days 

∆dv > 0.5

Number of Days 

∆dv > 1.0

Arches NP

2001 72 42 22 7

2002 94 57 27 6

2003 71 47 18 5

Black Canyon NP

2001 11 5 0 0

2002 20 5 0 0

2003 14 6 1 0

Bryce Canyon NP

2001 13 5 0 0

2002 15 11 4 0

2003 8 3 0 0

Canyonlands NP

2001 86 53 25 8

2002 109 67 37 13

2003 82 55 27 10

Capitol Reef NP

2001 31 25 9 0

2002 54 40 21 7

2003 46 26 12 2

Flat Tops Wilderness

2001 14 5 0 0

2002 20 6 2 0

2003 30 6 0 0

Grand Canyon NP

2001 10 7 2 0

2002 19 9 2 0

2003 11 3 0 0

Mesa Verde NP

2001 15 5 0 0

2002 25 9 0 0

2003 23 8 0 0

Zion NP

2001 8 6 1 0

2002 10 5 2 0

2003 3 0 0 0
11

Table S.A.7 – Total Predicted Number of Days Greater than 0.5 and 1.0 Δdv between 2001 and 2003 for Pacificorp – Hunter Units (EPA Model Cases #1 and #2).

Class I Area

EPA Model Case #1 EPA Model Case #2

Baseline #1

(Includes Units 1 & 2 

Excludes Unit 3)

LNB/SOFA/SCR #1

(Includes Units 1 & 2 with SCR

Excludes Unit 3)

Baseline #2

(Includes Units 1 to 3)

LNB/SOFA/SCR #2

(Includes Units 1 & 2 with SCR

Includes Baseline Unit 3)

Number of Days 

∆dv > 0.5

Number of Days 

∆dv > 1.0

Number of Days 

∆dv > 0.5

Number of Days 

∆dv > 1.0

Number of Days 

∆dv > 0.5

Number of Days 

∆dv > 1.0

Number of Days 

∆dv > 0.5

Number of Days 

∆dv > 1.0

Arches NP 251 140 60 14 293 170 158 71

Black Canyon NP 52 13 1 0 68 22 14 1

Bryce Canyon NP 36 18 4 0 42 22 20 6

Canyonlands NP 320 208 94 32 359 240 223 111

Capitol Reef NP 155 106 50 14 175 118 114 55

Flat Tops Wilderness 61 19 1 0 77 31 22 1

Grand Canyon NP 41 25 7 1 49 32 25 9

Mesa Verde NP 64 19 2 0 82 32 21 4

Zion NP 23 9 4 0 29 14 10 4

Table S.A.8 – Total Predicted Number of Days Greater than 0.5 and 1.0 Δdv between 2001 and 2003 for Pacificorp – Hunter Units (EPA Model Case #3).

EPA Model Case #3

Class I Area

Baseline LNB/SOFA/SCR

(Includes Units 1 & 2 with SCR)

Number of Days 

∆dv > 0.5

Number of Days 

∆dv > 1.0

Number of Days 

∆dv > 0.5

Number of Days 

∆dv > 1.0

Arches NP 237 146 67 18

Black Canyon NP 45 16 1 0

Bryce Canyon NP 36 19 4 0

Canyonlands NP 277 175 89 31

Capitol Reef NP 131 91 42 9

Flat Tops Wilderness 64 17 2 0

Grand Canyon NP 40 19 4 0

Mesa Verde NP 63 22 0 0

Zion NP 21 11 3 0