Ron Curry, Administrator 

US EPA, Region 6 (6-RA) 

1445 Ross Avenue, Suite 1200 

Dallas, Texas 75202 

RE: Recommendations for Designation of2010 Sulfur Dioxide National Ambient Air Quality 

Standards (S02 NAAQS) of De Soto Parish, Louisiana 

Review of Sierra Club Modeling 

Dear Mr. Curry: 

On October 20,2015, the United States Environmental Protection Agency (US EPA) solicited 

the review of modeling information provided by the Sierra Club in regards to the Dolet Hills 

Power Station in De Soto Parish, Louisiana. 

Upon receipt of the Sierra Club modeling files, the Louisiana Department of Environmental 

Quality (LDEQ) reprocessed the files using the most recent version of AERMOD, 15181, along 

with the proposed default low wind modification. 1 The result of this modeling of actual 

emissions from 2012-2014 as prescribed in the S02 NAAQS Designations Modeling Technical 

Assistance Document was 195.5 11g/m3. Based on this result, coupled with monitoring data 

currently being collected by Dolet Hills Power Station2, LDEQ believes that a change in the 

September 18,2015 recommendation is warranted. 

Therefore, in accordance with Section 107(d) of the Clean Air Act Amendments of 1990 the 

state of Louisiana, through the Louisiana Department of Environmental Quality (LDEQ), 

updates the recommendation for De Soto Parish as follows: 

• Based on technical reviews of available monitoring data and supportive modeling 

results that demonstrate the ambient air in the area surrounding the facility located in 

DeSoto Parish is in compliance with 2010 S02 NAAQS, the LDEQ recommends a 

designation of attainment. 

1 The low wind modification has been proposed to correct issues with model overprediction under low wind speed 

conditions. The low wind option increases the minimum value of the lateral turbulence intensity (sigma-v) from 0.2 

to 0.3 and adjusts the dispersion coefficient to account for the effects of horizontal plume meander on the plume 

centerline concentration. It also eliminates upwind dispersion which is incongruous with a straight-line, steady-state 

plume dispersion model such as AERMOD. 

The site was located according to the Source-Oriented Sulfur Dioxide (S02) Monitoring Technical Assistance 

Document. 

Post Office Box 4301 • Baton Rouge, Louisiana 70821-4301 • Phone 225-219-3953 • Fax 225-219-3971 

www.deq .louisiana.gov 
Peggy M. Hatch 

Secretary 

C: Guy Donaldson, Chief Air Planning Section 

Mark Hansen, Acting Associate Director of Air Programs 

PMH/vth 

Enclosures: 

De Soto Parish Modeling Results 

Modeling Files Available Electronically 
modeling. We find the inputs for the actual emissions to be acceptable and re-ran the modeling using 

the most recent version of AERMOD. 

LDEQ used USEPA's AERMOD program, v. 1S181, as available from the Support Center for Regulatory 

Atmospheric Modeling (SCRAM) website, in conjunction with a third-party modeling software program, 

AERMOD View, sold by Lakes Environmental Software. 

The AERMOD model was run using the Sierra Club input files with the following control options: 

• 1-hour average air concentrations 

• Regulatory defaults and the proposed default LOWWIND3 

• Flagpole receptors at l.S meters height 

• Rural option 

The receptors used by the Sierra Club were retained along with all associated elevations and processing 

done by the Sierra Club. 

The hourly emission file dolethills1214.hrq, and met files KSHV1214.pfl and KSHV1214.sfc were used as 

provided by the Sierra Club. 

The background value of 31.4 was also used. Emissions from the area in a SO km radius around the 

Shreveport Airport monitor were compared to emissions from a SO km radius around the Dolet Hills 

Power Station. Actual emissions surrounding the Shreveport Airport monitor as reported to LDEQ in 

2013 were 1793.S04 tons. This compares to emissions surrounding the Dolet Hills Power Station of 

188S.4SS tons in 2013. It would be reasonable to expect that the contribution of the facilities not 

modeled would be comparable to the monitored impact at Shreveport Airport. 

The result of this modeling was a total impact of 163.1271lg/m3 from the Dolet Hills facility. Combined 

with a background of 31.41lg/m3, the total modeled impact in the area is 194.Silg/m3• 
PROJECT TITLE: 

Do let Hills Power Station 

- Mansfield, Louisiana 

Evaluation of Compliance with the 1-hour NAAQS for 502 

AERMOD View • Lakes Environmental Software 

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COMMENTS: 

SOURCES: 

2 

RECEPTORS: 

13601 

OUTPUT TYPE: 

Concentration 

MAX: 

195 ugfmAJ 

COMPANY NAME: 

MODELER: 

DATE: 

11/12/2015 

SCALE: 

1

:303,230 

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PROJECT NO.: 

C

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aLW\SierraLW.isc