97
commenters
agreed
that
sources
should
not
be
required
to
go
below
that
level
(
e.
g.,
to
an
arbitrary
level
such
as
0.2),
arguing
that
EPA
has
neither
a
legal
mandate
nor
a
rational
basis
for
limiting
the
HI
to
less
than
1.0.

One
of
the
commenters
stated
that
the
comparison
of
RfC
or
similarly­
derived
health
benchmarks
to
modeled
maximum
annual
average
concentrations
is
extremely
health­
protective
and
meets
the
"
ample
margin
of
safety"
requirement
of
the
statute.
Given
this
high
degree
of
conservatism,
the
commenter
stated
that
neither
the
CAA
nor
sound
policy
requires
that
background
and
multipathway
exposures
be
incorporated
into
an
evaluation
of
the
degree
of
risk
posed
by
affected
sources.
Under
these
circumstances,
the
commenter
argued,
the
mere
possibility
of
exposure
from
multiple
sources,
or
multiple
HAP
from
a
single
source,
does
not
justify
a
uniform
adjustment
to
all
RfC
values
or
similarly­
derived
health
benchmarks
for
all
facilities.

Similarly,
the
commenter
believed
that
EPA
should
not
mandate
modeling
risks
from
the
entire
facility,
but
rather
only
from
the
portions
of
the
facility
that
are
within
the
source
category.

Two
other
commenters
objected
to
a
noncancer
HI
of
1.0
(
or
greater).
The
first
commenter
stated
that,
while
the
HI
is
useful
in
evaluating
site­
specific
impacts,
choosing
a
generic
HI
(
some
multiple
of
1.0)
for
application
to
a
wide
range
of
sites
is
inappropriate.
The
commenter
added
that
selection
of
an
arbitrary
multiple
of
1.0
is
not
science,
does
not
conform
with
98
section
112(
d)(
4),
and
does
not
protect
public
health.
The
commenter
stated
that
the
selection
of
a
HI
of
0.2
as
a
rough
screening
tool
seemed
reasonable,
although
it
was
unsupported
by
any
analysis.
The
commenter
added
that
if
a
default
HI
is
used,

then
EPA
should
include
a
provision
that
would
disallow
its
use
to
exclude
a
facility
from
MACT
if
better
background
information
is
available
suggesting
the
default
HI
does
not
protect
public
health.
However,
the
commenter
believed
that
the
CAA
does
not
support
an
interpretation
that
includes
the
use
of
such
a
default
to
allow
exemptions
for
individual
sources.
The
commenter
believed
that
the
expansion
of
the
interpretation
to
include
nonthreshold
pollutants
is
in
direct
conflict
with
section
112(
d)(
4).

The
second
commenter
evaluated
the
four
potential
options
that
EPA
proposed
to
ensure
that
a
risk
analysis
under
section
112(
d)(
4)
considered
the
total
ambient
air
concentrations
of
all
the
HAP
to
which
the
public
is
exposed.
Option
1,
which
requires
that
the
HI
for
all
pollutants
be
no
greater
than
1.0,
does
not
consider
additional
sources
or
background
and
is
unacceptable,

according
to
the
commenter.
Option
3,
which
uses
existing
data
such
as
NATA
to
determine
background
and
requires
that
the
HI
be
no
greater
than
1.0,
is
also
unacceptable,
according
to
the
commenter.
The
commenter
pointed
out
that
EPA
has
clearly
stated
at
public
meetings
that
the
NATA
is
not
to
be
used
to
make
regulatory
decisions.
(
As
the
first
commenter
noted,
NATA
99
information
includes
warnings
that
the
information
is
useful
for
large­
scale
planning
purposes
and
not
for
local
area
assessment.)

The
commenter
added
that
NATA
relies
on
data
submitted
to
EPA
voluntarily
and
has
been
reported
to
consistently
underestimate
measured
concentrations.
Until
EPA
requires
that
HAP
inventories
be
submitted
as
proposed
in
the
CERR,
and
the
NATA
conducts
refined
modeling
around
stationary
sources,
the
commenter
argued
that
NATA
should
not
be
considered
for
estimating
background
concentrations.
Option
4,
which
allows
individual
facilities
to
monitor
the
HAP
backgrounds
for
use
in
their
own
analysis,

requires
oversight
and
evaluation
by
the
States
to
ensure
proper
site
selections
and
analytical
methods
and
should
not
be
considered,
according
to
the
commenter.
The
commenter
believed
Option
2,
which
requires
that
the
HI
be
no
greater
than
0.2,

would
be
the
only
viable
option
at
this
time
using
a
conservative
risk
screening
analysis.
However,
the
commenter
did
not
endorse
using
any
of
the
proposed
threshold
limit
applicability
methods
to
exempt
process
sources
from
NESHAP
requirements.

Two
other
commenters
raised
additional
objections
to
EPA's
proposed
methodologies
for
determining
the
contribution
of
other
sources
to
the
overall
hazard.
The
first
commenter
stated
that
EPA
had
not
discussed
the
need
to
assess
cumulative
risks,

aggregate
exposures,
and
health
impacts
associated
with
exposure
to
chemical
mixtures
emitted
from
facilities
within
the
source
categories.
The
commenter
referred
EPA
to
the
extensive
progress
100
that
has
been
made
in
more
completely
addressing
risks
from
exposure
to
air
pollution
and
integrated
decisionmaking
in
such
areas
as
children's
risk
issues,
cumulative
exposure,
and
chemical
mixtures.
The
commenter
requested
that
the
recent
advancements
be
incorporated
into
the
risk
assessment
methods
and
overall
cost
estimates
associated
with
risk­
based
exemptions
in
the
proposed
rules.

The
second
commenter
stated
that
EPA's
proposed
alternative
methodologies
for
determining
the
contribution
of
other
sources
to
cumulative
risk
are
untenable
and
deeply
flawed.
According
to
the
commenter,
the
first
and
second
approaches
(
HI
of
1.0
and
HI
of
0.2)
would
allow
exemptions
based
on
blanket
assumptions
about
exposure,
but
EPA
provided
no
basis
for
making
any
assumption.

The
commenter
noted
that
the
third
option
suggests
relying
on
existing
estimates
of
background
levels
of
certain
HAP,
but
argued
that
these
information
sources
(
e.
g.,
NATA,
ATSDR)
are
neither
designed
nor
adequately
precise
to
be
used
as
the
basis
of
regulatory
applicability
determinations.
According
to
the
commenter,
EPA
has
cautioned
that
NATA
emission
estimates
"
cannot
be
used
to
identify
exposures
and
risks
for
specific
individuals,

or
even
to
identify
exposures
and
risks
in
small
geographic
regions
such
as
a
specific
census
tract."
(
U.
S.
EPA,
Limitations
in
the
1996
National­
Scale
Air
Toxics
Assessment)
The
commenter
pointed
out
that
NATA
does
not
estimate
exposure
to
a
number
of
HAP,
(
e.
g.,
hydrogen
fluoride
(
HF),
HCl),
and
the
ATSDR
profiles
101
offer
generalized
assessments,
but
are
not
specific
enough
to
establish
as
baseline
for
a
given
facility.

Response:
For
today's
final
PCWP
rule,
we
are
considering
an
HI
limit
of
1.0
to
provide
an
ample
margin
of
safety
for
protecting
public
health
under
section
112(
c)(
9).
However,
we
do
not
believe
that
increasing
the
HI
limit
above
1.0
is
justified
by
currently
available
science.
Safety
factors
are
included
in
the
dose­
response
values
used
to
calculate
the
HI
to
account
for
scientific
uncertainties,
and
their
inclusion
helps
ensure
that
using
a
HI
limit
of
1.0
provides
an
ample
margin
of
safety.
The
TOSHI
approach
required
for
site­
specific
risk
assessment
in
today's
final
PCWP
rule
assumes
additivity
in
mixtures
of
chemicals
that
target
the
same
organ
system.

We
are
not
using
background
concentrations
from
NATA
in
today's
final
PCWP
rule.
Several
commenters
presumed
the
use
of
CAA
section
112(
d)(
4)
for
the
PCWP
delisting.
However,
we
are
using
CAA
section
112(
c)(
9)
and
not
section
112(
d)(
4).
Discussion
of
our
authority
to
consider
background
and
multipathway
exposures
is
provided
elsewhere
in
this
section.

e.
Tiered
approach
Comment:
Several
commenters
supported
EPA's
proposed
tiered
modeling
approach,
which
begins
with
simple
"
look­
up
tables"
and
102
progresses
to
more
refined
facility­
specific
risk
assessments.

One
commenter
noted
that
the
State
of
Wisconsin
uses
a
tiered
approach
similar
to
the
approach
proposed
by
EPA,
and
in
general,

this
approach
has
worked
well.
The
approach
first
allows
sources
to
demonstrate
compliance
if
their
potential
emissions,
stack
height,
and
exhaust
direction
are
within
the
ranges
provided
in
conservative
look­
up
tables.
The
second
tier
allows
facilities
to
provide
site­
specific
modeling
to
demonstrate
compliance
with
ambient
air
standards
at
the
property
line.
Another
commenter
added
that
EPA
should
be
flexible
in
accepting
evolving
improvements
in
exposure
assessment
and
risk
modeling,
and
should
take
into
account
the
inherent
strengths
and
weaknesses
of
the
types
of
modeling
used.
A
third
commenter
noted
that
most
sources
would
use
the
tiered
modeling
approach
but
believed
that
facilities
should
be
allowed
to
use
any
EPA­
approved
modeling
technique
to
demonstrate
that
their
emissions
are
below
the
applicable
health
benchmark.
The
commenter
also
recommended
that,
for
the
final
PCWP
rule,
EPA
adopt
the
model
regulatory
text
that
they
provided
for
the
risk­
based
framework.

One
commenter
opposed
EPA's
proposed
tiered
modeling
approach,
stating
that
if
EPA
decided
to
pursue
a
generic
risk
screening
approach
under
section
112(
d)(
4),
it
would
need
to
be
conservative.
According
to
the
commenter,
the
use
of
a
(

nontiered
conservative
approach
would
represent
the
least
cost
to
the
regulated
community
and
would
be
the
least
time­
consuming
for
103
1EPA
1999
States
reviewing
the
facility's
application.

Response:
We
acknowledge
the
model
regulatory
text
submitted
by
one
of
the
commenters.
However,
we
developed
our
own
regulatory
text
to
specify
how
facilities
must
demonstrate
that
they
are
part
of
the
low­
risk
subcategory.
For
air
toxics
risk
assessments,
we
are
implementing
a
tiered
approach.
The
screening
level
or
tier
of
analysis
is
designed,
through
the
use
of
conservative
inputs,
to
identify
situations
for
risks
are
unlikely
to
be
of
concern.
Screening
tier
analyses
are
designed
to
be
relatively
simple,
inexpensive,
and
quick,

,
defined
decision
criteria,
and
models
with
simplifying
conservative
assumptions
as
inputs.
More
refined
levels
of
analysis
include
the
refinement
of
aspects
of
the
analysis
that
are
thought
to
influence
risk
most
or
may
contain
the
greatest
uncertainty.
At
the
refined
tier,
each
analysis
requires
more
effort,
but
produces
results
that
are
less
uncertain
and
less
conservative
(
i.
e.,
less
likely
to
overestimate
risk).
1
Appendix
B
to
Subpart
DDDD
describes
a
process
based
on
this
air
toxics
approach
that
must
be
used
by
facilities
attempting
to
demonstrate
eligibility
for
the
low­
risk
subcategory
of
PCWP
facilities.
Facilities
may
demonstrate
eligibility
for
the
low­
risk
subcategory
using
either
the
"
look­
up
table"
analysis
(
described
in
Appendix
B
to
Subpart
DDDD)
or
a
tiered
site­
104
specific
analysis
(
described
in
Appendix
B
to
Subpart
DDDD
and
the
"
Air
Toxics
Risk
Assessment
Reference
Library.")
As
discussed
elsewhere
in
this
section,
we
will
be
reviewing
the
low­
risk
demonstrations
submitted
by
PCWP
facilities
to
remove
the
burden
of
reviewing
tiered
risk
assessments
from
States.

We
will
review
all
risk
assessments
performed
in
support
of
a
demonstration
of
eligibility
for
the
low­
risk
subcategory
with
regard
to
a
variety
of
aspects,
including
the
consistency
of
the
methodology
and
modeling
techniques
with
those
currently
accepted
by
the
scientific
community
and
EPA.
However,
we
will
consider
assessments
that
use
risk
methodology
and
modeling
techniques
other
than
those
described
in
EPA's
"
Air
Toxics
Risk
Assessment
Reference
Library,"
provided
they
have
undergone
scientific
peer
review
pertinent
to
their
use
in
the
submitted
assessment.

Comment:
One
commenter
stated
that,
for
EPA
to
conduct
an
up­
front
risk
analysis,
the
procedure
would
need
to
be
conducted
using
the
most
conservative
stack
parameters,
with
a
hypothetical
facility
fence
line
to
satisfy
the
many
impact
scenarios
that
could
occur.

Response:
We
conducted
a
rough
risk
assessment
to
estimate
the
number
of
PCWP
facilities
that
might
qualify
for
the
delisted
low­
risk
subcategory.
The
data
used
in
our
rough
risk
assessment
were
a
combination
of
facility­
specific
data
(
e.
g.,
process
unit
throughput)
and
industry
average
data
(
e.
g.,
industry
average
stack
parameters,
average
emission
factors
for
estimating
105
emissions).
Facilities
do
not
qualify
for
the
low­
risk
subcategory
based
on
our
rough
risk
assessment,

.
However,

facilities
can
qualify
for
inclusion
in
the
delisted
subcategory
by
using
site­
specific
emissions
test
data
and
the
look­
up
tables
or
by
conducting
a
low­
risk
demonstration,
as
described
in
Appendix
B
to
Subpart
DDDD
and/
or
in
the
"
Air
Toxics
Risk
Assessment
Reference
Library."
Look­
up
tables
were
developed
using
the
conservative
air
dispersion
model
SCREEN3.
Stack
height
and
fenceline
distance
vary
in
the
tables,
so
facilities
will
choose
the
most
appropriate
combination
of
these
parameters.

Invariant
facility
parameters
built
into
the
look­
up
tables
are
either
average
values
or
biased
towards
conservative
values,

based
on
available
data.
Thus,
we
believe
the
look­
up
tables
are
appropriately
conservative.

f.
Risk
assessment
guidance
Comment:
Several
commenters
stated
that
EPA
neglected
to
follow
its
own
guidelines
and
science
policies
in
its
proposal
for
risk­
based
exemptions.
One
commenter
argued
that
EPA
had
proposed
a
disorganized
and
cursory
approach
to
implement
riskbased
exemptions
that
fell
far
below
the
quality
of
risk
analysis
typically
required
by
EPA
across
its
other
programs.
According
106
to
the
commenter,
the
proposal
did
not
adhere
to
EPA's
established
guidelines
for
characterizing
human
health
and
ecological
risks,
did
not
incorporate
risk
assessment
guidelines
for
conducting
multi­
pathway
risk
assessments,
and
did
not
reference
EPA
guidelines
for
cumulative
risk
assessment
that
specifically
require
consideration
of
non­
inhalation
pathways.

The
commenter
noted
that
EPA's
March
1995
Risk
Characterization
Policy
set
goals
of
transparency,
clarity,
consistency,
and
reasonableness
which
apply
to
risk
assessment
practices
across
EPA.
The
commenter
argued
that
the
inconsistencies
between
EPA's
proposal
to
provide
risk­
based
exemptions
in
the
MACT
standard
process
and
its
risk
assessment
guidelines
would
undermine
many
regulatory
programs
throughout
EPA.

The
commenter
stated
that
the
risk­
based
scheme
was
based
on
a
fundamental
misunderstanding
of
the
use
of
public
health
and
ecological
risk
assessments
in
the
regulatory
process.
The
commenter
added
that
the
Federal
risk
assessment
guidelines
require
EPA
to
conduct
risk
assessments
consistently
across
all
Federal
environmental
programs.
According
to
the
commenter,
the
approaches
outlined
by
industry's
white
papers
neglected
to
include
risk
characterization,
which
provides
needed
and
appropriate
information
to
decision
makers.
The
approaches
also
did
not
incorporate
the
critical
recommendation
of
the
Commission
of
Risk
Assessment
and
Risk
Management
to
establish
a
framework
for
stakeholder­
based
risk
management
decision
making.
The
107
commenter
stated
that
these
omissions
in
the
proposal
would
prevent
regulatory
agencies
from
demonstrating
to
the
public
that
public
health
and
the
environment
are
adequately
protected.

Several
commenters
stated
that
EPA
also
needed
to
be
consistent
with
residual
risk
guidelines
currently
under
development.
One
commenter
stated
that
the
tools
needed
to
identify
sources
eligible
for
the
risk­
based
exemption
would
be
the
same
tools
necessary
for
a
section
112(
f)
residual
risk
assessment,
which
the
commenter
understood
were
not
yet
ready
for
general
use.
Another
commenter
noted
that
the
cancer
risk
guidelines
are
currently
undergoing
public
review.

A
third
commenter
stated
they
had
serious
reservations
about
EPA's
apparent
attempt
to
conduct
an
ad­
hoc
risk
analysis
for
specific
source
categories
by
seeking
comments
on
the
specific
elements
to
be
included
in
the
risk
analysis.
The
commenter
did
not
believe
these
rulemakings
were
an
adequate
forum
to
develop
this
risk
analysis
process.
The
commenter
indicated
that
any
risk
analysis
conducted
by
the
EPA
must
adhere
to
the
risk
assessment
principles
outlined
in
the
Residual
Risk
Report
to
Congress.

One
commenter
argued
that
the
proposal
is
consistent
with
EPA
risk
assessment
guidelines
and
policies
and
believed
that
others'
technical
objections
were
without
merit.
The
commenter
added
that
the
contemplated
risk­
based
applicability
criteria
were
not
in
conflict
with
the
classification
of
carcinogens
and
108
non­
carcinogens.

Response:
The
tiered
approach
to
risk
assessment
for
risk
management
decision
making
under
CAA
section
112(
c)(
9)
being
implemented
with
this
rule
is
consistent
with
that
described
in
the
Residual
Risk
Report
to
Congress.
For
air
toxics
risk
assessments
in
general,
we
are
implementing
a
tiered
approach.

The
screening
level
or
tier
of
analysis
is
designed,
through
the
use
of
conservative
inputs,
to
identify
situations
for
risks
are
unlikely
to
be
of
concern.
Screening
tier
analyses
are
designed
to
be
relatively
simple,
inexpensive,
and
quick,

,
defined
decision
criteria,
and
models
with
simplifying
conservative
assumptions
as
inputs.
More
refined
levels
of
analysis
include
the
refinement
of
aspects
of
the
analysis
that
are
thought
to
influence
risk
most
or
may
contain
the
greatest
uncertainty.
At
the
refined
tier,
each
analysis
requires
more
effort,
but
produces
results
that
are
less
uncertain
and
less
conservative
(
i.
e.,
less
likely
to
overestimate
risk).
While
Appendix
B
to
Subpart
DDDD
describes
a
process
based
on
this
air
toxics
approach
particular
to
risk
assessment
for
112(
c)(
9),
the
basis
for
this
process
stems
from
the
general
air
toxics
tiered
approach
presented
in
the
Residual
Risk
Report
to
Congress,
which
was
developed
with
full
consideration
of
EPA
risk
assessment
policy,
guidance,
and
methodology.

Section
112(
c)(
9)
requires
us
to
determine
whether
the
public
and
the
environment
are
protected.
Any
analyses
we
did
to
109
establish
the
feasibility
of
the
risk­
based
approach
or
to
develop
health
protective
look­
up
tables
included
consideration
of
human
health
as
well
as
ecological
criteria.
The
supporting
information
to
this
rule
details
the
assessment
we
conducted
to
determine
the
feasibility
of
delisting
a
low­
risk
subcategory
and
the
look­
up
tables
we
developed
to
be
used
by
facilities
in
their
demonstrations,
thereby
providing
a
public
demonstration
of
the
method
employed
to
ensure
protection
of
the
public
health
and
environment
in
decisions
associated
with
this
rule.

Additionally,
potential
for
exposures
via
non­
inhalation
pathways
(
e.
g.,
ingestion)
is
also
inherent
in
the
values
for
persistent,

bioaccumulative
HAP
in
the
look­
up
tables.

We
agree
that
the
tools
needed
to
identify
sources
eligible
for
the
delisted
low­
risk
subcategory
of
PCWP
facilities
are
the
same
tools
necessary
for
a
section
112(
f)
residual
risk
assessment.
And,
as
stated
in
the
Residual
Risk
Report
to
Congress,
we
intend
to
rely
on
the
general
methodology
and
process
illustrated
by
the
framework
presented
in
that
report
in
our
risk
assessment
activities
throughout
the
air
toxics
program.

Facilities
must
determine
eligibility
for
the
delisted
low­
risk
subcategory
using
either
a
look­
up
table
analysis
(
based
on
the
110
2U.
S.
EPA.
1999.
Guidelines
for
Carcinogen
Risk
Assessment.
NCEA­
F­
0644.
Risk
Assessment
Forum,
Washington,
DC
look­
up
tables
included
in
Appendix
B
to
Subpart
DDDD)
or
using
the
suggested
site­
specific
methodology
described
together
with
the
criteria
in
Appendix
B
to
Subpart
DDDD.
The
"
Air
Toxics
Risk
Assessment
Guidance
Library"
is
the
same
document
that
could
be
used
for
facility­
specific
residual
risk
assessments
required
under
CAA
section
112(
f).
This
document
has
been
peer­
reviewed
and
was
developed
according
to
the
principles,
tools
and
methods
outlined
in
the
Residual
Risk
Report
to
Congress.

The
comment
that
the
new
cancer
guidelines
are
still
under
review
is
correct
but,
as
stated
in
the
November
29,
2001
Federal
Register
notice
(
66
FR
59593),
these
1999
draft
guidelines
are
to
be
considered
the
interim
guidance.
2
4.
Implementation
a.
State
and
local
resources
Comment:
Several
commenters
contended
that
the
proposal
would
place
a
very
intensive
resource
demand
on
State
and
local
agencies
(
e.
g.,
permitting
authorities)
to
review
sources'
risk
assessments.
State
and
local
agencies
may
not
have
expertise
in
risk
assessment
methodology
or
the
resources
needed
to
verify
information
submitted
with
each
risk
assessment.
The
commenters
argued
that,
if
EPA
intends
to
have
the
affected
industries
111
conduct
the
analysis,
then
EPA
must
consider
the
cost
incurred
by
States,
which
may
lack
the
necessary
expertise
to
evaluate
and
review
these
analyses.

One
commenter
pointed
out
that
the
proposal
only
considered
cost
for
the
regulated
source
category,
and
not
for
regulatory
agencies.
According
to
the
commenter,
EPA
did
not
consider
the
cost
and
resources
associated
with
the
following:
(
1)
the
public
process
required
in
reviewing
and
approving
the
proposed
approaches
and,
if
approved,
making
substantial
changes
to
existing
regulations;
(
2)
the
development
of
methods
and
guidance
for
human
health
and
ecological
risk
assessments
of
affected
sources;
(
3)
the
review
by
already
budgetarily
constrained
State
agencies
of
the
assessments
and
assurance
of
adequate
public
participation
in
the
process;
and
(
4)
the
collection
and
verification
of
source­
specific
data
needed
for
conducting
risk
assessments
(
e.
g.,
emissions
data
and
stack
parameters).
The
commenter
added
that
the
proposal
did
not
address
the
critical
need
for
qualified
risk
assessors
to
evaluate
the
scientific
and
technical
basis
for
exempting
facilities
from
regulation
on
a
case­
by­
case
basis.
The
commenter
estimated
that
if
one
additional
full­
time
employee
(
FTE)
were
required
per
State
to
review
risk­
based
exemptions,
then
the
cost
would
be
an
additional
$
7.5
million
annually.

Another
commenter
pointed
out
that
the
ongoing
assurance
that
low­
risk
facilities
remain
low­
risk
would
also
increase
the
112
burden
for
the
State
and
local
agencies.
The
commenter
also
stated
that
diverting
State
and
local
resources
to
focus
on
presumably
insignificant
sources
would
detract
from
efforts
associated
with
significant
sources.

A
third
commenter
stated
that,
since
States
generally
do
not
have
the
right
staff
or
resources
to
hire
additional
staff
to
review
lengthy
and
complex
risk
analyses,
they
may
refuse
delegation
of
the
PCWP
rule,
which
would
shift
the
burden
to
EPA
in
a
time
of
tight
budgets.
According
to
the
commenter,
large
expenditures
are
not
justified
when
only
a
small
number
of
facilities
may
end
up
qualifying
for
an
exemption.

By
contrast,
several
commenters
believe
that
a
risk­
based
program
approaches
could
be
structured
and
implemented
in
a
manner
that
would
not
impose
a
substantial
cost
or
resource
burden
on
States.
One
commenter
stated
that
assuring
compliance
with
risk­
based
applicability
criteria
would
be
straightforward
and
would
not
entail
an
added
resource
burden.
Another
commenter
suggested
that
EPA
work
closely
with
States
and
industry
to
implement
the
risk­
based
approach
in
a
non­
burdensome
manner.

Two
commenters
stated
that
the
risk­
based
approaches,
like
other
MACT
standards,
would
simply
be
incorporated
into
each
State's
existing
title
V
program.
Because
the
title
V
framework
already
exists,
the
addition
of
a
risk­
based
MACT
standard
would
not
require
States
to
overhaul
existing
permitting
programs.
One
commenter
stated
that
the
risk­
based
approach
would
not
increase
113
the
number
of
sources
regulated
by
each
State.
The
commenter
believed
that
the
final
MACT
rule
itself
should
set
forth
the
applicability
criteria,
including
the
threshold
levels
of
exposure,
that
sources
must
meet
to
qualify
for
a
risk­
based
determination.
Each
source
would
have
the
burden
of
demonstrating
that
its
exposures
are
below
this
limit,
and,

therefore,
the
States
would
not
be
required
to
develop
their
own
risk
assessment
guidance
or
to
conduct
source­
specific
risk
assessments.
One
commenter
stated
that
the
risk
assessment
guidance
to
be
issued
by
EPA
within
the
next
several
months
would
streamline
the
risk­
based
approach
and
further
reduce
any
burden
on
the
States.
Three
commenters
supported
having
States
charge
reasonable
increased
fees
(
as
a
component
of
annual
operating
permit
fees
or
other
fees)
to
cover
any
significant
additional
workload
demands
associated
with
reviewing
more­
detailed
tier
2/
3
modeling.

Response:
We
acknowledge
that
review
of
the
eligibility
demonstrations
for
the
delisted
low­
risk
subcategory
will
require
resources
for
verification
of
information
and
may
require
expertise
in
risk
assessment
methodology
that
is
not
yet
available
is
some
States.
We
also
acknowledge
that
States
may
reject
delegation
of
the
PCWP
rule.
To
alleviate
these
concerns
and
to
ensure
consistency
in
the
applicability
determinations
for
the
delisted
low­
risk
subcategory
from
State­
to­
State,
we
will
review
and
approve/
disapprove
the
low­
risk
subcategory
114
eligibility
demonstrations
submitted
by
PCWP
facilities.

We
have
considered
the
above
comments
in
developing
the
criteria
defining
the
delisted
low­
risk
subcategory
of
PCWP
facilities,
and
we
believe
that
the
approach
that
is
included
in
today's
final
PCWP
rule
provides
clear,
flexible
requirements
and
enforceable
compliance
parameters.
Today's
final
PCWP
rule
provides
two
ways
that
a
facility
may
demonstrate
that
they
are
part
of
the
delisted
low­
risk
subcategory
of
PCWP
facilities.

First,
look­
up
tables,
which
are
included
in
Appendix
B
to
Subpart
DDDD,
allow
facilities
to
determine,
using
a
limited
number
of
site­
specific
input
parameters,
whether
emissions
from
their
sources
might
cause
an
HI
limit
to
be
exceeded.
Finally,
a
tiered
modeling
approach
(
each
tier
less
conservative
and
more
complex
than
the
previous)
can
be
used
by
those
facilities
that
cannot
demonstrate
that
they
are
part
of
the
delisted
low­
risk
subcategory
using
the
look­
up
tables.
With
respect
to
guidance
for
performing
low­
risk
demonstrations,
all
of
the
procedures
for
performing
risk
assessments
are
provided
in
EPA's
"
Air
Toxics
Risk
Assessment
Reference
Library,"
and,
therefore,
no
additional
guidance
needs
to
be
developed.

Only
a
portion
of
the
223
PCWP
major
sources
will
submit
eligibility
demonstrations
for
low­
risk
subcategory.
Of
this
portion
of
major
sources,
we
believe
that
most
will
find
themselves
in
the
low­
risk
subcategory
based
on
screening
analyses
(
e.
g.,
look­
up
table
or
tier
1
site­
specific
risk
115
assessment).
However,
it
is
likely
that
some
facilities
will
submit
more
detailed
tiered
risk
modeling
results.
We
are
experienced
in
reviewing
emission
test
results
and
site­
specific
risk
assessments
and
will
allocate
resources
for
completion
of
these
tasks.
We
will
review
and
approve/
disapprove
low­
risk
subcategory
eligibility
demonstrations
based
on
look­
up
table
analyses
and
low­
risk
demonstrations.
Following
review
of
each
low­
risk
subcategory
eligibility
demonstration
for
a
facility,
we
will
issue
a
letter
of
approval/
disapproval
to
the
facility
and
will
send
a
carbon
copy
to
the
facility's
title
V
permitting
authority.
The
criteria
for
low­
risk
subcategory
delisting
are
clearly
spelled
out
in
today`
s
final
PCWP
rule,
along
with
criteria
needed
to
ensure
that
facilities
in
the
low­
risk
subcategory
remain
low­
risk.
Because
these
requirements
are
clearly
spelled
out
in
today's
final
PCWP
rule
and
because
any
standards
or
requirements
created
under
section
112
are
considered
applicable
requirements
under
40
CFR
Part
70,
the
lowrisk
subcategory
delisting
would
be
incorporated
into
title
V
programs,
and
States
would
not
have
to
overhaul
existing
permitting
programs.

With
respect
to
the
burden
associated
with
ongoing
assurance
that
facilities
remain
low­
risk,
the
burden
to
States
of
assuring
that
facilities
continue
to
be
low­
risk
will
be
no
more
than
the
burden
associated
with
ongoing
title
V
enforcement
because
the
parameters
that
rendered
a
facility
low­
risk
will
be
incorporated
116
into
the
title
V
permit.
We
have
developed
continuous
compliance
requirements
for
facilities
that
initially
qualify
as
low­
risk,

and
the
facilities
will
be
responsible
for
demonstrating
that
they
continue
to
be
low­
risk
if
changes
are
made
to
the
facilities'
operations
that
would
affect
the
risk
that
the
facilities
pose
to
human
health
and
the
environment.
We
will
review
and
approve/
disapprove
revised
low­
risk
demonstrations.

With
respect
to
our
consideration
of
the
public
process
required
in
reviewing/
approving
the
proposed
approaches
and
making
substantial
changes
to
existing
regulations,
our
inclusion
of
a
risk­
based
compliance
option
in
today's
final
PCWP
rule
applies
only
to
the
PCWP
rule
and
does
not
directly
impact
other
regulations.
Furthermore,
the
PCWP
proposal
provided
the
public
with
the
opportunity
to
comment
on
the
consideration
of
risk
in
the
PCWP
rule.

Regarding
the
costs
and
resources
associated
with
assuring
adequate
public
participation
in
the
process
of
reviewing
the
risk
analyses,
draft
permits
and
permit
applications
must
be
made
available
from
the
state
or
local
agency
responsible
for
issuing
the
permit,
or
in
the
case
where
EPA
is
issuing
the
permit,
from
the
EPA
regional
office.
Members
of
the
public
may
request
that
the
state
or
local
agency
include
them
on
their
public
notice
mailing
list,
thus
providing
the
public
the
opportunity
to
review
the
risk
analysis.
Therefore,
most
of
the
burden
of
assuring
public
participation
falls
on
the
public
to
notify
the
permitting
117
authority
of
their
interest
in
the
permitting
process.
Regarding
the
opportunity
for
public
participation,
every
proposed
Title
V
permit
has
a
30
day
public
comment
period
and
a
45
day
EPA
review
period.
If
EPA
does
not
object
to
the
permit,
any
member
of
the
public
may
petition
EPA
to
object
to
the
permit
within
60
days
of
the
end
of
the
EPA
review
period.

Comment:
One
commenter
stated
that
if
EPA
intends
to
have
the
affected
industries
conduct
the
analysis,
then
EPA
must
consider
the
additional
cost
incurred
by
smaller
sources
to
do
the
analysis.

Response:
As
mentioned
previously,
there
are
two
ways
that
a
PCWP
facility
may
demonstrate
eligibility
for
the
delisted
lowrisk
subcategory:
(
1)
look­
up
tables,
and
(
2)
a
tiered
modeling
approach
(
each
tier
less
conservative
and
more
complex
than
the
previous)
that
can
be
used
by
facilities
that
cannot
demonstrate
eligibility
for
the
delisted
low­
risk
subcategory
using
the
lookup
tables.
The
look­
up
tables
included
in
Appendix
B
to
Subpart
DDDD
allow
facilities
to
determine,
using
a
limited
number
of
site­
specific
input
parameters,
whether
they
are
eligible
for
the
low­
risk
subcategory.
Attempting
to
demonstrate
eligibility
for
the
delisted
low­
risk
subcategory
is
completely
voluntary.

Facilities
that
are
not
eligible
for
the
delisted
low­
risk
subcategory
based
on
look­
up
tables
are
not
required
to
pursue
any
of
the
tiered
analyses
(
which
are
increasingly
complex
and
expensive
for
each
tier).
Each
facility
must
weigh
the
costs
of
118
making
a
low­
risk
demonstration
with
the
costs
of
MACT
compliance.
We
believe
the
costs
associated
with
demonstrating
eligibility
for
the
low­
risk
subcategory
will
be
lower
than
the
costs
associated
with
complying
with
MACT
for
many
facilities,

particularly
smaller
facilities.
The
majority
of
the
cost
associated
with
demonstrating
eligibility
for
the
delisted
lowrisk
subcategory
will
be
emissions
testing
costs.
Smaller
facilities
have
fewer
process
units
to
be
tested,
and,
because
of
their
lower
production
rates
relative
to
larger
facilities,
they
will
also
likely
have
lower
emissions.
Thus,
smaller
PCWP
facilities
may
be
more
likely
than
their
larger
counterparts
to
fall
into
the
delisted
low­
risk
subcategory.
Successfully
demonstrating
eligibility
for
the
low­
risk
provisions
will
result
in
cost­
savings
for
smaller
facilities
because
these
facilities
will
not
have
to
expend
the
costs
(
e.
g.,
the
costs
of
installing
operating,
and
maintaining
emission
controls)
for
MACT
compliance.

The
cost
and
economic
analyses
developed
as
part
of
the
MACT
rulemaking
were
based
on
the
costs
to
install
controls
and
comply
with
the
MACT
requirements.
The
costs
associated
with
voluntarily
conducting
risk
analyses
were
not
estimated.

Therefore,
our
estimate
of
costs
associated
with
today's
final
PCWP
rule
are
conservative,
because
the
control
costs
are
significantly
higher
than
the
costs
of
conducting
emissions
tests
and
risk
analyses.
119
b.
Title
V
Comment:
Two
commenters
opposed
implementing
the
risk­
based
approaches
through
the
States'
existing
title
V
programs.
One
commenter
stated
that
risk­
based
exemptions
are
such
an
implausible
interpretation
of
the
CAA
that
States
do
not
even
have
the
authority
to
grant
them
under
their
title
V
permit
programs.
The
commenter
was
not
aware
of
any
approach
to
ensure
that
emissions
remain
below
specified
levels.
According
to
the
commenter,
MACT
standard
applicability
is
the
gate­
keeper
for
being
subject
to
a
title
V
operating
permit.
Once
a
source
is
exempt
from
a
MACT
standard,
it
would
be
exempt
from
the
monitoring,
reporting
and
recordkeeping
requirements
needed
to
demonstrate
compliance.

The
other
commenter
stated
that
implementing
the
section
112(
d)(
4)
exemption
interpretation
through
title
V
would
be
unlawful
and
unworkable.
The
commenter
stated
that
Congress
knew
how
to
authorize
States
to
establish
case­
by­
case
emission
standards
and
implement
them
using
post­
rulemaking
title
V
permits
because
it
did
so
in
section
112(
j).
However,
it
did
not
do
so
in
section
112(
d)(
4).
The
commenter
argued
that
EPA
lacks
the
authority
to
delegate
section
112(
d)(
4)
to
the
States
and
may
not
implement
any
section
112(
d)(
4)
applicability
cutoff
through
a
post­
rulemaking
mechanism
such
as
a
title
V
permit.
With
the
exception
of
carefully
delineated
compliance
monitoring,

reporting,
and
certification
provisions
in
the
statute,
title
V
120
permits
may
not
create
applicable
requirements
or
exemptions
from
applicable
requirements.
The
commenter
added
that,
even
if
this
approach
is
legal,
it
is
still
unworkable
because
of
the
resource
challenges
faced
by
States
and
the
widespread
delays
in
issuing
title
V
permits.
The
commenter
noted
that
State
permit
engineers
and
officials
that
prepare
and
issue
title
V
permits
generally
are
not
experts
in
risk
assessment
or
air
dispersion
modeling.

According
to
the
commenter,
States
and
the
public
would
be
confronted
with
more
self­
serving
facility
arguments
and
data
than
could
be
adequately
scrutinized,
which
could
cause
important
health
and
risk
determinations
to
be
rubber
stamped
or
cause
the
permit
process
to
grind
to
a
halt.
The
commenter
added
that
most
State
title
V
permit
programs
are
already
behind
the
statute's
permit
issuance
deadlines,
and
implementation
of
EPA's
risk­
based
approach
would
exacerbate
this
unlawful
situation
further.

Several
commenters
supported
implementing
the
risk­
based
approaches
in
the
PCWP
rule
through
the
States'
existing
title
V
programs.
One
commenter
suggested
that
States
which
qualify
and
choose
to
do
so
should
be
delegated
the
authority
to
implement
the
risk­
based
alternatives.
The
commenter
added
that
this
would
allow
States
to
coordinate
between
the
MACT
alternatives
and
State
air
toxics
requirements.

A
second
commenter
stated
that
implementing
the
section
112(
d)(
4)
risk­
based
approach
though
title
V
would
be
lawful
and
workable.
According
to
the
commenter,
no
facility­
specific
post­
121
rulemaking
mechanisms
nor
expansion
of
the
scope
of
title
V
permit
process
would
be
necessary,
just
the
incorporation
of
the
NESHAP's
risk­
based
compliance
option,
which
would
contain
the
criteria
for
showing
what
the
source
would
have
to
meet
to
qualify
for
the
risk­
based
approach.
The
commenter
believed
that
the
objections
from
other
commenters
to
the
risk­
based
criteria
were
invalid,
arguing
that
their
objections
were
in
tension
with
the
conclusions
of
a
CAAAC
Workgroup
on
State/
Local/
Tribal
air
toxics
issues
and
that
their
comments
provided
no
basis
for
concluding
that
States
lack
the
legal
authority
to
implement
the
risk­
based
approach.

A
third
commenter
noted
that
title
V
permits
could
provide
enforceable
limitations,
appropriate
recordkeeping
requirements,

and
periodic
review
upon
renewal.
The
commenter
added
that,

since
the
PCWP
rule
would
apply
only
to
major
sources,
title
V
permits
already
are
required
and
would
not
be
an
added
burden;

title
V
could
also
be
used
to
implement
applicability
cutoffs.

However,
the
workload
involved
with
the
options
requiring
modeling,
ambient
monitoring,
or
other
means
to
establish
background
concentrations
would
be
a
hindrance
to
any
implementation
mechanism.
The
commenter
stated
that,
with
respect
to
potential
risk­
based
provisions,
monitoring
is
more
useful
for
demonstrating
non­
compliance
than
compliance
because
the
regulation
would
apply
to
potential
emissions
under
any
weather
conditions,
whereas
monitoring
reflects
current
weather
122
and
emission
conditions.

A
fourth
commenter
suggested
changes
to
the
§
63.2240
of
the
proposed
rule
that
would
incorporate
permitting
procedures
similar
to
those
under
40
CFR
Part
70,
which
would
allow
facilities
that
pose
little
risk
in
their
respective
airsheds
to
apply
for
a
risk
determination
to
be
incorporated
into
their
title
V
permits.
Each
source
applying
to
be
permitted
as
a
subcategorized
toxic
emitter
with
an
acceptable
risk
determination
would
be
required
to
perform
detailed
risk
analyses
for
review
by
the
public
at
large,
local
citizens,
State
agencies,
and
Federal
authorities.
This
permitting
exercise
would
allow
managers
of
the
airshed
to
develop
custom­
fit
compliance
plans
that
address
source­
specific
risks
and
would
allow
the
most
flexibility
for
forest
producers
to
reduce
their
identified
risks.

Response:
As
discussed
previously,
we
have
determined
that
a
section
112(
d)(
4)
risk­
based
exemption
would
not
be
appropriate
for
the
PCWP
source
category.
Instead,
using
our
discretion
in
establishing
subcategories
of
sources
based
on
size,
type,
or
class,
we
have
established
and
delisted
a
low­
risk
subcategory
of
PCWP
facilities.
The
requirements
for
qualifying
for
and
remaining
in
the
delisted
low­
risk
subcategory
are
clearly
spelled
out
in
Appendix
B
to
Subpart
DDDD,
and
any
standards
or
requirements
created
under
section
112
are
considered
applicable
requirements
under
40
CFR
Part
70.
Therefore,
the
parameters
123
used
to
certify
that
facilities
are
part
of
the
delisted
low­
risk
subcategory
would
be
incorporated
into
title
V
permits,
and
States
would
not
have
to
overhaul
existing
permitting
programs.

Facilities
that
qualify
as
part
of
the
delisted
low­
risk
subcategory
will
initially
demonstrate
that
they
are
low­
risk
using
either
the
look­
up
tables
or
site­
specific
monitoring.

They
will
demonstrate
that
risk
does
not
increase
by
documenting
that
parameters
that
impact
the
risk
analysis
do
not
change
in
a
way
that
increases
risk.
Facilities
will
not
be
required
to
perform
detailed
risk
analyses
for
public
review.

We
acknowledge
the
resource
challenges
faced
by
States,
and,

therefore,
we
will
retain
the
authority
to
review
and
approve/
disapprove
the
low­
risk
subcategory
eligibility
demonstrations
submitted
by
PCWP
facilities.

With
regard
to
the
title
V
permit
programs
being
behind
the
statute's
permit
issuance
deadlines,
the
incorporation
of
the
NESHAP
requirements
is
a
necessary
step
that
will
require
some
resources.
Inclusion
of
the
low­
risk
subcategory
delisting
should
be
a
straightforward
part
of
the
process
and
should
not
cause
significant
delay.
