## Environmental solutions de livered uncommonly well 

# AIR DISPERSION MODELING REPORT
WILSON STATION
SO 2 

# 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,	20151-0 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 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 SO 2 

### 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 SO 2 

### DESIGNATION MODELING RESULTS 4-11-1 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 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 SO 2 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 SO 2 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 SO 2 Sources Near Wilson Station 3‐11

Figure 3

‐ 7. 99 th Percentile SO 2 Averages by Hour of Day for Baskett Monitor (21

‐ 101

‐ 0014) 3‐15

Figure 4

‐ 1. Spatial Display of 3

‐ year Average 99 th Percentile Annual Distribution 4‐21-2 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 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 4‐11-3 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report 

## 1. EXECUTIVE SUMMARY

The	Big	Rivers	Electric	Corporat ion	(BREC)	in	association	with our	air	quality	contract or,	Trinity	Consultants (Trinity),	submits	this	dispersio n	modeling	report	for	air	qual ity	modeling	analysis	that	was	performed	with respect	to	BREC’s	D.B.	Wilson	Station	(Wilson)	and	the	surround ing	area.		This	work	was undertaken	in	support of	the	Kentucky	Division	for	Air	Quality	(KDAQ	or	Division)	res ponse	to	the	March	20, 2015	letter	from	the	U.S. Environmental	Protection	Agency	(U.S.	EPA)	to	Commissioner	Scot t	of	the	Kentucky	Department	for Environmental	Protection	(KDEP) regarding	designations	of	areas currently	unclassified with	respect	to	the

2010	1‐hour	SO 2 National	Ambient	Air	Quality	Standard	(NAAQS).		In	that	letter ,	U.S.	EPA	identified	the	Wilson Station	as	one	of	the	Kentucky	s ources	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	recen t	Sierra	Club	vs.	Regina McCarthy	Consent	Decree 1 .		Wilson	was	also	identified	on the	U.S.	EPA	website	listing	a ll	areas	where designations	would	be	required	u nder	the	consent decree	by	the July	2,	2016	date 2 .		The	criteria	to	determine	if a	source	was	subject	to	the	Cons ent	Decree	are:	1)	a	nearby	mon itor	showing	a	violation,	and	2)	that	an	area contain	a	stationary	source	that	according	to	the	EPA’s	Air	Mar kets	Database	either	em itted	more	than	16,000

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

SO 2 /MMBtu	in	2012.		According	to	EPA’s Air	Markets	Database,	the	W ilson	Station	emitted	7,387	tons	SO 2 in 2012	and	had	an	average	SO 2 emission	rate	of	0.45	lbs	SO 2 /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	criteri a	alone	(Criteria	N o.	2)	as	no	SO 2 monitors	are	in	the	area. However,	U.S.	EPA	invited	state agencies	to	submit	updated	reco mmendations	and	supporting	information	that

could	be	considered	in	the	final designations.		To	that	end,	BR EC	commissioned	this	mode ling	analysis	to	aid KDEP/KDAQ	in	the	designation	det ermination	for	the	Ohio	County area.		This	modeling	was	designed	to	meet the	requirements	of	U.S.	EPA’s	mod eling	Technical	Assistance	Do cument	for	SO 2 NAAQS	designation	modeling guidance 3 (Modeling	TAD).

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

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

with	these	allowable limits,	a	Good	Engin eering	Practice	(GEP) stack	height	was	used	(the	use	of	the	actual	stack height	is	permissible under	the	TAD	if	act ual	emissions	were	us ed).		Nearby	sources	w ere	considered	within	the TAD‐suggested	20	km	range	of	Wilson	but	also	out	to	50	km	to	al low	comprehensive	con sideration	of	large nearby	sources.		Of	these	the	G reen	River	Station,	10	km	to	the south	of	Wilson	has	announced	shut	down	of their	units	by	April	2016;	the	T VA	Paradise	Station	about	22	km to	the	southeast	of	Wil son	has	announced	shut down	of	Units	1	and	2	by	April 2016	leaving	Unit	3	to	be	includ ed	in	the	modeling;	severa l	facilities	at	about	40‐

50	km	to	the	northwest	of	Wilson were	distant	enou gh	to	fall	ou tside	of	the	TAD	general consideration	guidance and	were	likely	captured	as	part of	the	regional,	rural	backgro und	concentration.		Given	this	strategy	and characterization	of	sources	affecting	air	quality	in	the	Ohio	C ounty	area,	modeling	perf ormed	demonstrated	that

ambient	concentrations	in	the	a rea	would	be	below	the	3‐year	av erage	of	the	99 th percentile	of	the	annual distribution	of	daily	maximum	1‐ hr	concentrations	which	is	the form	of	the	1‐hour	SO 2 NAAQS.		Therefore,	this modeling	demonstrates	that	the	a rea	will	be	considered	for	desi gnation	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	Envi ronmental	Protection	Agency,	United	States	District Court,	Northern	District	of	California,	Docket	Nos.	120,	149,	M arch	2,	2015.

2 http://www.epa.gov/airquality/sul furdioxide/designations/pdfs/ sourceareas.pdf

3 SO 2 NAAQS Designations Modeling Technical Assistance Document ,	Draft,	U.S.	EPA,	Office	of	Air	Quality	Planning	and Standards,	Air	Quality	Assessment	Division,	December	2013.2-0 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report 

## 2. INTRODUCTION

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

information	for	th e	basis	for	the	SO 2 designation	modeling.



### 2.1. FACILITY INFORMATION

Big	Rivers	Electric	Corporatio n	(BREC)	owns	and	operates	a	417M W	coal	fired	power	plan t	in	Centertown,	KY which	consists	of	one	generating unit	(EU01).		This	power	gener ating	unit	is	a	pulverized	coal	fired	boiler	with	a maximum	continuous	rating	of	4,585 MMBtu/hr.		The unit	is	equip ped	with	multiple	cont rol	devices	to	reduce emissions	of	pollutant s	regulated	under	vari ous	Federal	and	Com monwealth	programs.		The	controls	include:	an electrostatic	precipitator,	low	NO X burners,	hydrated	lime	injectio n,	wet	flue	gas	desulfurization (WFGD),	and selective	catalytic	reduction	(SC R).		This	unit	and	other	emiss ion	units	(emergency	generators,	etc.,	not

considered	under	the	Consent	Dec ree)	at	Wilson	Station	are	subj ect	to	permit	under	th e	now	draft	Title	V operating	permit	V‐12‐012	currentl y	pending	approval	by	KDAQ. EU01	is	the	only	significant	source	of	SO 2 emissions	at	Wilson	st ation	and	as	such	EU01	is	the	only	source represented	in	the	m odeling	analysis.

The	D.B.	Wilson	Station	is	located	in	Ohio	County,	approximatel y	3.5	miles	east	of	the	ci ty	of	Island,	Kentucky. An	aerial	photograph	and	area	map	of	the	facility	and	surroundi ng	area	are	provided	i n	Figures	2‐1	and	2‐2, respectively.		These	maps	show	t he	facility	relative	to	predomi nant	geographical	features	such	as	roads,	rivers, and	town	areas	as	well	as	signifi cant	features	of	the	property including	the	controlled	a rea	lines	and	buildings. Figure	2‐1	shows	the	co ntrolled	area	at	Wils on.		These	figures and	the	locations	of	all	emission	sources, structures,	and	receptors	in	the modeling	analysis	are	represen ted	in	the	Universal	Tra nsverse	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	W ilson	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 Station2-1 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 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	dispersio n	modeling	protocol	for	the	air quality	analysis	that	will	be	conducted	as	part	of	a required	response	to	the	recent enforceable	Sierra	Club	vs.	Reg ina	McCarthy	Consent	Decree 4 for	the	first	round of	unclassified	areas	subject	to	the	2010	1‐hour	SO 2 National	Ambient	Air	Qualit y	Standard	(NAAQS).		The	BREC facility	that	falls	under	this requirement	is	the	D.B.	Wilson	S tation	on	State	Highway	85 located	in	Ohio	County, Kentucky	just	east	of	Island,	Ke ntucky.		The	area	in	the	vicini ty	of	Wilson	Station	possi bly	including	some	or	all of	Ohio	County	and	because	of	its	proximity	may	include	portion s	of	McLean	and	Muhl enberg	Counties,	is required	to	be	designated	as	atta inment	or	nonattainment	accord ing	to	an	accelerated	sc hedule	as	compared	to the	Data	Requirements	R ule	(DRR)	schedule	( promulgated	August	1 0,	2015) 5

.

Under	the	SO 2 Data	Requirements	Rule	(prior	t o	the	consent	decree	which	is	n ot	dependent	on	the	DRR	as	per the	consent	decree),	KDAQ	had	th e	option	of	installing	a	new	mo nitor	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	modelin g	and	December	31,	2020	for	mon itoring.		Under	the	co nsent	decree,	however, the	designation	of	the	area	aroun d	the	Wilson	Station	must	be	c ompleted	no	later	than	July	2,	2016,	which	does

not	allow	suffic ient	time	for	collection of	three	(3)	years	of valid	data,	let	alone	und ergoing	the	monitor	siting

process.

Thus,	KDAQ	is	required	to	perfor m	dispersion	modeling	of	the	Wi lson	Station	to	determin e	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	Envi ronmental	Protection	Agency,	United	States	District Court,	Northern	District	of	California,	Docket	Nos.	120,	149,	M arch	2,	2015.

5 Data Requirements Rule for the 1

‐ Hour Sulfur Dioxide (SO 2 ) Primary National Ambient Air Quality Standards (NAAQS): Proposed Rule, Federal	Register	Vol.	79	No. 92,	pages	27445‐27472,	May	13,	201 4.2-2 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report designation	process.		This	modeli ng	follows	the	methodology	and modeling	guidance	fro m	the	U.S.	EPA	in	the

form	of	the	SO 2 NAAQS	designation	mo deling	guidance	TAD 6 and	assists	in	KDAQ’s	determination	of	the	ambient

levels	of	SO 2 at	the	1‐hour	averaging	period	in	the	area	around	Wilson	Stati on.		This	report	only	covers	the dispersion	modeling	requirement and	does	not	cover	the	other	it ems	required	to	be	included	in	KDAQ’s

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



### 2.3. REGULATORY BACKGROUND

The	U.S.	Environmental	Protectio n	Agency	(U.S.	EPA)	is	currentl y	going	through	a	multi‐phase	designation process	with	variable	timeline s	with	respect	to	the	2010	1‐hour SO 2 National	Ambient	Air	Quality	Standard (NAAQS).		The	process	of	designati ng	areas	has	been	slowed	cons iderably	compared	to	form er	criteria	pollutant NAAQS	whereby	monitoring	data	wa s	the	primary	tool	for	assessin g	attainment/nonattain ment	status	of	areas around	the	country.		Inadequate monitoring	at	a	sparse	number	o f	sites	does	not	allow	th is	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	SO 2 NAAQS, On	September	21,	2011	sought	public comment	on	draft	guidance	f or	implementing	the	new	NAAQS, May	and	June	2012	held	stakehold er	meetings	with	industry,	trad e	groups,	and	enviro nmental	groups	to

ascertain	the	interest	and	conc ern	over	using	dispersion	modeli ng	versus	monitoring	data	which	had	been the	standard	methodology	prior	to	this	NAAQS; February	2013	developed	and	relea sed	white	papers	on	the	strate gy	for	states	to	characterize	air	quality near	large	sources, August	5,	2013	designat ed	29	areas	in	16	st ates	as	nonattainmen t	based	on	monitoring, 2014,	released	a	draft	an d	final	draft	set	of	two	Technical	Ass istance	Documents	(TADs)	offering	guidance	to states	on	a	methodology	to	perfor m	modeling	(modeling	TAD)	or	t o	conduct	source‐oriented	monitoring (monitoring	TAD)	to	suppo rt	a	designation	approach 7,8

, May	13,	2014	released	the	proposed Data	Requirement	Rule	(DRR), And	March	2,	2015	signed	the	Con sent	Decree	with	Sierra	Club	to require	certain	larg e	sources	across	the U.S.	to	undergo	early	cons ideration	for	designation. August	10,	2015	release d	the	final	Data	Req uirement	Rule	(DRR).

Following	the	U.S	EPA’s	May	2014 publication	of	the	proposed	Da ta	Requirements	Rule,	t he	U.S.	EPA	was	sued for	“failing	to	undertake	a	cert ain	nondiscretionary	duty	under the	Clean	Air	Act	(“CAA”),	42	U.S.C.	§§	7401‐ 7671q,	and	that	such	alleged	fail ure	is	actionable	under	sectio n	304(a)(2)	of	the	CAA,	42	U.S.C.	§	7604(a)(2)”.
The	lawsuit	resulted	in	the	Co nsent	Decree	that	was	entered	on March	2,	2015	in	the	U.S.	Di strict	Court	for	the Northern	District	of	California	(same	as	that	mentioned	above	a nd	referenced	in	Footnote	1).		As	a	result	of	the Consent	Decree,	an	additional	designation	phase	was	added	to	th e	two	designation	phas es	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	spe cific	emission	criteria	laid	ou t	in	the	Consent	Decree	an d	described	above.	The
U.S.	EPA	released	a	memorandum on	March	20,	2015	(referred	to	h erein	as	the	2015	SO 2 Area	Designation Guidance)	to	the	Regional	Directo rs	clarifying	the	path	forward for	states	with	sources affected	by	the	decree 9

. BREC	is	very	aware	of	these	requi rements	and	has	had	informal	d iscussions	with	KDAQ to	determine	a	path
forward	to	meet	the	deadlines	for modeling,	strategic	assessmen t,	and	eventual	designation	of	the	area	around
the	Wilson	Station.

6 Ibid.

7 Ibid.

8 SO 2 NAAQS Designations Source

‐ Oriented Monitoring Technical Assistance Document ,	draft,	U.S.	Environmental Protection	Agency,	Research	Tr iangle	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,	2015.2-3 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report Figure 2

‐ 3. Location of 1

‐ hour SO 2 Modeling Sources in Relation to Wilson Station and Nearby Towns



### 2.4. EMISSION RATES FOR WILSON STATION

As	discussed	under	Section	5.3	A llowable	Emissions	of	the	guida nce	provided	in	the	modeling	TAD,	the dispersion	modeling	can	be	cond ucted	either	at	allowable	emissi on	rate	or	at	actual	emi ssions	preferably	on	an hour	by	hour	basis.		The	modelin g	TAD	states	that	the	approach of	using	allowable	emissions	is	a	simpler	way	to perform	the	modeling	and	provide air	quality	imp acts	for	the	de signation	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	interes t,	in	this	case	the	Ohio	Coun ty	area	and	surrounding	por tions	of	other	counties. For	this	modeling	analysis,	an	a llowable	emission	rate	less	tha n	the	current	rate	was used,	namely	0.85	lb

SO 2 /MMBtu	rather	than	the	current	1.2	lb	SO 2 /MMBtu.		As	per	Section	V.B.1.(b)	of	the	proposed	Data Requirements	Rule,	as	long	as	th is	limit	is	agreed	to	and	permi tted	by	the	designations	pr ocess	decision	date	of January	15,	2016	(when	KDAQ	has	t o	select	either	a	modeling	or monitoring	path),	its	consideration	in	the modeling	is	acceptable.

This	modeling	of	the	Wilson	Stat ion	will	allow	proactive	partic ipation	with	KDAQ	in	terms of	what	actions	can	be taken	and	the	designation	of	non attainment	area	boundaries	as	d escribed	in	the	March	20,	2015	guidance memorandum.		This	dispersion	mode ling,	thus,	is	the	appropriate tool	for	designating	attainment	status	of	the

area.3-0 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report 

## 3. 1-HOUR SO 2 

## DESIGNATION MODELING METHODOLOGY

As	prescribed	by	the	EPA	in	the	D ata	Requirements Rule	and	mode ling	TAD,	dispersion	modeling	was	used	to

evaluate	the	attainment status	of	the	area	in	the	vicinity	of	t he	BREC	Wilson	Station.		EPA’s	rationale	for	allowing the	use	of	dispersion	modeling rather	than	req uiring	new	SO 2 monitors	to	be	esta blished	are	that	SO 2 sources are	limited	in	distance	to	where ambient	concentration	impacts occur	and	thus,	modeling	is	applicable	and representative.		In	preparation	fo r	providing	modeling	guidance for	designation	analysis,	EPA	reviewed	SO 2 ambient	monitoring	and	modeling of	concentrations	around	and	ne ar	SO 2 sources	and	found	that	most	of	the highest	impacts	fall	within	a	few	10’s	of	kilometers	for	large sources	and	a	few	kilomet ers	for	smaller	sources. Also	of	note	was	that	the	gradie nt	of	these	concentrations	fall s	off	significantly	after the	maximum	is	reached. Thus,	this	modeling	focused	on	t he	use	of	appropriate	computati onal	methods	such	that	EPA’s	primary preferred	industrial	source	mode l,	the	AERMOD	Model,	is	the	pri mary	model	recommended	for	use.		In	addition to	AERMOD	and	to	allow	the	best	representation	of	simulated	amb ient	air	concentrations,	the	modeling	TAD

recommends:

Using	actual	emissions	as	an	inpu t	for	assessing	violations	to provide	results	that	reflect	current	actual	air quality	(i.e.,	modeling	that	simulates	a	monitor)	or	use	allowa ble	emissions	which	wi ll	result	in	a	more conservative	estimate	of	actual	ambient	air	impacts	of	the	sour ce; Using	three	years	of	m odeling	results	to	ca lculate	a	simulated design	value	consistent	with	the	3‐year monitoring	period	required	to	deve lop	a	design	value	for	compar ison	to	the	NAAQS; Placing	receptors	for	the	model ing	only	in	loca tions	where	a	mo nitor	could	be	placed;	and Using	actual	stack	heights	rather	than	following	the	Good	Engin eering	Practice	(GEP) stack	height	policy when	using	actual	emissions	and the	GEP	stack	height	when	using allowable	emissions.

Following	these	modeling	guidel ines	for	DRR	modeling,	dispersio n	modeling	was	performed	for	the	Wilson

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

followed	for	the	Wilson	Station which	was	approved	by	KDAQ 10 in	the	modeling	protocol 11 submitted	for	Wilson Station	modeling.



### 3.1. MODEL SELECTION

Modeling	was	performed	for	1‐hour	SO 2 analysis	using	the	AERMOD	Model in	its	most	current	version	at the time	of	the	modeling.		The	cu rrent	applicable	version	is	Versio n	15181	which	released	by U.S.	EPA	on	July	24,

2015.		U.S.	EPA	also	released	an	u pdated	proposed	version	of	it s	modeling	guidance	in	the	form	of	the Guideline

on Air Quality Models 12 about	that	same	time.		This	prop osed	guidance	and	enhanced	AERM OD	model	has	new beta	options	that	are	expected	t o	affect	the	outcome	of	designa tion	modeling	with	respect	to	some	of	the	low wind	options	(LOWWIND)	in	the	mod el.		As	of	the	release	of	the proposed	Guideline,	the options	remained	beta and	were	subject	to	scr utiny	at	the	U.S.	EP A	Regional	and	Clear inghouse	level	prior	to use.		These	options	were not	used	in	this	modeling for	the	Wilson	Station.

Of	the	options	in	the	AERMOD	Mod el,	the	followin g	were	selected .		The	pollutant	identif ication	was	set	to	“SO 2 ” in	AERMOD,	which	allowed	additional	internal	model	options	to	b e	available	thus	enablin g	the	output	options	to

10 Letter	from	Ben	Cordes,	Supervi sor,	Air	Dispersion	Modeling	Se ction	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,	Kentuc ky,	June	12,	2015.

12 Guideline on Air Quality Models. Appendix W to 40 CFR Parts 51 and 52. Federal Register, November 9, 2005. pp.
68217-68261.3-1 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report be	configured	properly	for	SO 2 .		Because	of	the	probabilistic form	of	the	1‐hour	NAAQS,	selec ting	these	correct input	options	allowed	AERMOD to	properly	calculate	an	SO 2 design	value	based	on	the 3‐year	average	of	the	99 th percentile	of	the	annual	distribution	of	the	daily	maximum	1‐ho ur	concentrations	for	comparison	with	the	1‐

hour	SO 2 NAAQS	of	75	ppb	(196  g/m 3 ).



### 3.2. RURAL URBAN OPTION IN AERMOD

As	stated	by	Section	6.3,	Urban/R ural	Determination	of	the	mode ling	TAD,	for	any	dispers ion	modeling	exercise

for	SO 2 ,	the	“urban”	or	“rural”	determin ation	of	the	location	surround ing	the	subject	sour ce	is	important	in determining	the	applicable	boundary	layer	characteristics	that affect	a	model’s	calculation	of	ambient concentrations	as	well	as	the	po ssible	invocation	of	AERMOD’s	4 ‐hour	half‐life.		Thus,	a determination	was	made

of	whether	the	area	aro und	the	Wilson	Stati on	was	urban	or	rura l.

The	first	method	discussed	in	t he	modeling	TAD	(also	referred	t herein	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	a round	Wilson.		This	is the	so‐called	“land	use”	techniq ue	because	it	examines	the	vari ous	land	use	within	3	km	of	Wilson	and	quantifies the	percentage	of	area	in	variou s	land	use	categ ories.		Followi ng	this	guidance,	2011	land use	data	(most	recent available)	were	obtained	from the	U.S.	Geological	Survey 13 through	ArcGIS	and	a	3	km	radius	circle	inscribed electronically	around	the	Wils on	stack	coordinates.		All	data	w ere	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,	yello ws	and	browns	are	farmla nd,	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	ru ral	by	an	overwhe lming	margin at	99.2	percent	and	theref ore	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 Auer Land-Use Classification 2011 NLCD Land Cover Classification3-2 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 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 Station3-3 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report 

### 3.3. METEOROLOGICAL DATA

Meteorological	data	was	required	as	input	to	the	AERMOD	model	t o	allow	the	characteriza tion	of	the	transport and	dispersion	of	the	Wilson	Station	SO 2 emissions	in	the	atmosphere.		As per	the	modeling	TAD,	three	y ears	of

recent	data	were	obtained.		Onsit e	meteorological	data	was	coll ected	by	BREC.		A	prelimin ary	evaluation	of	the onsite	meteorological	data	ind icated	that	the	2014	data	was	ava ilable	and	thus,	was	evaluated	for	inclusion	in the	study.		The	wind	instruments are	located	on	the	northwest	p ortion	of	the	BREC	pro perty	on	a	cell	and

microwave	transmission	tower.		The placement	and	disposition	of the	instruments	were	ev aluated	to	determine if	they	were	located	such	that	th e	tower	was	not influencing	th e	reading	of	wind	speed	and	direction	and	causing any	potential	bias	in	the	data	p rior	to	use.		Although	onsite	d ata	are	generally	preferred	for	modeling,	in	this	case the	proximity	of	the	instrument sensors	to	the	cell	tower	on	wh ich	they	were	placed	did	not	meet	the	siting

criteria	for	such	instruments	whi ch	caused	significant	bias	in the	measurements.		Theref ore,	this	data	was	not

considered	further	for the	analysis.

Data,	therefore,	were	obtained	fro m	the	National Weather	Servic e	(NWS).		The	data	collected	was	reported	in three	formats	including surface	data	in	both the	hourly	average d	format	as	well	as	the	minute	data	and	upper	air (radiosonde)	meteorological	da ta.		The	most	recent	three	full	y ear	data	set	(2012,	2013,	a nd	2014)	was	obtained and	processed	from	archived	data from	the	most	representative	N WS	meteorological	station	in	the	vicinity	of

the	Wilson	Station. This	representativene ss	was	determined	on the	basis	of	proximity, similarity	in	terms	of land	use	(and	its	effect	on	surf ace	roughness,	albedo,	and	Bowe n	ratio),	and	meteorolog ical	judgement	as	to applicability	to	the	Wilson	Stat ion	area.		Details	on	the	data selection	are	provided	in	th e	following	subsections.

AERMOD‐ready	meteorological	data were	prepared	using	the	latest version	of	the	AERMET	meteorological processing	utility	(Version	15181) .		Standard	U.S.	EPA	meteorol ogical	data	processing guidance	was	used	as
outlined	in	a	recent U.S.	EPA	memorandum 14 as	well	as	other	AERMET	and	associated	processor	documentation

.

NWS	sites	were	located	nearby	a nd	were	of	similar	geographical setting	to	the	Wilson	S tation.		A	preliminary evaluation	of	the	NWS	meteorolog ical	data	sites	within	approxim ately	150	km	indicated	that	several	airports were	located	in	the	region.		Se veral	of	these	were	smaller	airp orts	in	the	region	includin g	Madisonville	Municipal Airport	(MADI,	30	km	to	Wilson	S tation),	Owensboro‐Davies	Count y	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	ai rports	lack	sufficient	hour‐by ‐hour	full	year	meteorolog ical	data	sets	that	can be	used	in	the	dispersion	mode ling.		Thus,	other	airports	were evaluated	in	t he	region.

Figure	3‐2	shows	the	lo cations	of	the	airpo rts	having	meteorolo gical	data	sets	that	were	considered	for	this modeling.		Of	these	candidate	si tes,	the	most	representative	si te,	the	Evansville	Regional Airport,	was	one	of	only three	sites	having	the	sufficient hour‐by‐hour	and	one‐minute	m eteorological	data	sets that	can	be	used	in	the dispersion	modeling.		Table	3‐3	p resents	the	results	of	a	NWS	i dentification	exercise	based	on	proximity	to Wilson	Station	and	availability	of	data	with	all	candidate	site s.		As	can	be	seen	the	th ree	smaller	airports	are closer	than	Evansville	but	fail	to	have	adequate	data.		As	can be	seen,	other	candidate	si tes	are	located	farther away	and	in	a	different	geographic al	setting	than	the	Wilson	St ation.

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/g uidance/clarification/20130308_Me t_Data_Clarification.pdf3-4 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report

Figure 3

‐ 2. Meteorological Stations and SO 2 Monitors in the Area Near Wilson Station

The	most	representative	2012‐2014	su rface	meteorology	data	was determined	to	be	from	the	Evansville Regional	Airport	(KEVV,	WBAN	No.	93817)	with	upper	air	data	fro m	the	Nashville	Internat ional	Airport	(KBNA, WBAN	No.	13897).		The	Evansville	R egional	Airport	lies	about	76 .5	km	to	the	northwest	of	the	Wilson	Station.



### 3.3.1. Surface Data

Unprocessed	hourly	surface	meteo rological	field	data	was	obtain ed	from	the	U.S.	National	Climatic	Data	Center (NCDC)	for	the	Evansville	Regio nal	Airport	(KEVV)	for	2012‐2014 in	the	standard	ISHD (integrated	surface hourly	data)	format 15 .		This	data	was	supplemented,	a s	recommended	by	the	U.S.	EPA	w ith	TD‐6405	format	(so‐

15 ftp://ftp.ncdc.noaa.gov/pub/data/noaa/3-5 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report Table 3

‐ 3. Proximity Analysis of Meteorological Stations to Wilson Station

called	“1‐minute”)	wind	data also	from	the	KEVV	archives 16 and	processed	using	the latest	version	of	the AERMINUTE	pre‐processing	tool	( version	14337).		The	“Ice‐Free	W inds	Group”	AERMINUTE	option	was selected	for	processing	due	to	th e	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	oth er	boundary	layer	turbulence	par ameters.		Upper	air	data	f rom	the	nearest	U.S. NWS	radiosonde	equipped	station was	utilized	in the	modeling	an alysis.	In	this	case,	u pper	air	data	from	the Nashville	International	Airport (KBNA,	WBAN	No.	13897)	was	obta ined	from	the	National	Oceanic	and Atmospheric	Administration	(NOAA) in	FSL	(Forecas t	Systems	Labo ratory)	format 17

.



### 3.3.3. Land Use Analysis

Parameters	derived	from	analysis of	land	use	data	(surface	roug hness,	Bowen	ratio,	and	albedo)	are	also required	by	AERMET.		In	accordance	with	U.S.	EPA	guidance,	thes e	values	will	be	determ ined	using	the	latest version	of	the	AERSURFACE	tool	(version	13016). 18 AERSURFACE	reads	gridded	l and	use,	land	cover	data	as provided	by	the	USGS 19 and	associates	such	data	with	rep resentative	values	of	the	thr ee	parameters	listed above.		Specific	AERSURFACE	se ttings	will	be	used	that	represen t	the	location	of	the	Ev ansville	meteorological station.		These	include	settings like	location	coordinates,	mon thly	versus	seasonal	diff erentiation,	aridity,	and

surface	moisture	determination.		T he	surface	moisture	will	be	d etermined	based	on	whether	precipitation	at	the Evansville	Airport	is	classified as	wet,	dry,	or	average	in	com parison	to	a	recent	30‐year climatological	record	at

the	site.		This	determination	is used	in	AERSURFACE	to	adjust	t he	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/scram001/7thc onf/aermod/aersurface_userguide .pdf

19 http://www.mrlc.gov/viewerjs/ Station Name WBAN

Station

ID Station Call

Si gn Lat. Lon g

. UTM East ( m ) UTM North ( m ) ASOS One

Minute Data

A vailable Distance

to Wilson

( km )

Madisonville	Munici p al	Air p or 00421 MADI 37.350 ‐87.400 464,573 4,133,775 No 30.4

Owensboro‐Daviess	Count y Air p 53803 KOWB 37.750 ‐87.167 485,288 4,178,091 No 34.2

Henderson	Cit y ‐Count y Ar p t 53886 KEHR 37.800 ‐87.683 439,872 4,183,845 No 65.9

Evansville	Re g ional	Air p ort 93817 KEVV 38.044 ‐87.521 454,285 4,210,825 Yes 76.5

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

Bow	Grn‐Warren	Co.	R g nl	A p 93808 KBWG 36.965 ‐86.424 551,274 4,091,145 Yes 79.3

Huntin g bur g Air p ort 53896 KHNB 38.249 ‐86.954 504,025 4,233,444 No 89.4

Cam p bell	Aaf	Air p ort 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	Air p ort 13807 KFTK 37.900 ‐85.967 590,819 4,195,223 No 110.2

Glas g ow	Munici p al	Air p ort 00361 KGLW 37.033 ‐85.950 593,386 4,099,049 No 110.4

Carmi	Minici p al	Air p or t 63840 KCUL 38.089 ‐88.123 401,521 4,216,285 No 116.0

Harrisbur g ‐Ralei g h	Air p ort 53897 KHSB 37.811 ‐88.549 363,649 4,185,976 No 135.6

Mount	Carmel	Munici p al	Air p or 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

K y le	Oakle y Field	Air p ort 00437 KCE Y 36.665 ‐88.373 377,299 4,058,589 No 144.2

Bowman	Field	Air p ort 13810 KLOU 38.228 ‐85.664 616,936 4,231,956 Yes 151.6

Nashville	International	Air p o 13897 KBNA 36.119 ‐86.689 527,988 3,997,192 Yes 151.7

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

Fairfield	Munici p al	Ar p t 53891 KFWC 38.379 ‐88.413 376,581 4,248,812 No 156.0

Olne y ‐Noble	Air p ort 53822 KOL Y 38.722 ‐88.176 397,769 4,286,584 No 170.8

Flora	Munici p al	Air p ort 53889 KFOA 38.665 ‐88.453 373,588 4,280,604 No 180.8

Central Coordinates of Wilson: 492,883 4,144,7683-6 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report in	turn	affects	the	calculation of	the	daytime	mixing	heights	u sed	in	AERMOD.		To	make	the	moisture	conditions determination,	climatological	rec ords	of	the	annual	precipitati on	in	each	modeled	y ear	(2012‐2014)	will	be compared	to	the	1985‐2014	climatol ogical	record	for	each	site 20

.

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

30 th percentile	high	and	low	values .		These	were	compared	to	the	ac tual	rainfall	in	each	season	for	each	year	of January	1,	2012	through	Decemb er	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	emissi on	sources,	structures, and	receptors	will	be represented	in	the	appropriate	Zo ne	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	T AD	in	terms	of	o nly	putting	receptors	in	areas where	it	is	feasible	to	place	an actual	monitor.		As	shown	in	t he	example	Figure	3‐3	fr om	the	modeling	TAD,	no receptors	were	placed	in	lakes, rivers	or	similar	areas.		As	th e	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	modelin g	of	the	Wilson	Station	combin ed	a	multi‐nested	Cartesian	grid	at	various spacing	centered	on	the	main	Wil son	Station	stack	along	with	re ceptor	points	along	the	faci lity’s	controlled	area. For	the	air	dispersion	modeling	a nalyses,	ground‐level	concentr ations	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	o f	evenly‐spaced	receptors	50	me ters	apart	placed	along	the controlled	area	of	the	Wilson	Station	including	the	main	genera tion	area,	coal	piles	and	conveying	areas	and the	ash	landfills,

Fine Cartesian Grid: A	“fine”	grid	contai ning	100‐meter	spaced	receptors	extending to	3	km	from	the center	of	the	property	and	beyond the	fence	line,	including	rec eptors	along	Sta te	Route	85,

Medium

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

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

20 National	Climactic	Data	Center. 2014	Local	Climatological	Data (LCD).3-7 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 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 J AN FEB MAR A PR MAY J UN J UL A UG SEP OCT NOV DEC A NNUAL Winter S p rin g 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/da tatools/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 A3-8 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report Medium

‐ Coarse Cartesian Grid: A	“medium‐coarse”	grid	contain ing	500‐meter	spaced	receptors extending	from	5	km	to	10	km	from	the	center	of	the	facility,	e xclusive	of	receptors	on	the	fine	and	medium‐ fine	grids,

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

20	km	from	the	center	of	the	fac ility,	exclusive	of	receptors	o n	the	fine,	medium‐fine,	and	medium‐coarse grids.

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

20	km	to	50	km	from	the	center	of the	facility,	exclusive	of	re ceptors	on	the	fine,	medium‐fine,	medium‐ coarse,	and	coarse	grids.

The	latter	grid	extended	out	to	5 0	km	and	was	deemed	adequate	t o	capture	the	maximum	impacts	of	Wilson Station	and	combined	impacts	due to	other	nearby	sources	and	ba ckground	concentrations.		This	domain

distance	was	deemed	sufficient	to capture	the	dist ances	to	maxi mum	concentrations	as	well	as	the	significant gradients	of	concentrations.

Figures	3‐4	and	3‐5	show	the	inn ermost	grids	of	the	receptors	a s	well	as	the	overall	receptor	grid	across	the modeling	domain,	respectively. As	can	be	seen,	receptors	in	va rious	nearby	creeks and	lakes	have	been eliminated	from	the	analysis.		A lso	shown	is	the	current	contro lled	area	of	the	facility	(innermost	line	of	yellow receptors).

Figure 3

‐ 4. Innermost Portion of the Modeling Receptor Grid for Wilson3-9 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 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	u sing	USGS	1	arc‐second National	Elevation	Data	(NED).		The	NED,	obtained	from	the	USGS 21 ,	has	terrain	elevations at	30‐meter	intervals. Using	the	AERMOD	terrain	processo r,	AERMAP	(version	11103),	the terrain	height	for	each receptor,	building,

and	emission	source	included	in the	model	were	determined	by	as signing	the	interpolat ed	height	from	the digital	terrain	elevations	surro unding	each	point	of	interest. These	were	used	directly	in	the	AERMOD	model.

In	addition,	AERMAP	was	used	to	c ompute	the	hill	height	scales associated	with	each	ele vated	receptor	located

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

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

AERMAP	searches	all	ne arby	elevation	points	for	the	terrain	hei ght	and	location	that	has the	greatest	influence on	each	receptor	to	determine	the hill	height	scale	for	that	re ceptor.		AERMOD	then	uses	the	hill	height	scale	in order	to	select	the	po int	where	a	plume	may divide	between	goin g	around	a	terrain	featu re	and	lofting	over	the feature.		Initial	review	of	the	area	does	not	indicate	that	any significant	terrain	feature s	exist	near	the	Wilson Station,	but	the	terra in	will	be	incorporated	as	required.

21 http://www.mrlc.gov/viewerjs/3-10 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report 

### 3.7. WILSON STATION EMISSION SOURCES

The	Wilson	Station	has	only	one	source	of	SO 2 emissions,	which	is	the	flue	in	the	main	stack	associated	with coal‐

fired	Unit	1.		Table	3‐5	below	su mmarizes	the	stack	parameters that	were	used	in	this	ini tial	modeling	of	the Wilson	Station	main	stack.		Modeling	was	performed	at	an	emissi on	rate	of	0.853	lb	SO 2 /MMBtu	and	4,585 MMBtu/hr	capacity	which	is	a	limi t	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	R ule	guidance	for

emissions	to	be	considered	for	m odeling	in	Section	V.B.1.b	(Emi ssions	–	Accounting	f or	Recent	Emission Reductions	in	Modeling	Analyses 22 ).		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	perfor m	this	modeling	to	assist	KDAQ in	demonstrating	that the	area	around	the Wilson	Station	is	in	attainment	via	the	modeling	route.		This	e mission	limit	would	be	enforceable	by	January 2017	and	thus,	qualifies	for	this modeling	demonstration.		As	p er	the	modeling	TAD	a nd	guidance	on	area designations,	if	this	analysis	results	in	concentrations	less	t han	the	NAAQS,	then	the area	can	be	designated attainment.		In	the	spirit	of	the	modeling	TAD	and	related	DRR guidance,	the	modeli ng	was	performed	to simulate	what	a	monitor	may	have measured	if	one	had	been	avail able.		To	this	end, the	modeling	herein

demonstrates	what	the	ambient	ai r	quality	would	be	if	a	monitor were	measuring	th e	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	1 b 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	SO 2 /MMBtu	and	4,585	MMBtu/hr	capacity.

Most	other	sources	at	the	Wilson Station	are	related	to	coal	an d	ash	handling,	conveyin g,	and	transport	and	do

not	relate	to	SO 2 emissions.		However	two other	sources	of	SO 2 emissions	at	the	Wilson	Station	facility	include	a 380	hp	Fire	Pump	engine	(EU06)	whi ch	runs	on	diese l	fuel	and	an 1,130	hp	emergency	gener ator	which	runs	on diesel	fuel.		According	to	the	p ending	Title	V	permit	for	the	W ilson	Station,	each	unit	is	limited	to	50	hours	of non‐emergency	operation.		Mainten ance	checks	and	readiness	test ing	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	si gnificantly	to	the	annual	distr ibution	of	maximum	daily	1‐hour	concentrations should	be	considered.		As	per	th e	TAD‐referenced	U.S.	EPA	clari fication	memorandum 23 ,	for	the	reasons	stated therein,	i.e.,	these	sources	do	n ot	operate	continuous	or	often enough	to	contribute	to	the	annual	distribution	of daily	maximum	1‐hour	SO 2 concentrations,	these	two	sourc es	were	excluded	from	the	dispe rsion	modeling	of

the	Wilson	Station.	No	other	sources	of	SO 2 emissions	exist	at	the	Wilson	Station.

22 FR	Volume	79	No.	92, Data Requirements Rule for the 1

‐ Hour Sulfur Dioxide (SO 2 ) 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	Region al	Air	Division	Directors,	U.S. Environmental	Protection Agency.	March	11,	2011.3-11 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report 

### 3.8. OTHER SOURCE INVENTORY

Other	sources	of	SO 2 emissions	in	the	area	surroundi ng	the	Wilson	Station	were	incl uded	as	required	for	the modeling	of	the	Wilson	Station	to	fully	characterize	the	air	qu ality	in	the	area.		Sources	within	about	20	km	of Wilson	were	included	(or	large	sou rces	just	beyond	the	20	km	ra nge)	in	the	modeling	a nd	were	obtained	from available	inventories	from	KDAQ. Other	large	sources	in	the	20 km	to	50	km	range	fro m	Wilson	were	reviewed to	determine	if	they	should	be	in cluded	in	the	modeling	and	wer e	reviewed	on	the	basis	of	KDAQ	data	archives as	well	as	from	a	perspective	of possible	future	shut	downs	(th ereby	not	requiring	consideration).

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

sources	of	SO 2 emissions	within	the	50	km	range	of	Wilson.

Figure 3

‐ 6. Map Showing Regional SO 2 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	SO 2 /MMBtu.3-12 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report TVA	–	Paradise	Station	–	Units	1	and	2	will	shut	down	by	April 2016 24 ;	Unit	3	modeled	using	hourly	2013‐

2014	CEMs	data	from	the	U.S.	EPA Air	Markets	Program	Data	for	e missions	only 25 ;	temperature	and	gas	exit velocity	were	not	available	and were,	therefore	set	equal	to	th at	in	the	KDAQ	archive	data.

Green	River	Station	–	all	unit s	will	shut	down	by	April	2016 26

.

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;	SO 2 impacts	were	treated	as	regional in	nature	and	assumed	to	be	ca ptured	by	the	ambien t	monitor	at	the Henderson	County	monitor	locate d	at	the	Baskett	Fire	House	(AQS ‐ID	21‐101‐0014)	which	is	downwind	a large	portion	of	the	time	when	w inds	are	from	the	southwest	thr ough	southeast	as	shown	by	the	monitor location	and	wind	rose	for	2012‐2014	in	Figure	3‐6.

The	Reid/Henderson	Station	II	Ge nerating	Station	and	BREC	Landf ill	are	located over	40	km	to	the northwest	of	Wilson	Station,	whi ch	is	distant	en ough	that	their impacts	would	be	sign ificantly	reduced	in terms	of	its	impacts	overlapping	with	those	of	Wilson	Station; SO 2 impacts	were	treated	as	regional	in nature	and	assumed	to	be	captured by	the	ambient	monitor	at	the Henderson	County	moni tor	located	at	the Baskett	Fire	House	(AQS‐ID	21‐101‐ 0014)	which	is	downwind	a	lar ge	portion	of	the	ti me	when	winds	are from	the	southwest	through	south east	as	shown	by	the	monitor	lo cation	and	wind	rose	for	2012‐2014	in Figure	3‐6.

Green	Station	located	over	40	km	t o	the	northwest	of	Wilson	Sta tion	was	distant	enough	that	its	impacts would	be	significantly	reduced	in	terms	of	its	impacts	overlapp ing	with	those	of	Wilson	Station;		SO 2 impacts were	treated	as	regional	in	natu re	and	assumed	to	be	captured	b y	the	ambient	monito r	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	t he	southwest	through	southeast as	shown	by	the	monitor	location	and wind	rose	for	2012‐2014	in	Figure	3‐6.

The	Elmer	Smith	Statio n	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	concent rations	due	to	Wilson	nor	is	Wilson	likely	to contribute	significantly	to	conc entrations	in	the	vicinity	of	E lmer	Smith	Station.

Thus,	only	TVA	Paradise	Unit	3	w as	included	as	a	direct	source in	the	modeling	analysis.		Table	2‐2	provides	the pertinent	sources	parameters	a nd	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	 CEM S

a UTM	Zone	16,	NAD	83.

b Based	on	CEMS	emission	data	fr om	2012‐2014	from	Air	Markets	Pr ogram	Data

24 U.S.	Energy	Information	Adminis tration	reporting,	http://www.e ia.gov/todayinenergy/detail.cfm?id=15491

25 Air	Markets	Program	Data,	h ttp://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#.VckdfflVhBc3-13 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report 

### 3.9. BUILDING INFLUENCES

The	U.S.	EPA’s	Building	Profile Input	Program	(B PIP)	with	Plume Rise	Model	Enhancements	(PRIME)	(version 04274),	will	be	used	to	account	fo r	building	downwash	influence s	on	the	Unit	1	main	stack.		The	purpose	of	a building	downwash	analysis	is	to determine	if	the	plume	dischar ged	from	a	stack	will	be	influenced	by	the turbulent	wake	of	any	onsite	bui ldings	or	other	structures,	res ulting	in	downwash	of	the	plume.		The	downwash of	the	plume	can	result	in	eleva ted	ground‐level	concentrations in	the	near	wake	of	a	building	and	is	required	for consideration	in	the	modeling.		F or	“other”	sources	that	are	mo deled	in	the	area,	do wnwash	will	not	be

considered.



### 3.10. SOURCE CONTRIBUTIONS

A	number	of	output	opti ons	are	available	in	AERMOD	to	tabulate and	display	the	concentr ation	estimates	made. The	outputs	that	were of	best	use	were	MAXD CONT	and	the	summary of	maximum	4 th ‐highest	maximum	daily 1‐hour	concentrations	averaged	o ver	the	three	period.		Beyond	j ust	the	maximum	values ,	the	use	of	MAXDCONT allows	the	model	to	generate	output	that	provides	the	maximum	4 th ‐highest	maximum	daily	1‐hour concentrations	averaged	over	th e	three	period	for	every	recepto r	(or	for	those	abov e	a	user	established threshold	value)	and	indicates	bo th	the	cumulative	concentratio ns	as	well	as	individual	contributions	from	each user‐specified	group	or	individua l	source.	The	output	from	this computation	is	in	the	f ormat	and	over	the	time period	that	is	commensurate	with the	form	of	the	NAAQS.		Sectio n	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	mo nitored	concentrations as	part	of	the	modeled	concentra tions	is	important	in	determini ng	and	deciphering	the	cumulative	ambient	air impacts.		The	TAD	discusses	a	fi rst	tier	approach	based	on	the overall	highest	hourly	monitored	SO 2 concentration	and	goes	on	to	not e	that	this	is	a	very	conservat ive	method	to	establish	the	background concentration.		A	second,	less	co nservative	method,	is	recommen ded	whereby	the	monitored design	values	for the	latest	three	year	period	is	us ed.		For	a	relatively	isolate d	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.		T his	regional	source	should	be representative	of	all	so urces	impacting	an	area
and	should	not	double‐count	sour ce	impacts	in	the	modeling	and monitoring.		The	oth er	alternative	for determining	the	appropriate	back ground	concentrations	is	the	us e	of	the	3‐year	averages	of	the	99 th percentiles by	season	and	hour	of	day	or	the 3‐year	averages	by	hour	of	day (across	all	seasons).

As	with	many	locations	in	Kentuc ky,	a	nearby	monitor	does	not	e xist	and	a	regional	site	was	determined	to	be

the	best	choice	for	characterizi ng	background	concentrations. In	the	previously	presented	Figure	3‐2,	four	SO 2 monitors	were	determined	to	be	w ithin	100	km	of	the	Wilson	Stat ion,	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	P ark,	95	km	east	southeast	o f	Wilson

Consideration	of	each	monitor	as an	appropriate	background	moni tor	will	consider	a)	the	distance	from	Wilson Station	to	the	monitor,	2)	the	l and	use	in	the	surrounding	area as	compared	between	W ilson	Station	and	the monitor,	3)	the	likelihood	of	in fluencing	nearby	local	populati on‐related	sources	(vehicl es,	residential	heating, etc.),	4)	ability	of	the	monitor to	capture	the	impacts	of	sour ces	distant	from	the	Wilson	Station	that	may	not3-14 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report explicitly	be	modeled	because	of the	distance	between	them	and Wilson	Station	and	the	apparent	lack	of overlapping	significant	concentra tion	gradients,	and	5)	compari son	of	persistent	wind directions	with	likely downwind	impact	areas	for	regiona l	source	influences	on	the	can didate	monitors.

The	Mammoth	Cave	NP	monitor	( 21‐061‐0501)	site	had	the	lowest	S O 2 concentrations	due to	its	location	and monitoring	objective,	i.e.,	“Gen eral/Background”.		This	monitor was	the	one	located	farthest	from	Wilson	Station at	about	95	km	to	the	east	southeast.		Due	to	its	background	st atus,	this	monitor	was	thought	to	not	be representative	of	the	small	towns and	rural	community	that	infl uence	the	air	quality	around	Wilson	Station. Also	this	monitor,	given	the	wind	patterns	in	the	area	(as	show n	by	the	Evansville	Airport	wind	rose	in	Figure	3‐ 6)	will	not	reflect	any	contribut ions	from	sources	located	nort h	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	mon itor	(Site	No.	18‐163‐0021)	site is	located	as	a	“Neighbo rhood”	site	just	to	the

north	of	downtown	Evansville.		T his	monitor	is	approximately	75 km	to	the	northwest	of	the	Wilson	Station. The	surrounding	land	us e	and	location	being in	such	an	urban	si tuation	as	well	as	its	distance	from	the	Wilson Station	do	not	make	it	a	suitable	monitor	for	background	concen trations	for	the	DRR	ana lysis.		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	lo cated	as	a	“Neighborhood”	site	just	northeast of	the	city	of	Owensboro.		Of	th e	candidate	monitors	this	one	i s	the	closest	to	the	Wilso n	Station	at	about	35	km to	the	north.		The	surrounding	l and	use	and	loca tion	are	reside ntial	and	just	outside	and	downwind	of	the	urban

core	of	Owensboro	in	a	less	densel y	populated	area	but	likely	i nfluenced	by	the	more	de nse	urban	population‐

related	sources.		The	monitor	is located	only	2	km	from	the	Owe nsboro	Municipal	Elmer	Smith	Station	located up	river.		The	potential	influence of	this	station	when	winds	a re	from	the	northeast	wind	fetch	and	by	the	City	of Owensboro	for	all	south	through west	wind	fetches	likely	overwh elm	any	general	regional	SO 2 impacts	and make	this	an	unlikely	candidate for	using	as	the	background	for the	Wilson	Station modeling	analysis. Therefore,	this	site	was	not	cho sen	to	represent	the	background concentrations	for	the Wilson	Station	modeling analysis.

The	Baskett	Fire	House	monitor (Site	No.	21‐101‐0014)	site	is	l ocated	as	a	general	“Pop ulation	Exposure”	site

about	8‐9	km	southeast	of	Evansv ille,	Indiana.		This	candidate monitor	is	located	about 55	km	to	the	northwest of	the	Wilson	Station.		The	surrounding	land	use	and	location	a re	very	light	density	res idential	surrounded	by rural	agricultural	and	woodland	a reas	similar	to	Wilson	Station .			All	sources	noted	to	t he	northwest	of	Wilson Station	at	the	40‐50	km	range	inc luding	Century	Aluminum,	BREC Landfill,	and	Green	Sta tion	are	located	with respect	to	the	monitor	and	with respect	to	the	prevailing	winds (see	Figure	3‐6)	that	th eir	regional	impacts	are likely	captured	by	the	Baskett	mo nitor.		Also	due	to	its	proxim ity	to	the	Baskett	mo nitor	and	given	the

downwind	direction	for	certain	me teorological	events,	the	Elmer Smith	Station	was	assumed	to	also	affect	the Baskett	monitor	at	a	regional	sc ale.		On	these	bases,	therefore ,	this	site	was	chosen	to represent	the	background

concentrations	for	the	Wilson Station	modeling	analysis.

Of	the	methods	described	above	f or	the	determination	of	the	bac kground	concentrations,	the	method	chosen was	the	use	of	the	3‐year	averages	of	the	99 th percentiles	by	hour	of	day	(acro ss	all	seasons). This	selecti on	was based	on	the	review	of	the	99 th percentile	hourly	values	acro ss	2012‐2014	which	shows	a	diurna l	variation	of

lowest	SO 2 concentrations	at	night	and	highest	in	the	day.		Figure	3‐7	sh ows	the	daily	distri bution	of	hourly	99 th percentile	concentrations	ac ross	all	three	years	of	data.3-15 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report Figure 3

‐ 7. 99 th Percentile SO 2 Averages by Hour of Day for Baskett Monitor (21

‐ 101

‐ 0014)



### 3.12. MODELING FILES

All	modeling	files	will	be	provi ded	to	KDAQ	in	electronic	forma t	on	a	compact	disk.		Model	and	processor	input, output,	and	data	files	will	be	p rovided.		Spreadsheets	tabulati ng	source,	emission,	and	ot her	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 SO 2 NAAQS Designation Modeling Report 

## 4. 1-HOUR SO 2 

## DESIGNATION MODELING RESULTS

Dispersion	modeling	of	the	Wilson	Station	was	conducted	using	t he	AERMOD	Model	(Version	15181).		Included in	this	modeling	was	the	W ilson	Station	at	0.85	lb	SO 2 /MMBtu,	TVA	Unit	3	using	the	Air	Markets	CEMS	SO 2 data, and	background	concentrations	(w ith	the	assumption	that	it	was characteristic	of	the regional	impacts	from more	distant	large	SO 2 sources	as	well	as	general	rural and	natural	background	source s.		Table	4‐1	presents	the overall	results	of	the	modeling	f or	all	sources	and	a	contribut ion	distribution	for	each	source(s)	and	background to	the	3‐year	average	of	the	99 th percentile	of	the	annual	distribution	of	daily	maximum	1‐hr	co ncentrations,
which	is	the	form	of	the	1‐hour	SO 2 NAAQS.		As	can	be	seen	from	Ta ble	4‐1,	the	concentrations	are all	less	than the	NAAQS	and	thus,	th e	area	can	be	said	to	be	achieving	the	st andards	and	be	designa ted	as	attainment.		To further	show	this,	Table	4‐1	not only	gives	the	overall	maximum concentration	but	also presents	the	highest ranked	10	highest	4 th high	concentrations,	all	at	d ifferent	receptors	which	further demonstrates	compliance

across	a	broader	area	than at	the	maximum	receptor.

Figure	4‐1	shows the	distribution	of	1‐hour	SO 2 concentrations	acro ss	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 Sources 1

(μg/ m 3 ) All Source Percent

of 1

‐ hour SO 2 NAAQS 2

(μg/ m 3 ) Wilson Station

Contribution
(μg/ m 3 ) TVA Unit 3

Contribution
(μg/ m 3 ) Background

Contribution 1

(μg/ m 3 ) 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	concentrat ion	determined	by	taking	the	3‐year	average	of	the	99th	percent ile	of	the annual	distribution	of	daily	maximum	1‐hr	concentrations	at	the Baskett	Fire	Department	SO 2 Monitor	northwest	of	Wilson	Station.

2 Based	on	the	Primary	National	Ambient	Air	Quality	Standard	(NA AQS)	for	SO 2 for	the	averaging	period	of	1‐hr,	75	ppb	(196 μ g/m 3 ).4-2 Big Rivers Electric Corporation – Wilson Station
1-Hour SO 2 NAAQS Designation Modeling Report Figure 4

‐ 1. Spatial Display of 3

‐ year Average 99 th Percentile Annual Distribution

of Daily Maximum 1

‐ hr SO 2 Concentrations