John Mooney, Chief 

Air Programs Branch 

Region 5 Air and Radiation Division 

U.S. Environmental Protection Agency 

77 West Jackson Boulevard Chicago, IL 60604-3590 

Re: Sierra Club Sulfur Dioxide Modeling Dear Mr. Mooney: 

Thank you for the opportunity to comment on the modeling and related information 

provided by the Sierra Club to USEPA. As you may know, the Sierra Club provided this 

same modeling information to Illinois EPA, urging the State to use the information in our 

recommendations to USEPA- however, the information was mailed by the Sierra Club 

on September 15 and received by Illinois EPA on September 22, after Illinois EPA had 

already submitted its recommendations to USEPA, which were due on September 18. 

Notwithstanding, Illinois EPA, of its own accord and at USEPA's request, has reviewed 

the modeling files and descriptive information provided by the Sierra Club and has noted 

a number of issues with that modeling, some of which apply to all three of the power 

plants at issue in the designation recommendation, others of which are more specific to 

the area being modeled. As such, the comments that follow are broken into two types -

general and area-specific. 

Some of the more significant modeling differences common across all of Sierra Club's 

methodology are: 

1) Sierra Club modeling did not utilize hourly varying temperatures and exit 

velocities for the power plants or any near-field sources included in the modeling. 

Instead, they used constant values for those modeling inputs. The S02 Technical 

Assistance Document (TAD) notes, .. In some cases, exit temperatures or exit 

velocities change with emission levels." Ambient pollutant concentrations may be 

better characterized using hourly varying temperatures and exit velocities. Thus, 

Illinois EPA utilized varying, not constant, modeling inputs, which it believes 

yields modeling results that are more accurate. 

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Illinois EPA is more accurate than that in the USEPA Air Markets Database. 

3) Sierra Club modeling did not include nor account for structure-induced plume 

down wash from buildings, tanks, or other structures, whereas Illinois EPA's 

modeling does. The Illinois EPA's use of such detailed information provides a 

better, and more accurate, representation of ambient pollutant concentrations. 

4) Sierra Club did not include fenceline receptors in the receptor network to aid in 

specifying ambient air/non-ambient air boundaries, whereas Illinois did. Illinois 

EPA finds that the use of fenceline receptors for defining ambient versus nonambient air is appropriate if the general public is precluded access to property. 

The inclusion of fenceline receptors aids in defining areas that need not be 

modeled because they represent non-ambient air, and thus provides additional 

accuracy in the Illinois EPA modeling. 

5) Sierra Club set a "flagpole height" of 1.5 meters above ground level as the height 

at which modeling concentrations would be determined, rather than ground level. 

Sierra Club referred to this as the "inhalation height." However, the following text 

from page 9 of the TAD speaks directly to this matter, indicating that use of the 

"flagpole height" is unnecessary: "In recent years, many modeling exercises of 

S02 have used a receptor height other than ground level to account for the 

breathing height of individuals. This is achieved using the AERMOD 

FLAGPOLE option. While it may seem that modeling concentrations at breathing 

height would lead to better characterization of air quality at the level most 

individuals are breathing, the use of FLAGPOLE receptors is not necessary. 

Appendix W does not specify that receptors should be placed at levels other than 

ground level for comparison to the NAAQS." 

6) Sierra Club used a constant annual S02 background value (201 1-2013 Design 

Value) from the Oglesby, Illinois, monitor for all three areas. Illinois EPA did not 

use the older Oglesby monitoring data. Rather it used more recent (2012-2014) 

and geographically appropriate data from Nilwood (IL), Houston (IL), and 

Paducah (KY) for Newton, Marion, and Joppa power plants, respectively. 

Moreover, the Illinois EPA used hourly and seasonally varying background 

values, not an invariant annual value. Illinois EPA's background, as well as 

hourly and seasonal varying inputs, are more accurate and appropriate for 

modeling. 
EPA. Sierra Club's own modeling shows an extremely small contribution from the 

Newton plant to any supposed nonattainment area near Rain CII Carbon, notwithstanding 

the suggestion by Sierra Club that the Newton power plant is causing nonattainment. 

Illinois EPA's modeling demonstration shows that neither Rain CII Carbon nor the 

Newton power plant is causing nonattainment. 

Marion Power Plant 

The Sierra Club included emissions from the Joppa Steam Coal Power Plant ( 48 

kilometers to the south) in the Marion Power Plant modeling. Illinois EPA modeled the 

Marion and Joppa plants separately. On the other hand, the Illinois EPA explicitly 

modeled the U.S. Penitentiary as a near-field background source in the Marion Power 

Plant study area to ensure additional accuracy, whereas the Sierra Club did not. Sierra 

Club's method of including more distant sources that are already being modeled 

separately while excluding nearby sources from the same modeling exercise does not 

appear to be the best way to reach the most accurate conclusion. 

Joppa Steam Coal Power Plant 

1) Sierra Club used an incorrect release height for the Joppa Power Plant stacks. Per 

the TAD, states should use the actual physical height of the stacks in designations 

(Phase II) modeling. It appears Sierra Club used GEP height for the Joppa stacks 

(407.32 feet), whereas the Illinois EPA used actual stack heights (500 feet). The 

Sierra Club's use of stack heights that presumably reflect GEP stack heights runs 

counter to the TAD modeling guidance (see page 21 ): "For the purposes of 

modeling with actual emissions to characterize air quality for use in a future S02 

designations process, actual stack heights should be used rather than follow the 

GEP stack height policy (use ofGEP stack heights for stack heights exceeding 

GEP and actual stack height for stacks below GEP). The EPA recommends the 

use of actual stack heights so that the modeling analysis can most closely 

represent the actual ambient air quality conditions as influenced by the source." 

The Illinois EPA modeling most closely represents the actual ambient air quality 

conditions. 

2) The Illinois EPA explicitly modeled Lafarge Midwest Inc., Trunkline Gas 

Company, Honeywell International Inc., and Midwest Electric Power Inc. as nearfield background sources in the Joppa Power Plant study area to ensure additional 

accuracy, whereas the Sierra Club did not. 
The Illinois EPA maintains the modeling it submitted is conservative, accurate, and 

representative of actual ambient conditions, and clearly supports Illinois' designation 

recommendations. 

Should you have any questions or wish to discuss this matter further, please contact 

David Bloomberg at 217-524-4949. 

ulie 

~(~

K. Armitage, Chief 

Bureau of Air