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September 17, 2015 

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Certified Mail: Return Receipt Requested 

Ms. Janet G. McCabe 

Assistant Administrator, Office of Air and Radiation 

U.S. Environmental Protection Agency 

1200 Pennsylvania Avenue, NW 

Washington, DC 20760 

Re: NRG Texas Power LLC 

Demonstrations of 1- Hour S02 NAAQS Attainment Status 

Limestone Electric Generating Station 

W.A. Parish Electric Generating Station 

Dear Ms. McCabe: 

NRG Texas Power LLC 

1000 Main 

Houston, Tx 77002 

NRG Texas Power LLC ("NRG Texas") respectfully offers the attached air quality 

demonstrations for the Limestone and W.A. Parish facilities regarding United States 

Environmental Protection Agency (EPA) proposed actions on the 1-hour S02 National 

Ambient Air Quality Standard (NAAQS) in Texas. 

NRG Texas is a subsidiary of NRG Energy, Inc., a Fortune 250 Company and one of 

the country's largest power generation and retail electricity businesses. NRG Energy's 

power plants provide about 52,000 megawatts of generation capacity and its retail 

businesses serve more than 3 million customers throughout the country. In Southeast 

Texas, NRG Texas owns more than 11,000 MW of generation capacity from nine electric 

generating stations. NRG supports clean energy resources and technologies critical to our 

transition to a sustainable, low carbon society. 

We believe that the areas surrounding the Limestone and Parish plants should be 

designated attainment or unclassified/attainment for the 1-hour S02 NAAQS, which is 

consistent with EPA's updated designations guidance for S02 dated March 20, 2015, which 

states that in the absence of information that clearly shows attainment or nonattainment, 

the EPA intends to designate an area unclassifiable/attainment. Monitoring data is necessary 

for accurate characterization of actual air quality for attainment and nonattainment 

designations. We note that all regulatory-quality S02 monitoring data in Texas currently 

reflects attainment of the NAAQS, and thus available monitor-based evidence supports 

attainment or unclassifiable/attainment designations. 

As a further demonstration that the ambient air around NRG's Limestone and Parish 

plants meets the 1-hour S02 NAAQS, we are providing the attached S02 dispersion 

modeling analyses. These modeling results provide further confirmation that, based on 

representative actual emissions and stack conditions, the emissions from NRG's Limestone 

and Parish plants cannot reasonably be anticipated to cause or contribute to nonattainment 

for the S02 NAAQS. These demonstrations have been made in a manner consistent with 

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EPA and Texas Commission on Environmental Quality (TCEQ) air quality regulations and 

modeling guidelines, and in accordance with EPA's S02 NAAQS Designations Modeling 

Technical Assistance Document (Draft)," December 2013. We are also providing the 

associated electronic modeling files for EPA review in its analysis of the status of these 

areas. 

NRG appreciates your consideration of this information. Please contact me at 832-

357-5291 or craig.eckberg@nrg.com if you have any questions or require additional 

information. 

Sincerely, 

c:~y%L Craig Eckberg 0 

Director, Environmental Services 

NRG Energy, Inc 

Attachments(2) 

Cc: Steve Hagle, TCEQ 

Ron Curry, EPA R6 

Guy Donaldson, EPA R6 (w/electronic files) 

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Attachments 

A. S02 Air Dispersion Modeling Report for W.A. Parish Generating Station (September, 

2015) ("Parish Report"). 

B. S02 Air Dispersion Modeling Report for Limestone Generating Station (September, 

2015) ("Limestone Report"). 

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