ILLINOISENVIRONMENTALPROTECTIONAGENCY1021NORTHGRANOAVE'WEEAsT,P.O.Box19276,SPRINGFIELD,ILli'>;OIS62794-9276•(217)782-3.397BRUCERAUNER,GOVERNORLISABONNETT,DIRECTOR(217)782-9846November9,2015JohnMooney,ChiefAirProgramsBranchRegion5AirandRadiationDivisionU.S.EnvironmentalProtectionAgency77WestJacksonBoulevardChicago,IL60604-3590Re:SierraClubSulfurDioxideModelingDearMr.Mooney:ThankyoufortheopportunitytocommentonthemodelingandrelatedinformationprovidedbytheSierraClubtoUSEPA.Asyoumayknow,theSierraClubprovidedthissamemodelinginformationtoIllinoisEPA,urgingtheStatetousetheinformationinourrecommendationstoUSEPA-however,theinformationwasmailedbytheSierraClubonSeptember15andreceivedbyIllinoisEPAonSeptember22,afterIllinoisEPAhadalreadysubmitteditsrecommendationstoUSEPA,whichweredueonSeptember18.Notwithstanding,IllinoisEPA,ofitsownaccordandatUSEPA'srequest,hasreviewedthemodelingfilesanddescriptiveinformationprovidedbytheSierraClubandhasnotedanumberofissueswiththatmodeling,someofwhichapplytoallthreeofthepowerplantsatissueinthedesignationrecommendation,othersofwhicharemorespecifictotheareabeingmodeled.Assuch,thecommentsthatfollowarebrokenintotwotypes-generalandarea-specific.SomeofthemoresignificantmodelingdifferencescommonacrossallofSierraClub'smethodologyare:1)SierraClubmodelingdidnotutilizehourlyvaryingtemperaturesandexitvelocitiesforthepowerplantsoranynear-fieldsourcesincludedinthemodeling.Instead,theyusedconstantvaluesforthosemodelinginputs.TheS02TechnicalAssistanceDocument(TAD)notes,..Insomecases,exittemperaturesorexitvelocitieschangewithemissionlevels."Ambientpollutantconcentrationsmaybebettercharacterizedusinghourlyvaryingtemperaturesandexitvelocities.Thus,IllinoisEPAutilizedvarying,notconstant,modelinginputs,whichitbelievesyieldsmodelingresultsthataremoreaccurate.-4302N.MainSt,Rockford,IL61103[815,987·7760595S.Stlltc,Elg1\IL60123(8-47)008-313121255.FltiTSI,Chompcolgn,IL61820,217)278-58002009MallSt.Calllns•llle,IL62234f618)3-46-5120951ISt,Do>PlcslnnIL00016(847)29-4.-4000412SWWa>hlngtonSt.SunoD,IL6160213091671-30222309W.MainSr..Sui"'116,Morlon,ll62959l618j993·7200100W.Randolph.SulhlI0-300,Chicago,IL60601P•E•SEP1>:rnOtt2) Sierra Club modeling utilized hourly S02 emissions
data from USEPA's

Air Market Database

for the power plants. Illinois EPA used hourly data specifically requested from the sources being modeled. USEPA's

Air Market data

is readily available for use. However,

the data requested

and obtained

by the Illinois EPA reflects hourly varying temperatures

and exit velocities, substitute values
for missing data, and explanations

for any discrepancies between USEPA's

Air Markets Database data and company-supplied

data. The data relied upon
by 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 S0

2 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

l e vel 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
S0

2 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.Some
of the more significant modeling differences specific

to individual study areas are

: Newton Power Plant The Sierra Club included emissions
from another source, Rain Cll Carbon, which

is 48 kilometers away. The Sierra Club also used outdated emissions
data for Rain CII Carbon, which has more recently conducted emissions
tests and provided
that data

to the Illinois 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 S0

2 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.3) The Sierra Club included emissions from the Marion Power Plant

( 48 kilometers to the north)

in the Joppa Steam Coal Power Plant modeling, whereas Illinois EPA modeled

the source separately

. The Illinois EPA notes that the Sierra Club modeled sources very distant from each other, yet did not include other nearby sources

in the modeling.

In doing
so, the Sierra Club's modeling

is less accurate than that of Illinois EPA

. 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