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AIR DISPERSION MODELING REPORT 

 WILSON STATION 

 SO2 DESIGNATION ANALYSIS 

REVISION 1 

Prepared for:

Mark	Bertram	

Manager,	Environmental	

Big	Rivers	Electric	Corporation	

201	Third	Street	

Henderson,	KY	42420	

Prepared By:

TRINITY	CONSULTANTS	

1717	Dixie	Highway	

Suite	900	

Covington,	Kentucky	41011	

Project	151801.0045	

August	25,	2015	
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Big Rivers Electric Corporation – Wilson Station 

1-Hour SO2 NAAQS Designation Modeling Report 

TABLE OF CONTENTS 

1. EXECUTIVE SUMMARY 1-3

2. INTRODUCTION 2-0

2.1. Facility Information..............................................................................................................................................2‐0

2.2. Basis for Analysis...................................................................................................................................................2‐1

2.3. Regulatory Background.......................................................................................................................................2‐2

2.4. Emission Rates for Wilson Station ...................................................................................................................2‐3

3. 1‐HOUR SO2 DESIGNATION MODELING METHODOLOGY 3-0

3.1. Model Selection......................................................................................................................................................3‐0

3.2. Rural Urban Option in AERMOD .......................................................................................................................3‐1

3.3. Meteorological Data..............................................................................................................................................3‐3

3.3.1. Surface Data................................................................................................................................................................................3‐4

3.3.2. Upper Air Data ...........................................................................................................................................................................3‐5

3.3.3. Land Use Analysis......................................................................................................................................................................3‐5

3.4. Coordinate System ................................................................................................................................................3‐6

3.5. Receptor Locations ...............................................................................................................................................3‐6

3.6. Terrain Elevations.................................................................................................................................................3‐9

3.7. Wilson Station Emission Sources ..................................................................................................................3‐10

3.8. Other Source Inventory ....................................................................................................................................3‐11

3.9. Building Influences ............................................................................................................................................3‐13

3.10. Source Contributions ......................................................................................................................................3‐13

3.11. Background Concentrations.........................................................................................................................3‐13

3.12. Modeling Files ...................................................................................................................................................3‐15

4. 1‐HOUR SO2 DESIGNATION MODELING RESULTS 4-1

		
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Big Rivers Electric Corporation – Wilson Station 

1-Hour SO2 NAAQS Designation Modeling Report 

LIST OF FIGURES 

Figure 2‐1.		Aerial Photograph of Wilson Station 2‐0

Figure 2‐2.		Area Map of Wilson Station 2‐1

Figure 2‐3. Location of 1‐hour SO2 Modeling Sources in Relation to Wilson Station and Nearby Towns 2‐3

Figure 3‐1. Distribution of Land Use Within 3 km of Wilson Station 3‐2

Figure 3‐2. Meteorological Stations and SO2 Monitors in the Area Near Wilson Station 3‐4

Figure 3‐3. Modeling TAD Receptor Grid Showing Example Excluded Locations Over Water 3‐7

Figure 3‐4. Innermost Portion of the Modeling Receptor Grid for Wilson 3‐8

Figure 3‐5. Overall Modeling Receptor Grid for Wilson 3‐9

Figure 3‐6. Map Showing Regional SO2 Sources Near Wilson Station 3‐11

Figure 3‐7. 99th Percentile SO2 Averages by Hour of Day for Baskett Monitor (21‐101‐0014) 3‐15

Figure 4‐1. Spatial Display of 3‐year Average 99th Percentile Annual Distribution 4‐2
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1-Hour SO2 NAAQS Designation Modeling Report 

LIST OF TABLES 

Table 3‐1. Modeling TAD Urban / Rural Categories 3‐1

Table 3‐2. Wilson Station Urban/Rural Determination 3‐2

Table 3‐3. Proximity Analysis of Meteorological Stations to Wilson Station 3‐5

Table 3‐4. Moisture Calculation for Evansville Airport (inches of precipitation) 3‐7

Table 3‐5. Wilson Station Source Characterization 3‐10

Table 3‐6. Nearby Source Characterization 3‐12

Table 4‐1. Highest 4th High Modeled 1‐hour SO2 Results for Comparison to the NAAQS 4‐1
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Big Rivers Electric Corporation – Wilson Station 

1-Hour SO2 NAAQS Designation Modeling Report 

1. EXECUTIVE SUMMARY 

The	Big	Rivers	Electric	Corporation	(BREC)	in	association	with	our	air	quality	contractor,	Trinity	Consultants	

(Trinity),	submits	this	dispersion	modeling	report	for	air	quality	modeling	analysis	that	was	performed	with	

respect	to	BREC’s	D.B.	Wilson	Station	(Wilson)	and	the	surrounding	area.		This	work	was	undertaken	in	support	

of	the	Kentucky	Division	for	Air	Quality	(KDAQ	or	Division)	response	to	the	March	20,	2015	letter	from	the	U.S.	

Environmental	Protection	Agency	(U.S.	EPA)	to	Commissioner	Scott	of	the	Kentucky	Department	for	

Environmental	Protection	(KDEP)	regarding	designations	of	areas	currently	unclassified	with	respect	to	the	

2010	1‐hour	SO2	National	Ambient	Air	Quality	Standard	(NAAQS).		In	that	letter,	U.S.	EPA	identified	the	Wilson	

Station	as	one	of	the	Kentucky	sources	meeting	the	criteria	for	evaluation	of	unclassified	areas	in	the	first	round	

of	designations	through	modeling	as	part	of	a	required	response	by	U.S.	EPA	to	the	recent	Sierra	Club	vs.	Regina	

McCarthy	Consent	Decree1.		Wilson	was	also	identified	on	the	U.S.	EPA	website	listing	all	areas	where	

designations	would	be	required	under	the	consent	decree	by	the	July	2,	2016	date2.		The	criteria	to	determine	if	

a	source	was	subject	to	the	Consent	Decree	are:	1)	a	nearby	monitor	showing	a	violation,	and	2)	that	an	area	

contain	a	stationary	source	that	according	to	the	EPA’s	Air	Markets	Database	either	emitted	more	than	16,000	

tons	of	SO2	in	2012	or	emitted	more	than	2,600	tons	of	SO2	and	had	an	emission	rate	of	at	least	0.45	lbs	

SO2/MMBtu	in	2012.		According	to	EPA’s	Air	Markets	Database,	the	Wilson	Station	emitted	7,387	tons	SO2	in	

2012	and	had	an	average	SO2	emission	rate	of	0.45	lbs	SO2/MMBtu	in	2012.		Wilson	Station	is	located	on	State	

Highway	85	just	east	of	Island,	Kentucky	in	Ohio	County.			

Just	after	the	Consent	Decree	was	signed,	U.S.	EPA	stated	that	it	would	base	the	designation	of	the	Ohio	County	

and	surrounding	area	on	the	emission	criteria	alone	(Criteria	No.	2)	as	no	SO2	monitors	are	in	the	area.		

However,	U.S.	EPA	invited	state	agencies	to	submit	updated	recommendations	and	supporting	information	that	

could	be	considered	in	the	final	designations.		To	that	end,	BREC	commissioned	this	modeling	analysis	to	aid	

KDEP/KDAQ	in	the	designation	determination	for	the	Ohio	County	area.		This	modeling	was	designed	to	meet	

the	requirements	of	U.S.	EPA’s	modeling	Technical	Assistance	Document	for	SO2	NAAQS	designation	modeling	

guidance3		(Modeling	TAD).			

To	that	end,	dispersion	modeling	was	conducted	following	the	TAD	guidance.		As	allowed	by	the	guidance,	an	

allowable	emission	rate	was	used	for	the	Wilson	Station	as	a	surrogate	for	actual	emissions.		Commensurate	

with	these	allowable	limits,	a	Good	Engineering	Practice	(GEP)	stack	height	was	used	(the	use	of	the	actual	stack	

height	is	permissible	under	the	TAD	if	actual	emissions	were	used).		Nearby	sources	were	considered	within	the	

TAD‐suggested	20	km	range	of	Wilson	but	also	out	to	50	km	to	allow	comprehensive	consideration	of	large	

nearby	sources.		Of	these	the	Green	River	Station,	10	km	to	the	south	of	Wilson	has	announced	shut	down	of	

their	units	by	April	2016;	the	TVA	Paradise	Station	about	22	km	to	the	southeast	of	Wilson	has	announced	shut	

down	of	Units	1	and	2	by	April	2016	leaving	Unit	3	to	be	included	in	the	modeling;	several	facilities	at	about	40‐

50	km	to	the	northwest	of	Wilson	were	distant	enough	to	fall	outside	of	the	TAD	general	consideration	guidance	

and	were	likely	captured	as	part	of	the	regional,	rural	background	concentration.		Given	this	strategy	and	

characterization	of	sources	affecting	air	quality	in	the	Ohio	County	area,	modeling	performed	demonstrated	that	

ambient	concentrations	in	the	area	would	be	below	the	3‐year	average	of	the	99th	percentile	of	the	annual	

distribution	of	daily	maximum	1‐hr	concentrations	which	is	the	form	of	the	1‐hour	SO2	NAAQS.		Therefore,	this	

modeling	demonstrates	that	the	area	will	be	considered	for	designation	as	attainment.	

																																																															

1 Order Granting Joint Motion to Approve and Enter Consent Decree and Denying Other Motions as Moot,	Sierra	Club	et.	

al.	v.	Regina	McCarthy,	Administrator	of	the	United	States	Environmental	Protection	Agency,	United	States	District	

Court,	Northern	District	of	California,	Docket	Nos.	120,	149,	March	2,	2015.	 2	http://www.epa.gov/airquality/sulfurdioxide/designations/pdfs/sourceareas.pdf	 3 SO2 NAAQS Designations Modeling Technical Assistance Document,	Draft,	U.S.	EPA,	Office	of	Air	Quality	Planning	and	

Standards,	Air	Quality	Assessment	Division,	December	2013.	
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2. INTRODUCTION 

This	section	of	the	modeling	report	provides	an	overview	of	the	Wilson	Station	along	with	background	

information	for	the	basis	for	the	SO2	designation	modeling.	

2.1. FACILITY INFORMATION 

Big	Rivers	Electric	Corporation	(BREC)	owns	and	operates	a	417MW	coal	fired	power	plant	in	Centertown,	KY	

which	consists	of	one	generating	unit	(EU01).		This	power	generating	unit	is	a	pulverized	coal	fired	boiler	with	a	

maximum	continuous	rating	of	4,585	MMBtu/hr.		The	unit	is	equipped	with	multiple	control	devices	to	reduce	

emissions	of	pollutants	regulated	under	various	Federal	and	Commonwealth	programs.		The	controls	include:	an	

electrostatic	precipitator,	low	NOX	burners,	hydrated	lime	injection,	wet	flue	gas	desulfurization	(WFGD),	and	

selective	catalytic	reduction	(SCR).		This	unit	and	other	emission	units	(emergency	generators,	etc.,	not	

considered	under	the	Consent	Decree)	at	Wilson	Station	are	subject	to	permit	under	the	now	draft	Title	V	

operating	permit	V‐12‐012	currently	pending	approval	by	KDAQ.		EU01	is	the	only	significant	source	of	SO2

emissions	at	Wilson	station	and	as	such	EU01	is	the	only	source	represented	in	the	modeling	analysis.			

The	D.B.	Wilson	Station	is	located	in	Ohio	County,	approximately	3.5	miles	east	of	the	city	of	Island,	Kentucky.		

An	aerial	photograph	and	area	map	of	the	facility	and	surrounding	area	are	provided	in	Figures	2‐1	and	2‐2,	

respectively.		These	maps	show	the	facility	relative	to	predominant	geographical	features	such	as	roads,	rivers,	

and	town	areas	as	well	as	significant	features	of	the	property	including	the	controlled	area	lines	and	buildings.		

Figure	2‐1	shows	the	controlled	area	at	Wilson.		These	figures	and	the	locations	of	all	emission	sources,	

structures,	and	receptors	in	the	modeling	analysis	are	represented	in	the	Universal	Transverse	Mercator	(UTM)	

coordinate	system.		The	datum	is	based	on	North	American	Datum	1983	(NAD	83).		UTM	coordinates	for	this	

analysis	are	located	in	UTM	Zone	16.		The	central	location	of	Wilson	Station	is	approximately	492,883	meters	

East	and	4,144,768	meters	North	in	Zone	16	of	the	UTM	system.	

Figure 2‐1.		Aerial Photograph of Wilson Station
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Big Rivers Electric Corporation – Wilson Station 

1-Hour SO2 NAAQS Designation Modeling Report 

Figure 2‐2.		Area Map of Wilson Station

2.2. BASIS FOR ANALYSIS 

Big	Rivers	Electric	Corporation	(BREC)	in	association	with	our	air	quality	contractor,	Trinity	Consultants	

(Trinity)	submits	this	dispersion	modeling	protocol	for	the	air	quality	analysis	that	will	be	conducted	as	part	of	a	

required	response	to	the	recent	enforceable	Sierra	Club	vs.	Regina	McCarthy	Consent	Decree4	for	the	first	round	

of	unclassified	areas	subject	to	the	2010	1‐hour	SO2	National	Ambient	Air	Quality	Standard	(NAAQS).		The	BREC	

facility	that	falls	under	this	requirement	is	the	D.B.	Wilson	Station	on	State	Highway	85	located	in	Ohio	County,	

Kentucky	just	east	of	Island,	Kentucky.		The	area	in	the	vicinity	of	Wilson	Station	possibly	including	some	or	all	

of	Ohio	County	and	because	of	its	proximity	may	include	portions	of	McLean	and	Muhlenberg	Counties,	is	

required	to	be	designated	as	attainment	or	nonattainment	according	to	an	accelerated	schedule	as	compared	to	

the	Data	Requirements	Rule	(DRR)	schedule	(promulgated	August	10,	2015)5.	

Under	the	SO2	Data	Requirements	Rule	(prior	to	the	consent	decree	which	is	not	dependent	on	the	DRR	as	per	

the	consent	decree),	KDAQ	had	the	option	of	installing	a	new	monitor	in	the	area	around	Wilson	Station	or	

performing	dispersion	modeling.		In	either	case,	a	schedule	for	completion	of	the	designations	was	established	

as	December	31,	2017	for	modeling	and	December	31,	2020	for	monitoring.		Under	the	consent	decree,	however,	

the	designation	of	the	area	around	the	Wilson	Station	must	be	completed	no	later	than	July	2,	2016,	which	does	

not	allow	sufficient	time	for	collection	of	three	(3)	years	of	valid	data,	let	alone	undergoing	the	monitor	siting	

process.			

Thus,	KDAQ	is	required	to	perform	dispersion	modeling	of	the	Wilson	Station	to	determine	the	attainment	status	

of	the	area.		BREC	has	performed	this	modeling	analyses	and	is	providing	the	results	to	KDAQ	to	assist	in	the	

																																																															

4 Order Granting Joint Motion to Approve and Enter Consent Decree and Denying Other Motions as Moot,	Sierra	Club	et.	

al.	v.	Regina	McCarthy,	Administrator	of	the	United	States	Environmental	Protection	Agency,	United	States	District	

Court,	Northern	District	of	California,	Docket	Nos.	120,	149,	March	2,	2015.	

5 Data Requirements Rule for the 1‐Hour Sulfur Dioxide (SO2) Primary National Ambient Air Quality Standards (NAAQS):

Proposed Rule, Federal	Register	Vol.	79	No.	92,	pages	27445‐27472,	May	13,	2014.	
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designation	process.		This	modeling	follows	the	methodology	and	modeling	guidance	from	the	U.S.	EPA	in	the	

form	of	the	SO2	NAAQS	designation	modeling	guidance	TAD6	and	assists	in	KDAQ’s	determination	of	the	ambient	

levels	of	SO2	at	the	1‐hour	averaging	period	in	the	area	around	Wilson	Station.		This	report	only	covers	the	

dispersion	modeling	requirement	and	does	not	cover	the	other	items	required	to	be	included	in	KDAQ’s	

consideration	of	the	five‐factor	analysis	components	for	determining	the	boundary	of	the	attainment	area.			

2.3. REGULATORY BACKGROUND 

The	U.S.	Environmental	Protection	Agency	(U.S.	EPA)	is	currently	going	through	a	multi‐phase	designation	

process	with	variable	timelines	with	respect	to	the	2010	1‐hour	SO2	National	Ambient	Air	Quality	Standard	

(NAAQS).		The	process	of	designating	areas	has	been	slowed	considerably	compared	to	former	criteria	pollutant	

NAAQS	whereby	monitoring	data	was	the	primary	tool	for	assessing	attainment/nonattainment	status	of	areas	

around	the	country.		Inadequate	monitoring	at	a	sparse	number	of	sites	does	not	allow	this	primary	tool	to	be	

used	as	in	the	past.		Under	the	current	regulatory	guidance	and	proposed	rules,	EPA:	

On	June	2,	2010	issued	a	new	1‐hr	SO2	NAAQS,	

On	September	21,	2011	sought	public	comment	on	draft	guidance	for	implementing	the	new	NAAQS,	

May	and	June	2012	held	stakeholder	meetings	with	industry,	trade	groups,	and	environmental	groups	to	

ascertain	the	interest	and	concern	over	using	dispersion	modeling	versus	monitoring	data	which	had	been	

the	standard	methodology	prior	to	this	NAAQS;	

February	2013	developed	and	released	white	papers	on	the	strategy	for	states	to	characterize	air	quality	

near	large	sources,	

August	5,	2013	designated	29	areas	in	16	states	as	nonattainment	based	on	monitoring,		

2014,	released	a	draft	and	final	draft	set	of	two	Technical	Assistance	Documents	(TADs)	offering	guidance	to	

states	on	a	methodology	to	perform	modeling	(modeling	TAD)	or	to	conduct	source‐oriented	monitoring	

(monitoring	TAD)	to	support	a	designation	approach7,8,	

May	13,	2014	released	the	proposed	Data	Requirement	Rule	(DRR),

And	March	2,	2015	signed	the	Consent	Decree	with	Sierra	Club	to	require	certain	large	sources	across	the	

U.S.	to	undergo	early	consideration	for	designation.	

August	10,	2015	released	the	final	Data	Requirement	Rule	(DRR).

Following	the	U.S	EPA’s	May	2014	publication	of	the	proposed	Data	Requirements	Rule,	the	U.S.	EPA	was	sued	

for	“failing	to	undertake	a	certain	nondiscretionary	duty	under	the	Clean	Air	Act	(“CAA”),	42	U.S.C.	§§	7401‐

7671q,	and	that	such	alleged	failure	is	actionable	under	section	304(a)(2)	of	the	CAA,	42	U.S.C.	§	7604(a)(2)”.		

The	lawsuit	resulted	in	the	Consent	Decree	that	was	entered	on	March	2,	2015	in	the	U.S.	District	Court	for	the	

Northern	District	of	California	(same	as	that	mentioned	above	and	referenced	in	Footnote	1).		As	a	result	of	the	

Consent	Decree,	an	additional	designation	phase	was	added	to	the	two	designation	phases	that	were	already	

included	in	the	U.S.	EPA’s	May	2014	proposed	Data	Requirements	Rule.		The	additional	phase	affects	areas	with	

stationary	sources	that	meet	specific	emission	criteria	laid	out	in	the	Consent	Decree	and	described	above.	The	

U.S.	EPA	released	a	memorandum	on	March	20,	2015	(referred	to	herein	as	the	2015	SO2	Area	Designation	

Guidance)	to	the	Regional	Directors	clarifying	the	path	forward	for	states	with	sources	affected	by	the	decree9.		

BREC	is	very	aware	of	these	requirements	and	has	had	informal	discussions	with	KDAQ	to	determine	a	path	

forward	to	meet	the	deadlines	for	modeling,	strategic	assessment,	and	eventual	designation	of	the	area	around	

the	Wilson	Station.				

																																																															

6	Ibid.	

7	Ibid.	

8 SO2 NAAQS Designations Source‐Oriented Monitoring Technical Assistance Document,	draft,	U.S.	Environmental	

Protection	Agency,	Research	Triangle	Park,	NC,	December	2013.	 9 Updated Guidance for Area Designations for the 2010 Primary Sulfur Dioxide National Ambient Air Quality Standard,	

memorandum	from	Stephen	Page	to	Regional	Air	division	Directors,	Regions	1‐10,	March	20,	2015.	
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1-Hour SO2 NAAQS Designation Modeling Report 

Figure 2‐3. Location of 1‐hour SO2 Modeling Sources in Relation to Wilson Station and Nearby Towns

2.4. EMISSION RATES FOR WILSON STATION 

As	discussed	under	Section	5.3	Allowable	Emissions	of	the	guidance	provided	in	the	modeling	TAD,	the	

dispersion	modeling	can	be	conducted	either	at	allowable	emission	rate	or	at	actual	emissions	preferably	on	an	

hour	by	hour	basis.		The	modeling	TAD	states	that	the	approach	of	using	allowable	emissions	is	a	simpler	way	to	

perform	the	modeling	and	provide	air	quality	impacts	for	the	designation	process.		The	TAD	goes	on	to	say	that	

an	air	agency	may	choose	to	follow	this	type	of	approach	if	the	conservative	analysis	of	this	type	still	indicates	

attainment	for	the	area	of	interest,	in	this	case	the	Ohio	County	area	and	surrounding	portions	of	other	counties.		

For	this	modeling	analysis,	an	allowable	emission	rate	less	than	the	current	rate	was	used,	namely	0.85	lb	

SO2/MMBtu	rather	than	the	current	1.2	lb	SO2/MMBtu.		As	per	Section	V.B.1.(b)	of	the	proposed	Data	

Requirements	Rule,	as	long	as	this	limit	is	agreed	to	and	permitted	by	the	designations	process	decision	date	of	

January	15,	2016	(when	KDAQ	has	to	select	either	a	modeling	or	monitoring	path),	its	consideration	in	the	

modeling	is	acceptable.	

This	modeling	of	the	Wilson	Station	will	allow	proactive	participation	with	KDAQ	in	terms	of	what	actions	can	be	

taken	and	the	designation	of	nonattainment	area	boundaries	as	described	in	the	March	20,	2015	guidance	

memorandum.		This	dispersion	modeling,	thus,	is	the	appropriate	tool	for	designating	attainment	status	of	the	

area.	
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3. 1-HOUR SO2 DESIGNATION MODELING METHODOLOGY 

As	prescribed	by	the	EPA	in	the	Data	Requirements	Rule	and	modeling	TAD,	dispersion	modeling	was	used	to	

evaluate	the	attainment	status	of	the	area	in	the	vicinity	of	the	BREC	Wilson	Station.		EPA’s	rationale	for	allowing	

the	use	of	dispersion	modeling	rather	than	requiring	new	SO2	monitors	to	be	established	are	that	SO2	sources	

are	limited	in	distance	to	where	ambient	concentration	impacts	occur	and	thus,	modeling	is	applicable	and	

representative.		In	preparation	for	providing	modeling	guidance	for	designation	analysis,	EPA	reviewed	SO2

ambient	monitoring	and	modeling	of	concentrations	around	and	near	SO2	sources	and	found	that	most	of	the	

highest	impacts	fall	within	a	few	10’s	of	kilometers	for	large	sources	and	a	few	kilometers	for	smaller	sources.		

Also	of	note	was	that	the	gradient	of	these	concentrations	falls	off	significantly	after	the	maximum	is	reached.		

Thus,	this	modeling	focused	on	the	use	of	appropriate	computational	methods	such	that	EPA’s	primary	

preferred	industrial	source	model,	the	AERMOD	Model,	is	the	primary	model	recommended	for	use.		In	addition	

to	AERMOD	and	to	allow	the	best	representation	of	simulated	ambient	air	concentrations,	the	modeling	TAD	

recommends:	

Using	actual	emissions	as	an	input	for	assessing	violations	to	provide	results	that	reflect	current	actual	air	

quality	(i.e.,	modeling	that	simulates	a	monitor)	or	use	allowable	emissions	which	will	result	in	a	more	

conservative	estimate	of	actual	ambient	air	impacts	of	the	source;	

Using	three	years	of	modeling	results	to	calculate	a	simulated	design	value	consistent	with	the	3‐year	

monitoring	period	required	to	develop	a	design	value	for	comparison	to	the	NAAQS;	

Placing	receptors	for	the	modeling	only	in	locations	where	a	monitor	could	be	placed;	and	

Using	actual	stack	heights	rather	than	following	the	Good	Engineering	Practice	(GEP)	stack	height	policy	

when	using	actual	emissions	and	the	GEP	stack	height	when	using	allowable	emissions.	

Following	these	modeling	guidelines	for	DRR	modeling,	dispersion	modeling	was	performed	for	the	Wilson	

Station	and	the	area	around	it.		The	remainder	of	this	section	provides	an	overview	of	the	modeling	that	was	

followed	for	the	Wilson	Station	which	was	approved	by	KDAQ10	in	the	modeling	protocol11	submitted	for	Wilson	

Station	modeling.	

3.1. MODEL SELECTION 

Modeling	was	performed	for	1‐hour	SO2	analysis	using	the	AERMOD	Model	in	its	most	current	version	at	the	

time	of	the	modeling.		The	current	applicable	version	is	Version	15181	which	released	by	U.S.	EPA	on	July	24,	

2015.		U.S.	EPA	also	released	an	updated	proposed	version	of	its	modeling	guidance	in	the	form	of	the	Guideline

on Air Quality Models12 about	that	same	time.		This	proposed	guidance	and	enhanced	AERMOD	model	has	new	

beta	options	that	are	expected	to	affect	the	outcome	of	designation	modeling	with	respect	to	some	of	the	low	

wind	options	(LOWWIND)	in	the	model.		As	of	the	release	of	the	proposed	Guideline,	the	options	remained	beta	

and	were	subject	to	scrutiny	at	the	U.S.	EPA	Regional	and	Clearinghouse	level	prior	to	use.		These	options	were	

not	used	in	this	modeling	for	the	Wilson	Station.	

Of	the	options	in	the	AERMOD	Model,	the	following	were	selected.		The	pollutant	identification	was	set	to	“SO2”	

in	AERMOD,	which	allowed	additional	internal	model	options	to	be	available	thus	enabling	the	output	options	to	

																																																															

10	Letter	from	Ben	Cordes,	Supervisor,	Air	Dispersion	Modeling	Section	to	Mark	Bertram,	Big	River	Electric	

Corporation,	July	15,	2015.	

11 Air Dispersion Modeling Protocol Wilson Station So2 Designation Analysis,	prepared	for	Big	Rivers	Electric	

Corporation,	prepared	by	Trinity	Consultants,	Covington,	Kentucky,	June	12,	2015.	 12 Guideline on Air Quality Models. Appendix W to 40 CFR Parts 51 and 52. Federal Register, November 9, 2005. pp. 

68217-68261.
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Big Rivers Electric Corporation – Wilson Station 

1-Hour SO2 NAAQS Designation Modeling Report 

be	configured	properly	for	SO2.		Because	of	the	probabilistic	form	of	the	1‐hour	NAAQS,	selecting	these	correct	

input	options	allowed	AERMOD	to	properly	calculate	an	SO2	design	value	based	on	the	3‐year	average	of	the	99th

percentile	of	the	annual	distribution	of	the	daily	maximum	1‐hour	concentrations	for	comparison	with	the	1‐

hour	SO2	NAAQS	of	75	ppb	(196	g/m3).	

3.2. RURAL URBAN OPTION IN AERMOD 

As	stated	by	Section	6.3,	Urban/Rural	Determination	of	the	modeling	TAD,	for	any	dispersion	modeling	exercise	

for	SO2,	the	“urban”	or	“rural”	determination	of	the	location	surrounding	the	subject	source	is	important	in	

determining	the	applicable	boundary	layer	characteristics	that	affect	a	model’s	calculation	of	ambient	

concentrations	as	well	as	the	possible	invocation	of	AERMOD’s	4‐hour	half‐life.		Thus,	a	determination	was	made	

of	whether	the	area	around	the	Wilson	Station	was	urban	or	rural.			

The	first	method	discussed	in	the	modeling	TAD	(also	referred	therein	to	Section	7.2.3c	of	the	Guideline	on	Air	

Quality	Models,	Appendix	W)	was	used	to	determine	the	urban	or	rural	status	of	the	area	around	Wilson.		This	is	

the	so‐called	“land	use”	technique	because	it	examines	the	various	land	use	within	3	km	of	Wilson	and	quantifies	

the	percentage	of	area	in	various	land	use	categories.		Following	this	guidance,	2011	land	use	data	(most	recent	

available)	were	obtained	from	the	U.S.	Geological	Survey13	through	ArcGIS	and	a	3	km	radius	circle	inscribed	

electronically	around	the	Wilson	stack	coordinates.		All	data	were	georeferenced	and	tabulated	using	the	

categories	shown	in	Table	3.1	for	urban	and	rural	designation.	

Table 3‐1. Modeling TAD Urban / Rural Categories

Figure	3‐1	shows	the	layout	of	the	land	use	where	greens,	yellows	and	browns	are	farmland,	forests,	and	grasses	

and	red	and	pinks	are	urban	areas.		Table	3‐2	shows	the	results	of	this	land	categorization	process.		As	can	be	

seen	the	area	is	predominantly	rural	by	an	overwhelming	margin	at	99.2	percent	and	therefore	was	treated	as	

rural	in	the	AERMOD	Model.			

																																																															

13	http://www.mrlc.gov/viewerjs/	

Modeling TAD 

Rural or Urban

11 Open Water A5 Water Surfaces rural

12 Perennial Ice/Snow A5 Water Surfaces rural

21 Developed, Open Space A1 Metropolitan Natural rural

22 Developed, Low Intensity R1 Common Residential rural

23 Developed, Medium Intensity I1, I2, C1, R2, R3 Industrial/Commercial/Compact 

Residential urban

24 Developed, High Intensity I1, I2, C1, R2, R3 Industrial/Commercial/Compact 

Residential urban

31 Barren Land A3 Undeveloped (Grasses/Shrub) rural

41 Deciduous Forest A4 Undeveloped (Wooded) rural

42 Evergreen Forest A4 Undeveloped (Wooded) rural

43 Mixed Forest A4 Undeveloped (Wooded) rural

52 Shrub/Scrub A3 Undeveloped (Grasses/Shrub) rural

71 Grassland/Herbaceous A3 Undeveloped (Grasses/Shrub) rural

81 Pasture/Hay A2 Agricultural rural

82 Cultivated Crops A2 Agricultural rural

90 Woody Wetlands A4 Undeveloped (Wooded) rural

95 Emergent Herbaceous Wetlands A3 Undeveloped (Grasses/Shrub) rural

2011 NLCD Land Cover Classification Auer Land-Use Classification
3-2 

Big Rivers Electric Corporation – Wilson Station 

1-Hour SO2 NAAQS Designation Modeling Report 

Figure 3‐1. Distribution of Land Use Within 3 km of Wilson Station

Table 3‐2. Wilson Station Urban/Rural Determination

Category

ID Category Description Percent

11 Open	Water 3.8%

21 Developed,	Open	Space 4.3%

22 Developed,	Low	Intensity 0.4%

23 Developed,	Medium	Intensity 0.3%

24 Developed,	High	Intensity 0.1%

31 Barren	Land 0.7%

41 Deciduous	Forest 27.3%

42 Evergreen	Forest 0.1%

43 Mixed	Forest 0.0%

52 Shrub/Scrub 0.0%

71 Grassland/Herbaceous 1.9%

81 Pasture/Hay 8.9%

82 Cultivated	Crops 44.1%

90 Woody	Wetlands 4.3%

95 Emergent	Herbaceous	Wetlands 3.8%

Total 100%

Urban 0.8%

Rural 99.2%

Percent Land Categorization

ArcGIS Analysis Results for Wilson Station
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Big Rivers Electric Corporation – Wilson Station 

1-Hour SO2 NAAQS Designation Modeling Report 

3.3. METEOROLOGICAL DATA 

Meteorological	data	was	required	as	input	to	the	AERMOD	model	to	allow	the	characterization	of	the	transport	

and	dispersion	of	the	Wilson	Station	SO2	emissions	in	the	atmosphere.		As	per	the	modeling	TAD,	three	years	of	

recent	data	were	obtained.		Onsite	meteorological	data	was	collected	by	BREC.		A	preliminary	evaluation	of	the	

onsite	meteorological	data	indicated	that	the	2014	data	was	available	and	thus,	was	evaluated	for	inclusion	in	

the	study.		The	wind	instruments	are	located	on	the	northwest	portion	of	the	BREC	property	on	a	cell	and	

microwave	transmission	tower.		The	placement	and	disposition	of	the	instruments	were	evaluated	to	determine	

if	they	were	located	such	that	the	tower	was	not	influencing	the	reading	of	wind	speed	and	direction	and	causing	

any	potential	bias	in	the	data	prior	to	use.		Although	onsite	data	are	generally	preferred	for	modeling,	in	this	case	

the	proximity	of	the	instrument	sensors	to	the	cell	tower	on	which	they	were	placed	did	not	meet	the	siting	

criteria	for	such	instruments	which	caused	significant	bias	in	the	measurements.		Therefore,	this	data	was	not	

considered	further	for	the	analysis.					

Data,	therefore,	were	obtained	from	the	National	Weather	Service	(NWS).		The	data	collected	was	reported	in	

three	formats	including	surface	data	in	both	the	hourly	averaged	format	as	well	as	the	minute	data	and	upper	air	

(radiosonde)	meteorological	data.		The	most	recent	three	full	year	data	set	(2012,	2013,	and	2014)	was	obtained	

and	processed	from	archived	data	from	the	most	representative	NWS	meteorological	station	in	the	vicinity	of	

the	Wilson	Station.		This	representativeness	was	determined	on	the	basis	of	proximity,	similarity	in	terms	of	

land	use	(and	its	effect	on	surface	roughness,	albedo,	and	Bowen	ratio),	and	meteorological	judgement	as	to	

applicability	to	the	Wilson	Station	area.		Details	on	the	data	selection	are	provided	in	the	following	subsections.			

AERMOD‐ready	meteorological	data	were	prepared	using	the	latest	version	of	the	AERMET	meteorological	

processing	utility	(Version	15181).		Standard	U.S.	EPA	meteorological	data	processing	guidance	was	used	as	

outlined	in	a	recent	U.S.	EPA	memorandum14	as	well	as	other	AERMET	and	associated	processor	documentation.		

NWS	sites	were	located	nearby	and	were	of	similar	geographical	setting	to	the	Wilson	Station.		A	preliminary	

evaluation	of	the	NWS	meteorological	data	sites	within	approximately	150	km	indicated	that	several	airports	

were	located	in	the	region.		Several	of	these	were	smaller	airports	in	the	region	including	Madisonville	Municipal	

Airport	(MADI,	30	km	to	Wilson	Station),	Owensboro‐Davies	County	Airport	(KOWB,	34	km	to	Wilson	Station),	

and	Henderson	City‐County	Airport	(66	km	to	Wilson	Station)	and	are	in	close	proximity	to	the	Wilson	Station.		

However,	each	of	these	smaller	airports	lack	sufficient	hour‐by‐hour	full	year	meteorological	data	sets	that	can	

be	used	in	the	dispersion	modeling.		Thus,	other	airports	were	evaluated	in	the	region.			

Figure	3‐2	shows	the	locations	of	the	airports	having	meteorological	data	sets	that	were	considered	for	this	

modeling.		Of	these	candidate	sites,	the	most	representative	site,	the	Evansville	Regional	Airport,	was	one	of	only	

three	sites	having	the	sufficient	hour‐by‐hour	and	one‐minute	meteorological	data	sets	that	can	be	used	in	the	

dispersion	modeling.		Table	3‐3	presents	the	results	of	a	NWS	identification	exercise	based	on	proximity	to	

Wilson	Station	and	availability	of	data	with	all	candidate	sites.		As	can	be	seen	the	three	smaller	airports	are	

closer	than	Evansville	but	fail	to	have	adequate	data.		As	can	be	seen,	other	candidate	sites	are	located	farther	

away	and	in	a	different	geographical	setting	than	the	Wilson	Station.			

																																																															

14	Fox,	Tyler,	U.S.	Environmental	Protection	Agency.	2013.		“Use	of	ASOS	Meteorological	Data	in	AERMOD	Dispersion	

Modeling.”	Available	Online:	

http://www.epa.gov/ttn/scram/guidance/clarification/20130308_Met_Data_Clarification.pdf
3-4 

Big Rivers Electric Corporation – Wilson Station 

1-Hour SO2 NAAQS Designation Modeling Report 

Figure 3‐2. Meteorological Stations and SO2 Monitors in the Area Near Wilson Station

The	most	representative	2012‐2014	surface	meteorology	data	was	determined	to	be	from	the	Evansville	

Regional	Airport	(KEVV,	WBAN	No.	93817)	with	upper	air	data	from	the	Nashville	International	Airport	(KBNA,	

WBAN	No.	13897).		The	Evansville	Regional	Airport	lies	about	76.5	km	to	the	northwest	of	the	Wilson	Station.	

3.3.1. Surface Data 

Unprocessed	hourly	surface	meteorological	field	data	was	obtained	from	the	U.S.	National	Climatic	Data	Center	

(NCDC)	for	the	Evansville	Regional	Airport	(KEVV)	for	2012‐2014	in	the	standard	ISHD	(integrated	surface	

hourly	data)	format15.		This	data	was	supplemented,	as	recommended	by	the	U.S.	EPA	with	TD‐6405	format	(so‐	

																																																															

15	ftp://ftp.ncdc.noaa.gov/pub/data/noaa/	
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Big Rivers Electric Corporation – Wilson Station 

1-Hour SO2 NAAQS Designation Modeling Report 

Table 3‐3. Proximity Analysis of Meteorological Stations to Wilson Station

called	“1‐minute”)	wind	data	also	from	the	KEVV	archives16	and	processed	using	the	latest	version	of	the	

AERMINUTE	pre‐processing	tool	(version	14337).		The	“Ice‐Free	Winds	Group”	AERMINUTE	option	was	

selected	for	processing	due	to	the	fact	that	a	sonic	anemometer	has	been	installed	at	KEVV	in	2006.	

3.3.2. Upper Air Data 

In	addition	to	surface	meteorological	data,	AERMET	requires	the	use	of	data	from	an	upper	air	sounding	to	

estimate	mixing	heights	and	other	boundary	layer	turbulence	parameters.		Upper	air	data	from	the	nearest	U.S.	

NWS	radiosonde	equipped	station	was	utilized	in	the	modeling	analysis.	In	this	case,	upper	air	data	from	the	

Nashville	International	Airport	(KBNA,	WBAN	No.	13897)	was	obtained	from	the	National	Oceanic	and	

Atmospheric	Administration	(NOAA)	in	FSL	(Forecast	Systems	Laboratory)	format17.	

3.3.3. Land Use Analysis 

Parameters	derived	from	analysis	of	land	use	data	(surface	roughness,	Bowen	ratio,	and	albedo)	are	also	

required	by	AERMET.		In	accordance	with	U.S.	EPA	guidance,	these	values	will	be	determined	using	the	latest	

version	of	the	AERSURFACE	tool	(version	13016).18			AERSURFACE	reads	gridded	land	use,	land	cover	data	as	

provided	by	the	USGS19	and	associates	such	data	with	representative	values	of	the	three	parameters	listed	

above.		Specific	AERSURFACE	settings	will	be	used	that	represent	the	location	of	the	Evansville	meteorological	

station.		These	include	settings	like	location	coordinates,	monthly	versus	seasonal	differentiation,	aridity,	and	

surface	moisture	determination.		The	surface	moisture	will	be	determined	based	on	whether	precipitation	at	the	

Evansville	Airport	is	classified	as	wet,	dry,	or	average	in	comparison	to	a	recent	30‐year	climatological	record	at	

the	site.		This	determination	is	used	in	AERSURFACE	to	adjust	the	Bowen	ratio	estimated	by	AERSURFACE	which	

																																																															

16	ftp://ftp.ncdc.noaa.gov/pub/data/asos‐onemin	

17	http://www.esrl.noaa.gov/raobs/	

18	U.S.	Environmental	Protection	Agency.		2013.	“AERSURFACE	User’s	Guide.”		EPA‐454/B‐08‐001,	Revised	

01/16/2013.		Available	Online:	http://www.epa.gov/scram001/7thconf/aermod/aersurface_userguide.pdf 19	http://www.mrlc.gov/viewerjs/	

Station Name

WBAN

Station

ID

Station Call

Sign Lat. Long.

UTM East

(m)

UTM North

(m)

ASOS One

Minute Data

Available

Distance

to Wilson

(km)

Madisonville	Municipal	Airpor 00421 MADI 37.350 ‐87.400 464,573 4,133,775 No 30.4

Owensboro‐Daviess	County	Airp 53803 KOWB 37.750 ‐87.167 485,288 4,178,091 No 34.2

Henderson	City‐County	Arpt 53886 KEHR 37.800 ‐87.683 439,872 4,183,845 No 65.9

Evansville	Regional	Airport 93817 KEVV 38.044 ‐87.521 454,285 4,210,825 Yes 76.5

Bowling	Green	21	Nne 63849 NBWG 37.250 ‐86.233 568,021 4,122,882 No 78.3

Bow	Grn‐Warren	Co.	Rgnl	Ap 93808 KBWG 36.965 ‐86.424 551,274 4,091,145 Yes 79.3

Huntingburg	Airport 53896 KHNB 38.249 ‐86.954 504,025 4,233,444 No 89.4

Campbell	Aaf	Airport 13806 KHOP 36.667 ‐87.483 456,838 4,058,041 No 93.9

Clarksville 03894 KCKV 36.624 ‐87.419 462,536 4,053,245 Yes 96.4

Godman	Aaf	Airport 13807 KFTK 37.900 ‐85.967 590,819 4,195,223 No 110.2

Glasgow	Municipal	Airport 00361 KGLW 37.033 ‐85.950 593,386 4,099,049 No 110.4

Carmi	Minicipal	Airport 63840 KCUL 38.089 ‐88.123 401,521 4,216,285 No 116.0

Harrisburg‐Raleigh	Airport 53897 KHSB 37.811 ‐88.549 363,649 4,185,976 No 135.6

Mount	Carmel	Municipal	Airpor 63853 KAJG 38.607 ‐87.727 436,701 4,273,417 No 140.4

Louisville		Intl‐Standiford	F 93821 KSDF 38.181 ‐85.739 610,442 4,226,649 Yes 143.3

Kyle	Oakley	Field	Airport 00437 KCEY 36.665 ‐88.373 377,299 4,058,589 No 144.2

Bowman	Field	Airport 13810 KLOU 38.228 ‐85.664 616,936 4,231,956 Yes 151.6

Nashville	International	Airpo 13897 KBNA 36.119 ‐86.689 527,988 3,997,192 Yes 151.7

Lrncvll‐Vincnes	Intl	Arpt 13809 KLWV 38.764 ‐87.606 447,351 4,290,762 Yes 152.9

Fairfield	Municipal	Arpt 53891 KFWC 38.379 ‐88.413 376,581 4,248,812 No 156.0

Olney‐Noble	Airport 53822 KOLY 38.722 ‐88.176 397,769 4,286,584 No 170.8

Flora	Municipal	Airport 53889 KFOA 38.665 ‐88.453 373,588 4,280,604 No 180.8

Central Coordinates of Wilson: 492,883 4,144,768
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1-Hour SO2 NAAQS Designation Modeling Report 

in	turn	affects	the	calculation	of	the	daytime	mixing	heights	used	in	AERMOD.		To	make	the	moisture	conditions	

determination,	climatological	records	of	the	annual	precipitation	in	each	modeled	year	(2012‐2014)	will	be	

compared	to	the	1985‐2014	climatological	record	for	each	site20.		

Table	3‐4	shows	the	30	year	precipitation	by	month	for	Evansville	along	with	the	seasonal	totals,	averages,	and	

30th	percentile	high	and	low	values.		These	were	compared	to	the	actual	rainfall	in	each	season	for	each	year	of	

January	1,	2012	through	December	31,	2014	which	determined	the	average,	wet,	or	dry	option	in	AERSURFACE	

for	each	year	and	each	season.		

3.4. COORDINATE SYSTEM 

In	all	modeling	input	and	output	files,	the	locations	of	emission	sources,	structures,	and	receptors	will	be	

represented	in	the	appropriate	Zone	of	the	Universal	Transverse	Mercator	(UTM)	coordinate	system	using	the	

North	American	Datum	1983	(NAD83).		The	Wilson	Station	and	the	surrounding	area	lies	within	Zone	16.			

3.5. RECEPTOR LOCATIONS 

The	dispersion	modeling	followed	the	guidance	of	the	modeling	TAD	in	terms	of	only	putting	receptors	in	areas	

where	it	is	feasible	to	place	an	actual	monitor.		As	shown	in	the	example	Figure	3‐3	from	the	modeling	TAD,	no	

receptors	were	placed	in	lakes,	rivers	or	similar	areas.		As	the	modeling	TAD	states:	

		

receptor placement should be of sufficient density to provide resolution needed to detect significant

gradients in the concentrations, with receptors placed closer together near the source to detect local

gradients and placed farther apart away from the source. In addition, the user should place receptors at

key locations such as around facility fence lines (which define the ambient air boundary for a particular

source) or monitor locations (for comparison to monitored concentrations for model evaluation purposes).

The	receptor	grid	for	the	modeling	of	the	Wilson	Station	combined	a	multi‐nested	Cartesian	grid	at	various	

spacing	centered	on	the	main	Wilson	Station	stack	along	with	receptor	points	along	the	facility’s	controlled	area.		

For	the	air	dispersion	modeling	analyses,	ground‐level	concentrations	were	calculated	from	the	controlled	area	

out	to	50	km.		The	receptors	are	characterized	by	the	following	grids:	

Fence Line Grid:		“Fence	line”	grid	consisting	of	evenly‐spaced	receptors	50	meters	apart	placed	along	the	

controlled	area	of	the	Wilson	Station	including	the	main	generation	area,	coal	piles	and	conveying	areas	and	

the	ash	landfills,	

Fine Cartesian Grid:		A	“fine”	grid	containing	100‐meter	spaced	receptors	extending	to	3	km	from	the	

center	of	the	property	and	beyond	the	fence	line,	including	receptors	along	State	Route	85,	

Medium‐Fine Cartesian Grid:		A	“medium‐fine”	grid	containing	250‐meter	spaced	receptors	extending	

from	3	km	to	5	km	from	the	center	of	the	facility,	exclusive	of	receptors	on	the	fine	grid,		

																																																															

20	National	Climactic	Data	Center.	2014	Local	Climatological	Data	(LCD).		
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1-Hour SO2 NAAQS Designation Modeling Report 

Table 3‐4. Moisture Calculation for Evansville Airport (inches of precipitation)

Figure 3‐3. Modeling TAD Receptor Grid Showing Example Excluded Locations Over Water

YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL Winter Spring Summer Fall

1985 1.76 4.24 6.10 3.80 2.97 4.68 1.18 3.76 3.59 4.46 7.61 1.74 45.89 7.74 12.87 9.62 15.66

1986 1.15 5.77 2.64 2.29 2.93 3.77 5.39 2.07 3.84 3.30 2.35 2.18 37.68 9.10 7.86 11.23 9.49

1987 0.77 3.51 2.11 2.31 3.90 5.97 3.19 0.47 1.98 1.23 3.36 5.71 34.51 9.99 8.32 9.63 6.57

1988 3.28 3.94 2.89 1.77 1.33 1.11 6.63 2.72 1.19 2.86 7.96 2.75 38.43 9.97 5.99 10.46 12.01

1989 3.35 7.00 6.40 4.19 3.72 4.00 7.83 3.46 2.21 2.16 1.64 1.38 47.34 11.73 14.31 15.29 6.01

1990 4.26 5.60 2.15 3.75 11.34 3.22 1.01 3.47 2.54 4.81 2.92 7.45 52.52 17.31 17.24 7.70 10.27

1991 3.02 2.99 4.27 2.56 3.11 0.65 2.58 0.46 2.60 3.05 3.67 3.72 32.68 9.73 9.94 3.69 9.32

1992 0.85 1.51 4.50 1.19 3.44 1.44 8.40 4.39 2.89 1.17 4.34 1.69 35.81 4.05 9.13 14.23 8.40

1993 3.57 2.61 3.23 4.38 4.20 4.65 2.37 2.17 5.59 3.76 6.62 2.68 45.83 8.86 11.81 9.19 15.97

1994 3.18 2.32 1.88 5.77 0.94 3.45 2.30 2.52 2.61 2.67 6.52 2.59 36.75 8.09 8.59 8.27 11.80

1995 2.82 2.98 2.53 5.59 13.51 4.56 2.88 3.60 0.47 2.01 2.32 3.19 46.46 8.99 21.63 11.04 4.80

1996 3.51 1.50 5.19 11.83 7.32 7.78 4.56 1.20 8.45 2.53 6.66 3.50 64.03 8.51 24.34 13.54 17.64

1997 4.20 3.35 6.90 4.16 7.57 6.12 1.71 4.02 1.31 1.73 4.17 2.34 47.58 9.89 18.63 11.85 7.21

1998 2.24 2.71 3.07 8.50 5.91 5.31 3.89 3.91 0.49 3.38 2.78 3.48 45.67 8.43 17.48 13.11 6.65

1999 6.00 1.94 4.30 6.15 3.21 6.27 2.00 0.64 0.39 2.80 0.51 5.13 39.34 13.07 13.66 8.91 3.70

2000 4.36 7.26 3.21 2.35 2.60 5.86 4.14 5.60 5.03 0.59 3.43 4.12 48.55 15.74 8.16 15.60 9.05

2001 1.29 3.26 2.23 1.60 3.82 3.82 5.54 6.09 2.40 7.27 5.40 7.16 49.88 11.71 7.65 15.45 15.07

2002 3.72 0.74 6.20 8.58 5.70 2.86 4.32 0.63 5.22 3.75 2.97 5.65 50.34 10.11 20.48 7.81 11.94

2003 0.90 4.92 2.60 3.91 6.48 4.50 4.38 1.88 3.17 1.61 4.36 1.20 39.91 7.02 12.99 10.76 9.14

2004 2.95 0.59 2.17 1.91 9.31 1.66 7.56 3.08 0.09 5.62 6.23 2.31 43.48 5.85 13.39 12.30 11.94

2005 4.59 2.77 2.85 2.13 2.33 4.88 2.69 8.51 2.00 0.73 5.93 1.76 41.17 9.12 7.31 16.08 8.66

2006 4.09 2.17 9.36 3.44 5.77 3.73 6.46 7.41 8.75 5.46 4.95 4.59 66.18 10.85 18.57 17.60 19.16

2007 5.47 3.41 2.66 2.88 2.73 2.71 1.97 0.99 2.22 4.64 1.77 6.34 37.79 15.22 8.27 5.67 8.63

2008 3.97 5.97 12.34 5.07 8.07 3.09 3.90 0.52 1.16 1.61 3.42 4.76 53.88 14.70 25.48 7.51 6.19

2009 2.85 2.76 3.32 6.01 6.47 2.20 6.46 1.91 5.17 8.21 1.22 3.62 50.20 9.23 15.80 10.57 14.60

2010 2.41 1.58 3.97 3.27 3.03 2.49 3.51 0.84 0.36 1.06 8.46 1.80 32.78 5.79 10.27 6.84 9.88

2011 1.65 4.52 5.34 11.77 7.90 6.52 6.66 0.62 8.20 2.49 8.32 6.04 70.03 12.21 25.01 13.80 19.01

2012 3.39 1.75 2.51 1.44 2.29 0.15 2.34 4.10 7.60 2.90 1.19 3.47 33.13 8.61 6.24 6.59 11.69

2013 6.76 2.77 4.08 3.86 5.08 7.55 3.59 1.64 2.81 6.07 2.04 7.33 53.58 16.86 13.02 12.78 10.92

2014 1.69 2.26 2.85 10.97 3.72 3.87 4.02 4.80 2.55 4.20 2.85 3.43 47.21 7.38 17.54 12.69 9.60

Precipitation	location	from	http://www.ncdc.noaa.gov/cdo‐web/datatools/findstation Upper	30th 11.11 17.31 12.88 11.94

KEVV	precipitation	data	‐	obtained	2014	cumulative	report	from	http:/wwwi.ncdc.noaa.gov/pub/orders Lower	30th 8.58 8.97 9.11 8.65

A	=	Average	Precipitation 2012 A D D A

W	=	Wet	Precipitation 2013 W A A A

D	=	Dry	Precipitation 2014 D W A A
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Medium‐Coarse Cartesian Grid:		A	“medium‐coarse”	grid	containing	500‐meter	spaced	receptors	

extending	from	5	km	to	10	km	from	the	center	of	the	facility,	exclusive	of	receptors	on	the	fine	and	medium‐

fine	grids,	

Coarse Cartesian Grid:		A	“coarse	grid”	containing	1,000‐meter	spaced	receptors	extending	from	10	km	to	

20	km	from	the	center	of	the	facility,	exclusive	of	receptors	on	the	fine,	medium‐fine,	and	medium‐coarse	

grids.	

Very Coarse Cartesian Grid:		A	“very	coarse	grid”	containing	2,000‐meter	spaced	receptors	extending	from	

20	km	to	50	km	from	the	center	of	the	facility,	exclusive	of	receptors	on	the	fine,	medium‐fine,	medium‐

coarse,	and	coarse	grids.	

The	latter	grid	extended	out	to	50	km	and	was	deemed	adequate	to	capture	the	maximum	impacts	of	Wilson	

Station	and	combined	impacts	due	to	other	nearby	sources	and	background	concentrations.		This	domain	

distance	was	deemed	sufficient	to	capture	the	distances	to	maximum	concentrations	as	well	as	the	significant	

gradients	of	concentrations.			

Figures	3‐4	and	3‐5	show	the	innermost	grids	of	the	receptors	as	well	as	the	overall	receptor	grid	across	the	

modeling	domain,	respectively.		As	can	be	seen,	receptors	in	various	nearby	creeks	and	lakes	have	been	

eliminated	from	the	analysis.		Also	shown	is	the	current	controlled	area	of	the	facility	(innermost	line	of	yellow	

receptors).	

Figure 3‐4. Innermost Portion of the Modeling Receptor Grid for Wilson
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1-Hour SO2 NAAQS Designation Modeling Report 

Figure 3‐5. Overall Modeling Receptor Grid for Wilson

3.6. TERRAIN ELEVATIONS 

The	terrain	elevation	for	each	receptor,	building,	and	emission	source	were	determined	using	USGS	1	arc‐second	

National	Elevation	Data	(NED).		The	NED,	obtained	from	the	USGS21,	has	terrain	elevations	at	30‐meter	intervals.		

Using	the	AERMOD	terrain	processor,	AERMAP	(version	11103),	the	terrain	height	for	each	receptor,	building,	

and	emission	source	included	in	the	model	were	determined	by	assigning	the	interpolated	height	from	the	

digital	terrain	elevations	surrounding	each	point	of	interest.		These	were	used	directly	in	the	AERMOD	model.	

In	addition,	AERMAP	was	used	to	compute	the	hill	height	scales	associated	with	each	elevated	receptor	located	

at	a	different	elevation	than	the	base	of	the	Wilson	stack.		This	computation	enabled	the	AERMOD	Model	to	

determine	the	effect	that	terrain	has	on	plumes	from	the	Wilson	stack	as	well	as	other	sources	considered.		

AERMAP	searches	all	nearby	elevation	points	for	the	terrain	height	and	location	that	has	the	greatest	influence	

on	each	receptor	to	determine	the	hill	height	scale	for	that	receptor.		AERMOD	then	uses	the	hill	height	scale	in	

order	to	select	the	point	where	a	plume	may	divide	between	going	around	a	terrain	feature	and	lofting	over	the	

feature.		Initial	review	of	the	area	does	not	indicate	that	any	significant	terrain	features	exist	near	the	Wilson	

Station,	but	the	terrain	will	be	incorporated	as	required.	

																																																															

21	http://www.mrlc.gov/viewerjs/	
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3.7. WILSON STATION EMISSION SOURCES 

The	Wilson	Station	has	only	one	source	of	SO2	emissions,	which	is	the	flue	in	the	main	stack	associated	with	coal‐

fired	Unit	1.		Table	3‐5	below	summarizes	the	stack	parameters	that	were	used	in	this	initial	modeling	of	the	

Wilson	Station	main	stack.		Modeling	was	performed	at	an	emission	rate	of	0.853	lb	SO2/MMBtu	and	4,585	

MMBtu/hr	capacity	which	is	a	limit	that	BREC	is	willing	to	take	for	the	Wilson	Station.		This	use	of	a	new	

allowable	emission	rate	limit	is	commensurate	with	the	proposed	Data	Requirements	Rule	guidance	for	

emissions	to	be	considered	for	modeling	in	Section	V.B.1.b	(Emissions	–	Accounting	for	Recent	Emission	

Reductions	in	Modeling	Analyses22).		As	stated	in	Section	V.B.1.b:	

...the air agency may wish to consult with the source and conduct additional (modeling) analysis with the

source to identify a control measure or an emission limit that would ensure attainment with the 1‐hour SO2

standard for the area around the source.

Thus,	BREC	has	elected	to	perform	this	modeling	to	assist	KDAQ	in	demonstrating	that	the	area	around	the	

Wilson	Station	is	in	attainment	via	the	modeling	route.		This	emission	limit	would	be	enforceable	by	January	

2017	and	thus,	qualifies	for	this	modeling	demonstration.		As	per	the	modeling	TAD	and	guidance	on	area	

designations,	if	this	analysis	results	in	concentrations	less	than	the	NAAQS,	then	the	area	can	be	designated	

attainment.		In	the	spirit	of	the	modeling	TAD	and	related	DRR	guidance,	the	modeling	was	performed	to	

simulate	what	a	monitor	may	have	measured	if	one	had	been	available.		To	this	end,	the	modeling	herein	

demonstrates	what	the	ambient	air	quality	would	be	if	a	monitor	were	measuring	the	air	quality	in	the	area	after	

the	new	limit	is	set.		

Table 3‐5. Wilson Station Source Characterization

Stack

Identification

X

Coordinate

(m)a

Y

Coordinate

(m)a

Stack

Height

(ft)

Stack

Diameter

(ft)

Exit

Velocity

(ft/s)

Flow

Rate

(acfm)

Exit

Temperature

( ̊F)

Emission

Rate

(lb/hr)

Unit	1b	 492,876.8	 4,144,766	 600	 22	 67.4	 1,536,428	 130	 3,911	

a	UTM	Zone	16,	NAD	83.	

b	At	a	permitted	rate	of	0.853	lb	SO2/MMBtu	and	4,585	MMBtu/hr	capacity.	

Most	other	sources	at	the	Wilson	Station	are	related	to	coal	and	ash	handling,	conveying,	and	transport	and	do	

not	relate	to	SO2	emissions.		However	two	other	sources	of	SO2	emissions	at	the	Wilson	Station	facility	include	a	

380	hp	Fire	Pump	engine	(EU06)	which	runs	on	diesel	fuel	and	an	1,130	hp	emergency	generator	which	runs	on	

diesel	fuel.		According	to	the	pending	Title	V	permit	for	the	Wilson	Station,	each	unit	is	limited	to	50	hours	of	

non‐emergency	operation.		Maintenance	checks	and	readiness	testing	of	these	units	is	limited	to	100	hours	per	

year.		According	to	the	modeling	TAD,	Section	5.4	Intermittent	Emissions,	only	sources	that	are	continuous	or	

frequent	enough	to	contribute	significantly	to	the	annual	distribution	of	maximum	daily	1‐hour	concentrations	

should	be	considered.		As	per	the	TAD‐referenced	U.S.	EPA	clarification	memorandum23,	for	the	reasons	stated	

therein,	i.e.,	these	sources	do	not	operate	continuous	or	often	enough	to	contribute	to	the	annual	distribution	of	

daily	maximum	1‐hour	SO2	concentrations,	these	two	sources	were	excluded	from	the	dispersion	modeling	of	

the	Wilson	Station.	No	other	sources	of	SO2	emissions	exist	at	the	Wilson	Station.	

																																																															

22	FR	Volume	79	No.	92,	Data Requirements Rule for the 1‐Hour Sulfur Dioxide (SO2) Primary National Ambient Air

Quality Standard (NAAQS); Proposed Rule, May	13,	2014,	pp	27464‐27465.	 23 Additional Clarification Regarding Application of Appendix W Modeling Guidance for the 1‐Hour NO2 National

Ambient Air Quality Standard, from	Tyler	Fox,	Leader	to	Regional	Air	Division	Directors,	U.S.	Environmental	Protection	

Agency.	March	11,	2011.			
3-11 

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3.8. OTHER SOURCE INVENTORY 

Other	sources	of	SO2	emissions	in	the	area	surrounding	the	Wilson	Station	were	included	as	required	for	the	

modeling	of	the	Wilson	Station	to	fully	characterize	the	air	quality	in	the	area.		Sources	within	about	20	km	of	

Wilson	were	included	(or	large	sources	just	beyond	the	20	km	range)	in	the	modeling	and	were	obtained	from	

available	inventories	from	KDAQ.		Other	large	sources	in	the	20	km	to	50	km	range	from	Wilson	were	reviewed	

to	determine	if	they	should	be	included	in	the	modeling	and	were	reviewed	on	the	basis	of	KDAQ	data	archives	

as	well	as	from	a	perspective	of	possible	future	shut	downs	(thereby	not	requiring	consideration).			

Data	sets	were	reduced	by	eliminating	very	small	sources	(less	than	100	tons	per	year).		Figure	3‐5	shows	major	

sources	of	SO2	emissions	within	the	50	km	range	of	Wilson.			

Figure 3‐6. Map Showing Regional SO2 Sources Near Wilson Station

A	summary	of	the	consideration	of	each	source	in	the	area	is	as	follows:	

Wilson	Station,	Unit	1	–	modeled	at	0.853	lb	SO2/MMBtu.	
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TVA	–	Paradise	Station	–	Units	1	and	2	will	shut	down	by	April	201624;	Unit	3	modeled	using	hourly	2013‐

2014	CEMs	data	from	the	U.S.	EPA	Air	Markets	Program	Data	for	emissions	only25;	temperature	and	gas	exit	

velocity	were	not	available	and	were,	therefore	set	equal	to	that	in	the	KDAQ	archive	data.	

Green	River	Station	–	all	units	will	shut	down	by	April	201626.	

Century	Aluminum	located	over	40	km	to	the	northwest	of	Wilson	Station	was	distant	enough	that	its	

impacts	would	be	significantly	reduced	in	terms	of	its	impacts	overlapping	with	those	of	Wilson	Station;	SO2

impacts	were	treated	as	regional	in	nature	and	assumed	to	be	captured	by	the	ambient	monitor	at	the	

Henderson	County	monitor	located	at	the	Baskett	Fire	House	(AQS‐ID	21‐101‐0014)	which	is	downwind	a	

large	portion	of	the	time	when	winds	are	from	the	southwest	through	southeast	as	shown	by	the	monitor	

location	and	wind	rose	for	2012‐2014	in	Figure	3‐6.	

The	Reid/Henderson	Station	II	Generating	Station	and	BREC	Landfill	are	located	over	40	km	to	the	

northwest	of	Wilson	Station,	which	is	distant	enough	that	their	impacts	would	be	significantly	reduced	in	

terms	of	its	impacts	overlapping	with	those	of	Wilson	Station;	SO2	impacts	were	treated	as	regional	in	

nature	and	assumed	to	be	captured	by	the	ambient	monitor	at	the	Henderson	County	monitor	located	at	the	

Baskett	Fire	House	(AQS‐ID	21‐101‐0014)	which	is	downwind	a	large	portion	of	the	time	when	winds	are	

from	the	southwest	through	southeast	as	shown	by	the	monitor	location	and	wind	rose	for	2012‐2014	in	

Figure	3‐6.	

Green	Station	located	over	40	km	to	the	northwest	of	Wilson	Station	was	distant	enough	that	its	impacts	

would	be	significantly	reduced	in	terms	of	its	impacts	overlapping	with	those	of	Wilson	Station;		SO2	impacts	

were	treated	as	regional	in	nature	and	assumed	to	be	captured	by	the	ambient	monitor	at	the	Henderson	

County	monitor	located	at	the	Baskett	Fire	House	(AQS‐ID	21‐101‐0014)	which	is	downwind	a	large	portion	

of	the	time	when	winds	are	from	the	southwest	through	southeast	as	shown	by	the	monitor	location	and	

wind	rose	for	2012‐2014	in	Figure	3‐6.	

The	Elmer	Smith	Station	is	located	about	35	km	to	the	north	of	Wilson	Station	and	is	distant	enough	and	in	a	

location	that	is	not	likely	to	overlap	with	the	maximum	concentrations	due	to	Wilson	nor	is	Wilson	likely	to	

contribute	significantly	to	concentrations	in	the	vicinity	of	Elmer	Smith	Station.	

Thus,	only	TVA	Paradise	Unit	3	was	included	as	a	direct	source	in	the	modeling	analysis.		Table	2‐2	provides	the	

pertinent	sources	parameters	and	emissions	for	this	unit.	

Table 3‐6. Nearby Source Characterization

Stack

Identification

X

Coordinate

(m)a

Y

Coordinate

(m)a

Stack

Height

(ft)

Stack

Diameter

(ft)

Exit

Velocity

(ft/s)

Flow

Rate

(acfm)

Exit

Temperature

( ̊F)

Emission

Rate

(lb/hr)b

TVA3‐	EU03	 502,305.5	 4,123,697.4	 600	 37	 50.44	 3,254,000	 130	 CEMS	

a	UTM	Zone	16,	NAD	83.	

b	Based	on	CEMS	emission	data	from	2012‐2014	from	Air	Markets	Program	Data

																																																															

24	U.S.	Energy	Information	Administration	reporting,	http://www.eia.gov/todayinenergy/detail.cfm?id=15491	

25	Air	Markets	Program	Data,	http://ampd.epa.gov/ampd/	 26	Coal	Age,	http://www.coalage.com/news/latest/4152‐green‐river‐coal‐plant‐will‐remain‐in‐operation‐until‐april‐

2016.html#.VckdfflVhBc	
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3.9. BUILDING INFLUENCES 

The	U.S.	EPA’s	Building	Profile	Input	Program	(BPIP)	with	Plume	Rise	Model	Enhancements	(PRIME)	(version	

04274),	will	be	used	to	account	for	building	downwash	influences	on	the	Unit	1	main	stack.		The	purpose	of	a	

building	downwash	analysis	is	to	determine	if	the	plume	discharged	from	a	stack	will	be	influenced	by	the	

turbulent	wake	of	any	onsite	buildings	or	other	structures,	resulting	in	downwash	of	the	plume.		The	downwash	

of	the	plume	can	result	in	elevated	ground‐level	concentrations	in	the	near	wake	of	a	building	and	is	required	for	

consideration	in	the	modeling.		For	“other”	sources	that	are	modeled	in	the	area,	downwash	will	not	be	

considered.			

3.10. SOURCE CONTRIBUTIONS 

A	number	of	output	options	are	available	in	AERMOD	to	tabulate	and	display	the	concentration	estimates	made.		

The	outputs	that	were	of	best	use	were	MAXDCONT	and	the	summary	of	maximum	4th‐highest	maximum	daily	

1‐hour	concentrations	averaged	over	the	three	period.		Beyond	just	the	maximum	values,	the	use	of	MAXDCONT	

allows	the	model	to	generate	output	that	provides	the	maximum	4th‐highest	maximum	daily	1‐hour	

concentrations	averaged	over	the	three	period	for	every	receptor	(or	for	those	above	a	user	established	

threshold	value)	and	indicates	both	the	cumulative	concentrations	as	well	as	individual	contributions	from	each	

user‐specified	group	or	individual	source.	The	output	from	this	computation	is	in	the	format	and	over	the	time	

period	that	is	commensurate	with	the	form	of	the	NAAQS.		Section	4	of	this	report	will	utilize	these	output	

options.	

3.11. BACKGROUND CONCENTRATIONS 

As	described	in	Section	8	of	the	modeling	TAD,	the	inclusion	of	background	ambient	monitored	concentrations	

as	part	of	the	modeled	concentrations	is	important	in	determining	and	deciphering	the	cumulative	ambient	air	

impacts.		The	TAD	discusses	a	first	tier	approach	based	on	the	overall	highest	hourly	monitored	SO2

concentration	and	goes	on	to	note	that	this	is	a	very	conservative	method	to	establish	the	background	

concentration.		A	second,	less	conservative	method,	is	recommended	whereby	the	monitored	design	values	for	

the	latest	three	year	period	is	used.		For	a	relatively	isolated	source,	like	Wilson,	the	modeling	TAD	proposes	

using	a	regional	monitoring	site	that	is	located	away	from	the	Wilson	area	but	is	impacted	by	similar	natural	and	

distant	anthropogenic	sources.		This	regional	source	should	be	representative	of	all	sources	impacting	an	area	

and	should	not	double‐count	source	impacts	in	the	modeling	and	monitoring.		The	other	alternative	for	

determining	the	appropriate	background	concentrations	is	the	use	of	the	3‐year	averages	of	the	99th	percentiles	

by	season	and	hour	of	day	or	the	3‐year	averages	by	hour	of	day	(across	all	seasons).		

As	with	many	locations	in	Kentucky,	a	nearby	monitor	does	not	exist	and	a	regional	site	was	determined	to	be	

the	best	choice	for	characterizing	background	concentrations.		In	the	previously	presented	Figure	3‐2,	four	SO2

monitors	were	determined	to	be	within	100	km	of	the	Wilson	Station,	namely:	

1. 18‐163‐0021,	Evansville‐Buena	Vista,	75	km	northwest	of	Wilson	

2. 21‐101‐0014,	Baskett	Fire	House,	55	km	northwest	of	Wilson	

3. 21‐059‐0005,	Owensboro	Primary,	35	km	north	of	Wilson	

4. 21‐061‐0501,	Mammoth	Cave	National	Park,	95	km	east	southeast	of	Wilson	

Consideration	of	each	monitor	as	an	appropriate	background	monitor	will	consider	a)	the	distance	from	Wilson	

Station	to	the	monitor,	2)	the	land	use	in	the	surrounding	area	as	compared	between	Wilson	Station	and	the	

monitor,	3)	the	likelihood	of	influencing	nearby	local	population‐related	sources	(vehicles,	residential	heating,	

etc.),	4)	ability	of	the	monitor	to	capture	the	impacts	of	sources	distant	from	the	Wilson	Station	that	may	not	
3-14 

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1-Hour SO2 NAAQS Designation Modeling Report 

explicitly	be	modeled	because	of	the	distance	between	them	and	Wilson	Station	and	the	apparent	lack	of	

overlapping	significant	concentration	gradients,	and	5)	comparison	of	persistent	wind	directions	with	likely	

downwind	impact	areas	for	regional	source	influences	on	the	candidate	monitors.	

The	Mammoth	Cave	NP	monitor	(21‐061‐0501)	site	had	the	lowest	SO2	concentrations	due	to	its	location	and	

monitoring	objective,	i.e.,	“General/Background”.		This	monitor	was	the	one	located	farthest	from	Wilson	Station	

at	about	95	km	to	the	east	southeast.		Due	to	its	background	status,	this	monitor	was	thought	to	not	be	

representative	of	the	small	towns	and	rural	community	that	influence	the	air	quality	around	Wilson	Station.		

Also	this	monitor,	given	the	wind	patterns	in	the	area	(as	shown	by	the	Evansville	Airport	wind	rose	in	Figure	3‐

6)	will	not	reflect	any	contributions	from	sources	located	north	and	northwest	of	Wilson	Station.		Therefore,	this	

site	was	not	chosen	to	represent	the	background	concentrations	for	the	Wilson	Station	modeling	analysis.	

The	Evansville‐Buena	Vista	monitor	(Site	No.	18‐163‐0021)	site	is	located	as	a	“Neighborhood”	site	just	to	the	

north	of	downtown	Evansville.		This	monitor	is	approximately	75	km	to	the	northwest	of	the	Wilson	Station.		

The	surrounding	land	use	and	location	being	in	such	an	urban	situation	as	well	as	its	distance	from	the	Wilson	

Station	do	not	make	it	a	suitable	monitor	for	background	concentrations	for	the	DRR	analysis.		Therefore,	this	

site	was	not	chosen	to	represent	the	background	concentrations	for	the	Wilson	Station	modeling	analysis.	

The	Owensboro	Primary	monitor	(Site	No.	21‐059‐0005)	site	is	located	as	a	“Neighborhood”	site	just	northeast	

of	the	city	of	Owensboro.		Of	the	candidate	monitors	this	one	is	the	closest	to	the	Wilson	Station	at	about	35	km	

to	the	north.		The	surrounding	land	use	and	location	are	residential	and	just	outside	and	downwind	of	the	urban	

core	of	Owensboro	in	a	less	densely	populated	area	but	likely	influenced	by	the	more	dense	urban	population‐	

related	sources.		The	monitor	is	located	only	2	km	from	the	Owensboro	Municipal	Elmer	Smith	Station	located	

up	river.		The	potential	influence	of	this	station	when	winds	are	from	the	northeast	wind	fetch	and	by	the	City	of	

Owensboro	for	all	south	through	west	wind	fetches	likely	overwhelm	any	general	regional	SO2	impacts	and	

make	this	an	unlikely	candidate	for	using	as	the	background	for	the	Wilson	Station	modeling	analysis.		

Therefore,	this	site	was	not	chosen	to	represent	the	background	concentrations	for	the	Wilson	Station	modeling	

analysis.	

The	Baskett	Fire	House	monitor	(Site	No.	21‐101‐0014)	site	is	located	as	a	general	“Population	Exposure”	site	

about	8‐9	km	southeast	of	Evansville,	Indiana.		This	candidate	monitor	is	located	about	55	km	to	the	northwest	

of	the	Wilson	Station.		The	surrounding	land	use	and	location	are	very	light	density	residential	surrounded	by	

rural	agricultural	and	woodland	areas	similar	to	Wilson	Station.			All	sources	noted	to	the	northwest	of	Wilson	

Station	at	the	40‐50	km	range	including	Century	Aluminum,	BREC	Landfill,	and	Green	Station	are	located	with	

respect	to	the	monitor	and	with	respect	to	the	prevailing	winds	(see	Figure	3‐6)	that	their	regional	impacts	are	

likely	captured	by	the	Baskett	monitor.		Also	due	to	its	proximity	to	the	Baskett	monitor	and	given	the	

downwind	direction	for	certain	meteorological	events,	the	Elmer	Smith	Station	was	assumed	to	also	affect	the	

Baskett	monitor	at	a	regional	scale.		On	these	bases,	therefore,	this	site	was	chosen	to	represent	the	background	

concentrations	for	the	Wilson	Station	modeling	analysis.	

Of	the	methods	described	above	for	the	determination	of	the	background	concentrations,	the	method	chosen	

was	the	use	of	the	3‐year	averages	of	the	99th	percentiles	by	hour	of	day	(across	all	seasons).		This	selection	was	

based	on	the	review	of	the	99th	percentile	hourly	values	across	2012‐2014	which	shows	a	diurnal	variation	of	

lowest	SO2	concentrations	at	night	and	highest	in	the	day.		Figure	3‐7	shows	the	daily	distribution	of	hourly	99th

percentile	concentrations	across	all	three	years	of	data.	
3-15 

Big Rivers Electric Corporation – Wilson Station 

1-Hour SO2 NAAQS Designation Modeling Report 

Figure 3‐7. 99th Percentile SO2 Averages by Hour of Day for Baskett Monitor (21‐101‐0014)

3.12. MODELING FILES 

All	modeling	files	will	be	provided	to	KDAQ	in	electronic	format	on	a	compact	disk.		Model	and	processor	input,	

output,	and	data	files	will	be	provided.		Spreadsheets	tabulating	source,	emission,	and	other	input	data	sets	will	

also	be	provided.		Appendix	A	provides	a	listing	of	the	sources	included	for	KDAQ	consideration.	
4-1 

Big Rivers Electric Corporation – Wilson Station 

1-Hour SO2 NAAQS Designation Modeling Report 

4. 1-HOUR SO2 DESIGNATION MODELING RESULTS 

Dispersion	modeling	of	the	Wilson	Station	was	conducted	using	the	AERMOD	Model	(Version	15181).		Included	

in	this	modeling	was	the	Wilson	Station	at	0.85	lb	SO2/MMBtu,	TVA	Unit	3	using	the	Air	Markets	CEMS	SO2	data,	

and	background	concentrations	(with	the	assumption	that	it	was	characteristic	of	the	regional	impacts	from	

more	distant	large	SO2	sources	as	well	as	general	rural	and	natural	background	sources.		Table	4‐1	presents	the	

overall	results	of	the	modeling	for	all	sources	and	a	contribution	distribution	for	each	source(s)	and	background	

to	the	3‐year	average	of	the	99th	percentile	of	the	annual	distribution	of	daily	maximum	1‐hr	concentrations,	

which	is	the	form	of	the	1‐hour	SO2	NAAQS.		As	can	be	seen	from	Table	4‐1,	the	concentrations	are	all	less	than	

the	NAAQS	and	thus,	the	area	can	be	said	to	be	achieving	the	standards	and	be	designated	as	attainment.		To	

further	show	this,	Table	4‐1	not	only	gives	the	overall	maximum	concentration	but	also	presents	the	highest	

ranked	10	highest	4th	high	concentrations,	all	at	different	receptors	which	further	demonstrates	compliance	

across	a	broader	area	than	at	the	maximum	receptor.				

Figure	4‐1	shows	the	distribution	of	1‐hour	SO2	concentrations	across	the	near	modeling	domain	as	a	further	

graphical	presentation	of	the	air	concentrations	estimates	and	their	distribution.	

Table 4‐1. Highest 4th High Modeled 1‐hour SO2 Results for Comparison to the NAAQS

All Sources1

(μg/m3)

All Source Percent

of 1‐hour SO2

NAAQS2

(μg/m3)

Wilson Station

Contribution

(μg/m3)

TVA Unit 3

Contribution

(μg/m3)

Background

Contribution1

(μg/m3)

UTM

Easting

(m)

UTM

Northing

(m)

Elevation

(m)

186.5 95.2% 146.4 0.1 40.0 490,583 4,144,568 115.8

186.2 95.0% 144.0 0.1 42.1 489,983 4,144,468 116.8

185.9 94.8% 153.7 0.3 31.9 490,483 4,144,568 116.0

185.8 94.8% 155.1 0.3 30.5 490,483 4,144,468 115.9

185.4 94.6% 146.5 0.3 38.6 490,783 4,144,368 116.4

184.9 94.3% 144.8 0.1 40.0 490,083 4,144,468 118.4

184.8 94.3% 146.9 0.4 37.4 491,083 4,144,468 116.6

184.4 94.1% 146.5 0.4 37.4 491,183 4,144,468 117.4

184.3 94.1% 146.8 0.1 37.4 489,133 4,144,518 125.6

184.3 94.0% 146.5 0.4 37.4 490,683 4,144,368 117.0

1

	Modeled	concentrations	include	an	hourly	background	concentration	determined	by	taking	the	3‐year	average	of	the	99th	percentile	of	the	

annual	distribution	of	daily	maximum	1‐hr	concentrations	at	the	Baskett	Fire	Department	SO2	Monitor	northwest	of	Wilson	Station.

2

	Based	on	the	Primary	National	Ambient	Air	Quality	Standard	(NAAQS)	for	SO2	for	the	averaging	period	of	1‐hr,	75	ppb	(196	μg/m3).
4-2 

Big Rivers Electric Corporation – Wilson Station 

1-Hour SO2 NAAQS Designation Modeling Report 

Figure 4‐1. Spatial Display of 3‐year Average 99th Percentile Annual Distribution

of Daily Maximum 1‐hr SO2 Concentrations