Air Quality Modeling Technical Note 

Dolet Hills Power Station 

Mansfield, Louisiana

Prepared for 

Cleco Power, LLC 

and 

Southwestern Electric Power Company 

Prepared by 

David J. Long, PE and Ashley N. Ullstrom 

Air Quality Services Section 

American Electric Power Service Corporation 

March 30, 2016
i 

TABLE OF CONTENTS 

Introduction .............................................................................................. 1 

Description of Facility and Area ..................................................................... 1 

Sierra Club Modeling .................................................................................. 2 

Modeling Platform ...................................................................................... 3 

Sources Included in this Study......................................................................... 4 

Dolet Hills Power Station BPIP Data ................................................................ 4 

Background Values ...................................................................................... 4 

Plant Operating Data Considered and Results ...................................................... 4 

Conclusions ................................................................................................. 6 

References ................................................................................................... 7 

Appendix .................................................................................................... 8 

LIST OF FIGURES 

Figure 1. Dolet Hills Power Station, International Paper and the nearby area .................... 1 

LIST OF TABLES 

Table 1. Summary of Modeled Design Values for All Simulations Discussed (Values in ug/m3

with Background).......................................................................................... 6
1 

INTRODUCTION

American Electric Power Service Corporation (AEPSC) on behalf of Operating Owner Cleco 

Power LLC and AEP operating company Southwestern Electric Power Company has examined 

modeling performed by the Sierra Club and performed derivative modeling of the Dolet Hills 

Power Station located near Mansfield, Louisiana. This Technical Note briefly describes the 

Sierra Club modeling and outlines issues raised by that modeling that were addressed by the 

derivative modeling performed as part of this effort. The additional modeling and analysis 

performed as part of this effort demonstrated that when the stack parameters for Dolet Hills Plant 

are properly represented in AERMOD, emissions from Dolet Hills Plant and the nearby 

International Paper Mansfield Mill do not cause or contribute to nonattainment in the area. 

DESCRIPTION OF FACILITY AND AREA 

The Dolet Hills Power Station is a single unit 650 MW power generating facility. This unit is 

equipped with a wet scrubber for sulfur and acid gas control, and an electrostatic precipitator for 

particulate control. The plant is located in DeSoto Parish, Louisiana approximately 11.5 

kilometers east of Mansfield, Louisiana and approximately 13.5 kilometers south of an 

International Paper facility. The elevation of the Dolet Hills Station is 82 meters and the terrain 

is gently sloping down to the north, east and south of the facility. Figure 1 shows the nearfield 

view of the area surrounding the Dolet Hills Power Station and the International Paper Mansfield 

Mill. 

Figure 1. Dolet Hills Power Station, International Paper and the nearby area. 

Copyrighted map removed
2 

SIERRA CLUB MODELING 

As part of a larger program undertaken by the Sierra Club, the Sierra Club sponsored 

independent modeling of the Dolet Hills Power Station and submitted the results of this 

modeling to USEPA Region VI. This modeling used surface and upper air meteorology for the 

period 2012 – 2014 collected at the Shreveport, Louisiana national weather service site. The 

data was processed using the current version of AERMET as of June 2015 with no Beta Options 

being used. 

The receptor set used in the Sierra Club sponsored modeling was developed using AERMET. 

The only deviation from what would be considered standard SIP and PSD modeling practice is 

that the Sierra Club analyst used 1.5 meter tall flagpole receptors. A test simulation performed 

as part of this study indicated that the use of the 1.5 meter flagpole receptors served to increase 

the design value by an insignificant 0.003 ug/m3. 

The Sierra Club sponsored modeling also endeavored to generate an hourly input file for Dolet 

Hills Power Station using emissions data sources from the USEPA Clean Air Markets Division 

(CAMD). It does not appear that the Sierra Club Modeling made any attempt to use CAMD 

flow data and used a “flat” full load profile based on design conditions likely sourced from 

permit data that resulted in a flat flow and temperature profile that was paired with a load 

varying CEMS based emission rate sourced from CAMD. In doing this, it appears that the Sierra 

Club analyst did perform some data quality work and reasonably corrected much of the missing, 

substituted and troubled data received from CAMD. The potential issues with sourcing 

modeling data from CAMD data was publically reported by Long at the 11th USEPA Triennial 

Modeling Conference in August 20151

. 

The Sierra Club report also raised the following issues that they claimed caused their modeling 

to underestimate the actual concentrations present in the area around the Dolet Hills Power 

Station2

: 

• Allowable emissions are based on a limitation with an averaging period which is greater 

than the 1-hour average used for the SO2 air quality standard. Emissions and impacts 

during any 1-hour period may be higher than assumed for the modeling analysis. 

• No consideration of facility operation at less than 100% load. Stack parameters such as 

exit flow rate and temperature are typically lower at less than full load, reducing pollutant 

dispersion and increasing predicted air quality impacts. 

• No consideration of building or structure downwash. These downwash effects typically 

increase predicted concentrations near the facility. 

• No evaluation has been conducted to determine if the stack height exceeds Good 

Engineering Practice (GEP) height. If the stack height exceeds GEP, the predicted 

concentrations will increase. 

• No consideration of off-site sources. These other sources of SO2 will increase the 

predicted impacts. 
3 

The work performed as part of this review serves to address all of these issues in a fashion that 

demonstrates that the impacts of these issues either reduces concentrations or has minimal 

impact on the final conclusion of the modeling exercise. 

At this point, we will address one of the Sierra Club claims outlined above, that being the GEP 

Stack Height issue. Under the provisions of USEPA SO2 SIP Designations Modeling Technical 

Assistance Document specific to the 1-Hour SO2 Standard, it is permissible to use the full stack 

height for modeling of actual emissions, regardless of the GEP status of the stack for purposes of 

designation modeling of the 1-Hour SO2 Standard3

. Therefore, with regards to the actual 

emissions case, the GEP height of the stack is irrelevant to the analysis. We would add that since 

USEPA made major changes to the formulation of AERMOD regarding downwash in version 

11059, it is necessary to include a BPIP parameterization in the analysis of all stack emission 

points. The actual stack height of the Dolet Hills Power Station is 160.02 meters and the BPIP 

calculated GEP Height 247.85 meters. In order to determine what impact downwash would have 

on the analysis, a simulation was made that added the BPIP parameterization to the inputs for 

Dolet Hills Power Station. The results of this simulation were compared to the results of the 

base simulation performed by the Sierra Club and no change in the modeled design value was 

noted. Therefore, it can be concluded in the case of Dolet Hills Power Station that the GEP 

height issue and the lack of BPIP parameterization in the Sierra Club modeling described in the 

Sierra Club modeling report has no impact on the modeled design value. 

MODELING PLATFORM USED FOR THIS EVALUATION 

The Sierra Club sponsored modeling used the current versions of AERMOD and AERMET as of 

June 2015, that being version 14134. AERMOD and AERMET were exercised using none of 

the Beta Options installed in them. As part of this evaluation, the version of AERMOD used was 

Version 15181, which was issued in July 2015. Again, no Beta Options were used in AERMOD 

and an initial simulation was made using AERMOD Version 15181 that exactly matched the 

results from the Sierra Club modeling. This allows the conclusion that any changes in the results 

observed in new modeling simulations performed as part of this evaluation were due to other 

changes we introduced into the modeling system and not attributable to the change in the version 

of AERMOD. 

For purposes of this evaluation, we accepted the 2012 to 2014 meteorologic files developed in 

the Sierra Club sponsored modeling effort. The review of these files allows us to conclude that 

the meteorologic files were developed using proper modeling procedures. 

While not a standard SIP or PSD configuration, we also are using the Sierra Club developed 

receptor grid which included 1.5 meter flagpole receptors. We have previously noted that the 

use of the flagpole receptors resulted in an insignificant difference in modeled design values in 

this area. This conclusion cannot be applied to other work using flagpole receptors of this type 

that should be evaluated for their impact on a site by site basis. 

 
4 

SOURCES INCLUDED IN THE MODELING 

The sources included in various simulations conducted throughout this work included the Dolet 

Hills Power Station (all simulations) and the International Paper Mansfield Mill in the final two 

simulations following the obtaining of appropriate inputs for the International Paper facility. 

DOLET HILLS BPIP INFORMATION 

BPIP information for use in this evaluation was supplied by CB&I, the A/E firm used by Cleco 

Power for technical services relating to the generation units they operate. The information 

supplied appears to have been done using standard practices for developing a detailed BPIP 

analysis, and was used as received. 

This result of inserting this data into the input files originally developed as part of the Sierra 

Club sponsored modeling resulted in no change in the fourth high values generated by 

AERMOD at levels that would be of regulatory interest in the sensitivity simulation performed. 

BACKGROUND VALUES 

With the exception of the final simulation performed under this evaluation that used a seasonal 

hourly background value developed from the 2013-2015 Shreveport SO2 Monitor data by 

AECOM on behalf of International Paper, all simulations used the background value of 31.4 

ug/m3 used by the Sierra Club that are based on air quality data monitored during 2011 to 2013 at 

an SO2 monitor located in Bossier Parish, Louisiana. 

Based on that additive nature of percentile statistics, the 31.4 ug/m3 which is noted in the Sierra 

Club report as representing the 99th percentile value at the selected monitor results in the pooled 

modeled and monitored value representing the 99.99th percentile value of total impact, a value 

that is much more restrictive than the actual 1-Hour SO2 Standard. Please refer to the 

presentation of Sergio Garcia at the 11th USEPA Modeling Conference4

 for more information on 

this calculation. 

PLANT OPERATING DATA CONSIDERED AND RESULTS 

In the Sierra Club supported modeling of the Dolet Hills Power Station, the modeling study used 

both the permit limits for Dolet Hills and a processed version of the CAMD based emission data 

to generate an hourly emissions file for the period 2012-2014. The emissions portion of this file 

appears to have been inspected and corrected to remove missing, substituted, and otherwise 

invalid data that is reported to CAMD under the requirements of 40 CFR Part 75, but that is not 

reasonable for use in air quality modeling in a rational manner. However, the inputs for exit 

velocity (based on flow) and temperature are fixed at values that are represented as being full 

load values. The study admits that it does not account for reduced load operation, but states that 

they believe that this serves to reduce the modeled impacts from the study. 
5 

As the evaluation progressed, a limited amount of actual operating data became available for 

comparison to the values used by the Sierra Club and it became apparent that the current full 

load operating conditions were significantly different than were used by the Sierra Club. This 

brief evaluation suggested that the temperature used as a full load representation may be on the 

order of at least 40 F low and the flows and exit velocities would be higher due to the 

temperature induced differences in volume. In order to not overstate the changes in the initial 

test of this theory, the second lowest temperature was used and a low end flow value was 

selected and then corrected for temperature to be used as constant inputs as was done by the 

Sierra Club. This resulted in a 39 F temperature increase to 200 F from 161 F and an increase in 

exit velocity from 25.84 m/sec to 27.71 m/sec. This hourly file was then run with the BPIP 

inputs and the resulting model output found the modeled design value reduced from 218.7 ug/m3

in the Sierra Club modeling to 188.8 ug/m3

. While, this was not viewed as a definitive result, it 

did lead to a recommendation that a full actual operating inventory be built and run to see if the 

actual operating conditions would also give a comparable result. This recommendation was 

accepted and the full CEMS based operating record for heat input, flow, SO2 emissions, and 

temperature was supplied by CLECO Power to allow the development of a CEMS based hourly 

inventory for use in this exercise. 

The hourly CEMS based inventory developed by AEPSC as part of this exercise used the 

principles we have established during the development of a number of CEMS based hourly 

emissions inventories for some 11 AEP Operated or affiliated sites, to date. These principles are 

discussed in a paper to be presented by David Long at the AWMA Specialty Conference on Air 

Quality Models in April 2016 in Chapel Hill North Carolina3. Once the full data set was 

received from CLECO Power through their consultant CBI, an AERMOD ready CEMS based 

hourly inventory was prepared. 

When this inventory was run in AERMOD, the result was further reduced from the test value of 

188.8 ug/m3 to 185.8 ug/m3, much lower than the Sierra Club generated 218.7 ug/m3. Since this 

case used a fully developed actual operating based hourly inventory this result was viewed as a 

robust and credible demonstration that Dolet Hills Power Station did not violate the 1-Hour SO2

Standard under its actual operating conditions. This result also serves to rebut the view of the 

Sierra Club that moving from their flat full load parameterization to an actual hourly 

parameterization that properly reflected reduced load and startup operations would serve to 

increase the modeled concentrations. In this case it significantly reduces the modeled 

concentrations, which in our experience is not an uncommon outcome when compared to a flat 

operational profile. 

With this information in hand, the only question remaining was what interactive impacts would 

Dolet Hills Power Station have with the one other significant source of SO2 emissions in DeSoto 

Parish. That source being the International Paper Mansfield Mill approximately 13.5 kilometers 

to the north of Dolet Hills. After some discussions with International Paper, we were able to 

obtain a modeling inventory that they were using in an effort to potentially demonstrate that 

DeSoto Parish should be split with the portion of the county they are located in deemed as being 

in attainment with the 1-hour SO2 Standard. We did not use their Dolet Hills inventory since it 

was not based on full operating data from CEMS due to the CAMD data source not containing 
6 

the concurrent temperature data used to adjust the flow data from actual stack conditions to 

standard conditions (CAMD does not collect this data). The information supplied by 

International Paper also contained a more detailed analysis of background data from a monitor in 

the Shreveport area that allowed the generation of a seasonal hourly background value. In 

addition to using the 31.4 ug/m3 background value developed by the Sierra Club, we also ran the 

more detailed background data to allow a comparison of a more robust background analysis to 

the more simple single value that had been used. 

Adding the emissions from International Paper resulted in a domain wide design value of 186.2 

ug/m3, an increase of 0.4 ug/m3 when the International Paper facility with what are viewed as 

reasonable emissions are included in the model. The final simulation in this evaluation replaced 

the fixed SO2 background value from the Sierra Club modeling with the AECOM/International 

Paper developed seasonal hourly background. This change resulted in a further reduction in the 

peak design value from the 186.2 ug/m3

 to 171.0 ug/m3. This outcome was expected as the 

hourly SO2 concentrations used for background varied from 1.867 ppb in hour 7 in the Fall 

season (4.88 ug/m3) to 9.500 ppb during hour 10 in the Summer season (24.85 ug/m3), all below 

the constant 31.4 ug/m3

 used in all of the preceding simulations. 

The results of these two simulations containing both Dolet Hills and International Paper serve to 

refute the Sierra Club contention that considering the emissions from other significant sources in 

the area would further serve to significantly increase modeled SO2 values in the area, generating 

a more widespread nonattainment problem in the DeSoto Parish area. These simulations clearly 

demonstrate modeled attainment with the 1-Hour SO2 Standard under actual operating conditions 

at both Dolet Hills Power Station and International Paper. Table 1, below, consolidates all of the 

simulations discussed into a single table showing how the changes made in the modeling 

platform changed the results in ways that generally contradict the claims made by the Sierra Club 

sponsored modeling study and show that when actual conditions are properly represented in the 

model, the area demonstrates modeled attainment with the 1-Hour SO2 Standard. The modeling 

files used for all simulations except the Initial Sierra Club Model are included in electronic form 

as an appendix to this document. 

Table 1. Summary of Modeled Design Values for All Simulations Discussed (Values in ug/m3

with Background). 

Facility Initial 

Sierra 

Club 

Model 

Updated 

to 

AERMOD 

15181 

Added 

Dolet 

Hills 

BPIP 

Data 

Dolet Hills 

Temp/Flow 

Sensitivity 

Dolet 

Hills 

Actual 

Temp 

and 

Flow 

Added 

International 

Paper 

Updated to 

AECOM/IP 

Seasonal 

Background

Dolet Hills 218.7 218.7 218.7 188.8 185.8 185.8 170.5 

International 

Paper 

NA NA NA NA NA 113.0 95.2 

Combined NA NA NA NA NA 186.2 171.0 
7 

 

CONCLUSIONS

The additional modeling done to support this effort demonstrates that there are significant 

shortcomings in the Sierra Club’s modeling analysis. This work further demonstrates that the 

claims of conservatism made in the Sierra Club modeling report are not well-founded and are 

generally inaccurate when the specific issues are addressed. Further, this work demonstrates 

that EPA should make a final designation of attainment for DeSoto Parish for the1-hour SO2

standard. 

REFERENCES 

1. Long, David, The Use of CAMD Data in Air Quality Modeling, 11th USEPA Triennial 

Modeling Conference, Research Triangle Park, NC, August 12 – 13, 2015. 

2. Klafka, Steven, Dolet Hills Power Station Mansfield, Louisiana – Evaluation of Compliance 

with the 1-hour NAAQS for SO2, Revised December 2015, page 4. 

3. U.S. EPA, Office of Air Quality Planning and Standards, Air Quality Assessment Division, 

SO2 NAAQS Modeling Technical Assistance Document, page 22.

4. Garcia, Sergio, Background Concentrations and the Need for a New System to Update 

AERMOD, 11th USEPA Triennial Modeling Conference, Research Triangle Park, NC, August 12 

– 13, 2015. 

5. Long, David, The Use and Processing of USEPA Clean Air Markets Division CEMS Data for 

Air Quality Modeling and Other Applications, To be presented at The Air and Waste 

Management Association Specialty Conference The Guideline on Air Quality Models: The New 

Path, Chapel Hill, NC, April 12 – 14, 2016. 
8 

APPENDIX 

Modeling Inputs for the Reported Simulations in Electronic Form