SIERRA 

CLUB 

FOUNDED 1892 

September 17, 2015 

Scott Mathias 

Associate Director 

Air Quality Policy Division 

U.S. Environmental Protection Agency 

Research Triangle Park, NC 27711 

Re: Air Dispersion Modeling of Indiana Sulfur Dioxide Pollution 

Dear Associate Director Mathias, 

Sierra Club urges the U.S. Environmental Protection Agency to designate the areas 

surrounding the Gibson, Clifty Creek, Rockport, and A.B. Brown coal-fired power plants as 

nonattainment under the sulfur dioxide ("SOt) National Ambient Air Quality Standard 

("NAAQS"). Air dispersion modeling recently conducted by Wingra Engineering, S.C. on behalf of 

Sierra Club demonstrates tl1at ambient air concentrations in tl1ese areas exceed the NAAQS, which 

is tl1e maximum concentration of air pollution allowed to protect public health. 

First, air dispersion modeling demonstrates that S02 emissions from the Gibson coal-fired 

power plant in Indiana have caused downwind S02 ambient air concentrations to exceed the 196.2 

micrograms per cubic meter NAAQS. In particular, the modeling of acrual emissions from tlus 

facility alone shows peak concentrations as !ugh as 276.8 micrograms per cubic meter. When the 

actual emissions from another large source of S02 that is located within SO kilometers of the Gibson 

Generating Station are included, the peak concentration is as !Ugh as 726.9 micrograms per cubic 

meter. Moreover, the modeling results are consistent with the only monitor located in the modeled 

S02 plume. The 2012-14 design value measured at m01utor #5-18-05 1-0002 188 nucrograms per 

cubic meter. Based on actual hourly emissions from the Gibson plant and other regional sources, the 

modeling analysis predicted a concentration near tl1e monitor location without background of 181.9 

micrograms per cubic meter. Since tl1e predicted and actual measured design values arc in close 

agreement, this comparison supports tl1e accuracy of Sierra Club's modeling results. Accordingly, 

the U.S. Environmental Protection Agency should designate the area surrounding the Gibson coalfired power plant as nonattainment under tl1e NAAQS. 
Letter to Associate Director Mathias 

September 17, 2015 

Page 2 

Second, air dispersion modeling demonstrates that actual S02 emissions from the Clifty 

Creek coal-fued power plant in Indiana have caused downwind peak S02 ambient air concentrations 

as high as 281.4 micrograms per cubic meter. \'\'hen the actual emissions from two other sources of 

S02 that are located within 50 kilometers of the Clifty Creek Generating Station are included, the 

peak concentration is as high as 283.6 micrograms per cubic meter. Therefore, the U.S. 

Environmental Protection Agency should aJso designate the area surrounding the Clifty Creek coalfired power plant as nonattainment under the NAAQS. 

Finally, air dispersion modeling demonstrates that S02 emissions from the Rockport and 

A.B. Brown coal-fired power plants, along with actual emissions from other large S02 sources that 

are within 50 kilometers of the plants, have caused downwind so2 ambient air concentrations to 

exceed the NAAQS. Specifically, the modeling shows cumulative peak concentrations for Rockport 

Generating Station and A.B. Brown as high as 613.6 and 1,231.6 micrograms per cubic meter, 

respectively. The U.S. Environmental Protection Agency should thus designate the area surrounding 

the Rockport and A.B. Brown coal-fired power plant as nonattainment under the NAAQS. 

Enclosed, please find the results of the modeling analyses, along with the corresponding 

modeling input and output files. 

Sierra Club urges the U.S. Environmental Protection Agency to consider this information as 

it undertakes area designations in Indiana for the 2010 revised primary S02 NAAQS. This 

information is being provided to both EPA Region 5 and to appropriate personnel at the Indiana 

Department of Environmental Management. In the meantime, please let us know if we can provide 

any additional information. 

Thank you for your attention to and consideration of this matter, and please do not hesitate 

to contact us if you would like to discuss further. 
Letter to Associate Director Mathias 

September 17,2015 

Page 3 

Sincerely, 

Kristin A. Henry 

Sierra Club 

85 Second Street, 2"d Floor 

San Francisco, CA 94105 

415-977-57 16 

kristin.hcnry@sicrraclub.org 

Tony Mendoza 

Sierra Club 

85 Second Street, 2"d Floor 

San Francisco, CA 94105 

415-977-5589 

tony. mcnJoza@sicrraclub.org