BOBBY JINDAL GOVERNO

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### of JLoutstana DEPARTMENT OF ENVIRONMENTAL QUALITY OFFICE OF THE SECRETARY Ron Curry

, Administrator US EPA, Region
6 (6-RA) 1445 Ross Avenue, Suite 1200 Dallas, Texas 75202

P EGGY M . HATCH SECRETARY 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 S0 2 NAAQS Designations Modeling Technical Assistance Document was 195.5 11g/m

3 . Based on this result, coupled with monitoring data currently being collected by Dolet Hills Power Station

2 , 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 S0 2 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 incr e ases 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. Pos
t O f fi ce B ox 430 1 • Ba t o n R o u ge, L ouis

i a n a 70821

- 430 1 • Ph o n e 225-2

1 9 - 3953

• Fax 225
- 2 1 9 - 397 1 www

. deq .l o u isia n a . gov

### Modeling results to support the LDEQ's updated recommendation
for De Soto Parish can be found in the attached enclosures.
If you have any questions

, please contact Cheryl Nolan, Administrator ofthe Air Permits Division, Office ofEnvironmental Services at (225) 219-3408. 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

## Louisiana Department
of Environmental Quality Review and Reprocessing
of the Sierra Club Modeling of Do let Hills Power Station The Louisiana Department
of Environmental Quality (LDEQ) reviewed the inputs from the Sierra Club 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 em

i ssions 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/m

3 from the Dolet Hills facility. Combined with a background of 31.41lg/m

3 , the total modeled impact in the area is 194.Silg/m

3 •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 **O~oooo~** 1oooo1 **~oooo~5km**

PROJECT NO .: C : \Users\p00107358\Documents\Sierr a LW\SierraLW.isc