1
6560­
50­
P
ENVIRONMENTAL
PROTECTION
AGENCY
40
CFR
Part
51
[
FRL­
xxxx­
x]

RIN:
2060­
xxxxx
Regional
Haze
Regulations
and
Guidelines
for
Best
Available
Retrofit
Technology
(
BART)
Determinations
AGENCY:
Environmental
Protection
Agency
(
EPA).

ACTION:
Final
Rule.

SUMMARY:
On
July
1,
1999,
EPA
promulgated
regulations
to
address
regional
haze
(
64
FR
35714).
These
regulations
were
challenged,
and
on
May
24,
2002,
the
U.
S.
Court
of
Appeals
for
the
District
of
Columbia
Circuit
issued
a
ruling
vacating
the
regional
haze
rule
in
part
and
sustaining
it
in
part.
American
Corn
Growers
Ass'n
v.
EPA,
291
F.
3d
1
(
D.
C.

Cir.
2002).
Today's
rule
addresses
the
court's
ruling
in
that
case.

In
addition,
prior
to
the
court's
decision,
EPA
had
proposed
guidelines
for
implementation
of
the
best
available
retrofit
technology
(
BART)
requirements
under
the
regional
haze
rule,
(
66
FR
38108;
July
20,
2001).
The
proposed
guidelines
were
intended
to
clarify
the
requirements
of
the
regional
haze
rule's
BART
provisions.
We
proposed
to
add
the
guidelines
and
also
proposed
to
add
regulatory
text
2
requiring
that
these
guidelines
be
used
for
addressing
BART
determinations
under
the
regional
haze
rule.
In
addition,

we
proposed
one
revision
to
guidelines
issued
in
1980
for
facilities
contributing
to
"
reasonably
attributable"

visibility
impairment.

In
the
American
Corn
Growers
case,
the
court
vacated
and
remanded
the
BART
provisions
of
the
regional
haze
rule.

In
response
to
the
court's
ruling,
on
May
5,
2004
we
proposed
new
BART
provisions
and
reproposed
the
BART
guidelines.
The
American
Corn
Growers
court
also
remanded
to
the
Agency
its
decision
to
extend
the
deadline
for
the
submittal
of
regional
haze
plans.
Subsequently,
Congress
amended
the
deadlines
for
regional
haze
plans
(
Consolidated
Appropriations
Act
for
Fiscal
Year
2004,
Public
Law
108­
199,

January
23,
2004).
The
May
5,
2004
proposed
rule
also
contained
an
amendment
to
the
regional
haze
rule
to
conform
to
the
new
statutory
deadlines.

We
received
numerous
comments
on
both
the
July
20,
2001
proposal
and
the
May
5,
2004
reproposal.
Today's
final
rule
reflects
our
review
of
the
public
comments.

DATES:
The
regulatory
amendments
announced
herein
take
effect
on
[
insert
date
60
days
after
publication
in
the
Federal
Register].
3
ADDRESSES:
Docket.
All
documents
in
the
docket
are
listed
in
the
EDOCKET
index
at
http://
www.
epa.
gov/
edocket.
Although
listed
in
the
index,
some
information
is
not
publicly
available,
i.
e.,
CBI
or
other
information
whose
disclosure
is
restricted
by
statute.
Certain
other
material,
such
as
copyrighted
material,
is
not
placed
on
the
Internet
and
will
be
publicly
available
only
in
hard
copy
form.
Publicly
available
docket
materials
are
available
either
electronically
in
EDOCKET
or
in
hard
copy
at
the
OAR
Docket,

EPA/
DC,
EPA
West,
Room
B102,
1301
Constitution
Ave.,
NW.,

Washington,
DC.
The
Public
Reading
Room
is
open
from
8:
30
a.
m.
to
4:
30
p.
m.,
Monday
through
Friday,
excluding
legal
holidays.
The
telephone
number
for
the
Public
Reading
Room
is
(
202)
566­
1744,
and
the
telephone
number
for
the
OAR
Docket
is
(
202)
566­
1742.

FOR
FURTHER
INFORMATION
CONTACT:
Kathy
Kaufman
at
919­
541­

0102
or
by
e­
mail
at
Kaufman.
Kathy@
epa.
gov
or
Todd
Hawes
at
919­
541­
5591
or
by
e­
mail
Hawes.
Todd@
epa.
gov.

SUPPLEMENTARY
INFORMATION:

Regulated
Entities.
This
final
rule
will
affect
the
following:
State
and
local
permitting
authorities
and
Indian
Tribes
containing
major
stationary
sources
of
pollution
affecting
visibility
in
federally
protected
scenic
areas.
4
This
list
is
not
intended
to
be
exhaustive,
but
rather
provides
a
guide
for
readers
regarding
entities
likely
to
be
regulated
by
this
action.
This
list
gives
examples
of
the
types
of
entities
EPA
is
now
aware
could
potentially
be
regulated
by
this
action.
Other
types
of
entities
not
listed
could
also
be
affected.
To
determine
whether
your
facility,
company,
business,
organization,
etc.,
is
regulated
by
this
action,
you
should
examine
the
applicability
criteria
in
Part
II
of
this
preamble.
If
you
have
any
questions
regarding
the
applicability
of
this
action
to
a
particular
entity,
consult
the
people
listed
in
the
preceding
section.

Outline.
The
contents
of
today's
preamble
are
listed
in
the
following
outline.

I.
Overview
of
Today's
Proposed
Actions
II.
Background
A.
Regional
Haze
Rule
B.
Partial
Remand
of
the
Regional
Haze
Rule
in
American
Corn
Growers
C.
Changes
to
the
Visibility
Regulations
D.
Changes
to
the
BART
Guidelines
III.
Detailed
Discussion
of
the
BART
Guidelines
A.
Introduction
B.
Scope
of
the
Rule
­
Whether
to
Require
States
to
Follow
the
Guidelines
for
All
BART
Sources
C.
How
to
Identify
BART­
eligible
Sources
D.
How
to
Determine
Which
BART­
eligible
Sources
are
Subject
to
BART
E.
The
BART
Determination
Process
IV.
Statutory
and
Executive
Order
Reviews
A.
Executive
Order
12866:
Regulatory
Planning
and
Review
B.
Paperwork
Reduction
Act
5
C.
Regulatory
Flexibility
Act
D.
Unfunded
Mandates
Reform
Act
E.
Executive
Order
13132:
Federalism
F.
Executive
Order
13175:
Consultation
and
Coordination
with
Indian
Tribal
Governments
G.
Executive
Order
13045:
Protection
of
Children
from
Environmental
Health
Risks
and
Safety
Risks
H.
Executive
Order
13211:
Actions
That
Significantly
Affect
Energy
Supply,
Distribution,
or
Use.
I.
National
Technology
Transfer
Advancement
Act
J.
Executive
Order
12898:
Federal
Actions
to
Address
Environmental
Justice
in
Minority
Populations
and
Low­
Income
Populations
I.
Overview
of
Today's
Actions
Today's
rulemaking
provides
the
following
changes
to
the
regional
haze
regulations:

(
1)
revised
regulatory
text
in
response
to
the
American
Corn
Growers
court's
remand,
to
require
that
the
BART
determination
include
an
analysis
of
the
degree
of
visibility
improvement
resulting
from
the
use
of
control
technology
at
each
source
subject
to
BART,

(
2)
revised
regulatory
text
in
40
CFR
51.308(
b)
and
deletion
of
40
CFR
51.308(
c)
Options
for
regional
planning
in
response
to
Congressional
legislation
amending
the
deadlines
for
submittal
of
regional
haze
implementation
plans.
This
provision
had
provided
for
an
alternative
process
for
States
to
submit
regional
haze
implementation
plans
in
attainment
areas,

(
3)
BART
guidelines,
contained
in
a
new
Appendix
Y
to
40
CFR
part
51,
6
(
4)
new
and
revised
regulatory
text,
to
be
added
to
40
CFR
51.308(
e),
to
require
the
use
of
Appendix
Y
in
establishing
BART
emission
limits,
and
(
5)
revised
regulatory
language
at
51.302
to
clarify
the
relationship
between
New
Source
Performance
Standards
(
NSPS)
and
BART
for
reasonably
attributable
visibility
impairment.

How
This
Preamble
Is
Structured.
Section
II
provides
background
on
the
Clean
Air
Act
(
CAA)
BART
requirements
as
codified
in
the
regional
haze
rule,
on
the
D.
C.
Circuit
Court
decision
which
remanded
parts
of
the
rule,
and
on
the
April
2004
reproposal
responding
to
the
remand.
Section
III
discusses
specific
issues
in
the
BART
guidelines
in
more
detail,
including
background
on
each
issue,
major
comments
we
received
on
the
July
2001
proposal
and
May
2004
reproposal,
and
our
responses
to
those
comments.
Section
IV
provides
a
discussion
of
how
this
rulemaking
complies
with
the
requirements
of
Statutory
and
Executive
Order
Reviews.

II.
Background
The
Regional
Haze
Rule
In
1999,
we
published
a
final
rule
to
address
a
type
of
visibility
impairment
known
as
regional
haze
(
64
FR
35714;

July
1,
1999).
The
regional
haze
rule
requires
States
to
submit
implementation
plans
(
SIPs)
to
address
regional
haze
visibility
impairment
in
156
Federally­
protected
parks
and
1
See,
e.
g.
CAA
Section
169A(
a)(
1).

7
wilderness
areas.
These
156
scenic
areas
are
called
"
mandatory
Class
I
Federal
areas"
in
the
Clean
Air
Act
(
CAA),
1
but
are
referred
to
simply
as
"
Class
I
areas"
in
today's
rulemaking.
The
1999
rule
was
issued
to
fulfill
a
long­
standing
EPA
commitment
to
address
regional
haze
under
the
authority
and
requirements
of
sections
169A
and
169B
of
the
CAA.

As
required
by
the
CAA,
we
included
in
the
final
regional
haze
rule
a
requirement
for
BART
for
certain
large
stationary
sources
that
were
put
in
place
between
1962
and
1977.
We
discussed
these
requirements
in
detail
in
the
preamble
to
the
final
rule
(
64
FR
35737­
35743).
The
regulatory
requirements
for
BART
were
codified
at
40
CFR
51.308(
e),
and
in
definitions
that
appear
in
40
CFR
51.301.

The
CAA,
in
sections
169A(
b)(
2)(
A)
and
in
169A(
g)(
7),

uses
the
term
"
major
stationary
source"
to
describe
those
sources
that
are
the
focus
of
the
BART
requirement.
To
avoid
confusion
with
other
CAA
requirements
which
also
use
the
term
"
major
stationary
source"
to
refer
to
a
somewhat
different
population
of
sources,
the
regional
haze
rule
uses
the
term
"
BART­
eligible
source"
to
describe
these
sources.

The
BART­
eligible
sources
are
those
sources
which
have
the
potential
to
emit
250
tons
or
more
of
a
visibility­
impairing
8
air
pollutant,
were
put
in
place
between
August
7,
1962
and
August
7,
1977,
and
whose
operations
fall
within
one
or
more
of
26
specifically
listed
source
categories.
Under
the
CAA,

BART
is
required
for
any
BART­
eligible
source
which
"
emits
any
air
pollutant
which
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
visibility
in
any
such
area."
Accordingly,
for
stationary
sources
meeting
these
criteria,
States
must
address
the
BART
requirement
when
they
develop
their
regional
haze
SIPs.

Section
169A(
g)(
7)
of
the
CAA
requires
that
States
must
consider
the
following
factors
in
making
BART
determinations:

(
1)
the
costs
of
compliance,

(
2)
the
energy
and
nonair
quality
environmental
impacts
of
compliance,

(
3)
any
existing
pollution
control
technology
in
use
at
the
source,

(
4)
the
remaining
useful
life
of
the
source,
and
(
5)
the
degree
of
improvement
in
visibility
which
may
reasonably
be
anticipated
to
result
from
the
use
of
such
technology.

These
statutory
factors
for
BART
were
codified
at
40
CFR
51.308(
e)(
1)(
ii).

In
the
preamble
to
the
regional
haze
rule,
we
committed
to
issuing
further
guidelines
to
clarify
the
requirements
of
9
the
BART
provision.
The
purpose
of
this
rulemaking
is
to
fulfill
this
commitment
by
providing
guidelines
for
States
to
use
in
identifying
their
BART­
eligible
sources,
in
identifying
which
of
those
sources
must
undergo
a
detailed
BART
analysis
(
i.
e.,
which
are
"
sources
subject
to
BART"),

and
in
conducting
the
technical
analyses
of
possible
controls
in
light
of
the
statutory
factors
listed
above
("
the
BART
determination").

American
Corn
Growers
v.
EPA
In
response
to
challenges
to
the
regional
haze
rule
by
various
petitioners,
the
D.
C.
Circuit
in
American
Corn
Growers
et
al.
v.
EPA,
291
F.
3d
1
(
2002)
issued
a
ruling
striking
down
the
regional
haze
rule
in
part,
and
upholding
it
in
part.
This
section
discusses
the
court's
opinion
in
that
case,
as
background
for
the
discussion
of
specific
changes
to
the
regional
haze
rule
and
the
BART
guidelines
presented
in
the
next
two
sections,
respectively.

We
explained
in
the
preamble
to
the
1999
regional
haze
rule
that
the
BART
requirements
in
section
169A(
b)(
2)(
A)
of
the
CAA
demonstrate
Congress'
intent
to
focus
attention
directly
on
the
problem
of
pollution
from
a
specific
set
of
existing
sources
(
64
FR
35737).
The
CAA
requires
that
any
of
these
existing
sources
"
which,
as
determined
by
the
State,
emits
any
air
pollutant
which
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
2
CAA
Sections
169A(
b)(
2)
&
(
g)(
7).

10
visibility
[
in
a
Class
I
area],"
shall
install
the
best
available
retrofit
technology
for
controlling
emissions.
2
In
determining
BART,
the
CAA
requires
the
State
to
consider
several
factors
that
are
set
forth
in
section
169(
g)(
2)
of
the
CAA,
including
the
degree
of
improvement
in
visibility
which
may
reasonably
result
from
the
use
of
such
technology.

The
regional
haze
rule
addresses
visibility
impairment
resulting
from
emissions
from
a
multitude
of
sources
located
across
a
wide
geographic
area.
Because
the
problem
of
regional
haze
is
caused
in
large
part
by
the
long­
range
transport
of
emissions
from
multiple
sources,
and
for
certain
technical
and
other
reasons
explained
in
that
rulemaking,
we
had
adopted
an
approach
that
required
States
to
look
at
the
contribution
of
all
BART
sources
to
the
problem
of
regional
haze
in
determining
both
applicability
and
the
appropriate
level
of
control.
Specifically,
we
had
concluded
that
if
a
source
potentially
subject
to
BART
is
located
within
an
upwind
area
from
which
pollutants
may
be
transported
downwind
to
a
Class
I
area,
that
source
"
may
reasonably
be
anticipated
to
cause
or
contribute"
to
visibility
impairment
in
the
Class
I
area.
Similarly,
we
had
also
concluded
that
in
weighing
the
factors
set
forth
in
the
statute
for
determining
BART,
the
States
should
consider
3
See
66
FR
35737­
35743
for
a
discussion
of
the
rationale
for
the
BART
requirements
in
the
1999
regional
haze
rule.

11
the
collective
impact
of
BART
sources
on
visibility.
In
particular,
in
considering
the
degree
of
visibility
improvement
that
could
reasonably
be
anticipated
to
result
from
the
use
of
such
technology,
we
stated
that
the
State
should
consider
the
degree
of
improvement
in
visibility
that
would
result
from
the
cumulative
impact
of
applying
controls
to
all
sources
subject
to
BART.
We
had
concluded
that
the
States
should
use
this
analysis
to
determine
the
appropriate
BART
emission
limitations
for
specific
sources.
3
In
American
Corn
Growers
v.
EPA,
industry
petitioners
challenged
EPA's
interpretation
of
both
these
aspects
of
the
BART
determination
process
and
raised
other
challenges
to
the
rule.
While
rejecting
industry's
other
challenges,
the
court
in
American
Corn
Growers
concluded
that
the
BART
provisions
in
the
1999
regional
haze
rule
were
inconsistent
with
the
provisions
in
the
CAA
"
giving
the
states
broad
authority
over
BART
determinations."
291
F.
3d
at
8.
Specifically,
with
respect
to
the
test
for
determining
whether
a
source
is
subject
to
BART,
the
court
held
that
the
method
that
we
had
prescribed
for
determining
which
eligible
sources
are
subject
to
BART
illegally
constrained
the
authority
Congress
had
conferred
on
the
States.
Id.
However,
the
court
expressly
declined
to
hold
12
that
the
general
collective
contribution
approach
to
determining
BART
applicability
was
necessarily
inconsistent
with
the
CAA,
were
it
not
for
the
infringement
on
State
authority.
Id.
at
9.
Rather,
the
court
stated
that
the
collective
contribution
approach
may
have
been
acceptable
if
EPA
had
allowed
for
a
State
exemption
process
based
on
an
individualized
contribution
determination.
Id.
at
12.

The
court
in
American
Corn
Growers
also
found
that
our
interpretation
of
the
CAA
requiring
the
States
to
consider
the
degree
of
improvement
in
visibility
that
would
result
from
the
cumulative
impact
of
applying
controls
in
determining
BART
was
inconsistent
with
the
language
of
the
Act.
291
F.
3d
at
8.
Based
on
its
review
of
the
statute,

the
court
concluded
that
the
five
statutory
factors
in
section
169A(
g)(
2)
"
were
meant
to
be
considered
together
by
the
states."
Id.
at
6.

Changes
in
Response
to
American
Corn
Growers
Today's
rule
responds
to
the
American
Corn
Growers
court's
decision
on
the
BART
provisions
by
including
changes
to
the
regional
haze
rule
at
40
CFR
51.308,
and
by
finalizing
changes
to
the
BART
guidelines.
This
section
outlines
the
changes
to
the
regional
haze
rule
due
to
the
court's
remand.
It
also
explains
the
minor
change
we
are
making
to
the
section
of
the
regulation
governing
the
use
of
the
1980
BART
guidelines
when
conducting
BART
analyses
for
13
certain
power
plants
for
reasonably
attributable
(
i.
e.,

localized)
visibility
impairment.

1.
Determination
of
Which
Sources
are
Subject
to
BART
Today's
action
addresses
the
American
Corn
Growers
court's
vacature
of
the
requirement
in
the
regional
haze
rule
requiring
States
to
assess
visibility
impacts
on
a
cumulative
basis
in
determining
which
sources
are
subject
to
BART.
Because
this
requirement
was
found
only
in
the
preamble
to
the
1999
regional
haze
rule
(
see
291
F.
3rd
at
6,

citing
64
FR
35741),
no
changes
to
the
regulations
are
required.
Instead,
this
issue
is
addressed
in
the
BART
guidelines,
which
provide
States
with
processes
for
determining
which
BART­
eligible
sources
"
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
visibility
in
any
mandatory
Class
I
Federal
area."
These
processes
has
been
designed
to
address
the
holding
of
American
Corn
Growers
by
eliminating
the
previous
constraint
on
State
discretion,
as
explained
in
further
detail
in
sections
II.
D.
and
III
below.

2.
Consideration
of
Anticipated
Visibility
Improvements
in
BART
Determinations
Pursuant
to
the
remand
in
American
Corn
Growers,
we
are
amending
the
regional
haze
rule
to
require
the
States
to
consider
the
degree
of
visibility
improvement
resulting
from
a
source's
installation
and
operation
of
retrofit
14
technology,
along
with
the
other
statutory
factors
set
out
in
CAA
section
169A(
g)(
2),
when
making
a
BART
determination.

This
would
be
accomplished
by
listing
the
visibility
improvement
factor
with
the
other
statutory
BART
determination
factors
in
section
308(
e)(
1)(
A),
so
that
States
will
be
required
to
consider
all
five
factors,

including
visibility
impacts,
on
an
individual
source
basis
when
making
each
individual
source
BART
determination.

Center
for
Energy
and
Economic
Development
v.
EPA
After
the
May
2004
reproposal
of
the
BART
guidelines,

the
D.
C.
Circuit
decided
another
case
where
BART
provisions
were
at
issue,
Center
for
Energy
and
Economic
Development
v.

EPA,
No.
03­
1222,(
D.
C.
Cir.
Feb.
18,
2005)("
CEED").
In
this
case,
the
court
granted
a
petition
challenging
provisions
of
the
regional
haze
rule
governing
the
optional
emissions
trading
program
for
certain
western
States
and
Tribes
(
the
"
WRAP
Annex
Rule").

The
court
in
CEED
affirmed
our
interpretation
of
CAA
169A(
b)(
2)
as
allowing
for
non­
BART
alternatives
where
those
alternatives
are
demonstrated
to
make
greater
progress
than
BART.
(
CEED,
slip.
op.
at
13).
The
court,
however,
took
issue
with
provisions
of
the
regional
haze
rule
governing
the
methodology
of
that
demonstration.
Specifically,
40
CFR
51.308(
e)(
2)
required
that
visibility
improvements
under
15
source­
specific
BART
 
the
benchmark
for
comparison
to
the
alternative
program
 
must
be
estimated
based
on
the
application
of
BART
controls
to
all
sources
subject
to
BART.

(
This
section
was
incorporated
into
the
WRAP
Annex
rule
by
reference
at
40
CFR
51.309(
f)).
The
court
held
that
we
could
not
require
this
type
of
group
BART
approach
 
vacated
in
American
Corn
Growers
in
a
source­
specific
BART
context
 
even
in
a
program
in
which
State
participation
was
wholly
optional.

The
BART
Guidelines
as
proposed
in
May
2004
contained
a
section
offering
guidance
to
States
choosing
to
address
their
BART­
eligible
sources
under
the
alternative
strategy
provided
for
in
40
CFR
51.308(
e)(
2).
This
guidance
included
criteria
for
demonstrating
that
the
alternative
program
achieves
greater
progress
towards
eliminating
visibility
impairment
than
would
BART.

In
light
of
the
D.
C.
Circuit's
decision
in
CEED,
and
the
consequent
need
to
revise
§
308(
e)(
2),
we
are
removing
the
section
of
the
BART
guidelines
addressing
alternative
programs
from
today's
rulemaking.
We
remain
committed
to
providing
States
with
the
flexibility
to
address
BART
through
alternative
means
 
and
we
note
again
that
our
authority
to
do
so
was
upheld
in
CEED.
Therefore
we
intend
to
revise
the
provisions
of
the
regional
haze
rule
governing
such
alternatives,
and
provide
any
additional
guidance
16
needed,
in
a
subsequent
rulemaking
conducted
as
expeditiously
as
practicable.

Overview
of
The
BART
Process
The
process
of
establishing
BART
emission
limitations
can
be
logically
broken
down
into
three
steps:
First,

States
identify
those
sources
which
meet
the
definition
of
"
BART­
eligible
source"
set
forth
in
40
CFR
51.301.
Second,

States
determine
whether
such
sources
"
emit[]
any
air
pollutant
which
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
visibility
[
in
a
Class
I
area.]"
A
source
which
fits
this
description
is
"
subject
to
BART."
Third,
for
each
source
subject
to
BART,
States
then
identify
the
appropriate
type
and
the
level
of
control
for
reducing
emissions.

Identifying
BART­
eligible
sources
The
CAA
defines
BART­
eligible
sources
as
those
sources
which
fall
within
one
of
26
specific
source
categories,
were
built
during
the
15­
year
window
of
time
from
1962
to
1977,

and
have
potential
emissions
greater
than
250
tons
per
year.

The
remand
did
not
address
the
step
of
identifying
BARTeligible
sources,
which
is
conceptually
the
simplest
of
the
three
steps.

Sources
reasonably
anticipated
to
cause
or
contribute
to
visibility
impairment
(
sources
subject
to
BART)
4
64
FR
335740,
July
1,
1999.
The
regional
haze
rule
discusses
at
length
why
we
believe
that
States
should
draw
17
As
we
noted
in
the
preamble
to
the
1999
regional
haze
rule,
defining
the
individual
contributions
of
specific
sources
of
the
problem
of
regional
haze
can
be
timeconsuming
and
expensive.
Moreover,
Congress
established
a
very
low
threshold
in
the
CAA
for
determining
whether
a
source
is
subject
to
BART.
We
are
accordingly
finalizing
several
approaches
for
States
for
making
the
determination
of
whether
a
source
"
emits
any
pollutants
which
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
visibility
impairment."
The
first
two
of
these
approaches
would
allow
States
to
avoid
undertaking
unnecessary
and
costly
studies
of
an
individual
source's
contribution
to
haze
by
allowing
States
to
adopt
more
streamlined
processes
for
determining
whether,
or
which,
BART­
eligible
sources
are
subject
to
BART.

In
1999,
we
adopted
an
applicability
test
that
looked
to
the
collective
contribution
of
emissions
from
an
area.

In
particular,
we
stated
that
if
"
a
State
should
find
that
a
BART­
eligible
source
is
`
reasonably
anticipated
to
cause
or
contribute'
to
regional
haze
if
it
can
be
shown
that
the
source
emits
pollutants
within
a
geographic
area
from
which
pollutants
can
be
emitted
and
transported
downwind
to
a
Class
I
area."
4
States
have
the
discretion
to
consider
that
this
conclusion.
64
FR
35739­
40.

5
CAA
§
169A(
b)(
2)(
A).

18
all
BART­
eligible
sources
within
the
State
are
"
reasonably
anticipated
to
cause
or
contribute"
to
some
degree
of
visibility
impairment
in
a
Class
I
area.

This
option
is
consistent
with
the
American
Corn
Growers
court's
decision.
As
previously
noted,
the
court's
concern
with
our
original
approach
governing
BART
applicability
determinations
was
that
it
would
have
"
tie[
d]

the
states'
hands
and
force[
d]
them
to
require
BART
controls
at
sources
without
any
empirical
evidence
of
the
particular
source's
contribution
to
visibility
impairment."
291
F.
3d
at
8.
By
the
same
rationale,
we
believe
it
would
be
an
impermissible
constraint
of
State
authority
to
force
States
to
conduct
individualized
analysis
in
order
to
determine
that
a
BART­
eligible
source
"
emits
any
air
pollutant
which
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
visibility
in
any
[
Class
I]
area."
5
In
this
respect,
we
believe
that
it
is
important
to
note
that
the
court
in
American
Corn
Growers
expressly
declined
to
hold
that
consideration
of
visibility
impact
on
a
cumulative
basis
would
be
invalid
in
all
circumstances.
291
F.
3d
at
9.

Given
the
court's
emphasis
on
the
importance
of
the
role
of
the
States
in
making
BART
determinations,
we
believe
that
a
6
See
64
FR
35714,
35721.
See
also
July
29,
1997
memorandum
to
the
regional
haze
docket
A­
95­
38,
"
Supporting
Information
for
Proposed
Applicability
of
Regional
Haze
Regulations,"
by
Richard
Damberg,
EPA,
Office
of
Air
Quality
Planning
and
Standards.

19
State's
decision
to
use
a
cumulative
analysis
at
the
eligibility
stage
would
be
consistent
with
the
CAA
and
the
findings
of
the
D.
C.
Circuit.

We
believe
there
is
ample
technical
evidence
supporting
a
finding
by
a
State
that
all
BART­
eligible
sources
within
the
State
are
subject
to
BART,
without
further
analysis
at
that
stage
in
the
process.
6
Any
potential
for
inequity
towards
sources
would
be
addressed
at
the
BART
determination
stage,
which
contains
an
individualized
consideration
of
a
source's
contribution
in
establishing
BART
emission
limits.

States
also
have
the
option
of
performing
an
analysis
to
show
that
the
full
group
of
BART­
eligible
sources
in
a
State
cumulatively
do
not
cause
or
contribute
to
any
visibility
impairment
in
Class
I
areas.
We
anticipate
that
in
most,
if
not
all
States,
the
BART­
eligible
sources
are
likely
to
cause
or
contribute
to
some
visibility
impairment
in
Class
I
areas.
However,
it
is
possible
that
using
a
cumulative
approach,
a
State
could
show
that
its
BART
sources
do
not
collectively
pose
a
measurable
problem.
20
Finally,
States
may
consider
the
individualized
contribution
of
a
BART­
eligible
source
to
determine
whether
a
specific
source
is
subject
to
BART.
Specifically,
States
may
choose
to
undertake
an
analysis
of
each
BART­
eligible
source
in
the
State
in
considering
whether
each
such
source
meets
the
test
set
forth
in
the
CAA
of
"
emit[
ting]
any
air
pollutant
which
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
visibility
in
any
[
Class
I]

area."
Alternatively,
States
may
choose
to
presume
that
all
BART­
eligible
sources
within
the
State
meet
this
applicability
test,
but
provide
sources
with
the
ability
to
demonstrate
on
a
case
by
case
basis
that
this
is
not
the
case.
This
approach
is
consistent
with
the
D.
C.
Circuit's
statement
that
a
collective
contribution
approach
may
be
appropriate
so
long
as
the
States
are
allowed
to
exempt
sources
on
the
basis
of
an
individualized
contribution
determination.
291
F.
3d
at
8.

For
assessing
the
impact
of
BART­
eligible
sources
on
nearby
Class
I
areas,
we
are
including
a
process
whereby
the
States
would
use
an
air
quality
model
able
to
estimate
a
single
source's
contribution
to
visibility
impairment.

States
may
also
choose
to
use
other,
less
resource­
intensive
methods
of
assessing
a
source's
individualized
contribution
to
regional
haze
visibility
impairment.

The
BART
determination
21
The
State
must
determine
the
appropriate
level
of
BART
control
for
each
source
subject
to
BART.
Section
169A(
g)(
7)

of
the
CAA
requires
States
to
consider
the
following
factors
in
making
BART
determinations:
(
1)
the
costs
of
compliance,

(
2)
the
energy
and
nonair
quality
environmental
impacts
of
compliance,
(
3)
any
existing
pollution
control
technology
in
use
at
the
source,
(
4)
the
remaining
useful
life
of
the
source,
and
(
5)
the
degree
of
improvement
in
visibility
which
may
reasonably
be
anticipated
to
result
from
the
use
of
such
technology.
The
remand
did
not
address
the
first
four
steps
of
the
BART
determination.
The
remand
did
address
the
final
step,
mandating
that
we
must
provide
a
way
for
States
to
take
into
account
the
degree
of
improvement
in
visibility
that
would
result
from
imposition
of
BART
on
each
individual
source.

The
first
four
factors
are
somewhat
similar
to
the
engineering
analysis
in
the
original
BART
guidelines
proposed
in
2001
and
reproposed
in
2004.
The
BART
guidelines
also
contains
a
detailed
discussion
of
available
and
cost­
effective
controls
for
reducing
SO2
and
nitrogen
oxicdes
(
NOx)
emissions
from
large
coal­
fired
electric
generating
units
(
EGUs).

For
assessing
the
fifth
factor,
the
degree
of
improvement
in
visibility
from
various
BART
control
options,

the
States
may
run
CALPUFF
or
other
EPA
approved
model
to
22
predict
visibility
impacts.
Scenarios
would
be
run
for
the
pre­
controlled
and
post­
controlled
emission
rates
for
each
of
the
BART
control
options
under
review.
The
maximum
hourly
emission
rates
would
be
modeled
for
a
period
of
three
or
five
years
of
meteorological
data.
States
have
the
flexibility
to
develop
their
own
methods
to
evaluate
model
results.

III.
Detailed
Discussion
of
the
Final
BART
Guidelines
A.
Introduction
In
this
section
of
the
preamble,
we
discuss
changes
or
clarifications
to
the
reproposed
BART
guidelines.
Where
relevant,
we
also
respond
to
comments
received
during
the
comment
period
on
the
2001
proposal.
For
each
provision
of
the
guidelines
that
we
are
changing
or
clarifying,
we
provide
discussion
of,
as
appropriate:

 
background
information,

 
how
the
provision
was
addressed
in
the
May
2004
reproposal
(
and
in
the
2001
proposal,
if
different
from
the
reproposal),

­
a
summary
of
comments
received
on
the
provision,

either
from
the
May
2004
reproposal,
from
the
July
2001
proposal,
or
from
both,
and
­
the
changes
or
clarifications
that
we
are
finalizing
and
the
reasons
for
these
changes
or
clarifications.
23
B.
Scope
of
the
Rule
 
Whether
to
Require
States
to
follow
the
Guidelines
for
All
BART
Sources
Background.
Section
169A(
b)(
1)
of
the
CAA
requires
EPA
to
issue
regulations
to
provide
guidelines
to
States
on
the
implementation
of
the
visibility
program.
In
addition,
the
last
sentence
of
section
169A(
b)
states:

In
the
case
of
a
fossil­
fuel
fired
generating
powerplant
having
a
capacity
in
excess
of
750
megawatts,
the
emission
limitations
required
under
this
paragraph
shall
be
determined
pursuant
to
guidelines,
promulgated
by
the
Administrator
under
paragraph
(
1).

This
statutory
requirement
clearly
requires
us
to
promulgate
BART
guidelines
that
the
States
must
follow
in
establishing
BART
emission
limitations
for
power
plants
with
a
total
capacity
exceeding
the
750
megawatt
cutoff.
The
statute
is
less
clear
regarding
the
import
of
the
guidelines
for
sources
other
than
750
megawatt
power
plants.

Proposed
rules.
Both
the
2001
proposal
and
the
2004
reproposal
included
a
requirement
for
States
to
follow
the
procedures
set
out
in
the
guidelines
in
determining
BART
for
sources
in
all
of
the
26
listed
BART
categories.
The
2001
proposal
requested
comment
on
whether
the
regional
haze
rule
should:
(
1)
require
the
use
of
the
guidelines
only
for
750
megawatt
utilities,
with
the
guidelines
applying
as
guidance
24
for
the
remaining
categories,
or
(
2)
require
the
use
of
the
guidelines
for
all
of
the
affected
source
categories.

Comments.
We
received
comments
on
this
issue
in
both
2001
and
2004.
Comments
varied
widely
on
whether
we
can
or
should
require
the
use
of
the
guidelines
for
all
of
the
affected
source
categories.

Comments
from
State,
local
and
tribal
air
quality
agencies
generally
supported
our
proposal
to
require
the
use
of
the
guidelines
for
all
of
the
source
categories.
These
comments
cited
a
need
for
national
consistency
in
the
application
of
the
BART
requirement
across
the
source
categories,
and
from
State
to
State.
One
State
agency
commenter
questioned
our
legal
authority
to
require
the
use
of
the
guidelines
for
all
source
categories;
and
several
State
agency
commenters,
while
supporting
the
proposal,

requested
that
we
provide
clarification
of
the
legal
authority
for
requiring
the
States
to
use
the
guidelines
in
establishing
BART
emission
limitations
for
all
categories.

Comments
from
the
utility
industry,
from
various
manufacturing
trade
groups,
and
from
individual
companies
were
critical
of
the
proposal
to
require
States
to
follow
the
guidelines
generally.
Many
commenters
also
argued
that
EPA
lacked
the
authority
to
issue
guidelines
for
any
industrial
category
other
than
750
megawatt
powerplants,

whether
the
use
of
such
guidelines
were
mandatory
or
not.
25
Other
commenters
stated
that
the
language
in
the
CAA
clearly
restricts
the
scope
of
mandatory
guidelines
to
larger
powerplants.
The
commenters
cited
the
legislative
history
of
the
1977
Clean
Air
Act
amendments
in
support
of
this
position,
and
frequently
claimed
that
requiring
the
guidelines
for
all
26
categories
of
sources
would
deprive
States
of
flexibility
in
implementing
the
program.

Comments
from
environmental
organizations
and
the
general
public
supported
the
approach
in
the
proposed
rule
and
stated
that
EPA
is
obligated
to
establish
regional
haze
BART
guidelines
by
rulemaking
for
all
26
categories
of
stationary
sources.
Environmental
organization
comments
noted
that
while
Congress
expressed
a
particular
concern
for
750
MW
powerplants,
this
added
emphasis
on
one
sector
does
not
change
requirements
in
the
Act
for
all
BART­
eligible
sources.
Accordingly,
these
commenters
believed
that
we
should
not
construe
a
special
emphasis
on
powerplants
as
a
restriction
on
our
authority
to
require
use
of
the
guidelines
for
all
categories.

Final
rule.
The
CAA
and
the
relevant
legislative
history
make
clear
that
EPA
has
the
authority
and
obligation
to
publish
mandatory
guidelines
for
powerplants
exceeding
750
megawatts.
As
previously
noted,
Congress
in
section
169A(
b)
of
the
CAA
expressly
provided
that
emission
limitations
for
powerplants
larger
than
750
megawatts
"
shall
26
be
determined
pursuant
to
guidelines
promulgated
by
the
Administrator."
(
Emphasis
added).
This
unambiguous
language
leaves
little
room
to
dispute
that
the
guidelines
EPA
is
required
to
promulgate
must
be
used
by
States
when
making
BART
determinations
for
this
class
of
sources.

Having
carefully
considered
the
comments
and
further
reviewed
the
CAA
and
the
legislative
history,
we
have
concluded
that
it
would
not
be
appropriate
for
EPA
to
require
States
to
use
the
guidelines
in
making
BART
determinations
for
other
categories
of
sources.
The
better
reading
of
the
Act
indicates
that
Congress
intended
the
guidelines
to
be
mandatory
only
with
respect
to
750
megawatt
powerplants.
Thus,
while
we
agree
with
the
State
agency
comments
noting
the
strong
policy
reasons
in
support
of
covering
all
categories
in
order
to
establish
consistency
across
States
in
how
BART
determinations
are
made,
we
are
not
requiring
States
to
use
the
BART
guideline
for
these
other
categories.
In
response
to
State
concerns
about
equitable
application
of
the
BART
requirement
to
source
owners
with
similar
sources
in
different
states,
we
do
encourage
States
to
follow
the
guidelines
for
all
source
categories
but
are
not
requiring
States
to
do
so.
States
should
view
the
guidelines
as
guidance
for
these
other
categories.
27
We
disagree
with
comments
that
the
CAA
and
the
legislative
history
prohibit
us
from
issuing
guidance
for
other
source
categories.
As
the
guidelines
make
clear,

States
are
not
required
to
follow
the
approach
in
the
guidelines
for
sources
other
than
750
megawatt
powerplants.

As
such,
although
we
believe
that
the
guidelines
provide
useful
advice
in
implementing
the
BART
provisions
of
the
regional
haze
rule,
we
do
not
believe
that
they
hamper
State
discretion
in
making
BART
determinations.

C.
How
to
Identify
BART­
eligible
Sources
Section
II
of
the
BART
guidelines
contains
a
step­

bystep
process
for
identifying
stiationary
sources
that
are
"
BART­
eligible"
under
the
definitions
in
the
regional
haze
rule.
The
four
basic
steps
are:

Step
1:
Identify
the
emission
units
in
the
BART
categories
Step
2:
Identify
the
start­
up
dates
of
those
emissin
units
Step
3:
Compare
the
potential
emissions
from
units
identified
in
Steps
1
and
2
to
the
250
ton/
year
cutoff
Step
4:
Identify
the
emission
units
and
pollutants
that
constitute
the
BART­
eligible
source.

In
this
section
of
the
preamble,
we
discuss
some
of
the
comments
we
received
on
the
steps
in
this
process,
and
any
changes
we
are
making
in
light
of
those
comments.
28
Step
1:
Identify
the
emission
units
in
the
BART
categories
The
BART
guidelines
list
the
26
source
categories
that
the
CAA
uses
to
describe
the
types
of
stationary
sources
that
are
BART­
eligible.
Both
proposals
clarified
the
descriptions
of
particular
source
categories.

Comments.
The
final
rule
addresses
comments
on
the
following
source
categories.
Some
comments
discussed
below
were
submitted
in
response
to
the
2001
propoosal
and
were
not
addressed
in
the
reproposal;
other
comments
were
submitted
in
response
to
the
reproposal
in
2004.

(
1)
"
Charcoal
production
facilities."
We
received
comments
in
2001
from
two
industry
trade
groups
requesting
that
the
final
guidelines
explicitly
exclude
"
low­
emission"

charcoal
production
facilities
from
BART.
These
comments
cited
a
1975
study
considered
by
Congress
in
development
of
the
BART
category
list
in
the
1977
CAA
amendments.
This
1975
study
noted
that
some
charcoal
production
facilities
have
much
higher
emissions
factors
(
i.
e.,
352
pounds
of
PM
per
ton
of
charcoal
produced
versus
20
to
25
pounds
of
PM
per
ton
of
charcoal
produced).
Accordingly,
the
comments
asserted
that
the
intent
of
Congress
in
the
1977
CAA
amendments
was
to
provide
incentives
for
higher­
emitting
facilities
to
reduce
their
emissions,
rather
than
to
make
the
entire
category
BART­
eligible.
29
(
2)
"
Chemical
process
plants."
In
2001
a
trade
group
representing
the
pharmaceutical
industry
requested
that
we
determine
in
the
guidelines
that
the
term
"
chemical
process
plants"
does
not
include
pharmaceutical
plants.

(
3)
"
Primary
aluminum
ore
reduction."
Comments
from
the
aluminum
industry
in
2001
noted
that
not
all
emissions
units
at
these
facilities
are
necessarily
involved
in
"
primary
ore
reduction."
Thus,
the
comments
recommended
that
we
clarify
that
contiguous
sources
that
are
not
related
to
primary
aluminum
ore
reduction,
such
as
fabricating
facilities
and
ingot
operations,
are
not
BART­
eligible.

Further,
the
comments
recommended
that
we
use
definitions
in
the
NSPS
for
primary
aluminum
plants
to
describe
the
BARTeligible
emissions
units.

(
4)
"
Fossil­
fuel
fired
steam
electric
plants
of
more
than
250
million
Btu/
hour
heat
input."
The
2004
reproposal
contained
the
clarification,
requested
by
commenters,
that
this
source
category
refers
only
to
those
fossil­
fuel
fired
steam
electric
plants
that
generate
electricity
for
sale.

One
commenter
objected
to
this
clarification
on
the
basis
that
emissions
from
co­
generators
would
be
excluded;
many
other
commenters
supported
the
clarification.
Another
commenter
requested
that
we
also
clarify
that
this
category
includes
only
those
steam
electric
plants
that
burn
greater
than
50
percent
fossil
fuel,
in
order
to
be
consistent
with
30
the
definition
of
fossil­
fuel
boilers
proposed
in
the
guidelines.
Other
commenters
requested
that
we
clarify
whether
the
definition
includes
units
which
are
located
at
a
steam
electric
plant,
but
which
themselves
are
not
in
any
of
the
26
BART
source
categories,
such
as
simple
cycle
turbines,
emergency
diesel
engines,
and
reciprocating
internal
combustion
engines
(
RICE).

Several
commenters
opined
that
the
category
should
exclude
combined
cycle
units
with
heat
recovery
steam
generators
that
lack
auxilliary
firing,
arguing
that
these
units
should
count
as
simple
cycle
turbines.
These
commenters
pointed
to
other
EPA
regulatory
programs
that
treat
combined
cycle
units
with
supplemental
firing
differently
from
combined
cycle
units
without
supplemental
firing.
They
argued
that
we
should
only
consider
a
combined
cycle
unit
to
be
a
"
steam
electric
plant"
if
it
has
supplemental
firing.

(
5)
"
Fossil­
fuel
boilers
of
more
than
250
million
Btu/
hour
heat
input."
The
2004
reproposal
clarified
that
this
category
should
be
read
as
including
only
those
boilers
individually
greater
than
250
million
Btu/
hour
heat
input.

We
received
many
comments
on
this
interpretation,
both
in
favor
and
opposed.
Those
favoring
this
interpretation
(
generally
industry
commenters)
cited
the
implementation
burden
that
including
smaller
boilers
would
pose,
the
high
31
cost­
effectiveness
of
controlling
smaller
boilers,
and
the
relatively
smaller
impact
on
regional
haze
that
smaller
boilers
would
pose.
They
also
noted
that
this
interpretation
is
most
consistent
with
definitions
in
the
NOx
SIP
call
and
new
source
performance
standards
(
NSPS).

Commenters
opposing
this
interpretation
(
environmental
groups,
one
state,
and
one
regional
planning
organization)

noted
that
regarding
all
boilers,
irrespective
of
size,
as
BART­
eligible
so
long
as
the
aggregate
heat
input
exceeds
250
million
Btu/
hour
is
more
consistent
with
the
definition
of
stationary
source
under
the
Prevention
of
Significant
Deterioration
(
PSD)
program.
These
commenters
noted
that
under
the
CAA,
BART
and
PSD
are
complementary
programs
aimed
at
regulating
the
same
source
categories;
either
one
or
the
other
applies
depending
upon
when
the
source
was
constructed.

The
2004
reproposal
also
clarified
that
if
a
boiler
smaller
than
250
million
Btu/
hour
heat
input
is
an
integral
part
of
an
industrial
process
in
a
BART
source
category
other
than
electric
utilities,
then
the
boiler
should
be
considered
part
of
the
BART­
eligible
source
in
that
category.
Under
these
circumstances,
the
boiler,
as
part
of
the
BART­
eligible
source,
should
be
considered
for
emission
control.
Some
commenters
opposed
this
interpretation,

asserting
that
it
would
result
in
an
"
arbitrary
and
32
capricious"
inconsistency,
in
that
some
smaller
boilers
would
be
BART­
eligible,
and
others
would
not.
These
commenters
also
noted
that
these
boilers
could
be
included
in
regional
haze
SIPs
as
necessary
for
making
"
reasonable
progress"
toward
CAA
visibility
goals,
even
if
they
are
not
considered
to
be
BART­
eligible.

Final
rule.
After
considering
the
comments,
we
have
made
the
following
determinations
on
the
definitions
of
the
following
source
categories:

(
1)
"
Charcoal
production
facilities."
We
believe
that
in
using
the
term
"
charcoal
production
facilities"
Congress
intended
to
encompass
all
types
of
charcoal
production
facilities.
We
do
not
agree
with
comments
that
any
inferences
can
necessarily
be
made
regarding
the
presence
of
different
PM
emission
factors
for
different
types
of
charcoal
production
facilities
in
the
1975
report.
For
example,
if
Congress
only
intended
to
regulate
a
subset
of
the
charcoal
production
industry,
the
we
believe
Congress
could
have
easily
indicated
this
in
the
source
category
title,
as
was
done
for
"
kraft
pulp
mills"
and
for
"
coal
cleaning
plants
(
thermal
dryers)."
We
also
note
that
it
is
more
likely
that
plants
in
the
charcoal
production
industry
with
lower
emission
factors
have
emissions
that
are
less
than
the
250
tons
per
year
cutoff
for
BART
eligibility.
33
(
2)
"
Chemical
process
plants."
We
believe
that
there
is
a
clear
precedent
to
include
pharmaceutical
manufacturing
operations
as
"
chemical
process
plants."
In
the
standard
industrial
classification
(
SIC)
system,
pharmaceutical
operations
are
generally
in
SIC
codes
2833
and
2834,
which
are
a
subset
of
2­
digit
category
28
"
Chemical
and
Allied
products."
Similarly,
in
the
new
North
American
Industrial
Classification
Codes
(
NAICS),
pharmaceutical
manufacturing
is
codes
32541
and
32542,
which
is
a
subset
of
the
"
chemical
manufacturing
subsector"
which
is
code
325.
Accordingly,

in
the
PSD
program,
pharmaceutical
plants
have
been
treated
as
"
chemical
process
plants."
The
commenter
is
correct
in
noting
that
EPA
has
consistently
distinguished
between
chemical
manufacturing
and
pharmaceutical
manufacturing.

Examples
where
different
standards
or
guidelines
are
established
included
control
technique
guideline
(
CTG)

documents,
NSPS
standards
under
section
111
of
the
CAA,
and,

most
recently,
maximum
achievable
control
technology
(
MACT)

standards
under
section
112
of
the
CAA.
We
do
not
agree
that
these
differentiations
for
emissions
standards
necessarily
require
differentiation
for
purposes
of
determining
BART
eligibility.
Therefore
we
believe
pharmaceuticals
should
not
be
excluded
from
BART.
However,

we
expect
that
because
of
the
MACT
standards,
there
is
a
very
low
probability
that
BART
determinations
will
lead
to
34
further
control
requirements
from
chemical
production
processes
at
pharmaceutical
plants.

(
3)
"
Primary
aluminum
ore
reduction."
We
agree
with
commenters
that
BART­
eligible
units
in
this
source
category
should
be
defined
consistently
with
the
NSPS
definition
for
primary
aluminum
ore
reduction.
Therefore
we
have
added
a
clarification
to
that
effect
in
the
final
BART
guidelines.

We
note
that
this
definition
is
also
consistent
with
the
definition
at
40
CFR
63.840,
which
establishes
applicability
for
this
source
category
for
the
MACT
program.

(
4)
"
Fossil­
fuel
fired
steam
electric
plants
of
more
than
250
million
Btu/
hour
heat
input."
We
have
retained
the
clarification
that
this
source
category
refers
only
to
those
fossil­
fuel
fired
steam
electric
plants
that
generate
electricity
for
sale.
We
believe
that
this
clarification
helps
to
distinguish
those
plants
that
are
electric
utilities
from
plants
in
other
industrial
categories.
We
also
believe
that
while
large
co­
generators
would
be
excluded
from
the
fossil­
fuel
fired
steam
electric
plant
source
category,
most
large
co­
generators
will
be
BARTeligible
under
the
fossil­
fuel
fired
boilers
source
category.

We
do
not
believe
it
makes
sense
for
this
category
to
include
only
those
steam
electric
plants
that
burn
greater
than
50
percent
fossil
fuel.
We
do
not
believe
that
a
35
boiler
should
be
excluded
from
BART
review
simply
because
it
is
located
at
a
plant
which
burns
less
than
50
percent
fossil
fuel.
Emissions
from
any
such
boiler
could
be
a
significant
contributor
to
regional
haze,
and
as
such,
we
believe
that
each
fossil­
fuel
fired
boiler
merits
a
BART
review.

We
do
wish
to
clarify
that
units
which
are
located
at
a
steam
electric
plant,
but
which
themselves
are
not
in
any
of
the
26
BART
source
categories,
should
not
be
considered
to
be
BART­
eligible
units.
We
believe
that
Congress
intended
that
BART
review
be
focused
on
units
in
the
source
categories
it
delineated.
This
interepretation
is
most
consistent
with
the
definition
of
BART­
eligible
source
as
we
have
explained
it
elsewhere
in
this
preamble
in
reference
to
whether
entire
plants
are
included
if
only
some
units
at
the
plant
meet
the
statutory
criteria.

Finally,
we
believe
that
all
combined
cycle
units
are
included
in
the
definition
of
fossil
fuel
fired
steam
electric
plant,
regardless
of
whether
the
combined
cycle
unit's
heat
recovery
steam
generator
lacks
auxilliary
firing.
Commenters
are
correct
that
some
EPA
programs
have
treated
combined
cycle
units
with
supplemental
firing
differently
from
combined
cycle
units
without
supplemental
firing.
However,
while
some
EPA
programs
do
not
consider
a
unit
to
be
a
combined
cycle
unit
unless
it
contains
7
See
http://
www.
epa.
gov/
Region7/
programs/
artrd/
air/
nsr/
nsrmemos/
t
urbines.
pdf
36
supplemental
firing,
the
definition
at
issue
here
is
the
definition
of
fossil­
fuel
fired
steam
electric
plant,
not
fossil­
fuel
fired
unit.
The
CAA
defines
both
"
stationary
source"
(
for
visibility
purposes)
and
"
major
emitting
facility"
(
for
PSD
purposes)
to
include
"
fossil
fuel
fired
steam
electric
plants."
In
previous
guidance
for
PSD,
we
have
explained
that
combined
cycle
gas
turbines
do
fall
within
the
category
of
"
fossil­
fuel
fired
steam
electric
plants."
7
(
5)
"
Fossil­
fuel
boilers
of
more
than
250
million
Btu/
hour
heat
input."
We
have
decided
to
retain
the
interpretation
that
this
category
should
be
read
as
including
only
those
boilers
individually
greater
than
250
million
Btu/
hour
heat
input.
We
agree
with
commenters
who
noted
that
including
smaller
boilers
would
pose
considerable
implementation
burden.
As
noted
in
the
2004
reproposal
notice,
we
do
not
believe
that
this
interpretation
is
likely
to
have
a
substantial
impact.
Because
smaller
boilers
are
generally
less
cost­
effective
to
control,
we
believe
that
BART
review
would
be
unlikely
to
result
in
a
significant
amount
of
control
on
these
boilers.

We
are
also
retaining
the
clarification
that
if
a
boiler
smaller
than
250
million
Btu/
hour
heat
input
is
an
37
integral
part
of
an
industrial
process
in
a
BART
source
category
other
than
electric
utilities,
then
the
boiler
should
be
considered
part
of
the
BART­
eligible
source
in
that
category.
(
By
"
integral
to
the
process",
we
mean
that
the
process
uses
any
by­
product
of
the
boiler.
We
have
added
this
clarification
to
the
definition
in
the
BART
guidelines.)
We
believe
that
if
a
State
is
already
considering
a
BART­
eligible
industrial
process
for
control,

and
a
boiler
is
integrated
into
that
process,
it
makes
common
sense
not
to
rule
out
control
options
for
that
process
as
a
whole.
Including
the
boiler
in
consideration
of
control
options
for
the
process
adds
minimal
additional
burden
while
leaving
maximum
discretion
to
the
State
in
determining
BART
for
the
process
as
a
whole.

We
are
also
clarifying
today
that
we
have
determined
that
this
category
should
include
all
individual
boilers
of
greater
than
250
million
Btu/
hour
heat
input
burning
any
amount
of
fossil
fuel,
as
opposed
to
only
those
boilers
that
burn
greater
than
50
percent
fossil
fuel.
We
believe
that
it
is
quite
possible
that
boilers
of
this
size
could
contribute
to
regional
haze
in
a
Class
I
area,
even
if
they
burn
less
than
50
percent
fossil
fuel.
Therefore
we
believe
that
each
fossil
fuel­
fired
boiler
merits
a
BART
review
and
should
not
be
prematurely
ruled
out.
38
Step
2:
Identify
the
start­
up
dates
of
those
emission
units.

Background.
BART
applies
only
to
a
major
stationary
source
which
"
was
in
existence
on
August
7,
1977
but
which
has
not
been
in
operation
for
more
than
fifteen
years
as
of
such
date."
The
visibility
regulations
define
"
in
existence"
and
"
in
operation"
in
40
CFR
51.301.
Under
these
regulations,
promulgated
in
1980,
"
in
existence"
means
that
the
owner
or
operator
has
obtained
all
necessary
preconstruction
approvals
or
permits
.
.
.
and
either
has
(
1)
begun,
or
caused
to
begin,
a
continuous
program
of
physical
on­
site
construction
of
the
facility
or
(
2)

entered
into
binding
agreements
or
contractual
obligations.

The
term
"
in
operation"
means
engaged
in
activity
related
to
the
primary
design
function
of
the
source.

Step
2
also
addresses
the
treatment
of
"
reconstructions"
and
"
modifications."
Under
the
definition
of
BART­
eligible
facility,
sources
which
were
in
operation
before
1962
but
reconstructed
during
the
1962
to
1977
time
period
are
treated
as
new
sources
as
of
the
time
of
reconstruction.
The
same
policies
and
procedures
for
identifying
reconstructed
"
affected
facilities"
under
the
NSPS
are
used
to
determine
whether
a
source
has
been
reconstructed
for
purposes
of
the
BART
requirements.
39
"
Modifications"
under
the
CAA
refers
to
physical
change
or
change
in
the
method
of
operation
at
a
source
which
has
lead
to
an
increase
in
emissions.
In
the
proposed
BART
guidelines,
we
stated
that
the
best
interpretation
of
the
visibility
provisions
is
that
a
modification
to
a
source
does
not
change
an
emission's
unit
construction
date
for
purposes
of
BART
applicability.
We
requested
comment
on
an
alternative
interpretation
that
we
believed
would
be
more
difficult
to
implement.
Under
this
approach,
sources
built
before
1962
but
modified
during
the
1962
to
1977
time
frame
would
be
considered
"
new"
at
the
time
of
modification.

Comments.
We
received
comments
in
2001
and
2004
on
the
discussion
in
the
guideline
of
the
term
"
in
existence."

These
comments
were
critical
of
our
statement
in
the
guidelines
that
sources
which
had
"
commenced
construction,"

that
is,
those
which
had
entered
into
binding
contracts,

would
be
considered
to
be
in
existence,
even
if
actual
operations
did
not
begin
until
after
the
August
7,
1977
cutoff
date.
These
commenters
asserted
that
Congress
did
not
intend
to
treat
a
source
as
"
existing"
in
1977
if
it
was
not
yet
built.

Other
commenters
interpreted
the
proposed
guidelines
as
expanding
the
definition
of
BART­
eligible
sources
by
requiring
States
to
find
that
all
emission
units
at
a
facility
are
BART­
eligible
if
one
part
of
the
facility
was
40
built
within
the
1962­
1977
time
period.
Other
comments
did
not
suggest
that
we
had
already
expanded
the
definition
in
the
proposed
guidelines,
but
did
suggest
that
we
should
expand
the
definition
in
that
way
in
the
final
guidelines.

Some
commenters
noted
that
there
was
a
degree
of
confusion
in
the
regulated
community
on
whether
the
proposed
guidelines
were
requiring
BART
for
all
units
at
a
power
plant,
including
those
that
were
in
operation
before
August
7,
1962,
if
these
units
are
co­
located
with
one
or
more
units
that
were
put
in
place
within
the
1962­
1977
time
period.
These
commenters
requested
that
we
clarify
that
such
pre­
1962
units
would
not
be
BART­
eligible.

Some
commenters
asserted
that
our
proposed
approach
is
unworkable,
because
the
approach
requires
States
to
identify
all
emissions
units
put
in
place
between
the
1962
and
1977.

Some
of
these
commenters
asserted
that
Congress
intended
that
BART
would
apply
only
if
entire
plants
satisfy
the
statutory
criteria.
These
comments
suggested
that
BART
should
apply
only
if
an
entire
plant
that
is
one
of
the
26
listed
source
category
types
had
been
placed
in
operation
at
a
discrete
point
within
the
15
year
time
period
for
BART
eligibility.
These
commenters
asserted
that
our
proposed
guidelines,
which
involved
the
identification
and
aggregation
of
individual
emission
units
within
the
1962­

1977
time
period,
were
inconsistent
with
Congress'
intent.
41
Other
comments
suggested
that
EPA
could
improve
implementation
of
the
program
by
covering
discrete
projects
rather
than
individual
emissions
units.
A
few
commenters
suggested
that
for
purposes
of
identifying
such
discrete
projects,
we
consider
using
the
term
"
process
or
production
unit"
that
we
used
in
hazardous
air
pollutant
regulations
under
CAA
section
112(
g).

One
commenter
requested
that
the
guidelines
clarify
that
emissions
from
"
linked"
emission
units
should
not
be
considered
in
determining
BART
eligibility.
That
is,
even
if
changes
in
emissions
from
one
unit
could
affect
the
emissions
from
a
"
linked"
unit
that
was
not
put
in
place
within
the
1962­
1977
time
period,
that
would
not
affect
whether
the
"
linked"
unit
was
BART­
eligible.
Another
commenter
suggested
that
the
approach
set
forth
in
the
guidelines
for
identifying
BART­
eligible
sources
is
inappropriate
because
the
particular
set
of
units
identified
as
BART­
eligible
will
not
necessarily
"
provide
a
reasonable
and
logical
platform
for
the
installation
of
controls."

Other
commenters
stated
that
facilities
that
had
been
modified
after
1977
should
not
be
included
in
the
pool
of
sources
subject
to
BART.
Such
facilities,
it
was
argued,

already
meet
the
BART
requirements
because
of
the
controls
installed
to
meet
the
requirements
of
PSD,
NSR,
or
the
NSPS.
42
Final
rule.
We
disagree
with
the
comments
recommending
that
we
interpret
the
term
"
in
existence"
to
refer
to
sources
that
are
in
actual
operation.
The
discussion
of
this
term
in
Step
2
is
based
on
the
regulatory
definition
which
has
been
in
place
since
1980.
The
guidelines
reiterate
this
definition
and
provide
examples
of
its
application.
Interpreting
the
term
"
in
existence"
as
suggested
by
commenters
would
not
be
consistent
with
the
plain
language
of
the
regulations.

In
the
2001
and
2004
proposed
guidelines,
we
noted
that
"
the
term
`
in
existence'
means
the
same
thing
as
the
term
`
commence
construction'
as
that
term
is
used
in
the
PSD
regulations."
Commenters
were
critical
of
this
statement,

claiming
that
EPA
was
unlawfully
reinterpreting
section
169A
in
the
guidelines.
The
statement
in
Step
2
of
guidelines,

however,
is
not
a
reinterpretation
of
the
term
"
in
existence,"
but
merely
a
statement
noting
that
the
definitions
used
in
the
visibility
regulations
and
the
PSD
regulations
are
essentially
identical.

To
the
extent
that
commenters
are
claiming
that
the
existing
regulatory
definition
of
"
in
existence"
is
unlawful,
EPA's
interpretation
of
this
term
in
promulgating
the
1980
regulations
was
a
reasonable
one.
First,
it
is
worth
noting
that
the
regulations
adopting
this
interpretation
of
the
term
"
in
existence"
were
in
effect
in
8
See
CAA
section
193.

43
1990
and
implicitly
endorsed
by
Congress
in
its
1990
amendments
to
the
CAA.
8
Moreover,
the
definition
at
issue
accurately
reflects
Congress'
intent
that
the
BART
provision
apply
to
sources
which
had
been
"
grandfathered"
from
the
new
source
review
permit
requirements
in
parts
C
and
D
of
title
I
of
the
CAA.
For
all
the
above
reasons,
we
are
neither
revising
the
regional
haze
regulations
to
change
the
definition
of
"
in
existence,"
nor
adopting
a
strained
interpretation
of
the
regulation
in
the
guidelines.

We
agree
with
commenters
that
the
definition
of
"

BARTeligible
source"
does
not
require
States
to
find
that
all
emission
units
at
a
facility
are
subject
to
the
requirement
of
the
BART
provisions
if
only
one
part
of
the
facility
was
built
within
the
1962­
1977
time
period.
We
received
comments
on
this
issue
in
2001
and
clarified
in
2004
that
the
BART
guidelines
do
not
direct
States
to
find
that
all
boilers
at
a
facility
are
BART­
eligible
if
one
or
more
boilers
at
the
facility
were
put
in
place
during
the
relevant
time
period.
Under
Step
2
of
the
process
for
identifying
BART­
eligible
sources
set
out
in
the
guidelines,

States
are
required
to
identify
only
those
boilers
that
were
put
in
place
between
1962
and
1977.
As
explained
in
the
preamble
to
the
2004
reproposed
guidelines,
only
these
boilers
are
potentially
subject
to
BART.
44
We
do
not
agree
with
those
commenters
claiming
that
Congress
clearly
intended
to
apply
BART
only
if
an
"
entire
plant"
was
put
into
place
between
1962
and
1977.
Most
of
the
BART
source
categories
are
broad
descriptions
types
of
industrial
facilities
such
as
"
kraft
pulp
mills,"
"
petroleum
refinineries"
or
"
primary
copper
smelters."
For
such
source
categories,
the
implication
of
commenters'
argument
would
that
if
any
portion
of
the
plant
was
in
operation
before
August
7,
1962,
then
Congress
intended
to
exempt
the
entire
plant
from
BART.
Such
an
interpretation
is
problematic
and
inequitable.
For
example,
under
this
approach
BART
would
not
apply
if
a
company
chose
to
expand
its
production
by
building
a
second
production
line
at
an
existing
line
in
1965,
but
would
apply
if
the
same
company
chose
to
build
the
same
equipment
at
a
greenfield
site.
Under
the
approach
set
forth
in
the
guidelines,
such
a
production
line
would
be
treated
similarly
under
either
set
of
facts.
We
do
not
believe
that
either
the
plain
language
of
the
statute
or
the
relevant
legislative
history
indicate
that
Congress
intended
for
major­
emitting
sources
of
visibility­
impairing
pollutants
to
be
exempted
from
the
BART
requirements
because
a
plant
contains
some
emission
units
that
began
operation
before
1962.

Also,
we
disagree
with
the
comment
that
modifications
after
1977
should
change
an
emissions'
unit
date
of
construction
for
purposes
of
BART
applicability.
The
45
commenter's
suggestion
that
such
sources
already
meet
BART
requirements
may
be
accurate,
but
does
not
provide
a
basis
for
exempting
the
source
from
review.
As
we
note
in
the
guideline,
the
review
process
will
take
into
account
the
controls
already
in
place
and
the
State
may
find
that
these
controls
are
consistent
with
BART.

We
agree
with
the
comments
related
to
"
linked"
emission
units.
The
comment
appears
to
address
whether
emissions
from
the
"
linked"
units
are
considered
in
determining
BART
eligibility.
In
the
guidelines,
we
are
focusing
on
only
the
emissions
units
that
were
put
in
place
during
the
1962
to
1977
dates
and
the
emissions
from
those
units.
We
agree
that
even
if
changes
in
emissions
from
one
unit
could
affect
the
emissions
from
a
"
linked"
unit
that
was
not
put
in
place
within
the
1962­
1977
time
period,
this
would
not
affect
whether
the
"
linked"
unit
was
BART­
eligible.

We
disagree
with
commenters
that
the
approach
set
forth
in
the
guidelines
for
identifying
BART­
eligible
sources
is
inappropriate
because
the
particular
set
of
units
identified
as
BART­
eligible
will
not
necessarily
"
provide
a
reasonable
and
logical
platform
for
the
installation
of
controls."
We
do
not
agree
that
this
factor
is
relevant
to
the
identification
of
those
emissions
units
which
meet
the
definition
of
BART­
eligible
source.
Such
factors
are
important
in
the
States'
consideration
of
control
strategies
and
options
but
do
not
clearly
relate
to
the
first
step
of
46
identifying
those
sources
which
fall
within
one
of
26
source
categories,
were
built
during
the
15
year
window
of
time
from
1962
to
1977,
and
have
potential
emissions
of
greater
than
250
tons
per
year.
We
do
thus
agree
generally
with
the
commenter's
recommendation
of
allowing
States
to
consider
the
particular
history
and
control
potential
of
units
in
determining
BART,
but
do
not
agree
that
it
is
relevant
to
the
predicate
question
of
identifying
the
BART­
eligible
source.

Finally,
the
approach
to
identifying
a
"
BART­
eligible
source"
in
the
guidelines
is
based
on
the
definitions
in
the
regional
haze
rule
of
the
relevant
terms.
For
750
MW
power
plants,
States
are
required
to
apply
the
definitions
as
set
forth
in
the
guidelines;
for
other
sources,
States
may
adopt
a
different
approach
to
the
task
of
identifying
BARTeligible
sources,
so
long
as
that
approach
is
consistent
with
the
Act
and
the
implementing
regulations.
In
other
words,
while
the
guidelines
adopt
an
approach
for
large
power
plants
which
involves
the
aggregation
of
all
emissions
units
put
into
place
between
1962
and
1977,
States
have
the
flexibility
to
consider
other
reasonable
approaches
to
the
question
of
identifying
BART­
eligible
sources
for
other
source
categories.

For
750
MW
power
plants,
many
of
the
issues
identified
by
commenters
with
the
approach
of
looking
at
a
facility
on
an
emission
unit
by
emission
unit
basis
do
not
exist.
47
Unlike
many
types
of
industrial
processes,
power
plants
consist
generally
of
a
discrete
number
of
very
large
emission
units.
For
other
types
of
facilities
such
as
kraft
pulp
mills
or
chemical
process
plants
which
may
have
many
small
emission
units
that
have
undergone
numerous
changes,

the
guidelines
do
not
limit
the
ability
of
the
States
to
approach
the
question
of
identifying
BART­
eligible
sources
in
ways
which
make
sense
for
the
particular
sources
given
their
design
and
history.

Step
3:
Compare
the
potential
emissions
to
the
250
ton/
yr
cutoff.

Background.
Step
3
of
the
guidelines
addresses
the
question
of
whether
the
units
identified
in
Steps
1
and
2
have
emissions
in
excess
of
the
threshold
for
major
sources
set
forth
in
section
169A(
g)(
7)
of
the
CAA.
The
guidelines
pose
the
following
questions
to
help
the
States
in
determining
whether
the
relevant
emissions
units
have
the
potential
to
emit
in
excess
of
the
250
tons
per
year
threshold
of
any
single
visibility­
impairing
pollutant:

(
1)
What
pollutants
should
I
address?

The
2001
proposed
guidelines
included
the
following
list
of
visibility­
impairing
pollutants:
sulfur
dioxide
(
SO2),
nitrogen
oxides
(
NOX),
particulate
matter,
volatile
organic
compounds
(
VOCs),
and
ammonia.
We
proposed
in
2001
and
again
in
2004
that
States
use
PM10
as
the
indicator
for
48
particulate
matter.
As
explained
in
the
guidelines,
there
is
no
need
to
have
separate
250
ton
thresholds
for
PM10
and
PM2.5
because
emissions
of
PM10
include
the
components
of
PM2.5
as
a
subset.
In
addition,
because
of
various
uncertainties
associated
with
regulating
VOCs
and
ammonia,
we
requested
comment
in
2004
on
the
level
of
discretion
States
should
exercise
in
making
BART
determinations
for
VOCs
and
took
ammonia
off
the
list
of
visibility­
impairing
pollutants.

In
both
proposals,
we
clarified
that
the
250
tons
per
year
cutoff
applies
to
emissions
on
a
pollutant
by
pollutant
basis.
In
other
words,
a
source
is
subject
to
BART
only
if
it
emits
at
least
250
tons
per
year
of
an
individual
visibility­
impairing
pollutant.

(
2)
What
does
the
term
"
potential"
emissions
mean?

The
proposed
guidelines
in
2001
and
the
reproposed
guidelines
in
2004
excerpt
the
definition
of
"
potential
to
emit"
from
the
regulations
at
40
CFR
51.301.
As
the
definition
makes
clear,
the
potential
to
emit
of
a
source
is
calculated
based
on
its
capacity
to
emit
a
pollutant
taking
into
account
its
physical
and
operational
design.
Under
this
definition,
federally
enforceable
emission
limits
may
be
taken
into
account
in
calculating
a
source's
potential
emissions;
however,
emission
limitations
which
are
enforceable
only
by
state
and
local
agencies,
but
not
by
EPA
and
citizens
in
Federal
court,
cannot
be
used
to
limit
a
49
source's
potential
to
emit
for
purposes
of
the
regional
haze
program.

(
3)
What
is
a
"
stationary
source?"

As
explained
above,
States
are
required
to
make
a
BART
determination
only
for
"
stationary
sources"
of
a
certain
size
that
fall
within
one
of
26
types
of
industrial
categories
listed
in
the
statute
and
that
were
built
within
a
certain
time
frame.
The
regional
haze
rule
(
64
FR
3714,

July
1,
1999)
contains
definitions
that
are
relevant
to
the
determination
of
the
emissions
units
that
comprise
a
"
stationary
source."
First,
the
regulations
define
"
stationary
source"
as
"
any
building,
structure,
facility,

or
installation
which
emits
or
may
emit
any
air
pollutant."

Second,
the
terms
"
building,
structure,
or
facility"
are
defined
in
part
based
on
grouping
pollutant­
emitting
activities
by
industrial
category:

Building,
structure,
or
facility
means
all
of
the
pollutant­
emitting
activities
which
belong
to
the
same
industrial
grouping,
are
located
on
one
or
more
contiguous
or
adjacent
properties,
and
are
under
the
control
of
the
same
person
(
or
persons
under
common
control).
Pollutant­
emitting
activities
must
be
considered
as
part
of
the
same
industrial
grouping
if
they
belong
to
the
same
Major
Group
(
i.
e.,
which
have
the
same
two­
digit
50
code)
as
described
in
the
Standard
Industrial
Classification
Manual,
1972
as
amended
by
the
1977
Supplement
(
U.
S.
Government
Printing
Office
stock
numbers
4101­
0066
and
003­
005­
00176­
0
respectively).

In
the
2001
proposed
guideline,
we
noted
that
support
facilities,
i.
e.
facilities
used
to
convey,
store,
or
otherwise
assist
in
the
production
of
the
principal
product,

are
considered
to
fall
within
the
same
industrial
grouping
as
the
primary
facility.
To
clarify
this,
in
2004
we
proposed
to
add
language
to
the
guideline
noting
that
emission
units
at
a
plant,
even
if
they
are
a
"
support
facility"
for
purposes
of
other
programs,
would
not
be
subject
to
BART
unless
they
were
within
one
of
the
26
listed
source
categories
and
were
built
within
the
1962
to
1977
time
frame.

Discussion
of
"
what
pollutants
should
I
address?"

Comments.
PM10
as
an
indicator.
Some
comments
questioned
the
use
of
PM10
(
which
includes
both
coarse
and
fine
particulate
matter)
as
the
indicator
for
particulate
matter.
Commenters
noted
that
the
coarse
fraction,
that
is
particulate
matter
between
10
and
2.5
micrograms
in
diameter,
fundamentally
differs
compared
to
the
fine
mass
in
how
it
interacts
with
light.
Commenters
suggested
that
only
the
fine
mass
(
PM2.5)
component
of
particulate
matter
is
51
likely
to
contribute
to
visibility
impairment.

Accordingly,
these
commenters
recommended
that
the
250
ton
cutoff
for
particulate
matter
should
be
based
upon
emissions
of
PM2.5.

Ammonia.
Many
commenters
addressed
the
exclusion
of
ammonia
from
the
list
of
visibility­
impairing
pollutants.
A
number
of
commenters,
primarily
from
industry
but
also
from
one
state
and
one
regional
planning
organization,
supported
the
exclusion
of
ammonia.
These
commenters
generally
cited
the
complexity
and
variability
of
ammonia's
role
in
the
formation
of
PM2.5
in
the
atmosphere,
the
relative
greater
benefits
of
controlling
NOx
and
SO2,
the
uncertainties
in
the
inventory
of
ammonia
emissions,
and
the
inherent
complexities
of
gauging
the
contribution
of
potential
ammonia
reductions
to
improving
visibility
in
Class
I
areas.

In
addition,
commenters
noted
that
few,
if
any,
point
sources
emit
ammonia
in
amounts
that
exceed
the
250
ton
per
year
threshold.

Other
commenters,
including
a
number
of
environmental
groups
and
several
states,
regional
planning
organizations,

and
industry
commenters,
argued
that
ammonia
should
be
included
in
the
list
of
visibility­
impairing
pollutants
in
the
guidelines.
In
support
of
this
view,
commenters
cited
evidence
that
ammonia
is
a
known
precursor
to
PM2.5.
One
commenter
noted
that
improvements
are
being
made
to
ammonia
inventories
and
to
the
understanding
of
ammonia's
role
in
9
See
http://
wrapair.
org/
forums/
ioc/
meetings/
030728/
index.
html
(
specifically
presentation
by
John
Vimont,
National
Park
Service).

10
NARSTO
(
2004)
Particulate
Matter
Assessment
for
Policy
Makers:
A
NARSTO
Assessment.
P.
McMurry,
M.
Shepherd,
and
J.
Vickery,
eds.
Cambridge
University
Press,
Cambridge,
England.
ISBN
0
52
184287
5.

52
the
formation
of
haze.
Other
commenters
pointed
to
a
National
Park
Service
(
NPS)
analysis
of
monitoring
data
that
indicates
that
visibility­
impairment
due
to
nitrate
aerosol
formation
(
to
which
ammonia
contributes)
is
of
significant
concern9,
and
2003
direction
to
policy­
makers
from
the
North
American
Research
Strategy
for
Tropospheric
Ozone
(
NARSTO)
10
indicating
that
consideration
of
control
strategies
needs
to
include
ammonia
in
combination
with
other
precursors
to
particle
formation.
Many
commenters
also
argued
that
EPA
should
encourage
or
allow
the
States
to
consider
ammonia
in
their
visibility
protection
plans,
and
noted
that
ammonia
reductions
could
be
a
cost­
effective
way
to
improve
visibility
under
certain
conditions.

Volatile
Organic
Compounds
(
VOCs).
Several
commenters
responded
to
our
request
for
comments
on
whether
States
should
treat
VOCs
in
urban
areas
differently
from
VOCs
in
rural
areas.
Environmental
groups
and
a
few
States
argued
that
the
current
state
of
scientific
knowledge
does
not
support
a
differentiation
between
urban
and
rural
sources
of
VOCs.
One
environmental
commenter
cited
evidence
that
53
organic
aerosols
are
a
major
constituent
of
visibilityreducing
aerosols
and
that
VOCs
are
important
precursors
to
the
formation
of
secondary
organic
aerosols.
One
commenter
also
stated
that
VOCs
may
play
a
particularly
significant
role
in
particle
formation
in
those
rural
areas
with
significant
nearby
sources
of
NOx.
Commenters
also
cited
evidence
that
the
contribution
of
VOC
to
particle
formation
likely
varies
widely
in
different
areas
of
the
country,
and
argued
that
States
should
retain
flexibility
to
address
local
VOC
sources
if
they
determine
that
those
sources
are
contributors
of
concern.

Several
industry
commenters
stated
that
more
focus
should
be
placed
on
controlling
VOCs
in
urban
rather
than
rural
areas.
A
few
commenters
from
industry
argued
that
VOCs
in
rural
areas
have
not
been
shown
to
be
a
significant
contributor
to
particle
formation,
and
should
be
excluded
from
the
list
of
pollutants
to
be
addressed
in
the
BART
process.
One
argued
that
VOCs
should
be
excluded
from
BART
entirely
based
upon
uncertainties
in
the
current
state
of
knowledge,
and
a
few
argued
that
VOCs
from
both
power
plants
and
rural
sources
should
be
excluded
from
BART,
based
on
low
emissions
and
the
cost
of
controls.
One
regional
planning
organization
requested
that
EPA
clarify
the
definitions
of
"
urban"
and
"
rural"
areas.
11
See
Fine
particles:
Overview
of
Atmospheric
Chemistry,
Sources
of
Emissions,
and
Ambient
Monitoring
Data,
Memorandum
to
Docket
OAR
2002­
0076,
April
1,
2005.

12
These
methods
are
described
at
the
following
website:
http://
vista.
cira.
colostate.
edu/
improve/
Tools/
ReconBext/
reco
nBext.
htm
.

54
Final
rule.
PM10
as
an
indicator.
The
guideline
continues
to
recommend
that
States
use
PM10
as
the
indicator
for
particulate
matter
for
the
applicability
step,
i.
e.
in
determining
whether
a
source
is
BART­
eligible.
We
disagree
with
comments
that
the
coarse
fraction
of
PM
does
not
contribute
to
visibility
impairment;
while
we
agree
that
the
coarse
fraction
is
less
efficient
at
light
scattering
than
fine
particles,
there
is
ample
evidence
that
the
coarse
fraction
does
contribute
to
visibility
impairment.
11
For
example,
standard
methods
for
calculating
reconstructed
light
extinction
routinely
include
a
calculation
for
the
contribution
to
light
extinction
from
the
coarse
fraction,

an
implicit
recognition
that
these
particles
contribute
measurably
to
visibility
impairment.
12
Thus,
we
believe
that
States
will
need
to
take
the
coarse
fraction
of
particulate
matter
into
account
in
determining
whether
a
source
meets
the
threshold
for
BART
applicability.

However,
because
long­
range
transport
of
fine
particles
is
of
particular
concern
in
the
formation
of
regional
haze,

we
also
believe
that
it
is
very
important
to
estimate
the
PM2.5
fraction
of
direct
particulate
emissions
as
correctly
13
Fine
particles:
Overview
of
Source
Testing
Approaches,
Memorandum
to
Docket
OAR
2002­
0076,
April
1,
2005.

55
as
possible.
In
addition,
we
believe
that
air
quality
modeling
results
will
be
more
meaningful
if
the
inputs
account
for
the
relative
particle
size
of
directly
emitted
particulate
matter
(
e.
g.
PM10
vs.
PM2.5).

The
acceptability
of
existing
stationary
source
test
methods
for
regional
haze
SIPs
depends
upon
what
is
measured
under
your
current
test
methods
for
particulate
matter.

Your
current
test
methods
for
measuring
particulate
matter
emissions
from
stationary
sources
may
not
be
acceptable
for
regional
haze
SIP
purposes
if
these
methods
ignore
the
condensible
fraction
of
particulate
matter.
More
specifically,
for
purposed
of
makig
a
BART
determination,
a
test
method
that
ignores
a
significant
fraction
of
emissions
may
artificially
limit
the
control
measures
considered
in
the
BART
analysis.
Therefore
you
should
revise
any
such
stationary
source
test
methods
to
ensure
that
you
account
for
the
condensible
fraction
of
particulate
emissions.
See
the
source
testing
technical
support
document
(
TSD)
in
the
docket
for
this
rule,
which
discusses
test
methods
for
particulate
matter
in
more
detail.
13
Ammonia.
In
regard
to
ammonia,
we
believe
there
is
sufficient
uncertainty
about
emission
inventories
and
about
the
potential
efficacy
of
control
measures
from
location
to
location
such
that
the
most
appropriate
approach
for
States
14
See
Fine
particles:
Overview
of
Atmospheric
Chemistry,
Sources
of
Emissions,
and
Ambient
Monitoring
Data,
Memorandum
to
Docket
OAR
2002­
0076,
April
1,
2005.

56
to
take
is
a
case­
by­
case
approach.
There
are
ample
scientific
data
illustrating
that
ammonia
in
the
atmosphere
can
be
a
precursor
to
the
formation
of
particles
such
as
ammonium
sulfate
and
ammonium
nitrate;
14
however,
it
is
less
clear
whether
a
reduction
in
ammonia
emissions
in
a
given
location
would
result
in
a
reduction
in
particles
in
the
atmosphere
and
a
concomitant
improvement
in
visibility.
In
other
words,
the
question
of
whether
ammonia
does
contribute
to
visibility
impairment
in
a
specific
instance
can
be
a
difficult
one.

It
may
be
that
States
will
not
be
faced
often
with
the
question
of
addressing
ammonia
in
making
BART
determinations.
As
noted
above,
States
are
required
to
make
BART
determinations
only
for
stationary
sources
that
fall
within
certain
industrial
categories.
The
types
of
sources
subject
to
the
BART
provisions
are
not
typically
significant
emitters
of
ammonia.
Because
of
this,
it
is
unlikely
that
including
ammonia
on
the
list
of
visibility­
impairing
pollutants
in
the
BART
guidelines
would
have
much
impact
on
the
States'
determinations
of
whether
a
source
is
BARTeligible
Thus,
while
we
believe
ammonia
can
contribute
to
visibility
impairment,
the
decision
whether
to
consider
ammonia
as
a
visibility­
impairing
pollutant
in
a
specific
15
Ibid.

57
case
where
a
potential
BART
source
actually
emits
more
than
250
tons
per
year
of
ammonia
will
be
left
up
to
the
State
to
make
a
reasoned
determination.

VOCs.
Organic
compounds
can
be
categorized
according
to
their
varying
degrees
of
volatility:
highly
reactive,

volatile
compounds
with
six
or
fewer
carbon
atoms
which
indirectly
contribute
to
PM
formation
through
the
formation
of
oxidizing
compounds
such
as
the
hydroxyl
radical
and
ozone;
semivolatile
compounds
with
between
seven
and
24
carbon
atoms
which
can
exist
in
particle
form
and
can
readily
be
oxidized
to
form
other
low
volatility
compounds;

and
high
molecular
weight
organic
compounds
 
those
with
25
carbon
atoms
or
more
and
low
vapor
pressure
­­
which
are
emitted
directly
as
primary
organic
particles
and
exist
primarily
in
the
condensed
phase
at
ambient
temperatures.

The
latter
organic
compounds
are
considered
to
be
primary
PM2.5
emissions
and
not
VOCs
for
BART
purposes.

Current
scientific
and
technical
information
clearly
shows
that
carbonaceous
material
is
a
significant
fraction
of
total
PM2.5
mass
in
most
areas,
and
that
certain
aromatic
VOC
emissions
such
as
toluene,
xylene,
and
trimethyl­
benzene
are
precursors
to
the
formation
of
secondary
organic
aerosol.
15
However,
while
significant
progress
has
been
made
in
understanding
the
role
of
VOCs
in
the
formation
of
16
Ibid.

58
organic
PM,
this
relationship
remains
complex,
and
issues
such
as
the
relative
importance
of
biogenic
versus
anthropogenic
emissions
remain
unresolved.

Therefore
we
believe
that
the
best
approach
for
States
to
follow
in
considering
whether
VOC
emissions
are
precursors
to
PM2.5
formation
is
a
case­
by­
case
approach.

States
should
consider,
in
particular,
whether
a
source's
VOC
emissions
are
those
higher­
carbon
VOCs
that
are
more
likely
to
form
secondary
organic
aerosols.
In
addition,

given
the
variable
contribution
of
a
given
amount
of
VOC
emissions
to
PM2.5
formation,
States
may
also
wish
to
exercise
discetion
in
considering
only
relatively
larger
VOC
sources
to
be
BART­
eligible.

After
careful
consideration
of
the
comments,
we
agree
with
commenters
who
assert
that
EPA
should
not
suggest
a
general
distinction
between
the
relative
contributions
of
urban
and
rural
VOC
emissions
to
particle
formation.
The
state
of
knowledge
in
this
area
is
complex
and
rapidly
evolving.
Monitoring
data
in
the
East16
suggest
that
there
may
be
a
greater
contribution
to
particle
formation
in
urban
areas
from
VOCs
as
compared
to
rural
areas,
but
we
recognize
that
further
research
is
needed
to
better
determine
the
extent
of
the
contribution
of
specific
VOC
compounds
to
organic
PM
mass.
We
do
not
agree,
however,
59
with
commenters
who
make
the
blanket
assertion
that
rural
VOCs
are
not
a
significant
contributor
to
particle
formation,
as
it
is
possible
that
in
specific
areas,
such
as
where
NOx
emissions
are
high,
rural
anthropogenic
VOCs
could
potentially
play
a
significant
role.

Discussion
of
the
term
"
potential"
emissions.

Comments.
A
number
of
commenters
were
critical
of
the
restriction
in
the
regional
haze
rule
that
allows
States
to
credit
federally
enforceable
limitations
on
emissions
but
not
limitations
that
are
enforceable
only
by
States
and
local
agencies.
These
commenters
believed
that
this
restriction
had
been
rejected
by
the
D.
C.
circuit
court
for
a
number
of
other
EPA
regulations
and
noted
that
EPA
has
developed
policies
that
currently
credit
state­
enforceable
limits.
The
comments
recommended
that
EPA
issue
guidance
consistent
with
what
commenters
claimed
were
current
policies
for
other
regulations.
In
addition,
we
received
comments
arguing
that
in
determining
whether
a
source
is
a
major
stationary
source,
the
States
should
consider
a
source's
actual
­­
rather
than
potential
­­
emissions.
These
commenters
stated
that
using
a
source's
potential
emissions
overstates
a
source's
actual
emissions
and
impacts
on
visibility.

Final
rule.
CAA
§
169A(
g)(
7)
defines
a
"
major
stationary
source"
as
a
source
with
the
potential
to
emit
60
250
tons
or
more
any
pollutant.
Based
inter
alia
on
that
statutory
definition,
EPA's
implementing
regulations
define
BART­
eligible
sources
as
those
with
the
potential
to
emit
250
tons
or
more
of
any
air
pollutant.
As
these
definitions
clearly
require
consideration
of
a
source's
potential
emissions,
the
guidelines
state
that
a
State
should
determine
whether
a
source's
potential
emissions
exceed
the
250
ton
threshold
in
determining
whether
the
source
is
BARTeligible

As
explained
in
the
2001
and
2004
proposed
guidelines,

the
regional
haze
regulations
define
"
potential
to
emit."

The
guidelines
repeat
that
regulatory
definition
and
provide
an
example
illustrating
its
application.
EPA
did
not
propose
to
change
the
definition
in
2001
or
2004,
but
merely
highlighted
the
current
definition
in
40
CFR
51.301.

Although
we
noted
in
the
2001
proposed
guidelines
that
we
expected
to
undertake
a
rulemaking
to
determine
whether
only
federally
enforceable
limitations
should
be
taken
into
account
in
the
regional
haze
program
definition,
we
have
not
yet
begun
the
process
for
such
a
rulemaking.
However,
we
consider
the
comments
criticizing
EPA's
definition
of
"
potential
to
emit"
as
a
request
for
reconsideration
of
the
visibility
regulations
and
will
take
these
requests
into
account
in
determining
any
future
rulemaking
efforts
to
address
the
general
definition
of
"
potential
to
emit."
61
As
we
have
not
yet
undertaken
such
a
rulemaking,
the
guidelines
continue
to
refer
to
the
existing
regulatory
definition
of
"
potential
to
emit."

Discussion
of
what
emissions
units
should
be
considered
part
of
a
"
stationary
source".

Comments.
A
number
of
comments
in
2001
expressed
concern
with
our
statement
that
a
"
support
facility"
should
be
grouped
with
a
primary
facility
in
determining
which
emissions
units
belong
to
the
same
industrial
grouping.

These
comments
generally
coincided
with
comments
discussed
above
that
EPA
should
determine
BART
on
a
plantwide
basis,

rather
than
by
aggregating
emissions
units.
Commenters
on
the
2004
reproposal
noted
with
approval
the
clarification
that
"
support
facilities"
should
only
be
considered
BARTeligible
if
these
units
themselves
were
both
constructed
within
the
1962­
1977
time
frame
and
fell
within
one
of
the
listed
source
categories.

Final
rule.
The
guidelines
continue
to
note
that
the
definition
of
"
building,
structure
or
facility"
in
the
regional
haze
rule
is
based
upon
aggregating
emissions
units
within
the
same
industrial
grouping.
This
discussion
in
the
guidelines
is
consistent
with
the
language
in
the
definition
of
"
building,
structure
or
facility"
in
the
regional
haze
rule
which
contains
a
specific
reference
to
the
2­
digit
SIC
classifications.
The
BART
guidelines
refer
to
this
62
definition
and
explain
how
2­
digit
SIC
codes
are
used
in
determining
the
scope
of
BART
for
a
given
plantsite.
(
In
the
rare
situation
where
industrial
groupings
in
separate
2­

digit
SIC
codes
exist
at
a
single
plant
site,
then
there
would
be
more
than
one
separate
"
stationary
source"
present.

In
that
situation,
each
"
stationary
source"
should
be
looked
at
individually
for
purposes
of
determining
BARTeligibility

Step
4:
Identify
the
emission
units
and
pollutants
that
constitute
the
BART­
eligible
source.

Background.
The
final
step
in
identifying
a
"

BARTeligible
source"
is
to
use
the
information
from
the
previous
three
steps
to
identify
the
universe
of
equipment
that
makes
up
the
BART­
eligible
source.
The
2001
and
2004
proposed
BART
guidelines
stated
that
if
the
emissions
from
the
list
of
emissions
units
at
a
stationary
source
exceed
a
potential
to
emit
of
250
tons
per
year
for
any
individual
visibilityimpairing
pollutant,
then
that
collection
of
emissions
units
is
a
BART­
eligible
source.
The
guidelines
also
stated
that
a
BART
analysis
would
be
required
for
each
visibilityimpairing
pollutant
emitted
from
this
collection
of
emissions
units.

In
the
2004
reproposed
BART
guidelines,
we
noted
that
we
believed
that
section
169A(
b)(
2)(
A)
of
the
CAA
requires
a
State
to
undertake
a
BART
analysis
for
"
any"
visibility­
63
impairing
pollutant
emitted
by
a
BART­
eligible
source,

regardless
of
the
amount
emitted.
We
proposed,
however,
to
provide
the
States
with
the
flexibility
to
identify
de
minimis
levels
for
pollutants
at
BART­
eligible
sources,
but
limited
that
flexibility
so
that
any
such
de
minimis
levels
could
not
be
higher
than
those
used
in
the
PSD
program:
40
tons
per
year
for
SO2,
NOx,
and
VOC,
and
15
tons
per
year
from
PM10.
We
requested
comment
on
this
provision
and
on
the
use
of
de
minimis
values.

Discussion
of
whether
to
include
all
emitted
visibility­
impairing
pollutants
in
the
BART
analysis
Comments.
A
number
of
commenters
supported
the
concept
of
including
all
pollutants
in
the
BART
analysis
once
an
individual
pollutant
triggers
the
BART
review.
Other
commenters,
although
supportive
of
the
concept
generally,

recommended
that
we
should
add
the
pollutants
together
before
the
comparison
with
the
threshold.

A
number
of
commenters
disagreed
with
EPA's
conclusion
that
the
CAA
requires
States
to
make
a
BART
determination
for
any
visibility­
impairing
air
pollutant
emitted
by
a
BART
eligible
source.
These
commenters
stated
that
undertaking
a
BART
analysis
for
all
pollutants
emitted
by
a
major
stationary
source
is
an
unnecessary
administrative
burden
with
minimal
environmental
benefit.
Commenters
argued
that
Congress
intended
for
BART
to
apply
only
to
those
pollutants
64
for
which
a
source
is
major.
Commenters
accordingly
recommended
that
the
250
ton
per
year
threshold
apply
to
each
pollutant
emitted
by
a
source
and
that
BART
apply
only
to
those
pollutants
which
meet
this
threshold.
A
number
of
these
commenters
argued
alternatively
that
only
those
pollutants
from
a
source
demonstrated,
individually,
to
cause
or
contribute
to
visibility
impairment
are
required
to
go
through
a
BART
determination.

Final
rule.
We
disagree
with
the
comment
that
emissions
of
different
visibility­
impairing
pollutants
must
added
together
to
determine
whether
a
source
exceeds
the
250
ton
per
year
threshold.
The
CAA,
in
section
169A(
g)(
7),

defines
a
"
major
stationary
source"
as
one
with
the
potential
to
emit
250
tons
or
more
of
"
any
pollutant."

We
disagree
with
comments
that
the
BART
analysis
is
required
only
for
those
pollutants
that
individually
exceed
the
250
ton
per
year
threshold.
Section
169A(
b)(
2)(
A)

specifically
requires
States
to
submit
SIPs
that
include
a
requirement
that
a
major
stationary
source
which,
as
determined
by
the
State
.
.
.
emits
any
air
pollutant
which
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
visibility
in
any
[
Class
I
area],
shall
procure,

install,
and
operate
.
.
.
the
best
available
retrofit
technology,
as
determined
by
the
State
.
65
.
.
for
controlling
emissions
from
such
source
for
the
purpose
of
eliminating
or
reducing
any
such
impairment.

The
regional
haze
regulations
similarly
require
that
the
States
submit
a
SIP
that
contains
A
determination
of
BART
for
each
BART­
eligible
source
in
the
State
that
emits
any
air
pollutant
which
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
visibility
in
any
mandatory
Class
I
Federal
area.

40
CFR
51.308(
e)(
1)(
ii).
Nothing
in
these
statutory
or
regulatory
requirement
suggests
that
the
BART
analysis
is
limited
to
those
pollutants
for
which
a
source
is
considered
major.
At
best,
these
provisions
can
be
read
as
requiring
a
BART
determination
only
for
those
emissions
from
a
specific
source
which
do,
in
fact,
cause
or
contribute
to
visibility
impairment
in
a
particular
Class
I
area,
or
at
least
which
could
reasonably
be
anticipated
to
do
so.
Commenters,

however,
have
not
presented
any
evidence
that
as
a
general
matter
emissions
of
less
than
250
tons
per
year
of
PM2.5,

SO2,
or
other
visibility­
impairing
pollutants
from
potential
BART
sources
do
not
"
cause
of
contribute
to
any
impairment
of
visibility"
in
any
of
the
Class
I
areas
covered
by
the
regional
haze
rule.
As
there
is
no
such
evidence
currently
before
us,
there
is
no
basis
to
conclude
that
the
States
are
66
required
to
make
BART
determinations
only
for
those
pollutants
emitted
in
excess
of
250
tons
per
year.

At
the
same
time,
we
agree
with
certain
commenters
that
the
CAA
does
not
require
a
BART
determination
for
any
visibility
impairing
pollutant
emitted
by
a
source,

regardless
of
the
amount.
After
reviewing
the
language
of
the
Act
and
the
comments
received,
we
have
concluded
that
our
interpretation
of
the
relevant
language
in
section
169A(
b)(
2)(
A)
of
the
Act
in
the
2004
proposed
guidelines
is
not
necessarily
the
best
reading
of
the
BART
provisions.

Section
169A(
b)(
2)(
A)
of
the
Act
can
be
read
to
require
the
States
to
make
a
determination
as
to
the
appropriate
level
of
BART
controls,
if
any,
for
emissions
of
any
visibility
impairing
pollutant
from
a
source.
Given
the
overall
context
of
this
provision,
however,
and
that
the
purpose
of
the
BART
provision
is
to
eliminate
or
reduce
visibility
impairment,
it
is
reasonable
to
read
the
statute
as
requiring
a
BART
determination
only
for
those
emissions
from
a
source
which
are
first
determined
to
contribute
to
visibility
impairment
in
a
Class
I
area.
The
distinction
between
these
two
interpretations
of
this
provision
is
unlikely
to
be
significant
in
practice,
however,
as
one
of
the
factors
to
be
taken
into
account
in
making
a
BART
determination
is
the
degree
of
visibility
improvement
resulting
from
the
use
of
controls.
67
The
interpretation
of
the
requirements
of
the
regional
haze
program
reflected
in
the
discussion
above
does
not
necessitate
costly
and
time­
consuming
analyses.
Consistent
with
the
CAA
and
the
implementing
regulations,
States
can
adopt
a
more
streamlined
approach
to
making
BART
determinations
where
appropriate.
Although
BART
determinations
should
be
based
on
the
totality
of
circumstances
in
a
given
situation,
such
as
the
distance
of
the
source
from
a
Class
I
area,
the
type
and
amount
of
pollutant
at
issue,
and
the
availability
and
cost
of
controls,
it
is
clear
that
in
some
situations,
one
or
more
factors
will
clearly
suggest
an
outcome.
Thus,
for
example,

a
State
need
not
undertake
an
exhaustive
analysis
of
a
source's
impact
on
visibility
resulting
from
relatively
minor
emissions
of
a
pollutant
where
it
is
clear
that
controls
would
be
costly
and
any
improvements
in
visibility
resulting
from
reductions
in
emissions
of
that
pollutant
would
be
negligible.
In
a
scenario,
for
example,
where
a
source
emits
thousands
of
tons
of
SO2
but
less
than
one
hundred
tons
of
NOx,
the
State
could
easily
conclude
that
requiring
expensive
controls
to
reduce
NOx
would
not
be
appropriate.
In
another
situation,
however,
inexpensive
NOx
controls
might
be
available
and
a
State
might
reasonably
conclude
that
NOx
controls
were
justified
as
a
means
to
improve
visibility
despite
the
fact
that
the
source
emits
less
than
one
hundred
tons
of
the
pollutant.
Moreover,
as
68
discussed
below,
we
are
revising
the
regional
haze
regulations
to
allow
the
States
to
exempt
de
minimis
emissions
of
SO2,
NOx,
and
PM2.5
from
the
BART
determination
process
which
should
help
to
address
the
concerns
of
certain
commenters
associated
with
the
burden
of
a
broad
BART
analysis.

De
minimis
levels
Comments.
Many
commenters
agreed
that
we
should
establish
de
minimis
levels
for
individual
pollutants
in
order
to
allow
States
and
sources
to
avoid
BART
determinations
for
pollutants
emitted
in
relatively
trivial
amounts.
Many
commenters
suggested
that
States
would
be
unlikely
to
impose
emission
limits
for
pollutants
emitted
at
the
proposed
de
minimis
levels
because
it
would
not
be
costeffective
to
do
so
and
such
emission
reductions
could
not
be
expected
to
produce
any
perceptible
improvements
in
visibility.
Several
commenters
agreed
that
the
pollutant
coverage
requirements
for
BART
eligibility
should
be
consistent
with
those
for
the
PSD
program,
but
others
argued
that
BART
should
be
required
only
for
pollutants
emitted
in
amounts
greater
than
250
tons
per
year.
Commenters
also
noted
that
the
guidelines
were
not
clear
as
to
whether
the
de
minimis
provision
would
apply
on
a
plant­
wide
or
unit
by
unit
basis.
A
few
commenters
also
noted
that
the
final
17
EDF
et
al.
v.
EPA,
82
F.
3d
451,
466
(
D.
C.
Cir.
1996)
citing
Alabama
Power
v.
Costle,
636
F.
2d
323
(
D.
C.
Cir.
1979).

69
guidelines
should
clarify
where
in
the
BART
determination
process
de
minimis
levels
may
be
used.

Other
commenters
opposed
the
use
of
de
minimis
exemptions.
These
commenters
argued
that
it
would
be
unreasonable
to
rule
categorically
that
a
certain
level
of
emissions
had
a
trivial
impact
on
visibility
without
assessing
the
impacts
of
these
emissions
in
particular
circumstances.
These
commenters
argued
that
States
should
consider
the
emissions
of
all
visibility­
impairing
pollutants
in
a
BART
determination
regardless
and
that,

consequently,
there
should
be
no
de
minimis
levels.

Final
rule.
As
proposed
in
2004,
we
believe
that
it
is
reasonable
to
give
States
the
flexibility
to
establish
de
minimis
levels
so
as
to
allow
them
to
exempt
from
the
BART
determination
process
pollutants
emitted
at
very
low
levels
from
BART­
eligible
sources.
As
explained
by
the
D.
C.

Circuit,
"
categorical
exemptions
from
the
requirements
of
a
statute
may
be
permissible
`
as
an
exercise
of
agency
power,

inherent
in
most
statutory
schemes,
to
overlook
circumstances
that
in
context
may
fairly
be
considered
de
minimis.'"
17
The
ability
to
create
de
minimis
exemptions
18
Id.

70
from
a
statute
is
a
tool
to
be
used
in
implementing
the
legislative
design.
18
The
intent
of
Congress
in
requiring
controls
on
emissions
from
certain
major
stationary
sources
was
to
eliminate
or
reduce
any
anticipated
contribution
to
visibility
impairment
from
these
sources.
This,
as
section
169A(
b)(
2)(
A)
states,
is
the
"
purpose"
of
BART.
In
making
a
determination
as
to
the
appropriate
level
of
controls,

however,
the
States
are
required
to
take
into
account
not
only
the
visibility
benefits
resulting
from
imposing
controls
on
these
sources
but
also
the
costs
of
complying
with
the
BART
provision.
The
BART
provision
is
accordingly
designed
to
ensure
that
the
States
take
into
consideration
all
emissions
of
certain
stationary
sources
in
making
a
BART
determination,
but
also
to
provide
States
with
the
flexibility
to
include
the
costs
and
benefits
of
controlling
these
sources
in
the
calculus
of
determining
the
appropriate
level
of
BART.

Although
as
discussed
above,
it
is
not
possible
based
on
the
information
before
us
to
assume
that
emissions
of
250
tons
per
year
of
a
visibility­
impairing
pollutant
do
not
cause
or
contribute
to
visibility
impairment,
we
do
believe
it
would
be
permissible
for
States
to
create
de
minimis
levels
at
a
much
lower
level.
If
a
State
were
to
undertake
71
a
BART
analysis
for
emissions
of
less
than
40
tons
of
SO2
or
NOx
or
15
tons
of
PM10
from
a
source,
it
is
unlikely
to
result
in
anything
but
a
trivial
improvement
in
visibility.

This
is
because
reducing
emissions
at
these
levels
would
have
little
effect
on
regional
emissions
loadings
or
visibility
impairment.
We
believe
most
States
would
be
unlikely
to
find
that
the
costs
of
controlling
a
few
tons
of
emissions
were
justified.
Because
the
overall
benefits
to
visibility
of
requiring
BART
determinations
for
emissions
of
less
than
the
de
minimis
levels
would
be
trivial,
we
are
amending
the
regional
haze
rule
to
allow
the
States
this
flexibility.

The
de
minimis
levels
we
provide
for
today
apply
on
a
plant­
wide
basis.
Applying
de
minimis
levels
on
a
unit
by
unit
basis
as
suggested
by
certain
commenters
could
exempt
hundreds
of
tons
of
emissions
of
a
visibility­
impairing
pollutant
from
BART
analysis.
In
at
least
some
of
the
twenty­
six
source
categories
covered
by
the
BART
provisions,

a
single
control
device
can
be
used
to
control
emissions
from
multiple
units.
Thus,
it
is
possible
that
while
emissions
from
each
unit
are
relatively
trivial,
the
costs
of
controlling
emissions
from
multiple
units
might
be
costeffective
in
light
of
the
BART­
eligible
source's
total
emissions
of
the
pollutant
at
issue.
States
should
consider
the
control
options
in
such
situations
and
determine
the
appropriate
approach
for
the
specific
source.
72
We
are
revising
the
regional
haze
rule
to
provide
States
with
the
ability
to
establish
de
minimis
levels
up
to
the
levels
proposed
in
2004.
States
can
accordingly
exclude
from
the
BART
determination
process
potential
emissions
from
a
source
of
less
than
forty
tons
per
year
of
SO2
or
NOx,
or
15
tons
per
year
for
PM10.
In
the
guidelines,
we
include
this
as
part
of
the
BART
determination
in
section
IV
of
the
guidelines.
(
We
note
that
these
emission
levels
represent
the
maximum
allowable
de
minimis
thresholds
 
States
retain
their
discretion
to
set
the
thresholds
at
lesser
amounts
of
each
pollutant,
or
to
not
provide
any
pre­
determined
de
mininis
levels.)
We
believe
that
this
approach
is
the
clearest
method
for
exempting
trivial
emissions
from
the
BART
determination
process.
Alternatively,
States
may
find
it
useful
to
exclude
de
minimis
emissions
in
identifying
whether
a
source
is
subject
to
BART
in
section
III
of
the
guidelines.
Either
approach
is
consistent
with
the
regulation
issued
in
this
rule.

D.
How
to
Determine
Which
BART­
eligible
Sources
are
"
Subject
to
BART"

"
Cause
or
Contribute"

Background.
The
visibility
provisions
in
the
CAA
establish
a
low
triggering
threshold
for
determining
whether
a
BART­
eligible
source
is
required
to
undergo
a
BART
determination.
Central
Ariz.
Water
Conservation
District,
73
990
F.
2d
1531,
1541
(
9th
Cir.
1993).
Under
section
169A(
b)(
2)(
A)
of
the
Act,
each
State
must
review
all
BART
eligible
sources
and
determine
whether
the
sources
emit
"
any
air
pollutant
which
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
visibility
in
[
a
Class
I]

area."
If
a
source
meets
this
threshold,
the
State
must
then
determine
what
is
BART
for
that
source.

Proposed
rule.
In
the
reproposed
guidelines,
we
identified
three
options
for
States
to
use
in
determining
which
BART­
eligible
sources
meet
the
test
set
forth
in
section
169A(
b)(
2)(
A)
of
the
CAA.
To
determine
whether
a
BART­
eligible
source
is
"
reasonably
anticipated
to
cause
or
contribute
to
visibility
impairment,"
the
first
proposed
option
was
that
a
State
could
choose
to
consider
the
collective
contribution
of
emissions
from
all
BART­
eligible
sources
and
conclude
that
all
BART­
eligible
sources
within
the
State
are
"
reasonably
anticipated
to
cause
or
contribute"
to
some
degree
of
visibility
impairment
in
a
Class
I
area.
The
preamble
to
the
1999
regional
haze
rule
explains
at
length
why
we
believe
that
looking
to
the
collective
contribution
of
many
sources
over
a
broad
area
is
a
reasonable
approach,
and
we
explained
in
the
2004
reproposed
guideline
that
we
believed
that
a
State's
decision
to
use
a
cumulative
analysis
at
this
stage
of
the
BART
determination
process
would
be
consistent
with
the
CAA
74
and
the
findings
of
the
D.
C.
Circuit
in
American
Corn
Growers.

The
second
proposed
option
was
to
allow
a
State
to
demonstrate,
using
a
cumulative
approach,
that
none
of
its
BART­
eligible
sources
contribute
to
visibility
impairment.

Specifically,
we
proposed
to
provide
States
with
the
option
of
performing
an
analysis
to
show
that
the
full
group
of
BART­
eligible
sources
in
a
State
cumulatively
do
not
cause
or
contribute
to
visibility
impairment
in
any
Class
I
areas.

As
a
third
option,
we
proposed
that
a
State
may
choose
to
determine
which
sources
are
subject
to
BART
based
on
an
analysis
of
each
BART­
eligible
source's
individual
contribution.
We
labeled
this
option
as
an
"
Individualized
Source
Exemption
Process,"
and
proposed
that
States
use
an
air
quality
model
to
determine
an
individual
source's
contribution
to
visibility
impairment,
calculated
on
a
24
hour
bases,
and
compared
to
an
established
threshold.

Comments.
Several
commenters
expressed
the
view
that
EPA
was
misinterpreting
the
American
Corn
Growers
case
to
allow
the
States
to
apply
a
collective
contribution
test
in
determining
whether
BART­
eligible
sources
are
subject
to
BART.
Commenters
argued
that
because
this
approach
does
not
allow
for
a
source
to
show
that
it
does
not
individually
cause
or
contribute
to
visibility
impairment,
it
is
incompatible
with
the
language
of
section
169A(
b)(
2)(
A)
of
75
the
Act.
Commenters
stated
that
EPA
should
modify
the
provisions
in
the
proposed
rule
to
ensure
that
an
individual
source
is
afforded
the
opportunity
to
conduct
an
analysis
to
demonstrate
that
its
emissions
do
not
impair
visibility
in
any
Class
I
area.
Conversely,
several
commenters
indicated
that
the
option
to
determine
that
all
potential
BART
sources
contribute
to
regional
haze
should
be
the
starting
point
of
determining
BART
eligibility.

Many
industry
commenters
and
some
States
supported
the
second
proposed
option
which
would
allow
a
State
to
demonstrate
through
an
analysis
of
the
collective
contribution
of
all
its
BART­
eligible
sources
that
none
of
these
sources
contribute
to
visibility
impairment.
Several
of
these
commenters
added,
however,
that
if
this
cumulative
analysis
were
to
show
a
contribution,
then
consistent
with
the
decision
in
American
Corn
Growers,
the
State
must
allow
each
individual
source
to
demonstrate
that
its
own
emissions
do
not,
by
themselves,
contribute
to
the
problem
of
visibility
impairment.
One
commenter
requested
clarification
on
what
visibility
threshold
a
State
should
use
in
determining
that
no
sources
are
reasonably
anticipated
to
cause
or
contribute
to
any
impairment
in
a
Class
I
area.

A
number
of
commenters
supported
the
third
option
for
determining
BART
applicability
based
on
an
analysis
of
76
source­
specific
impacts
on
visibility.
However,
many
of
the
commenters
stated
that
the
CAA
requires
that
the
States
either
conduct
such
an
analysis
in
determining
those
sources
subject
to
BART,
or
allow
an
individual
source
to
make
a
showing
that
it
does
not
cause
or
contribute
to
visibility
impairment.
In
addition,
although
supportive
of
the
general
notion
of
allowing
for
an
exemption
process
for
BARTeligible
sources,
several
commenters
stated
that
the
third
option
contained
burdensome
modeling
requirements,
and
that
States
need
a
more
flexible,
straightforward,
and
less
costly
method
to
make
the
"
cause
or
contribute"

determination.
Several
environmental
groups
commented
that
the
proposed
options
potentially
go
too
far
in
allowing
sources
to
be
exempted
from
the
BART
requirements.
These
commenters
asserted
that
EPA
should
clarify
that
States
may
not
allow
a
BART­
eligible
source
to
avoid
the
BART
requirements
without
an
affirmative
demonstration
by
the
State,
or
by
the
source,
showing
that
the
source
does
not
emit
any
air
pollutant
which
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
visibility
in
a
Class
I
area.
Absent
such
a
demonstration,
these
commenters
added
that
a
State
may
not
choose
to
waive
the
requirement
to
conduct
a
BART
review
of
the
source.

Final
rule.
The
CAA
provides
the
States
with
broad
authority
over
BART
determinations.
In
the
American
Corn
77
Growers
case,
the
D.
C.
Circuit
found
that
EPA's
1999
regional
haze
regulations
"
impermissibly
constrain[
ed]
state
authority"
by
requiring
States
to
look
to
the
collective
contribution
of
BART­
eligible
sources
in
determining
whether
these
sources
could
"
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
visibility."
The
final
rule
acknowledges
the
States'
authority
in
this
area
and
does
not
constrain
the
States
in
adopting
reasonable
approaches
to
meeting
the
requirements
of
the
visibility
provisions
and
implementing
regulations.

The
guideline
contains
the
three
options
proposed
in
2004
for
making
the
determination
of
whether
a
source
can
reasonably
be
anticipated
to
cause
or
contribute
to
visibility,
but
does
not
as
a
general
matter
require
the
States
to
use
any
of
the
three
approaches
we
have
outlined.

The
one
exception
to
this
general
rule
is
when
the
State
is
making
the
determination
as
to
whether
large
power
plants
meet
the
BART
applicability
test.
In
other
words,
we
are
not
limiting
in
this
rule
the
ability
of
the
States
in
reviewing
BART­
eligible
sources
to
determine
whether
a
source
meets
the
low
threshold
established
in
the
Act,

except
where
the
source
is
a
power
plant
with
a
generating
capacity
in
excess
of
750
MW.
The
State
must
exercise
its
authority
reasonably,
see
Cominco
v.
EPA
[
cite],
but
can
adopt
approaches
other
than
those
set
forth
in
the
guideline
19
64
Fed.
Reg.
at
35721.

78
for
determining
whether
a
source
can
be
anticipated
to
contribute
to
the
problem
of
haze.

We
are
not
requiring
the
States
to
conduct
sourcespecific
analyses
of
a
source's
impacts
in
order
to
determine
whether
the
source
should
be
subject
to
review.

Although
many
industry
commenters
argued
that
the
American
Corn
Growers
case
required
such
a
limitation
on
the
States'

authority,
the
court
in
that
case
"[
did]
not
accept
the
industry
petitioners'
contention
that
section
169A(
b)(
2)

bars
a
collective
determination
of
whether
a
source
is
subject
to
BART."
American
Corn
Growers
v.
EPA,
[
cite]
J.

Garland
dissenting.
States
may
therefore
apply
a
collective
contribution
approach
to
determining
whether
a
source
is
subject
to
BART
if
they
choose
to
do
so.

We
believe
that
the
first
option
outlined
in
the
guideline
is
one
reasonable
approach
to
determining
which
sources
meet
the
threshold
for
BART.
In
the
1999
regional
haze
rule,
EPA
concluded
that
all
States
contain
sources
whose
emissions
are
reasonably
anticipated
to
cause
or
contribute
to
regional
haze
in
a
Class
I
area.
19
Moreover,

as
explained
in
1999,
it
is
reasonable
to
conclude
that
if
a
BART­
eligible
source
emits
pollutants
in
an
upwind
area,
and
pollution
from
that
area
is
transported
downwind
to
a
Class
I
area,
then
the
BART­
eligible
source
"
may
reasonably
be
79
anticipated"
to
"
contribute"
to
"
any"
impairment
in
the
Class
I
area.
Thus,
in
implementing
the
requirements
of
the
visibility
program,
we
believe
that
a
State
could
conclude
that,
cumulatively,
its
BART­
eligible
sources
contribute
to
visibility
impairment
in
one
or
more
Class
I
areas.

However,
more
up­
to­
date
emissions
inventories
and
more
refined
modeling
tools
are
available
now
as
compared
to
1999
when
EPA
conducted
its
assessment,
States
exercising
this
option
should
use
the
data
being
developed
by
the
regional
planning
organizations,
or
on
their
own,
as
part
of
the
regional
haze
SIP
development
process
to
make
the
showing
that
the
State
(
LW
­
this
isn't
clear
­
it's
not
the
State
as
a
whole
­
it's
the
BART
sources,
isn't
it?)
contributes
to
visibility
impairment
in
one
or
more
Class
I
areas.

Contrary
to
many
industry
comments,
this
approach
does
not
deny
a
source
the
opportunity
to
demonstrate
that
it
should
not
be
subject
to
controls
as
part
of
a
plan
to
address
visibility
impairment.
First,
the
CAA
and
40
CFR
51.308(
e)(
4)
specifically
provide
for
an
exemption
from
BART
for
any
source
that
does
not
contribute
to
significant
visibility
impairment.
Second,
a
conclusion
that
a
source
is
subject
to
BART
requires
only
that
the
source
undergo
review
by
the
State.
In
establishing
the
appropriate
level
of
controls,
if
any,
that
an
existing
source
should
install,

the
degree
of
visibility
improvement
resulting
from
the
use
of
controls
is
one
of
the
factors
to
be
taken
into
80
consideration
by
the
State.
If
a
State
finds
that
a
source
has
only
a
very
minor
impact
on
visibility
in
a
Class
I
area,
it
will
take
that
fact
into
consideration
in
deciding
whether
the
source
should
be
required
to
install
and
operate
BART
controls.

We
agree
that
the
second
option
of
allowing
a
State
to
demonstrate
that
the
full
group
of
BART­
eligible
sources
in
the
State
do
not
contribute
to
visibility
impairment
would,

by
default,
satisfy
an
individual
source
contribution
assessment.
Commenters
have
not
shown
any
reason
to
believe
that
if
the
sum
total
of
emissions
from
the
BART­
eligible
sources
in
a
State
do
not
"
cause
or
contribute"
to
visibility
impairment
in
any
Class
I
area,
that
emissions
from
one
such
source
will
meet
the
threshold
for
BART
applicability.
A
State
following
this
approach
accordingly
need
not
undertake
an
affirmative
demonstration
based
on
a
source
by
source
analysis
of
visibility
impacts
to
find
that
its
sources
are
not
subject
to
BART.

We
agree
with
commenters
that
a
State
may
not
"
exempt"

a
BART­
eligible
source
from
the
requirements
to
undergo
review
without
a
demonstration
either
by
the
State,
or
by
the
source,
that
the
source
does
not
emit
any
air
pollutant
which
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
visibility
in
a
Class
I
area.
Although
we
used
the
term
"
Individualized
Source
Exemption
Process"

in
the
reproposed
guideline,
the
third
option
generally
can
81
be
better
described
as
an
"
Individualized
Source
Attribution
Process."
This
option,
which
is
based
on
a
source­
specific
assessment
of
visibility
impacts
using
an
appropriate
air
quality
model,
as
discussed
below,
satisfies
the
demonstration.

Use
of
CALPUFF
for
Visibility
Modeling
Background.
In
providing
the
States
with
the
option
of
making
a
determination
as
to
which
sources
are
subject
to
BART
based
on
a
consideration
of
each
source's
individual
contribution
to
visibility
impairment,
we
proposed
that
States
use
an
air
quality
model
such
as
CALPUFF.
We
also
proposed
that
States
use
an
approved
model
such
as
CALPUFF
in
the
BART
analysis
itself.
The
CALPUFF
system,
as
explained
in
the
2004
reproposed
guideline,
consists
of
a
diagnostic
meteorological
model,
a
gaussian
puff
dispersion
model
with
algorithms
for
chemical
transformation
and
complex
terrain,
and
a
post
processor
for
calculating
concentration
fields
and
visibility
impacts.

The
regional
haze
rule
addresses
visibility
impairment
caused
by
emissions
of
fine
particles
and
their
precursors.

As
fine
particle
precursors,
such
as
SO2
or
NOx,
are
dispersed,
they
react
in
the
atmosphere
with
other
pollutants
to
form
visibility­
impairing
pollutants.
In
fact,
Congress
implicitly
recognized
in
1977
the
role
of
chemical
transformation
in
creating
visibility
impairment,
20
H.
R.
Rep.
No.
95­
294
at
204
(
1077).

82
when
it
stated
that
the
"
visibility
problem
is
caused
primarily
by
emissions
of
SO2,
[
NOx],
and
particulate
matter."
20
In
most
cases,
to
predict
the
impacts
of
a
source's
specific
contribution
to
visibility
impairment,
a
State
will
need
a
tool
that
takes
into
account
not
only
the
transport
and
diffusion
of
directly
emitted
PM2.5
but
also
one
that
can
address
chemical
transformation.

Because
the
air
quality
model
CALPUFF
is
currently
the
best
application
available
to
predict
the
impacts
of
a
single
source
on
visibility
in
a
Class
I
area,
we
proposed
that
a
CALPUFF
assessment
be
used
as
the
preferred
approach
first,
for
determining
whether
an
individual
source
is
subject
to
BART,
and
second,
in
the
BART
determination
process.
The
CALPUFF
assessment
is
specific
to
each
source,

taking
into
account
the
individual
source's
emission
characteristics,
location,
and
the
particular
meteorological,
topographical,
and
climatological
conditions
of
the
area
in
which
the
source
is
located,
any
of
which
may
have
an
impact
on
the
transport
of
PM2.5
and
its
precursors.

CALPUFF
can
be
used
to
estimate
not
only
the
effects
of
directly
emitted
PM2.5
emissions
from
a
source,
but
also
to
predict
the
visibility
impacts
from
the
transport
and
chemical
transformation
of
fine
particle
precursors.
21
To
determine
whether
a
BART­
eligible
source
"
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
visibility
impairment
in
any
Class
I
area,"
it
may
not
always
be
sufficient
for
the
State
to
predict
the
impacts
of
a
BART­
eligible
source
only
on
the
nearest
Class
I
area
(
or
on
the
nearest
receptor
in
the
nearest
Class
I
area).
The
particular
meteorological
and
topographical
conditions,
for
example,
could
mean
that
a
source's
greatest
impacts
occurred
at
a
Class
I
area
other
than
the
nearest
one.

22
PLUVUEII
is
a
model
used
for
estimating
visual
range
reduction
and
atmospheric
discoloration
caused
by
plumes
resulting
from
the
emissions
of
particles,
nitrogen
oxides,
and
sulfur
oxides
from
a
single
source.
The
model
predicts
the
transport,
dispersion,
chemical
reactions,
optical
effects
and
surface
deposition
of
point
or
area
source
emissions.
It
is
available
at
http://
www.
epa.
gov/
scram001/
tt22.
htm#
pluvue.

83
The
CALPUFF
model
is
generally
intended
for
use
on
scales
from
50
km
to
several
hundred
kilometers
from
a
source.
As
a
general
matter,
States
will
typically
need
to
assess
the
impacts
of
potential
BART
sources
on
Class
I
areas
located
more
than
50
km
from
the
source.
21
However,

in
situations
where
the
State
is
assessing
visibility
impacts
for
source­
receptor
distances
less
than
50
km,
we
proposed
that
States
use
their
discretion
in
determining
visibility
impacts,
giving
consideration
to
both
CALPUFF
and
other
EPA­
approved
methods.
As
an
example,
we
suggested
that
States
could
use
an
appropriate
local­
scale
plume
impact
model,
such
as
PLUVUEII22,
to
determine
whether
a
source's
emissions
are
below
a
level
that
would
be
reasonably
anticipated
to
cause
or
contribute
to
visibility
impairment
in
any
Class
I
area.
84
Comments.
A
number
of
States,
environmental
groups,

and
some
industry
commenters
strongly
supported
the
use
of
CALPUFF
as
proposed.
Many
commenters
supported
the
use
of
CALPUFF
but
indicated
that
States
must
have
the
flexibility
to
use
additional
tools
for
their
individual
source
analyses.
Some
suggested
options
for
the
"
cause
or
contribute"
determination
were
the
use
of
photochemical
grid
models,
or
more
simplified,
non­
modeling
approaches.

Commenters
claimed
that
States
must
have
the
option
to
incorporate
advances
in
science
and
technologies
into
models
or
other
applications
that
may
produce
more
accurate
simulations
of
meteorology,
chemistry,
and
visibility
impairment.
Other
industry
groups
and
States
argued
that
CALPUFF
has
significant
limitations,
especially
simulating
complex
atmospheric
chemistry,
and
that
EPA's
recommendation
of
CALPUFF
as
the
preferred
approach
is
therefore
inappropriate.

Another
issue
raised
by
commenters
was
the
use
of
CALPUFF
for
estimating
secondary
particulate
matter
formation.
Commenters
recognized
that
CALPUFF
was
incorporated
into
the
"
Guideline
on
Air
Quality
Models"
at
40
CFR
Part
51,
Appendix
W
in
April
2003
as
the
preferred
model
for
Prevention
of
Significant
Deterioration
(
PSD)

increment
and
National
Ambient
Air
Quality
Standards
(
NAAQS)

compliance
assessments
of
long
range
transport
of
primary
23The
model
code
and
its
documentation
are
available
at
no
cost
for
download
from
the
model
developers'
Internet
Web
site:
http://
www.
src.
com/
calpuff/
calpuff1.
htm.
The
Beta­
Test
version
is
not
officially
accepted
for
use
by
EPA,
and
should
not
be
used.

85
emissions
of
SO2
and
PM2.5.
However,
commenters
stated
that
CALPUFF
has
not
been
incorporated
into
the
Guideline
on
Air
Quality
Models
for
predicting
the
secondary
formation
of
PM.

The
commenters
remarked
that
EPA
guidance
indicates
that
photochemical
grid
models
be
used
to
simulate
secondary
PM
formation
and
concluded
on
this
basis
that
the
application
of
CALPUFF
as
we
proposed
is
in
conflict
with
our
guidance.

Final
rule.
We
believe
that
CALPUFF
is
an
appropriate
application
for
States
to
use
for
the
particular
purposes
of
this
rule,
to
determine
if
an
individual
source
is
reasonably
anticipated
to
cause
or
contribute
to
impairment
of
visibility
in
Class
I
areas,
and
to
predict
the
degree
of
visibility
improvement
which
could
reasonably
be
anticipated
to
result
from
the
use
of
retrofit
technology
at
an
individual
source.
We
accordingly
encourage
States
to
use
it
for
these
purposes23.

CALPUFF
is
the
best
modeling
application
available
for
predicting
a
single
source's
contribution
to
visibility
impairment.
It
is
the
only
EPA­
approved
model
for
use
in
estimating
single
source
pollutant
concentrations
resulting
from
the
long
range
transport
of
primary
pollutants.
In
addition,
it
can
also
be
used
for
some
purposes,
such
as
the
86
visibility
assessments
addressed
in
today's
rule,
to
account
for
the
chemical
transformation
of
SO2
and
NOx.
As
explained
above,
simulating
the
effect
of
precursor
pollutant
emissions
on
PM2.5
concentrations
requires
air
quality
modeling
that
not
only
addresses
transport
and
diffusion,
but
also
chemical
transformations.
CALPUFF
incorporates
algorithms
for
predicting
both.
At
a
minimum,

CALPUFF
can
be
used
to
estimate
the
relative
impacts
of
BART­
eligible
sources.
We
are
confident
that
CALPUFF
distinguishes,
comparatively,
the
relative
contributions
from
sources
such
that
the
differences
in
source
configurations,
sizes,
emission
rates,
and
visibility
impacts
are
well­
reflected
in
the
model
results.
States
can
make
judgements
concerning
the
conservativeness
or
overestimation,
if
any,
of
the
results.
In
fact,
although
we
focused
on
the
use
of
CALPUFF
for
primary
pollutants
in
revising
the
Guideline
of
Air
Quality
Modeling,
section
7.2.1.
e.
of
the
Guideline
states:

e.
CALPUFF
(
Section
A.
3)
may
be
applied
when
assessment
is
needed
of
reasonably
attributable
haze
impairment
or
atmospheric
deposition
due
to
one
or
a
small
group
of
sources.
This
situation
may
involve
more
sources
and
larger
modeling
domains
than
that
to
which
VISCREEN
ideally
may
be
applied.
The
procedures
and
analyses
should
be
87
determined
in
consultation
with
the
appropriate
reviewing
authority
(
paragraph
3.0(
b)
and
the
affected
FLM(
s).

We
believe
that
our
proposed
use
of
CALPUFF
is
thus
fully
in
keeping
with
the
Guideline
of
Air
Quality
Modeling,

especially
in
light
of
the
low
triggering
threshold
for
determining
whether
a
source
is
reasonably
anticipated
to
cause
or
contribute
to
visibility
impairment
in
a
Class
I
area,
and
the
fact
that
the
modeling
results
are
used
as
only
one
of
five
statutory
criteria
evaluated
to
determine
BART
emission
limits.

Even
so,
as
commenters
point
out,
CALPUFF
has
not
yet
been
fully
evaluated
for
secondary
pollutant
formation.
For
the
specific
purposes
of
the
regional
haze
rule's
BART
provisions,
however,
we
have
concluded
that
CALPUFF
is
sufficiently
reliable
to
inform
the
decision
making
process.

EPA
revised
the
Guideline
on
Air
Quality
Models
in
2003
(
40
CFR
Part
51,
Appendix
W,
April
2003),
in
part,
to
add
CALPUFF
to
the
list
of
approved
models
for
particular
uses.

At
that
time,
we
considered
comments
that
CALPUFF
should
be
approved
for
use
in
predicting
the
impact
of
secondary
emissions
on
particulate
matter
concentrations.
As
we
stated
in
the
revision,
CALPUFF
represents
a
substantial
improvement
in
methods
for
assessing
long­
range
transport
of
air
pollutants.
However,
as
explained
in
the
response
to
comments
for
that
rulemaking,
the
modeling
results
in
the
24
Under
CAA
section
165(
a),
a
major
emitting
facility
may
not
be
constructed
unless
the
owner
or
operator
of
the
facility
demonstrates
that
the
emissions
from
the
facility
will
not
cause
or
contribute
air
pollution
in
excess
of
an
increment
or
NAAQS.

25
CALPUFF
Analysis
in
Support
of
the
Regional
Haze
Rule,
U.
S.
Environmental
Protection
Agency,
April
15,
2005,
Docket
No.
OAR­
2002­
0076.

88
context
of
a
PSD
review
may
be
used
as
the
sole
determining
factor
in
denying
a
source
a
permit
to
construct.
24
Although
its
use
in
simulating
long­
range
transport
is
beneficial,
given
the
significance
of
the
modeling
results
in
assessing
increment
consumption
due
to
a
single
source's
impacts,
we
made
a
determination
that
it
would
not
be
appropriate
in
the
rulemaking
revising
Appendix
W
to
approve
CALPUFF
for
use
in
modeling
secondary
emissions
.

In
contrast
to
the
significance
of
the
modeling
results
in
the
PSD
context,
the
use
of
CALPUFF
in
the
context
of
the
regional
haze
rule
is
not
determinative
of
a
source's
ability
to
construct
or
operate.
A
State
may
use
CALPUFF
to
determine
whether
a
source
can
reasonably
be
anticipated
to
cause
or
contribute
to
visibility
impairment
and
so
should
be
subject
to
additional
review
to
determine
if
the
source
should
be
subject
to
control.

Based
on
our
analysis
of
the
power
plants
covered
by
the
guidelines,
we
believe
that
all
but
a
handful
of
these
plants
have
impacts
of
greater
than
1.0
deciviews
on
one
or
more
Class
I
areas.
25
In
fact,
we
anticipate
that
most
of
26
Ibid.

89
these
plants
are
predicted
to
have
impacts
even
higher.
26
Because
of
the
scale
of
the
predicted
impacts
from
these
sources,
CALPUFF
is
an
appropriate
or
a
reasonable
application
to
determine
whether
such
a
facility
can
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
visibility.
In
other
words,
to
find
that
a
source
with
a
predicted
maximum
impact
greater
than
2
or
3
deciviews
meets
the
low
triggering
threshold
in
the
Act
does
not
require
the
degree
of
certainty
in
the
results
of
the
model
that
might
be
required
for
other
regulatory
purposes.

In
the
unlikely
case
that
a
State
were
to
find
that
a
750
MW
power
plant's
predicted
contribution
to
visibility
impairment
is
within
a
very
narrow
range
between
exemption
from
or
being
subject
to
BART,
the
State
can
work
with
EPA
to
evaluate
the
CALPUFF
results
in
combination
with
information
derived
from
other
appropriate
techniques
for
estimating
visibility
impacts
to
inform
the
BART
applicability
determination.

As
discussed
in
in
section
E.
below
we
also
recommend
that
the
States
use
CALPUFF
as
a
screening
application
in
estimating
the
degree
of
visibility
improvement
that
may
reasonably
be
expected
from
controlling
a
single
source
in
order
to
inform
the
BART
determination.
As
we
noted
in
2004,
this
estimate
of
visibility
improvement
does
not
by
90
itself
dictate
the
level
of
control
a
State
would
impose
on
a
source;
"
the
degree
of
improvement
in
visibility
which
may
reasonably
be
anticipated
to
result
from
the
use
of
[
BART],"

is
only
one
of
five
criteria
that
the
State
must
consider
together
in
making
a
BART
determination.
The
State
makes
a
BART
determination
based
on
the
best
estimates
available
for
each
criterion,
and
as
the
CAA
does
not
specify
how
the
State
should
take
these
factors
into
account,
the
States
are
free
to
determine
the
weight
and
significance
to
be
assigned
to
each
factor.
American
Corn
Growers
v.
EPA,
[
cite
to
dissent,
fn.
10].
CALPUFF
accordingly
is
an
appropriate
application
for
use
in
combination
with
an
analysis
of
the
other
statutory
factors,
to
inform
decisions
related
to
BART.

We
understand
the
concerns
of
commenters
that
the
chemistry
modules
of
the
CALPUFF
model
are
less
advanced
than
some
of
the
more
recent
atmospheric
chemistry
simulations.
To
date,
no
other
modeling
applications
with
updated
chemistry
have
been
approved
by
EPA
to
estimate
single
source
pollutant
concentrations
from
long
range
transport.
In
its
next
review
of
the
Guideline
on
Air
Quality
Models,
EPA
will
evaluate
these
and
other
newer
approaches
and
determine
whether
they
are
sufficiently
documented,
technically
valid,
and
reliable
to
approve
for
general
use.
In
the
meantime,
as
the
Guideline
makes
clear,
91
States
are
free
to
make
individualized
showings
that
these
or
other
alternative
approaches
are
valid
and
appropriate
for
their
intended
applications.

Theoretically,
the
CALPUFF
chemistry
simulations,
in
total,
may
lead
to
model
predictions
that
are
generally
overestimated
at
distances
downwind
of
200
km.
Again,
States
can
make
judgements
concerning
the
conservativeness
or
overestimation,
if
any,
of
the
results.

The
use
of
other
models
and
techniques
to
estimate
if
a
source
causes
or
contributes
to
visibility
impairment
may
be
considered
by
the
State,
and
the
BART
Guidelines
preserve
a
State's
ability
to
use
other
models.
Regional
scale
photochemical
grid
models
may
have
merit,
but
their
design
has
been
to
assess
cumulative
impacts,
not
impacts
from
individual
sources.
Such
models
are
very
resource
intensive
and
time
consuming
relative
to
CALPUFF,
but
States
may
consider
their
use
for
SIP
development
in
the
future
as
they
are
adapted
and
demonstrated
to
be
appropriate
for
single
source
applications
and
such
use
has
been
approved
by
the
appropriate
EPA
regional
offices.
However,
regional
models
have
not
been
evaluated
for
single
source
applications
to
show
if
the
source
causes
or
contributes
to
visibility
impairment.
Their
use
may
be
more
appropriate
in
Options
1
27For
regional
haze
applications,
regional
scale
modeling
typically
involves
use
of
a
photochemical
grid
model
that
is
capable
of
simulating
aerosol
chemistry,
transport,
and
deposition
of
airborne
pollutants,
including
particulate
matter
and
ozone.
Regional
scale
air
quality
models
are
generally
applied
for
geographic
scales
ranging
from
a
multi­
state
to
the
continental
scale.
Because
of
the
design
and
intended
applications
of
grid
models,
they
may
not
be
appropriate
for
BART
assessments,
so
States
should
consult
with
the
appropriate
EPA
Regional
Office
prior
to
carrying
out
any
such
modeling.

92
and
2
discussed
above27.
A
conclusion
that
a
source
is
subject
to
BART
requires
only
that
the
source
undergo
review
by
the
State,
and
the
source
should
use
CALPUFF
to
make
that
determination.
In
evaluating
visibility
improvement
as
one
of
the
five
factors
to
consider
in
setting
BART
controls,

other
models,
used
in
combination
with
CALPUFF,
may
be
helpful
in
providing
a
relative
sense
of
the
source's
visibility
impact
and
can
aid
in
informing
the
BART
decision.
A
discussion
of
the
use
of
alternative
models
is
given
in
the
Guideline
in
Appendix
W,
section
3.2.
Our
preference
for
the
use
of
the
CALPUFF
model
to
estimate
if
a
single
BART­
eligible
source
is
reasonably
anticipated
to
cause
or
contribute
to
visibility
impairment,
and
to
evaluate
visibility
improvement
resulting
from
controls
at
a
Class
I
area
remains
unchanged
from
the
2004
reproposal.

Metric
for
Visibility
Degradation
Background.
The
2004
reproposed
guidelines
contained
a
proposed
threshold
for
the
States
to
use
in
determining
whether
an
individual
source
could
be
considered
to
cause
or
28U.
S.
EPA.
September
2003.
Guidance
for
Estimating
Natural
Visibility
Conditions
Under
the
Regional
Haze
Rule.
http://
www.
epa.
gov/
ttncaaa1/
t1/
memoranda/
rh_
envcurhr_
gd.
pdf
This
document
has
estimates
of
default
conditions
as
well
as
measures
to
develop
refined
estimates
of
natural
conditions.

29
National
Acid
Precipitation
Assessment
Program
(
NAPAP).
Acid
Deposition:
State
of
Science
and
Technology
Report
24,
Visibility:
Existing
and
Historical
Conditions
 
Causes
and
Effects
(
Washington,
DC,
1991),
Appendix
D,
p.
24­
D2
("
changes
in
light
extinction
of
5%
will
evoke
a
just
noticeable
change
in
most
landscapes").
Converting
a
5%
change
in
light
extinction
to
a
change
in
deciviews
yields
a
change
of
approximately
0.5
deciviews.

93
contribute
to
visibility
impairment
in
a
Class
I
area.
We
proposed
a
0.5
deciview
change
(
delta­
deciview),
relative
to
natural
background
conditions,
as
a
numerical
threshold
for
making
this
cause
or
contribute
determination.
Natural
background
conditions,
expressed
in
deciviews,
are
defined
for
each
Class
I
area28.
The
0.5
delta­
deciview
threshold
is
a
unit
change,
perceived
or
measured
equally
for
each
Class
I
area.
We
noted
that
a
0.5
deciview
change
in
visibility
is
linked
to
"
perceptibility,"
or
a
just
noticeable
change
in
most
landscapes.
29
We
proposed
the
CALPUFF
model
as
the
preferred
approach
for
predicting
whether
a
single
source
caused
or
contributed
to
visibility
impairment
if
the
modeled
results
showed
impacts
from
the
source
that
exceeded
the
threshold
on
any
given
day
during
a
five­
year
period.
30
National
Acid
Precipitation
Assessment
Program
(
NAPAP).
Acid
Deposition:
State
of
Science
and
Technology
Report
24,
Visibility:
Existing
and
Historical
Conditions
 
Causes
and
Effects
(
Washington,
DC,
1991),
Appendix
D,
p.
24­
D2
94
We
also
proposed
that
if
a
source
had
an
estimated
impact
on
visibility
of
less
than
0.5
deciviews,
a
State
could
choose
to
exempt
the
source
from
further
BART
analysis.

Comments.
One
commenter
said
that
the
proposal
would
"
change
the
regulatory
role
of
the
deciview
metric
by
converting
it
into
a
regulatory
0.5
deciview
standard
(
versus
a
`
goal')
for
defining
how
States
must
exercise
their
authority
and
discretion
in
determining
whether
an
individual
source
`
causes
or
contributes'
to
visibility
impairment
in
a
Class
I
area."

We
received
numerous
comments
supporting
the
proposed
threshold.
A
number
of
commenters
stated
that
the
0.5
deciview
threshold
is
appropriate
given
the
extremely
low
triggering
threshold
for
applicability
established
by
Congress,
and
that
the
literature
supports
it
as
the
minimum
level
of
perceptibility.
Some
Commenters
cited
published
documentation
supporting
their
assertions
that
a
minimum
change
in
deciviews
necessary
for
perceptibility
is
0.5
deciviews.
30
Many
commenters,
however,
criticized
the
threshold
as
too
low.
They
stated
that
a
change
of
0.5
deciviews
is
inconsistent
with
language
in
the
regional
haze
rule
31
Henry,
R.
C.
"
Just­
Noticeable
Differences
in
Atmospheric
Haze",
Journal
of
the
Air
&
Waste
Management
Association,
52:
1238­
1243,
October
2002.

95
pointing
to
1.0
deciview
as
the
appropriate
perceptibility
threshold,
and
they
cited
more
recent
literature
justifying
perceptibility
as
greater
than
a
change
of
1
deciview31.
One
commenter
said
that
we
should
allow
States
and
RPOs
the
flexibility
to
determine
appropriate
visibility­
impact
thresholds
in
light
of
current
knowledge
about
a
range
of
perceptibility
thresholds.
Another
commenter,
representing
a
regional
planning
organization
(
RPO),
said
that
we
should
explain
our
basis
for
establishing
a
threshold
of
a
one­
time
impact
of
greater
than
0.5
deciviews,
in
light
of
the
form
of
the
regional
haze
goal.

Conversely,
several
commenters
said
that
the
0.5
deciview
threshold
is
too
high.
A
recurring
comment
was
that
the
statutory
BART
applicability
test
from
CAA
Section
169A(
b)(
2)(
A)
contains
two
separate
elements:
"
causation"
of
any
visibility
impairment
and
"
contribution"
to
any
such
impairment.
Commenters
pointed
out
that
by
setting
a
threshold
of
0.5
deciviews,
we
had
combined
"
cause
or
contribute"
into
a
single
test
of
causality,
thus
effectively
eliminating
the
"
contribution"
element
of
the
BART
applicability
test.
The
commenters
asserted
that
a
single
BART­
eligible
source
can
"
contribute"
to
visibility
impairment
with
impacts
much
lower
than
0.5
deciviews.
They
96
argued
that
we
must
set
the
minimum
threshold
for
individual
source
contribution
to
visibility
impairment
at
the
lowest
level
detectable
by
modeling
or
other
appropriate
analysis,

and
that
this
minimum
individual
contribution
level
must
in
any
event
be
set
at
no
greater
than
a
0.1
deciview
change
relative
to
natural
conditions,
which
is
a
clearly
measurable
level.
One
commenter
suggested
that
a
cause
or
contribute
threshold
be
set
at
some
percentage
of
the
"
just
noticeable"
change
of
0.5
deciviews.

Another
commenter
said
that
in
a
case
where
multiple
sources
each
have
a
visibility
impact
of
less
than
a
0.5
deciview
change,
but
together
result
in
a
change
of
more
than
0.5
deciview,
each
of
these
sources
contributes
to
the
resulting
visibility
impairment.
This
commenter
asserted
that
BART
guidelines
that
result
in
exemptions
for
these
"
contributing"
sources
would
subvert
the
goals
of
the
regional
haze
program.

Similarly,
several
commenters
suggested
we
require
that
for
any
combination
of
BART
eligible
sources
causing
visibility
impairment
in
a
Class
I
area
of
more
than
0.5
deciviews
(
by
CALPUFF
modeling
for
any
24­
hour
period,
for
example),
each
individual
source
must
be
subject
to
BART.

Thus,
the
commenter
added,
the
court's
concern
about
the
lack
of
"
empirical
evidence
of
a
source's
contribution
to
visibility
impairment"
would
be
addressed.
97
Two
utilities
said
that
our
requirement
to
use
the
maximum
24­
hour
value
over
the
5­
year
period
of
meteorological
data
in
the
modeling,
as
proposed,
is
too
stringent,
unreasonable,
inappropriate,
and
departs
from
the
previous
methodologies
for
the
regional
haze
program.

Additionally
they
said
that
the
threshold
is
restrictive
because
the
single
highest
24­
hour
modeled
impact
over
a
three
or
five
year
period
may
be
influenced
by
short­
term
weather
conditions,
like
high
humidity,
and
the
BART
applicability
determination
should
not
be
made
on
just
a
one­
time
occurrence.

One
Federal
Land
Manager
said
that
whatever
the
final
threshold
for
a
single­
source
impact
for
BART
sources,
EPA
should
clarify
that
the
purpose
of
this
modeling
assessment
is
to
evaluate
a
source's
anticipated
contribution
to
uniform
regional
haze
over
the
Class
I
area.
EPA
should
state
that
the
assumption
of
a
uniform
haze
contribution
based
on
CALPUFF
modeling
eliminates
the
need
to
assess
issues
related
to
the
size
of
the
Class
I
area,
views
within
a
Class
I
area,
and
weather
impact
interactions.
Finally,

one
commenter
said
that
thresholds
should
be
established
separately
for
the
eastern
and
western
regions
of
the
United
States,
as
natural
visibility
conditions
are
established
separately
for
eastern
and
western
regions
in
the
guidance.
32
Moreover,
the
fact
that
the
ultimate
purpose
of
the
visibility
provisions
is
expressed
as
a
"
goal"
does
not
mean
that
all
aspects
of
the
program
are
merely
aspirational.
CAA
169A(
a)(
4)
requires
EPA
to
establish
regulations
to
ensure
that
reasonable
progress
is
made
toward
the
national
visibility
goal,
and
169A(
b)(
2)
provides
that
EPA
must
require
SIPs
to
contain
emission
limits,
schedules
of
compliance,
and
other
measures
as
may
be
necessary
to
make
reasonable
progress
towards
meeting
the
goal.

98
Final
Rule.
We
believe
that
it
is
appropriate
for
States
to
use
the
deciview
in
establishing
a
threshold
for
BART
applicability.
CAA
169A(
b)(
2)(
A)
provides
for
a
BART
determination
for
any
BART­
eligible
source
which
"
emits
any
air
pollutant
which
may
reasonably
be
anticipated
to
cause
or
contribute
to
any
impairment
of
visibility
in
any
[
Class
I]
area."
States
will
need
some
means
of
determining
whether
a
source
"
causes
or
contributes
to"
visibility
impairment.

Today's
guidelines
advise
States
to
use
a
deciview
metric
in
defining
"
cause
or
contribute,
as
explained
further
below.

The
fact
that
the
deciview
is
also
used
to
track
progress
toward
the
goal
of
natural
visibility
does
not
in
any
way
indicate
that
we
are
"
converting"
a
"
goal"
into
a
requirement.
32
Use
of
the
same
metric
in
the
"
cause
or
contribute"
context
as
used
for
establishing
reasonable
progress
goals,
tracking
changes
in
visibility
conditions,

and
defining
baseline,
current,
and
natural
conditions
simply
provides
for
a
consistent
approach
to
quantifying
visibility
impairment.
While
we
do
not
necessarily
agree
with
commenters
who
said
we
conflated
the
"
cause
or
99
contribute"
test,
we
recognize
that
some
clarification
of
our
treatment
of
this
test
would
be
helpful.
Specifically,

we
wish
to
clarify
here
that
we
are
establishing
a
change
of
0.5
deciview
as
the
maximum
visibility
change
we
believe
should
be
used
to
determine
whether
a
source
"
contributes"

to
impairment.

In
proposing
a
"
cause
or
contribute"
threshold
of
0.5
deciviews,
we
acknowledged
that
there
is
uncertainty
associated
with
identifying
an
absolute
deciview
change
as
"
just
noticeable,"
or
"
perceptible".
This
is
consistent
with
our
observations
in
the
preamble
to
1999
Regional
Haze
Rule,
where
we
noted
"
that
a
1.0
deciview
change
should
not
be
considered
the
threshold
of
perception
in
all
cases
for
all
scenes",
and
that
"
visibility
changes
of
less
than
1.0
deciview
are
likely
to
be
perceptible
in
some
cases,

especially
where
the
scene
being
viewed
is
highly
sensitive
to
small
amounts
of
pollution".
We
also
acknowledged
that
a
change
greater
than
1.0
deciview
may
be
required
for
perceptibility
under
certain
site­
specific
conditions.

However,
even
where
a
change
of
0.5
deciviews
cannot
be
considered
to
"
cause"
(
i.
e.,
directly
result
in)
visibility
impairment,
we
believe
that
in
all
cases
a
change
of
this
magnitude
"
contributes"
to
impairment.

Logically,
to
"
contribute
to"
a
condition
must
mean
something
less
than
"
causing"
that
condition.
In
this
100
context,
if
"
causing"
visibility
impairment
means
causing
a
humanly
perceptible
change
in
visibility,
then
"
contributing"
to
visibility
impairment
must
mean
having
some
impact
on
the
conditions
affecting
visibility
which
does
not
rise
to
the
level
of
human
perception.
The
question
is
how
much
change
which
is
not
humanly
perceptible
should
a
source
be
allowed
to
bring
about
before
it
is
considered
to
be
"
contributing"
to
impairment.
Given
the
low
threshold
suggested
by
the
language
of
the
CAA,
it
would
be
reasonable
to
conclude
that
a
source
with
any
predicted
impacts
 
for
example,
as
low
as
0.1
delta­
deciviews
or
less
 
could
be
considered
to
contribute
to
visibility
impairment.
By
setting
the
criterion
for
"
contribute"
at
the
threshold
of
human
perceptibility
(
that
is,
a
level
which
can
be
perceived
in
some
but
not
all
situations),
we
are
in
effect
providing
a
conservative
benchmark
for
"
contribution."
In
other
words,
a
source
whose
emissions
are
predicted
to
result
in
perceptible
or
nearly
perceptible
results
can
definitely
be
considered
to
contribute
to
impairment.

Therefore,
States
should
establish
a
change
of
0.5
deciviews
as
the
maximum
definition
of
"
contribute
to."
We
believe
it
may
be
reasonable
for
States
to
use
a
lower
delta­
deciview
threshold
to
determine
whether
a
source
"
contributes
to"
impairment,
but
it
would
not
be
reasonable
33
A
threshold
of
0.1
deciviews
is
not
dictated
by
the
limitations
of
modeling,
as
model
output
can
be
generated
to
whatever
number
of
decimal
places
specified.

101
to
use
a
higher
threshold,
because
that
could
result
in
ignoring
perceptible
changes
from
BART
eligible
sources.

While
we
agree
that
it
may
be
reasonable
for
States
to
define
"
contribute"
as
an
impact
as
low
as
0.1
deciview,
we
can
see
no
basis
for
requiring
this
to
be
the
maximum
threshold
for
"
contribute."
33
We
disagree
with
commenters
who
believe
the
impacts
of
multiple
BART­
eligible
sources
should
be
aggregated
and
then
compared
to
the
0.5
delta­
deciview
threshold.
In
effect,

this
would
change
the
test
to
make
BART
applicable
to
sources
which
"
contribute
to
a
contribution"
and
as
such
would
run
afoul
of
the
American
Corn
Growers
decision.

Wherever
the
threshold
for
"
contribute
to"
is
set,
it
must
be
evaluated
on
a
source­
specific
basis.

Finally,
we
note
that
as
a
practical
matter,
because
all
sources
which
directly
"
cause"
impairment
will
by
definition
also
have
exceeded
the
standard
for
"
contributing"
to
impairment
and
therefore
be
subject
to
a
BART
determination,
it
is
not
necessary
to
establish
a
definitive
criterion
in
delta­
deciviews
for
the
"
causation"

element
of
"
cause
or
contribute."

We
disagree
that
the
use
of
the
24­
hour
maximum
modeled
visibility
impact
over
five
years
of
meteorological
data
is
102
overly
strict,
and
we
believe
that
the
comparison
of
this
impact,
to
the
cause
or
contribute
threshold,
to
determine
if
a
source
is
subject
to
BART
is
appropriate.
The
commenters
contend
that
the
maximum
modeled
24­
hour
impact,

or
impacts,
may
be
an
outlier
unduly
influenced
by
weather.

Finally,
we
disagree
that
separate
threshold
levels
should
be
established
based
on
geography
since
a
unit
change
in
visibility
expressed
in
deciviews,
perceived
or
measured,

is
the
same
regardless
of
geography.
The
change
in
deciviews,
which
is
compared
to
the
threshold,
is
based
on
the
percentage
change
that
occurs
in
existing
light
extinction
at
a
Class
I
area,
measured
relative
to
the
natural
conditions
estimate
at
the
Class
I
area.
Natural
conditions
may
be
different
at
each
Class
I
area,
and
so
a
given
change
in
light
extinction
may
result
in
a
higher
or
lower
percentage.
As
such,
a
source
may
"
pass"
the
threshold
test
in
one
Class
I
area,
but
"
fail"
in
another.

The
use
of
Natural
Conditions
in
determining
visibility
impacts
for
Reasonable
Progress
and
comparison
to
threshold
values
Background.
As
set
out
in
section
169A(
a)
of
the
CAA
and
stated
in
the
1999
Regional
Haze
Rule,
a
return
to
natural
visibility
conditions,
or
the
visibility
conditions
that
would
be
experienced
in
the
absence
of
human­
caused
impairment,
is
the
ultimate
goal
of
the
regional
haze
34
U.
S.
EPA.
September
2003.
Guidance
for
Estimating
Natural
Visibility
Conditions
Under
the
Regional
Haze
Rule.
http://
www.
epa.
gov/
ttncaaa1/
t1/
memoranda/
rh_
envcurhr_
gd.
pdf
This
document
has
estimates
of
default
conditions
as
well
as
measures
to
develop
refined
estimates
of
natural
conditions.

103
program.
To
implement
the
CAA
goal,
the
regional
haze
rule
requires
that
a
comparison
with
natural
conditions
for
the
20
percent
best
and
worst
days
to
calculate
"
reasonable
progress"
determinations.
Default
values
for
natural
visibility
conditions
are
provided
in
EPA
guidance,
34
which
also
offers
methods
for
calculating
more
refined
estimates
of
natural
visibility.
In
the
2004
reproposal
of
the
BART
guidelines,
we
proposed
that
changes
in
visibility,

expressed
in
deciviews,
should
be
determined
by
comparing
the
impact
from
a
single
source
to
natural
visibility
conditions.
That
impact
should
then
be
compared
to
a
threshold
impact,
also
expressed
in
deciviews,
to
assess
if
a
BART­
eligible
source
should
be
subject
to
a
BART
review.

Comments.
Opposing
commenters
said
that
a
return
to
natural
conditions
is
unattainable
as
it
would
require
the
elimination
of
every
manmade
source,
and
that
changes
should
be
compared
against
currently
existing
conditions.
They
added
that
true
"
natural
conditions"
cannot
be
verified,
do
not
account
for
manmade
emissions
from
other
countries,
and
are
not
a
realistic
target
for
improvement.
Further,
they
argued
that
natural
conditions
are
a
"
goal"
representing
a
104
benchmark
that
is
relevant
to
the
States'
determination,

under
the
regional
haze
program,
of
the
level
of
"
reasonable
progress"
to
achieve;
however
they
stated
that
there
is
no
legal
requirement
(
and
there
could
not
be
a
legal
requirement)
that
the
natural
conditions
goal
ultimately
must
be
achieved.
Several
commenters
added
that
current
visibility
conditions
make
more
sense
as
a
baseline
because
sources
that
are
subject
to
BART
today
will
likely
not
be
in
operation
in
the
2064
time
frame.
A
commenter
added
that
using
current
visibility
conditions
for
the
analysis
will
give
a
more
realistic,
real­
world
prediction
of
whether
controlling
the
source
pursuant
to
BART
will
actually
improve
visibility.
The
commenter
said
that
Congress
did
not
intend
for
sources
to
have
to
consider
retrofitting
controls
under
the
BART
provision
if
those
sources
currently
are
not
impacting
real­
world
visibility.
Other
utility
groups
stated
that
in
addition
to
international
emissions,

the
estimated
natural
visibility
conditions
failed
to
account
for
natural
phenomena
such
as
sea
salt,
wildfires,

and
natural
organics.
Commenters
noted
that
there
is
official
sanction
(
via
a
Department
of
Interior
letter
of
January
2003)
for
considering
meteorological
impairment
as
a
component
of
natural
conditions
in
permit
applications
under
the
Federal
Land
Managers
AQRV
Work
Group
guidance;
the
same
approach
should
be
allowed
for
BART
analyses.
One
commenter
noted
that
natural
visibility
estimates
will
be
revised
and
105
refined
over
time
and
it
would
be
unwise
to
compare
impacts
and
improvements
to
a
moving
baseline.

On
the
other
hand,
numerous
commenters
supported
the
use
of
natural
visibility
conditions
as
a
baseline
for
measuring
visibility
improvements.
Several
environmental
groups
said
that
any
increase
in
the
baseline
beyond
natural
visibility
conditions
will
unlawfully
distort
and
weaken
the
BART
requirement
by
effectively
raising
the
applicability
threshold
in
less
protected,
highly
polluted
areas,
which
would
be
illogical.
Further,
they
pointed
out
that
these
BART­
eligible
sources
clearly
are
contributing
to
the
very
manmade
visibility
impairment
that
the
Act
is
explicitly
designed
to
remedy
by
a
return
to
natural
conditions.
They
added
that
measuring
natural
conditions
as
opposed
to
baseline
conditions
is
a
more
appropriate
approach,
given
that
the
planning
goal
is
to
achieve
natural
visibility
by
the
end
of
the
program.
They
also
added
that
a
baseline
other
than
natural
conditions
would
never
assure
"
reasonable
progress".

Finally,
two
commenters
asked
for
clarification
on
the
values
for
natural
conditions
to
be
used
estimating
changes
in
visibility.
The
commenters
appeared
to
assume
that
we
intended
for
the
comparison
to
be
done
for
natural
visibility
conditions
on
the
20%
best
days.

Final
Rule.
We
disagree
with
commenters
saying
that
the
use
of
natural
conditions
as
the
baseline
for
making
35
See
also
our
explanation
of
the
CAA
goal
provided
in
the
regional
haze
rule
at
64
FR
xxxx.

36
Ibid.

106
visibility
impact
determinations
is
inappropriate.
The
visibility
goal
of
the
CAA
is
both
the
remedying
of
existing
impairment,
and
prevention
of
future
impairment.
The
court,

in
American
Corn
Growers,
upheld
our
interpretation
of
that
goal
as
the
return
to
natural
visibility
conditions.
35
Longterm
regional
haze
strategies
are
developed
to
make
"
reasonable
progress"
towards
the
CAA
goal,
and
States
must
demonstrate
reasonable
progress
in
their
regional
haze
State
implementation
plans
(
SIPs).
Since
the
BART
program
is
one
component
of
that
demonstration,
visibility
changes
due
to
BART
are
appropriately
measured
against
the
target
of
natural
conditions.
We
acknowledge
and
support
the
fact
that
estimates
of
natural
conditions
may
be
refined
in
the
future,
as
discussed
in
the
Guidance
for
Estimating
Natural
Visibility
Conditions
Under
the
Regional
Haze36.
As
is
the
case
in
all
EPA
rules
or
guidance,
if
our
understanding
of
facts
or
science
change,
we
will
review
them
at
the
time
that
they
do
to
determine
whether
the
changes
warrant
revisions
or
other
corrective
action.

In
establishing
the
goal
of
natural
conditions,

Congress
made
BART
applicable
to
sources
which
"
may
be
reasonably
anticipated
to
cause
or
contribute
to
any
107
impairment
of
visibility
at
any
Class
I
area".
Congress
used
sweeping
terms
(
cause
or
contribute
to
any
impairment
at
any
Class
I
area)
to
describe
the
low
triggering
threshold
for
BART
review.
Using
existing
conditions
as
the
baseline
for
single
source
visibility
impact
determinations
would
be
fundamentally
at
odds
with
the
low
triggering
threshold
for
BART
review,
because
it
would
create
the
following
untenable
paradox:
the
dirtier
the
existing
air,

the
less
likely
it
would
be
that
any
control
is
required
from
any
one
source.
This
is
true
because
of
the
nonlinear
nature
of
visibility
impairment.
In
other
words,
as
a
Class
I
area
becomes
more
polluted,
any
individual
source's
contribution
to
changes
in
impairment
becomes
geometrically
less.
Therefore
the
more
polluted
the
Class
I
area
would
become,
the
less
control
would
seem
to
be
needed
from
an
individual
source.
We
agree
that
this
kind
of
calculation
would
essentially
raise
the
"
cause
or
contribute"

applicability
threshold
to
a
level
that
would
never
allow
enough
emission
control
to
significantly
improve
visibility.

Such
a
reading
would
render
the
visibility
provisions
meaningless,
as
EPA
and
the
States
would
be
prevented
from
assuring
"
reasonable
progress"
and
fulfilling
the
statutorily­
defined
goals
of
the
visibility
program.

Conversely,
measuring
improvement
against
clean
conditions
37
U.
S.
EPA.
September
2003.
Guidance
for
Estimating
Natural
Visibility
Conditions
Under
the
Regional
Haze
Rule.
http://
www.
epa.
gov/
ttncaaa1/
t1/
memoranda/
rh_
envcurhr_
gd.
pdf
This
document
has
estimates
of
default
conditions
as
well
as
measures
to
develop
refined
estimates
of
natural
conditions.

108
would
ensure
reasonable
progress
toward
those
clean
conditions.

With
regard
to
BART­
eligible
sources
not
being
in
operation
for
the
duration
of
the
program,
a
State,
in
making
BART
determinations,
is
explicitly
directed
by
the
CAA
to
account
for
the
remaining
useful
life
of
a
source.

Thus,
States
may
factor
into
their
reasonable
progress
estimates
those
shut­
downs
that
are
required
and
effected
in
permit
or
SIP
provision.
In
addition,
as
provided
for
under
our
guidance37,
proper
accounting
for
international
emissions
and
natural
phenomena
is
in
the
5
year
SIP
progress
report,

not
in
the
setting
of
natural
visibility
estimates.

Finally,
these
final
BART
guidelines
use
the
natural
visibility
baseline
for
the
20%
best
visibility
days
for
comparison
to
the
"
cause
or
contribute"
applicability
thresholds.
We
believe
this
estimated
baseline
is
likely
to
be
reasonably
conservative
and
consistent
with
the
goal
of
natural
conditions.

[
Insert
Weather
information]

Modeling
Protocol
Background.
The
2004
guidelines
proposed
that
a
written
modeling
protocol
be
submitted
for
assessing
109
visibility
impacts
from
sources
at
distances
greater
than
200
km
from
a
Class
I
area.
The
proposal
indicated
that
the
protocol
should
include
a
description
of
the
methods
and
procedures
to
follow,
for
approval
by
the
appropriate
reviewing
authority.
Some
critical
items
to
include
in
the
protocol
are
meteorological
and
terrain
data,

sourcespecific
information
(
stack
height,
temperature,
exit
velocity,
elevation,
and
allowable
emission
rate
of
applicable
pollutants),
and
receptor
data
from
appropriate
Class
I
areas.

Comments.
All
of
the
comments
supported
the
development
of
a
written
modeling
protocol.
Industry,

Federal,
and
State
commenters
said
a
modeling
protocol
should
be
required
of
all
States
and
stakeholders
who
are
performing
the
BART
modeling
analysis.
Commenters
said
the
protocol
should
allow
all
interested
parties
(
e.
g.,
EPA,

States,
Federal
Land
Managers,
environmentalists,

stakeholders,
etc.)
an
opportunity
to
understand
the
modeling
approach
and
how
the
results
will
be
used,
and
should
provide
opportunity
for
comments
on
the
procedures
prior
to
the
publication
of
the
final
results.
One
State
commenter
said
that
a
modeling
protocol
should
be
developed
for
all
modeling
demonstrations,
but
agreed
with
the
exception
proposed
for
sources
located
less
than
200
km
from
a
Class
I
area
if
a
detailed
generic
national
protocol
is
developed
and
sources
are
required
to
follow
it.
Another
110
commenter
said
a
protocol
should
be
required
irrespective
of
the
distance
of
the
source
from
the
Class
I
area.

Many
utility
groups
commented
that
the
protocol
should
provide
States
with
flexibility,
and
that
the
choice
of
model
should
be
at
the
States'
(
or
RPOs')
discretion.
Some
commenters
stressed
that
it
is
important
that
states
and
sources
retain
the
flexibility
to
decide
how
to
set
up
and
run
the
selected
model,
while
others
asked
for
specific
guidance
on
the
setup
of
CALPUFF
or
other
approved
models,

including
on
specific
parameters
(
e.
g.
how
to
adjust
for
cases
where
sources
are
greater
than
200
km
from
a
Class
I
area).

Regarding
the
approval
of
a
modeling
protocol,
some
commenters
said
that
the
protocol
should
be
approved
by
EPA.

Others
stated,
however,
that
we
should
have
only
an
advisory
role
in
development
of
the
protocol.
They
said
that
States
are
in
a
better
position
to
determine
which
modeling
input
values
best
reflect
conditions
in
their
States.

Several
commenters
representing
environmental
groups
said
we
should
develop
a
CALPUFF
protocol
that
must
be
followed
and
should
include,
among
other
items,

meteorological
data
(
i.
e.,
where
available
5
years
of
data
should
be
used),
emissions
reported
for
the
same
meteorological
years,
documented
source
parameters,
model
physical
parameters,
and
assumed
background
concentrations
for
ozone
and
ammonia
(
based
on
nearby
reliable
observations
111
and/
or
regional
modeling
results).
They
added
that
a
protocol
developed
by
us
would
help
to
produce
consistent
BART
determinations
across
various
sources
and
geographic
areas
for
both
shorter
and
longer
distances.
FLMs
stated
that
this
is
also
an
appropriate
time
to
create
regional
modeling
platforms
for
CALPUFF,
which
would
allow
States
and
sources
to
run
the
model
more
expeditiously
and
more
consistently.
They
recommended
that
we
consider
a
multiagency
process
to
reach
agreement
on
an
appropriate
modeling
protocol
prior
to
allowing
BART
applicability
and
control
determinations
to
be
based
on
model
results.
FLMs
added
that
it
would
be
helpful
to
establish
a
national
procedure
for
this
process,
including
a
methodology
for
establishing
natural
background
conditions,
background
ammonia
concentrations,
and
determining
sulfuric
acid
emission
rates.
Such
a
process,
they
said,
could
reasonably
be
engaged
in
prior
to
deadlines
for
state
implementation
plans,
and
would
not
delay
implementation
of
the
BART
guidelines.
The
FLMs
noted
that
consistent,
nationally
applicable
guidance
is
essential,
and
that
once
it
is
developed,
virtually
no
deviations
should
be
allowed.

Finally,
they
added
that
the
CALPUFF
modeling
exercises
should
follow
the
Interagency
Workgroup
on
Air
Quality
Modeling
(
IWAQM)
Phase
2
Summary
Report
and
Recommendations
38Interagency
Workgroup
on
Air
Quality
Modelig
(
IWAQM)
Phase
2
Summary
Report
and
Recommendations
for
Modeling
Long
Range
Transport
Impacts,
U.
S.
Environmental
Protection
Agency,
EPA­
454/
R­
98­
019,
December
1998.

112
for
Modeling
Long
Range
Transport
Impacts38
recommendations,

but
that
we,
in
consultation
with
the
FLMs
and
States,

should
also
publish
additional
guidance
to
address
more
recent
issues
such
as
particle
speciation,
emission
rate
averaging
times,
and
"
natural
obscuration."
Another
State
commenter
said
that
The
Guideline
on
Air
Quality
Models
(
CFR
Part
51,
Appendix
W)
should
be
included
along
with
the
IWAQM
Report
as
a
reference
for
CALPUFF
setup.
One
RPO
commented
that
we
should
provide
data,
perhaps
using
example
facilities,
to
demonstrate
the
effect
of
the
process
so
that
States
can
get
a
better
feeling
for
which
sources
are
likely
to
fall
below
the
0.5
deciview
threshold.
This
would
help
States
understand
the
net
effect
of
all
of
the
parameters
chosen
in
the
exemption
process.

Commenters
also
said
that
we
should
continuously
revise
modeling
protocols
by
providing
a
modeling
clearinghouse
to
States,
and
further,
that
we
should
consider
new
models
for
use,
such
as
the
Community
Multiscale
Air
Quality
(
CMAQ)

model.

There
were
specific
comments
requesting
guidance
for
calculating
visibility
impacts
and
other
general
modeling
concerns.
One
technical
comment
was
that
the
guidelines
113
should
specify
that
the
IMPROVE
monitor
is
the
receptor
by
which
modeled
visibility
impacts
should
be
evaluated
with
the
CALPUFF
model.
Another
commenter
suggested
using
recent
scientific
evidence
to
update
the
light
extinction
coefficients
used
by
CALPUFF
to
calculate
visibility
changes.
These
commenters
also
stated
that
CALPUFF
might
be
improved
by
capping
the
relative
humidity
to
lower
values
than
are
currently
used.

Additional
commenters
representing
utility
organizations
discussed
how
to
identify
Class
I
areas
that
should
be
modeled.
They
said
that
the
guidelines
should
require
sources
to
model
only
the
nearest
Class
I
area
(
or
possibly
the
two
closest),
and
one
commenter
said
that
we
should
provide
a
reasonable
methodology
to
minimize
the
effort
needed
to
address
impacts
from
BART­
eligible
sources
on
multiple
Class
I
areas.

Final
Rule.
We
agree
that
a
modeling
protocol
should
be
required
for
all
modeling
demonstrations,
regardless
of
the
distance
from
the
BART­
eligible
source
and
the
Class
I
area
impacted.
We
are
therefore
dropping
the
200
km
and
greater
distance
requirement
and
will
require
the
modeling
protocol
for
all
modeling
cases.
As
in
the
proposal,
we
believe
that
potential
uncertainties
in
model
performance
may
be
greater
at
distances
greater
than
200
km
for
a
source.
However,
a
mechanism
(
i.
e.
a
modeling
protocol)
is
needed
in
all
modeling
situations
to
ensure
that
the
model
114
and
the
BART
exemption
test
are
applied
consistently
and
equitably
across
BART­
eligible
sources,
States,
regions,
and
nationwide.
A
modeling
protocol
for
all
cases
will
ensure
agreement
on
the
data
bases
used,
and
the
modeling
techniques
and
the
overall
technical
approach
used
prior
to
the
actual
analyses.
Thus,
misunderstandings
concerning
model
results
will
be
mitigated,
and
this
may
reduce
the
need
for
additional
analyses.
We
favor
coordination
among
States,
EPA
regions,
RPOs,
and
other
federal
agencies
to
agree
on
a
modeling
protocol(
s)
which
would
provide
consistent
application
of
the
model.
Such
coordination
may
relieve
the
administrative
burden
of
examining
and
approving
a
protocol
for
each
separate
BART­
eligible
source.
A
protocol
developed
by
and
acceptable
to
all
stakeholders
would
expedite
the
modeling
process
and
further
ensure
nationwide
consistency
in
application
of
the
model.

Coordinated
efforts
could
help
develop
standardized
data
sets
to
provide
the
added
benefit
of
reducing
the
cost
and
time
needed
for
a
modeling
analysis
and
facilitating
comparability
between
individual
analyses.
A
centralized
regional
database,
accessible
on
a
web
site,
may
provide
quality­
assured
upper
air,
surface,
precipitation,

monitoring,
land
use,
and
terrain
data
already
in
modelready
format.
Some
of
the
RPOs,
for
instance,
have
developed
data
sets
for
model
inputs
that
can
be
used
by
States,
further
reducing
time
and
cost
constraints
while
115
standardizing
the
model
input
requirements.
The
use
of
predefined
receptor
networks
developed
by
the
FLMs
can
also
relieve
resource
constraints.

In
developing
a
modeling
protocol,
we
also
encourage
States
to
use
the
framework
provided
for
model
setup
in
EPA's
IWAQM.
CALPUFF
model
users
may
find
default
settings
in
that
document
which
may
be
appropriate
for
their
modeling
situations
and
add
an
element
of
consistency
to
model
applications.
The
Guideline
on
Air
Quality
Models
(
CFR
Part
51,
Appendix
W)
also
provides
useful
guidance.

We
do,
however,
understand
and
agree
that
a
modeling
protocol
should
provide
flexibility
to
States
for
setting
up
and
running
the
model,
as
the
diversity
of
the
nation's
topography
and
climate,
and
variations
in
source
configurations
and
operating
characteristics,
dictate
against
a
strict
modeling
"
cookbook".
A
State
may
need
to
address
site­
specific
circumstances
at
individual
sources
potentially
affecting
a
specific
Class
I
area.
For
example,

a
State
may
have
hourly
relative
humidity
data
from
a
National
Weather
Service
site
or
ammonia
data
available
which
may
supplement
the
model
defaults.
States
should
work
with
the
appropriate
EPA
regional
office
and
Federal
Land
Managers
in
adjusting
the
model
input
parameters
if
necessary.
The
modeling
input
recommendations
in
the
IWAQM
report
are
designed
for
visibility
impact
applications,
and
39
http://
www.
src.
com/
calpuff/
calpuff1.
htm.

40Analysis
in
Support
of
Changes
to
the
Regional
Haze
Rule,
U.
S.
Environmental
Protection
Agency,
April
15,
2005,
Docket
No.
OAR­
2002­
0076.

116
those
defaults
allow
for
tailoring
for
a
given
application
(
e.
g.
puff
splitting).
The
model
developers
website39
also
has
a
series
of
frequently
asked
questions
with
answers
to
assist
users
in
tailoring
model
applications.

We
agree
that
we
should
have
only
an
advisory
role
in
development
of
the
protocol
as
the
States
better
understand
the
BART­
eligible
source
configurations
and
the
geophysical
and
meteorological
data
affecting
their
particular
Class
I
area(
s).

We
believe,
however,
that
EPA
should
have
final
approval
of
State
protocols
so
that
the
model,
and
the
BART
control
decision
which
depends,
in
part,
on
the
model
results,
is
applied
equitably
across
all
regions.
EPA
approval
will
help
ensure
that
vastly
different
modeling
results
are
not
produced
for
modeled
BART­
eligible
sources
that
have
similar
emission
configurations
and
operate
under
comparable
geophysical
and
meteorological
conditions.

In
the
protocol
approval
process,
we
support
the
idea
of
designing
example
runs,
as
we
have
done
in
our
example
analysis
for
EGUs40,
so
that
States
may
get
a
better
understanding
of
what
visibility
impacts
might
be
expected
from
a
particular
type
of
source
or
sources.
Once
a
117
protocol
has
been
approved,
a
State
may
be
able
to
use
example
runs
as
a
proxy
in
making
BART
determinations
which
could
potentially
eliminate
the
need
for
case­
by­
case
review
for
every
BART­
eligible
source.
In
developing
generic
or
specific
examples,
special
consideration
should
be
given
to
promoting
consistency
regarding
technical
decisions
such
as
settings
for
light
extinction
coefficients,
relative
humidity
caps,
and
background
pollutant
concentrations,
all
of
which
affect
visibility
estimates.
A
common
sense
approach
should
be
taken,
particularly
where
an
analysis
may
add
a
significant
resource
burden
to
a
State.
For
example,

if
there
are
multiple
Class
I
areas
in
relatively
close
proximity
to
a
BART­
eligible
source,
a
State
may
model
a
full
field
of
receptors
at
the
closest
Class
I
area.
Then
a
few
strategic
receptors
may
be
added
at
the
other
Class
I
areas
(
perhaps
at
the
closest
point
to
the
source,
a
receptor
at
the
highest
and
lowest
elevation
in
the
Class
I
area,
a
receptor
at
the
IMPROVE
monitor,
and
a
few
receptors
that
are
expected
to
be
at
the
approximate
plume
release
height).
If
the
highest
modeled
impacts
are
observed
at
the
nearest
Class
I
area,
a
State
may
choose
not
to
analyze
the
other
Class
I
areas
any
further
and
additional
analyses
might
be
unwarranted.

As
models
are
revised
and
advances
in
science
are
incorporated
into
the
models,
we
can
make
certain
that
revisions
to
protocols
are
made
accordingly.
We
will
work
118
closely
with
States
and
FLMs,
as
should
States;
we
expect
that
States
will
also
work
closely
with
FLMs
throughout
the
protocol
development
and
approval
process.
We
expect
a
similar
protocol
development
and
approval
process
for
other
models
that
may
be
used,
once
those
models
are
developed
to
predict
and
track
single
source
impacts,
demonstrate
acceptable
model
performance,
and
are
approved
by
us
for
use.
States
should
contact
the
appropriate
FLM
and
EPA
regional
office
for
the
latest
guidance
and
modeling
updates.

Alternatives
for
determining
visibility
impacts
from
individual
sources
Background.
In
the
2004
reproposal,
we
requested
comment
on
the
following
alternatives
to
CALPUFF
modeling
for
determining
whether
individual
sources
cause
or
contribute
to
visibility
impairment:
look­
up
tables
developed
from
screening­
level
air
quality
modeling;
running
CALPUFF
in
a
simpler
screening
mode
than
the
preferred
approach;
a
source
ranking
methodology;
and
an
emissions
divided
by
distance
(
Q/
D)
method.
Except
for
the
simplified
CALPUFF
approach,
all
alternatives
were
based
on
developing
a
relationship
between
source
emissions
and
the
source's
distance
to
a
Class
I
area.
Each
of
these
approaches
was
intended
to
reduce
the
resource
burden
on
States.
41Analysis
of
the
CALMET/
CALPUFF
Modeling
System
in
a
Screening
Mode,
EPA­
454/
R­
98­
010,
November
1998.

119
Comments.
Some
commenters
supported
the
use
of
alternative
approaches,
while
others
suggested
that
the
alternatives
could
be
used
either
in
conjunction,
or
in
hierarchical
fashion,
with
modeling
approaches.
Many
commenters
were
opposed
to
their
use.
The
opposing
comments
were
consistent
in
stating
that
the
alternatives
were
inappropriate
because
they
did
not
account
for
important
factors
such
as
terrain,
local
meteorological
data,

prevailing
wind
directions
(
which
influence
pollutant
transport),
and
differences
in
stack
release
parameters.

Commenters
added
that
there
is
no
direct
connection
between
emissions,
distance,
and
visibility
impairment,
and
that
the
methods
treat
SO2
and
NOx
equally
for
impairment
estimates.

Final
Rule.
We
disagree
that
the
alternatives
are
entirely
inappropriate,
but
we
share
most
of
the
concerns
articulated
by
the
opposing
commenters.
We
believe
that
alternatives
should
not
be
used
to
exempt
a
source
from
BART
review
without
more
rigorous
evaluations
and
sensitivity
tests
showing
that
the
results
are
at
least
as
conservative
as
the
CALPUFF
model.
We
know
of
at
least
one
study
showing
that,
for
one
location
and
for
one
year,
there
is
no
guarantee
that
the
simplified
CALPUFF
technique
is
as
conservative
as
the
preferred
approach41.
While
we
are
not
adopting
any
specific
alternative
to
modeling
we
believe
a
120
State
may
develop
its
own
alternative
approach
for
determining
that
a
source
would
be
subject
to
BART,
provided
that
it
is
demonstrated
to
provide
a
sufficient
basis
to
determine
clearly
that
the
source
causes
or
contributes
to
visibility
impairment,
or
that
more
refined
analysis
is
warranted.
We
recommend
that
alternatives
not
be
used
to
waive
the
single
source
BART
applicability
determination.

Use
of
an
alternative
approach
could
be
a
conservative
nonmodeling
method
for
easing
a
State's
resource
burden.
We
believe
conservatism
is
needed
because
of
the
purpose
of
the
test:
i.
e.
solely
to
determine
if
a
closer
look
at
the
source
is
warranted.

E.
The
BART
Determination
Prcess
Background.
CAA
section
169A(
g)(
7)
directs
States
to
consider
five
factors
in
making
BART
determinations.
The
regional
haze
rule
codified
these
factors
in
40
CFR
51.308(
e)(
1)(
ii)(
B),
which
directs
States
to
identify
the
"
best
system
of
continuous
emissions
control
technology"

taking
into
account
"
the
technology
available,
the
costs
of
compliance,
the
energy
and
nonair
quality
environmental
impacts
of
compliance,
any
pollution
control
equipment
in
use
at
the
source,
and
the
remaining
useful
life
of
the
source."
Section
IV.
of
the
BART
Guidelines
provides
a
step­
by­
step
guide
to
a
conducting
a
BART
determination
which
takes
these
factors
into
account.
121
This
section
of
the
preamble
addresses
a
number
of
issues
relative
to
the
process
for
conducting
a
BART
determination
contained
in
Section
IV
of
the
BART
Guidelines.

1.
What
is
meant
by
"
technical
feasibility
of
the
control
options"
in
step
2
of
the
BART
determination?

Comments.
We
received
several
comments
on
this
discussion,
both
on
the
2001
proposal
and
on
the
2004
reproposal.
One
commenter
recommended
that
the
concept
of
available
technology
for
regional
haze
should
be
expanded
to
include
those
in
the
pilot
scale
testing
phase,
because
these
guidelines
will
precede
the
installation
of
controls
by
about
10
years.
Other
commenters
believed
that
the
discussion
of
technical
feasibility
introduced
terms
and
concepts
that
were
not
clear,
for
example,
what
is
meant
by
"
commercial
demonstration."
One
commenter
raised
issues
with
deeming
technologies
used
in
foreign
countries
"
available"
unless
their
performance
has
been
demonstrated
in
the
United
States.
A
few
commenters
expressed
concern
with
the
provision
in
the
guidelines
that
new
technologies
should
be
considered
up
to
the
time
of
a
State's
public
comment
period
on
the
BART
determination.
The
commenter
believed
that
this
could
create
an
endless
review
loop
for
States
if
new
technologies
continually
became
available.
122
Final
rule.
In
the
final
guidelines,
we
have
retained
the
language
that
was
in
the
proposed
guidelines.
Because
the
guidelines
call
for
consideration
of
technologies
that
become
available
by
the
time
of
the
State's
public
comment
process
on
the
BART
determination,
technologies
should
be
considered
that
become
available
well
after
we
finalize
the
BART
guidelines.
We
continue
to
believe
that
States
need
not
consider
technologies
to
be
"
commericially
available"
if
they
are
only
in
the
pilot
test
phase
as
of
the
date
the
State
conducts
its
public
comment
period.
We
also
note,
for
clarity,
that
the
Guidelines
state
that
technologies
need
to
be
both
licensed
and
commercially
available
(
i.
e.

commercially
demonstrated
and
sold).

2.
What
is
meant
by
"
ranking
of
all
technically
feasible
control
options"
in
step
2
of
the
BART
determination?

Comments.
The
comments
on
this
section
of
the
guidelines,
as
proposed
in
2001
and
reproposed
in
2004,

generally
were
directed
at
issues
related
to
sources
emitting
more
than
one
pollutant.
While
our
proposed
guidelines
call
for
a
separate
ranking
for
each
pollutant,
a
number
of
comments
suggested
approaches
for
considering
combinations
of
pollutants
in
developing
a
ranking
of
control
measures.
Some
comments
recommended
that
the
guidelines
consider
control
measures
favorably
if
the
total
123
visibility
impairing
pollutant
reduction
is
greater
than
for
a
technology
reducing
emissions
of
only
one
pollutant.

Other
comments
suggested
developing
a
weighting
approach.

In
this
approach,
a
method
would
be
developed
under
which
emissions
of
pollutants
with
greater
contributions
to
light
extinction
would
be
given
a
greater
weight
than
emissions
of
other
pollutants.

Final
rule.
We
agree
with
comments
that
there
could
be
situations
where
the
control
technology
selected
as
BART
could
involve
judgments
on
controls
for
a
combination
of
pollutants.
Nonetheless,
we
continue
to
believe
that
the
most
practical
approach
to
taking
this
into
account
as
a
general
matter
is
to
begin
with
a
separate
ranking
for
each
pollutant.
We
do
not
believe
that
it
would
be
feasible
to
develop
a
weighted
ranking
system
given
the
regional
differences
in
contributions
to
extinction
from
various
constituents.
As
noted
above,
however,
States
may
find
that
it
is
appropriate
to
place
greater
overall
emphasis
on
controlling
emissions
of
direct
PM,
SO2,
and
NOx
than
on
controlling
emissions
of
VOCs
and
ammonia.

3.
How
should
the
costs
of
control
be
estimated
in
step
4
of
the
BART
determination?

Comments.
This
section
of
the
guidelines
remained
unchanged
between
the
2001
proposal
and
the
2004
reproposal.

Comments
varied,
ranging
from
questioning
the
reliance
on
124
EPA's
Air
Pollution
Control
Cost
Manual
(
hereafter
called
the
"
Control
Cost
Manual")
to
requesting
that
we
not
include
the
concept
of
incremental
cost
effectiveness
in
the
guidelines.
A
commenter
expressed
concerns
that
incremental
cost
effectiveness
calculations,
the
cost
of
implementing
each
succeeding
control
option,
is
too
dependent
on
the
number
of
interim
options
included
in
the
analysis.
Moreover,
the
commenter
believed
that
incremental
cost
calculations
increase
the
complexity
of
the
analysis,
and
they
also
increase
the
possibility
for
inconsistent
cost
results.

Final
rule.
We
have
finalized
this
section
of
the
guidelines
with
minor
changes
to
how
it
was
proposed.
We
believe
that
the
Control
Cost
Manual
provides
a
good
reference
tool
for
cost
calculations
and
it
serves
to
provide
for
consistency.
If
there
are
elements
or
sources
that
are
not
addressed
by
the
Control
Cost
Manual
or
there
are
additional
cost
methods
that
could
be
used,
we
believe
that
these
could
serve
as
useful
supplemental
information
to
that
available
from
using
the
methods
in
the
Control
Cost
Manual.

In
addition,
the
guidelines
continue
to
include
both
average
and
incremental
costs.
We
continue
to
believe
that
both
average
and
incremental
costs
provide
information
useful
for
making
control
determinations.
However,
we
believe
that
these
techniques
should
not
be
misused.
For
125
example,
a
source
may
be
faced
with
a
choice
between
two
available
control
devices,
control
A
and
control
B,
where
control
B
achieves
slightly
greater
emission
reductions.

The
average
cost
(
total
annual
cost/
total
annual
emission
reductions)
for
each
may
be
deemed
to
be
reasonable.

However,
the
incremental
cost
(
total
annual
costA­
B
/
total
annual
emission
reductionsA­
B)
of
the
additional
emission
reductions
to
be
achieved
by
control
B
may
be
very
great.

In
such
an
instance,
it
may
be
inappropriate
to
choose
control
B,
based
on
its
high
incremental
costs,
even
though
its
average
cost
may
be
considered
reasonable.

Finally,
it
is
important
to
note
that,
while
BART
determinations
are
focused
at
individual
sources,
it
is
likely
that
in
response
to
SIP
requirements,
States
will
be
making
BART
determinations
for
many
units
in
a
subject
source
category
all
at
the
same
time.
In
doing
so,
States
are
likely
to
compare
costs
across
each
source
category
as
well
as
looking
at
costs
for
individual
units
in
order
to
respond
to
SIP
requirements
in
an
efficient
manner
(
from
the
State's
perspective).
This
also
mirrors
how
we
used
cost
information
in
setting
the
presumptive
limits
for
EGUs
described
earlier.

4.
How
should
"
remaining
useful
life"
be
considered
in
step
4
of
the
BART
determination?

Comments.
We
received
a
number
of
comments
on
the
issue
of
remaining
useful
life,
both
on
the
2001
proposal
126
and
on
the
2004
reproposal.
One
commenter
asserted
that
remaining
useful
life
should
not
be
considered
in
the
cost
analysis
and
that
if
a
source
is
in
operation
at
the
time
of
a
State's
SIP
submittal,
it
must
have
plans
to
install
controls.
Other
commenters
believed
that,
to
the
extent
that
assertions
regarding
a
plant's
remaining
useful
life
influences
the
BART
decision,
there
must
be
an
enforceable
requirement
for
the
plant
to
shut
down
by
that
date.
Other
comments
questioned
whether
Congress
intended
enforceable
restrictions
in
order
to
take
into
account
the
remaining
useful
life
and
whether
EPA
had
the
authority
under
the
CAA
to
require
plant
shutdowns.

A
number
of
comments
were
received
regarding
our
request
for
comments
on
how
to
provide
flexibility
for
situations
where
market
conditions
change.
Some
comments
interpreted
this
provision
as
a
loophole
that
would
allow
sources
to
continue
operation
for
a
number
of
years
without
BART.
Another
comment
supported
the
concept
of
allowing
a
source
to
later
change
its
mind,
so
long
as
BART
is
installed.

Final
rule.
We
have
retained
the
approach
in
the
proposed
guidelines,
including
the
provision
for
flexibility
for
sources
to
continue
operating,
with
BART
in
place,

should
conditions
change.
We
believe
that
the
CAA
mandates
consideration
of
the
remaining
useful
life
in
the
analysis
and
that
effects
on
costs
may
not
be
disregarded.
We
127
believe
that,
because
the
source
would
not
be
allowed
to
operate
after
the
5­
year
point
without
such
controls,
the
option
for
providing
flexibility
would
not
create
a
loophole
for
sources.
Moreover,
any
source
operating
after
this
point
without
BART
controls
in
place
would
be
subject
to
enforcement
actions
for
violating
the
BART
limit.
For
any
source
that
does
not
agree
to
shut
down
before
the
5­
year
point,
the
State
should
identify
a
specific
BART
emission
limit
that
would
apply
after
this
point
in
time.

5.
How
should
"
visibility
impacts"
be
considered
in
step
5
of
the
BART
determination?

Background.
The
fifth
statutory
factor
addresses
the
degree
of
improvement
in
visibility
which
may
reasonably
be
anticipated
to
result
from
the
use
of
the
"
best
control
technology"
for
sources
subject
to
BART.
The
2004
reproposal
focuses
on
the
use
of
single
source
emissions
modeling
to
evaluate
the
BART
control
options.
As
part
of
the
BART
determination,
we
proposed
that
a
State
or
individual
source
would
run
CALPUFF,
or
another
EPA­
approved
model,
to
estimate,
in
deciviews,
a
BART
source's
visibility
impact
at
a
Class
I
area.
The
source
would
run
the
model
once
using
its
allowable
emission
rates,
and
then
again
at
the
various
post­
control
emissions
rates
being
evaluated
for
the
BART
determination.
The
24­
hour
model
results
would
then
be
tabulated
for
the
pre­
and
post­
control
scenarios,

for
the
average
of
the
20
percent
worst
modeled
days
at
each
128
receptor,
over
the
time
period
of
meteorology
modeled.
The
difference
in
the
averages
for
each
receptor
is
the
expected
degree
of
improvement
in
visibility.
Alternatively,
the
proposal
requested
comment
on
the
option
of
using
the
hourly
modeled
impacts
from
CALPUFF
at
each
receptor
and
determining
the
improvement
in
visibility
based
on
the
number
of
hours
above
the
0.5
deciview
threshold
for
both
the
pre­
and
post­
control
model
runs.
We
also
requested
comment
on
combinations
of
the
proposed
and
alternative
options
and
on
the
use
of
the
simpler
screening
version
of
CALPUFF
to
do
the
analysis.

Comments.
Several
environmental
groups
said
that
issues
relating
to
the
determination
of
visibility
improvement
for
evaluating
BART
controls
are
in
many
ways
the
same
as
for
determining
which
BART­
eligible
sources
are
subject
to
BART.
Thus,
the
commenter
pointed
out,
the
issues
concerning
the
BART
applicability
test,
discussed
in
section
D.,
are
all
equally
applicable
here,
including
comments
on:
using
the
0.5
deciview
threshold
on
an
aggregate
basis
for
determining
visibility
impairment
and
potential
exemption
for
BART­
eligible
sources,
use
of
a
natural
visibility
baseline
versus
current
visibility,
using
a
substantially
lower
deciview
threshold
than
0.5
deciviews
to
determine
the
contribution
to
visibility
impairment
by
an
individual
source,
and
demonstration
of
those
thresholds
by
129
means
of
appropriate
modeling
rather
than
other
less
reliable
and
more
subjective
techniques.

An
industry
commenter
claimed
that
the
Corn
Growers
case
emphasized
the
fact
that
the
CAA
clearly
provides
that
BART
determinations
should
balance
the
visibility
benefits
of
controls
comprehensively
against
their
burdens;
the
commenter
noted
that
this
is
not
mentioned
in
our
proposal;

the
commenter
said
that
although
the
proposal
would
allow
States
to
run
the
CALPUFF
model,
it
fails
to
specify
how
they
might
consider
the
results.

One
State
commenter
opposed
the
use
of
visibility
modeling
for
the
purpose
of
informing
the
choice
of
control
option,
stating
that
it
is
unnecessary,
confusing
and
without
adequate
standards
or
guidance
for
implementation.

The
State
added
that
the
analysis
of
control
options
in
the
BART
process
should
yield
the
greatest,
most
cost­
effective
control
efficiency
for
NOx
and
SO2
at
or
above
our
presumptive
levels
of
control.
Moreover,
it
said
that
analysis
of
the
degree
of
visibility
improvement
may
result
in
very
small
increments
of
visibility
improvements
within
Class
I
areas
from
an
individual
source,
thus
tilting
the
selection
to
the
lower
control
efficiency
option.
The
State
added
that
we
should
remove
this
criterion
from
the
analysis
to
ensure
that
the
best
cost
effective
controls
will
result.

Another
State
agency
said
that
modeling
impacts
should
not
130
be
considered
in
BART
determinations
because
they
are
not
considered
when
determining
BACT
for
the
PSD
program.

A
variety
of
commenters
pointed
out
several
areas
where
the
guidelines
should
be
improved
or
clarified
in
regard
to
the
degree
of
visibility
improvement
determination:

°
We
should
clarify
that
the
analysis
is
pollutantspecific
(
e.
g.,
the
modeling
evaluation
of
a
BART
control
option
for
SO2
reduction
should
not
be
combined
with
the
modeling
evaluation
of
a
BART
control
option
for
NOx.)

°
We
should
clarify
that
only
the
closest
Class
I
area
must
be
modeled.

°
We
should
describe
CALPUFF
as
one
possible
model
to
use,
rather
than
as
the
only
model
that
may
be
used.

°
States
and
sources
should
have
the
flexibility
to
perform
multiple
modeling
runs
based
on
different
levels
of
available
control.

°
Predicted
visibility
improvements
that
are
imperceptible
should
be
given
no
weight
in
determining
the
level
of
control
that
constitutes
BART.

°
States
should
be
allowed
to
establish
a
factor
for
the
required
degree
of
visibility
improvement.

Several
industry
and
utility
commenters
expressed
concern
about
using
allowable
emission
rates
to
predict
visibility
impacts
for
BART
control
options;
they
argued
that
actual
emission
rates
should
be
considered
instead.
131
Three
commenters
stated
that
we
must
make
clear
that
States
should
use
emission
rates
that
will
be
permissible
at
the
time
BART
controls
take
effect,
not
current
emissions
rates.

Additional
comments
from
utilities,
industry,
and
one
State
opposed
the
approach
wherein
the
results
from
the
20
percent
worst
modeled
days
(
pre­
and
post­
control)
were
used
to
evaluate
the
visibility
improvements
expected
from
the
various
control
options.
Some
believed
this
was
too
stringent,
while
others
said
it
was
not
stringent
enough.

Two
utilities
added
that
the
criteria
should
use
the
20
percent
worst
days
based
on
monitored
data,
not
modeled
data.
An
environmental
group
stated
that
sources
should
not
be
limited
to
just
the
worst
days,
but
the
improvements
should
be
based
upon
controls
reducing
visibility
impairment
on
any
day.
The
commenter
added
that
this
rationale
ignores
the
middle
60
percent
of
days
in
which
visibility
may
worsen,
because
sources
may
increase
emissions
on
these
days
as
a
trade­
off
for
cutting
emissions
on
the
worst
days.
The
commenter
further
argued
that
there
are
no
data
to
support
our
assertion
that
improvement
on
the
worst
days
means
improvement
on
other
days.
They
noted
that
default
"
natural
condition"
deciview
values
for
Class
I
areas
in
our
natural
conditions
guidance
exist
only
for
the
average
of
the
20
percent
best
and
worst
days.
The
commenter
added
that
we
used
the
average
default
natural
conditions
(
for
the
20%
132
best
days)
for
the
visibility
impairment
analysis,
but
there
are
no
default
"
maximum
24­
hour"
values
in
the
guidance.

Nine
commenters
supported
implementation
of
visibility
improvement
thresholds,
which
were
not
proposed
in
2004.
A
State
commenter
said
it
is
unclear
how
the
modeled
net
visibility
improvement
would
be
specifically
utilized
in
the
BART
analysis,
and
requested
a
target
level
of
improvement
or
a
de
minimis
level
by
which
to
measure
improvement.
Two
industry
commenters
suggested
alternatives
to
the
24­
hour
value.
One
said
that
setting
a
threshold
for
comparison,
as
in
the
BART­
applicability
test,
is
more
appropriate
than
the
overall
comparison
of
the
20
percent
worst
case
days,
and
that
the
threshold
for
comparison
should
be
on
at
least
a
daily
average
(
or
longer),
not
an
hourly
average,
due
to
the
possibility
of
short­
term
spikes
based
on
certain
meteorological
conditions.

These
commenters
also
said
that
a
comparison
of
the
number
of
days
above
or
below
a
certain
threshold
is
preferable
since
below
a
certain
threshold,
the
impacts
of
visibility
are
not
perceptible;
unlike
concentration
levels
of
certain
pollutants
(
i.
e.,
ozone)
which
do
not
have
a
threshold
below
which
there
are
no
effects,
there
are
concentration
levels
of
particulate
below
which
there
is
no
visibility
impact.
They
also
asserted
that
comparing
the
number
of
days
would
allow
for
a
more
complete
picture
of
how
controls
would
potentially
improve
visibility.
As
noted
133
previously,
a
small
number
of
unusual
meteorological
conditions
can
produce
significant
spikes
on
a
single
day
or
days.
Since
the
overall
goal
of
the
regional
haze
rule
is
long­
term
visibility
improvement,
they
said
that
a
comparison
of
the
total
number
of
days
exceeding
a
threshold
over
multiple
years
will
provide
a
better
overall
indicator
of
visibility
improvement.
One
commenter
suggested
that
if
we
retain
the
maximum
24­
hour
value
for
the
visibility
impairment
analysis,
we
should
at
least
allow
the
use
of
only
1
year,
rather
than
5
years,
of
meteorological
data.

That
would
simplify
the
modeling
and
would
lessen
the
chance
that
one
day
with
atypical,
extreme
conditions
would
dictate
the
result.

One
FLM
supported
our
proposed
method
to
determine
visibility
improvement
associated
with
installation
of
BART.

However,
with
regard
to
the
use
of
hourly
data
instead
of
24
hour
data
for
the
degree
of
visibility
improvement
assessment,
another
FLM
said
that
while
hourly
model
data
are,
by
their
nature,
less
reliable
in
predicting
actual
conditions,
a
measure
that
reports
the
total
number
of
hours
above
a
given
threshold
would
still
be
a
useful
measure
of
the
long­
term
effect
of
BART
control.
They
said
we
should
require
States
to
report
a
combination
of
measures
of
the
visibility
improvement
expected
from
BART.
Such
measures
would
be
the
change
in
the
20
percent
worst
days
as
well
as
a
metric
that
examines
the
amount
of
time
during
a
year
that
42
Pitchford,
M.
and
Malm,
W.,
"
Development
and
Applications
of
a
Standard
Visual
Index,"
Atmospheric
Environment,
V.
28,
no.
5,
March
1994.

43
Henry,
R.
C.
"
Just­
Noticeable
Differences
in
Atmospheric
Haze",
Journal
of
the
Air
&
Waste
Management
Association,
52:
1238­
1243,
October
2002.

134
the
source's
visibility
impact
would
exceed
a
threshold
with
and
without
BART.

Another
utility
commenter
added
that,
if
a
BART
control
option
would
result
in
no
perceptible
improvement
in
visibility
at
a
Class
I
area,
then
it
is
not
a
costeffective
option.
This
commenter
said
that
based
on
Pitchford
and
Malm
(
1994)
42
and
Henry
(
2002)
43
a
2
deciview
threshold
of
perception
would
be
appropriate,
with
a
1
deciview
threshold
providing
a
margin
of
safety.
Another
commenter
said
that
we
should
clarify
that
visibility
improvement
differences
among
BART
control
options
should
be
considered
insignificant
if
the
differences
are
less
than
the
perceptibility
threshold
level,
which
should
be
set
in
excess
of
1
deciview.
Other
commenters
said
the
minimum
threshold
should
be
1
deciview.

Final
Rule.
We
disagree
with
the
comment
that
modeling
should
not
be
part
of
a
BART
review
because
it
is
not
considered
for
BACT.
CAA
section
169A(
g)(
2)
clearly
requires
an
evaluation
of
the
expected
degree
of
improvement
in
visibility
from
BART
controls.
All
five
statutory
factors,
including
cost­
effectiveness
and
expected
135
visibility
improvement,
should
be
reflected
in
the
level
of
BART
control
that
the
State
implements.
We
believe
that
modeling,
which
provides
model
concentration
estimates
that
are
readily
converted
to
deciviews,
is
the
most
efficient
way
to
determine
expected
visibility
improvement.

For
the
purposes
of
determining
visibility
improvement,

States
may
evaluate
visibility
changes
on
a
pollutantspecific
basis.
If
expected
improvement
is
shown
from
the
various
control
choices,
the
State
can
weigh
the
results
with
the
other
four
BART
determination
factors
when
establishing
BART
for
a
particular
source.
For
example,
a
State
can
use
the
CALPUFF
model
to
predict
visibility
impacts
from
an
EGU
in
examining
the
option
to
control
NOx
and
SO2
with
SCR
technology
and
a
scrubber,
respectively.
A
comparison
of
visibility
impacts
might
then
be
made
with
a
modeling
scenario
whereby
NOx
is
controlled
by
combustion
controls.
If
expected
visibility
improvements
are
significantly
different
under
one
control
scenario
than
under
another,
then
a
State
may
use
that
information,
along
with
information
on
the
other
BART
factors,
to
inform
its
BART
determination.

Even
though
the
visibility
improvement
from
an
individual
source
may
not
be
perceptible
(
i.
e.
the
expected
improvement
may
be
less
than
0.5
deciviews),
it
should
still
be
considered
in
setting
BART
because
the
contribution
to
haze
may
be
significant
relative
to
other
source
136
contributions
in
the
Class
I
area.
Thus,
we
disagree
that
the
degree
of
improvement
should
be
contingent
upon
perceptibility.
Failing
to
consider
less­
than­
perceptible
contributions
to
visibility
impairment
would
ignore
the
CAA's
intent
to
have
BART
requirements
apply
to
sources
that
contribute
to,
as
well
as
cause,
such
impairment.

We
disagree
that
actual
emission
rates
should
be
used
to
predict
visibility
impacts.
A
source
may
be
operating
at
its
full
permitted
level
at
any
time,
and
visibility
impairment
is
appropriately
measured
against
that
allowable
emission
rate
(
hourly),
as
visitors
may
experience
visibility
in
Class
I
areas
at
any
time.

We
do
not
believe
that
using
the
maximum
24­
hour
average
over
the
meteorological
period
modeled
(
three
or
five
years)
is
too
restrictive
in
determining
if
a
BARTeligible
source
is
subject
to
a
BART
review,
or
for
evaluating
the
degree
of
visibility
improvement
expected
from
BART
reductions.
A
scenic
vista
is
observed
instantaneously,
which
may
suggest
an
even
shorter
averaging
time
for
estimating
impairment;
models,
however,
must
account
for
chemical
transformations
and
long
range
transport
which
occur
over
time.
A
24­
hour
averaging
time
may
be
the
most
practical
way
to
simulate
chemical
and
physical
processes,
but
we
do
agree
that
averaging
times
of
even
1
hour
have
merit.
[
insert
information
regarding
137
modeling
meteorology]
In
response
to
the
comment
about
reliance
on
monitoring
rather
than
modeling
receptors,
a
monitoring
site
may
not
coincide
with
the
location
of
the
maximum
modeled
impact
in
a
Class
I
area.
Consequently,
we
believe
that
sole
reliance
on
monitored
data
to
assess
maximum
visibility
impacts
is
not
appropriate.
In
addition,

monitoring
data
may
not
be
useful
for
predicting
future
visibility
impacts.

We
agree
with
commenters
that
the
difference
between
the
pre­
and
post­
control
scenarios
on
the
average
of
the
20
percent
worst
modeled
days
may
not
be
the
best
approach
in
determining
visibility
improvement.
The
importance
of
an
average
as
a
data
point
can
depend
on
the
variation
in
the
data
as
a
whole.
In
other
words,
there
may
be
a
few
days
of
very
high
impairment
in
a
Class
I
area,
but
many
days
of
lower
impairment.
The
average
would
tend
towards
the
lower
values,
but
that
is
not
meaningful
to
an
observer
that
may
be
experiencing
impairment
on
one
of
the
worst
days.
Also,

average
visibility
is
considered
uniformly
across
the
Class
I
area,
and
in
this
context,
it
is
an
average
due
to
the
pollutant
contributions
of
all
sources
around
the
Class
I
area
(
not
the
average
due
just
to
one
source,
and
the
average
of
the
20%
worst
modeled
days
would
be
of
minimal
value).
138
Because
each
Class
I
area
is
unique,
we
believe
States
should
have
flexibility
to
assess
visibility
improvements
due
to
BART
controls
by
one
or
more
methods,
or
by
a
combination
of
methods,
and
we
agree
with
the
commenters
suggestions
to
do
so.
Although
the
analysis
using
the
20
percent
average
worst
modeled
days
(
pre­
and
post­
control)

may
not
capture
the
data
maxima,
its
use
may
be
reasonable
in
evaluating
the
fifth
factor
as
part
of
its
BART
determination.
However,
we
believe
that
it
is
important
to
consider
the
frequency,
magnitude,
and
duration
components
of
impairment
when
making
the
visibility
improvement
determination;
both
"
average"
and
"
peak"
tests
are
crucial
in
making
the
assessment.

We
agree
with
the
suggestion
that
the
use
of
a
comparison
threshold,
as
is
done
for
determining
if
BARTeligible
sources
should
be
subject
to
a
BART
determination,

is
an
appropriate
way
to
evaluate
visibility
improvement.

However,
we
believe
the
States
should
have
flexibility
in
setting
absolute
thresholds,
target
levels
of
improvement,

or
de
minimis
levels
since
the
deciview
improvement
must
be
weighed
among
the
five
factors,
and
States
are
free
to
determine
the
weight
and
significance
to
be
assigned
to
each
factor.
For
example,
a
0.3
deciview
improvement
may
merit
a
stronger
weighting
in
one
case
versus
another,
so
one
"
bright
line"
may
not
be
appropriate.
44CALPUFF
Analysis
in
Support
of
the
Regional
Haze
Rule,
U.
S.
Environmental
Protection
Agency,
April
15,
2005,
Docket
No.
OAR­
2002­
0076.

45
Ibid.

139
In
addition,
comparison
thresholds
can
be
used
in
a
number
of
ways
in
evaluating
visibility
improvement
(
e.
g.

the
number
of
days
or
hours
that
the
threshold
was
exceeded,

a
single
threshold
for
determining
whether
a
change
in
impacts
is
significant,
a
threshold
representing
an
x
percent
change
in
improvement,
etc.).
In
our
example
modeling
analysis
of
a
hypothetical
source44,
we
used
three
different
24­
hour
thresholds
(
1.0,
0.5,
and
0.1
deciviews)

and
examined
the
number
of
days
that
those
thresholds
were
exceeded
for
a
source
with
a
90
percent
change
in
SO2
emissions
(
i.
e.
10,000
TPY
and
1,000
TPY).
The
number
of
days
that
the
thresholds
were
exceeded
in
the
10,000
TPY
case
was
substantial,
and
the
visibility
improvement
due
to
the
reduction
in
emissions
was
dramatic
(
i.
e.
the
number
of
days
exceeding
the
thresholds
dropped
considerably)
45.

Other
ways
that
visibility
improvement
may
be
assessed
to
inform
the
control
decisions
would
be
to
examine
distributions
of
the
hourly
or
daily
impacts,
compare
the
hourly
values
to
thresholds,
determine
if
the
time
of
year
is
important
(
e.
g.
high
impacts
are
occurring
during
tourist
season),
or
simply
compare
the
worst
case
days
for
the
pre­
140
and
post­
control
runs.
States
may
develop
other
methods
as
well.

6.
In
what
sequence
should
alternatives
be
assessed
in
step
5
of
the
BART
determination?

Background.
Both
the
2001
proposal
and
the
2004
reproposal
requested
comments
on
two
options
for
evaluating
the
ranked
options.
Under
the
first
option,
which
was
the
preferred
approach,
States
would
use
a
sequential
process
for
conducting
the
impacts
analysis,
beginning
with
a
complete
evaluation
of
the
most
stringent
control
option.

If
a
State
determines
that
the
most
stringent
alternative
in
the
ranking
does
not
impose
unreasonable
costs
of
compliance,
taking
into
account
both
average
and
incremental
costs,
the
analysis
begins
with
a
presumption
that
this
level
is
selected.
Under
this
option,
States
would
then
proceed
to
consider
whether
energy
and
non­
air
quality
environmental
impacts
would
justify
selection
of
an
alternative
control
option.
If
there
are
no
outstanding
issues
regarding
energy
and
non­
air
quality
environmental
impacts,
the
analysis
is
ended
and
the
most
stringent
alternative
is
identified
as
the
"
best
system
of
continuous
emission
reduction."
If
a
State
determines
that
the
most
stringent
alternative
is
unacceptable
due
to
such
impacts,

this
approach
would
require
them
to
document
the
rationale
for
this
finding
for
the
public
record.
Then,
the
next
most­
effective
alternative
in
the
listing
becomes
the
new
141
control
candidate
and
is
similarly
evaluated.
This
process
would
continue
until
the
State
identifies
a
technology
which
does
not
pose
unacceptable
costs
of
compliance,
energy
and/
or
non­
air
quality
environmental
impacts.

We
also
requested
comment
on
an
alternative
decisionmaking
approach
that
would
not
begin
with
an
evaluation
of
the
most
stringent
control
option.
For
example,
States
could
choose
to
begin
the
BART
determination
process
by
evaluating
the
least
stringent
technically
feasible
control
option
or
by
evaluating
an
intermediate
control
option
drawn
from
the
range
of
technically
feasible
control
alternatives.

Under
this
approach,
States
would
then
consider
the
additional
emissions
reductions,
costs,
and
other
effects
(
if
any)
of
successively
more
stringent
control
options.

Under
such
an
approach,
States
would
still
be
required
to
(
1)
display
and
rank
all
of
the
options
in
order
of
control
effectiveness
and
to
identify
the
average
and
incremental
costs
of
each
option;
(
2)
consider
the
energy
and
non­
air
quality
environmental
impacts
of
each
option;
and
(
3)

provide
a
justification
for
adopting
the
technology
selected
as
the
"
best"
level
of
control,
including
an
explanation
as
to
other
more
stringent
control
technologies
were
rejected.

In
selecting
a
"
best"
alternative,
the
proposed
guidelines
included
a
discussion
on
whether
the
affordability
of
controls
should
be
considered.
We
noted
in
142
the
guidelines
that,
as
a
general
matter,
for
plants
that
are
essentially
uncontrolled
at
present
and
emit
at
much
greater
levels
per
unit
of
production
than
other
plants
in
the
category,
EPA
is
unlikely
to
accept
as
BART
any
analysis
that
preserves
a
source's
uncontrolled
status.
The
proposed
guidelines
noted,
however,
that
we
recognize
there
may
be
unusual
circumstances
that
justify
taking
into
consideration
the
conditions
of
the
plant
and
the
economic
effects
of
requiring
the
use
of
a
given
control
technology.
These
effects
would
include
effects
on
product
prices,
the
market
share,
and
profitability
of
the
source.
We
did
not
intend,

for
example,
that
the
most
stringent
alternative
must
always
be
selected
if
that
level
would
cause
a
plant
to
shut
down,

while
a
slightly
lesser
degree
of
control
would
not
have
this
effect.

Comments.
We
received
comments
supporting
both
of
the
approaches
for
evaluating
ranked
control
alternatives.
Many
commenters,
including
commenters
from
State
agencies,
were
supportive
of
the
first
approach.
Comments
from
State
air
quality
agencies
were
strongly
supportive
of
this
approach.

These
commenters
believed
that
this
approach
is
consistent
with
past
approaches
by
States
for
considering
control
options
for
case­
by­
case
determinations,
is
well
understood
by
all
parties,
and
thus
easier
to
implement.
The
first
approach
also
was
strongly
supported
in
comments
from
environmental
organizations
and
private
citizens.
Some
143
comments
noted
that
the
plain
terminology
"
best"
suggests
that
there
must
be
a
sound
reason
for
not
using
the
most
stringent
control
level.

Many
comments
from
industrial
trade
organizations
were
critical
of
the
first
approach
and
believed
that
any
requirement
to
use
this
approach
would
reduce
State
discretion
because
this
approach,
in
the
judgment
of
the
commenters,
would
amount
to
use
of
the
most
stringent
alternative
as
a
default.
Some
of
these
comments
asserted
that
the
approach
in
option
1
would
shift
the
BART
analysis
away
from
a
cost­
benefit
approach
mandated
by
the
CAA
towards
a
BACT­
like
technology
analysis.
Other
commenters
believed
that
EPA
should
recognize
that
BART,
as
a
control
requirement
for
retrofitting
existing
sources,
should
differ
from
BACT
or
other
controls
for
new
equipment.
A
number
of
comments,
in
supporting
the
second
approach,
believed
that
this
approach
provides
greater
consideration
of
the
incremental
cost
of
each
succeeding
option.

Final
rule.
In
the
final
guidelines,
we
have
noted
that
States
retain
discretion
to
evaluate
control
options
in
whatever
order
they
choose,
so
long
as
the
State
fully
documents
its
analysis
of
the
CAA
factors.
If
it
chooses
a
control
alternative
other
than
the
"
best"
emissions
control,

it
should
document
its
justification,
based
on
the
factors,

for
not
choosing
each
available
more
stringent
option.
We
agree
with
commenters
who
noted
that
the
plain
terminology
144
"
best"
suggests
that
the
most
stringent
control
should
be
selected
unless
analysis
of
one
or
more
of
the
factors
provides
a
clear
and
strong
justificaiton
for
a
lesser
level
of
control.
We
do
not
agree
with
commenters
who
asserted
that
the
method
for
assessing
controls
for
existing
sources
must
differ
from
the
method
of
assessing
controls
for
new
sources;
so
long
as
the
factors
are
analyzed
properly,
there
is
no
inherent
need
for
a
different
process.

7.
What
should
be
the
presumptive
limits
for
SO2
and
NOx
for
utility
boilers?

Background.
In
the
2004
reproposal,
we
proposed
that
States,
as
a
general
matter,
should
require
EGUs
greater
than
250
MW
in
size
at
power
plants
larger
than
750
MW
to
control
95
percent
of
their
SO2
emissions,
or
control
to
within
an
SO2
emission
range
of
0.1
to
0.15
lb/
mmBtu.
We
also
proposed
to
establish
a
rebuttable
presumption
that
States
should
impose
these
BART
SO2
limits
on
all
EGUs
greater
than
250
MW,
regardless
of
the
size
of
the
power
plant
at
which
they
are
located.

For
NOx,
we
proposed
a
rebuttable
presumptive
emissions
limit
of
0.20
lbs/
mmbtu
for
all
EGUs
without
SCRs,
where
the
EGUs
were
greater
than
250
MW
in
size
at
power
plants
larger
than
750
MW.
We
also
suggested
that
States
impose
these
specific
BART
NOx
presumptive
limits
on
all
EGUs
greater
than
250
MW,
regardless
of
the
size
of
the
power
plant
at
145
which
they
are
located.
In
addition,
we
proposed
that
States
should
require
BART­
eligible
units
with
existing
SCRs
to
run
those
controls
year
round.
Many
commenters
responded
both
in
favor
and
in
opposition
to
these
proposed
BART
presumptive
limits.

Comments.
A
number
of
utility
groups
said
the
presumptive
SO2
emissions
control
approach
inappropriately
ignores
the
need
for
a
visibility
impact
evaluation
which
is
required
in
step
5
of
the
proposed
case­
by­
case
BART
engineering
analysis.
They
said
that
setting
presumptive
limits
infringes
on
a
state's
authority
to
establish
BART
on
a
case­
by­
case
basis
considering
not
only
visibility
improvement,
but
the
other
statutory
factors
as
well.
The
commenters
said
that
visibility
is
both
Class
I
area
and
source
specific,
which
is
the
reason
Congress
gave
the
States
the
lead
role
and
discretion
in
the
BART
program
to
determine
which
sources
need
to
install
or
upgrade
controls.

Through
the
use
of
presumptions
and
default
values,
however,

our
prescriptive
process,
as
proposed,
would
make
the
installation
of
maximum
controls
more
likely
without
regard
to
visibility
benefits.
Instead,
they
argued,
we
should
give
the
states
maximum
flexibility
to
use
the
five
statutory
factors
in
their
BART
determinations.
Commenters
said
sources
must
be
allowed
to
assess
the
visibility
improvements
of
a
variety
of
control
options.
146
Several
utilities
raised
concern
that
sources
with
existing
controls
should
not
be
required
to
meet
the
presumptive
limits
without
the
chance
to
evaluate
the
degree
of
visibility
improvement
expected
from
the
additional
emission
reduction
requirements.
They
said
that
if
a
source
can
demonstrate
a
reduction
in
visibility
impairment
below
the
specified
threshold
(
whether
that
threshold
is
our
currently
proposed
0.5
deciview
or
an
alternative
level)

with
less
stringent
controls,
then
neither
we
nor
States
should
impose,
by
default,
more
stringent
reduction
requirements.

Commenters
from
industry,
utilities,
and
States
said
that
we
had
not
indicated
what
previously­
controlled
sources
must
do
to
comply
with
BART,
while
we
had
determined
what
controls
are
necessary
for
uncontrolled
sources.
They
were
concerned
that
the
guidelines
would
lead
States
to
require
previously­
controlled
sources
to
remove
the
controls
and
replace
them
with
even
newer
controls
at
great
cost
and
very
little,
if
any,
improvement
in
emission
levels
and
visibility
in
Class
I
areas.
Commenters
added
that
States
should
be
able
to
use
their
discretion
to
determine
whether
additional
controls
are
needed.

Some
utilities
were
concerned
that
the
proposed
rule
would
require
some
plants
to
install
SCR
to
meet
the
NOx
control
level
proposed,
as
the
potential
retrofit
of
SCR
technology
for
the
BART
determination
may
be
supported
by
147
the
degree
of
visibility
improvement
expected.
They
said
that
the
guidelines
indicate
that
if
a
State
finds
that
a
source's
visibility
contribution
warrants
the
installation
of
SCR,
then
SCR
may
be
imposed.
The
commenter
added,

however,
that
the
guidelines
also
need
to
provide
for
instances
where
the
visibility
condition
warrants
a
lesser
control
level
than
what
would
be
achieved
by
advanced
combustion
control;
the
commenter
claimed
there
was
reference
to
this
concept
in
the
preamble
but
not
the
guidelines.

Final
rule.
In
these
guidelines,
we
are
finalizing
specific
presumptive
limits
for
SO2
and
NOx
for
certain
EGUs
based
on
fuel
type,
unit
size,
cost
effectiveness,
and
the
presence
or
absence
of
pre­
existing
controls.
The
presumptive
limits
finalized
in
today's
rulemaking
reflect
highly
cost­
effective
technologies
as
well
as
provide
enough
flexibility
for
States
to
take
particular
circumstances
into
account.

The
presumptive
limits
apply
to
EGUs
at
power
plants
with
a
total
generating
capacity
in
excess
of
750
MW.
As
explained
in
greater
detail
below,
for
these
sources
we
are
establishing
a
BART
presumptive
emission
limit
for
coalfired
EGUs
greater
than
200
MW
in
size
without
existing
SO2
control.
These
EGUs
should
achieve
either
95
percent
or
greater
SO2
removal,
or
an
emission
rate
of
0.15
lb
SO2/
mmBtu
or
lower.
For
NOx,
we
are
establishing
BART
presumptive
148
emission
limits
for
coal­
fired
EGUs
greater
than
200
MW
in
size
based
upon
boiler
size
and
coal
type,
and
based
upon
whether
selective
catalytic
reduction
(
SCR)
or
selective
noncatalytic
reduction
(
SNCR)
are
already
employed
at
the
source.
See
section
d.
below
for
a
table
listing
those
specific
limits.
Based
on
our
analysis
of
emissions
from
power
plants,
we
believe
that
applying
these
highly
costeffective
controls
at
the
large
power
plants
covered
by
the
guidelines
would
result
in
significant
improvements
in
visibility
and
help
to
ensure
reasonable
progress
toward
the
national
visibility
goal.

States,
as
a
general
matter,
must
require
owners
and
operators
of
greater
than
750
MW
power
plants
to
meet
these
BART
emission
limits.
We
are
establishing
these
requirements
based
on
the
consideration
of
certain
factors
discussed
below.
Although
we
believe
that
these
requirements
are
extremely
likely
to
be
appropriate
for
all
greater
than
750
MW
power
plants
subject
to
BART,
a
State
may
establish
different
requirements
if
the
State
can
demonstrate
that
an
alternative
determination
is
justified
based
on
a
consideration
of
the
evidence
before
it.
Our
intent
is
that
a
State
will
face
a
high
hurdle
if
it
chooses
to
justify
a
BART
determination
less
than
these
requirements
for
a
power
plant
greater
than
750
MW
in
size.

In
addition,
while
States
are
not
required
to
follow
these
guidelines
for
EGUs
located
at
power
plants
with
a
46Summary
of
Technical
Analyses
for
the
Proposed
Rule,
Mark
Evangelista,
U.
S.
Environmental
Protection
Agency,
April
12,
2004,
Docket
No.
OAR­
2002­
0076.

149
generating
capacity
of
less
than
750
MW
,
based
on
our
analysis
detailed
below,
we
believe
that
States
will
find
these
same
presumptive
controls
to
be
highly­
cost
effective,

and
to
result
in
a
significant
degree
of
visibility
improvement,
for
most
EGUs
greater
than
200
MW,
regardless
of
the
size
of
the
plant
at
which
they
are
located.
A
State
is
free
to
reach
a
different
conclusion
if
the
State
believes
that
an
alternative
determination
is
justified
based
on
a
consideration
of
the
evidence
before
it.

Nevertheless,
our
analysis
indicates
that
these
controls
are
likely
to
be
among
the
most
cost­
effective
controls
available
for
any
source
subject
to
BART,
and
that
they
are
likely
to
result
in
a
significant
degree
of
visibility
improvement.

The
rest
of
this
section
discusses
these
presumptive
limits
for
SO2
and
NOx
for
EGUs
and
the
additional
visibility
impact
and
cost­
effectiveness
analyses
we
have
performed
since
proposal
of
the
guidelines
in
2004.

g.
Visibility
Analysis
for
SO2
and
NOx
emissions
from
EGUs
In
the
2004
reproposal,
our
preliminary
CALPUFF
modeling46
suggested
that
controlling
a
single
250
MW
EGU
at
a
90
percent
level
would
improve
visibility
substantially
from
that
source.
Based
on
the
expected
degree
of
47
CALPUFF
Analysis
in
Support
of
the
Regional
Haze
Rule,
U.
S.
Environmental
Protection
Agency,
April
15,
2005,
Docket
No.
OAR­
2002­
0076.

150
improvement
in
visibility
and
the
use
of
highly
effective
control
technologies
that
are
available
for
sources
of
this
capacity
and
greater,
we
concluded
that
the
specific
control
levels
in
the
proposal
were
appropriate.
Even
at
that
level
of
control
however,
our
analysis
indicated
that
emissions
from
the
source
might
still
cause
a
perceptible
impact
on
visibility.

Following
comments
that
we
had
ignored
the
need
to
consider
the
degree
of
improvement
in
visibility
which
could
reasonably
be
anticipated
from
the
use
of
the
presumptive
control
technologies,
we
undertook
a
more
comprehensive
modeling
analysis
of
the
anticipated
visibility
impacts
of
controlling
large
EGUs.
Based
on
this
modeling
analysis,
we
anticipate
that
a
majority
of
the
currently
uncontrolled
EGUs
at
power
plants
covered
by
the
guideline
are
predicted
to
have
24­
hour
maximum
impacts
of
greater
than
a
change
of
2
or
3
deciviews47.
Our
modeling
was
representative
of
a
typical
EGU,
but
we
conservatively
assumed
SO2
emissions
of
10,000
tons
per
year
(
TPY)
and
NOx
emissions
of
approximately
3,500
TPY.
Such
levels
of
emissions
are
well
below
those
that
may
be
expected
of
an
uncontrolled
200
MW
EGU
(
i.
e.
approximately
27,000
TPY
of
SO2
and
9,400
TPY
of
NOx,
according
to
the
ratio
in
our
example,
burning
2
151
percent
bituminous
coal).
Not
only
were
the
maxima
considerable,
but
the
number
of
days
during
any
year
that
such
sources
are
predicted
to
have
visibility
impacts
of
greater
than
0.5
deciviews
or
even
1.0
deciviews
were
substantial.
Furthermore,
when
this
same
source
was
modeled
with
SO2
emissions
of
1,000
TPY
(
which
is
a
reduction
of
90
percent),
the
source
was
still
a
significant
contributor
to
visibility
impairment,
even
though
maximum
visibility
was
very
much
improved.

The
modeled
emission
rates
in
the
example
were
representative
of
an
EGU
smaller
than
200
MW.
For
much
larger
EGUs
with
capacities
of
750
MW
or
more,
and
emission
rates
much
higher
than
those
which
were
modeled,
visibility
degradation
is
expected
to
be
far
worse.
Clearly
there
is
a
substantial
degree
of
visibility
improvement
which
is
likely
from
emission
reductions
at
these
sources.

Although
we
are
confident
that
the
EGUs
for
which
we
are
establishing
presumptive
limits
each
have
a
significant
impact
on
visibility
at
one
or
more
Class
I
areas,
a
State
retains
the
option
and
flexibility
to
allow
a
source
to
try
to
demonstrate
that
it
should
not
be
subject
to
BART
based
on
its
visbility
impacts.
Based
on
our
modeling
results,
we
believe
that
such
a
showing
would
be
extremely
difficult
for
these
large
EGUs.

b.
BART
Presumptive
Limits
for
SO2
from
Coal­
fired
Units
48
Technical
Support
Document
for
BART
SO2
Limits
for
Electric
Generating
Units,
Memorandum
to
Docket
OAR
2002­
0076,
April
1,
2005.

152
For
currently
uncontrolled
coal­
fired
EGUs
greater
than
200
MW
in
size,
we
are
establishing
a
presumptive
BART
limits
of
95
percent
or
greater
SO2
removal,
or
an
emission
rate
of
0.15
lb
SO2/
mmBtu
or
lower.
We
are
not
establishing
a
presumptive
limit
for
EGUs
with
existing
post­
combustion
SO2
controls
or
for
EGUs
that
burn
oil.

In
2004,
we
proposed
presumptive
limits
for
SO2
of
95
percent
control
or
a
comparable
performance
level
of
0.1
to
0.15
lbs
per
million
BTU
as
controls
that
would
be
achievable
and
cost­
effective.
We
requested
comment
on
the
removal
effectiveness
of
flue
gas
desulfurization
("
FGD"
or
"
scrubber"
controls)
for
various
coal
types
and
sulfur
content
combinations.
Having
considered
the
comments
received,
we
have
determined
that
there
is
ample
data
to
support
the
determination
that
the
BART
presumptive
limits
outlined
in
today's
action
are
readily
achievable
by
new
wet
or
semi­
dry
FGD
systems
across
a
wide
range
of
coal
types
and
sulfur
contents
based
on
proven
scrubber
technologies
currently
operational
in
the
electric
industry.
48
We
agree
with
the
commenters
who
stated
that
our
dual
recommendation
provided
equity
across
sources
burning
coals
of
varying
sulfur
content.
We
believe
the
presumptive
limits
provide
enough
flexibility
that
absent
extreme
49
Ibid.

153
circumstances,
any
BART­
eligible
coal­
fired
EGU
will
be
able
to
achieve
one
of
the
limits
with
a
new
FGD
system.
We
expect
that
BART­
eligible
EGUs
burning
medium
to
high
sulfur
coal
will
be
able
to
achieve
a
removal
efficiency
of
95%
in
a
cost
effective
manner
by
utilizing
various
wet
FGD
technologies,
and
that
those
EGUs
burning
lower
sulfur
coals
could
meet
the
emission
limit
of
0.15lb/
mmBtu
in
a
cost
effective
manner
by
utilizing
dry
FGD
technologies.
As
described
below,
EPA's
unit
specific
economic
modeling
showed
that
the
majority
of
BART
eligible
units
greater
than
200
MW
can
meet
the
presumptive
BART
limit
at
a
cost
of
$
400
to
$
2000
per
ton
of
SO2
removed.

Some
commenters
expressed
concerns
that
the
proposed
limits
were
too
stringent
in
particular
for:
(
1)
EGUs
less
than
750
MW
in
size,
(
2)
EGUs
burning
low
sulfur
coals,
and
(
3)
EGUs
burning
lignite
coals.
However,
numerous
examples
exist
of
smaller
EGUs
and
EGUs
burning
low
sulfur
or
lignite
coals
achieving
these
SO2
limits
at
reasonable
cost.
49
We
recognize
that
semi­
dry
FGD
systems
are
most
commonly
utilized
on
units
burning
lower
sulfur
coals
and
are
not
typically
designed
for
removal
efficiencies
of
95
percent
or
greater.
However,
we
believe
that
these
EGUs
can
readily
achieve
the
presumptive
emission
rate
limit
of
0.15
lb
SO2/
mmBtu.
An
analysis
of
EPA's
RACT/
BACT/
LEAR
50
PQA
Analysis
154
Clearinghouse
Dry
FGD
cost
effectiveness
data
ranged
from
$
393
to
$
2132
per
ton
SO2
removed,
with
an
average
cost
effectiveness
of
$
792
per
ton50.

We
received
a
few
comments
expressing
the
belief
that
the
presumptive
limits
should
be
more
stringent,
given
that
BART
emission
limits
will
not
be
fully
implemented
until
2013
or
2014.
We
recognize
that
while
some
scrubber
units
currently
achieve
reductions
greater
than
95%,
not
all
units
can
do
so.
The
individual
units
that
currently
achieve
greater
than
95%
control
efficiencies
do
not
necessarily
represent
the
wide
range
of
unit
types
across
the
universe
of
BART­
eligible
sources.
An
analysis
of
the
Department
of
Energy's
U.
S.
FGD
Installation
Database
supports
our
belief
that
95
percent
removal
efficiencies
would
be
obtainable
by
all
types
of
EGUs
burning
medium
and
high
sulfur
coal
by
2014,
including
BART­
eligible
EGUs.
In
addition,
we
note
that
the
presumption
does
not
limit
the
States'
ability
to
consider
whether
more
(
or
less)
stringent
controls
are
appropriate
in
a
particular
case.
If,
upon
closer
examination
of
an
individual
EGU,
a
State
determines
that
a
different
emission
limit
is
appropriate
based
upon
its
analysis
of
the
five
factors,
then
the
State
may
apply
a
more
or
less
stringent
limit.
51
Ibid.

52
Ibid.

155
Our
analysis
of
presumptive
BART
limits
accounted
for
variations
in
existing
SO2
controls.
We
accordingly
considered
(
1)
coal­
fired
EGUs
without
existing
SO2
controls,
and
(
2)
coal­
fired
EGUs
with
existing
SO2
controls.
This
analysis
consisted
of
the
following
key
elements:
(
1)
identification
of
all
potentially
BARTeligible
EGUs,
and
(
2)
technical
analyses
and
industry
research
to
determine
applicable
and
appropriate
SO2
control
options,
(
3)
economic
analysis
to
determine
cost
effectiveness
for
each
potentially
BART­
eligible
EGU,
and
(
4)
evaluation
of
historical
emissions
and
forecast
emission
reductions
for
each
potentially
BART­
eligible
EGU.
51
We
identified
491
potentially
BART­
eligible
coal­
fired
units
based
on
the
following
criteria:
(
1)
the
unit
was
put
in
place
between
August
7,
1962
and
August
7,
1977,
and
(
2)

the
unit
had
the
potential
to
emit
more
than
250
tons
annually
of
SO2.
Our
assessment
of
potential
controls
included
various
industry
case
studies,
technical
papers,

public
comments,
BACT
analyses,
and
historical
Acid
Rain
emissions
data.
Our
analysis
is
described
in
detail
in
the
TSD.
52
156
We
calculated
cost
effectiveness
and
projected
SO2
emission
reductions
on
a
per
unit
basis
based
on
removal
efficiencies
of
90
percent
for
dry
FGD
systems,
in
particular
spray
dry
lime
systems,
and
95
percent
for
wet
FGD
systems,
in
particular
limestone
forced
oxidation
systems.
Based
on
our
analysis,
the
average
cost
effectiveness
for
controlling
all
BART­
eligible
EGUs
greater
than
200
MW
without
existing
SO2
controls
was
estimated
to
$
919
per
ton
of
SO2
removed.
Moreover,
the
range
of
costs
effectiveness
numbers
demonstrates
that
the
majority
of
these
units
can
meet
the
presumptive
limits
at
a
cost
of
$
400
to
$
2000
per
ton
of
SO2
removed.

Unit
Capacity
(
MW)
Tons
(
K)
of
SO2
Emitted
in
2001
%
of
BART
Eligible
Coalfired
Unit's
2001
Emissions
Calculated
Average
Cost
Effectiveness
for
MW
Grouping
($/
ton
SO2
removed)
%
of
Estimated
Removable
BART
SO2
Emissions
From
coal­
fired
Units*

<
50
MW
26
0.4%
1962
0.9%

50
­
100
MW
93
1.4
2399
1.6%

100
­
150
MW
171
2.5%
1796
2.2%

150
­
200
MW
235
3.5%
1324
3.4%

200
­
250
MW
253
3.8%
1282
3.1%

250
­
300
MW
281
3.2%
1128
4.0%

>
300
MW
5712
85.2%
84.8%

All
Units
6707
100%
984
100%
157
BART
Units
(>
200MW)
6246
92.2%
919
91.9%

Figure
1.

In
establishing
presumptive
BART
limits,
we
were
cognizant
of
the
fact
that
upgrading
an
existing
scrubber
system
is
typically
considered
more
cost
effective
than
constructing
a
new
scrubber
system.
However,
due
to
the
diverse
and
complex
nature
of
upgrading
existing
FGD
systems
(
scrubber
type,
reagents,
online
year,
absorber
characteristics,
current
operating
procedures,
etc.),
there
is
no
single
solution
or
standard
appropriate
for
all
EGUs.

As
a
result,
we
are
not
including
specific
numerical
presumptive
limits
for
EGUs
with
pre­
existing
scrubbers.

However,
for
scrubbers
currently
achieving
removal
efficiencies
of
at
least
50
percent,
we
strongly
encourage
States
to
evaluate
a
range
of
scrubber
upgrade
options
available
for
improving
the
SO2
removal
performance
of
existing
units.
There
are
numerous
scrubber
enhancements
available
to
upgrade
the
average
removal
efficiencies
of
all
types
of
existing
scrubber
systems,
and
the
guidelines
contains
a
discussion
of
the
options
that
States
should
evaluate
in
making
BART
determinations
for
EGUs
with
existing
scrubbers.
158
The
guidelines
do
not
require
EGUs
with
existing
FGD
systems
to
remove
these
controls
and
replace
them
with
new
controls,
but
the
guidelines
do
state
that
coal
fired
EGUs
with
existing
SO2
controls
achieving
removal
efficiencies
of
less
than
50
percent
should
consider
constructing
a
new
FGD
system
to
meet
the
presumptive
limits
of
95
percent
removal
or
0.15
lb/
mmBtu
in
addition
to
evaluating
the
suit
of
upgrade
options.
For
these
EGUs,
the
suite
of
available
"
upgrades"
may
not
be
sufficient
to
remove
significant
SO2
emissions
in
a
cost
effective
manner,
and
States
may
determine
that
these
EGUs
should
be
retrofitted
with
new
FGD
systems.

c.
BART
Limits
for
SO2
from
Oil­
Fired
Units
We
are
not
establishing
a
presumptive
BART
limit
for
SO2
from
oil­
fired
EGUs.
The
guidelines
state
that
the
most
appropriate
control
option
for
oil­
fired
EGUs,
regardless
of
capacity,
is
to
set
limits
on
the
sulfur
content
of
the
fuel
oil
burned
in
the
unit.

Commenters
suggested
EPA
evaluate
two
primary
control
options
for
BART
oil­
burning
units:
(
1)
sulfur
content
fuel
oil
limitations,
and
(
2)
flue
gas
desulfurization
systems.

We
have
been
unable
to
find
any
FGD
application
in
the
U.
S.

electric
industry
on
an
oil­
fired
unit.
As
a
result,
our
analysis
for
oil­
fired
units
focused
on
benchmarking
previously
imposed
fuel
oil
restrictions
on
the
electric
159
industry
and
(
2)
a
regional
economic
analysis
of
switching
from
high
sulfur
to
low
sulfur
fuel
oil.

Our
study
of
currently
imposed
fuel
oil
restrictions
on
the
electric
industry
suggested
that
all
BART­
eligible
EGUs
currently
have
some
sort
of
imposed
sulfur
content
or
emission
rate
limitation.
Of
the
74
BART­
eligible
oilburning
EGUs,
32
currently
have
sulfur
fuel
oil
restrictions
of
less
than
1%,
and
67
have
some
sort
of
sulfur
content
limitation.
In
addition,
our
economic
analysis
suggests
that
switching
to
low
sulfur
fuel
oil
is
a
cost
effective
method
in
reducing
SO2
emission
from
oil
fired
units.

As
approximately
43
percent
of
the
BART
eligible
oil
units
currently
have
a
sulfur
content
limitation
that
is
either
equivalent
to,
or
more
stringent
than,
one
percent
sulfur
by
weight,
the
guidelines
require
States
to
consider
a
1
percent
or
lower
sulfur
by
weight
fuel
oil
restriction
on
all
BART
eligible
EGUs
as
part
of
their
BART
analysis,

and
recommends
that
States
establish
appropriate
and
sustainable
sulfur
content
fuel
oil
restrictions,
taking
into
account
fuel
oil
availability.
States
should
accordingly
evaluate
a
one
percent
sulfur
content
limitation
as
a
starting
point
of
their
BART
determination
for
oilfired
EGUs
subject
to
BART.

d.
BART
Presumptive
Limits
for
NOx
from
Coal­
fired
Units
53
Technical
Support
Document
for
BART
NOx
Limits
for
Electric
Generating
Units,
Memorandum
to
Docket
OAR
2002­
0076,
April
1,
2005.

160
In
the
2004
reproposal,
in
discussing
NOx
controls
on
EGUs,
we
suggested
that
States
should
require
EGUs
without
SCRs
to
achieve
the
lowest
possible
emission
rate
without
installing
post­
combustion
controls.
We
proposed
a
presumptive
emissions
limit
of
0.20
lbs/
mmbtu
for
all
units
­
one
that
could
generally
be
achieved
through
the
use
of
combustion
controls.
We
also
proposed
that
States
should
require
BART­
eligible
units
with
existing
SCRs
to
run
those
controls
year
round.
These
would
be
cost
effective
reductions,
since
the
large
capital
costs
associated
with
the
SCR
have
already
been
incurred.
In
the
reproposal
we
also
noted
that,
unlike
the
methods
for
controlling
SO2
(
which
fall
within
a
fairly
narrow
range
of
cost
effectiveness
and
control
efficiencies),
the
removal
efficiencies
and
costs
associated
with
the
control
techniques
for
NOx
vary
considerably,
depending
on
the
design
of
the
boiler
and
the
type
of
coal
used.

In
response
to
comments
on
the
proposal,
we
have
performed
additional
analyses
of
all
individual
BART­
eligible
coal­
fired
units53
(
details
of
the
analysis
performed
are
found
in
the
TSD
cited
below,
and
the
spreadsheet
tool
itself
has
been
placed
in
the
docket).
Our
54
Technical
Support
Document
for
BART
NOx
Limits
for
Electric
Generating
Units,
Memorandum
to
Docket
OAR
2002­
0076,
April
1,
2005.

161
analyses
indicated
that
both
cost
effectiveness
and
post­
control
rate
did
depend
largely
on
boiler
design
and
type
of
coal
burned.
Based
on
these
analyses,
we
believe
that
States
should
require
specific
NOx
rate
limits
for
different
categories
of
coal­
fired
utility
units,

differentiated
by
boiler
design
and
type
of
coal
burned.
We
also
analyzed
BART­
eligible
oil­
and
gas­
fired
units,
and
we
recommend
that
these
units
install
current
combustion
control
technology.

Population
of
Units
The
guidelines
indicates
that
States
should
require
NOx
controls
meeting
specific
presumptive
limits
on
coal­
fired
EGUs
greater
than
200
MW
at
power
plants
greater
than
750
MW.
The
guidelines
also
recommend
that
States
strongly
consider
the
same
NOx
limits
for
all
coal­
fired
EGUs
greater
than
200
MW,
regardless
of
the
size
of
the
power
plant
at
which
they
are
located.
Our
data
indicated
that
370
of
the
491
BART­
eligible
coal­
fired
EGUs
are
greater
than
200
MW,

and
that
these
EGUs
account
for
over
90
percent
of
the
total
NOx
emissions
from
BART­
eligible
units
in
2004.54
Addressing
the
remaining
10
percent
of
the
emissions
would
involve
controlling
a
large
number
of
smaller
EGUs.
55
The
current
combustion
control
technology
EPA
analyzed
for
cyclone
units
is
coal
reburning.

162
Categories
of
controls
The
table
below
indicates
the
types
of
boilers
installed
at
the
491
BART­
eligible
coal­
fired
EGUs.

Drybottom
wall­
fired
boiler
units
and
tangentially­
fired
boiler
units
make
up
a
large
majority
of
the
total
BART­
eligible
EGUs.

Table
1.
Population
of
BART­
eligible
coal­
fired
EGUs.

Boiler
Type
Number
Number
Number
All
units
Units
>
200
MW
Units
>
200
MW
at
750
MW
plants
Cyclone
56
35
19
Cell
Burner
35
35
29
Dry
Bottom
­
Wall
fired
188
121
77
Dry
Bottom
Turbo­
fired
14
10
4
Stoker
5
0
0
Tangentially­
fired
186
164
112
Wet
Bottom
6
5
5
Other
1
0
0
Total
BART­
eligible
coalfired
EGUs
491
370
246
Current
combustion
control
technology
is
generally,
but
not
always,
more
cost
effective
than
post
combustion
SCRs.

For
cyclone
boilers,
SCRs
were
found
to
be
more
cost
effective
than
current
combustion
control
technology;
55
thus
163
the
NOx
limits
are
set
based
on
using
SCRs.
SNCRs
are
generally
not
cost­
effective
except
in
very
limited
applications
and
therefore
were
not
included
in
EPA's
analysis
(
see
further
discussion
of
BART­
eligible
units
with
SNCRs
later
in
this
section).
The
types
of
current
combustion
control
technology
options
assumed
include
low
NOx
burners,
over­
fire
air,
and
coal
reburning.

We
also
believe
that
for
units
with
existing
SCRs,

running
them
year
round
would
represent
cost
effective
reductions.

We
provide
presumptive
NOx
limits
for
the
different
categories
of
units
below,
based
on
our
analysis
of
the
expected
costs
and
performance
of
controls
on
BART­
eligible
units
greater
than
200
MW.
The
limits
provided
were
chosen
at
levels
that
approximately
75
percent
of
the
units
with
current
combustion
control
technology
could
achieve.
The
presumptive
limits
do
not
assume
the
installation
of
advanced
combustion
controls,
and
our
analysis
indicates
that
a
large
majority
of
the
remaining
25
percent
of
units
could
in
fact
meet
the
presumptive
limits
using
advanced
combustion
controls,
which
have
already
been
demonstrated
on
a
variety
of
coal­
fired
units.

Information
used
in
our
analysis
To
perform
the
analysis,
we
used
emissions
and
existing
control
technology
information
for
BART­
eligible
EGUs.
The
56
We
define
current
combustion
control
technology
as
low
NOx
burners
and
over­
fire
air
installed
in
1997
or
later.
See
further
discussion
later
in
this
section.

57
164
primary
source
of
this
information
was
EPA's
Clean
Air
Markets
Division
database.
[
ADD
CITE].
We
also
used
NOx
emissions
data
gathered
for
purposes
of
phase
II
of
the
Acid
Rain
Program
to
estimate
"
uncontrolled"
NOx
emission
rates
for
BART­
affected
units,
i.
e.,
the
NOx
rate
assuming
the
unit
had
no
NOx
controls
of
any
kind
installed.
[
ADD
CITE].

This
"
uncontrolled"
NOx
rate
was
used
in
calculating
the
controlled
NOx
rate
for
new
or
"
current
combustion
control
technology."
56
Also
used
in
the
analysis
were
estimates
of
the
efficiencies
and
costs
of
NOx
control
technologies.
These
estimates
were
developed
by
us
and
represent
current
cost
and
performance
of
current
combustion
control
technology,

advanced
combustion
controls,
and
SCRs.
57
Methodology
for
and
results
of
applying
NOx
control
technologies
A.
Current
Combustion
Control
Technology
If
a
BART­
eligible
EGU
("
unit")
currently
had
no
NOx
controls
installed,
i.
e.,
an
"
uncontrolled"
unit,
we
applied
a
complete
set
of
combustion
controls.
A
complete
set
of
combustion
controls
for
most
units
includes
a
low
NOx
burner
58
Setting
Presumptive
BART
NOx
Limits
for
Electric
Generating
Units,
Memorandum
to
Docket
OAR
2002­
0076,
April
1,
2005.

165
and
over­
fire
air.
If
a
unit
had
"
partial"
combustion
controls
installed,
i.
e.,
either
low
NOx
burners
or
overfire
air
but
not
both,
we
added
whichever
component
was
missing
until
the
unit
had
a
complete
set
of
combustion
controls.
For
example,
if
a
unit
had
a
low
NOx
burner
but
no
over­
fire
air,
we
added
over­
fire
air.
Conversely,
if
a
unit
had
over­
fire
air
but
no
low
NOx
burner,
we
added
a
low
NOx
burner.
If
a
unit
had
a
complete
or
partial
set
of
combustion
controls
but
installed
them
prior
to
1997,
our
analysis
assumed
that
such
controls
were
not
current
combustion
control
technology
and
replaced
them
with
a
complete
set
of
combustion
controls.
We
chose
1997
as
a
cutoff
because
the
current
generation
of
NOx
combustion
control
technology
became
operational
at
approximately
this
time.
If,
after
applying
current
combustion
control
technology,
a
unit's
new
controlled
NOx
emission
rate
was
higher
than
the
average
NOx
emission
rate
reported
for
the
unit
in
the
most
recent
year
(
2004),
we
assumed
the
unit
already
had
current
combustion
control
technology.

Our
analysis
described
above
was
done
in
an
Excel
spreadsheet
and
is
included
in
the
docket
as
a
technical
support
document
(
TSD).
58
This
TSD
also
includes
detailed
59
No
Cell
burners,
dry­
turbo­
fired
units,
stokers,
nor
wet­
bottom
units
burning
lignite
were
identified
as
BARTeligible
thus
no
presumptive
limit
was
determined.
Similarly,
no
wet­
bottom
units
burning
sub­
bituminous
were
166
descriptions
of
the
control
algorithms
used
to
calculate
the
performance
and
cost
of
the
NOx
control
technologies
used.

To
determine
a
NOx
emission
rate
that
would
become
the
BART
standard,
we
selected
a
rate
that
a
vast
majority
of
the
units
could
meet
using
current
combustion
control
technology.
For
this,
we
selected
a
rate
that
approximately
75
percent
of
the
units
could
meet.
Table
1
below
shows
the
results
of
our
analysis
including
the
NOx
emission
rate
for
each
unit
type
and
coal
type
that
approximately
75
percent
of
the
units
could
meet
using
current
combustion
control
technology.

Our
analysis
of
Stoker
units
included
BART­
eligible
and
non­
BART­
eligible
Stoker
units
because
we
identified
only
one
BART­
eligible
Stoker
unit
with
coal­
type
information.

We
believed
a
larger
population
was
needed
to
determine
a
reasonable
presumptive
limit
for
Stoker
units.
For
all
other
boiler
designs,
we
only
analyzed
BART­
eligible
units
because
we
believed
there
was
a
sufficient
population
upon
which
to
determine
a
presumptive
limit.

Table
1.
Presumptive
NOx
emission
limits
for
BARTeligible
coal­
fired
units59
identified
as
BART­
eligible.

167
Unit
type
Coal
type
NOx
presumptive
limit
(
lb/
mmbtu)

Dry­
bottom
wallfired
Bituminous
0.39
Sub­
bituminous
0.23
Lignite
0.29
Tangential­
fired
Bituminous
0.28
Sub­
bituminous
0.15
Lignite
0.17
Cell
Burners
Bituminous
0.40
Sub­
bituminous
0.45
Dry­
turbo­
fired
Bituminous
0.32
Sub­
bituminous
0.23
Stoker
Bituminous
0.37
Wet­
bottom
tangential­
fired
Bituminous
0.62
[
Placeholder
for
cost­
effectiveness
of
presumptive
limits]
60
Setting
Presumptive
BART
NOx
Limits
for
Electric
Generating
Units,
Memorandum
to
Docket
OAR
2002­
0076,
April
1,
2005.

168
B.
Advanced
Combustion
Controls
We
expect
most
units
that
cannot
meet
the
BART
standard
by
using
current
combustion
control
technology
to
meet
the
BART
standard
by
using
advanced
combustion
controls.
The
advanced
combustion
control
technology
we
used
in
our
analysis
is
recently
available
and
has
been
demonstrated
on
a
variety
of
unit
types.
This
technology
is
called
rotating
opposed
fire
air
or
"
ROFA."
It
can
achieve
significantly
lower
NOx
emission
rates
than
conventional
over­
fire
air
and
has
been
installed
on
a
variety
of
coal­
fired
units
including
T­
fired,
Wall­
fired
and
Stoker
units.
We
expect
the
ROFA
technology
will
have
gained
experience
and
improved
its
performance
by
the
time
units
are
required
to
comply
with
this
rule.
We
also
acknowledge
that
more
refinements
in
combustion
control
technologies
will
likely
have
been
developed
by
that
time.
As
a
result,
we
believe
our
analysis
and
the
presumptive
NOx
limits
we
are
finalizing
in
this
rule
are
conservative.
60
C.
Selective
Catalytic
Reduction
("
SCR")
and
Cyclone
Units.

As
mentioned
previously,
when
we
applied
SCR
to
each
unit
and
fuel
type,
the
cost­
effectiveness
was
generally
higher
than
for
current
combustion
control
technology
except
61
Ibid.

169
for
one
unit
type,
i.
e.,
cyclone
units.
Because
of
the
relatively
high
cost
and
limited
reduction
efficiency
of
combustion
controls
available
for
cyclone
units
and
the
relatively
high
NOx
emission
rates
of
cyclone
units,
SCR
is
more
cost­
effective.
See
the
TSD
for
this
section61
for
further
information
on
the
difference
in
cost­
effectiveness
between
combustion
controls
and
SCR
for
cyclone
units.
As
a
result,
we
are
basing
our
presumptive
NOx
limit
for
cyclone
units
on
the
use
of
SCR.

NOx
emission
rates
for
cyclone
units
that
currently
do
not
have
SCRs
but
received
SCRs
in
our
analysis
had
controlled
NOx
emission
rates
of
0.10
lb/
mmbtu
and
below
on
bituminous
coal,
subbituminous
coal,
and
lignite.
For
cyclone
units
without
SCRs
burning
bituminous,

subbituminous,
and
lignite,
we
are
finalizing
a
presumptive
NOx
emission
limit
of
0.10
lb/
mmbtu.
For
cyclone
units
with
SCRs,
the
guidelines
indicate
that
States
should
require
year­
round
operation
of
the
existing
SCRs.

D.
BART­
eligible
units
with
existing
SNCRs.

We
identified
five
BART­
eligible
units
that
currently
have
SNCRs
installed.
Our
analysis
assumed
no
further
controls
were
required
for
these
units
due
to
the
relatively
small
incremental
benefits
of
adding
combustion
controls
to
62
Ibid.

170
units
with
existing
SNCRs.
Therefore,
for
units
with
SNCRs,

the
guidelines
indicated
that
States
should
require
yearround
operation
of
the
existing
SNCRs.
We
also
believe
that
States
could
consider
SCR
as
an
alternative
to
annual
operation
of
SNCR
in
light
of
the
relatively
high
operating
costs
associated
with
SNCR.

Oil
and
Gas­
fired
Units
We
performed
an
analysis
of
BART­
eligible
oil
and
gasfired
units
similar
to
the
analysis
done
for
coal­
fired
units.
Our
analysis
indicated
that
a
number
of
units
can
make
significant
reductions
in
NOx
emissions
which
are
highly
cost­
effective
through
the
application
of
current
combustion
control
technology.
62
However,
the
total
amount
of
NOx
reductions
from
applying
current
combustion
control
technology
to
oil
and
gas­
fired
units
greater
than
200
MW
is
substantially
smaller
(
approximately
7
times
smaller)
than
the
total
NOx
reductions
from
coal­
fired
units.
Therefore,

we
believe
it
more
appropriate
to
make
a
recommendation
to
the
States
regarding
oil
and
gas
units,
rather
than
establishing
presumptive
limits.

We
strongly
recommend
that
States
require
the
installation
of
current
combustion
control
technology
on
oil
and
gas­
fired
units
greater
than
200
MW.
171
