DEPARTMENT OF ENVIRONMENTAL QUALITY

AIR QUALITY DIVISION

BART Application Analysis

AP-6044

August 4, 2008

NAME OF FIRM: FMC Wyoming Corporation

NAME OF FACILITY: Granger Facility

FACILITY LOCATION: Section 36, T20N, R111W

Sweetwater County, Wyoming

TYPE OF OPERATION: Sodium Products Plant

RESPONSIBLE OFFICIAL: Otto Schnauber, Environmental Team Leader

MAILING ADDRESS: PO Box 872

Green River, WY 82935

TELEPHONE NUMBER: (307) 872-2257

REVIEWING ENGINEERS: Cole Anderson, Air Quality Engineer

Josh Nall, Air Quality Modeler

PURPOSE OF APPLICATION:

FMC Wyoming Corporation has submitted a Best Available Retrofit Technology (BART) 

application for the two 358.5 million BTU (MMBtu) coal-fired boilers that operate at their 

Granger facility in Sweetwater County, Wyoming. Regulations governing the BART program 

have been established by the U.S. EPA in 40 CFR Part 51 - Appendix Y. As stated in the 

regulations, a source is eligible for BART if it belongs within a group of stationary source

categories, was not in operation prior to August 7, 1962, was in existence on August 7, 1977, and 

has the potential to emit 250 tons per year (tpy) or more of any visibility impairing air pollutant. 

Fossil fuel boilers of more than 250 MMBtu per hour heat input are listed as an eligible source 

type. Potential emissions from both boilers at Granger (installed in 1976) for two visibility 

impairing air pollutants, nitrogen oxides (NOx) and sulfur dioxide (SO2), exceed 250 tpy and 

therefore the units are eligible for BART.

A BART-eligible unit is “subject” to BART unless valid air quality dispersion modeling 

demonstrates that the unit will not cause or contribute to visibility impairment in any Class I area. 

A single source that is responsible for a 0.5 deciview (dv) change or more is considered to 

“contribute” to visibility impairment at a Class I area, while a source that is responsible for a 1.0

dv change or more is considered to “cause” visibility impairment at a Class I area. A source is 

exempt from BART if the 98th percentile daily change in visibility, as compared against natural 

background conditions, is less than 0.5 dv at all Class I areas for the entire multi-year modeling 

period. 
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AP-6044 BART Application Analysis

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Initial dispersion modeling (screening) conducted by the Division indicated that the Granger 

facility would be subject to BART, and therefore FMC Wyoming Corporation submitted a BART 

analysis to the Division on February 28, 2007. Refined dispersion modeling, submitted in the 

BART analysis and described in detail below, indicates that the two boilers at Granger do not 

contribute to visibility impairment at any Class I area.

DESCRIPTION OF BART ELIGIBLE UNITS:

Operating parameters and potential emissions for the BART-eligible units at the Granger facility 

are summarized in the table below.

Unit Description

Heat 

Input 

(MMBtu)

SO2 

Emission 

Limit –

lb/hr (tpy)

NOxEmission 

Limit – lb/hr 

(tpy)

PM 

Emission 

Limit –

lb/hr (tpy)

UIN-14 #1 Coal-Fired Boiler with FGD 

scrubber and ESP control

358.5 71.70 (314) 250.95 (1099) 35.85 (157)

UIN-15 #2 Coal-Fired Boiler with FGD 

scrubber and ESP control

358.5 71.70 (314) 250.95 (1099) 35.85 (157)

ESP = electrostatic precipitator

FGD = flue gas desulfurization

lb/hr = pounds per hour

MMBtu = million British thermal units

NOx = nitrogen oxides

PM = particulate matter

SO2 = sulfur dioxide

tpy = tons per year

VISIBILITY IMPROVEMENT DETERMINATION:

The fifth of five factors that must be considered for a BART determination analysis, as required 

by 40 CFR Part 51 - Appendix Y, is the degree of Class I area visibility improvement that results 

from the possible options for control technology. This factor was evaluated for the FMC Granger 

facility by using an EPA-approved dispersion modeling system (CALPUFF) to predict the change 

in Class I area visibility. The Division had previously determined that the FMC Granger facility 

was subject to BART based on the results of initial screening modeling that was conducted using 

current (baseline) emissions from the facility. The screening modeling, as well as more refined 

modeling conducted by the applicant, is described in detail below. 

Bridger Wilderness Area (WA) and Fitzpatrick WA are the two closest Class I areas to the FMC 

Granger facility, as shown in Figure 1 below. Bridger WA is located approximately 116

kilometers (km) northeast of FMC Granger, while Fitzpatrick WA is located approximately 143

km northeast of the facility. 

Only those Class I areas most likely to be impacted by the Granger sources were modeled, as 

determined by source/Class I area locations, distances to each Class I area, and professional 
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AP-6044 BART Application Analysis

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judgment considering meteorological and terrain factors. Areas greater than 300 km from 

Granger were excluded. All source-Class I area distances from Granger to Bridger WA and 

Fitzpatrick WA exceed 50 km and are less than 300 km, thus falling within the range of 

recommended CALPUFF application. If impacts are less than the BART threshold for the Class I 

areas modeled, it can be reasonably assumed that areas at a greater distance and in directions of 

less frequent plume transport will not experience significant impacts.

 Figure 1

-400 -300 -200 -100 0 100 200

LCC East (km)

FMC Granger and Class I Areas

-300

-200

-100

0

100

200

300

400

LCC North (km)

Billings

Casper

Lander

Pocatello

RockSpr

Sheridan

SLC

Bridger WA

Fitzpatrick WA

FMC

Granger

 
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SCREENING MODELING

To determine if the FMC Granger facility would be subject to BART, the Division conducted 

CALPUFF modeling using three years of meteorological data. These data, from 1995-1996 and 

2001, consisted of surface and upper-air observations and gridded output from the prognostic 

MM5 model. Resolution of the MM5 data was 36-km for all three of the modeled years. Sources 

input to the modeling included the potential emissions (current operation) from the two BARTeligible emission units at the Granger facility, the coal-fired boilers UIN-14 and UIN-15. 

Results of the modeling showed that the 98th percentile value for the change in visibility (delta 

deciview [Δdv]) was above 0.5 dv for Bridger Wilderness for the meteorological data from 1996. 

As defined in EPA’s final BART rule, a 98th percentile 0.5 dv impact from a given source 

indicates that the source contributes to visibility impairment, and therefore is subject to BART. 

The results of the screening modeling are shown in the table below.

Results of the Class I Area Screening Modeling

Class I Area

Maximum 

Modeled 

Value (Δdv)

98th

Percentile 

Value (Δdv)

1995

Bridger WA 0.86 0.27

Fitzpatrick WA 0.26 0.12

1996

Bridger WA 1.72 0.70

Fitzpatrick WA 1.14 0.23

2001

Bridger WA 1.09 0.495

Fitzpatrick WA 0.27 0.19

Δdv = delta deciview

WA = wilderness area

REFINED MODELING

Because of the results of the Division’s screening modeling, FMC was required to conduct a 

refined BART analysis that included CALPUFF visibility modeling for the two coal-fired boilers 

at the facility. The modeling approach followed the requirements described in the Division’s 

BART modeling protocol, BART Air Modeling Protocol - Individual Source Visibility 

Assessments for BART Control Analyses (WDEQ-AQD, September 2006).

CALPUFF System

Predicted visibility impacts from the FMC Granger sources were determined with the EPA 

CALPUFF modeling system, which is the EPA-preferred modeling system for long-range 

transport. As described in the EPA Guideline on Air Quality Models (Appendix W of 40 CFR 

Part 51), long-range transport is defined as modeling with source-receptor distances greater than 

50 km. Because all modeled areas are located more than 50 km from the sources in question, the 

CALPUFF system was appropriate for use.
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The CALPUFF modeling system consists of a meteorological data pre-processor (CALMET), an 

air dispersion model (CALPUFF), and post-processor programs (POSTUTIL, CALSUM, 

CALPOST). The CALPUFF model was developed as a non-steady-state air quality modeling 

system for assessing the effects of time- and space-varying meteorological conditions on pollutant 

transport, transformation, and removal. 

CALMET is a diagnostic wind model that develops hourly wind and temperature fields in a threedimensional, gridded modeling domain. Meteorological inputs to CALMET can include surface 

and upper-air observations from multiple meteorological monitoring stations. Additionally, the 

CALMET model can utilize gridded analysis fields from various mesoscale models such as MM5 

to better represent regional wind flows and complex terrain circulations. Associated twodimensional fields such as mixing height, land use, and surface roughness are included in the 

input to the CALMET model. The CALMET model allows the user to “weight” various terrain 

influence parameters in the vertical and horizontal directions by defining the radius of influence 

for surface and upper-air stations. 

CALPUFF is a multi-layer, Lagrangian puff dispersion model. CALPUFF can be driven by the 

three-dimensional wind fields developed by the CALMET model (refined mode), or data from a 

single surface and upper-air station in a format consistent with the meteorological file used to 

drive steady-state dispersion models. All far-field modeling assessments described here were 

completed using the CALPUFF model in a refined mode.

CALSUM is a post-processing program that can operate on multiple CALPUFF output files to 

combine the results for further post-processing. POSTUTIL is a post-processing program that 

processes CALPUFF concentrations and wet/dry flux files. The POSTUTIL model operates on 

one or more output data files from CALPUFF to sum, scale, and/or compute species derived from 

those that are modeled, and outputs selected species to a file for further post-processing. 

CALPOST is a post-processing program that can read the CALPUFF (or POSTUTIL or 

CALSUM) output files, and calculate parameters such as visibility impacts. 

All of the refined CALPUFF modeling was conducted with the version of the CALPUFF system 

that was recognized as the EPA-approved release at the time of the development of the Division’s 

modeling protocol. Version designations of the key programs are listed in the table below.

Key Programs in CALPUFF System

Program Version Level

CALMET 5.53a 040716

CALPUFF 5.711a 040716

CALPOST 5.51 030709

Meteorological Data Processing (CALMET)

As required by the Division’s modeling protocol, the CALMET model was used to construct the 

initial three-dimensional windfield using data from the Mesoscale Model (MM5). Surface and 

upper-air data were then used by CALMET to adjust the initial windfield, but because of the

relative scarcity of observations in the modeling domain, the influence of the observations was 

limited. Because the MM5 data were afforded a high degree of influence on the CALMET 
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windfields, the Division obtained MM5 data at 12-km resolution for the modeling domain that 

spanned the years 2001-2003. Surface, upper-air, and precipitation data for the domain was 

incorporated into the CALMET windfield. Locations of the various observations are shown in 

the figure below. The Division provided the BART applicants all raw meteorological inputs for 

the CALMET model.

Default settings were used in the CALMET input files for most of the technical options. The 

following table lists the key user-defined CALMET settings that were selected. 

-400 -300 -200 -100 0 100 200 300

LCC East (km)

CALMET Surface, Upper-Air, and Precipitation Stations

-300

-200

-100

0

100

200

300

400

LCC North (km)

FMC

BIL

CPR

CYS

LND

PIH

RKS

SHR

SLC

Precipitation Station

Surface Station

Upper-Air Station
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Key User-Defined CALMET Settings

Variable Description Value 

PMAP Map projection LCC 

DGRIDKM Grid spacing (km) 4 

NZ Number of layers 10 

ZFACE Cell face heights (m) 0, 20, 40, 100, 140, 320, 

580, 1020, 1480, 2220, 3400 

RMIN2 Minimum distance for extrapolation -1 

IPROG Use gridded prognostic model output 14 

RMAX 1 Maximum radius of influence (surface 

layer, km) 

30 

RMAX 2 Maximum radius of influence (layers 

aloft, km) 

50 

TERRAD Radius of influence for terrain (km) 15 

R1 Relative weighting of first guess wind 

field and observations (km) 

5 

R2 Relative weighting aloft (km) 25 

CALPUFF Modeling Setup

To allow chemical transformations within CALPUFF with the recommended chemistry scheme 

(MESOPUFF II), the model required input of background ozone and ammonia. For ozone, 

hourly data collected from the following stations were used:

Rocky Mountain National Park, Colorado (NP)

Craters of the Moon National Monument, Idaho

Highland, Utah

Thunder Basin, Wyoming

Yellowstone NP, Wyoming

Centennial, Wyoming

Pinedale, Wyoming

For any hour that was missing ozone data from all stations, a default value of 44 parts per billion 

(ppb) was used by the model as a substitute. For ammonia, a domain-wide background value of 2 

ppb was used. 

Discrete receptors for the Class I areas that were modeled (Bridger WA and Fitzpatrick WA) 

were provided by the Division. 
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CALPUFF Inputs – Baseline Conditions

Baseline stack parameters and emissions input to CALPUFF for the two units that were eligible 

for BART are shown in the tables below. 

Stack Parameters 

Source

LCC 

East 

(km)(1)

LCC 

North 

(km)(1)

Base 

Elevation 

(m)

Stack 

Height 

(m)

Stack 

Diameter 

(m)

Exhaust 

Tempera

ture (K)

Exit 

Velocity 

(m/s)

UIN-14 -108.329 -93.371 1938.8 45.72 1.98 352.6 20.6

UIN-15 -108.317 -93.385 1938.8 45.72 1.98 352.6 20.6

(1) Coordinates based on UTM for UIN-14: 591757 m, 4613883 m and for UIN-15: 591770 m, 4613884 m 

K = Kelvin

km = kilometers 

LCC = Lambert Conformal Conic

m = meters

m/s = meters per second

Emission Rates

Source

SO2 

(lb/hr)

SO4 

(lb/hr)

NOx 

(lb/hr)

PMF 

(lb/hr)

UIN-14 71.7 3.2 250.95 35.85

UIN-15 71.7 3.2 250.95 35.85

Note: Sulfuric acid (H2SO4) emissions modeled in CALPUFF as SO4 [H2SO4 * (96/98)]

lb/hr = pounds per hour

NOx = nitrogen oxides

PMF = fine particulate

SO2 = sulfur dioxide

SO4 = sulfates 
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Visibility Post-Processing (CALPOST) Setup

The changes in visibility were calculated using Method 6 within the CALPOST post-processor. 

Method 6 requires input of monthly relative humidity factors [f(RH)] for each Class I area. 

Monthly f(RH) factors that were used for Bridger WA and Fitzpatrick WA are shown in the table 

below. 

Relative Humidity Factors for CALPOST

Month Bridger WA

Fitzpatrick WA

January 2.50

February 2.30

March 2.30

April 2.10

May 2.10

June 1.80

July 1.50

August 1.50

September 1.80

October 2.00

November 2.50

December 2.40

According to the final BART rule, natural background conditions as a reference for determination 

of the Δdv change within CALPOST should be representative of the 20% best natural visibility 

days. EPA BART guidance provides the 20% best days deciview values for each Class I area on 

an annual basis, but does not provide species concentration data for the 20% best background 

conditions. 

 

Species concentrations corresponding to the 20% best days were calculated for each Class I area

by scaling back the annual average concentrations given in Table 2-1 of the EPA document

Guidance for Estimating Natural Visibility Conditions Under the Regional Haze Rule. A separate 

scaling factor was derived for each Class I area such that, when multiplied by the guidance table 

annual concentrations, the 20% best days dv value for that particular Class I area would be 

calculated. The scaled aerosol concentrations were averaged for the Bridger WA and Fitzpatrick 

WA because of their geographical proximity and similar annual background visibility. The 20% 

best days aerosol concentrations that were used for each month are listed in the table below.
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Natural Background Aerosol Concentrations (μg/m3)

Aerosol 

Component 

Fitzpatrick WA 

Bridger WA 

Ammonium Sulfate 0.045 

Ammonium Nitrate 0.038 

Organic Carbon 0.178 

Elemental Carbon 0.008 

Soil 0.189 

Coarse Mass 1.136 

Visibility Post-Processing Results

The results of the visibility modeling for both units combined are shown in the table below. For 

each year modeled, the 98th percentile result was less than 0.5 Δdv at both Bridger WA and 

Fitzpatrick WA. These results show that the combined baseline emissions (current operation) of 

the two coal-fired boilers at the FMC Granger facility do not contribute to Class I area visibility 

impairment. Based on this modeling, which was performed with higher resolution MM5 data 

than was used for the Division’s screening modeling, the Division has determined that the facility 

is not subject to BART. 

Results of the Class I Area Refined CALPUFF Modeling

Class I Area

Maximum 

Modeled 

Value 

(Δdv)

98th

Percentile 

Value 

(Δdv)

2001

Bridger WA 0.573 0.327

Fitzpatrick WA 0.284 0.137

2002

Bridger WA 1.395 0.260

Fitzpatrick WA 0.609 0.201

2003

Bridger WA 0.749 0.390

Fitzpatrick WA 0.375 0.170
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CONCLUSIONS:

A refined CALPUFF visibility modeling analysis performed for the two BART-eligible units at 

the FMC Wyoming Granger facility demonstrated that the predicted 98th percentile impacts at the 

nearest Class I areas would be below 0.5 dv for all meteorological periods modeled. This 

modeling was conducted by the applicant, and verified by the Division, using higher-resolution 

meteorological data as compared to the data used by the Division for the initial screening 

modeling that identified the facility as “subject” to BART. 

As stated in the final BART rule, sources with predicted visibility impacts less than 0.5 dv do not 

contribute to Class I area visibility impairment and are not “subject” to BART. Therefore, the 

two BART-eligible units at the FMC Wyoming Granger facility are not “subject” to BART and 

no additional controls are required to address visibility impacts in Class I areas.