Document ID: EPA-HQ-OAR-2003-0048-0093
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2004-02-25T05:00Z

Teresa
Clemons
To:
Edmond_
Toy@
omb.
eop.
gov,
afraas@
omb.
eop.
gov
02/
06/
04
04:
56
PM
cc:
Jeff
Holmstead/
DC/
USEPA/
US@
EPA,
Bill
Wehrum/
DC/
USEPA/
US@
EPA,
Alexander
Cristofaro/
DC/
USEPA/
US@
EPA,
Patricia
Embrey/
DC/
USEPA/
US@
EPA,
Mike
Thrift/
DC/
USEPA/
US@
EPA,
Keith
Mason/
DC/
USEPA/
US@
EPA,
(
bcc:
Mary
Kissell/
RTP/
USEPA/
US)
Subject:
Advance
Copy
of
Risk
Information
­
Plywood
and
Composite
Wood
Products
Attached
are
advanced
copies
of
the
risk
information
for
the
Plywood
and
Composite
Wood
Products.
We
are
still
drafting
sections
and
revising
text
for
the
risk
portion
of
the
MACT,
so
these
files
are
not
yet
complete.
Please
call
Mary
Tom
Kissell
at
919­
541­
4516
if
you
have
any
questions.

(
See
attached
file:
pcwp_
appB
06feb04.
wpd)(
See
attached
file:
plywood
risk
preamble.
wpd)

THANKS!
Teresa
Clemons
Emission
Standards
Division
919­
541­
0252
919­
541­
0072
(
Fax)
1
02/
05/
04
revised
draft
§
63.2231
Does
this
subpart
apply
to
me?

This
subpart
applies
to
you
if
you
meet
the
criteria
in
paragraphs
(
a)
and
(
b)
of
this
section
(
a)
You
own
or
operate
a
plywood
and
composite
wood
products
(
PCWP)
manufacturing
facility.
A
PCWP
manufacturing
facility
is
a
facility
that
manufactures
plywood
and/
or
composite
wood
products
by
bonding
wood
material
(
fibers,
particles,

strands,
veneers,
etc.)
or
agricultural
fiber,
generally
with
resin
under
heat
and
pressure,
to
form
a
structural
panel
or
engineered
wood
product.
Plywood
and
composite
wood
products
manufacturing
facilities
also
include
facilities
that
manufacture
dry
veneer
and
lumber
kilns
located
at
any
facility.
Plywood
and
composite
wood
products
include
(
but
are
not
limited
to)
plywood,

veneer,
particleboard,
oriented
strandboard,
hardboard,

fiberboard,
medium
density
fiberboard,
laminated
strand
lumber,

laminated
veneer
lumber,
wood
I­
joists,
kiln­
dried
lumber,
and
glue­
laminated
beams.

(
b)
The
PCWP
manufacturing
facility
is
located
at
a
major
source
of
HAP
emissions.
A
major
source
of
HAP
emissions
is
any
stationary
source
or
group
of
stationary
sources
within
a
2
contiguous
area
and
under
common
control
that
emits
or
has
the
potential
to
emit
any
single
HAP
at
a
rate
of
9.07
megagrams
(
10
tons)
or
more
per
year
or
any
combination
of
HAP
at
a
rate
of
22.68
megagrams
(
25
tons)
or
more
per
year.
3
Appendix
B
to
Subpart
DDDD
 
Methodology
and
Criteria
for
Demonstrating
That
An
Affected
Source
is
Part
of
the
Low­
risk
Subcategory
of
Plywood
and
Composite
Wood
Products
Manufacturing
Facilities
1.
Purpose
This
appendix
provides
the
methodology
and
criteria
for
demonstrating
that
your
affected
source
is
part
of
the
low­
risk
subcategory
of
plywood
and
composite
wood
products
(
PCWP)

manufacturing
facilities.
You
must
determine
if
your
facility
is
part
of
the
low­
risk
subcategory
using
either
a
look­
up
table
analysis
(
based
on
the
look­
up
tables
included
in
this
appendix)

or
using
a
site­
specific
risk
assessment
performed
according
to
the
criteria
specified
in
this
appendix.
This
appendix
also
specifies
how
and
when
you
must
obtain
approval
of
the
low­
risk
demonstrations
for
your
affected
source
and
how
to
ensure
that
your
affected
source
remains
in
the
low­
risk
subcategory
of
PCWP
facilities.

2.
Who
is
eligible
to
demonstrate
that
they
are
part
of
the
lowrisk
subcategory
of
PCWP
facilities?

Each
new,
reconstructed,
or
existing
affected
source
at
a
PCWP
manufacturing
facility
may
demonstrate
that
they
are
part
of
the
low­
risk
subcategory
of
PCWP
facilities.
Section
§
63.2232
of
4
subpart
DDDD
defines
the
affected
source
and
explains
which
affected
sources
are
new,
existing,
or
reconstructed.

3.
What
parts
of
my
facility
have
to
be
included
in
the
low­
risk
demonstration?

Every
process
unit
that
is
part
of
the
PCWP
affected
source
(
as
defined
in
§
63.2292
of
subpart
DDDD)
and
that
emits
one
or
more
HAP
listed
in
Table
1
of
this
appendix
must
be
included
in
the
low­
risk
demonstration.
You
are
not
required
to
include
process
units
outside
of
the
affected
source
in
the
low­
risk
demonstration.

4.
What
are
the
criteria
for
determining
if
my
facility
is
low
risk?

(
a)
Determine
the
individual
HAP
emission
rates
from
each
process
unit
within
the
affected
source
using
the
procedures
specified
in
section
5
of
this
appendix.

(
b)
Perform
chronic
and
acute
risk
assessments
using
the
dose­
response
values
found
at
http://
www.
epa.
gov/
ttn/
atw/
toxsource/
summary.
html,
as
specified
in
paragraphs
(
b)(
1)
and
(
2)
of
this
section.

(
1)
For
a
look­
up
table
analysis
or
site­
specific
chronic
inhalation
risk
assessment,
you
should
use
the
cancer
and
5
noncancer
dose­
response
values
listed
on
the
EPA
Air
Toxics
website
(
http://
www.
epa.
gov/
ttn/
atw/
toxsource/
summary.
html)
to
estimate
carcinogenic
and
non­
carcinogenic
chronic
inhalation
risk,
respectively.

(
2)
For
site­
specific
acute
inhalation
risk
assessment,
you
must
use
the
acute
exposure
guidance
level
(
AEGL­
1)
value
for
acrolein
and
the
California
EPA
(
CalEPA)
acute
reference
exposure
level
(
REL)
value
for
formaldehyde
for
estimating
acute
inhalation
risk.

(
c)
Determine
if
your
facility
is
part
of
the
low­
risk
subcategory
by
estimating
the
maximum
chronic
and
acute
impacts
of
your
facility
using
one
of
the
methods
described
in
either
section
6
of
this
appendix
(
look­
up
table
analysis)
or
section
7
of
this
appendix
(
site­
specific
risk
assessment)
and
comparing
the
results
to
the
low­
risk
criteria.
Your
facility
is
low
risk
if
the
estimated
maximum
individual
lifetime
cancer
risk
is
less
than
1
in
a
million,
the
estimated
maximum
chronic
hazard
index
values
for
respiratory
effects
and
central
nervous
system
(
CNS)

effects
are
less
than
1,
and
the
estimated
maximum
acute
hazard
quotient
values
for
acrolein
and
formaldehyde
are
less
than
1.

5.
How
do
I
determine
HAP
emissions
from
my
affected
source?

(
a)
You
must
conduct
HAP
emissions
tests
according
to
the
6
requirements
in
paragraphs
(
b)
through
(
g)
of
this
section
and
the
methods
specified
in
Table
2
of
this
appendix
for
every
process
unit
within
the
affected
source
that
emits
one
or
more
of
the
HAP
listed
in
Table
1.
You
must
test
the
process
units
at
your
facility
to
obtain
the
emission
rates
in
pounds
per
hour
(
lb/
hr)
for
each
of
the
pollutants
listed
in
Table
1.

(
b)
Periods
when
emissions
tests
must
be
conducted.

(
1)
You
must
not
conduct
emissions
tests
during
periods
of
startup,
shutdown,
or
malfunction,
as
specified
in
§
63.7(
e)(
1).

(
2)
You
must
test
under
worst­
case
operating
conditions
as
defined
in
this
appendix.
You
must
describe
your
worst­
case
operating
conditions
in
your
performance
test
report
for
the
process
and
control
systems
(
if
applicable)
and
explain
why
the
conditions
are
worst­
case.

(
c)
Number
of
test
runs.
You
must
conduct
three
separate
test
runs
for
each
test
required
in
this
section,
as
specified
in
§
63.7(
e)(
3).
Each
test
run
must
last
at
least
1
hour
except
for:

testing
of
a
temporary
total
enclosure
(
TTE)
conducted
using
Methods
204A
through
204F
which
require
three
separate
test
runs
of
at
least
3
hours
each;
and
testing
of
an
enclosure
conducted
using
the
alternative
tracer
gas
method
in
appendix
A
to
subpart
DDDD
which
requires
a
minimum
of
three
separate
runs
of
at
least
7
20
minutes
each.

(
d)
Sampling
locations.
Sampling
sites
must
be
located
at
the
outlet
of
the
control
device,
including
wet
control
devices,

and
prior
to
any
releases
to
the
atmosphere.

(
e)
Collection
of
monitoring
data
for
HAP
control
devices.

During
the
emissions
test,
you
must
collect
operating
parameter
monitoring
system
or
continuous
emissions
monitoring
system
(
CEMS)
data
at
least
every
15
minutes
during
the
entire
emissions
test
and
establish
the
site­
specific
operating
requirements
(
including
the
parameter
limits
or
total
hydrocarbon
(
THC)

concentration
limit)
in
Table
2
of
subpart
DDDD
using
data
from
the
monitoring
system
and
the
procedures
specified
in
paragraphs
(
k)
through
(
o)
of
§
63.2262
of
subpart
DDDD.

(
f)
Nondetect
data.
You
may
treat
emissions
of
an
individual
HAP
as
zero
if
all
of
the
test
runs
result
in
a
nondetect
measurement
and
the
conditions
in
paragraphs
(
1)
and
(
2)
are
met
for
the
relevant
test
method.
Otherwise
nondetect
data
(
as
defined
in
§
63.2292
of
subpart
DDDD)
for
individual
HAP
must
be
treated
as
one­
half
of
the
method
detection
limit.

(
1)
The
method
detection
limit
is
less
than
or
equal
to
1
part
per
million
by
volume,
dry
(
ppmvd)
for
pollutant
emissions
8
measured
using
Method
320
in
appendix
A
to
40
CFR
part
63;
or
the
NCASI
Method
IM/
CAN/
WP­
99.02;
or
ASTM
D6348­
03.

(
2)
For
pollutants
measured
using
Method
29
in
appendix
A
to
40
CFR
part
60,
you
analyze
samples
using
atomic
absorption
spectroscopy
(
AAS).

(
g)
For
purposes
of
your
low­
risk
demonstration,
assume
that
17
percent
of
your
total
chromium
measured
using
EPA
Method
29
in
appendix
A
to
40
CFR
part
60
is
chromium
(
VI).
For
purposes
of
your
low­
risk
demonstration,
assume
that
65
percent
of
your
total
nickel
measured
using
EPA
Method
29
in
appendix
A
to
40
CFR
part
60
is
nickel
subsulfide.

6.
How
do
I
conduct
a
look­
up
table
analysis?

Use
the
look­
up
tables
to
determine
if
your
facility
is
part
of
the
low­
risk
subcategory,
following
the
procedures
in
paragraphs
(
a)
through
(
d)
of
this
section.

(
a)
Using
the
emission
rate
of
each
HAP
required
to
be
included
in
your
low­
risk
demonstration,
determine
your
total
toxicity­
weighted
carcinogen
and
non­
carcinogen
emission
rates
for
each
of
your
process
units
using
Equations
1
and
2
of
this
appendix,
respectively.
9
TWCER
=

(
ERi
x
UREi)
Eqn.
1
TWCER
=
Toxicity­
weighted
carcinogenic
emission
rate,

(
lb/
hr)/(
µ
g/
m3)

ERi
=
Emission
rate
of
pollutant
i,
pounds
per
hour
(
lb/
hr)

UREi
=
Unit
risk
estimate
for
pollutant
i,
1
per
microgram
per
cubic
meter
(
µ
g/
m3)­
1
TWNER
=

(
ERi
/
RfCi)
Eqn.
2
TWNER
=
Toxicity­
weighted
non­
carcinogenic
emission
rate,

(
lb/
hr)

ERi
=
Emission
rate
of
pollutant
i,
pounds
per
hour
(
lb/
hr)

RfCi
=
Reference
concentration
for
pollutant
i,

milligrams
per
cubic
meter
(
mg/
m3)

(
b)
Cancer
risk.
Determine
the
total
toxicity­
weighted
carcinogen
emission
rate
for
your
affected
source
by
summing
the
toxicity­
weighted
carcinogen
emission
rates
for
each
of
your
process
units.
Select
the
maximum
allowable
toxicity­
weighted
10
carcinogen
emission
rate
from
Table
3
of
this
appendix
for
your
facility
using
the
average
stack
height
of
your
process
units
and
the
minimum
distance
between
any
HAP
emission
point
at
the
facility
and
the
closest
boundary
of
the
nearest
residential,
or
residentially
zoned,
area.
If
one
or
both
of
these
values
do
not
match
the
values
in
the
lookup
tables
then
use
the
next
lowest
table
value.
Your
facility
is
low­
risk
for
carcinogenic
effects
if
your
toxicity­
weighted
carcinogen
emission
rate,
determined
using
the
methods
specified
in
this
appendix,
does
not
exceed
the
values
specified
in
Table
3
of
this
appendix.

(
c)
Non­
cancer
risk.
Determine
the
total
CNS
and
respiratory
target
organ
specific
toxicity­
weighted
noncarcinogen
emission
rate
for
your
affected
source
by
summing
the
toxicity­
weighted
emission
rates
for
each
of
your
emission
points.
Select
the
maximum
allowable
toxicity­
weighted
noncarcinogen
emission
rate
from
Table
4
of
this
appendix
for
your
facility
using
the
average
stack
height
of
your
process
units
and
the
minimum
distance
between
any
HAP
emission
point
at
the
facility
and
the
closest
boundary
of
the
nearest
residential,
or
residentially
zoned,
area.
If
one
or
both
of
these
values
do
not
match
the
values
in
the
lookup
tables
then
use
the
next
lowest
table
value.
Your
facility
is
low­
risk
for
non­
carcinogenic
effects
if
your
toxicity­
weighted
non­
carcinogen
emission
rate,

determined
using
the
methods
specified
in
this
appendix,
does
not
11
exceed
the
values
specified
in
Table
4
of
this
appendix.

(
d)
Low­
risk
demonstration.
Your
facility
is
part
of
the
low­
risk
subcategory
of
PCWP
sources
if
your
affected
source
is
determined
to
be
low
risk
for
both
carcinogenic
and
noncarcinogenic
effects
using
the
look­
up
table
analysis
described
in
this
section
and
you
meet
the
criteria
specified
in
Section
11
of
this
appendix.

7.
How
do
I
conduct
a
site­
specific
risk
assessment?

Perform
a
site­
specific
risk
assessment
following
the
procedures
specified
in
this
section.
You
may
use
any
scientifically­
accepted
peer­
reviewed
assessment
methodology
for
your
site­
specific
risk
assessment.
An
example
approach
to
performing
a
site­
specific
risk
assessment
for
air
toxics
is
provided
in
the
"
Air
Toxics
Risk
Assessment
Guidance
Reference
Library".
You
may
obtain
a
copy
of
the
"
Air
Toxics
Risk
Assessment
Reference
Library"
from
EPA's
air
toxics
website
(
a)
Your
facility
is
low­
risk
for
carcinogenic
chronic
inhalation
effects
if
your
site­
specific
risk
assessment
demonstrates
that
maximum
off­
site
individual
lifetime
cancer
risk
at
a
location
where
people
can
live
is
less
than
one
in
one
million.
12
(
b)
Your
facility
is
low­
risk
for
non­
carcinogenic
chronic
inhalation
effects
if
your
site­
specific
risk
assessment
demonstrates
that
every
maximum
off­
site
target­
organ
specific
hazard
index
(
TOSHI)
at
a
location
where
people
can
live
is
less
than
1.

(
c)
Your
facility
is
low­
risk
for
non­
carcinogenic
acute
inhalation
effects
if
your
site­
specific
risk
assessment
demonstrates
that
the
maximum
off­
site
acute
hazard
quotients
for
both
acrolein
and
formaldehyde
are
less
than
1.

(
d)
Your
facility
is
part
of
the
low­
risk
subcategory
of
PCWP
facilities
if
the
affected
source
is
determined
to
be
low
risk
for
all
of
the
applicable
effects
listed
in
paragraphs
(
a)

through
(
c)
of
this
section
and
you
meet
the
criteria
specified
in
section
11
of
this
appendix.

8.
What
information
must
I
submit
for
the
low­
risk
demonstration?

(
a)
Your
low­
risk
demonstration
must
include
the
information
specified
in
paragraphs
(
a)(
1)
through
(
5)
of
this
section
and
the
information
specified
in
either
paragraph
(
b)
or
(
c)
of
this
section.

(
1)
Identification
of
each
process
unit
at
the
affected
source.

(
2)
Stack
parameters
for
each
HAP
emission
point
including,
13
but
not
limited
to,
the
parameters
listed
in
(
a)(
2)(
i)
through
(
iv)
below:

(
i)
Emission
release
type.

(
ii)
Stack
height,
stack
area,
stack
gas
temperature,
and
stack
gas
exit
velocity.

(
iii)
Plot
plan
showing
all
HAP
emission
points,
nearby
residences,
and
fenceline.

(
iv)
Identification
of
any
HAP
control
devices
used
to
reduce
emissions
from
each
process
unit.

(
3)
Emission
test
reports
for
each
process
unit
based
on
the
test
methods
specified
in
Table
2
of
this
appendix,
including
a
description
of
the
process
parameters
identified
as
being
worst
case.

(
4)
Identification
of
the
dose­
response
values
used
in
your
risk
analysis
(
look­
up
table
analysis
or
site­
specific
risk
assessment),
according
to
section
5(
b)
of
this
appendix.

(
5)
Identification
of
the
controlling
process
factors
(
including,
but
not
limited
to,
production
rate,
annual
emission
rate,
type
of
control
devices,
process
parameters
documented
as
worst­
case
conditions
during
the
emissions
testing
used
for
your
low­
risk
demonstration)
that
will
become
Federally
enforceable
permit
conditions
used
to
show
that
your
facility
remains
in
the
low­
risk
subcategory.
14
(
b)
If
you
use
the
look­
up
table
analysis
in
section
6
of
this
appendix
to
demonstrate
that
your
facility
is
low
risk,
your
low­
risk
demonstration
must
contain
the
information
in
paragraphs
(
a)
and
(
b)(
1)
through
(
4)
of
this
section.

(
1)
Identification
of
the
process
unit
stack
heights
included
in
the
calculation
of
average
stack
height.

(
2)
Identification
of
the
process
unit
with
the
nearest
distance
to
a
residential,
or
residentially
zoned,
area.

(
3)
Calculations
used
to
determine
the
toxicity­
weighted
carcinogen
and
non­
carcinogen
emission
rates
according
to
section
6(
a)
of
this
appendix.

(
4)
Comparison
of
the
values
in
the
look­
up
tables
(
Tables
3
and
4
of
this
appendix)
to
your
toxicity­
weighted
emission
rates
for
carcinogenic
and
non­
carcinogenic
HAP.

(
c)
If
you
are
using
a
site­
specific
risk
assessment
as
described
in
section
7
of
this
appendix
to
demonstrate
that
your
facility
is
low
risk
(
for
carcinogenic
and
non­
carcinogenic
chronic
inhalation
and
acute
inhalation
risks),
your
low­
risk
demonstration
must
contain
the
information
in
paragraphs
(
a)
and
(
c)(
1)
through
(
8)
of
this
section:

(
1)
Identification
of
the
risk
assessment
methodology
used.

(
2)
Documentation
of
the
fate
and
transport
model
used.

(
3)
Documentation
of
the
fate
and
transport
model
inputs,
15
including
the
information
described
in
paragraphs
(
a)(
1)
through
(
4)
of
this
section
converted
to
the
dimensions
required
for
the
model
and
all
of
the
following
that
apply:
meteorological
data;

building,
land
use,
and
terrain
data;
receptor
locations
and
population
data;
and
other
facility­
specific
parameters
input
into
the
model.

(
4)
Documentation
of
the
fate
and
transport
model
outputs.

(
5)
Documentation
of
exposure
assessment
and
risk
characterization
calculations.

(
6)
Comparison
of
the
carcinogenic
inhalation
risk
to
1
in
a
million,
as
required
in
section
7(
a)
of
this
appendix.

(
7)
Comparison
of
each
chronic
inhalation
TOSHI
(
for
respiratory
effects
and
CNS
effects)
to
the
limit
of
1,
as
required
in
section
7(
b)
of
this
appendix.

(
8)
Comparison
of
the
acute
inhalation
HQ
to
the
limit
of
1,

as
required
in
section
7(
c)
of
this
appendix.

9.
Where
do
I
send
my
low­
risk
demonstration?

You
must
submit
your
low­
risk
demonstration
to
EPA
for
review
and
approval.
Send
your
low­
risk
demonstration
to
U.
S.

EPA,
Risk
and
Exposure
Assessment
Group,
Emission
Standards
Division
(
C404­
01),
Attn:
Dr.
David
Guinnup,
Research
Triangle
Park,
NC
27711.
You
are
not
part
of
the
low­
risk
subcategory
16
until
you
meet
the
requirements
of
section
11
of
this
appendix.

10.
When
do
I
submit
my
low­
risk
demonstration?

(
a)
If
you
have
an
existing
affected
source,
you
must
complete
and
submit
for
approval
your
low­
risk
demonstration
no
later
than
[
INSERT
14
MONTHS
AFTER
DATE
OF
PUBLICATION].

(
b)
If
you
have
a
new
or
reconstructed
affected
source
that
starts
up
before
the
effective
date
of
subpart
DDDD,
or
an
affected
source
that
is
an
area
source
that
increases
its
emissions
or
its
potential
to
emit
such
that
it
becomes
a
major
source
of
HAP
before
[
INSERT
2
MONTHS
AFTER
PUBLICATION],
then
you
must
comply
with
the
requirements
of
subpart
DDDD
until
you
meet
the
criteria
in
section
11
of
this
appendix.

(
c)
If
you
have
a
new
or
reconstructed
affected
source
that
starts
up
after
[
INSERT
2
MONTHS
AFTER
PUBLICATION],
or
an
affected
source
that
is
an
area
source
that
increases
its
emissions
or
its
potential
to
emit
such
that
it
becomes
a
major
source
of
HAP
after
[
INSERT
2
MONTHS
AFTER
PUBLICATION],
then
you
must
follow
the
schedule
in
paragraphs
(
1)
and
(
2)
of
this
section.

(
1)
You
must
complete
and
submit
for
approval
a
preliminary
17
low­
risk
demonstration
based
on
the
information
(
e.
g.,
equipment
types,
estimated
emission
rates,
etc.)
used
to
obtain
your
title
V
permit.
You
must
base
your
preliminary
low­
risk
demonstration
on
the
maximum
emissions
allowed
under
your
title
V
permit.
If
EPA
concludes
that
your
affected
source
appears
to
be
part
of
the
low­
risk
subcategory
based
on
this
preliminary
low­
risk
demonstration,
then
your
may
start
up
your
affected
source
without
complying
with
the
compliance
options,
operating
requirements,
and
work
practice
requirements
in
subpart
DDDD.

(
2)
You
must
conduct
the
emission
tests
specified
in
section
4
of
this
appendix
upon
initial
startup
and
use
the
results
of
these
emissions
tests
to
complete
and
submit
your
low­
risk
demonstration
within
180
days
following
your
initial
startup
date.
To
be
included
in
the
low­
risk
subcategory,
you
must
meet
the
criteria
in
section
11
of
this
appendix
within
18
months
following
initial
startup
of
your
affected
source.

11.
How
does
my
facility
become
part
of
the
low­
risk
subcategory?

To
be
included
in
the
low­
risk
subcategory,
you
must
meet
the
criteria
in
paragraphs
(
a)
and
(
b)
of
this
section.
If
you
do
not
meet
these
criteria,
then
your
affected
source
is
subject
to
the
applicable
compliance
options,
operating
requirements,
and
18
work
practice
requirements
in
Subpart
DDDD.

(
a)
Your
demonstration
of
low­
risk
must
be
approved
by
EPA.

(
b)
The
parameters
that
defined
your
affected
source
as
part
of
the
low­
risk
subcategory
(
including,
but
not
limited
to,

production
rate,
annual
emission
rate,
type
of
control
devices,

process
parameters
documented
as
worst­
case
conditions
during
the
emissions
testing
used
for
your
low­
risk
demonstration)
must
be
incorporated
as
Federally
enforceable
limits
into
your
title
V
permit.

12.
What
must
I
do
to
ensure
my
facility
remains
a
low­
risk
facility?

(
a)
You
must
meet
the
requirements
in
Table
2
of
subpart
DDDD
for
each
HAP
control
device
used
at
the
time
when
you
completed
your
low­
risk
demonstration.
You
must
monitor
and
collect
data
according
to
§
63.2270
of
subpart
DDDD
to
show
continuous
compliance
with
your
control
device
operating
requirements.
You
must
demonstrate
continuous
compliance
with
the
control
device
operating
requirements
that
apply
to
you
by
collecting
and
recording
the
monitoring
system
data
listed
in
Table
2
of
this
subpart
for
the
process
unit
according
to
§
§
63.2269(
a),
(
b),
and
(
d)
of
subpart
DDDD;
AND
reducing
the
monitoring
system
data
to
the
specified
averages
in
units
of
the
19
applicable
requirement
according
to
calculations
in
§
63.2270
of
subpart
DDDD;
AND
maintaining
the
average
operating
parameter
at
or
above
the
minimum,
at
or
below
the
maximum,
or
within
the
range
(
whichever
applies)
established
according
to
section
4(
e)

of
this
appendix.

13.
What
happens
if
the
critera
used
in
the
risk
determination
change?

(
a)
You
must
certify
with
each
Title
V
permit
renewal
that
the
basis
for
your
facility's
low­
risk
determination
has
not
changed.
You
must
submit
this
certification
to
the
permitting
authority.
You
must
consider
the
following:

(
1)
Process
changes
that
increases
HAP
emissions,
including,

but
not
limited
to,
production
rate
increase,
annual
emission
rate
increase,
change
in
type
of
control
device,
changes
in
process
parameters
documented
as
worst­
case
conditions
during
the
emissions
testing
used
for
your
approved
low­
risk
demonstration.

(
2)
Population
shifts.

(
3)
Unit
risk
estimate
increases.

(
4)
Reference
concentration
decreases.

(
5)
Dose
response
values
(
URE,
RfC,
CSF,
and
RfD)
on
the
EPA
website
(
http://
www.
epa.
gov/
ttn/
atw/
toxsource/
summary.
html).
20
(
b)
At
any
time
a
change
occurs
that
was
not
a
permit
condition,
including
the
changes
listed
in
paragraphs
(
a)(
1)

through
(
5),
you
must
notify
the
permitting
authority
immediately.

(
1)
If
the
change
does
not
change
the
risk
designation
of
the
facility,
you
must
explain
the
change
and
why
the
facility
is
still
low
risk.
You
must
also
certify
that
the
facility
is
still
low
risk
and
part
of
the
low­
risk
subcategory.

(
2)
If
the
change
results
in
the
facility
no
longer
being
low
risk,
then
the
facility
is
no
longer
part
of
the
low­
risk
subcategory
and
is
subject
to
all
the
applicable
requirements
of
subpart
DDDD.

(
3)
If
your
facility
is
no
longer
low
risk,
you
may
update
your
low­
risk
demonstration
and
resubmit
it
to
EPA.
You
must
submit
your
revised
low­
risk
demonstration
to
EPA
prior
to
revising
your
permit
to
incorporate
the
process
change.
If
you
use
the
same
approach/
risk
assessment
model,
you
may
.
.
.
[
text
needed
if
possible
to
expedite
reveiw
 
REAG]
time
14.
What
records
must
I
keep?

(
a)
You
must
keep
records
of
the
information
used
in
developing
the
low­
risk
demonstration
for
your
affected
source,

including
all
of
the
information
specified
in
section
8
of
this
appendix.
21
(
b)
You
must
keep
the
records
required
in
section
12(
d)
of
this
appendix
to
show
continuous
compliance
with
the
operating
requirements
for
control
devices.

(
c)
For
each
THC
CEMS,
you
must
keep
the
records
specified
in
§
63.2282(
c)
of
subpart
DDDD.

15.
Definitions.

The
definitions
in
§
63.2292
of
subpart
DDDD
apply
to
this
appendix.
Additional
definitions
applicable
for
this
appendix
are
as
follows:

Direct­
fired
process
unit
means
a
process
unit
that
is
heated
by
the
passing
of
combustion
exhaust
directly
through
the
process
unit
such
that
the
process
material
is
contacted
by
the
combustion
exhaust.

Hazard
Index
(
HI)
means
the
sum
of
more
than
one
hazard
quotient
for
multiple
substances
and/
or
multiple
exposure
pathways.

Hazard
Quotient
(
HQ)
means
the
ratio
of
the
predicted
media
concentration
of
a
pollutant
to
the
media
concentration
at
which
no
adverse
effects
are
expected.
For
inhalation
exposures,
the
22
HQ
is
calculated
as
the
air
concentration
divided
by
the
RfC.

Look­
up
table
analysis
means
a
risk
screening
analysis
based
on
comparing
the
toxicity­
weighted
HAP
emission
rate
from
the
affected
source
to
the
maximum
allowable
toxicity­
weighted
HAP
emission
rates
specified
in
Tables
3
and
4
of
this
appendix.

Reference
Concentration
(
RfC)
means
an
estimate
(
with
uncertainty
spanning
perhaps
an
order
of
magnitude)
of
a
continuous
inhalation
exposure
to
the
human
population
(
including
sensitive
subgroups)
that
is
likely
to
be
without
an
appreciable
risk
of
deleterious
effects
during
a
lifetime.
It
can
be
derived
from
various
types
of
human
or
animal
data,
with
uncertainty
factors
generally
applied
to
reflect
limitations
of
the
data
used.

Target
organ
specific
hazard
index
(
TOSHI)
means
the
sum
of
hazard
quotients
for
individual
chemicals
that
affect
the
same
organ
or
organ
system
(
e.
g.,
respiratory
system,
central
nervous
system).

Unit
Risk
Estimate
(
URE)
means
the
upper­
bound
excess
lifetime
cancer
risk
estimated
to
result
from
continuous
exposure
to
an
agent
at
a
concentration
of
1
µ
g/
m3
in
air.
23
Worst­
case
operating
conditions
means
operation
of
a
process
unit
during
emissions
testing
under
the
conditions
that
result
in
the
highest
HAP
emissions
or
that
result
in
the
emissions
stream
composition
(
including
HAP
and
non­
HAP)
that
is
most
challenging
for
the
control
device
if
a
control
device
is
used.
For
example,

worst
case
conditions
could
include
operation
of
the
process
unit
at
maximum
throughput,
at
its
highest
temperature,
with
the
wood
species
mix
likely
to
produce
the
most
HAP,
and/
or
with
the
resin
formulation
containing
the
greatest
HAP.
24
Table
1
to
Appendix
B
of
Subpart
DDDD.
HAP
that
must
be
included
in
the
demonstration
of
eligibility
for
the
low­
risk
PCWP
subcategory.

For
your
analysis
of
the
following
effects...
You
must
include
the
following
HAP...

(
1)
Chronic
inhalation
cancer
acetaldehyde,
benzene,
arsenic,
beryllium,
cadmium,
chromium,
lead,
nickel,
formaldehyde.

(
2)
Chronic
inhalation
noncancer
respiratory
acetaldehyde,
acrolein,
formaldehyde,
.

(
3)
Chronic
inhalation
noncancer
CNS
manganese,
phenol.

(
4)
Acute
inhalation
acrolein,
formaldehyde.
25
Table
2
to
Appendix
B
of
Subpart
DDDD.
Emission
Test
Methods.

For...
You
must...
Using...

(
1)
each
process
unit
select
sampling
ports'
location
and
the
number
of
traverse
points
Method
1
or
1A
of
40
CFR
part
60,
appendix
A
(
as
appropriate).

(
2)
each
process
unit
determine
velocity
and
volumetric
flow
rate;
Method
2
in
addition
to
Method
2A,
2C,
2D,
2F,
or
2G
in
appendix
A
to
40
CFR
part
60
(
as
appropriate).

(
3)
each
process
unit
conduct
gas
molecular
weight
analysis
Method
3,
3A,
or
3B
in
appendix
A
to
40
CFR
part
60
(
as
appropriate).

(
4)
each
process
unit
measure
moisture
content
of
the
stack
gas
Method
4
in
appendix
A
to
40
CFR
part
60.

(
5)
each
process
unit
measure
emissions
of
the
following
HAP:
acetaldehyde,
acrolein,
formaldehyde,
and
phenol
NCASI
Method
IM/
CAN/
WP­
99.02;
OR
Method
320
in
appendix
A
to
40
CFR
part
63;
OR
ASTM
D6348­
03
provided
that
%
R
as
determined
in
Annex
A5
of
ASTM
D6348­
03
is
equal
or
greater
than
70%
and
less
than
or
equal
to
130%.

(
6)
each
process
unit
measure
emissions
of
benzene
Method
320
in
appendix
A
to
40
CFR
part
63;
OR
ASTM
D6348­
03
provided
that
%
R
as
determined
in
Annex
A5
of
ASTM
D6348­
03
is
equal
or
greater
than
70%
and
less
than
or
equal
to
130%.

(
7)
each
press
that
processes
board
containing
methylene
diphenyl
diisocyanate
(
MDI)
resin
measure
emissions
of
MDI
Method
320
in
appendix
A
to
40
CFR
part
63;
OR
Conditional
Test
Method
(
CTM)
031
which
is
posted
on
http://
www.
epa.
gov/
ttn/
emc
/
ctm.
html
(
8)
each
direct­
fired
process
unit
measure
emissions
of
the
following
HAP
metals:
arsenic,
beryllium,
cadmium,
chromium,
lead,
manganese,
and
nickel.
Method
29
in
appendix
A
to
40
CFR
part
60.
You
must
analyze
samples
using
atomic
absorption
spectroscopy
(
AAS).

(
9)
any
process
unit
that
is
known
to
emit
HAP
not
otherwise
listed
in
this
table
measure
emissions
of
the
HAP
emitted
the
methods
specified
in
this
table
(
as
appropriate)
or
petition
the
Administrator
for
approval
of
an
alternative
test
method.
26
(
11)
each
reconstituted
wood
product
press
or
reconstituted
wood
product
board
cooler
with
a
HAP
control
device
meet
the
design
specifications
included
in
the
definition
of
wood
products
enclosure
in
§
63.2292
of
subpart
DDDD
OR
determine
the
percent
capture
efficiency
of
the
enclosure
directing
emissions
to
an
add­
on
control
device
Methods
204
and
204A
through
204F
of
40
CFR
part
51,
appendix
M
to
determine
capture
efficiency
(
except
for
wood
products
enclosures
as
defined
in
§
63.2292).
Enclosures
that
meet
the
definition
of
wood
products
enclosure
or
that
meet
Method
204
requirements
for
a
PTE
are
assumed
to
have
a
capture
efficiency
of
100%.
Enclosures
that
do
not
meet
either
the
PTE
requirements
or
design
criteria
for
a
wood
products
enclosure
must
determine
the
capture
efficiency
by
constructing
a
TTE
according
to
the
requirements
of
Method
204
and
applying
Methods
204A
through
204F
(
as
appropriate).
As
an
alternative
to
Methods
204
and
204A
through
204F,
you
may
use
the
tracer
gas
method
contained
in
appendix
A
to
this
subpart.

(
12)
each
reconstituted
wood
product
press
or
reconstituted
wood
product
board
cooler
determine
the
percent
capture
efficiency
a
TTE
and
Methods
204
and
204A
through
204F
(
as
appropriate)
of
40
CFR
part
51,
appendix
M.
As
an
alternative
to
installing
a
TTE
and
using
Methods
204
and
204A
through
204F,
you
may
use
the
tracer
gas
method
contained
in
appendix
A
to
this
subpart.

(
13)
each
process
unit
with
a
HAP
control
device
establish
the
sitespecific
operating
requirements
(
including
the
parameter
limits
or
THC
concentration
limits)
in
Table
2
of
subpart
DDDD
data
from
the
parameter
monitoring
system
or
THC
CEMS
and
the
applicable
performance
test
method(
s).
27
Table
3
to
Appendix
B
of
Subpart
DDDD.
Maximum
allowable
toxicity­
weighted
carcinogen
emission
rate
(
lb/
hr)/(
µ
g/
m3)

Fenceline
(
m)

Stack
height
(
m)
0
50
100
150
200
250
500
1000
1500
2000
3000
5000
5
8.72E­
07
8.72E­
07
8.72E­
07
9.63E­
07
1.25E­
06
1.52E­
06
1.25E­
06
4.25E­
06
4.39E­
06
4.39E­
06
4.39E­
06
5.00E­
06
10
2.47E­
06
2.47E­
06
2.47E­
06
2.47E­
06
2.47E­
06
2.61E­
06
3.58E­
06
5.03E­
06
5.89E­
06
5.89E­
06
5.89E­
06
6.16E­
06
20
5.81E­
06
5.81E­
06
5.81E­
06
5.81E­
06
5.81E­
06
5.81E­
06
5.90E­
06
7.39E­
06
8.90E­
06
9.97E­
06
9.97E­
06
1.12E­
05
30
7.74E­
06
7.74E­
06
7.74E­
06
7.74E­
06
7.74E­
06
7.74E­
06
8.28E­
06
9.49E­
06
1.17E­
05
1.35E­
05
1.55E­
05
1.61E­
05
40
9.20E­
06
9.20E­
06
9.20E­
06
9.20E­
06
9.20E­
06
9.20E­
06
9.24E­
06
1.17E­
05
1.34E­
05
1.51E­
05
1.98E­
05
2.22E­
05
50
1.02E­
05
1.02E­
05
1.02E­
05
1.02E­
05
1.02E­
05
1.02E­
05
1.02E­
05
1.36E­
05
1.53E­
05
1.66E­
05
2.37E­
05
2.95E­
05
60
1.13E­
05
1.13E­
05
1.13E­
05
1.13E­
05
1.13E­
05
1.13E­
05
1.13E­
05
1.53E­
05
1.76E­
05
1.85E­
05
2.51E­
05
3.45E­
05
70
1.23E­
05
1.23E­
05
1.23E­
05
1.23E­
05
1.23E­
05
1.23E­
05
1.23E­
05
1.72E­
05
2.04E­
05
2.06E­
05
2.66E­
05
4.07E­
05
80
1.34E­
05
1.34E­
05
1.34E­
05
1.34E­
05
1.34E­
05
1.34E­
05
1.34E­
05
1.92E­
05
2.15E­
05
2.31E­
05
2.82E­
05
4.34E­
05
100
1.52E­
05
1.52E­
05
1.52E­
05
1.52E­
05
1.52E­
05
1.52E­
05
1.52E­
05
1.97E­
05
2.40E­
05
2.79E­
05
3.17E­
05
4.49E­
05
200
1.76E­
05
1.76E­
05
1.76E­
05
1.76E­
05
1.76E­
05
1.76E­
05
1.76E­
05
2.06E­
05
2.94E­
05
3.24E­
05
4.03E­
05
5.04E­
05
MIR=
1E­
06
Emission
rates
in
table
expressed
as
equivalents
normalized
to
theoretical
HAP
with
URE
=
1(
µ
g/
m3)­
1
28
Table
4
to
Appendix
B
of
Subpart
DDDD.
Maximum
allowable
toxicity­
weighted
non­
carcinogen
emission
rate
(
lb/
hr)

Fenceline
(
m)

Stack
height
(
m)
0
50
100
150
200
250
500
1000
1500
2000
3000
5000
5
2.51E­
01
2.51E­
01
3.16E­
01
3.16E­
01
3.16E­
01
3.16E­
01
3.16E­
01
3.46E­
01
4.66E­
01
6.21E­
01
9.82E­
01
1.80E+
00
10
5.62E­
01
5.62E­
01
5.62E­
01
5.62E­
01
5.62E­
01
5.62E­
01
5.62E­
01
5.70E­
01
6.33E­
01
7.71E­
01
1.13E+
00
1.97E+
00
20
1.43E+
00
1.43E+
00
1.43E+
00
1.43E+
00
1.43E+
00
1.43E+
00
1.43E+
00
1.43E+
00
1.68E+
00
1.83E+
00
2.26E+
00
3.51E+
00
30
2.36E+
00
2.36E+
00
2.36E+
00
2.36E+
00
2.36E+
00
2.36E+
00
2.53E+
00
3.04E+
00
3.04E+
00
3.33E+
00
4.45E+
00
5.81E+
00
40
3.11E+
00
3.11E+
00
3.11E+
00
3.11E+
00
3.11E+
00
3.11E+
00
3.42E+
00
4.04E+
00
5.07E+
00
5.51E+
00
6.39E+
00
9.63E+
00
50
3.93E+
00
3.93E+
00
3.93E+
00
3.93E+
00
3.93E+
00
3.93E+
00
4.49E+
00
4.92E+
00
6.95E+
00
7.35E+
00
8.99E+
00
1.25E+
01
60
4.83E+
00
4.83E+
00
4.83E+
00
4.83E+
00
4.83E+
00
4.83E+
00
5.56E+
00
6.13E+
00
7.80E+
00
1.01E+
01
1.10E+
01
1.63E+
01
70
5.77E+
00
5.77E+
00
5.77E+
00
5.77E+
00
5.77E+
00
5.77E+
00
6.45E+
00
7.71E+
00
8.83E+
00
1.18E+
01
1.36E+
01
1.86E+
01
80
6.74E+
00
6.74E+
00
6.74E+
00
6.74E+
00
6.74E+
00
6.74E+
00
7.12E+
00
9.50E+
00
1.01E+
01
1.29E+
01
1.72E+
01
2.13E+
01
100
8.87E+
00
8.87E+
00
8.87E+
00
8.87E+
00
8.87E+
00
8.87E+
00
8.88E+
00
1.19E+
01
1.37E+
01
1.55E+
01
2.38E+
01
2.89E+
01
200
1.70E+
01
1.70E+
01
1.70E+
01
1.70E+
01
1.70E+
01
1.70E+
01
1.70E+
01
2.05E+
01
2.93E+
01
3.06E+
01
4.02E+
01
4.93E+
01
HI=
1
Emission
rates
in
table
expressed
in
lbs/
hr
as
equivalents
normalized
to
theoretical
HAP
with
RfC
=
1.0
IV.
Summary
of
Responses
to
Major
Comments
and
Changes
to
the
Plywood
and
Composite
Wood
Products
NESHAP
K.
Risk­
based
approaches
1.
General
comments
a.
Risk­
based
approaches
Comment:
Numerous
commenters
encouraged
EPA
to
exercise
all
of
the
flexibility
within
its
authority
and
offer
the
widest
possible
array
of
options
so
that
facilities
that
pose
no
significant
risk
to
public
health
or
the
environment
would
not
be
forced
to
add
expensive
and
unproductive
control
equipment
which
would
weaken
them
financially
or
cause
them
to
close.
Commenters
specifically
recommended
that
EPA
incorporate
risk­
based
options
similar
to
all
three
industry
"
white
papers,"
which
would
exclude
facilities
that
pose
no
significant
risk
to
public
health
or
the
environment.
(
As
an
alternative,
one
commenter
recommended
that
EPA
at
least
incorporate
the
concentration­
based
de
minimis
applicability
exemption.)

Commenters
stated
that
inclusion
of
risk
provisions
has
the
potential
to
achieve
overall
environmentally
superior
results
in
a
cost­
effective
manner,
particularly
in
cases
where
criteria
pollutants
from
control
devices
(
i.
e.,
incinerators)
may
result
in
greater
impacts
that
the
HAP
emissions
that
they
control.

According
to
a
life
cycle
analysis
conducted
by
one
commenter,

incinerators
used
to
limit
HAP
emissions
from
low­
risk
wood
products
facilities
would
create
more
harm
than
good
through
their
consumption
of
electricity
and
natural
gas.
The
commenter
2
noted
that
incinerators
emit
carbon
monoxide
(
CO2)
and
criteria
pollutants,
which
could
affect
a
State's
ability
to
meet
the
National
Ambient
Air
Quality
Standards
(
NAAQS)
attainment
requirements
under
the
CAA.
In
particular,
the
commenter
referred
to
EPA's
projection
that
adoption
of
MACT
floor
level
controls
would
result
in
increased
emissions
of
NOx,
a
precursor
to
ozone
and
PM.
According
to
the
commenter,
the
draft
rule
(
without
risk
provisions)
would
work
against
the
industry's
voluntary
commitment,
in
response
to
President
Bush's
initiative,

to
reduce
the
emissions
of
greenhouse
gases
by
12
percent
over
the
next
10
years.
The
commenter
noted
that
the
costly
mandatory
controls
proposed,
coupled
with
stiff
foreign
competition
and
regulatory
mandates
under
other
MACT
rules,
would
also
create
significant
financial
hardship
across
all
sectors
of
the
industry
and
jeopardize
the
commercial
viability
of
numerous
facilities,

many
of
which
are
the
principal
employer
in
the
small,
rural
towns
in
which
they
are
located.
The
projected
costs
for
the
proposed
rule
are
enormous
amounts
of
money
for
an
industry
already
operating
at
the
margin
in
a
depressed
economic
climate.

Noting
EPA's
prediction
that
the
draft
rule
would
avert
0.07
cases
of
cancer
per
year,
or
one
case
every
14
years,
the
commenter
stated
that
this
would
yield
a
cost­
effectiveness
of
$
2.4
billion
per
cancer
case
averted.
The
commenter
compared
the
cost
per
premature
death
averted
for
several
rules
and
found
the
PCWP
rule
to
be
one
of
the
more
costly.
The
commenter
concluded
3
that,
in
its
current
form,
the
draft
rule
would
impose
hundreds
of
millions
of
dollars
of
additional
cost
with
virtually
no
gain
to
either
the
environment
or
the
health.
The
commenter
stated
that
the
draft
rule
would
be
one
of
the
most
cost­
ineffective
rules
ever
promulgated
by
EPA.
According
to
the
commenter,
the
overwhelming
advantage
of
the
risk­
based
approach
is
that
it
avoids
imposing
high
costs
on
low­
risk
facilities,
where
there
is
little
or
no
benefit
to
be
gained
for
either
the
environment
or
the
public
interest.
The
commenter
stated
that
the
wood
products
industry
as
a
whole
poses
a
small­
to­
insignificant
risk
to
human
health
and
the
environment.

The
commenter
stated
that
the
final
rule
should
include
reasonable
risk­
based
mechanisms
to
allow
facilities
posing
no
significant
risk
to
limit
their
emissions
below
levels
of
concern
without
having
to
install
incinerator
controls.
The
commenter
stated
that
facilities
wishing
to
take
advantage
of
the
risk­
based
compliance
option
would
take
a
federally­
enforceable
permit
limit
that
would
guarantee
that
their
emissions
remain
below
the
risk­
based
emission
standard.
This
would
constitute
an
"
emission
limitation,"
within
the
statutory
definition
of
the
term,
and
it
would
allow
facilities
to
forego
the
installation
of
incinerators
where
they
are
not
warranted
by
public
health
and
environmental
considerations.

Commenters
argued
that
the
risk­
based
options
are
legally
justified,
protective
of
human
health
and
the
environment,
and
4
economically
sensible.
Commenters
stated
that
the
risk­
based
options
are
supported
under
the
CAA,
through
EPA's
authority
under
sections
112(
d)(
4)
and
112(
c)(
9)
to
set
emission
standards
other
than
MACT
for
certain
low­
risk
facilities
and
delist
technology­
defined
low­
risk
subcategories,
respectively,
and
through
EPA's
inherent
de
minimis
authority
to
avoid
undertaking
regulatory
action
in
the
absence
of
meaningful
risk.
One
commenter
pointed
out
that,
by
meeting
the
stringent
health
benchmarks
necessary
to
qualify
for
the
risk­
based
compliance
approaches,
facilities
already
would
have
satisfied
the
residual
risk
provisions
8
years
ahead
of
the
statutory
requirements
set
forth
in
section
112(
f)
of
the
CAA.

Two
commenters
believed
that
the
risk­
based
approach
would
particularly
benefit
small
mills
located
in
rural
areas
with
timber­
dependent
economies.
One
commenter
stated
that,
by
offering
manufacturers
an
opportunity
to
apply
for
subcategorization
on
a
site­
specific
basis,
facilities
that
are
remotely
located,
or
which
were
originally
planned
and
sited
with
thorough
consideration
of
airshed
impacts,
would
not
be
unduly
burdened
with
MACT
requirements
which
yield
little
or
no
public
health
benefits.

Commenters
argued
that
such
low­
risk
facilities
should
not
be
burdened
with
the
requirements
of
MACT.
One
commenter
noted
that
the
regulatory
framework
exists
within
their
State
to
implement
a
risk­
based
approach.
Another
commenter
agreed
with
5
the
concept
of
a
risk­
bsed
approach
but
stated
that
it
would
not
be
appropriate
for
State
and
local
programs
to
determine
which
facilities
should
be
exempted
from
MACT.
Another
commenter
suggested
that
exemptions
be
provided
on
a
case­
by­
case
basis
to
individual
facilities
that
are
able
to
demonstrate
that
they
pose
no
significant
risk
to
public
health
or
the
environment.

Several
commenters
opposed
the
risk­
based
exemptions.
Two
commenters
stated
that
the
use
of
risk­
based
concepts
to
evade
MACT
applicability
is
contrary
to
the
intent
of
the
CAA
and
is
based
on
a
flawed
interpretation
of
section
112(
d)(
4)
written
by
an
industry
subject
to
regulation.
One
commenter
added
that
the
CAA
requires
a
technology­
based
floor
level
of
control
and
does
not
provide
exclusions
for
risk
or
secondary
impacts
in
applying
the
MACT
floor.
The
other
commenter
was
particularly
concerned
about
industry's
unprecedented
proposal
to
include
"
de
minimis
exemptions"
and
"
cost"
in
the
MACT
standard
process.
The
commenter
stated
that
including
case­
by­
case
risk­
based
exemptions
would
jeopardize
the
effectiveness
of
the
national
air
toxics
program
to
adequately
protect
public
health
and
the
environment
and
to
establish
a
level
playing
field.
A
third
commenter
noted
that
subcategorization
and
source
category
deletions
under
section
112(
c)
have
been
implemented
several
times
since
the
MACT
program
began.

Commenters
pointed
out
that
they
have
not
been
able
to
comment
on
the
technical
merit
of
the
risk
analysis
employed
by
6
the
EPA.
They
argued
that,
until
the
residual
risk
analysis
procedures
have
been
implemented
via
the
section
112(
f)
process,

risk
analysis
should
not
be
used
in
making
MACT
determinations
pursuant
to
section
112(
d)(
4).
Also,
risk
analysis
could
never
be
used
to
establish
a
MACT
floor.

One
commenter
pointed
out
that,
in
separate
rulemakings
and
lawsuits,
EPA
adopted
legal
positions
and
policies
that
refute
and
contradict
the
very
risk­
based
and
cost­
based
approaches
contained
in
the
proposal.
In
these
other
arenas,
EPA
properly
rejected
risk
assessment
to
alter
the
establishment
of
MACT
standards.
The
EPA
also
properly
rejected
cost
in
determining
MACT
floors
and
in
denying
a
basis
for
avoiding
the
MACT
floor.

(
See
Brief
for
Respondent
Environmental
Protection
Agency,
Sierra
Club
v.
EPA;
Brief
for
Respondent
Environmental
Protection
Agency,
Cement
Kiln
Recycling
Coalition
v.
EPA,
No.
99­
1457
and
consolidated
cases,
(
D.
C.
Cir.)
(
Jan.
18,
2001);
Brief
for
Respondent
Environmental
Protection
Agency,
National
Lime
Ass'n
v.
EPA,
233
F.
3D
625
(
D.
C.
Cir.
2000)
(
July
14,
2000).)

Response:
We
believe
that
the
assertions
by
one
commenter
about
the
negative
environmental
disbenefits
of
the
PCWP
rule
are
overstated.
We
disagree
that
the
PCWP
industry
as
a
whole
poses
a
small­
to­
insignificant
risk
to
human
health
and
the
environment.
However,
we
acknowledge
that
there
are
some
PCWP
facilities
that
pose
little
risk
to
human
health
and
the
environment.
Consequently,
we
have
included
an
option
in
today's
7
final
PCWP
rule
that
would
allow
individual
facilities
to
be
delisted
(
as
part
of
a
low­
risk
subcategory)
if
they
demonstrate
that
they
do
not
pose
a
significant
risk
to
human
health
or
the
environment.
The
low­
risk
subcategory
delisting
in
today's
final
PCWP
rule
is
based
on
our
authority
under
CAA
sections
112(
c)(
1)

and
(
9).
This
statute
requires
that
categories
or
subcategories
meet
specific
risk
criteria,
and
to
determine
this,
risk
analyses
may
be
used.
We
disagree
with
the
commenter
that
we
must
wait
for
implementation
of
CAA
section
112(
f)
before
utilizing
risk
analysis
in
this
manner.
Section
112(
d)(
1)
of
the
CAA
gives
us
the
authority
to
distinguish
among
classes,
types,
and
sizes
of
sources
within
a
category.
We
believe
these
provisions
of
the
CAA
allow
us
to
define
a
subcategory
of
sources
in
terms
of
risk.

Thus,
the
low­
risk
subcategory
of
PCWP
facilities
is
defined
in
terms
of
risk,
not
cost.
We
are
not
subcategorizing
or
determining
MACT
floors
based
on
cost.
Furthermore,
as
discussed
elsewhere
in
this
section,
the
MACT
level
of
emissions
reduction
required
by
today's
final
rule
is
not
affected
by
facilities
becoming
part
of
the
low­
risk
subcategory.

For
many
of
the
reasons
provided
by
the
commenters,
we
are
not
pursuing
the
risk­
based
exemptions
based
on
section
112(
d)(
4).
We
do
not
believe
that
a
risk­
based
approach
based
on
section
112(
d)(
4)
is
appropriate
for
the
PCWP
industry
because
PCWP
facilities
emit
HAP
for
which
no
health
thresholds
have
been
established
and
because
the
legislative
history
of
the
1990
8
Amendments
to
the
CAA
indicates
that
Congress
considered
and
rejected
allowing
us
to
grant
such
source­
specific
exemptions
from
the
MACT
floor.
We
also
are
not
relying
on
de
minimis
authority.
Legal
issues
associated
with
the
risk­
based
provisions
are
addressed
elsewhere
in
this
section.

In
today's
final
PCWP
rule,
we
are
identifying
the
criteria
we
will
use
to
identify
low­
risk
PCWP
facilities
and
requesting
that
any
candidate
facilities
submit
information
to
us
based
on
those
criteria
so
that
we
can
evaluate
whether
they
might
be
low­
risk.
Today's
final
PCWP
rule
also
establishes
a
low­
risk
PCWP
subcategory
based
on
the
criteria
and
delists
the
subcategory
based
on
our
finding
that
no
source
that
would
be
eligible
to
be
included
in
the
subcategory
based
on
our
adopted
criteria
emits
HAP
at
levels
that
exceed
the
thresholds
specified
in
section
112(
c)(
9)(
B)
of
the
CAA.
To
be
found
eligible
to
be
included
in
the
delisted
source
category,
facilities
will
have
to
demonstrate
to
us
that
they
meet
the
criteria
established
by
today's
final
PCWP
rule
and
assume
federally
enforceable
limitations
that
ensure
their
HAP
emissions
do
not
subsequently
increase
to
exceed
levels
reflected
in
their
eligibility
demonstrations.

The
criteria
defining
the
low­
risk
subcategory
of
PCWP
facilities
are
included
in
Appendix
B
to
Subpart
DDDD.
The
criteria
in
the
appendix
were
developed
for
and
apply
only
to
the
PCWP
industry
and
are
not
applicable
to
other
industries.
9
Today's
final
PCWP
rule
provides
two
ways
that
a
facility
may
demonstrate
that
they
are
part
of
the
low­
risk
subcategory
of
PCWP
facilities.
First,
look­
up
tables
allow
facilities
to
determine,
using
a
limited
number
of
site­
specific
input
parameters,
whether
emissions
from
their
sources
might
cause
an
HI
limit
for
non­
carcinogens
or
a
cancer
benchmark
of
one
in
a
million
to
be
exceeded.
Second,
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
low­
risk
subcategory
using
the
look­
up
tables.

The
low­
risk
subcategory
delisting
that
is
included
in
today's
final
PCWP
rule
is
intended
to
avoid
imposing
unnecessary
controls
on
facilities
that
do
not
pose
a
significant
risk
to
human
health
or
the
environment.
Facilities
will
have
to
select
controls
or
other
methods
of
limiting
risk
and
then
demonstrate,

using
Appendix
B
to
Subpart
DDDD
and/
or
the
"
Air
Toxics
Risk
Assessment
Reference
Library,"
that
their
emissions
qualify
them
to
be
included
in
the
low­
risk
subcategory,
and,
therefore,
are
not
subject
to
the
compliance
options
included
in
today's
final
PCWP
rule.

Comment:
Several
commenters
objected
to
EPA
using
the
preambles
of
individual
rule
proposals
as
the
forum
for
introducing
significant
changes
in
the
way
that
MACT
standards
are
established.
One
commenter
stated
that,
for
many
years,
they
have
coordinated
with
EPA
on
development
of
MACT
standards
for
10
the
national
air
toxics
program,
and
there
has
been
no
indication
of
any
kind
regarding
inclusion
of
risk­
based
exemptions
in
the
first
phase
of
the
MACT
program.
The
commenter
thought
it
was
unprecedented
and
alarming
that
EPA
was
proposing
such
a
radical
change
at
the
end
of
Phase
1
of
the
MACT
standard
process.
The
commenter
believed
that
allowing
risk­
based
exemptions
requires
changes
to
existing
law
and
that
such
a
debate
should
take
place
within
the
democratic
legislative
process
and
not
in
the
MACT
standard
process.
Another
commenter
stated
that
precedentsetting
change
of
the
magnitude
that
EPA
has
raised
should
be
discussed
openly
and
carefully
with
all
affected
parties
instead
of
being
buried
in
the
preambles
of
individual
standards.
A
third
commenter
expressed
concern
that
other
parties
may
miss
commenting
on
the
risk­
based
exemptions
because
they
are
contained
within
six
separate
proposals.
The
commenter
added
that
to
give
the
issue
full
consideration,
the
risk
provisions
should
not
be
adopted
within
any
of
the
final
rules
but
should
be
addressed
in
one
place,
such
as
in
revisions
to
the
General
Provisions
of
40
CFR
Part
63,
Subpart
A.

Response:
The
discussion
of
risk­
based
provisions
in
MACT
was
included
in
individual
proposals
for
several
reasons.
First,

we
recognize
that
such
provisions
are
only
appropriate
for
certain
source
categories,
and
our
decision­
making
process
required
source
category­
specific
input
from
stakeholders.

Second,
the
10­
year
MACT
standards,
which
are
now
being
11
completed,
are
the
last
group
of
MACT
standards
currently
planned
for
development,
and
for
any
risk
provisions
to
be
useful,
the
provisions
must
be
finalized
in
a
timely
manner
(
i.
e.,
not
later
than
the
promulgation
of
the
MACT
standards).
Third,
these
final
MACT
source
categories
were
included
in
the
"
10­
year
bin"
because
they
were
considered
to
be
the
lowest
risk
source
categories.

Finally,
the
risk­
based
provisions
are
not
available
for
standards
that
have
already
been
implemented,
and
any
decisions
regarding
risk
must,
therefore,
be
applied
on
a
source
categoryspecific
basis.
We
do
not
agree
that
changes
to
existing
law
are
necessary
because
of
the
discretion
provided
to
the
Administrator
under
section
112(
d)(
1)
to
distinguish
among
classes,
types,
and
sizes
of
sources
within
a
category.
We
consider
low­
risk
facilities
to
be
a
class
of
sources
within
the
PCWP
source
category.

Comment:
Several
commenters
stated
that
the
risk­
based
exemption
proposal
removes
the
"
level
playing
field"
that
would
result
from
the
proper
implementation
of
technology­
based
MACT
standards.
According
to
the
commenters,
establishing
a
baseline
level
of
control
is
essential
to
prevent
industry
from
moving
to
areas
of
the
country
that
have
the
least
stringent
air
toxics
programs,
which
was
one
of
the
primary
goals
of
developing
a
uniform
national
air
toxics
program
under
section
112
of
the
1990
CAA
amendments.
The
commenters
argued
that
risk­
based
approaches
12
would
jeopardize
future
reductions
of
HAP
in
a
uniform
and
consistent
manner
across
the
nation.
One
commenter
stated
that
National
Air
Toxics
Assessment
(
NATA)
data
show
that
virtually
no
area
of
the
country
has
escaped
measurable
concentrations
of
toxic
air
pollution.
The
NATA
information
indicates
that
exposure
to
air
toxics
is
high
in
both
densely
populated
and
remote
rural
areas.

One
commenter
disagreed
with
the
assertion
that
the
level
playing
field
would
be
removed.
The
commenter
pointed
out
that
the
argument
that
EPA
should
impose
unnecessary
and
potentially
environmentally
damaging
controls
for
the
sole
purpose
of
equalizing
control
costs
across
facilities
would
be
at
odds
with
the
stated
purpose
of
the
CAA.
According
to
the
commenter,
the
claim
that
the
risk­
based
approach
would
favor
facilities
located
away
from
population
centers
is
incorrect.
As
contemplated,
the
risk­
based
approaches
to
the
NESHAP
would
be
keyed
to
the
comparison
of
health
benchmarks
with
potential
maximum
exposure,

regardless
of
whether
actual
receptors
are
present
at
the
exposure
location.
According
to
the
commenter,
the
presence
or
absence
of
human
populations
would
have
no
effect
on
whether
facilities
would
qualify.

Response:
We
agree
that
one
of
the
primary
goals
of
developing
a
uniform
national
air
toxics
program
under
section
112
of
the
1990
CAA
amendments
was
to
establish
a
level
playing
field.
We
do
not
believe
that
defining
a
low­
risk
subcategory
in
13
today's
final
PCWP
rule
does
anything
to
remove
the
level
playing
field
for
PCWP
facilities.
Today's
final
PCWP
rule
and
its
criteria
for
demonstrating
eligibility
for
the
delisted
low­
risk
subcategory
apply
uniformly
to
all
PCWP
facilities
across
the
nation.
Today's
final
PCWP
rule
establishes
a
baseline
level
of
emission
reduction
or
a
baseline
level
of
risk
(
for
the
low­
risk
subcategory).
All
PCWP
facilities
are
subject
to
these
same
baseline
levels,
and
all
facilities
have
the
same
opportunity
to
demonstrate
that
they
are
part
of
the
delisted
low­
risk
subcategory.
The
criteria
for
the
low­
risk
subcategory
are
not
dependent
on
local
air
toxics
programs.
Therefore,
concerns
regarding
facilities
moving
to
areas
of
the
country
with
lessstringent
air
toxics
programs
should
be
alleviated.

Although
NATA
may
show
measurable
concentrations
of
toxic
air
pollution
across
the
country,
these
data
do
not
suggest
that
facilities
that
do
not
contribute
to
the
high
exposures
and
risk
should
be
included
in
regulations.
A
discussion
is
provided
elsewhere
in
this
section
regarding
how
background
concentrations
are
accounted
for
by
facilities
demonstrating
eligibility
for
the
delisted
low­
risk
subcategory.

Comment:
One
commenter
stated
that
the
dockets
for
the
MACT
proposals
that
contain
the
risk
approaches
make
it
clear
that
the
White
House
Office
of
Management
and
Budget
(
OMB)
and
industry
were
the
driving
forces
behind
the
appearance
of
these
unlawful
approaches
in
EPA's
proposals.
The
commenter
cited
internal
e­
14
mails
between
the
White
House
OMB
and
EPA
that
reveal
OMB
officials
exerting
pressure
on
EPA
to
"
take
ownership"
of
the
deregulatory
approaches
developed
by
industry.
The
commenter
noted
that
comparison
of
the
proposal
language
for
the
Brick
and
Structural
Clay
Products
(
BSCP)
rule
and
PCWP
rule
makes
it
clear
that
EPA
capitulated
to
OMB
pressure
to
remove
references
to
the
risk­
based
exemptions
in
the
PCWP
proposal
preamble
as
being
"
industry's
suggested
approaches."
The
commenter
cited
preamble
edits
from
OMB
that
the
commenter
believes
reveals
an
OMB
agenda
to
dictate
EPA
adoption
of
industry's
risk­
based
approaches,
and
to
signal
these
plans
in
the
rulemaking
proposals,
even
before
public
comment
has
been
taken.
The
commenter
also
noted
that
OMB
urged
support
of
a
dangerous
and
technically
unfounded
HI
of
10.0.
The
commenter
condemned
the
industry­
driven
agenda
that
is
being
promoted
by
the
White
House
OMB.

A
second
commenter
stated
that
the
accusations
that
EPA
succumbed
to
industry
lobbying
and
internal
pressures
are
entirely
unfounded.
The
commenter
stated
that
risk­
based
approaches
are
warranted
because
EPA's
NESHAP
program
has
now
turned
to
the
low­
risk
source
categories
that
Congress
instructed
EPA
to
address
last.
The
commenter
pointed
out
that
80
source
categories
have
already
been
addressed
with
MACT
standards.

According
to
the
commenter,
the
remaining
source
categories
are
lower
priority
and
include
a
large
number
of
facilities
that
pose
negligible
risk
to
public
health
and
environment.
The
commenter
15
stated
that
EPA
purposefully
saved
those
categories
for
last
in
accordance
with
Congress'
explicit,
risk­
based
priority­
setting
mandate
expressed
in
section
112(
e)(
2).
The
commenter
concluded
that
EPA
has
now
reached
the
point
where
regulation
by
MACT
would
result
in
more
environmental
harm
than
good.

Response:
The
first
commenter
is
correct
in
stating
that
industry
representatives
and
OMB
support
the
inclusion
of
riskbased
approaches
in
today's
final
PCWP
rule
as
a
method
of
reducing
costs.
We
are
required
by
Executive
Order
12866
to
submit
to
OMB
for
review
all
proposed
and
final
rulemaking
packages
that
would
have
an
annual
effect
on
the
economy
of
$
100
million
or
more.
The
comments
we
received
from
OMB
reflect
their
position.

b.
Effects
on
MACT
program
Comment:
Several
commenters
expressed
concern
about
the
impact
of
a
risk­
based
approach
on
the
MACT
program.
Some
commenters
stated
that
the
proposal
to
include
risk­
based
exemptions
is
contrary
to
the
1990
CAA
Amendments,
which
calls
for
MACT
standards
based
on
technology
rather
than
risk
as
a
first
step.
The
commenters
pointed
out
that
Congress
incorporated
the
residual
risk
program
under
section
112(
f)
to
follow
the
MACT
standards,
not
to
replace
them.
One
commenter
added
that
risk­
based
approaches
would
be
used
separately
to
augment
and
improve
technology­
based
standards
that
do
not
adequately
provide
protection
to
the
public.
16
Another
commenter
believed
that
section
112(
b)(
4)
and
the
regulatory
precedent
established
in
over
80
MACT
standards
reject
the
inclusion
of
risk
in
the
first
phase
of
the
MACT
standards
process.
The
commenter
argued
that
the
use
of
risk
assessment
at
this
stage
of
the
MACT
program
is,
in
fact,
directly
opposed
to
Title
III
of
the
CAA.

Response:
We
disagree
that
inclusion
of
a
low­
risk
subcategory
in
today's
final
PCWP
rule
is
contrary
to
the
1990
CAA
Amendments.
The
PCWP
rule
is
a
technology­
based
standard
developed
using
the
procedures
dictated
by
section
112
of
the
CAA.
The
only
difference
between
today's
final
PCWP
rule
and
other
MACT
rules
is
that
we
used
our
discretion
under
CAA
sections
112(
c)(
1)
and
(
9)
to
subcategorize
low­
risk
facilities.

The
CAA
requires
that
categories
or
subcategories
meet
specific
risk
criteria,
and
to
determine
this,
risk
analyses
may
be
used.

We
disagree
with
the
commenter
that
we
must
wait
for
implementation
of
CAA
section
112(
f)
before
utilizing
risk
analysis
in
this
manner.
We
believe
that
today's
final
PCWP
rule
is
particularly
well­
suited
for
a
risk­
based
option
because
of
the
specific
pollutants
that
are
emitted.
For
many
facilities,

the
pollutants
are
emitted
in
amounts
that
do
not
pose
a
significant
risk
to
the
surrounding
population.
However,
the
cost
of
controlling
these
pollutants
is
high,
and
may
not
be
justified
by
environmental
benefits
for
these
low­
risk
facilities.
Only
those
PCWP
facilities
that
demonstrate
that
17
they
are
low­
risk
are
eligible
for
inclusion
in
the
delisted
lowrisk
subcategory.
The
criteria
included
in
today's
final
PCWP
rule
defining
the
delisted
low­
risk
subcategory
are
based
on
sufficient
information
to
develop
health­
protective
estimates
of
risk
and
will
provide
ample
protection
of
human
health
and
the
environment.

Inclusion
of
a
low­
risk
subcategory
in
today's
final
PCWP
rule
does
not
alter
the
MACT
program
or
affect
the
schedule
for
promulgation
of
the
remaining
MACT
standards.
We
recognize
that
such
provisions
are
only
appropriate
for
certain
source
categories,
and
our
decision­
making
process
required
source
category­
specific
input
from
stakeholders.
The
10­
year
MACT
standards,
which
are
now
being
completed,
are
the
last
group
of
MACT
standards
currently
planned
for
development,
and
for
any
risk
provisions
to
be
useful,
the
provisions
must
be
finalized
in
a
timely
manner
(
i.
e.,
not
later
than
the
promulgation
of
the
MACT
standards).
These
final
MACT
source
categories
were
included
in
the
"
10­
year
bin"
because
they
were
considered
to
be
the
lowest­
risk
source
categories.

Comment:
Several
commenters
stated
that
the
inclusion
of
a
risk­
based
approach
would
delay
the
MACT
program
and/
or
promulgation
of
the
PCWP
MACT
standard.
Commenters
stated
that
the
proposal
to
allow
risk­
based
exemptions
would
divert
back
to
the
time­
consuming
NESHAP
development
process
that
existed
prior
18
to
the
1990
CAA
Amendments.
Under
this
process,
which
began
with
a
risk
assessment
step,
only
eight
NESHAP
were
promulgated
during
a
20­
year
period.
If
the
proposed
approaches
are
inserted
into
upcoming
standards,
the
commenters
feared
the
MACT
program
(
which
is
already
far
behind
schedule)
would
be
further
delayed.

One
commenter
stated
that
they
were
strongly
opposed
to
returning
to
the
morass
of
risk­
based
analysis
in
an
attempt
to
preempt
the
application
of
technology­
based
MACT
standards
and
exempt
facilities.
The
commenter
stated
that
designing
a
riskbased
analysis
procedure
would
also
take
significant
resources,

as
evidenced
by
the
fact
that
it
took
five
plus
pages
in
the
Federal
Register
to
discuss
just
the
basic
issues
to
be
considered
in
the
analysis.
The
commenter
indicated
that
the
demand
on
government
resources
could
cause
a
delay
in
the
application
of
MACT
nationwide.
The
commenter
stated
that
EPA
should
also
consider
the
issue
of
fairness
since
the
rest
of
the
industrial
sector
whose
NESHAP
have
already
been
promulgated
did
not
have
a
risk­
based
option.

Another
commenter
stated
that
it
is
evident
that
the
proposed
risk­
based
exemptions
would
require
extensive
debate
and
review
in
order
to
launch,
which
would
further
delay
promulgation
of
the
remaining
MACT
standards.
The
commenter
stated
that
delays
could
be
exacerbated
by
litigation
following
legal
challenges
to
the
rules,
and
such
delays
would
trigger
the
section
112(
j)
MACT
hammer
provision,
which
would
unnecessarily
19
burden
the
State
and
local
agencies
and
the
industries.
The
commenter
concluded
that,
obviously,
further
delay
is
unacceptable.
Another
commenter
agreed,
stating
that
it
is
imperative
that
EPA
meet
the
new
deadlines
for
promulgating
the
final
MACT
standards.

Two
commenters
stated
that
EPA's
proposal
to
improperly
incorporate
risk
assessment
into
the
technology­
based
standard
process
would
cripple
a
MACT
program
already
in
disarray.
The
commenters
argued
that
the
risk­
based
approach
could
exacerbate
the
delay
in
HAP
emissions
reductions
required
by
section
112.

One
commenter
noted
that
EPA's
Office
of
Inspector
General
recently
found
that
EPA
is
nearly
2
years
behind
in
fulfilling
its
statutory
responsibilities
for
implementing
Phase
1
MACT
standards.
According
to
the
commenter,
this
delay
potentially
harms
the
public
and
environment.
The
inclusion
of
risk­
based
exemptions
in
10­
year
MACT
standards
would
only
further
delay
this
process.
The
other
commenter
noted
that
EPA
lacks
adequate
emissions
and
exposure
data,
source
characterization
data,
and
health
and
ecological
effects
information
to
conduct
this
process
anyway.
This
commenter
believed
that
the
air
toxics
program
is
flawed
and
failing
to
protect
public
health
and
the
environment
and
argued
that
it
was
irresponsible
for
EPA
to
pursue
a
deregulatory
agenda
that
would
further
weaken
the
effectiveness
of
the
air
toxics
program.
The
commenter
noted
that
EPA
acknowledged
the
complexity
and
delays
associated
with
the
20
proposed
risk­
based
approaches
in
deciding
not
to
adopt
the
approaches
in
the
final
BSCP
rule.

Response:
We
disagree
that
identification
and
delisting
of
a
low­
risk
subcategory
in
today's
final
PCWP
rule
will
alter
the
MACT
program
or
affect
the
schedule
for
promulgation
of
the
remaining
MACT
standards.
We
do
not
anticipate
any
further
delays
in
completing
the
remaining
MACT
standards.
The
delisting
of
a
low­
risk
subcategory
in
today's
final
PCWP
rule
affects
only
the
PCWP
rule,
and
not
all
other
MACT
standards
that
have
yet
to
be
promulgated.

We
believe
that
the
PCWP
rule
is
particularly
well­
suited
for
a
risk­
based
option
because
of
the
specific
pollutants
that
are
emitted.
For
many
facilities,
the
pollutants
are
emitted
in
amounts
that
do
not
pose
a
significant
risk
to
the
surrounding
population.
However,
the
cost
of
controlling
these
pollutants
is
high
and
may
not
be
justified
by
environmental
benefits
for
these
low­
risk
facilities.
Only
those
PCWP
facilities
that
demonstrate
that
they
are
low­
risk
are
eligible
for
inclusion
in
the
delisted
low­
risk
subcategory.
The
criteria
defining
the
delisted
lowrisk
subcategory
are
based
on
sufficient
information
to
develop
health­
protective
estimates
of
risk
and
will
provide
ample
protection
of
human
health
and
the
environment.

Delisting
of
a
low­
risk
subcategory
of
PCWP
facilities
does
not
mean
that
we
will
provide
risk­
based
options
for
other
industries.
Furthermore,
we
have
no
intentions
of
reopening
21
previously
promulgated
NESHAP
in
light
of
decisions
made
specific
to
the
PCWP
source
category.
The
PCWP
NESHAP
is
being
promulgated
by
the
February
2004
court­
ordered
deadline.
Any
delays
in
implementation
of
the
PCWP
NESHAP
caused
by
legal
challenges
are
beyond
our
control.

2.
Legal
authority
a.
Section
112(
d)(
4)

Comment:
We
received
multiple
comments
stating
that
section
112(
d)(
4)
provides
EPA
with
authority
to
exclude
sources
that
emit
threshold
pollutants
from
regulation.
The
commenters
cited
the
language
in
section
112(
d)(
4)
and
CAA
legislative
history.

The
commenters
pointed
out
that
EPA
exercised
its
section
112(
d)(
4)
authority
previously
in
choosing
not
to
impose
control
requirements
on
hydrogen
chloride
(
HCl)
emissions
from
chemical
recovery
furnaces
at
pulp
mills
(
40
CFR
Part
63,
Subpart
MM,
See
63
FR
18754,
18765
(
April
15,
1998)).

We
also
received
multiple
comments
disagreeing
that
section
112(
d)(
4)
can
be
interpreted
to
allow
exemptions
for
individual
sources.
The
commenters
argued
that
section
112(
d)(
4)
applies
only
to
categories
or
subcategories
of
sources
and
not
to
individual
sources.
These
commenters
also
cited
the
language
of
section
112(
d)(
4)
and
CAA
legislative
history.
The
commenters
interpreted
section
112(
d)(
4)
to
state
that
health­
based
thresholds
can
be
considered
when
establishing
the
degree
of
the
22
MACT
floor
requirements,
but
they
should
not
be
used
in
lieu
of
the
requirements
established
pursuant
to
section
112(
d)(
3).
One
commenter
also
argued
that
the
third
scenario
suggested
by
EPA
 
application
of
section
112(
d)(
4)
exemption
to
emission
points
within
a
facility
 
is
unlawful
because
there
is
no
statutory
provision
within
the
CAA
to
authorize
emission
point­
by­
point
exemption.

Several
commenters
supported
the
use
of
section
112(
d)(
4)

applicability
cutoffs
for
both
threshold
and
non­
threshold
pollutants
and
believe
that
a
health
threshold
of
one
in
a
million
cancer
risk
is
appropriate
for
non­
threshold
pollutants.

The
commenters
interpreted
the
language
in
section
112(
d)(
4)
to
mean
EPA
may
issue
standards
for
any
pollutant
for
which
a
threshold
may
be
established.
The
commenters
believe
that
EPA
could
use
its
section
112(
d)(
4)
authority
to
establish
a
"
threshold"
risk
of
one
in
a
million
for
non­
threshold
carcinogens.
The
commenters
also
believe
that
section
112(
d)(
4)

may
be
properly
applied
to
carcinogenic
HAP
that
EPA
determines
have
a
threshold
of
safe
exposure.
The
commenters
noted
that
the
current
health
science
for
formaldehyde
and
aceteladehyde
shows
that
these
two
HAP
are
threshold
carcinogens
that
are
emitted
from
wood
products
facilities
at
levels
that
will
not
pose
a
significant
risk
to
human
health.

Multiple
other
commenters
stated
that
section
112(
d)(
4)
does
not
apply
for
source
categories
that
emit
carcinogens.
The
23
commenters
argued
that
EPA
may
only
use
the
section
112(
d)(
4)

authority
for
pollutants
with
a
well­
established
health
threshold.
The
commenters
stated
that
section
112(
d)(
4)
only
allows
EPA
to
substitute
a
health
threshold
for
a
MACT
standard
when
the
threshold
"
has
been
established."
The
commenters
contended
that
Congress
did
not
intend
for
EPA
to
spend
time
determining
if
a
threshold
exists
and
that
it
was
Congress'

intent
that
EPA
have
a
high
degree
of
scientific
certainty
before
using
its
section
112(
d)(
4)
authority.
The
commenters
cited
legislative
history.
(
See
S.
Rep.
101­
228
at
171.)
The
commenters
also
stated
that
Congress
specified
that
EPA
must
have
direct
evidence
of
no
effects,
i.
e.,
use
of
a
no
observable
effects
level
(
NOEL),
before
invoking
section
112(
d)(
4);
thus,

EPA
must
be
sure
that
there
are
no
effects
from
exposure
at
the
level
chosen
for
the
emission
standard.
The
commenters
further
argued
that
all
carcinogens
must
be
treated
as
non­
threshold
pollutants
and
noted
that
the
history
of
the
1990
CAA
Amendments
shows
that
Congress
legislated
with
an
understanding
that
carcinogens
do
not
have
a
safe
threshold.

Response:
We
acknowledge
the
commenters'
arguments
regarding
our
discussion
in
the
PCWP
proposal
preamble
regarding
potential
applicability
cutoffs
for
threshold
pollutants
under
the
authority
of
section
112(
d)(
4)
of
the
CAA.
We
believe
that
section
112(
d)(
4)
does
not
give
us
the
authority
to
exempt
facilities
or
emission
points
from
MACT
limitations
on
non­
24
threshold
pollutant
emissions.
All
PCWP
facilities
emit
carcinogens
(
e.
g.,
formaldehyde),
which
are
currently
considered
non­
threshold
pollutants.
Therefore,
we
are
not
using
section
112(
d)(
4)
authority
to
create
risk­
based
options
for
PCWP.
We
do
not
expect
to
further
explore
the
use
of
section
112(
d)(
4)
of
the
CAA
to
exempt
PCWP
facilities
from
the
MACT
floor
on
a
case­
by­
case
basis
or
to
set
alternative
standards,
because
PCWP
facilities
emit
HAP
for
which
no
health
thresholds
have
been
established
and
because
the
legislative
history
to
the
1990
Amendments
to
the
CAA
indicates
that
Congress
considered
and
rejected
allowing
us
to
grant
such
source­
specific
exemptions
from
the
MACT
floor.
(
See,
e.
g.,
1
Legis.
Hist.
at
866,
877;
2
Legis.
Hist.
at
2141­
42,
3939.)
As
discussed
below,
we
are
establishing
and
delisting
a
subcategory
of
low­
risk
PCWP
facilities
using
our
authority
under
CAA
sections
112(
c)(
1)
and
(
9).

We
are
establishing
criteria
in
today's
final
PCWP
rule
that
define
a
low­
risk
subcategory
of
PCWP
facilities,
which
requires
demonstration
that
a
facility
warrants
being
included
in
this
subcategory.
The
criteria
are
not
included
in
the
rule
as
"
emission
standards"
or
"
emission
limits"
but
are
included
in
an
appendix
to
the
rule
that
specifies
how
facilities
must
make
their
low­
risk
demonstrations
and
the
steps
that
facilities
must
take
to
ensure
that
they
remain
in
the
low­
risk
subcategory.
We
are
not
setting
a
risk­
based
emission
limit,
but,
rather,
we
are
25
using
our
section
112(
c)(
9)
authority
to
delist
facilities
that
demonstrate
they
meet
the
risk
and
hazard
criteria
for
being
included
in
this
low­
risk
subcategory.

b.
De
minimis
Comment:
Some
commenters
attempted
to
identify
a
source
of
authority
for
risk­
based
approaches
that
was
not
discussed
in
the
preamble
to
the
proposed
rule.
The
commenters
stated
that
a
risk­
based
compliance
option
for
both
threshold
and
non­
threshold
HAP
is
well
within
EPA's
authority
under
the
CAA
and
the
de
minimis
doctrine
articulated
by
appellate
courts.
The
commenters
cited
appellate
case
law
which
they
believe
makes
it
clear
that
EPA
may
lawfully
exempt
de
minimis
sources
of
risk
from
MACT­
level
controls
because
the
legislative
mandate
of
section
112
is
not
"
extraordinarily
rigid"
and
the
exemption
is
consistent
with
the
CAA's
health­
protective
purpose.
The
commenters
also
noted
that
sections
112(
c)(
9)
and
112(
f)(
2)

indicate
that
Congress
considered
a
cancer
risk
below
one
in
a
million
to
be
de
minimis
and
therefore
insufficient
to
justify
regulation
under
section
112.
The
commenters
stated
that
(
and
cited
examples
where)
EPA's
exercise
of
de
minimis
authority
has
withstood
judicial
challenge,
and
that
application
of
de
minimis
authority
(
as
well
as
its
treatment
by
reviewing
courts)
is
based
on
the
degree
of
risk
at
issue,
not
on
the
mass
of
emissions
to
be
regulated.
The
commenters
stated
that
the
D.
C.
Circuit
has
26
invalidated
EPA's
de
minimis
authority
only
where
it
was
applied
under
statutory
designs
that
are
"
extraordinarily
rigid."
The
commenters
stated
that
section
112
provides
clear
indication
of
Congressional
intent
as
to
the
degree
of
risk
that
properly
is
to
be
considered
de
minimis.
A
cancer
risk
of
one
in
a
million
triggers
further
review
under
the
"
residual"
risk
provision
of
section
112(
f),
and
a
one
in
a
million
cancer
risk
is
the
threshold
below
which
EPA
is
authorized
under
section
112(
c)(
9)(
B)
to
remove
source
categories
from
MACT
regulation.

One
commenter
attached
a
paper
they
developed
entitled
"
Legal
and
Policy
Basis
for
EPA's
Exercise
of
Its
De
minimis
Authority
Under
Section
112
of
the
Clean
Air
Act
in
the
Context
of
the
Wood
Products
MACT."

Other
commenters
argued
that
de
minimis
authority
does
not
exist
to
create
MACT
exemptions
on
a
facility­
by­
facility
or
category­
wide
basis.
In
addition,
the
commenters
stated
that
EPA
lacks
de
minimis
authority
to
delist
subcategories
based
on
risk.

The
commenters
cited
case
law
and
stated
that
EPA
may
not
rely
on
its
narrow
de
minimis
exemption
authority
to
escape
the
highly
prescriptive
provisions
in
section
112.
The
commenters
further
noted
that
EPA
has
not
revealed
any
administrative
record
justifying
a
de
minimis
exemption,
to
demonstrate
in
any
way
that
compliance
with
MACT
would
"
yield
a
gain
of
trivial
or
no
value."

Response:
We
disagree
with
the
commenters
who
claimed
that
the
low­
risk
approaches,
especially
the
concentration­
based
27
exemption,
can
be
justified
by
de
minimis
principles.
Our
de
minimis
authority
exists
to
help
avoid
excessive
regulation
of
tiny
amounts
of
pollutants,
where
regulation
would
yield
a
result
contrary
to
a
primary
legislative
goal.
It
is
unavailable
"
where
the
regulatory
function
does
provide
benefits,
in
the
sense
of
furthering
the
regulatory
objectives,
but
the
agency
concludes
that
the
acknowledged
benefits
are
exceeded
by
the
costs."
EDF
v.
EPA,
82
F.
3d
451,
466
(
D.
C.
Cir.
1996);
Public
Citizen
v.

Young,
831
F.
2d
1108,
1112­
13
(
D.
C.
Cir.
1987);
Alabama
Power
v.

EPA,
636
F.
2d
323,
360­
61
&
n.
89
(
D.
C.
Cir.
1979).
Accordingly,

a
de
minimis
exemption
to
section
112(
d)(
3)
is
unavailable
in
today's
final
PCWP
rule
because
it
would
frustrate
a
primary
legislative
goal
by
preventing
application
of
the
MACT
floor
to
tons
of
PCWP
facilities'
HAP
emissions.

The
U.
S.
Court
of
Appeals
for
the
District
of
Columbia
Circuit
has
already
addressed
the
de
minimis
concept
in
the
MACT
context,
in
National
Lime
Ass'n
v.
EPA,
233
F.
3d
625,
640
(
D.
C.

Cir.
2000)
(
National
Lime),
in
which
the
court
rejected
the
industry
petitioner's
claim
that,
in
light
of
both
the
high
costs
and
low
quantities
of
HAP
at
issue
in
that
case,
we
should
read
a
de
minimis
exception
into
the
requirement
that
it
regulate
all
HAP
emitted
by
major
sources.
In
that
case,
the
Court
found
that
"
EPA
reasonably
rejected
this
argument
on
the
ground
that
the
statute
`
does
not
provide
for
exceptions
from
emissions
standards
based
on
de
minimis
principles
where
a
MACT
floor
exists.'"
(
See
28
National
Lime
at
640.)
We
recently
re­
affirmed
our
position
on
the
unavailability
of
de
minimis
exemptions
from
the
MACT
floor
in
the
final
rule
regulating
organic
liquids
distribution.
(
See
69
FR
5038
(
February
3,
2004).)

We
see
no
reason
to
revisit
this
fundamental
issue.
Section
112
of
the
CAA
is
replete
with
careful
definitions
of
volume­
or
effect­
based
limitation
on
regulation,
indicating
that
Congress
has
already
defined
what
amounts
of
HAP
emissions
are
too
small
to
warrant
MACT
standards
or
other
controls
under
section
112.

The
requirement
to
adopt
MACT
emission
limitations,
for
example,

applies
without
exception
to
"
each
category
or
subcategory
of
major
sources...
of
[
HAP]."
(
See
CAA
section
112(
d)(
1).)
For
sources
below
the
major
source
threshold,
however,
we
have
discretion
to
require
"
generally
available
control
technologies
or
management
practices."
(
See
CAA
section
112(
d)(
5).)
Congress
has,
thus,
itself
defined
volumetrically
which
sources'
emissions
are
small
enough
not
to
warrant
mandatory
MACT
standards.

Congress
likewise
defined
several
MACT
exceptions
applicable
where
emissions
have
de
minimis
health
effects.
Section
112(
d)(
4)
of
the
CAA
allows
us
to
establish
standards
less
stringent
than
MACT
for
HAP
with
an
established
health
threshold,

so
long
as
we
set
a
standard
below
the
health
threshold
with
"
an
ample
margin
of
safety."
Section
112(
b)(
3)(
C)
of
the
CAA
directs
us
to
delist
HAP
 
precluding
section
112(
d)
MACT
standards
 
if
we
determine
that
"
there
is
adequate
data
on
the
health
and
29
environmental
effects
of
the
substance
to
determine
that
emissions,
ambient
concentrations,
bioaccumulation
or
deposition
of
the
substance
may
not
reasonably
be
anticipated
to
cause
any
adverse
effects
to
the
[
sic]
human
health
or
adverse
environmental
effects."
Section
112(
c)(
9)(
B)(
i)
of
the
CAA
(
discussed
further
below)
lets
us
delete
source
categories
and
subcategories
from
the
category
list
 
the
consequence
again
being
no
MACT
control
 
if
we
determine
that,
for
emissions
of
carcinogenic
HAP,
"
no
source
in
the
category...
emits
such
[
HAP]

in
quantities
which
may
cause
a
lifetime
risk
of
cancer
greater
than
one
in
one
million
to
the
individual
in
the
population
who
is
most
exposed
to
emissions
of
such
pollutant
from
the
source."

For
noncarcinogens,
we
may
delete
source
categories
and
subcategories
if
we
determine
that
"
emissions
from
no
source
in
the
category
or
subcategory...
exceed
a
level
which
is
adequate
to
protect
public
health
with
an
ample
margin
of
safety
and
no
adverse
environmental
effect
will
result
from
emissions
from
any
source."
(
See
CAA
section
112(
c)(
9)(
B)(
ii).)
Moreover,
in
defining
which
source
modifications
trigger
additional
regulatory
standards,
CAA
section
112(
g)(
1)(
A)
mentions
a
"
greater
than
de
minimis
increase
in
actual
emission
of
a
[
HAP]."
This
shows
that
Congress
knew
how
to
use
the
de
minimis
concept
when
it
considered
it
appropriate
in
section
112,
and
the
fact
that
Congress
did
not
use
it
in
section
112(
d)(
3)
supports
our
 
and
the
D.
C.
Circuit's
 
conclusion
that
it
is
unavailable
to
support
30
an
exception
to
a
MACT
floor
that
is
not
otherwise
authorized
under
section
112.

We
do
not
find
persuasive
the
proposition
that
the
overall
purpose
of
section
112
is
protecting
human
health
and
the
environment,
and
that,
therefore,
as
long
as
this
general
purpose
is
met,
we
may
fashion
de
minimis
exceptions
from
MACT
beyond
those
allowed
under
section
112.
First,
this
position
appears
to
assume
that
the
issue
is
to
be
drawn
on
a
clean
slate,
while
the
D.
C.
Circuit
has
affirmed
our
view
that
section
112(
d)(
3)

provides
no
discretion
to
use
a
de
minimis
rationale
to
avoid
MACT.
Second,
the
commenter
appears
to
give
prominence
to
an
over­
arching
statutory
goal
over
the
specific
language
of
the
statutory
provisions
themselves,
in
assessing
whether
those
provisions
are
"
extraordinarily
rigid"
regarding
EPA's
otherwiseinherent
de
minimis
authority;
the
logical
extension
of
such
an
approach
would
be
to
find
that
no
single
provision
in
the
CAA
could
restrict
our
de
minimis
authority,
in
light
of
the
CAA's
over­
arching
purpose
"
to
promote
the
public
health
and
welfare."

(
See
CAA
section
101(
b)(
1).)
Third,
the
commenter
does
not
present
any
persuasive
statutory
arguments
to
overcome
those
that
we
presented
to
the
court
 
and
which
the
court
affirmed
 
in
National
Lime.
Fourth,
we
are
unable
to
discern
the
basis
for
the
commenter's
suggestion
that
we
have
in
fact
been
relying
on
de
minimis
authority
in
the
MACT
program
for
several
years
in
establishing
applicability
thresholds,
and
we
are
not
aware
of
31
any
instance
in
which
we
have
explicitly
justified
an
exception
from
an
applicable
MACT
floor
based
on
a
de
minimis
rationale
that
would
be,
like
the
commenter's
requested
exemption,
in
contravention
of
the
Court's
ruling
in
NLA.
Finally,
to
the
extent
the
commenters
believe
such
a
de
minimis
exemption
is
justified
by
the
wish
to
reduce
the
costs
of
the
PCWP
rule,
we
are
not
free
to
grant
a
de
minimis
exemption
to
account
for
costs.
Congress
already
took
cost
into
account
in
section
112(
d),
relying
on
prior
business
judgments
by
the
best
performing
sources
to
substitute
for
the
judgment
of
the
rest
of
the
PCWP
industry,
therefore,
denying
us
the
leeway
to
consider
costs
as
a
factor
to
modify
the
MACT
floor.
Only
in
considering
more
stringent
"
beyond
floor"
standards
may
we
consider
costs
in
the
MACT
context.
Therefore,
we
do
not
believe
it
is
appropriate
or
necessary
to
revisit
our
and
the
D.
C.
Circuit's
prior
conclusions
regarding
the
availability
of
the
de
minimis
principle
in
today's
final
PCWP
rule.

c.
Section
112(
c)(
9)

Comment:
Two
commenters
opposed
using
subcategorization
as
a
mechanism
to
exempt
facilities.
One
of
the
commenters
stated
that
subcategorization
is
a
tool
that
should
be
used
in
the
standard
setting
process,
and
using
it
to
exempt
facilities
would
have
a
detrimental
effect
on
the
stringency
of
the
MACT
floor
and
would
generally
degrade
the
standard.
According
to
the
commenter,
the
two­
step
subcategorization
proposal
is
32
inconsistent
with
how
subcategorization
has
been
done
in
numerous
previous
NESHAP.

The
other
commenter
argued
that
EPA's
subcategorization
theories
are
unlawful.
According
to
the
commenter,
section
112(
c)(
9)
does
not
authorize
EPA
to
separate
identical
pollution
sources
into
subcategories
that
are
regulated
differently
to
weed
out
low­
risk
facilities
or
reduce
the
scope/
cost
of
the
standard.

The
commenter
stated
that
subcategories
based
solely
on
risk
do
not
bear
a
reasonable
relationship
to
Congress'
technology­
based
approach
or
the
statutory
structure
and
purposes
of
section
112,

and
are
not
authorized
by
the
CAA.
According
to
the
commenter,

categories
and
subcategories
are
required
to
be
consistent
with
the
categories
of
stationary
sources
in
section
111.
The
commenter
was
not
aware
of
any
instance
in
which
EPA
has
established
categories
or
subcategories
based
on
risk.
The
commenter
stated
that
EPA
routinely
defines
subcategories
based
on
equipment
characteristics
(
e.
g.,
technical
differences
in
emissions
characteristics,
processes,
control
device
applicability,
or
opportunities
for
pollution
prevention).

According
to
the
commenter,
EPA
has
not
offered
any
explaination
for
why
reinterpreting
the
statute
to
ignore
nearly
12
years
of
settled
practices
and
expectations
under
the
MACT
program
is
reasonable,
nor
why
reducing
the
applicability
of
HAP
emission
standards
serves
Congress's
goals
in
enacting
the
1990
CAA
Amendments.
33
The
commenter
noted
that
EPA's
discussion
of
the
risk­
based
exemptions
was
contained
in
a
preamble
section
entitled,
"
Can
We
Achieve
the
Goals
of
the
Proposed
Rule
in
a
Less
Costly
Manner,"

which
strongly
suggests
that
EPA's
motivation
for
considering
these
risk­
based
approaches
is
consideration
of
cost.
The
commenter
cited
prior
EPA
documentation
and
stated
that
EPA
in
the
past
has
rejected
the
notion
that
cost
should
influence
MACT
determination,
and
this
prior,
consistently
applied
interpretation
better
serves
the
purposes
of
section
112.
The
commenter
argued
that
subcategorizing
to
set
a
no­
control
MACT
floor
is
the
same
as
refusing
to
set
a
MACT
standard
because
the
benefits
would
be
negligible,
which
is
unlawful.

The
commenter
also
stated
that
section
112(
c)(
9)(
B)(
i)
does
not
authorize
EPA
to
delist
subcategories.
According
to
the
commenter,
section
112(
c)(
9)(
B)
contains
two
subsections:

subsection
(
i)
refers
only
to
categories,
and
subsection
(
ii)

refers
to
both
categories
and
subcategories.
The
commenter
argued
that
the
absence
of
the
term
"
subcategories"
in
section
112(
c)(
9)(
B)(
i)
indicates
a
Congressional
choice
not
to
permit
the
Administrator
to
delist
subcategories
of
sources
under
section
112(
c)(
9)(
B).
The
commenter
stated
that
this
is
consistent
with
Congress'
decision
to
require
a
higher
standard
to
delist
categories
that
emit
carcinogens.
According
to
the
commenter,
the
section
112(
c)(
9)(
B)(
ii)
requirement
of
less
than
one
in
a
million
lifetime
cancer
risk
for
the
most
exposed
34
individual
is
a
higher
and
more
specific
standard
than
the
standard
for
other
HAP.

To
the
contrary,
two
commenters
stated
that
EPA
has
ample
authority
under
sections
112(
c)(
1)
and
112(
c)(
9)
to
create
and
delist
low­
risk
categories
or
subcategories.
According
to
the
commenters,
section
112(
c)(
1)
provides
the
Administrator
with
significant
flexibility
to
create
categories
and
subcategories
as
needed
to
implement
section
112.
One
commenter
stated
that
there
is
nothing
in
the
statute
that
limits
the
criteria
the
Administrator
can
use
in
establishing
categories
and
subcategories.
The
commenter
added
that
there
is
also
nothing
in
the
history
of
EPA's
interpretation
of
section
112(
c)
that
precludes
subcategorization
based
on
risk.
In
addition,
EPA
has
stated
that
emission
characteristics
are
factors
to
be
considered
when
defining
categories.

The
commenter
stated
that
application
of
statutory
authority
to
exclude
sources
from
regulation
under
section
112(
d)(
3)
is
also
supported
by
relevant
case
law,
e.
g.,
in
the
Vinyl
Chloride
case.
(
NRDC
v.
EPA,
824
F.
2D
1126
(
D.
C.
Cir.
1987))
According
to
the
commenter,
the
court
in
that
case
established
a
range
of
acceptable
level
of
risk
in
establishing
limits
under
prior
language
in
section
112,
and
the
establishment
of
an
acceptable
level
of
risk
could
be
used
to
create
a
low­
risk
subcategory
that
could
be
delisted.
The
commenter
stated
that
technological
or
operational
differences
among
sources
may
also
help
discriminate
35
between
low­
risk
and
high­
risk
sources.
The
commenter
stated
that
effective
use
of
section
112(
c)(
1)
authority
to
create
riskbased
subcategories
would
significantly
improve
the
costeffectiveness
of
the
section
112
program
without
undermining
its
role
in
protecting
public
health
and
the
environment.

Both
commenters
noted
that
section
112(
c)(
9)(
B)
provides
EPA
with
broad
authority
to
remove
from
MACT
applicability
those
categories
and
subcategories
of
facilities
whose
HAP
emissions
are
sufficiently
low
as
to
demonstrate
a
cancer
risk
less
than
one
in
a
million
to
the
most
exposed
individual
in
the
population
(
for
non­
threshold
carcinogens)
and
no
adverse
environmental
or
public
health
effect
(
for
threshold
HAP).
(
The
commenter
asserted
that
Congress
used
the
terms
category
and
subcategory
interchangeably,
indicating
that
either
one
can
be
delisted.)

One
commenter
suggested
that
sources
able
to
demonstrate
a
basis
for
inclusion
in
the
delisted
category
on
a
case­
by­
case
basis
would
then
be
exempted
from
the
MACT,
subject
to
possible
federally­
enforceable
conditions
designed
by
EPA.
The
commenter
stated
that
the
new
category
could
include
the
following:
all
low­
risk
facilities,
facilities
producing
wood
products
found
to
pose
no
expected
risk
to
human
health
(
i.
e.,
fiberboard,
medium
density
fiberboard
and
plywood),
facilities
with
acrolein
emissions
below
a
certain
threshold,
or
facilities
selected
on
the
basis
of
some
other
risk
criterion.
The
commenter
suggested
that
the
low­
risk
category
be
included
in
the
final
rule
and
36
delisted
within
6
months
following
publication
of
the
final
rule.

The
delisting
notices
would
designate
health
benchmarks
and
facilities
would
be
required
to
submit
evidence
(
e.
g.,
tiered
dispersion
modeling)
demonstrating
that
their
emissions
result
in
exposures
that
fall
below
the
benchmarks.
Following
delisting
of
the
category,
an
affected
source
could
apply
to
EPA
for
a
determination
that
it
qualifies
for
inclusion
in
the
low­
risk
category.
After
evaluating
the
source's
petition,
EPA
would
issue
a
written
determination
of
applicability
based
on
the
petition
that
would
be
binding
on
the
permitting
authority
(
unless
the
petition
was
found
to
contain
significant
errors
or
omissions)
and
appealable
by
the
affected
source
or
interested
parties.
The
EPA
could
require
all
facilities
that
qualify
for
inclusion
in
the
delisted
category
to
comply
with
federally­
enforceable
conditions,
similar
to
the
conditions
established
in
permits
for
"
synthetic
minor"
sources
(
e.
g.,

limits
on
potential
to
emit,
production
limits).

The
commenter
also
responded
to
objections
regarding
the
subcategorization
and
delisting
of
low­
risk
facilities.
The
commenter
stated
that
the
contrasting
of
the
terms
"
category"
and
"
subcategory"
offered
a
distinction
that
in
no
way
limited
EPA's
authority
to
delist
low­
risk
facilities.
According
to
the
commenter,
the
argument
that
EPA
cannot
create
subcategories
based
on
risk
is
contradicted
by
the
statutory
language,
which
expressly
states
that
the
categories
and
subcategories
EPA
37
creates
under
section
112
need
not
match
those
created
under
section
111.
Furthermore,
prior
EPA
statements
do
nothing
to
detract
from
EPA's
broad
discretion
to
establish
categories
and
subcategories.
The
subcategorization
factors
previously
discussed
by
EPA
justify
subcategorization
based
on
risk.
The
authority
cited
by
one
commenter
does
not
establish
that
EPA's
discretion
to
alter
subcategorization
is
limited
in
any
way,
and
even
if
it
were,
EPA
is
not
bound
by
any
prior
position.
The
arguments
that
EPA
may
not
delist
subcategories
for
carcinogens
(
or
sources
emitting
carcinogens)
rest
on
a
formalistic
distinction
that
EPA
previously
has
rejected
as
meaningless,
and
that,
at
any
rate,
can
be
remedied
with
a
simple
recasting
of
a
subcategory
as
a
category.
The
commenter
stated
that
doing
so
is
undisputedly
within
EPA's
authority.

Three
commenters
addressed
the
issue
of
subcategorizing
PCWP
facilities
based
on
characteristics
other
than
risk.
One
commenter
stated
that
the
only
option
that
appears
consistent
with
the
CAA,
does
not
create
excessive
work
for
State
and
local
agencies,
and
may
be
able
to
be
based
on
science,
is
the
subcategorization
and
delisting
approach.
However,
the
commenter
added
that
the
subcategories
should
be
based
on
equipment
or
fuel
use,
not
risk.
The
commenter
stated
that
a
subcategory
based
on
site­
specific
risk
creates
a
circular
definition
and
does
not
make
sense.
The
commenter
also
stated
that
subcategory
delisting
should
occur
before
the
compliance
date
so
that
facilities
don't
38
put
off
compliance
in
the
hope
or
anticipation
of
delisting.

The
second
commenter
stated
that
EPA
requested
comment
on
the
establishment
of
PCWP
subcategories
ostensibly
based
on
physical
and
operational
characteristics,
but
in
reality
based
on
risk.
According
to
the
commenter,
this
indirect
approach
is
just
a
variation
on
the
approach
(
direct
reliance
on
risk)
that
EPA
itself
notes
would
disrupt
and
weaken
establishment
of
MACT
floors,
and
is
accordingly
unlawful.
The
commenter
stated
that,

even
if
these
approaches
were
lawful,
to
the
extent
that
EPA's
proposal
could
be
read
to
suggest
that
facilities
could
be
allowed
to
become
part
of
the
allegedly
low­
risk
subcategory
in
the
future
without
additional
EPA
rulemaking,
this
too
would
be
unlawful.
According
to
the
commenter,
section
112(
c)(
9)
provides
the
EPA
Administrator
alone
the
authority
to
make
delisting
determinations,
and
such
authority
may
not
be
delegated
to
other
government
authorities
or
private
parties.
The
commenter
stated
that
EPA's
proposal
suggests
an
approach
entirely
backward
from
the
statute
 
allowing
sources
to
demonstrate
after­
the­
fact
that
they
belong
in
a
subcategory
that
has
been
delisted
under
section
112(
c)(
9),
when
the
statute
requires
that
EPA
determine
that
no
source
in
the
category
emits
cancer­
causing
HAP
above
specified
levels,
or
that
no
source
in
the
category
or
subcategory
emit
non­
carcinogenic
HAP
above
specified
levels,
by
the
time
EPA
establishes
the
standard.
The
commenter
stated
that
EPA
has
provided
no
explanation
of
how
the
suggested
approaches
would
be
39
lawful
or
workable.

The
third
commenter
indicated
that
low
risk
is
an
adequate
and
appropriate
criterion
for
categorization.
The
commenter
disagreed
that
EPA
should
create
and
delist
categories
on
a
technology
basis
when
the
intent
is
delisting
of
low­
risk
facilities.
The
commenter
believed
that
seeking
a
technology­
based
surrogate
for
risk
is
unnecessary
within
the
statutory
framework.
The
commenter
noted
that
the
Congressional
intent
was
"
to
avoid
regulatory
costs
which
would
be
without
public
health
benefit."
(
S.
Rep.
No.
228,
101st
Cong.,
1st.

Sess.
175­
6
(
1990))
Nevertheless,
the
commenter
described
some
technology­
based
criteria
that
they
believed
could
be
used
to
develop
low­
risk
groups
of
PCWP
facilities.

Four
commenters
addressed
the
impact
that
creation
of
a
lowrisk
subcategory
under
CAA
section
112(
c)(
9)
could
have
on
the
establishment
of
MACT
floors
for
the
PCWP
category.
Two
commenters
argued
that
such
subcategorization
would
have
a
negative
effect.
One
commenter
stated
that
this
situation
provided
a
valid
reason
for
EPA
not
to
mix
risk­
based
and
technology­
based
standards
development.
The
commenter
added
that
EPA
also
did
not
address
how
the
"
once
in,
always
in"
policy
would
apply
in
such
a
situation.
The
other
commenter
stated
that
this
situation
was
another
compelling
reason
why
the
suggested
section
112(
c)(
9)
subcategorization
approach
was
unlawful
and
arbitrary.
The
commenter
stated
that
the
flaw
was
so
obvious,
40
inherent,
and
contrary
to
the
MACT
floor
provisions
of
section
112
and
its
legislative
history,
that
it
proves
the
undoing
of
the
suggested
section
112(
c)(
9)
exemption.
According
to
the
commenter,
EPA
cannot
simultaneously
exercise
its
source
category
delisting
authority
consistent
with
section
112(
c)(
9),
establish
appropriate
MACT
floors
under
section
112(
d),
and
establish
subcategory
exemptions
in
the
manner
suggested
by
EPA,
because
the
latter
approach
contravenes
both
section
112(
c)(
9)
and
the
section
112(
d)
floor­
setting
process.
The
commenter
stated
that
section
112'
s
major
source
thresholds
and
statutory
deadlines
make
clear
that
sources
meeting
MACT
by
the
time
EPA
is
required
to
issue
MACT
standards
must
install
MACT
controls
and
may
not
subsequently
throw
them
off
or
be
relieved
from
meeting
the
MACT­
level
standards.
While
the
section
112(
f)
residual
risk
process
allows
EPA
to
establish
more
stringent
emissions
standards,
there
is
nothing
in
the
CAA
that
suggests
EPA
possesses
authority
to
relax
promulgated
MACT
standards.

The
third
commenter
indicated
that
dilution
of
the
MACT
floor
would
not
occur
if
low­
risk
category
delisting
occurred
as
follows:
(
1)
propose
low­
risk
category
with
final
PCWP
rule,
(
2)

promulgate
low­
risk
category
6
months
after
proposal,
and
(
3)

delist
facilities
prior
to
MACT
compliance
deadline.
If
EPA
issued
the
final
PCWP
rule
 
thereby
setting
the
MACT
floor
 
before
it
allowed
affected
sources
to
apply
for
inclusion
in
the
low­
risk
category
to
be
delisted,
then
every
affected
source
41
would
be
considered
in
the
establishment
of
the
MACT
floor.

Thus,
as
a
result
of
this
timing,
the
MACT
floor
could
not
be
diluted
because
no
sources
would
be
exempted
from
MACT
before
the
MACT
floor
is
set.

The
fourth
commenter
believed
that
a
MACT
floor
reevaluation
would
be
appropriate
and
would
further
ensure
that
only
facilities
posing
significant
risk
are
required
to
install
expensive
controls.

Response:
We
believe
that
establishing
a
"
low­
risk"
PCWP
subcategory
under
CAA
section
112(
c)(
1)
and
deleting
that
subcategory
under
CAA
section
112(
c)(
9)
best
balances
Congress'

dual
concerns
that
categories
and
subcategories
of
major
sources
of
HAP
be
subject
to
technology­
based
(
and
possible
future
riskbased
emission
standards,
but
that
undue
burdens
not
be
placed
on
groups
of
sources
within
the
PCWP
source
category
whose
HAP
emissions
are
demonstrated
to
present
little
risk
to
public
health
and
the
environment.
We
do
not
contend
that
the
CAA
specifically
directs
us
to
establish
categories
and
subcategories
of
HAP
sources
based
on
risk,
and
we
recognize
that,
at
the
time
of
the
1990
CAA
Amendments,
Congress
may
have
assumed
that
we
would
generally
base
categories
and
subcategories
on
the
traditional
technological,
process,
output,
and
product
factors
that
had
been
considered
under
CAA
section
111.
However,
when
properly
considered,
it
becomes
apparent
that
Congress
did
not
intend
the
unduly
restrictive
 
and
consequently
over­
42
regulatory
 
reading
of
the
CAA
that
some
commenters
urge
regarding
low­
risk
PCWP
facilities.

Numerous
CAA
section
112
provisions
evidence
Congress'

intent
that
we
be
able
to
find
that
sources,
such
as
those
in
the
PCWP
category
whose
HAP
emissions
are
below
identified
risk
levels,
should
not
necessarily
be
subject
to
MACT.
These
provisions,
together
with
other
indications
of
Congressional
intent
regarding
the
goals
of
section
112,
must
all
be
considered
in
determining
whether
we
may
base
a
PCWP
subcategory
on
risk
and
delist
that
group
of
sources,
without
requiring
additional
HAP
regulation
that
would
be
redundant
for
purposes
of
meeting
Congress'
risk­
based
goals.

While
it
is
true
that
CAA
section
112(
c)(
1)
provides
that
"[
t]
o
the
extent
practicable,
the
categories
and
subcategories
listed
under
this
subsection
shall
be
consistent
with
the
list
of
source
categories
established
pursuant
to
section
111
and
part
C[,]"
the
provision
also
states
that
"[
n]
othing
in
the
preceding
sentence
limits
the
Administrator's
authority
to
establish
subcategories
under
this
section,
as
appropriate."
Therefore,
by
its
plain
terms,
section
112(
c)(
1)
does
not
preclude
basing
subcategories
on
criteria
other
than
those
traditionally
used
under
section
111
before
1990,
or
those
used
after
1990
for
sections
111
and
112.
Moreover,
while
after
1990
we
have
principally
used
the
traditional
criteria
to
define
categories
and
subcategories,
such
use
in
general
does
not
restrict
how
we
43
may
define
a
subcategory
in
a
specific
case,
"
as
appropriate,"

since
each
HAP­
emitting
industry
presents
its
own
unique
situation
and
factors
to
be
considered.
(
See,
e.
g.,
Sierra
Club
v.
EPA,
D.
C.
Cir.
No.
02­
1253,
2004
U.
S.
App.
LEXIS
348
(
decided
Jan.
13,
2004).)

Even
assuming
for
argument
that
the
language
of
section
112(
c)(
1)
may
initially
appear
to
restrict
our
authority
to
define
subcategories,
section
112(
c)(
1)
cannot
be
read
in
isolation.
A
broad
review
of
the
entire
text,
structure,
and
purpose
of
the
statute,
as
well
as
Congressional
intent
shows
that,
applied
within
the
context
of
CAA
section
112(
c)(
9),
our
approach
of
defining
a
low­
risk
subcategory
of
PCWP
facilities
is
reasonable,
at
the
very
least
as
a
way
to
reconcile
the
possible
tension
between
the
arguably
restrictive
language
of
section
112(
c)(
1)
and
the
Congressional
intent
behind
section
112(
c)(
9).

(
See,
e.
g.,
Virginia
v.
Browner,
80
F.
3d
869,
879
(
4th
Cir.

1996).)
Alternatively,
even
if
the
language
is
clear
on
its
face
in
restricting
our
ability
to
define
subcategories,
we
believe
that,
as
a
matter
of
historical
fact,
Congress
could
not
have
meant
what
the
commenter
asserts
it
appears
to
have
said,
and
that
as
a
matter
of
logic
and
statutory
structure,
it
almost
surely
could
not
have
meant
it.
(
See,
e.
g.,
Engine
Mfrs.
Ass'n
44
v.
EPA,
88
F.
3d
1075,
1089
(
D.
C.
Cir.
1996).)

Our
interpretation
of
the
CAA
is
a
reasonable
accommodation
of
the
statutory
language
and
Congressional
intent
regarding
the
relationship
of
the
statutory
categorization
and
subcategorization,
delisting,
MACT
and
residual
risk
provisions
that
apply
to
the
PCWP
category.
This
becomes
clear
in
light
of
the
issue
addressed
by
commenters,
which
is
whether
we
may
delist
a
subcategory
of
low­
risk
PCWP
facilities
only
if
such
a
group
of
sources
is
defined
by
criteria
we
have
traditionally
used
to
define
categories
and
subcategories
for
regulatory,
rather
than
delisting
purposes.
Our
approach
implements
Congressional
intent
to
avoid
the
over­
regulatory
result
that
flows
from
an
overly
rigid
reading
of
the
CAA.
When
the
CAA
is
read
as
a
whole,
it
is
apparent
that
Congress
 
which
in
1990
likely
did
not
fully
anticipate
the
policy
considerations
that
come
into
play
in
regulating
HAP
emissions
from
PCWP
facilities
 
has
not
spoken
clearly
on
the
precise
issue.
Our
interpretation
is
necessary
to
fill
this
statutory
"
gap"
and
prevent
the
thwarting
of
Congressional
intent
not
to
unnecessarily
burden
low­
risk
PCWP
facilities
by
forcing
them
to
meet
stringent
MACT
controls
when
they
already
meet
the
risk­
based
goals
of
section
112.
Our
interpretation
thus
lends
symmetry
and
coherence
to
the
statutory
scheme.

While
we
do
not
believe
section
112(
c)(
1)
actually
restricts
our
authority
to
establish
a
low­
risk
PCWP
subcategory,
even
if
45
the
language
is
so
restrictive,
it
must
be
read
within
the
context
of
Congress'
purpose
in
allowing
us
to
delist
categories
and
subcategories
of
low­
risk
sources
that
are
defined
according
to
the
traditional
criteria
under
section
111.
It
is
beyond
dispute
that
Congress
determined
that
certain
identifiable
groups
or
sets
of
sources
may
be
delisted
if,
as
a
group
and
without
a
single
constituent
source's
exception,
they
are
below
the
enumerated
eligibility
criteria
of
section
112(
c)(
9).
There
is
no
apparent
reason
why
such
a
group
or
set
of
sources
must
be
limited
to
those
defined
by
traditional
categorization
or
subcategorization
criteria.
This
is
because,
first,
Congress
in
section
112(
c)(
1)
clearly
did
not
absolutely
prohibit
us
from
basing
categories
and
subcategories
on
other
criteria
generally;

and,
second,
the
underlying
characteristic
of
an
eligible
set
or
group
of
sources
under
section
112(
c)(
9)
 
that
no
source
in
the
set
or
group
presents
risks
above
the
enumerated
levels
 
can
be
applied
under
several
approaches
to
defining
categories
and
subcategories
and
is
not
dependent
upon
such
set
or
group
being
traditionally
defined
in
order
to
implement
the
purpose
of
section
112(
c)(
9).
Put
another
way,
there
is
nothing
apparent
in
the
statute
that
precludes
us
from
delisting
a
discernible
set
of
low­
risk
PCWP
facilities
just
because
that
set
cannot
also
be
defined
according
to
other
traditional
criteria
that
have
nothing
to
do
with
the
question
of
whether
each
of
the
constituent
PCWP
facilities
is
low­
risk.
As
a
matter
of
logic
and
statutory
46
structure,
Congress
almost
surely
could
not
have
meant
to
require
that
every
identifiable
group
of
low­
risk
PCWP
facilities,
no
matter
how
large
in
number
or
in
percentage
with
respect
to
higher­
risk
facilities
in
the
PCWP
category,
must
remain
subject
to
section
112,
simply
because
that
group
could
not
be
subcategorized
as
separate
from
the
higher
risk
PCWP
facilities
by
application
of
traditional
subcategorization
criteria.

Where
Congress
squarely
confronted
the
issue,
it
explicitly
provided
relief
for
categories
and
subcategories,
defined
by
traditional
criteria,
that
also
happen
to
present
little
risk.

(
See
CAA
sections
112(
d)(
4),
112(
c)(
9),
and
112(
f)(
2).)
These
CAA
provisions
addressing
risk­
based
relief
from,
or
thresholds
for,
HAP
emissions
regulation
evidence
Congressional
concern
that
the
effects
of
such
pollution
be
taken
into
account,
where
appropriate,
in
determining
whether
regulation
under
section
112
is
necessary.
At
the
time
of
the
1990
Amendments,
Congress
did
not
consider
it
necessary
to
provide
express
relief
for
additional
groups
such
as
low­
risk
PCWP
facilities,
beyond
those
defined
by
traditional
category
and
subcategory
criteria,
because
it
assumed
we
could
implement
a
comprehensive
regulatory
scheme
for
air
toxics
that
would
both
address
situations
where
technology­
based
standards
were
needed
to
reduce
source
HAP
emissions
to
levels
closer
to
the
risk­
based
goals
of
section
112,
and
avoid
unnecessary
imposition
of
technology­
based
requirements
on
groups
of
sources
that
were
already
meeting
those
47
goals.
Congress
enacted
or
revised
various
CAA
air
toxics
provisions
 
including
sections
112(
c),
(
d)
and
(
f)
 
to
that
end.
Had
events
unfolded
in
that
anticipated
fashion,
in
the
case
of
each
industrial
category
and
subcategory,
there
would
have
been
a
perfect
correlation
between
the
traditional
criteria
for
defining
categories
and
subcategories
and
the
facts
showing
whether
those
groups
are
either
high­
or
low­
risk
HAP
sources.

This
context
turned
out
to
be
more
complex
than
Congress
anticipated,
and
in
the
case
of
PCWP
facilities
there
is
no
clear
differentiation
between
high­
versus
low­
risk
sources
that
corresponds
to
our
traditional
approach
for
identifying
source
categories
and
subcategories.
Nevertheless,
as
in
the
case
of
a
low­
risk
source
group
defined
by
traditional
category
or
subcategory
criteria,
for
the
PCWP
industry,
we
are
able
to
identify
a
significant
group
of
sources
whose
HAP
emissions
pose
little
risk
to
public
health
and
the
environment,
applying
the
same
section
112(
c)(
9)
delisting
criteria
that
would
apply
to
any
traditionally­
defined
source
group.
We
believe
it
is
reasonable
to
conclude
that
Congress
would
not
have
intended
to
overregulate
the
low­
risk
PCWP
facilities
due
to
the
inability
to
define
such
a
group
by
traditional
criteria
and
thereby
frustrate
the
coherent
scheme
Congress
set
forth
of
ensuring
that
HAP
sources
ultimately
meet
common
risk­
based
goals
under
section
112.

The
commenter's
assertion
that
we
are
inappropriately
48
altering
our
interpretation
of
the
applicable
statutory
provisions
and
departing
from
the
traditional
categorization
and
subcategorization
criteria
in
addressing
low­
risk
PCWP
facilities
is
thus
unfounded.
As
explained
above,
the
complexity
of
the
air
toxics
problem
and
the
relationship
between
the
traditional
criteria
and
what
might
be
groups
of
low­
risk
sources,
a
context
not
fully
understood
by
either
Congress
or
EPA
at
the
time
of
the
1990
Amendments,
provides
adequate
justification
for
any
unique
applications
of
the
our
approach
for
low­
risk
PCWP
facilities.

Our
approach
does
not
equate
to
one
that
Congress
considered
and
rejected
that
would
have
allowed
source­
by­
source
exemptions
from
MACT
based
on
individualized
demonstrations
that
such
sources
are
low­
risk.
This
is
because,
contrary
to
that
approach,
we
rely
upon
the
application
of
specific
eligibility
criteria
that
are
defined
in
advance
of
any
source's
application
to
be
included
in
the
low­
risk
PCWP
subcategory,
in
much
the
same
way
as
any
other
applicability
determination
process
works.

Moreover,
in
response
to
the
assertion
that
our
approach
nevertheless
conflicts
with
legislative
history
rejecting
a
similar
(
but
not
identical)
approach
Congress
considered
under
section
112,
this
legislative
history
is
not
substantive
legislative
history
demonstrating
that
Congress
voted
against
relief
from
MACT
in
this
situation
 
there
is
no
such
history.
The
commenters
point
to
a
provision
in
the
House
bill
that
was
not
enacted
but
that
would
have
provided
in
certain
situations
for
49
case­
by­
case
exemptions
for
low­
risk
sources.
There
is
no
evidence
that
this
provision
was
ever
debated,
considered,
or
voted
upon,
so
its
not
being
enacted
is
not
probative
of
congressional
intent
concerning
our
ability
to
identify
and
delist
a
group
of
low­
risk
PCWP
facilities.
Instead,
it
is
reasonable
to
assume
that,
had
Congress
been
aware
in
1990
of
the
possibility
that
an
identifiable
group
of
PCWP
facilities
is
lowrisk
while
that
group
does
not
correspond
to
traditional
criteria
differentiating
categories
and
subcategories,
Congress
would
have
expressly,
rather
than
implicitly,
authorized
our
action
here.

Moreover,
the
commenters
are
unable
to
cite
any
provision
in
CAA
section
112
that
would
prevent
us
from
being
able
to
add
individual
or
additional
groups
of
low­
risk
PCWP
facilities
to
the
group
we
initially
identify
in
our
final
delisting
action,
as
those
additional
low­
risk
PCWP
facilities
prove
their
eligibility
for
inclusion
in
the
delisted
group
over
time.
In
fact,
the
approach
we
are
taking
for
identifying
additional
low­
risk
PCWP
facilities
is
fully
consistent
with
the
approach
we
have
long
taken
in
identifying,
on
a
case­
by­
case
basis
and
subject
to
appropriate
review,
whether
individual
sources
are
members
of
a
category
or
subcategory
subject
to
standards
adopted
under
CAA
sections
111
and
112.

Regarding
the
comment
that
Congress
did
not
expressly
provide
relief
for
carcinogen­
emitting
low­
risk
groups
of
sources
50
within
the
PCWP
category
other
than
as
an
entire
category,
we
construe
the
provisions
of
section
112(
c)(
9)
to
apply
to
listed
subcategories
as
well
as
to
categories.
This
construction
is
logical
in
the
context
of
the
general
regulatory
scheme
established
by
the
statute,
and
it
is
the
most
reasonable
one
because
section
112(
c)(
9)(
B)(
ii)
expressly
refers
to
subcategories.
Under
a
literal
reading
of
section
112(
c)(
9)(
B),

no
subcategory
could
ever
be
delisted,
notwithstanding
the
explicit
reference
to
subcategories,
since
the
introductory
language
of
section
112(
c)(
9)(
B)
provides
explicit
authority
to
only
delist
categories.
Such
a
reading
makes
no
sense,
at
the
very
least
because
Congress
plainly
assumed
we
might
also
delist
another
collection
of
sources
besides
either
categories
or
subcategories,
even
in
the
case
of
sources
of
carcinogens.
Both
sections
112(
c)(
9)(
B)(
i)
and
(
ii)
refer
additionally
to
"
groups
of
sources
in
the
case
of
area
sources"
as
being
eligible
for
delisting,
even
though
only
a
"
category"
of
sources
is
specifically
identified
as
eligible
for
delisting
in
the
introductory
language
of
section
112(
c)(
9)(
B).
In
light
of
the
broader
congressional
purpose
behind
the
delisting
authority,
we
interpret
the
absence
of
explicit
references
to
subcategories
in
this
introductory
language
and
in
section
112(
c)(
9)(
B)(
i)
as
representing
nothing
more
than
a
drafting
error.

Regarding
the
comments
about
establishing
PCWP
subcategories
based
on
characteristics
other
than
risk,
the
criteria
for
the
51
low­
risk
subcategory
we
are
proposing
to
delist
are
based
solely
on
risk
and
not
on
technological
differences
in
equipment
or
emissions.
We
performed
an
analysis
to
determine
which
major
source
PCWP
facilities
may
be
low­
risk
facilities.
Whether
facilities
are
low­
risk
or
not
depends
on
the
facility
HAP
emissions;
and
facility
HAP
emissions
are
a
function
of
the
type
and
amount
of
product(
s)
produced,
the
type
of
process
units
(
e.
g.,
direct­
fired
versus
indirect­
fired
dryers)
used
to
produce
the
product,
and
the
emission
control
systems
in
place.
Our
analysis
indicates
that
the
facilities
which
show
low
risk
include
facilities
producing
particleboard,
molded
particleboard,

medium
density
fiberboard,
softwood
plywood,
softwood
veneer,

fiberboard,
engineered
wood
products,
hardboard,
and
oriented
strandboard.

However,
there
are
also
major
sources
that
produce
these
products
that
are
not
low­
risk,
and
therefore,

product
type
cannot
be
used
to
define
the
low­
risk
subcategory.

There
is
no
correlation
between
production
rate
and
low­
risk
facilities
(
e.
g.,
when
facilities
are
sorted
by
production
rate
for
their
product,
the
low­
risk
facilities
are
not
always
at
the
lower
end
of
the
production
rate
range),
so
production
rate
cannot
be
used
as
criteria
for
defining
the
low­
risk
subcategory.

The
low­
risk
facilities
use
a
variety
of
process
equipment
(
e.
g.,

veneer
dryers
at
softwood
plywood
plants
and
tube
dryer
at
MDF
52
plants).
This
same
equipment
is
used
at
PCWP
plants
that
are
not
low­
risk,
and
therefore,
there
is
no
process
unit
type
distinction
that
can
be
used
to
define
the
low­
risk
subcategory.

The
pollutant
that
drives
the
risk
estimate
can
vary
from
facility
to
facility
because
of
the
different
types
of
process
units
at
each
facility.
There
is
no
clear
distinction
among
lowrisk
and
non­
low­
risk
facilities
when
ranked
by
emissions
of
individual
pollutants
because
of
other
factors
that
contribute
to
facility
risk
such
as
presence
of
a
co­
located
PCWP
facility
or
variability
in
the
pollutants
emitted.
Thus,
there
is
no
emissions
distinction
that
can
be
used
to
define
the
low­
risk
subcategory.
There
is
no
technological
basis
for
creating
a
subcategory
of
PCWP
facilities
that
are
low­
risk.
The
commonality
between
all
of
the
low­
risk
PCWP
facilities
is
that
they
are
low­
risk,
and,
therefore,
we
have
established
the
lowrisk
subcategory
based
on
risk.

We
do
not
agree
with
the
commenters'
assertions
that
our
approach
for
the
low­
risk
PCWP
subcategory
undermines
our
ability
to
identify
the
MACT
floor
for
the
larger
PCWP
category,
either
in
today's
final
PCWP
rule
or
in
any
future
consideration
of
technological
development
under
section
112(
d)(
6).
This
is
because,
while
low­
risk
PCWP
facilities
will
literally
be
part
of
a
separate
subcategory,
there
is
nothing
in
the
CAA
that
prevents
us
from
including
them
in
any
consideration
of
what
represents
the
"
best
controlled
similar
source"
in
the
new
source
MACT
floor
53
context,
and
because
it
is
not
unprecedented
for
us
to
look
outside
the
relevant
category
or
subcategory
in
identifying
the
"
average
emission
limitation
achieved"
by
the
best
controlled
existing
sources
if
doing
so
enables
us
to
best
estimate
what
the
relevant
existing
sources
have
achieved.
In
fact,
EPA
has
taken
this
very
approach
in
the
Industrial
Boilers
MACT
rulemaking,
in
order
to
identify
the
MACT
floor
for
mercury
emissions.

Moreover,
the
unique
issues
presented
by
the
low­
risk
PCWP
subcategory
show
that
it
would
be
unreasonable
to
exclude
any
better­
performing
low­
risk
PCWP
sources
from
the
MACT
floor
pool
for
the
larger
PCWP
category.
Traditionally,
EPA
has
based
categories
and
subcategories
partly
on
determinations
of
what
pollution
control
measures
can
be
applied
to
the
relevant
groups
of
sources
in
order
to
effectively
and
achievably
reduce
HAP.
In
other
words,
EPA
has
identified
subcategories
for
purposes
of
identifying
the
MACT
floor
in
a
way
that
accounts
for
the
differences
of
sources
types
in
their
abilities
to
control
HAP
emissions.
But
whether
a
PCWP
source
is
a
low­
risk
source
does
not
necessarily
turn
on
such
a
distinction
 
two
sources
might
have
identical
abilities
to
control
HAP
emissions,
but
the
unique
circumstances
of
one
source
regarding
the
impacts
of
its
HAP
emissions
will
determine
whether
or
not
it
is
a
low­
risk
PCWP
source.
(
In
fact,
it
is
theoretically
possible
that
between
two
sources
the
better
performing
source
will
be
a
high­
risk
source,

and
the
worse­
performing
source
will
be
a
low­
risk
source,
based
54
on
circumstances
that
are
unrelated
to
the
question
of
what
abilities
the
sources
have
to
control
HAP
emissions
through
application
of
MACT,
such
as
the
sources'
locations
vis
a
vis
exposed
human
populations.)
Therefore,
EPA
believes
that
not
only
is
it
appropriate
to
include
any
better­
performing
low
risk
PCWP
sources
in
the
MACT
floor
determinations
for
the
larger
PCWP
category,
but
that
excluding
such
sources
simply
based
on
the
unique
facts
of
the
impacts
of
their
emissions,
with
there
being
no
difference
in
the
abilities
of
high­
risk
and
low­
risk
sources
to
apply
HAP
emission
control
measures,
would
be
an
unlawful
weakening
of
the
MACT
floor
for
the
larger
PCWP
category.
To
that
end,
the
MACT
floors
established
for
PCWP
process
units
today
are
in
no
way
affected
by
our
establishment
of
the
low­
risk
PCWP
subcategory.

Finally,
we
disagree
with
the
argument
by
one
commenter
that
the
low­
risk
PCWP
subcategory
approach
represents
an
impermissible
cost­
based
exemption
from
MACT
or
factor
in
determining
MACT.
Certainly
it
is
true
that
costs
may
not
be
considered
in
setting
the
MACT
floor.
However,
there
is
nothing
in
the
CAA
that
prevents
us
from
noting
the
cost
impacts,

beneficial
or
adverse,
of
our
actions
in
setting
MACT
floors,

assessing
possible
beyond­
the­
floor
measures,
or
conducting
riskbased
actions
under
section
112.
In
fact,
we
routinely
evaluate
the
costs
of
our
regulatory
actions,
even
when
cost
factors
may
not
be
used
to
influence
the
regulatory
decision
itself,
in
order
55
to
comply
with
applicable
Executive
Order
and
statutory
administrative
review
requirements.
Simply
because
there
is
a
cost
benefit
to
some
members
of
the
PCWP
category
in
our
establishing
a
low­
risk
PCWP
subcategory
does
not
make
that
action
impermissible,
provided
that
our
subcategorization
and
delisting
are
otherwise
properly
based
on
the
appropriate
riskbased
criteria
under
section
112(
c)(
9).
Section
112
by
its
own
terms
does
not
forbid
the
goal
of
achieving
environmental
protection
in
a
less
costly
manner.
Similarly,
it
is
appropriate
for
EPA
to
note
the
beneficial
air
pollution­
related
impacts
of
not
requiring
low­
risk
PCWP
sources
to,
for
example,
install
criteria
pollutant
emission­
producing
RTOs.
While
it
is
true
that
such
air
quality­
related
impacts
could
not
constitute
"

nonair
quality
health
and
environmental
impacts"
that
EPA
must
consider
when
setting
MACT
under
CAA
section
112(
d)(
2),
nothing
in
the
CAA
prevents
EPA
from
taking
account
of
such
impacts
in
developing
its
policy
regarding
whether
it
is
appropriate
to
delist
a
subcategory
under
section
112(
c)(
9)
when
that
subcategory
otherwise
meets
the
statutory
criteria
for
de­
listing.

Therefore,
EPA
does
not
agree
with
commenters
who
claim
that
its
approach
to
delisting
the
low
risk
PCWP
subcategory
conflicts
with
how
it
has
argued
issues
regarding
either
de
minimis
authority,
cost­
based
exemptions
from
MACT,
or
the
treatment
of
non­
air
quality
impacts
and
the
consideration
of
risk
in
setting
the
actual
MACT
standard
before
the
U.
S.
Court
of
Appeals
for
the
56
D.
C.
Circuit.
Nor
does
our
approach
contravene
any
of
that
Court's
rulings
on
these
issues.

3.
Criteria
for
demonstrating
low­
risk
a.
Dose­
response
values
Comment:
Two
commenters
suggested
that
EPA
incorporate
into
the
PCWP
rule
the
findings
of
the
nationwide
wood
products
risk
assessment,
which
demonstrates
that
the
vast
majority
of
wood
products
sources
cause
no
meaningful
risk
to
human
health
or
the
environment
at
current
emission
levels.
The
commenters
stated
that
the
risk
assessment
used
existing
air
dispersion
modeling
studies
of
34
wood
products
facilities
throughout
the
U.
S.
to
estimate
the
maximum
annual
off­
site
HAP
concentrations
at
wood
products
facilities
nationwide.
According
to
the
commenters,
the
risk
assessment
indicates
that
large
subgroups
of
facilities
that
are
affected
sources
under
the
PCWP
rule
(
i.
e.,
fiberboard,

medium
density
fiberboard,
and
plywood
facilities)
generally
are
expected
to
pose
insignificant
risks
to
human
health,
based
on
a
comparison
of
predicted
off­
site
concentrations
with
applicable
health
benchmarks.
One
of
the
commenters
stated
that
many
of
the
facilities
with
low
off­
site
concentrations
will
likely
be
smaller
plants
that
would
not
be
able
to
justify
installation
of
(
additional)
emission
controls
and
may
face
closure
without
a
risk­
based
compliance
option.
The
other
commenter
stated
that
a
comparison
of
off­
site
concentrations
of
formaldehyde
and
57
acetaldehyde
with
benchmarks
reflecting
the
latest
toxicological
evidence
indicates
that
exposures
to
those
HAP
are
well
below
levels
of
concern.
Acrolein
was
the
only
HAP
with
potential
exposures
at
some
facilities
(
i.
e.,
subset
of
fiberboard,
medium
density
fiberboard
and
plywood
facilities)
that
exceeded
the
health
benchmark.
However,
the
commenter
stated
that
the
acrolein
findings
may
not
represent
an
actual
risk
to
human
health
because
exceedences
of
the
benchmark
may
be
attributable
to
EPA
averaging
a
large
number
of
non­
detects
at
one­
half
the
detection
limit,
thereby
artificially
increasing
predicted
acrolein
emissions.
Based
on
these
overall
findings,
the
commenter
concluded
that
the
wood
products
risk
assessment
indicates
that
incinerator
control
is
not
warranted
on
the
basis
of
human
health
concerns
for
a
large
number
of
facilities.

Response:
We
acknowledge
receipt
of
the
industry­
sponsored
nationwide
wood
products
MACT
risk
assessment
submitted
by
the
commenter.
However,
we
conducted
our
own
risk
analysis
to
evaluate
the
merits
of
including
a
low­
risk
subcategory
in
today's
final
PCWP
rule.
The
methodology
used
in
our
risk
analysis
differed
widely
from
the
methodology
used
in
industry's
risk
assessment.
For
example,
industry's
risk
assessment
was
based
on
previously
conducted
air
dispersion
modeling
studies
for
34
PCWP
facilities,
while
our
analysis
used
emission
estimates
developed
for
each
PCWP
facility
believed
to
be
a
major
source
of
HAP.
We
used
different
(
generally
more
protective)
human
health
58
benchmarks
in
our
risk
assessment
than
were
used
in
industry's
risk
assessment.
We
also
considered
all
HAP
(
including
metal
HAP)
in
our
risk
analysis,
whereas
industry's
risk
assessment
considered
only
methanol,
formaldehyde,
acetaldehyde,
acrolein,

phenol,
and
propionaldehyde.

Based
on
our
risk
analysis,
we
conclude
that
HAP
emissions
from
some
PCWP
facilities
pose
little
risk
to
human
health
and
the
environment.
Therefore,
we
have
included
a
subcategory
of
low­
risk
PCWP
facilities
in
today's
final
PCWP
rule.
Appendix
B
to
Subpart
DDDD
includes
procedures
that
facilities
may
use
to
demonstrate
that
they
are
part
of
the
low­
risk
subcategory,
and,

therefore,
are
not
subject
to
the
compliance
options
included
in
today's
final
PCWP
rule.
To
demonstrate
eligibility
for
the
lowrisk
subcategory,
facilities
must
first
conduct
emissions
testing
for
up
to
13
pollutants
(
5
organic
HAP
from
all
process
units,
7
metal
HAP
from
direct­
fired
process
units,
and
MDI
from
presses
processing
product
containing
MDI
resin).
The
rationale
for
selection
of
these
13
pollutants
is
described
elsewhere
in
this
section.
Facilities
must
use
the
results
from
emissions
testing
to
determine
if
they
are
part
of
the
low­
risk
subcategory
using
either
a
look­
up
table
analysis
(
based
on
the
look­
up
tables
included
in
Appendix
B
to
Subpart
DDDD)
or
site­
specific
risk
assessment
methodology
(
described
in
Appendix
B
to
Subpart
DDDD
and
the
"
Air
Toxics
Risk
Assessment
Reference
Library")
and
risk
benchmarks
(
described
in
Appendix
B
to
Subpart
DDDD).
59
Regarding
acrolein,
the
commenter
is
correct
in
that,
when
developing
AP­
42
emission
factors,
we
used
a
value
of
one­
half
the
detection
limit
for
all
non­
detect
sample
runs
if
acrolein
was
detected
in
any
sample
runs
from
the
applicable
source
category.
Acrolein
has
been
detected
in
process
unit
emissions
from
all
sectors
of
the
PCWP
industry,
except
for
hardwood
plywood
manufacturing.
When
using
emission
factors
to
estimate
emissions
from
PCWP
facilities,
we
did
not
estimate
emissions
of
a
pollutant
when
all
of
the
emissions
test
runs
were
non­
detect.

However,
we
did
use
emission
factors
that
included
a
mixture
of
detectable
values
and
values
based
on
one­
half
of
the
method
detection
limit
(
MDL)
when
acrolein
was
detected
at
least
once
for
a
particular
type
of
process
unit.
We
maintain
that
this
approach
to
handling
non­
detects
is
appropriate
for
the
purposes
that
we
used
the
emissions
data.
Facilities
will
conduct
emissions
tests
instead
of
using
emission
factors
to
demonstrate
eligibility
for
the
low­
risk
subcategory.
To
prevent
facilities
from
including
HAP
that
are
not
detected
in
their
low­
risk
demonstrations,
Appendix
B
to
Subpart
DDDD
states
that
facilities
may
use
zero
for
non­
detects
when
all
of
the
emission
test
runs
are
below
the
MDL,
provided
that
certain
criteria
to
ensure
that
emissions
testing
and
analysis
procedures
are
adequate
to
detect
low
concentrations
of
HAP.

Comment:
One
commenter
stated
that
section
112(
d)(
4)
is
60
particularly
ill­
suited
to
the
PCWP
and
industrial
boiler
source
categories.
The
commenter
stated
that,
even
if
EPA
had
authority
to
create
individualized
MACT
exemptions
based
on
health
thresholds,
it
could
not
do
so
if
there
is
insufficient
evidence
on
the
pollutants
emitted
to
establish
a
NOEL.
According
to
the
commenter,
section
112(
d)(
4)
does
not
apply
for
chemicals
that
do
not
have
a
well­
defined
threshold
based
on
reliable
science.
The
commenter
stated
that
available
evidence
does
not
establish
a
noeffect
threshold
for
acetaldehyde,
acrolein,
benzene,
carbon
tetrachloride,
chloroform,
formaldehyde,
manganese,
methylene
chloride,
and
phenol.
As
rationale,
the
commenter
presented
a
summary
of
the
available
health
effects
data
for
each
of
these
pollutants.

Response:
As
stated
elsewhere
in
this
preamble,
we
are
not
pursuing
establishment
of
a
threshold
emission
rate
for
the
PCWP
source
category
under
section
112(
d)(
4)
because
PCWP
facilities
emit
non­
threshold
pollutants.
Therefore,
this
comment
is
irrelevant
in
the
context
of
the
PCWP
rule.
Comments
pertaining
to
the
Industrial/
Commercial/
Institutional
Boilers
and
Process
Heaters
NESHAP
are
addressed
in
the
comment­
response
document
for
that
rule.
(
See
Docket
ID
No.
OAR­
2002­
0058.)

Comment:
Two
commenters
expressed
concern
about
the
health
benchmark
data
sources
that
EPA
used.
The
first
commenter
argued
that
the
proposal
inappropriately
used
draft
guidelines
and
toxicity
profiles
that
had
not
been
subject
to
public
review
61
and/
or
were
not
publicly
available.
The
commenter
was
particularly
concerned
with
the
use
of
non­
linear
carcinogenic
risk
values
and
toxicity
profiles
(
for
HAP)
that
have
not
been
finalized
and
are
not
available
for
review
by
the
public.

The
second
commenter
argued
that
EPA
should
not
rely
solely
on
the
health
benchmarks
in
its
Integrated
Risk
Information
System
(
IRIS)
database.
The
commenter
stated
that
IRIS,
while
useful
for
obtaining
information
about
the
health
effects
of
chemicals,
is
far
from
definitive,
as
EPA
resource
constraints
have
resulted
in
many
chemical
summaries
that
are
significantly
outdated
and
do
not
reflect
the
most
recent
scientific
developments.
Moreover,
the
commenter
stated
that
the
IRIS
database
is
a
non­
statutory,
in­
house
EPA
activity,
and
IRIS
entries
are
not
subject
to
formal
notice
and
comment.
The
commenter
noted
that
EPA
management
has
repeatedly
emphasized
in
directives
that
other
information
must
be
considered,
in
addition
to
the
IRIS
database,
when
evaluating
the
health
effects
of
chemicals
in
a
regulatory
context.
The
commenter
concluded
that
EPA
must
use
a
scientifically
appropriate
health
benchmark
based
on
a
consideration
of
all
relevant
information
to
ensure
that
the
health
benchmark
is
up­
to­
date
and
scientifically
credible,
even
if
that
means
departing
from
the
value
in
IRIS.

A
third
commenter
agreed
with
EPA's
choice
to
derive
their
data
from
IRIS,
California
EPA
(
CalEPA),
and
Agency
for
Toxic
Substances
and
Disease
Registry
(
ATSDR)
for
its
documentation
for
62
1U.
S.
Environmental
Protection
Agency.
1999.
Residual
Risk
Report
to
Congress.
Office
of
Air
Quality
Planning
and
Standards,
Research
Triangle
Park,
NC
27711,
March
1999,
EPA­
453/
R­
99­
001;
available
at
http://
www.
epa.
gov/
ttn/
oarpg/
t3/
meta/
m8690.
html.
(
EPA
1999)
establishing
risk
based
threshold
and
non­
threshold
values.
The
commenter
added
that
almost
all
HAP
are
being
reviewed
and
reevaluated
on
a
regular
basis,
and
it
would
be
inappropriate
to
single
out
formaldehyde
and
acetaldehyde
at
this
time.
The
commenter
stated
that
EPA
can
only
rely
on
what
is
currently
published
and
has
underdone
either
peer
review
or
EPA
review.

According
to
the
commenter,
the
issue
of
changing
health­
based
guideline
values
will
always
be
a
concern
once
health­
based
regulations
are
promulgated.

Response:
We
agree
with
the
first
two
commenters
that
we
should
use
the
best
available
sources
of
health
effects
information
for
risk
or
hazard
determinations.
As
we
have
stated
previously,
we
will
not
be
relying
exclusively
on
IRIS
values,

but
will
be
considering
all
credible
and
readily
available
assessments.
1
For
air
toxics
risk
assessments,
we
identify
pertinent
toxicity
or
dose­
response
values
using
a
default
hierarchy
of
sources,
with
IRIS
being
the
preferred
source,
to
assist
us
in
identifying
the
most
scientifically
appropriate
benchmarks
for
our
analyses
and
decisions.
The
IRIS
process
contains
internal
and
external
peer
review
steps
and
represent
EPA
consensus
values.
When
adequate
toxicity
information
is
not
63
available
in
IRIS,
we
consult
other
sources
in
a
default
hierarchy
that
recognizes
the
desirability
of
these
qualities
in
ensuring
that
we
have
consistent
and
scientifically
sound
assessments.
Furthermore,
where
the
IRIS
assessment
substantially
lags
the
current
scientific
knowledge,
we
have
committed
to
consider
alternative
credible
and
readily
available
assessments.
For
our
use,
these
alternatives
need
to
be
grounded
in
publicly
available,
peer­
reviewed
information.
Formaldehyde
is
an
example
of
this
situation.
We
are
not
using
information
that
does
not
meet
these
requirements.
We
also
agree
with
the
third
commenter
that
the
issue
of
changing
health­
based
guideline
values
is
a
general
challenge
in
setting
health­
based
regulations.
However,
we
are
committed
to
setting
such
regulations
that
reflect
current
scientific
understanding,
to
the
extent
feasible.
Facilities
conducting
low­
risk
demonstrations
should
refer
to
Appendix
B
to
Subpart
DDDD
(
and/
or
the
"
Air
Toxics
Risk
Assessment
Reference
Library")
for
guidance
on
choosing
appropriate
dose­
response
values.

Comment:
With
the
support
of
several
others,
one
commenter
pointed
out
that
the
science
with
respect
to
formaldehyde
and
acetaldehyde
has
changed
since
EPA's
initial
IRIS
entries
for
those
pollutants
were
completed.
Consequently,
the
commenter
believed
it
would
be
inappropriate
for
EPA
to
rely
on
the
unit
risk
factors
for
those
pollutants
in
the
IRIS
database
in
establishing
a
property
line
concentration
threshold
in
the
PCWP
64
rule.
The
commenter
supported
EPA's
efforts
in
revising
its
formaldehyde
and
acetaldehyde
IRIS
assessment
and
noted
that
both
revisions
are
expected
to
be
finalized
before
the
PCWP
rule
is
published
in
2004.
Regarding
formaldehyde,
the
commenter
noted
that
EPA
plans
on
using
the
model
from
the
Chemical
Industry
Institute
of
Technology
(
CIIT)
to
revise
its
formaldehyde
IRIS
assessment
and
encouraged
this
action.
The
commenter
pointed
out
that
the
CIIT
model
has
been
recognized
by
several
authoritative
bodies
(
e.
g.,
Health
Canada/
Environment
Canada,
Organization
for
Economic
Coordination
and
Development,
and
World
Health
Organization)
as
providing
the
most
scientifically
defensible
analysis
of
formaldehyde.
(
Another
commenter
added
that
the
IRIS
risk
criteria
for
formaldehyde
clearly
cause
formaldehyde
risk
estimates
to
be
overstated
but
argued
that,
even
using
the
very
conservative
IRIS
numbers,
risks
are
still
low.
A
third
commenter
urged
EPA
not
to
use
the
formaldehyde
values
in
ATSDR,

stating
that
they
are
fundamentally
flawed,
as
detailed
in
their
comment.)
Regarding
acetaldehyde,
the
commenter
recommended
that
EPA
use
a
health
benchmark
between
27
and
390
micrograms
per
cubic
meter
(
µ
g/
m3)
and
included
their
rationale
in
an
attachment
to
their
comment.
If
EPA
is
unable
to
complete
its
reassessments
before
the
PCWP
rule
is
finalized,
the
commenter
encouraged
EPA
not
to
revert
to
the
original
IRIS
unit
risk
factors
for
formaldehyde
and
acetaldehyde.
Instead,
the
commenter
recommended
that
EPA
use
the
CIIT
model
(
or
alternatively
defer
65
to
Health
Canada/
Environment
Canada)
for
formaldehyde
and,
at
a
minimum,
use
the
IRIS
reference
concentration
(
RfC)
of
9
µ
g/
m3
for
acetaldehyde.

Response:
We
are
re­
evaluating
the
dose­
response
value
for
formaldehyde.
Currently,
the
CIIT
information
and
other
recent
information,
including
recently
published
epidemiological
studies,
are
being
reviewed
and
considered
in
the
reassessment
of
our
formaldehyde
unit
risk
estimate
(
URE).
We
plan
to
bring
this
reassessment
to
the
Science
Advisory
Board
in
the
summer
of
2004.

The
feasibility
of
delisting
a
subgroup
of
facilities
based
on
risk
is
not
compromised
by
the
existing
formaldehyde
doseresponse
value
because
some
facilities
would
qualify
for
delisting
based
on
this
current
value.
We
are
moving
forward
with
the
final
PCWP
rule
at
this
time
because
there
is
a
courtordered
deadline.
We
disagree
with
the
statement
by
one
of
the
commenters
that
"
risks
are
still
low"
using
the
current
IRIS
number
for
formaldehyde.
Our
analysis
has
demonstrated
that
not
all
PCWP
facilities
can
be
considered
low­
risk
when
either
the
current
IRIS
or
CIIT
URE
for
formaldehyde
is
employed.

While
we
recognize
the
similarities
between
acetaldehyde
and
formaldehyde
with
regard
to
suggested
modes
of
action,
the
reassessment
of
acetaldehyde
is
lagging
behind
that
of
formaldehyde.
The
formaldehyde
reassessment
is
further
along
because
of
the
preponderance
of
data
specific
to
formaldehyde
and
66
the
potentially
greater
impact
of
a
change
in
potency
to
our
regulatory
decisions.
Unlike
for
formaldehyde,
an
alternative,

peer­
reviewed,
publicly
available
assessment
does
not
currently
exist
for
acetaldehyde,
leaving
us
with
the
current
IRIS
assessment.
We
cannot
wait
for
our
acetaldehyde
reassessment
to
be
completed
due
to
the
court­
ordered
deadline
for
the
final
PCWP
rule.
Therefore,
we
are
relying
on
the
IRIS
values
for
acetaldehyde
in
both
cancer
and
non­
cancer
risk
assessments
for
this
rule.

Facilities
conducting
low­
risk
demonstrations
should
refer
to
Appendix
B
to
Subpart
DDDD
(
and/
or
the
"
Air
Toxics
Risk
Assessment
Reference
Library")
for
guidance
on
choosing
appropriate
dose­
response
values.

Comment:
One
commenter
stated
that
EPA
should
consider
formaldehyde
and
acetaldehyde
as
carcinogens
unless
a
reassessment
classifies
them
as
threshold
pollutants.
A
second
commenter
argued
that
formaldehyde
and
acetaldehyde
are
properly
treated
as
threshold
pollutants.
This
commenter
contended
that
the
legislative
history
of
the
CAA
makes
clear
that
Congress
considered
"
threshold
pollutants"
to
be
those
for
which
a
"
no
observed
effect
level"
can
be
established.
(
See,
e.
g.,
S.
Rep.

No.
228,
101st
Cong.,
1st
Sess.
175­
176
(
1990)).
By
contrast,
a
non­
threshold
pollutant
is
one
for
which
a
no
observed
effect
level
cannot
be
identified,
i.
e.,
a
pollutant
for
which
adverse
effects
may
be
seen
at
any
dose
level
above
zero.
The
commenter
67
noted
that
EPA
has
historically
assumed
that
all
carcinogens
are
non­
threshold
pollutants
that
may
trigger
a
carcinogenic
effect
at
any
exposure
level,
no
matter
how
small.
However,
as
mechanistic
data
on
the
mode
of
action
of
carcinogenesis
advances,
that
conservative
assumption
may
prove
not
to
be
accurate
for
certain
pollutants.
The
commenter
stated
that
the
available
science
strongly
suggest
that
these
pollutants
act
as
threshold
carcinogens.
The
commenter
contended
that
there
is
a
"
no
observed
effect
level"
for
formaldehyde
below
which
the
carcinogenic
risk
either
does
not
exist
or
cannot
be
measured,
as
documented
in
an
attachment
to
their
comment.
The
commenter
stated
that
acetaldehyde
should
be
viewed
similarly
because
acetaldehyde
is
similar
to
formaldehyde
structurally
and
toxicologically,
and
is
expected
to
behave
similarly
mechanistically.
Because
acetaldehyde
is
a
less
potent
carcinogen
than
formaldehyde
(
by
an
order
of
magnitude),

non­
cancer
health
effects
(
which
clearly
are
threshold
health
effects)
are
the
likely
risk
driver
for
that
pollutant.
Finally,

the
commenter
noted
that
EPA's
recently
issued
Draft
Final
Guidelines
for
Carcinogenic
Risk
Assessment
provide
that,
for
non­
linear
carcinogens,
EPA
will
calculate
an
reference
dose
(
RfD)
or
RfC,
which
are
safe
lifetime
doses
(
i.
e.,
doses
below
which
adverse
effects
will
not
occur).
The
commenter
stated
that
this
is
exactly
what
a
threshold
pollutant
is.
Thus,
EPA's
revised
guidelines
support
the
conclusion
that
formaldehyde
and
68
acetaldehyde
should
be
treated
as
threshold
pollutants.

Response:
We
agree
that
we
should
consider
formaldehyde
and
acetaldehyde
as
carcinogens
unless
a
reassessment
classifies
them
as
threshold
pollutants.
Currently,
formaldehyde
and
acetaldehyde
are
considered
probable
human
carcinogens.
Both
are
under
review,
and
their
dose­
response
values
for
carcinogenicity
are
likely
to
change.
For
this
rule,
we
are
using
an
alternative
dose­
response
value
for
formaldehyde
based
on
a
peer­
reviewed,

publicly
available
assessment.
However,
we
do
not
have
comparable
quantitative
information
for
acetaldehyde.
Therefore,

we
will
use
the
current
IRIS
value.
Facilities
conducting
lowrisk
demonstrations
should
refer
to
Appendix
B
to
Subpart
DDDD
(
and/
or
the
"
Air
Toxics
Risk
Assessment
Reference
Library")
for
guidance
on
choosing
appropriate
dose­
response
values.

Comment:
One
commenter
expressed
concern
about
some
of
the
health
benchmarks
that
EPA
plans
to
publish.
The
commenter
reviewed
various
health
studies
for
each
pollutant
and
recommended
several
RfC
values.
The
commenter
noted
that,

because
IRIS
does
not
have
an
RfC
for
methanol,
EPA
has
indicated
it
plans
to
determine
a
de
minimis
threshold
for
methanol
using
a
value
of
4.0
mg/
m3
as
an
RfC.
The
commenter
noted
that
this
value
is
the
Noncancer
Chronic
REL
derived
by
CalEPA.
The
commenter
stated
that
CalEPA's
derivation
of
that
REL
contains
some
errors
and
inaccurate
assumptions.
According
to
the
commenter,
a
more
accurate
estimate
of
a
human
safe
level
for
69
chronic
exposure
to
methanol
by
inhalation,
derived
from
the
same
mouse
study
data,
is
171
mg/
m3,
which
is
discussed
further
in
their
comments.
The
commenter
stated
that
their
discussion
presents
new
analyses
not
previously
reviewed
by
EPA
and
a
ground­
breaking
new
approach
to
a
hazard
assessment
for
methanol.

The
commenter
noted
that
EPA
is
currently
revising
its
assessment
for
acrolein
and
has
provided
for
public
information
a
draft
toxicological
review
and
draft
IRIS
summary
for
acrolein.

The
draft
IRIS
document
states
that
the
proposed
new
RfC
of
0.03
µ
g/
m3
replaces
the
previous
RfC
of
0.02
µ
g/
m3,
and
that
this
new
RfC
is
based
on
a
more
recent
interpretation
of
the
database.

The
commenter
noted
the
basis
for
the
revised
acrolein
RfC
(
Feron
et
al,
1978)
and
argued
that
EPA's
interpretation
of
this
study
is
overly
conservative.
The
commenter
stated
that
EPA
has
used
the
maximum
uncertainty
factors
that
could
reasonably
be
justifiable
and
thereby
developed
an
RfC
that
almost
certainly
goes
beyond
what
is
needed
to
protect
human
health.
The
commenter
suggested
that
EPA
should
instead
use
the
more
realistic
reference
exposure
level
developed
by
CalEPA,
which
is
more
conservative
than
the
Health
Canada
Tolerable
Concentration.

The
commenter
noted
that
EPA
has
not
published
a
health
benchmark
for
phenol.
The
commenter
agreed
with
EPA's
proposal
to
use
the
CalEPA
REL
of
200
µ
g/
m3
for
phenol
in
implementing
the
risk­
based
approach
for
wood
products
facilities.
According
to
the
commenter,
the
REL
is
intended
to
serve
the
same
goal
as
an
70
RfC.

The
commenter
supported
using
a
health
benchmark
of
110
µ
g/
m3
for
propionaldehyde
and
believed
that
this
value
would
protect
human
health
with
an
ample
margin
of
safety.
The
commenter
described
how
the
110
µ
g/
m3
value
was
derived
based
on
the
TLV
for
propionaldehyde
identified
by
the
American
Conference
of
Governmental
Industrial
Hygienists
(
ACGIH).
The
commenter
explained
that
this
benchmark
is
consistent
with
values
developed
by
other
organizations.

Response:
We
are
currently
developing
an
IRIS
assessment
for
methanol,
and
any
new
information
that
exists
that
has
undergone
peer
review
will
be
considered
in
this
re­
evaluation.

We
publish
yearly
in
the
Federal
Register
a
list
of
all
chemicals
for
which
we
are
planning
IRIS
assessment
activity.
This
notice
further
requests
submission
of
pertinent
data
for
these
chemicals.
In
lieu
of
the
pending
IRIS
assessment,
we
will
continue
to
draw
on
other
sources
identified
by
our
established
default
hierarchy
of
data
sources,
which
have
as
part
of
their
development
processes
external
or
peer
review,
in
addition
to
extensive
internal
reviews.

A
reassessment
of
acrolein
was
completed
in
June
of
2003.

The
RfC
resulting
from
that
reassessment
(
i.
e.,
an
RfC
of
0.02

g/
m3,
with
an
uncertainty
factor
of
1,000)
is
what
is
currently
on
IRIS.
As
with
all
announced
IRIS
reassessments,
time
was
provided
for
new
data
or
relevant
information
to
be
submitted.
71
In
addition,
each
assessment
undergoes
extensive
internal
review
as
well
as
external
peer
review
to
ensure
that
the
data
used
are
scientifically
sound.
We
believe
we
have
developed
the
most
scientifically
sound
RfC
that
will
ensure
that
risk
assessments
using
this
number
are
health­
protective.
Facilities
conducting
low­
risk
demonstrations
should
refer
to
Appendix
B
to
Subpart
DDDD
(
and/
or
the
"
Air
Toxics
Risk
Assessment
Reference
Library")

for
guidance
on
choosing
appropriate
dose­
response
values.

We
do
not
currently
have
plans
to
develop
an
IRIS
assessment
for
phenol.
We
will
continue
to
rely
on
our
hierarchy
of
other
sources
when
IRIS
values
are
not
available.

We
do
not
have
an
IRIS
file
for
proprionaldehyde,
and
an
assessment
is
not
available
from
the
alternative
sources
in
our
default
hierarchy.
The
hierarchy
sources
do
not
include
ACGIH,

as
that
organization
develops
reference
values
for
use
in
occupational
exposure
settings,
as
opposed
to
the
ambient
air
exposures
that
are
the
focus
of
this
action.
Development
of
an
IRIS
assessment
for
propionaldehyde
is
currently
underway.
Once
available,
it
will
be
used
in
future
risk
analyses.
In
the
meantime,
this
HAP
was
not
included
in
the
assessment
conducted
for
PCWP
facilities.

Comment:
One
commenter
stated
that
comparison
of
modeled
exposures
to
the
RfC
or
similarly­
derived
health
benchmark
is
highly
protective
and
meets
the
CAA's
"
ample
margin
of
safety"

requirement.
Although
the
CAA
does
not
explicitly
define
"
ample
72
margin
of
safety,"
in
the
Vinyl
Chloride
case,
the
D.
C.
Circuit
Court
of
Appeals
articulated
the
purpose
of
the
ample
margin
of
safety
determination
as
obtaining
a
"
reasonable
degree
of
protection"
in
light
of
scientific
uncertainties
and
information
gaps.
(
Natural
Res.
Def.
Council
v.
EPA,
824
F.
2D
1146,
1152­
53
(
D.
C.
Cir.
1987)).
The
commenter
stated
that,
in
regulatory
practice,
the
ample
margin
of
safety
analysis
consists
of
a
consideration
of
the
NOEL
for
a
pollutant
and
the
subsequent
application
of
factors
to
account
for
scientific
uncertainty
surrounding
that
safe
level
of
exposure.
According
to
the
commenter,
this
is
the
approach
called
for
by
the
Senate
Report
accompanying
the
1990
CAA
Amendments
(
S.
Rep.
No.
228,
101st
Cong.
Sess.
171
(
1990)),
and
this
is
exactly
what
is
done
in
deriving
an
RfC
or
similar
inhalation
health
benchmark.
The
commenter
stated
that
EPA's
derivation
of
the
RfC
contains
multiple
layers
of
conservatism
to
account
for
scientific
uncertainty.
The
commenter
believed
that
RfC
values
and
similar
inhalation
health
benchmarks
already
incorporate
sufficient
uncertainty
factors
to
fulfill
or
exceed
the
ample
margin
of
safety
mandate
of
CAA
sections
112(
d)(
4)
and
112(
c)(
9).

Response:
Today's
final
PCWP
rule
will
utilize
CAA
section
112(
c)(
9)
rather
than
CAA
section
112(
d)(
4).
We
agree
that
the
CAA
does
not
define
"
ample
margin
of
safety"
explicitly.
The
CAA
does,
however,
in
section
112(
f)
explicitly
recognize
our
Federal
Register
notice
of
September
14,
1989,
which
described
our
73
interpretation
of
"
ample
margin
of
safety"
in
the
case
of
linear
carcinogens,
and
our
approach
to
implementing
that
interpretation.
While
the
first
step
identifies
the
presumptive
limit
on
maximum
individual
risk,
the
second
step
of
that
2­
step
approach
describes
the
setting
of
the
risk­
based
standard
at
a
level
that
provides
"
an
ample
margin
of
safety,"
in
consideration
of
a
number
of
factors.
As
we
noted
in
the
1989
notice,
the
objective
in
protecting
public
health
with
an
ample
margin
of
safety
under
section
112
is
to
ensure
an
individual
lifetime
risk
level
no
higher
than
one
in
a
million
to
the
greatest
number
of
persons
possible,
and
to
limit
to
no
higher
than
one
in
ten
thousand
the
estimated
risk
for
a
person
living
near
a
plant
if
they
were
exposed
for
70
years.

In
assessing
risk
or
hazard
of
nonlinear
effects,
we
use
the
RfC
or
comparable
value.
This
value
represents
an
estimate
(
with
uncertainty
spanning
perhaps
an
order
of
magnitude)
of
a
continuous
inhalation
exposure
to
the
human
population
(
including
sensitive
subgroups)
that
is
likely
to
be
without
an
appreciable
risk
of
deleterious
non­
cancer
effects
during
a
lifetime.
The
RfC
values
and
comparable
values
are
derived
from
assessments
of
pertinent
toxicological
information
to
identify
the
lowest
point
of
departure
(
in
human
equivalent
terms)
from
the
experimental
data
that
is
also
representative
of
the
threshold
region
(
the
region
where
toxicity
is
apparent
from
the
available
data)
for
the
array
of
toxicity
data
for
that
chemical.
The
objective
is
74
2U.
S.
Environmental
Protection
Agency.
1994.
Methods
for
Derivation
of
Inhalation
Reference
Concentrations
and
Application
of
Inhalation
Dosimetry.
Office
of
Research
and
Development.
EPA/
600/
8­
90/
066F.
(
EPA
1994)
to
select
a
prominent
toxic
effect
that
is
pertinent
to
the
chemical's
key
mechanism
or
mode
of
action.
This
approach
is
based,
in
part,
on
the
assumption
that
if
the
critical
toxic
effect
is
prevented,
then
all
toxic
effects
are
prevented.
The
RfC
is
derived
from
the
point
of
departure
(
POD)
(
in
terms
of
human
equivalent
exposure)
for
the
critical
effect
by
consistent
application
of
uncertainty
factors,
which
are
to
account
for
recognized
uncertainties
in
the
extrapolations
from
the
experimental
data
conditions
to
an
estimate
appropriate
to
the
assumed
human
scenario.
2
In
considering
the
extrapolation
of
the
ample
margin
of
safety
objective
described
for
linear
cancer
risk
to
the
management
of
risk
for
nonlinear
effects
under
section
112(
c)(
9)

(
i.
e.,
in
decisions
to
delist
a
subcategory
from
any
further
regulatory
action),
we
consider
exposures
relative
to
the
RfC
or
comparable
values
for
all
of
the
emitted
HAP,
with
specific
attention
to
those
affecting
a
similar
physiological
target
organ
or
system,
and
the
contribution
of
co­
located
sources
of
the
same
HAP.

Comment:
One
commenter
stated
that
the
uncertainty
factors
used
in
deriving
the
wood
products
HAP
health
benchmarks
are
75
particularly
large.
The
unit
risk
factors
for
acetaldehyde
and
formaldehyde
were
calculated
using
the
linear
multi­
stage
model,

which
assumes
a
linear
relationship
between
cancer
incidence
and
exposure
to
the
pollutant
at
low
doses.
According
to
the
commenter,
the
available
data
on
acetaldehyde
and
formaldehyde
strongly
suggest
that
this
assumption
is
incorrect
and
overly
conservative.

The
commenter
pointed
out
that
EPA's
health
assessment
of
acrolein
is
two
to
three
times
more
conservative
than
CalEPA's,

even
though
both
are
intended
to
protect
sensitive
individuals
from
any
adverse
effects
following
a
lifetime
of
exposure.
The
commenter
stated
that
EPA
has
developed
an
extremely
conservative
RfC
for
acrolein.
The
commenter
argued
that
adopting
a
HI
of
0.2
would
add
another
five­
fold
safety
factor
to
this
already
extremely
conservative
RfC.
The
commenter
noted
that
acrolein
is
the
HAP
of
greatest
importance
in
determining
risk
from
PCWP
facilities.

Response:
The
dose­
response
values
used
to
determine
the
criteria
for
defining
the
low­
risk
subcategory
are
drawn
from
IRIS,
as
well
as
from
certain
alternative
sources.
The
IRIS
process
contains
internal
and
external
peer
review
steps
and
represents
EPA
consensus
values.
When
adequate
toxicity
information
is
not
available
in
IRIS,
we
consult
other
sources
in
a
default
hierarchy
that
recognizes
the
desirability
of
these
qualities
in
ensuring
that
we
have
consistent
and
scientifically
76
3Ibid.
sound
assessments.
In
the
case
of
acrolein,
specifically
mentioned
by
the
commenter,
consultation
of
other
sources
was
not
necessary
because
the
acrolein
assessment
was
completed
within
the
past
9
months
and
represents
current
scientific
knowledge.

In
those
cases
(
e.
g.,
formaldehyde),
where
the
IRIS
assessment
substantially
lags
the
current
scientific
knowledge,
we
consider
alternative
credible
and
readily
available
assessments.
As
pointed
out
elsewhere
in
this
section,
the
RfC
values
or
comparable
values
have
been
derived
with
the
incorporation
of
uncertainty
factors.
The
uncertainty
factors
are
to
account
for
recognized
uncertainties
in
the
extrapolations
from
the
experimental
data
conditions
pertaining
to
the
chemical's
particular
toxicological
data
set
to
an
estimate
appropriate
to
the
assumed
human
scenario.
3
The
size
variation
of
the
uncertainty
factors
across
RfC
values
reflects
the
size
variation
of
the
uncertainties
associated
with
that
extrapolation.

Comment:
One
commenter
stated
that
the
combination
of
conservative
air
dispersion
modeling
techniques
and
a
conservative
human
health
benchmark
ensure
that,
where
a
source
meets
the
requirements
for
a
risk­
based
compliance
option,
human
health
will
be
protected
with
an
ample
margin
of
safety.
The
commenter
pointed
out
that,
for
most
individuals
in
the
general
population,
actual
exposures
likely
are
one
or
more
orders
of
77
magnitude
below
the
maximum
exposures
predicted
by
the
tiered
modeling
approach.
The
commenter
noted
that
EPA's
tiered
modeling
methodology
is
designed
to
identify
the
highest
annual
property
line
or
off­
site
concentrations
that
might
occur
around
each
facility
(
as
opposed
to
actual
population
exposure).
The
tiered
approach
models
exposures
of
a
"
maximally
exposed
individual"
(
MEI)
and
incorporates
a
number
of
conservative
assumptions.
According
to
the
commenter,
actual
average
concentrations
are
likely
to
be
much
lower.
The
commenter
argued
that,
even
if
the
modeled
concentrations
were
reflective
of
continuous
average
concentrations,
it
is
highly
unlikely
that
any
individual
would
actually
be
exposed
to
such
concentrations
for
a
lifetime.
The
commenter
noted
that
the
Presidential/
Congressional
Commission
on
Risk
Assessment
and
Risk
Management
concluded
that
the
conservatism
inherent
in
use
of
the
MEI
"
was
often
so
unrealistic
that
its
use
impaired
the
scientific
credibility
of
health
risk
assessment."

Response:
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
that
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
78
4EPA
1999
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).
4
Appendix
B
to
Subpart
DDDD
describes
a
process
based
on
this
air
toxics
approach
particular
to
risk
assessment
for
CAA
section
112(
c)(
9).

b.
HAP
to
include
in
risk
assessments
Comment:
One
commenter
noted
that
the
regulatory
requirements
in
the
proposed
rule
focused
on
six
HAP
that
are
emitted
from
PCWP
facilities:
acrolein,
acetaldehyde,

formaldehyde,
methanol,
phenol,
and
propionaldehyde.
Those
HAP
represent
96
percent
of
the
emissions
from
PCWP
facilities.
The
commenter
believes
that
any
risk­
based
compliance
mechanisms
may
reasonably
be
limited
to
consideration
of
the
risks
from
these
six
HAP.
The
commenter
noted
that
EPA's
preliminary
risk
analysis
conducted
prior
to
proposal
narrowed
the
list
of
HAP
emitted
from
PCWP
facilities
to
include
the
following:
acrolein,

acetaldehyde,
formaldehyde,
methanol,
phenol,
benzene,
methylene
chloride,
and
manganese.
The
commenter
referred
to
the
results
of
their
sensitivity
analysis,
which
was
conducted
based
on
the
data
used
in
EPA's
pre­
proposal
risk
analysis.
The
analysis
evaluated
the
impact
of
increasing
or
decreasing
facility
79
emissions
by
30
percent,
using
different
health
benchmarks
than
those
identified
in
EPA's
analysis,
and
conducting
the
risk
assessment
with
the
six
HAP
targeted
in
the
proposed
rule
versus
the
additional
HAP
identified
by
EPA.
The
commenter's
sensitivity
analysis
showed
that
formaldehyde
and
acetaldehyde
made
up
the
bulk
of
the
cancer
risk,
while
benzene
and
methylene
chloride
had
little
or
no
influence
on
cancer
risk,
depending
on
the
scenario
considered.
Under
all
scenarios,
acrolein
contributed
the
most
non­
cancer
risk.
The
remainder
of
the
non­
cancer
risk
was
divided
between
acetaldehyde,
formaldehyde
and
manganese,
with
manganese
contributing
between
5.6
and
12.2
percent
of
the
non­
cancer
risk,
depending
on
the
scenario.
Under
all
scenarios,
methanol,
benzene,
methylene
chloride
and
phenol
did
not
contribute
at
all
to
the
non­
cancer
risk
from
wood
products
facilities
(
with
one
exception,
where
the
phenol
risk
contribution
was
0.1
percent).
Based
on
these
results,
the
commenter
stated
that
there
appeared
to
be
little
reason
to
include
evaluation
of
methylene
chloride
or
benzene
in
the
risk­
based
compliance
option.
However,
the
commenter
stated
that
it
may
be
reasonable
to
take
an
extremely
conservative
approach
and
include
evaluation
of
manganese
in
the
risk­
based
compliance
mechanisms.

Response:
We
agree
that
it
is
appropriate
to
limit
the
number
of
HAP
that
must
be
included
in
PCWP
facility
low­
risk
demonstrations
to
only
those
HAP
that
result
in
meaningful
80
contributions
to
the
facility
risk.
However,
we
disagree
that
limiting
the
HAP
included
in
the
low­
risk
demonstration
to
the
six
HAP
defined
as
"
total
HAP"
in
Subpart
DDDD
(
acrolein,

acetaldehyde,
formaldehyde,
methanol,
phenol,
and
propionaldehyde)
is
appropriate.
We
identified
the
most
prevalent
HAP
based
on
mass
emitted
for
purposes
of
developing
MACT
compliance
options
because
MACT
is
technology­
based
(
i.
e.,

the
same
technology
that
reduces
emissions
of
the
six
HAP
also
reduces
emissions
of
other
organic
HAP).
As
discussed
in
section
IV.
A
of
this
preamble,
the
six
HAP
defined
as
"
total
HAP"
in
Subpart
DDDD
are
the
HAP
that
are
most
often
emitted
in
detectable
amounts
from
the
most
PCWP
process
units,
and
these
HAP
make
up
96
percent
of
the
mass
of
nationwide
HAP
emissions
from
the
PCWP
industry.
However,
the
risk
associated
with
emissions
of
HAP
are
dependent
on
the
mass
emitted
and
the
relative
toxicity
of
each
HAP.
Thus,
the
HAP
emitted
in
the
greatest
mass
may
not
result
in
the
most
risk
because
the
HAP
may
not
be
as
potent
as
other
HAP
emitted
in
lower
mass.
For
example,
methanol
is
the
HAP
emitted
from
the
PCWP
industry
in
the
greatest
mass,
but
because
methanol
is
not
as
toxic
as
other
HAP
emitted
(
e.
g,
formaldehyde,
certain
HAP
metals),
it
does
not
result
in
as
much
risk
as
do
other
HAP.
To
ensure
protection
of
public
health,
all
HAP
must
be
considered
when
determining
which
facilities
are
low­
risk.

The
commenter
is
correct
in
that
our
preliminary
risk
81
analysis
conducted
prior
to
proposal
narrowed
the
list
of
HAP
emitted
from
PCWP
facilities.
We
acknowledge
receipt
of
the
commenter's
sensitivity
analysis
based
on
the
data
used
in
our
pre­
proposal
risk
analysis.
Following
proposal,
we
conducted
a
more
detailed
risk
analysis
to
evaluate
the
merits
of
including
a
low­
risk
subcategory
in
the
final
PCWP
rule.
This
post­
proposal
analysis
considered
emissions
of
more
than
30
HAP
emitted
from
the
PCWP
source
category.
Many
of
these
HAP
are
only
emitted
in
minute
amounts
that
have
been
detected
from
a
small
number
of
PCWP
process
units.
Nevertheless,
we
included
them
in
our
risk
analysis
to
determine
their
contribution
to
PCWP
facility
risk.

We
reviewed
the
toxicity
values
for
each
HAP
and
the
mass
of
each
emitted
from
PCWP
facilities
to
determine
if
it
would
be
appropriate
to
narrow
the
list
of
HAP
that
PCWP
facilities
must
consider
in
their
low­
risk
demonstrations.
Based
on
our
review,

we
determined
that
95
percent
of
the
cancer
risk
at
PCWP
facilities
is
accounted
for
by
the
following
HAP:
acetaldehyde,

benzene,
arsenic,
beryllium,
cadmium,
hexavalent
chromium,
lead,

nickel
subsulfide,
formaldehyde,
and
arsenic.
We
also
determined
that
95
percent
of
the
non­
cancer
risk
at
PCWP
facilities
is
accounted
for
by
the
following
HAP:
acetaldehyde,
acrolein,

formaldehyde,
phenol,
MDI,
arsenic,
cadmium,
and
manganese.
We
believe
that
inclusion
of
these
HAP
in
a
demonstration
of
eligibility
of
the
low­
risk
PCWP
subcategory
is
appropriate.

Limiting
the
list
of
HAP
that
must
be
included
in
the
low­
risk
82
demonstration
to
13
HAP
minimizes
emissions
testing
costs,
while
ensuring
that
the
HAP
that
drive
the
risk
at
PCWP
facilities
are
accounted
for
on
a
site­
specific
basis.

c.
Background,
multipathway,
and
ecological
exposures
Comment:
Two
commenters
argued
that
multipathway
exposures
should
not
be
considered
for
PCWP
facilities.
One
commenter
stated
that,
because
the
HAP
emitted
from
the
PCWP
source
category
are
not
bioaccumulative,
it
is
unnecessary
to
consider
multipathway
exposures.
The
other
commenter
stated
that
there
is
no
policy
basis
for
considering
multipathway
exposures
because
U.
S.
Government
surveys
and
regulatory
actions
demonstrate
that
non­
inhalation
exposure
to
the
six
HAP
emitted
by
wood
products
facilities
is
insignificant.
The
commenter
provided
rationale
for
the
conclusion
that
dietary
and
drinking
water
exposures
to
the
six
HAP
are
not
significant.
Because
the
six
HAP
emitted
from
the
PCWP
source
category
(
acetaldehyde,
acrolein,
and
formaldehyde,
methanol,
phenol,
and
propionaldehyde)
do
not
exhibit
bioaccumulative
characteristics,
the
commenter
considered
it
unnecessary
to
consider
multipathway
exposures.

Three
commenters
argued
that
multipathway
exposures
should
be
considered
for
PCWP
facilities.
One
commenter
stated
that,

when
persistent
biological
toxicant
or
metal
emissions
are
significant,
ingestion
and
other
pathways
should
be
considered
in
the
risk
screening.
Another
commenter
stated
that
the
concentration­
based
applicability
threshold
approach
in
the
83
proposed
PCWP
rule
does
not
address
non­
inhalation
exposures
or
adverse
effects
on
the
environment.
The
third
commenter
stated
that
section
112(
d)(
4)
requires
EPA
to
consider
all
possible
ways
that
a
pollutant
could
affect
human
health
or
the
environment
because
it
refers
to
pollutants
"
for
which
a
health
threshold
has
been
established,"
i.
e.,
pollutants
that
have
no
adverse
health
or
environmental
effects.
(
See
5
Legislative
History
at
8511.)

According
to
the
commenter,
EPA
has
recognized
repeatedly
in
the
past
that
many
of
the
pollutants
emitted
by
the
source
category
are
re­
deposited
from
the
atmosphere
and
then
contaminate
soil
and
water
for
long
periods
of
time.
The
commenter
added
that
these
pollutants
bioaccumulate
in
wildlife
and
food
sources,

poisoning
people
and
animals
alike.
(
See,
e.
g.,
64
FR
52828,

53014
(
September
30,
1999);
64
FR
31898,
31908­
31909
(
June
14,

1999);
63
FR
14182,
14193
(
March
28,
1998);
61
FR
17358,
17478
(
April
19,
1996)
(
due
to
bioaccumulation,
mercury
levels
may
be
10,000,000
times
higher
in
fish
than
in
water
those
fish
inhabit).)
The
commenter
concluded
that,
to
evaluate
whether
a
pollutant
is
a
threshold
pollutant
and
what
its
health
threshold
and
ample
margin
of
safety
must
be,
EPA
must
consider
all
the
potential
health
and
environmental
effects
of
deposition,

persistence
and
bioaccumulation
of
that
pollutant.
The
commenter
argued
that
EPA
would
contravene
section
112(
d)(
4)
by
considering
only
health
effects
caused
by
inhalation.

Response:
We
agree
with
the
last
commenter
that
CAA
section
84
112(
d)(
4)
requires
us
to
include
oral
exposures
as
well
as
inhalation
exposures
when
determining
the
applicability
of
section
112(
d)(
4).
This
rule
is
relying
not
on
CAA
section
112(
d)(
4),
but
on
section
112(
c)(
9),
which
also
has
similar
requirements
for
determining
risk
applicability.
Although
the
commenter
refers
to
CAA
section
112(
d)(
4),
their
concern
is
addressed
in
section
112(
c)(
9)
also.
We
agree
that
exposures
via
all
relevant
routes
need
to
be
considered,
and
we
have
conducted
a
multipathway
exposure
assessment
on
those
HAP
emitted
from
PCWP
facilities
(
including
HAP
not
among
the
six
mentioned
by
one
commenter)
that
we
have
identified
as
having
the
potential
health
concerns
by
pathways
other
than
inhalation
of
ambient
air.
The
three
HAP
identified,
and
which
were
analyzed
for
risk
associated
with
projected
oral
exposures,
are
mercury,
lead,
and
cadmium.

Comment:
Several
commenters
stated
that
there
is
no
legal
or
policy
basis
for
EPA
to
consider
background
or
multipathway
(
non­
inhalation)
exposures.
The
commenters
noted
that
CAA
section
112(
d)
requires
that
MACT
standards
be
based
only
on
emissions
from
the
MACT­
regulated
portion
of
the
facility;
it
does
not
give
EPA
the
authority
to
consider
existing
background
levels.
One
commenter
noted
that
section
112
can
be
distinguished
from
other
statutory
provisions,
both
in
the
CAA
and
in
other
environmental
legislation,
where
EPA
has
clearly
85
been
given
authority
to
consider
background
sources.

Another
commenter
noted
that
the
CAA's
legislative
history
does
not
support
a
requirement
to
consider
other
exposures.
The
commenter
also
pointed
out
that
the
statutory
provisions
on
which
EPA
would
rely
to
implement
the
risk­
based
mechanisms
(
i.
e.,

section
112(
d)(
4),
section
112(
c)(
9)(
B),
or
EPA's
de
minimis
authority)
exclusively
focus
on
the
emissions
from
the
source
in
making
regulatory
decisions.
According
to
the
commenter,
EPA
has
existing
regulatory
programs
(
e.
g.,
for
mobile
and
area
sources
[
Urban
Air
Toxics
Strategy])
in
place
to
address
HAP
emissions
from
other
sources.

The
commenter
argued
that
over­
control
of
PCWP
facilities
is
unjustified
because
PCWP
facilities
account
for
very
small
proportions
of
HAP
emissions
nationwide
 
less
than
1.75
percent
of
acetaldehyde,
1.7
percent
of
acrolein,
and
1
percent
of
formaldehyde
emissions,
according
to
their
industry­
sponsored
risk
assessment.
Given
these
results,
the
commenter
concluded
that
PCWP
facilities
cannot
reasonably
be
considered
to
contribute
meaningfully
to
background
concentrations.

The
commenter
stated
that
section
112(
d)(
4)
does
not
require
the
complete
absence
of
a
hazard
and
noted
that
all
substances
have
adverse
effects
on
health
and
the
environment
at
sufficiently
high
doses.
Accordingly,
section
112(
d)(
4)

incorporates
the
concept
of
exposure,
and
the
Senate
Report
made
clear
that
the
provision
was
applicable
in
instances
where
"
it
is
86
possible
to
establish
a
`
no
observable
effects
level'
(
NOEL)

below
which
human
exposure
is
presumably
"
safe."
In
addition,

delisting
criteria
and
the
so­
called
"
trigger"
component
of
the
residual
risk
provision
focus
exclusively
on
emissions
and
whether
the
risk
posed
by
any
source
in
the
category,
by
itself,

exceeds
one
in
a
million
cancer
risk.

Two
commenters
opposed
the
use
of
available
data
on
background
concentrations
and
facility­
specific
measurement
of
background
concentrations
to
determine
the
extent
of
exposures
from
other
sources,
arguing
that
the
CAA
and
sound
public
policy
warrant
a
focus
exclusively
on
the
emissions
from
the
source
category
at
hand
when
evaluating
the
applicability
of
a
risk­
based
compliance
option.
Because
a
HI
of
1.0
(
or
higher)
is
amply
protective
of
public
health
and
is
warranted
under
EPA's
statutory
mandate,
the
commenters
stated
that
consideration
of
background
concentration
is
not
appropriate.

Response:
We
disagree
that
we
do
not
have
the
authority
to
consider
background
and
multipathway
exposures.

Commenters
presumed
the
use
of
CAA
section
112(
d)(
4)

for
the
PCWP
delisting.
However,
we
are
using
section
112(
c)(
9)

and
not
section
112(
d)(
4).
For
delisting
purposes,
we
are
required
to
make
not
only
a
determination
of
a
level
which
is
"
safe"
to
the
individual
exposed
to
the
maximum
concentration
but
87
also
a
determination
whether
that
individual
and
the
general
population
are
protected
to
a
level
that
provides
a
"
clear"
ample
margin
of
safety
in
order
to
have
the
confidence
that
a
decision
to
exclude
these
facilities
from
regulation
(
including
residual
risk)
may
be
made.
These
are
the
same
requirements
that
are
found
as
the
"
trigger"
in
the
residual
risk
program
because
all
decisions
of
this
type
under
Title
III
of
the
CAA
(
sections
112(
c)(
9),
d(
4),
and
f(
2))
should
be
consistent
and
based
on
the
same
risk
approaches.

We
agree
that
imposition
of
costly
regulatory
requirements
on
sources
that
do
not
contribute
meaningfully
to
background
exposures
is
not
beneficial.
However,
regarding
the
results
of
the
industry­
sponsored
wood
products
MACT
risk
assessment,
we
note
that
section
112(
c)(
9)
requires
the
evaluation
of
all
facility
level
emission
points,
all
HAP,
and
all
pathways
in
order
to
satisfy
that
the
emissions
from
these
facilities
provide
protection
of
the
population
with
an
ample
margin
of
safety.
The
wood
products
MACT
risk
assessment
does
not
address
HAP
emitted
from
PCWP
facilities
that
have
the
potential
to
bioaccumulate
and
persist
in
the
environment
(
e.
g.,
lead,
cadmium,
and
mercury).

We
conducted
an
exposure
assessment
for
these
HAP
to
determine
exposure
from
ingestion
as
well
as
inhalation.

The
look­
up
tables
included
in
Appendix
B
to
subpart
DDDD
were
developed
88
using
conservative
input
parameters
to
ensure
that
facilities
qualifying
for
the
low­
risk
subcategory
based
on
the
look­
up
tables
would
not
pose
a
risk
to
multimedia
endpoints.

As
discussed
elsewhere,
for
today's
final
PCWP
rule,
we
are
considering
a
HI
limit
of
1.0
to
provide
an
ample
margin
of
safety
for
protecting
public
health
under
section
112(
c)(
9).

Safety
factors
are
included
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
look­
up
tables
included
in
Appendix
B
to
Subpart
DDDD
were
developed
based
on
a
HI
of
1.0.
For
site­
specific
chronic
inhalation
risk
assessments,
facilities
are
required
to
ensure
that
the
target
organ
specific
hazard
index
(
TOSHI)
for
exceeds
a
value
of
1.0.

Comment:
One
commenter
stated
that
EPA
had
provided
inadequate
discussion
of
how
environmental
risks
would
be
evaluated.
The
commenter
added
that
the
CAA
requires
EPA
consider
the
environment
as
well
as
public
health,
and
that,
at
a
minimum,
a
facility
would
be
required
to
conduct
an
assessment
based
on
EPA's
1998
Guidelines
for
Ecosystem
Assessment.
The
commenter
referred
EPA
to
Appendix
A
of
"
Generic
Assessment
for
Endpoints
for
Ecological
Risk
Assessment"
for
a
detailed
discussion
on
the
legal
basis
from
"
such
statutes
as
the
89
CAA...
that
require
EPA
to
consider
and
protect
organism­
level
attributes
or
various
taxa
including
fish,
birds,
and
plants
and
more
generally,
animals,
wildlife,
aquatic
life,
and
living
things."

Another
commenter
cited
an
analysis
they
commissioned
that
showed
it
to
be
highly
unlikely
that
emissions
from
PCWP
facilities
would
pose
a
hazard
to
ecological
receptors
at
levels
that
are
protective
of
human
health.
Thus,
concern
over
ecological
receptors
would
not
provide
a
valid
basis
for
reducing
the
HI
below
1.0.

Response:
An
ecological
assessment
is
required
under
Title
III
of
the
CAA,
including
sections
112(
d)(
4),
(
c)(
9),
and
(
f)(
2).

Therefore,
delisting
under
section
112(
c)(
9)
requires
consideration
of
ecological
effects.
The
look­
up
tables
developed
for
today's
final
PCWP
rule
are
intended
to
accommodate
enough
conservatism
that
any
facility
qualifying
for
inclusion
in
the
delisted
subcategory
using
them
will
qualify
based
on
all
endpoints,
including
ecological
endpoints.

Assuming
the
assessment
referenced
by
the
first
commenter
included
only
the
six
HAP
listed
in
subpart
DDDD,
we
disagree
that
these
six
HAP
should
be
the
sole
focus
of
an
ecological
assessment.
It
is
not
clear
from
the
comment
whether
the
commenter
is
suggesting
that
we
might
consider
lowering
the
human
90
health
HI
values
to
below
1.0
in
order
to
reflect
ecological
concerns
or
whether
they
are
suggesting
that
an
ecological
HI
value
should
not
be
reduced
below
1.0.
In
the
former
case,
that
is
not
done.
Human
health
and
ecological
assessments
are
independent
assessments
with
their
own
risk
management
criteria.

d.
Hazard
index
(
HI)

Comment:
Two
commenters
stated
that
hazard
quotients
(
HQ)

for
chemical
mixes
should
not
be
summed
to
determine
the
HI
unless
the
primary
effects
are
on
the
same
organ
by
the
same
mechanism;
otherwise
the
risk
would
be
overestimated.
One
commenter
stated
that
section
112(
d)(
4)
refers
to
threshold
pollutants,
with
each
health
threshold
augmented
by
an
ample
margin
of
safety.
These
ample
margin
of
safety
values
are
already
incorporated
into
RfC
values.
The
risk
criteria
applied
are
confined
to
the
effects
upon
which
the
RfC
is
based,
which
reflect
the
most
sensitive
target
organ.
According
to
the
commenter,
a
decision
to
add
risk
posed
by
chemicals
that
affect
the
same
target
organ
but
have
unknown
mechanisms
of
action
represents
an
unnecessarily
conservative
assumption
that
would
tend
to
inflate
the
final
risk
estimate.

The
commenters
also
noted
that,
according
to
the
National
Research
Council
and
the
Presidential/
Congressional
Commission
on
Risk
Assessment
and
Risk
Management,
additivity
at
low
doses
is
more
likely
to
overestimate
than
to
underestimate
total
risk.
As
stated
in
the
Commission's
1997
Final
Report:
"
When
the
91
5U.
S.
Environmental
Protection
Agency.
1986.
Guidance
for
Conducting
Health
Risk
Assessment
of
Chemical
Mixtures.
Risk
Assessment
Forum,
Washington,
DC.
EPA/
630/
R­
98/
002;
available
at
http://
cfpub.
epa.
gov/
ncea/
raf/
recordisplay.
cfm?
deid=
20533.
(
EPA
1986)

6U.
S.
Environmental
Protection
Agency.
2000.
Supplementary
Guidance
for
Conducting
Health
Risk
Assessment
of
Chemical
Mixtures.
Office
of
Research
and
Development.
EPA/
630/
R­
00/
002
(
EPA
2000)
individual
components
of
a
chemical
mixture
exhibit
different
kinds
of
toxicity
or
have
different
biological
mechanisms
of
toxicity,
they
do
not
interact
 
they
act
independently
at
low
doses.
In
that
case,
the
dose­
response
relationships
for
each
chemical
should
be
considered
independently...
[
By
contrast]

studies
in
which
similar
chemicals
with
similar
mechanisms
and
target
were
administered
simultaneously
indicate
that
antagonism
is
the
usual
outcome..."(
Falk
and
Kotin
1964,
Schmal
et
al.
1977)

Response:
Our
recommended
approach
for
assessing
risks
from
exposure
to
a
mixture
of
pollutants
is
to
utilize
a
dose­
response
assessment
developed
for
that
mixture.
5,6
There
are
few
mixtures
(
e.
g.,
coke
oven
emissions),
however,
for
which
such
assessments
are
available.
When
mixture­
specific
dose­
response
assessments
are
not
available,
a
component­
by­
component
approach
is
recommended.
The
method
for
component
data
depends
on
a
judgment
of
toxicologic
similarity
among
components.
The
specific
term
"
toxicologic
similarity"
represents
a
general
knowledge
about
the
action
of
a
chemical
or
a
mixture
and
can
be
expressed
in
broad
terms
such
as
at
the
target
organ
level
in
the
body.
In
our
92
7Ibid.

8Ibid.
guidance,
assumptions
about
toxicologic
similarity
are
made
in
order
to
choose
among
risk
assessment
methods.
In
general,
we
assume
a
similar
mode
of
action
across
mixtures
or
mixture
components
and,
in
some
cases,
this
requirement
may
be
relaxed
to
require
that
these
chemicals
act
only
on
the
same
target
organ.
7
The
primary
method
for
component­
based
risk
assessment
of
toxicologically
similar
chemicals
is
the
HI,
which
is
derived
from
dose
addition.
In
our
guidance,
dose
addition
is
interpreted
as
simple
similar
action,
where
the
component
chemicals
act
as
if
they
are
dilutions
or
concentrations
of
each
other
differing
only
in
relative
toxicity.
Dose
additivity
may
not
hold
for
all
toxic
effects.
Furthermore,
the
relative
toxic
potency
between
chemicals
may
differ
from
different
types
of
toxicity
or
toxicity
by
different
routes.
To
reflect
these
differences,
the
HI
is
then
usually
developed
for
each
exposure
route
of
interest,
and
for
a
single
specific
toxic
effect
of
toxicity
to
a
single
target
organ.
A
mixture
may
then
be
assessed
by
several
HI,
each
representing
one
route
and
one
toxic
effect
or
target
organ.
8
To
assess
the
cumulative
risk
or
hazard
associated
with
nonlinear
effects
of
HAP
in
our
analysis
of
PCWP
facilities,
HAP
hazard
quotients
pertaining
to
the
same
target
organs
or
systems
93
are
summed
to
generate
TOSHI.
While
it
may
be
preferable
to
focus
on
the
addition
of
HAP
HQ
that
involve
the
same
mechanism
or
mode
of
action,
that
level
of
information
is
not
generally
available
for
all
of
the
HAP
on
which
we
are
focusing.
Pending
the
availability
of
such
data
for
the
HAP
components
of
the
mixture
being
assessed,
the
method
employed
under
CAA
section
112(
c)(
9)
is
to
aggregate
HAP
HQ
by
target
organ
to
generate
a
TOSHI.

Comment:
Two
commenters
supported
a
HI
of
1.0
(
or
greater)

as
an
appropriate
benchmark
for
comparing
exposures
attributable
to
facility
emissions,
which
should
fully
provide
for
the
statutory
mandate
of
an
ample
margin
of
safety.
The
commenters
referred
to
the
1997
Final
Report
of
the
Presidential/
Congressional
Commission
on
Risk
Assessment
and
Risk
Management
in
Regulatory
Decision­
Making
as
support
for
their
position.
Specifically,
the
Commission
supported
a
noncancer
HI
of
10.0,
stating
that
there
are
few
HAP
with
RfC
values
within
a
factor
of
10
of
their
no
observable
adverse
effects
level
(
NOAEL).
Because
RfC
values
are
typically
one­
thousandth
of
a
NOAEL,
a
noncancer
HI
of
10.0
in
those
cases
would
still
leave
a
margin
of
exposure
of
100.
The
Commission
recommended
that
EPA
should,
on
the
basis
of
screening
assessments
of
source
categories,
do
further
risk
assessment
and
analysis
of
categories
where
the
noncancer
HI
exceeds
10.0.
Where
more
detailed
risk
assessments
yield
noncancer
hazard
indices
less
than
1.0,
the
94
Commission
recommended
that
no
further
action
be
required.
The