# SIERRA CLUB I · 0 U N 0 E D I 8 9 2

September 1 7, 2015 Scott MathL'l.S Associate Director Air Quality Policy Divi s ion U .S. Em'iro nmental Protection Agency Research Triang le P ark, r C 2771 1 Re: Air Dispersion f\ l odeling of Michigan Su lfur Dioxide Pollution Dear Associate Director Mathias, Sierra Club urges the U. S. Environmenra l Protection Agency to designate the areas s urrounding the St. C lair, Belle Rj,·er, and 1\[onroe coal-fired power plants as nonattainment under the s ulfur dioxide 

### ("SOt) Na tional Ambient Air Quality Standard(" Ar \Q ") . r \ir dispersion modeling recently conducted b y 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 S0 2 em ission s 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 s hows peak concentrati o n s as high as 

### 262A micrograms per cubic meter. When the actual emis s ion s from the Belle

**Ri, er**  p ower plant, which is another so urce of 50 2 tl1at is l oca ted witl1in 50 kilometers of the St. C lair power plant, are included the peak concentration is a s high as 270 . 2 micrograms per cubic meter. According l y, the U .. EnYironmenta l Protecti o n Agency sho uld designate the area surro unding tl1e S t. Clair coa l

- fired power plant, including the area where BeUe River is located, as nonatminment under the NAAQS. Second, air di s p e rs ion modeling demon strates that S0 2 emis s ions from the l\ l onroe power plant alone exceed the r 1 v\QS with peak concentrations as high as 283.9 micrograms per cubic meter . \'Vhen the acmal emissions from numero u s ot hers sources of 

## so:! that arc located wid1in 

## so kilometers of the f\ [ onroe power plant, are included, the peak concentrati o n is as high as 292.5Le tter to Associa te Director Ma thia s Sep temb e r 1 7, 2015 P age 2 micrograms per c ubi c m eter . A ccording ly, the U . S . Environmenta l Protection Age nc y s hould designate the area s urro unding the f'vlomoe coal -fired pow er pl ant as nonattainment under the NA. AQS . E nclo se d, plea se find the re s ults o f the modelin g analyses, along with the corre spo nding modeling input and output files . S i

erra C lub urges the U.S . E n v iro nmental Protecti o n Agen cy to consider this information as it undertakes area d es i g natio n s 

### in**Michigan** for the 2010 r evised prim ary S 0 2 NAAQS . Thi s information is b eing pro vide d to both E PA Regio n 5 an d to appropriate perso nnel at the TV lichiga n Departme nt of Environmental Quality. In the meantime, please let us know if we can pro vide any additio nal information . Thank yo u for yo ur attention to and con s ideration of this matter, and please do not hesitate to contact us if yo u w o uld like to disc u ss further. S ince rel y,

K.ristin A. Henry S ierra C lub 8S Seco nd S tre et, 2" ct Floor Sa n Francisco, CA 941 OS 41S-977-S716 kristi n.h enry@s icrraclub . org L aurie William s S i erra Club SO F Street, NW, 7 th Floor Washington, DC 20001 202-S48

- 4S9 7 lauric .wi.lliams@sic rr aclub.ori!