SIERRA 

CLUB 

FOUNDED 1892 

September 17, 2015 

Scott Mathias 

1\ssociate Director 

Air Quality Policy Division 

U.S. Environmental Protection Agency 

Research Triangle Park, NC 27711 

Re: Air Dispersion .Modeling of tvfissouri Sulfur Dioxide Pollution 

Dear Associate Director Mathias: 

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

surrounding the Labadie and Sibley coal-fired power plants as nonattainment under the 

sulfur dioxide ("SOz") National Ambient Air Quality Standard ("NAAQS"). Air dispersion 

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

demonstrates that ambient air concentrations in both areas exceed the NAAQS, which is the 

maximum concentration of air pollution allowed to protect public health. 

First, air dispersion modeling demonstrates that S02 emissions from the Labadie 

coal-fired power plant in Missouri have caused downwind S02 ambient air concentrations to 

exceed tl1e 196.2 micrograms per cubic meter NAAQS. In particular, tl1e modeling shows 

peak concentrations as high as 235.7 micrograms per cubic meter. This is consistent wiili 

tl1e tvlissouri Department of Natural Resources modeling results, which found emissions 

from tlUs facility exceeded ilie NA.AQS. Accordingly, ilie U.S. Environmental Protection 

Agency should designate tl1e area surrounding tl1e Labadie coal-fired power plant as 

nonattainment under the NA1\QS. 

Even though l\.f.issouri Department of Natural Resources' modeling found emissions 

from ilie Labadie plant exceeded the NAAQS, it presented anoilier option to nonattainmeot 

demonstration-unclassifiable. The agency suggested tlUs option because iliree months of 

data from a monitor recently installed by Ameren do not show violations of the NAAQS. 

U.S. EPA should not consider tlUs a viable option because the monitor is not located at ilie 
Letter to Associate Director Mathias 

September 1 7, 2015 

Page 2 

area of peak concentration and because three years of quality-assured monitoring data are 

required in order to determine whether an area complies with the 1-hour S02 NAAQS. In 

addition, Ameren presented modeling to the Missouri Department of Natural Resources 

which purportedly showed no violations of the NAAQS. U.S. EPA should not rely on 

Ameren's modeling as it was able to «engineer'' these results because it modified tluee 

important inputs. Sierra Club submitted comments to the agency, with copies to EPA 

Region 7, about why an unclassifiable designation was inappropriate and about why 

Amercn's modeling was deficient. Sec attached comment letters, which include copies of its 

modeling for the agency's consideration. Sierra Club intends to supplement its comments 

with a further critique of Ameren's Labadie modeling as there was not enough time to 

comprehensively review the modeling before the comment deadline. Sierra Club will copy 

EPA Region 7 and EPA's Office of Air Quality Planning and Standards on this comment 

supplement. 

Second, air dispersion modeling demonstrates that S02 emissions from the Sibley 

coal-fired power plant in :Missouri, along with other large sources of S02 that are located 

within so kilometers of the plant, have caused downwind so2 ambient air concentrations to 

exceed the NAAQS. In particular, the modeling shows peak concentrations as high as 43S.2 

micrograms per cubic meter. The modeling results are consistent with the only monitor 

located in the modeled S02 plume. The 2012-14 design value measured at monitor 

#72909S0034 was 1 SO ppb or 392.4 micrograms per cubic meter. Based on actual hourly 

emissions from the Sibley plant and other regional sources, the modeling analysis predicted a 

concentration near the monitor location of 382.5 micrograms per cubic meter. Since the 

predicted and actual measured design values are in close agreement, this comparison 

supports the accuracy of Sierra Club's modeling .results. Therefore, the U.S. Environmental 

Protection Agency should also designate the area surrounding the Sibley 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 and comments Sierra Club submitted to 

1\f.issouri Department of Natural Rcsou.rces. 

Sie.r.ra Club urges the U.S. Environmental Protection 1\ gency to consider this 

information as it undertakes area designations in l\lissouri for the 2010 revised primary so2 

NAAQS. This information has already been provided to :Missouri Department of Natural 

Resources and is also being provided to EPA Region 7. In the meantime, please let us know 

if we can provide any additional information. 
Letter to Associate Director ~vfathias 

September 17, 2015 

Page 3 

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, 

Kristin A. Henry 

Sierra Club 

85 Second Street, 2"d Floor 

San Francisco, CA 94105 

415-977-5716 

kristin.hcnry@sierraclub.org 

Sunil Bector 

Sierra Club 

85 Second Street, 2"d Floor 

San Francisco, CA 94105 

415-977-5759 

~u nil.bcctor@1~ emtclub. rg 

Maxine I. Lipeles 

Director, Interdisciplinary Environmental Clinic 

Senior Lecturer in Law 

Washington University School of Law 

One Brookings Drive - Campus Box 1120 

St. Louis, 'tviO 63130 

314-935-5837 

milipele@wusrl.edu