SIERRA 

CLUB 

I· 0 U N 0 E D I 8 9 2 

September 17, 2015 

Scott MathL'l.S 

Associate Director 

Air Quality Policy Division 

U.S. Em'ironmental Protection Agency 

Research Triangle Park, r C 2771 1 

Re: Air Dispersion f\ lodeling of Michigan Sulfur Dioxide Pollution 

Dear Associate Director Mathias, 

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

surrounding the St. Clair, Belle Rj,·er, and 1\[onroe coal-fired power plants as nonattainment under 

the sulfur dioxide ("SOt) National Ambient Air Quality Standard(" Ar\Q "). r\ir dispersion 

modeling recently conducted by Wingra Engineering, S.C. on behalf of Sierra Club demonstrates 

that ambient air concentrations in tl1ese areas exceed the AAQS, which is the maximum 

concentration of air poUution allowed to protect public health. 

First, air dispersion modeling demonstrates that S02 emissions from the St. Clair in 

f\lichigan have caused downwind so2 ambient air concentrations to exceed the 196.2 micrograms 

per cubic meter NAr\QS. In particular, tl1e modeling of actual emissions from this facility alone 

shows peak concentrations as high as 262A micrograms per cubic meter. When the actual emissions 

from the Belle Ri, er power plant, which is another source of 502 tl1at is located witl1in 50 

kilometers of the St. Clair power plant, are included the peak concentration is as high as 270.2 

micrograms per cubic meter. Accordingly, the U .. EnYironmental Protection Agency should 

designate the area surrounding tl1e St. Clair coa l-fired power plant, including the area where BeUe 

River is located, as nonatminment under the NAAQS. 

Second, air dispersion modeling demonstrates that S02 emissions from the l\lonroe power 

plant alone exceed the r 1v\QS with peak concentrations as high as 283.9 micrograms per cubic 

meter. \'Vhen the acmal emissions from numerous others sources of so:! that arc located wid1in so 

kilometers of the f\[onroe power plant, are included, the peak concentration is as high as 292.5 
Letter to Associate Director Mathias 

September 17, 2015 

Page 2 

micrograms per cubic meter. Accordingly, the U.S. Environmental Protection Agency should 

designate the area surrounding the f'vlomoe coal-fired power plant as nonattainment under the 

NA.AQS. 

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

modeling input and output files. 

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

it undertakes area designations in Michigan for the 2010 revised primary S0 2 NAAQS. This 

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

Department of Environmental Quality. 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. 

Sincerely, 

K.ristin A. Henry 

Sierra Club 

8S Second Street, 2"ct Floor 

San Francisco, CA 941 OS 

41S-977-S716 

kristin.henry@sicrraclub.org 

Laurie Williams 

Sierra Club 

SO F Street, NW, 7th Floor 

Washington, DC 20001 

202-S48-4S97 

lauric. wi.lliams@sicrraclub.ori!