# 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

- 18-051-0002 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 coal

fired 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 ,23 1.6 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 ifwe can provide any additional information. Thank you for your attention to and consideration of this matter, and please do not hesitate to contact us ifyou would like to discuss further.Letter to Associate Dir ector Mathias Septem ber 17,2015 Page 3 Sincerely,



### Kristin A. 

### Henry Sierra Club 85 Second Street, 2"d F l oor San Francisco, 

### CA 94105 415-977-57 16 kristin.hcnry@si crraclub .org T ony Mendoza Sierra Club 85 Second Street, 2"d Floor San Francisco, CA 94105 415-977-5589 tony .mcnJoza@ sicrraclub. org