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September 17, 2015 

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Certified Mail : Return Receipt Requested
Ms. Janet G. McCabe Assistant Administrator, Office ofAir 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 ofthis information. Please contact me at 832- 357-5291 or craig.eckberg@nrg.com ifyou 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)

-2-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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