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SO2 Air Dispersion Modeling 

Report for Independence 

Steam 

Electric Station

August 2015

ERM Project No. 0268066

www.erm.com
SO2 Air Dispersion Modeling 

Report for Independence

Steam 

Electric Station

August, 2015

ERM Project No. 0268066

_____________________________________

Peter T. Belmonte

Partner-in-Charge

_____________________________________

Richard P. Hamel

Project Manager

Environmental Resources Management

One Beacon Street, 5th Floor

Boston, MA 02108

T: 617-646-7800

F: 617-267-6447
ii

TABLE OF CONTENTS

1.0 INTRODUCTION 1-1

1.1 PROJECT OVERVIEW 1-1

1.2 OVERVIEW OF METHODOLOGY 1-2

2.0 FACILITY DESCRIPTION AND REGULATORY SETTING 2-1

2.1 FACILITY LOCATION 2-1

2.2 SO2 ATTAINMENT STATUS 2-1

2.3 SOURCE PARAMETERS AND EMISSION RATES 2-4

3.0 AIR DISPERSION MODELING ANALYSIS 3-1

3.1 MODEL SELECTION AND APPLICATION 3-1

3.2 THE 1-HOUR SO2 NAAQS 3-1

3.3 METEOROLOGICAL DATA 3-1

3.4 RECEPTOR GRID 3-3

3.5 GOOD ENGINEERING PRACTICE STACK HEIGHT ANALYSIS 3-4

3.6 AMBIENT SO2 BACKGROUND DATA FOR CUMULATIVE MODELING 3-4

4.0 MODELING RESULTS 4-1

4.1 CONCLUSIONS 4-1

5.0 REFERENCES 5-1
iii

LIST OF TABLES

Table 2-1 Independence Station Point Sources – Stack Parameters 2-5

Table 3-1 Characteristics of the Adams Field – Little Rock Meteorological Data 3-2

Table 3-2 Seasonal Diurnal SO2 Concentrations at Little Rock Monitor (g/m3) 3-5

Table 4-1 1-hour SO2 Modeling Results for Independence Station 4-1

LIST OF FIGURES

Figure 1-1 Independence Station Surroundings and Land Use 1-4

Figure 2-1 Independence Station Site Plan 2-2

Figure 2-2 Independence Station Local Topography 2-3

Figure 3-1 Relative Location of Facility, Airport, and Ambient Monitor 3-6

Figure 3-2 Three-year Wind Rose (2012-2014): Little Rock – Adams Field 3-7

Figure 3-3 Near-Field Model Receptors 3-8

Figure 3-4 Far-Field Model Receptors 3-9

Figure 4-1 Independence Station 1-hour SO2 Impact Contours 4-2

LIST OF APPENDICES

APPENDIX A ELECTRONIC MODELING ARCHIVE
ERM 1-1 INDEPENDENCE / 0268066 – AUGUST 2015

1.0 INTRODUCTION 

ERM Consulting & Engineering, Inc. (ERM), has prepared this report documenting that 

maximum model-predicted SO2 impacts from Entergy Arkansas Inc.’s (Entergy) 

Independence Steam Electric Station (Independence) are in attainment with the 1-hour 

Sulfur Dioxide (SO2) National Ambient Air Quality Standard (NAAQS) and will fulfill 

the requirements of the EPA’s 1-Hour SO2 Data Requirements Rule (DRR). This analysis 

shows that the ambient air quality in the vicinity of Independence, currently 

undesignated for the 1-hour SO2 NAAQS, is within the standard and should be 

identified as “attainment” in the next cycle of designations.

This modeling report describes the modeling methodology that was used to evaluate 

potential impacts of SO2 emissions from Independence on ambient air quality. Copies of 

the modeling files are provided in Appendix A, the Electronic Modeling Archive.

1.1 Project Overview

Unlike previous NAAQS attainment demonstrations, EPA has proposed to make 1-hour 

SO2 NAAQS attainment determinations using ambient air monitoring data and/or air 

dispersion modeling. In situations where air modeling is used to make this 

determination, the approach described in EPA’s proposed “Modeling Technical 

Assistance Document” (TAD)1, which sets forth a significantly different technical 

approach compared to conventional regulatory modeling prescribed by 40 CFR Part 51, 

Appendix W (EPA’s Guideline on Air Quality Models) could be used. This approach 

would also meet the requirements of the DRR.

EPA distinguishes the approaches described in the SO2 Modeling TAD to “reflect a 

view that designations are intended to address current actual air quality (i.e., modeling 

simulates a monitor), and thus are unlike attainment plan modeling, which must 

provide assurances that attainment will occur.” EPA’s proposed approach would utilize 

several distinctive technical approaches, including but not limited to the following:

 Simulating actual emissions and exhaust conditions (e.g., temperature and flowrate) 

on an hourly basis reflecting actual operations for a specified historical time period; 

 Representing actual stack heights, irrespective of the GEP regulations; 

 Limiting modeled ambient air receptors to locations where monitoring could 

actually take place by excluding waterways, roadways, railways, restricted access 

property, and other locations that would conventionally be considered “ambient 

air” for regulatory and permitting purposes; 

 

1

http://epa.gov/oaqps001/sulfurdioxide/pdfs/SO2ModelingTAD.pdf
ERM 1-2 INDEPENDENCE / 0268066 – AUGUST 2015

 Simulating a three-year period of meteorological and background monitoring data, 

concurrent with the actual operating conditions and emissions, to meet EPA’s 

objective that “modeling simulates monitoring” in this context. 

ERM performed a modeling analysis evaluating the impacts on ambient air quality 

from SO2 emissions at Independence. As discussed in this report, ERM’s approach to 

the modeling analysis used those refinements directly addressed in the proposed rule, 

i.e. the use of actual hourly emissions, actual stack heights, and seasonal diurnal 

ambient background concentrations. 

As shown in this modeling report, SO2 impacts from Independence emission sources, 

when combined with ambient air concentrations taken from a representative nearby 

monitor, are below the 1-hour SO2 NAAQS. 

This first section of this report describes the modeling methodology that was followed. 

Section 2 provides a description of the facility and the emissions included in the 

modeling. Model selection and the methodology used in the modeling are described in 

Section 3. The modeling results are presented in Section 4. References are provided in 

Section 5.

1.2 Overview of Methodology

ERM’s assessments were conducted in a manner consistent with United States 

Environmental Protection Agency (EPA) air quality regulations and modeling 

guidelines that are generally adopted by Arkansas Department of Environmental 

Quality (ADEQ), including the following: 

 Guideline on Air Quality Models – 40 CFR Part 51, Appendix W, Revised November 9, 

2005. 

 AERMOD Implementation Guide, Revised March 19, 2009; 

 “SO2 NAAQS Designations Modeling Technical Assistance Document (Draft),” 

December 2013; 

 “SO2 NAAQS Designations Monitoring Technical Assistance Document (Draft),” 

December 2013; 

 “Data Requirements Rule for the 2010 1-Hour Sulfur Dioxide (SO2) Primary National 

Ambient Air Quality Standard (NAAQS),” Pre-publication final rule, (submitted to 

the Federal Register on August 10, 2015, FRL-9928-18-OAR); and 

 “Guidance for 1-hour SO2 Nonattainment Area SIP Submissions,” April 23, 2014. 

The steps that were undertaken by ERM to conduct the air dispersion modeling 

analyses are summarized below:
ERM 1-3 INDEPENDENCE / 0268066 – AUGUST 2015

 Compiled information on the parameters and characteristics for all sources of SO2

emissions at Independence including the main EGU’s, the auxiliary boiler, the 

emergency diesel generator, and the fire pump engine;

 Developed a comprehensive receptor grid to capture the maximum off-site impacts 

from Independence sources using AERMAP (v.11103).

 Obtained ambient background concentration data for SO2 from nearby monitors to 

represent sources not explicitly included in the modeling runs;

 Developed 3 years (2012-2014) of meteorological data using surface observations 

from Adams Field in Little Rock, AR with upper air data from North Little Rock

Airport using the most recent version (v.15181) of AERMET, the meteorological data 

processor for AERMOD, and its two preprocessors: AERSURFACE (v.13016) and 

AERMINUTE (v.14337).

 Conducted an air dispersion modeling analysis using the most recent version of 

EPA’s regulatory dispersion model, AERMOD (v.15181) and 3 years of actual 

emissions data from Independence emissions sources, as well as other major sources 

of SO2 emissions in the region, consistent with the methodology described in the SO2

Data Requirements Rule and SO2 Modeling TAD.

 Summarized the results and compared them with the 1-hour SO2 NAAQS to 

determine a recommended attainment designation for the vicinity of Independence. 
ERM 1-4 INDEPENDENCE / 0268066 – AUGUST 2015

Figure 1-1 Independence Station Surroundings and Land Use
ERM 2-1 INDEPENDENCE / 0268066 – AUGUST 2015

2.0 FACILITY DESCRIPTION AND REGULATORY SETTING

2.1 Facility Location

The Independence Steam Electric Station is located in the town of Newark, Arkansas, in 

Independence County. The station is located about 2.5 miles southeast of downtown 

Newark. The site is accessed by Arkansas State Route 69. The station is approximately 

82 miles northeast of Little Rock, Arkansas and 84 miles west-northwest of Memphis, 

Tennessee. Approximate site coordinates are 35.678o North Latitude, 91.408o West 

Longitude. The Universal Transverse Mercator (“UTM”) coordinates of the facility are 

644,087 Easting and 3,949,438 Northing (using North American Datum of 1983 -

NAD83) in UTM Zone 15. The base elevation of the facility is 235’ (71.521m) above sea 

level. A full scale site plan of the power block area of Independence is shown in Figure 

2.1, and Figure 2.2 shows the site location marked on a United States Geological Survey 

(“USGS”) 7.5-minute topographic map.

2.2 SO2 Attainment Status

In July 2013, EPA issued a rule designating 29 counties or partial counties as nonattainment for 1-hour SO2. However, the vast majority of the country was not 

designated by EPA at that time due to the lack of monitors, or poor siting of existing 

monitors, for the purpose of capturing source based maximum ambient SO2

concentrations. None of the counties surrounding Independence, including 

Independence, the county in which Independence is located, have been designated as 

attainment or non-attainment for the 1-hour SO2 NAAQS.
ERM 2-2 INDEPENDENCE / 0268066 – AUGUST 2015

Figure 2-1 Independence Station Site Plan
ERM 2-3 INDEPENDENCE / 0268066 – AUGUST 2015

Figure 2-2 Independence Station Local Topography
ERM 2-4 INDEPENDENCE / 0268066 –AUGUST 2015

2.3 Source Parameters and Emission Rates

For this 1-hour SO2 NAAQS modeling demonstration, all sources of SO2 at the facility 

were included in the modeling. Per the 1-hour SO2 Data Requirements Rule and SO2

Modeling TAD, the most recent 3 years of actual emissions data were used where 

available, and the actual stack heights of all sources were used in the modeling. The 

following provides a description of all Independence SO2 emission sources and how 

they were represented in the model. Table 2-1 summarizes the characteristics of the 

emissions sources that were included in the modeling. The actual emissions data used 

in the modeling are described below:

 Units No. 1 and No. 2 (Source ID: SN01 and SN02). There are two boilers in 

operation at the Independence Station, Unit 1 and Unit 2. Units 1 and 2 are 

vented to a common, dual-flue stack. For these main units, three years (2012-

2014) of actual hourly emissions, stack temperature, and exhaust flow rate data 

were input into the model. This emissions data was provided by Entergy from 

prior submittals to the EPA’s Clean Air Markets Database, while temperature 

and exhaust flow rates were provided by Entergy from the facility CEM system. 

As per the 1-hour SO2 Data Requirements Rule, the actual 1000 ft. height of the 

main stack was represented in each case. The two Units at the facility were 

modeled as separate sources, each emitting from their own flue. This is a 

conservative representation because it neglects potentially enhanced buoyancy 

from a combined plume from both flues. 

 Auxiliary Boiler (Source ID: SN05). The auxiliary boiler was also modeled using 

actual hourly emissions data. For this source, however, exhaust temperature and 

velocity were not available, so for all hours the exit temperature and velocity 

were set to the values located in the ADEQ source registration tables for the 

auxiliary boiler.

 Emergency Diesel Generator (Source ID: SN20) and Emergency Fire Pump 

Engine (Source ID: SN21). The two emergency engines at the facility both have 

horizontal exhaust releases. This is represented in the modeling by setting the 

exit velocity of each source to 0.001 m/s to simulate the lack of vertical 

momentum out of the stack. Emissions data were only available on a month by 

month total emission basis for each engine. To convert that data into an emission 

rate for modeling, for each engine the total annual emissions for each year was 

determined and the highest annual total selected. That total was then divided by 

52 to represent that the engines are tested once per week during the year. The 

resulting emission rate was then used as the lb/hr emission rate in the modeling. 

Based on information provided by facility staff, the emergency generator is 

tested weekly on Wednesdays, while the fire pump is tested on Friday evenings. 

To simulate this standard practice, the emergency generator was set in the 
ERM 2-5 INDEPENDENCE / 0268066 –AUGUST 2015

modeling using the HRDOW7 emission factor (i.e., variable by hour of day and 7 

days per week) to emit during an 8 hour period on Wednesdays from 8 AM to 4 

PM, and the fire pump was set to operate on Friday’s from 4 PM until Midnight. 

While this significantly overestimates the total emissions of the emergency 

engines, because the form of the 1-hour SO2 standard only considers the hour 

with the highest concentration each day, at least 7 of these hours are “dropped” 

and thus only one hour worth of emission is potentially included in the 

maximum daily impacts. 

Data supporting the actual emissions used for the 5 sources included in the 

modeling are provided in the spreadsheets ISES_Hourly Actual Emissions 2012-

2014.xlsx, ISES Aux Boiler Data 010112 to 123114.xlsx, and ISES Em Gen Hours and 

Emissions 2012-2014.xlsx included in Appendix A: The Electronic Modeling 

Archive.

Table 2-1 Independence Station Point Sources – Stack Parameters

Description Model 

Source Stack Height Exit Temperature Exit Velocity Stack Diameter

(ft) (m) (F) (K) (ft/sec) (m/s) (ft.) (m)

Unit 1 Boiler1 SN01 1000 304.80 --- --- --- --- 25.7 7.83

Unit 2 Boiler1 SN02 1000 304.80 --- --- --- --- 25.7 7.83

Auxiliary Boiler SN05 15 4.57 475 519.26 65.0 19.81 3.0 0.91

Emergency Diesel Engine SN20 14 4.27 963 790.54 ---- 0.0012 0.8 0.25

Emergency Fire Pump SN22 14 4.27 700 644.26 ---- 0.0012 0.4 0.13

1. For the 2 main boilers, exit temperature and exit velocity varied on an hourly basis based on actual emissions 

data.

2. Emergency Diesel Engine and Emergency Fire Pump stacks are horizontal, so modeled exit velocity was 0.001 

m/s for both.
ERM 3-1 INDEPENDENCE / 0268066 – AUGUST 2015

3.0 AIR DISPERSION MODELING ANALYSIS

ERM conducted the modeling analysis for Independence to quantify ambient impacts of 

SO2 relative to the 1-hour NAAQS following the proposed approach described in the 

SO2 Modeling TAD.

3.1 Model Selection and Application

The latest version of USEPA’s AERMOD model (v.15181) was used for predicting 

ambient impacts for 1-hour SO2. Regulatory default options were used in the analysis. 

Model predicted impacts from Independence were combined with those of other large 

sources in the area and an ambient background concentration to represent emissions 

not explicitly modeled and compared to the 1-hour SO2 NAAQS to determine the 

recommended attainment status of the area in the vicinity of the facility.

3.2 The 1-hour SO2 NAAQS

This study focuses on the maximum model-predicted 1-hour SO2 impacts of 

Independence and compares them to the 1-hour SO2 NAAQS. The new standard came 

into effect in August, 2010. The form of the standard is the 99th percentile of the 3-year 

average 1-hour daily maximum concentration, and the standard was set to 75 ppb 

(196.5 g/m3).

3.3 Meteorological Data

Guidance for regulatory air quality modeling recommends the use of one year of on-site 

meteorological data or five years of representative off-site meteorological data. The SO2

Modeling TAD however, specifies that 3 years of meteorological data concurrent to the 

actual emissions data being input into the model be used. Since on-site data are not 

available for the Independence site, meteorological data available from the National

Weather Service (NWS) were used in this analysis. 

Three years (2012-2014) of surface observations from the NWS tower at Adams Field 

Airport in Little Rock, AR (WBAN No. 13963) and concurrent upper air data from 

North Little Rock Municipal Airport in North Little Rock, AR (WBAN No. 03952) were 

processed with the most recent version of AERMET (v.15181) the meteorological 

preprocessor for AERMOD, along with the two pre-processors to AERMET: 

AERSURFACE (v.13016) and AERMINUTE (v.14337). AERMET was applied to create 

the two meteorological data files required for input to AERMOD.

AERMET requires specification of site characteristics including surface roughness (zo), 

albedo (r), and Bowen ratio (Bo). These parameters were developed according to the 

guidance provided by EPA in the AERMOD Implementation Guide (AIG) (EPA, 2008a) 

using AERSURFACE. The area within 1 km of the meteorological tower at Adams Field 
ERM 3-2 INDEPENDENCE / 0268066 – AUGUST 2015

was broken into 12 sectors of 30 degrees each to analyze the surface characteristics in 

each 30 degree arc around the tower. AERMET uses the surface characteristics in the 

sector from which the wind approaches the tower as part of the meteorological data 

processing for each hour. 

In AERSURFACE, the various land cover categories are linked to a set of seasonal 

surface characteristics. As such, AERSURFACE requires specification of the seasonal 

category for each month of the year. The following five seasonal categories are offered 

by AERSURFACE:

1. Midsummer with lush vegetation; 

2. Autumn with unharvested cropland;

3. Late autumn after frost and harvest, or winter with no snow;

4. Winter with continuous snow on ground; and

5. Transitional spring with partial green coverage or short annuals.

The AERSURFACE run was performed using the seasonal temporal resolution option. 

The default seasonal distribution was used: December, January, and February were 

categorized as winter with no snow, March, April, and May as spring, June, July, and 

August as summer, and September, October, and November as fall. The precipitation 

was assumed to be average over the 3-year period. 

Additionally, 1-minute ASOS wind data, collected at the Adams Field meteorological 

tower, were processed using the AERMINUTE pre-processor for AERMET. The data 

characteristics of Adams Field are shown in Table 3-1. Figure 3-1 shows the relative 

location of Adams Field and Independence Station, and Figure 3-2 shows the 3-year

wind rose for Adams Field.

Table 3-1 Characteristics of the Adams Field – Little Rock Meteorological Data

Distance from Independence Station 80.1 miles

Average Wind Speed 3.42 m/s

Percent Calm Hours 1.10%

Data Completeness 99.95%

All files associated with the meteorological data processing are included in Appendix 

A: The Electronic Modeling Archive.
ERM 3-3 INDEPENDENCE / 0268066 – AUGUST 2015

3.4 Receptor Grid

A comprehensive Cartesian receptor grid extending out to approximately 20 kilometers 

(km) from Independence was used in the AERMOD modeling analysis to assess 

maximum ground-level 1-hour SO2 concentrations. The Modeling TAD states that the 

receptor grid must be sufficient to determine ambient air quality in the vicinity of the 

source being studied. The 20-kilometer receptor grid is more than sufficient to resolve 

the maximum 1-hour SO2 impacts in the area around Independence, and it clearly 

illustrates decreasing SO2 concentration gradients in relation to the plant. 

 

The Cartesian receptor grid consisted of the following receptor spacing:

 50-meter spacing along the facility fence line; 

 100-meter spacing extending from the fence line to 5 kilometers;

 500-meter spacing extending from 5 to 10 kilometers; and

 1,000-meter spacing extending from 10 to 20 kilometers.

The above receptor data was used without modification in the modeling. Per the 1-hour 

SO2 Modeling TAD, a number of receptors located over the White River could be 

excluded from the modeling domain because ambient monitors could not reasonably be 

placed at these locations, but these receptors were retained in this analysis as a measure 

of conservatism.

Terrain elevations from National Elevation Data (“NED”) from USGS were processed 

using the most recent version of AERMAP (v.11103) to develop the receptor terrain 

elevations required by AERMOD. NED data files contain profiles of terrain elevations, 

which in conjunction with receptor locations are used to generate receptor height scales. 

The height scale is the terrain elevation in the vicinity of a receptor that has the greatest 

influence on dispersion at that location and is used for model computations in complex 

terrain areas. The near-field (within 5 kilometers) and far-field (full grid) receptor grids 

are shown in Figures 3-3 and 3-4, respectively.
ERM 3-4 INDEPENDENCE / 0268066 – AUGUST 2015

3.5 Good Engineering Practice Stack Height Analysis

As described in the SO2 Modeling TAD, when modeling actual emissions from a facility 

in order to evaluate the attainment status of an area with regard to the 1-hour SO2

NAAQS, the full height of all stacks is allowed in the modeling regardless of their GEP 

Formula Heights. Therefore, no GEP stack height analysis is necessary for this study. 

Each source was modeled with its actual stack height in the analysis, and downwash 

effects were considered through the use of EPA’s building profile input program (BPIP). 

3.6 Ambient SO2 Background Data for Cumulative Modeling

It was assumed, after initial modeling, that impacts from Independence sources would 

exceed the 1-hour SO2 Significant Impact Level (SIL) of 7.9 g/m3. As a result, ambient 

background data from the closest, most representative SO2 monitor to Independence

was downloaded from the ADEQ ambient monitoring website to represent other 

sources of SO2 in the area. A review of the data showed that the most representative 

monitor for use in the modeling is located in Little Rock (Monitor ID# 05-119-0007). 

EPA guidance allows simulation of background values that vary by season and hour of 

day that could simulate a lower value than the 99th percentile. The modeling was 

performed with a set of seasonal diurnal values developed using the methodology 

described in the USEPA March 1st, 2011 Clarification Memorandum for 1-hour NO2

Modeling. Though this memorandum primarily addresses NO2 modeling, page 20 

describes the process for developing seasonal diurnal background values for SO2 as 

well. 

The location of the selected ambient monitor relative to Independence is shown in 

Figure 3-1. The seasonal diurnal values used are shown in Table 3-2. 
ERM 3-5 INDEPENDENCE / 0268066 – AUGUST 2015

Table 3-2 Seasonal Diurnal SO2 Concentrations at Little Rock Monitor (g/m3)

Hour1 Winter Spring Summer Fall

1 6.89 5.67 4.80 5.50

2 7.85 5.32 4.28 6.19

3 7.33 6.19 4.45 6.02

4 6.89 5.76 4.19 4.71

5 8.55 4.97 4.19 5.15

6 9.60 4.80 5.41 5.85

7 9.60 6.28 5.50 6.63

8 8.99 5.24 6.11 6.54

9 7.50 6.46 7.68 7.85

10 8.38 8.20 7.42 9.07

11 9.16 8.46 9.95 8.20

12 10.73 15.09 10.38 9.34

13 9.69 11.08 10.91 11.17

14 10.56 9.34 9.86 9.51

15 10.03 8.20 13.18 9.95

16 9.42 7.94 9.34 10.47

17 7.15 9.86 11.08 9.16

18 7.50 7.42 9.69 7.24

19 9.25 6.37 9.86 6.98

20 12.30 6.54 8.73 5.93

21 9.07 6.02 6.19 6.28

22 6.11 8.99 5.76 5.67

23 6.46 7.07 5.67 5.85

24 7.24 6.81 5.41 6.11

1. Hours in AERMOD are defined as hour-ending. i.e., Hour 1 is the period from 

midnight through 1 AM, etc.
ERM 3-6 INDEPENDENCE / 0268066 – AUGUST 2015

Figure 3-1 Relative Location of Facility, Airport, and Ambient Monitor
ERM 3-7 INDEPENDENCE / 0268066 – AUGUST 2015

Figure 3-2 Three-year Wind Rose (2012-2014): Little Rock – Adams Field
ERM 3-8 INDEPENDENCE / 0268066 – AUGUST 2015

Figure 3-3 Near-Field Model Receptors
ERM 3-9 INDEPENDENCE / 0268066 – AUGUST 2015

Figure 3-4 Far-Field Model Receptors
ERM 4-1 INDEPENDENCE / 0268066 – AUGUST 2015

4.0 MODELING RESULTS

The modeling results are shown in Table 4-1 below. The modeled design value 

represents the modeled 3-year average of the 99th percentile, maximum daily 1-hour 

average impact for Independence, which is then added to the ambient background 

concentration and the total impact compared to the NAAQS to demonstrate attainment.

Contours of the predicted impacts, as well as the location of the maximum predicted 

impact of 131.3 g/m3, are shown in Figure 4-1. The table shows that model predicted 

impacts from Independence, when modeled using the most recent three years of actual 

emissions data and added to a representative ambient background concentration, are 

below the level of the 1-hour SO2 NAAQS. 

Table 4-1 1-hour SO2 Modeling Results for Independence Station

Source

Independence 

Only

Independence and 

Background

1-hr. SO2

NAAQS

Below 

NAAQS?

Independence Station 122.2 131.3 196.5 Yes

4.1 Conclusions

The air dispersion modeling performed as described in this report shows that the SO2

emissions from Independence Station result in maximum predicted impacts below 

the 1-hour SO2 National Ambient Air Quality Standard. Therefore, an attainment 

designation for Independence County is recommended.
ERM 4-2 INDEPENDENCE / 0268066 – AUGUST 2015

Figure 4-1 Independence Station 1-hour SO2 Impact Contours
ERM 5-1 INDEPENDENCE / 0268066 – AUGUST 2015

5.0 REFERENCES

U.S. Environmental Protection Agency. (USEPA 2005) Guideline on Air Quality Models 

(GAQM, 40CFR Appendix W), November, 2005

U.S. Environmental Protection Agency. (USEPA 2009) AERMOD Implementation 

Guide, AERMOD Implementation Workgroup. March 19, 2009.

U.S. Environmental Protection Agency. (USEPA 2011) USEPA memo entitled 

“Additional Clarification Regarding Application of Appendix W Modeling Guidance 

for the 1-hour NO2 National Ambient Air Quality Standard”, USEPA, Office of Air 

Quality Planning and Standards, Raleigh, NC. March 1, 2011.

U.S. Environmental Protection Agency. (USEPA 2014) “SO2 NAAQS Designations 

Modeling Technical Assistance Document (Draft),” December 2013; 

U.S. Environmental Protection Agency. (USEPA 2014) “SO2 NAAQS Designations 

Monitoring Technical Assistance Document (Draft),” December 2013; 

U.S. Environmental Protection Agency. (USEPA 2014) “Data Requirements Rule for the

2010 1-Hour Sulfur Dioxide (SO2) Primary National Ambient Air Quality Standard 

(NAAQS),” Final rule submitted August 10, 2015; and

U.S. Environmental Protection Agency. (USEPA 2014) “Guidance for 1-hour SO2

Nonattainment Area SIP Submissions,” April 23, 2014. 
Appendix A

Electronic Modeling Archive