DEPARTMENT OF ENVIRONMENTAL QUALITY

AIR QUALITY DIVISION

Revised NOx BART Impact Analysis

AP-6047A

January 3, 2011

NAME OF FIRM: Basin Electric Power Cooperative

NAME OF FACILITY: Laramie River Station

FACILITY LOCATION: 347 Grayrocks Road

Platte County (Wheatland), Wyoming

UTM Zone 13, NAD 27:

509,900 m E; 4,661,675 m N 

TYPE OF OPERATION: Electric Power Generating Station

RESPONSIBLE OFFICIAL: Mr. Robert Eriksen

MAILING ADDRESS: 1717 East Interstate Avenue

Bismarck, North Dakota 58503

TELEPHONE NUMBER: (701) 355-5654

REVIEWERS: Cole Anderson, Air Quality Engineer

Josh Nall, Air Quality Modeler

1. INTRODUCTION

The Division of Air Quality of the Wyoming Department of Environmental Quality issued NOx

and PM Best Available Retrofit Technology (BART) determinations for Basin Electric Power 

Cooperative’s (Basin Electric) Laramie River Station in Air Quality Permit MD-6047. The 

permit was issued on December 31, 2009. On March 8, 2010, Basin Electric filed an appeal and 

petition for review with the Wyoming Environmental Quality Council (EQC), in accordance with 

Chapter I, Section 16, of the Department of Environmental Quality’s General Rules of Practice 

and Procedure. Basin Electric appealed Air Quality Permit MD-6047 and petitioned EQC to 

review the AQD’s permit Condition 16 regarding additional add-on NOx controls. Permit 

conditions 1 through 15 were not subject to appeal or protest. EQC established Docket No. 10-

2802 for the appeal and petition for review. Basin Electric and the AQD entered into settlement 

negotiations and through negotiation were able to reach a settlement. On November 16, 2010, the 

AQD and Basin Electric filed a proposed settlement with the EQC. A copy of the settlement is 

attached as Appendix A. Subsequently, EQC issued two orders, one approving the settlement 

agreement and staying appeal pending final dismissal and one denying Basin Electric’s motion 

for summary judgment, on November 19, 2010.

This analysis presents a summary of modeling conducted to predict visibility impacts from the 

BART emissions levels associated with the settlement agreement. Additional NOx emissions 

reductions achieved in the settlement, which are beyond BART, are discussed in the Long-Term 

Strategy section of this analysis.
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2. REVISED IMPACT ANALYSIS

Modeling was conducted by the AQD using the EPA CALPUFF modeling system, with the same 

CALMET/CALPUFF/CALPOST setup that was used for previous BART modeling of the LRS. 

In particular, the AQD used the larger CALMET windfield that was described on Page 24 and 

shown in Figure 3 of the AQD’s BART Application Analysis for MD-6047 (May 28, 2009). 

Although this larger CALMET windfield included Rawah Wilderness Area and Rocky Mountain 

National Park in Colorado, previous refined CALPUFF modeling by the AQD showed that 

predicted visibility impacts at these two Class I areas were less than 0.5 dv for the baseline 

scenario for each of the three units at the LRS, and therefore the AQD focused on Wind Cave and 

Badlands national parks in South Dakota for the modeling described here. 

Visibility modeling was conducted for the following emissions scenarios:

• Baseline from the BART Application Analysis for MD-6047

• NOx emissions from BART Permit MD-6047 (0.23 lb/MMBtu, 30-day rolling)

• NOx emissions from BART Settlement Agreement (0.21 lb/MMbtu, 30-day rolling)

• NOx Add-On Controls (SCR)

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Tables 2-1 and 2-2 list the modeling parameters and emission rates that were used for the 

modeling for Units 1 through 3 at the LRS. 

Table 2-1: Baseline Source Parameters

Parameter Unit 1: LNB, 

WFGD, ESP

Unit 2: LNB, 

WFGD, ESP

Unit 3: LNB, 

DFGD, ESP

Heat Input (MMBtu/yr) 46,814,433 46,557,738 47,765,529 

Base Elevation (m) 1348 1348 1348

Stack Height (m) 184.4 184.4 184.40

Stack Diameter (m) 8.69 8.69 8.69

Stack Temperature (K) 338.7 338.7 352.0

Exit Velocity (m/s) 21.33 21.03 22.25

SO2 Emissions (lb/MMBtu) 0.16 0.16 0.17

SO2 Emissions (tpy) 3745 3725 4060

HS2O4 Emissions (tpy) 3.06 2.80 0.22

NOx Emissions (lb/MMBtu) 0.27 0.27 0.27

NOx Emissions (tpy) 6320 6285 6448

PM Fine Emissions (lb/MMBtu) 0.03 0.03 0.03

PM Fine Emissions (tpy) 702 698 716

Note: Boiler heat input and lb/MMBtu emissions for NOx and SO2 based on continuous emissions 

monitoring (CEM) annual averages for 2001-2003.

DFGD = dry flue gas desulfurization

ESP = electrostatic precipitator

H2SO4 = sulfuric acid

K = Kelvin

lb/MMBtu = pounds per million British thermal units

LNB = low-NOx burners

m = meters

m/s = meters per second

MMBtu/yr = million British thermal units per year

NOx = nitrogen oxides

PM = particulate matter

SO2 = sulfur dioxide

tpy = tons per year

WFGD = wet flue gas desulfurization 
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AP-6047A Revised NOx BART Impact Analysis

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Table 2-2: Source Parameters and Emissions for BART Control Options

Parameter

NOx Emissions from New LNB + 

OFA Scenario from MD-6047

Application Analysis

NOx Emissions from BART 

Settlement Agreement

Unit 1 Unit 2 Unit 3 Unit 1 Unit 2 Unit 3 

Base Elevation (m) 1348 1348 1348 1348 1348 1348

Stack Height (m) 184.4 184.4 184.4 184.4 184.4 184.4

Stack Diameter (m) 8.69 8.69 8.69 8.69 8.69 8.69

Stack Temperature (K) 338.7 338.7 352.0 338.7 338.7 352.0

Exit Velocity (m/s) 21.33 21.03 22.25 21.33 21.03 22.25

SO2 Emissions (lb/MMBtu) 0.16 0.16 0.17 0.16 0.16 0.17

SO2 Emissions (tpy) 3745 3725 4060 3745 3725 4060

H2SO4 Emissions (tpy) 3.18 3.25 0.22 3.18 3.25 0.22

NOx Emissions (lb/MMBtu) 0.23 0.23 0.23 0.21 0.21 0.21

NOx Emissions (tpy) 5384 5354 5493 4916 4889 5015

PM Fine Emissions (lb/MMBtu) 0.030 0.030 0.030 0.030 0.030 0.030

PM Fine Emissions (tpy) 702 698 716 702 698 716

H2SO4 = sulfuric acid 

K = Kelvin

lb/MMBtu = pounds per million British thermal units

LNB = low NOx burners

m = meters

m/s = meters per second

NOx = nitrogen oxides

OFA = overfire air

PM = particulate matter

SCR = selective catalytic reduction

SO2 = sulfur dioxide

tpy = tons per year

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 Table 2-2: Source Parameters and Emissions for BART Control Options (cont.)

Parameter

NOx Control: SCR

Unit 1 Unit 2 Unit 3 

Base Elevation (m) 1348 1348 1348

Stack Height (m) 184.4 184.4 184.4

Stack Diameter (m) 8.69 8.69 8.69

Stack Temperature (K) 338.7 338.7 352.0

Exit Velocity (m/s) 21.33 21.03 22.25

SO2 Emissions (lb/MMBtu) 0.16 0.16 0.17

SO2 Emissions (tpy) 3745 3725 4060

H2SO4 Emissions (tpy) 3.18 3.25 0.22

NOx Emissions (lb/MMBtu) 0.07 0.07 0.07

NOx Emissions (tpy) 1639 1630 1672

PM Fine Emissions (lb/MMBtu) 0.030 0.030 0.030

PM Fine Emissions (tpy) 702 698 716

H2SO4 = sulfuric acid 

K = Kelvin

lb/MMBtu = pounds per million British thermal units

LNB = low NOx burners

m = meters

m/s = meters per second

NOx = nitrogen oxides

OFA = overfire air

PM = particulate matter

SCR = selective catalytic reduction

SO2 = sulfur dioxide

tpy = tons per year 

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Table 2-3 presents a summary of the results of the visibility modeling in terms of the 98th

percentile delta deciview (dv) levels and the number of days with predicted impacts above 0.5 dv 

for each of the four modeling scenarios. Figures 2-1 and 2-2 present the results graphically. 

Table 2-3: CALPUFF Visibility Modeling Results for Laramie River Station

Class I Area

Unit 1 Unit 2 Unit 3

98th 

Percentile 

Value 

(Δdv)

No. of 

Days > 0.5 

Δdv

98th 

Percentile 

Value 

(Δdv)

No. of 

Days > 0.5 

Δdv

98th 

Percentile 

Value 

(Δdv)

No. of 

Days > 0.5 

Δdv

Baseline – LNB, Wet FGD, ESP:

Badlands NP 0.73 14.7 0.73 14.7 0.74 14.3

Wind Cave NP 0.72 14.0 0.72 14.0 0.73 14.0

NOx from December 2009 BART Permit (MD-6047):

Badlands NP 0.66 10.7 0.65 11.3 0.67 12.3

Wind Cave NP 0.66 11.0 0.66 11.0 0.66 11.7

NOx from November 2010 Settlement Agreement:

Badlands NP 0.62 9.0 0.61 9.0 0.63 10.7

Wind Cave NP 0.62 9.7 0.63 9.7 0.62 10.7

Add-On NOx Control – SCR:

Badlands NP 0.34 4.3 0.35 4.3 0.36 4.7

Wind Cave NP 0.39 4.0 0.39 4.0 0.40 4.7

Note: Modeling results represent the three-year average of results using 2001-2003 meteorology.

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Figure 2-1: Modeled BART Impacts: Number of Days > 0.5 delta-dv

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

LRS U1 LRS U2 LRS U3 LRS U1 LRS U2 LRS U3

(# Days)

Baseline

Initial BART

BART Settlement

SCR

(Modeling results represent the three-year average using 2001-2003 meteorology)

LRS U1 = Laramie River Station Unit 1 (550 MW)

LRS U2 = Laramie River Station Unit 2 (550 MW)

LRS U3 = Laramie River Station Unit 3 (550 MW)

-----------------Badlands ------------------- ----------------- Wind Cave ------------------
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AP-6047A Revised NOx BART Impact Analysis

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Figure 2-2: Modeled BART Impacts: 98th Percentile (delta-dv)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

LRS U1 LRS U2 LRS U3 LRS U1 LRS U2 LRS U3

(Delta-dv)

Baseline

Initial BART

BART Settlement

SCR

(Modeling results represent the three-year average using 2001-2003 meteorology)

LRS U1 = Laramie River Station Unit 1 (550 MW)

LRS U2 = Laramie River Station Unit 2 (550 MW)

LRS U3 = Laramie River Station Unit 3 (550 MW)

-----------------Badlands------------------- --------------------Wind Cave ----------------------
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AP-6047A Revised NOx BART Impact Analysis

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3. BART IMPACTS

After considering Basin Electric’s proposed new NOx BART levels in relation to all five statutory BART 

factors, the AQD noted the following impacts to the standing BART determination of the installation and 

operation of new low NOx burners and overfire air for each of the three units at the Laramie River 

Station:

1. The NOx control level of 0.21 lb/MMBtu on a 30-day rolling average is lower than EPA’s 

established presumptive limit for dry-bottom, wall-fired boilers burning sub-bituminous coal.

2. The 3-year averaged cumulative visibility improvement as compared to the baseline across Wind 

Cave NP and Badlands NP achieved with new LNB with OFA at the 30-day limit of 0.21

lb/MMBtu (based on the 98th percentile modeled results) was 0.21-0.22 Δdv from each of the 

three units. The expected visibility improvement over the course of a full annual period would be 

even greater due to the annual BART limit that is based on 0.17 lb/MMBtu. 

3. Annual NOx emission reductions from baseline achieved in the settlement from the installation of 

new LNB with OFA on Units 1, 2, and 3 are 1,508-1,540 tons per unit for a total annual reduction 

of 4,580 tons. 

4. The 3-year averaged cumulative visibility improvement for SCR, above the improvement 

achieved by new LNB with OFA, summed across Wind Cave NP and Badlands NP (based on the 

98th percentile modeled results) was 0.49-0.51 Δdv for each of the three units.

Unit-by-unit NOx BART levels from settlement:

Laramie River Unit 1: 0.21 lb/MMBtu (30-day rolling average), 1,220 lb/hr (30-day rolling 

average), and 4,780 tpy (12-month rolling) as BART for NOx. 

Laramie River Unit 2: 0.21 lb/MMBtu (30-day rolling average), 1,220 lb/hr (30-day rolling 

average), and 4,780 tpy (12-month rolling) as BART for NOx. 

Laramie River Unit 3: 0.21 lb/MMBtu (30-day rolling average), 1,254 lb/hr (30-day rolling 

average), and 4,914 tpy (12-month rolling) as BART for NOx. 

The performance/efficiency-based, 30-day rolling average emission rate of 0.21 lb/MMBtu is set to allow 

for continuous compliance with proper operation of the control equipment, while taking into account the 

normal operational variability that is typical for a boiler. The 30-day limits that are expressed in terms of 

mass emissions (lb/hr) are based on 0.19 lb/MMBtu. Because reduced steam loads on a boiler can result 

in periods of increased emissions in terms of lb/MMBtu but lower emissions in terms of lb/hr, the AQD 

has chosen to set the dual 30-day limits, one set at 0.21 lb/MMBtu and one expressed in lb/hr based on 

0.19 lb/MMBtu. For the 12-month rolling emission limits, the AQD considered the ability of the source 

to maintain a lower mass emission rate over a longer time period and set the long-term limit (expressed in 

tpy) based on 0.17 lb/MMBtu.
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4. LONG-TERM STRATEGY FOR REGIONAL HAZE

Additional NOx emission reductions were required under the Long-Term Strategy of the Wyoming § 

309(g) Regional Haze SIP and were based on the AQD’s extensive BART analysis. Based on the costs 

and visibility improvement presented by Basin Electric in the BART applications for Laramie River 

Station Units 1-3, and taking into consideration the logistical challenge of managing multiple pollution 

control installations within the regulatory timeframe allotted for BART, the AQD required installation of 

two SCR (or equivalent performing) emission control systems under the Long-Term Strategy (LTS) of 

the Wyoming Regional Haze State Implementation Plan. Each proposed add-on NOx control would

achieve an emission rate, on an individual unit basis, at or below 0.07 lb/MMBtu on a 30-day rolling 

average. Additional add-on controls were required to be installed and operational on one of the Laramie 

River Station units by December 31, 2018 and on a second Laramie River Station unit by December 31, 

2023. The requirement to install additional add-on NOx control was contained in permit condition 16 of 

Air Quality Permit MD-6047.

Upon entering into the settlement agreement, the AQD agreed to remove condition 16 from Air Quality 

Permit MD-6047, thereby removing the requirement for Basin Electric to install additional add-on NOx

controls by December 31, 2018 and December 31, 2023. The AQD agreed to remove condition 16 

because Basin Electric agreed to additional NOx emissions reductions, which are contained in Sections 

7C, 7D, 7E, and 7F of the settlement. Lower BART levels, as evaluated in this analysis, are stipulated in 

Section 7C. Section 7D contains an agreement whereby Basin Electric will further reduce NOx emissions 

below the levels proposed in Section 7C. By December 31, 2017, NOx emissions from the three boilers 

will be reduced from 14,474 tons to 12,773 tons for a net reduction of 1,701 additional tons. In doing so, 

the AQD agrees to not require further NOx reductions from Units 1-3 for the purposes of meeting BART

or the Long-Term Strategy requirements and/or Reasonable Progress goals in the Wyoming Regional 

Haze SIP through December 31, 2018. Additional requirements may be imposed, for the purposes of 

regional haze, after 2018. In accordance with Section 7F, Basin Electric will submit a permit application 

by December 31, 2015, requesting to incorporate the 12,773 tons NOx limit for the three boilers into a 

permit. If Basin Electric determines that additional NOx control technology is required in order to comply 

with the 12,773 tons limit, then a demonstration that such control technology will be operated at the 

designed performance levels is required in the application under Section 7E.

By entering into a settlement with Basin Electric, the AQD has secured additional reductions beyond 

those achieved in Air Quality Permit MD-6047 during the first planning period (2008-2018). Under the 

initial NOx BART/LTS scenario, the AQD would have reduced NOx emissions during the period of 2013-

2019 by 20,646 tons. NOx emissions for the same period will now be reduced by 30,887 tons, an

additional reduction of 10,241 tons, in accordance with the settlement agreement. Figure 4-1 depicts the 

reductions on an annual basis. And while the AQD has committed to not requiring additional NOx

reductions for purposes of regional haze during the 2008-2018 planning period, additional reduction may 

be necessary from the Laramie River Station in subsequent planning periods.
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Figure 4-1: Annual NOx Emission Reductions from Units 1-3 (tons)

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

2013 2014 2015 2016 2017 2018 2019

NOx Reduction from Baseline (tons)

Initial

Settlement

Total Reduction 

from Baseline 

(2013-2019)

Initial: 20,646 tons

Settlement: 30,887 tons
Appendix A

Copy of Settlement Agreement Between

Wyoming Department of Environmental Quality,

Air Quality Division,

and Basin Electric Power Cooperative