Responses
to
Comments
Document:

MACT
Standard
for
Primary
Magnesium
Refining
Metals
Group
Emission
Standards
Division
Office
of
Air
Quality
Planning
and
Standards
U.
S.
Environmental
Protection
Agency
August
18,
2003
1
1.
Introduction
Only
one
short
comment
and
one
substantive
comment
were
received
on
the
proposed
rule.
The
short
comment
suggested
we
cut
the
proposed
standard
by
50
percent.
However,
the
commenter
did
not
provide
any
information
or
rationale
to
support
such
a
request.
Consequently,

we
could
not
consider
it
further
and
made
no
changes
to
the
rule
as
a
result
of
the
comment.

Substantive
comments
(
Docket
Item
OAR­
2002­
0043­
0002
dated
February
20,
2003)
were
received
from
US
Magnesium
LLC
and
are
addressed
in
the
following
sections.

2.
Comments
and
Responses
2.1
Dioxin/
Furan
Limit
Not
Needed
Comment:
The
commenter
stated
that
a
dioxin/
furan
emission
limit
is
not
appropriate
for
the
primary
magnesium
industry
because
EPA
has
applied
these
limits
primarily
to
facilities
that
burn
wastes.
Other
industries,
such
as
petroleum
refineries
and
iron
and
steel
foundries,
are
known
to
emit
dioxin/
furan;
however,
EPA
did
not
propose
limits
for
them.
The
commenter
also
stated
that
the
dioxin/
furan
limit
cannot
be
justified
on
the
basis
of
health
risk
because
the
facility
is
in
a
remote
location,
and
the
nearest
resident
is
25
miles
away.
The
commenter
recommended
that
EPA
use
PM
as
a
surrogate
for
dioxin/
furan
emissions
from
the
melt
reactor
because:

(
1)
EPA
established
MACT
for
dioxin/
furan
as
the
PM
control
devices
on
the
melt
reactor,
(
2)

PM
is
used
as
a
surrogate
for
other
pollutants
in
this
rule
and
has
been
used
as
a
surrogate
for
dioxin/
furan
in
other
rules,
(
3)
the
dioxin/
furan
emissions
are
mainly
in
particulate
form,
(
4)
the
dioxin/
furan
limit
will
obtain
no
additional
reduction
beyond
that
obtained
using
PM
as
a
surrogate,
and
(
5)
the
dioxin/
furan
limit
will
add
significantly
to
the
cost
of
stack
testing
with
no
apparent
gain.

Response:
We
set
a
dioxin/
furan
limit
because
it
is
a
HAP
of
concern
with
respect
to
toxicity,
we
have
adequate
test
data
(
two
tests
composed
of
three
runs
each)
to
characterize
emission
control
performance,
and
dioxin/
furan
formation
and
control
is
not
always
correlated
to
PM
formation
and
control.
First,
the
formation
of
dioxin/
furans
in
combustion
devices
with
an
available
source
of
chlorine
is
well
documented,
and
it
is
not
a
concern
only
for
facilities
that
burn
waste.
The
test
data
from
this
industry
confirms
the
formation
and
emissions
of
dioxin/
furans
from
this
emissions
source.
In
this
case,
it
is
more
appropriate
to
set
a
limit
for
dioxin/
furan
2
rather
than
to
use
PM
as
a
surrogate.
Second,
we
do
not
agree
that
the
control
device
for
PM
will
adequately
control
the
emissions
of
dioxin/
furans.
There
are
factors
other
than
the
PM
control
device
which
may
affect
the
formation
and
control
of
dioxin/
furan,
such
as
the
composition
and
concentrations
of
precursors,
temperature,
and
process
conditions.
Dioxins
are
formed
in
acid
gases
leaving
the
combustion
device,
and
the
means
of
control
is
not
necessarily
the
particulate
control
system
but
quenching
of
gases
to
control
the
temperature
in
the
device
(
to
assure
that
temperature
does
not
fall
in
the
range
which
optimizes
dioxin/
furan
formation).

The
MACT
control
system
for
dioxin/
furans
is
the
entire
scrubber
train
­
the
packed
tower
scrubbers
(
for
HCl
control)
and
the
venturi
scrubber
(
for
PM
control)
­
and
not
just
the
PM
control
device.
That
is,
the
control
of
dioxin/
furans
includes
the
rapid
cooling
of
the
exhaust
gas
that
occurs
in
the
packed
tower
absorbers,
which
limits
the
dioxin/
furan
formation.
Therefore,
we
believe
a
dioxin/
furan
limit
is
necessary
to
ensure
that
process
and
control
device
operations
do
not
change
in
the
future
in
a
manner
that
might
increase
the
formation
and
release
of
dioxin/
furan,

even
if
the
overall
PM
control
level
remains
the
same.

The
dioxin/
furan
limit
is
not
based
on
a
determination
that
health
risks
exist;
it
is
based
on
technology
and
the
floor
level
of
control
that
has
been
achieved.
We
do
not
believe
that
stack
testing
every
2.5
years
is
costly
or
unreasonable
to
provide
assurance
that
the
dioxin/
furan
limit
is
being
achieved.
Moreover,
the
commenter
did
not
provide
any
information
as
to
how
this
stack
testing
will
add
significantly
to
the
costs
of
compliance
with
the
NESHAP.

2.2
Dioxin/
Furan
Emission
Limit
Comment:
The
commenter
disagreed
with
the
approach
used
to
set
the
emission
limit
for
dioxin/
furan
and
claimed
it
does
not
provide
a
reasonable
margin
of
safety
to
ensure
continuous
compliance.
The
commenter
suggests
a
level
of
50
ng
TEQ/
dscm
is
statistically
valid.
However,

the
commenter
recommended
that
a
minimum
safety
factor
of
three
be
applied
to
the
average
of
results
from
the
two
stack
tests
(
21.5
ng
TEQ/
dscm)
to
develop
a
limit
of
65
ng
TEQ/
dscm
rather
than
a
limit
of
36
ng
TEQ/
dscm
as
proposed.
The
commenter
believes
this
is
reasonable
because
of
the
high
variability
in
the
test
results
and
because
of
the
inherent
inaccuracies
in
the
dioxin/
furan
sampling
and
analysis,
especially
at
these
extremely
low
levels
of
detection.
3
Response:
We
chose
36
ng
TEQ/
dscm
because
it
was
the
highest
result
from
any
of
the
six
runs.
This
approach
accounts
for
inherent
variability,
and
an
additional
margin
of
safety
is
provided
by
determining
compliance
from
the
average
of
three
runs.
It
appears
that
the
commenter
considered
the
six
test
runs
in
developing
a
standard
deviation
of
±
9.5
ng
TEQ/
dscm
and
estimating
a
99th
percentile
for
single
test
runs.
The
variability
of
the
average
of
three
runs
is
more
appropriate
than
the
variability
of
a
single
test
run
because
compliance
is
determined
from
the
average
of
three
test
runs
rather
than
for
each
single
test
run.

To
illustrate
the
impact
of
using
the
average
of
three
runs,
we
performed
a
Monte
Carlo
simulation
of
5,000
runs
based
on
a
normal
distribution
developed
from
the
test
results
for
six
runs.
(
Details
are
given
in
Appendix
A.)
From
the
simulation,
the
99th
percentile
for
individual
runs
was
44
ng
TEQ/
dscm
compared
to
a
99th
percentile
of
32
ng
TEQ/
dscm
for
the
average
of
three
runs.
Consequently,
since
the
emission
limit
is
enforced
based
on
three­
run
averages,
the
proposed
limit
of
36
ng
TEQ/
dscm
is
close
to
the
99th
percentile
of
performance.
We
believe
that
the
limit
as
proposed
is
achievable,
and
the
simulation
indicates
it
accounts
for
variability.

The
commenter
mentioned
process
variability
and
uncertainty
associated
with
sampling
and
analysis
as
reasons
for
a
higher
limit.
However,
the
variability
in
the
process,
sampling,
and
analysis
are
inherently
included
in
the
runs
we
used
to
derive
the
limit,
and
using
the
highest
run
accommodates
this
variability.
In
addition,
there
is
no
need
to
artificially
increase
the
limit
by
multiplying
the
average
of
the
test
results
by
three
because
the
statistical
simulation
shows
that
the
proposed
limit
is
reasonable.
With
testing
performed
every
2.5
years
and
a
limit
at
about
the
99th
percentile,
the
limit
would
be
exceeded
no
more
than
once
every
250
years
if
the
process
and
control
device
are
operated
as
they
were
during
the
two
performance
tests.

While
we
were
evaluating
the
data
discussed
by
the
commenter,
we
discovered
an
error
in
the
1998
test
report.
The
test
contractor
inadvertently
switched
the
TEF
for
two
congeners.
The
net
effect
is
that
the
overall
average
for
six
runs
is
18
ng
TEQ/
dscm
instead
of
21.5
ng
TEQ/
dscm.
This
correction
had
no
effect
on
the
highest
run
and
did
not
change
the
limit
that
was
originally
proposed.

2.3
Use
Updated
Toxicity
Equivalence
Factors
(
TEF)
4
Comment:
The
commenter
believes
that
the
World
Health
Organization's
1998
TEF
scheme
should
be
used
to
assign
toxic
equivalency,
and
this
scheme
should
be
stated
in
the
final
rule.

Response:
Based
on
our
dioxin
reassessment
report,
we
agree
with
the
commenter
and
have
incorporated
the
updated
TEF
scheme
in
the
final
rule.
The
effect
on
the
test
results
was
small,
and
the
highest
run
remained
at
36
ng
TEQ/
dscm.
Consequently,
the
level
of
the
standard
was
not
changed.
Details
are
provided
in
Appendix
B.

2.4
Health
Effects
of
Manganese
Comment:
The
commenter
stated
that
manganese
emissions
from
the
facility
are
very
low.
Workers
at
the
plant
do
not
show
any
evidence
of
the
health
effects
described
in
the
preamble
for
chronic
exposure
to
high
levels
of
manganese
by
inhalation.

Response:
We
did
not
imply
in
the
preamble
that
the
workers
at
this
plant
exhibited
the
characteristics
of
exposure
to
manganese.
The
preamble
contained
a
generic
description
of
the
health
effects
of
several
HAP,
including
manganese,
and
was
provided
only
as
background
to
show
why
these
pollutants
are
hazardous
air
pollutants.

2.5
Modern
Electrolytic
Cells
Comment
:
The
commenter
believes
the
rule
should
include
descriptions
and
requirements
for
modern
electrolytic
cells
and
the
proper
handling
and
collection
of
the
cell
offgases
The
modernization
of
electrolytic
cells
and
chlorine
capture
equipment
has
reduced
chlorine
emissions
by
75
percent.

Response:
We
did
not
include
a
detailed
description
of
the
modern
cell
technology,
and
we
agree
that
we
should
point
out
that
the
old
cell
technology
(
known
as
the
IG
Farben
cells)
has
been
replaced.
The
new
cell
technology
is
a
closed
system
and
has
resulted
in
reductions
in
chlorine
emissions.
The
old
cell
technology
allowed
chlorine
gas
to
escape
from
the
anode
section
of
the
cell
and
infiltrate
into
the
cathode
section,
where
it
was
difficult
to
capture
and
control.
The
improvement
in
emission
control
is
evidenced
by
the
reduced
chlorine
emissions
as
reported
for
the
Toxics
Release
Inventory
(
TRI).

Our
proposed
rule
is
based
on
the
most
current
permit
requirements
at
the
time
of
proposal
(
permit
dated
October
11,
2001).
This
permit
reflects
the
operating
conditions
after
the
5
old
cell
technology
was
replaced,
and
the
permit
specifies
the
old
cell
technology
must
be
replaced
by
October
1,
2001.
Consequently,
the
rule
and
operating
permit
reflect
current
operations
after
the
replacement
of
the
old
IG
Farben
cells.
1
From
the
test
reports
listed
as
Docket
Items
II­
A­
4
(
1998)
and
II­
A­
7
(
2000)
in
Docket
No.
A­
2002­
0027.

6
APPENDIX
A.
RESULTS
OF
THE
MONTE
CARLO
SIMULATION
OF
TEQ
RUNS
Issue
EPA
proposed
a
dioxin
limit
of
36
ng/
m3.
Commenter
OAR­
2002­
0043­
0002
(
US
Magnesium
LLC)
stated
that
the
99th
percentile
is
50
ng/
m3
and
requests
a
standard
of
65
ng/
m3
because
of
variability
and
inherent
inaccuracy
associated
with
sampling
and
analysis.

Background
°
The
test
results
are
given
in
Table
A­
1.
EPA
chose
the
highest
single
run
(
36
ng/
m3)
as
the
limit.
The
limit
is
based
on
the
average
of
3
runs,
which
further
allows
for
variability.

Table
A­
1.
Dioxin
Test
Results1
Run
(
year)
ng/
m3
Run
1
(
2000)
24.2
Run
2
(
2000)
36.0
Run
3
(
2000)
10.5
Run
1
(
1998)
13.6
Run
2
(
1998)
7.4
Run
3
(
1998)
17.4
Average
18.2
Standard
deviation
10.5
Maximum
36
Monte
Carlo
Simulation
°
According
to
the
Shapiro­
Wilke
test,
the
individual
runs
are
normally
distributed.

°
A
Monte
Carlo
simulation
was
performed
for
the
normal
distribution
and
results
for
5,000
runs
were
simulated.
Three­
run
averages
were
calculated.
Summary
statistics
are
given
in
Table
A­
2.

°
The
99th
percentile
for
single
runs
is
44
ng/
m3.
Averaging
over
3
runs
reduces
the
variability
and
results
in
a
99th
percentile
of
32
ng/
m3.
7
Conclusion
°
The
proposed
limit
adequately
accounts
for
variability,
especially
considering
the
limit
is
enforced
based
on
3­
run
averages.

Table
A­
2.
Results
of
the
Monte
Carlo
Simulation
(
5,000
Runs)

Individual
runs
(
ng/
m3)
3­
run
averages
(
ng/
m3)
Average
18.2
18.2
Standard
deviation
10.5
6.3
99th
percentile
44
32
Maximum
53
42
8
APPENDIX
B.
UPDATED
TOXICITY
EQUIVALENCE
FACTORS
Tables
B­
1
and
B­
2
present
the
calculated
toxicity
equivalence
(
TEQ)
based
on
the
toxicity
equivalence
factors
(
TEF)
recommended
by
the
World
Health
Organization
(
WHO)
in
1998.
The
most
significant
change
in
terms
of
these
test
results
was
that
the
TEF
for
1,2,3,7,8­
PeCDD
increased
from
0.5
to
1.
Other
TEFs
that
changed
include
a
reduction
by
a
factor
of
10
for
OCDD
and
OCDF.

Table
B­
1.
Summary
of
TEQ
Results
­
US
Magnesium
(
March
1998)

Congener
WHO
TEFs
(
1998)
PCDD/
PCDF
(
ng/
m3)
TEQ
(
ng/
m3)

Run
1
Run
2
Run
3
Run
1
Run
2
Run
3
2,3,7,8
­
TCDD
1
0.05
0.04
0.05
0.050
0.040
0.050
1,2,3,7,8­
PeCDD
1
0.14
0.08
0.22
0.140
0.080
0.220
1,2,3,4,7,8­
HxCDD
0.1
0
0
0
0.000
0.000
0.000
1,2,3,6,7,8­
HxCDD
0.1
0.1
0.1
0.2
0.010
0.010
0.020
1,2,3,7,8,9­
HxCDD
0.1
0.1
0.1
0.1
0.010
0.010
0.010
1,2,3,4,6,7,8­­
HpCDD
0.01
0.1
0.1
0.1
0.001
0.001
0.001
OCDD
0.0001
0.1
0
0.1
0.000
0.000
0.000
2,3,7,8­
TCDF
0.1
17.2
9
18.5
1.720
0.900
1.850
1,2,3,7,8­
PeCDF
0.05
21.9
13.4
30.7
1.095
0.670
1.535
2,3,4,7,8­
PeCDF
0.5
7.9
4.7
9.9
3.950
2.350
4.950
1,2,3,4,7,8­
HxCDF
0.1
13.1
8.8
18.5
1.310
0.880
1.850
1,2,3,6,7,8­
HxCDF
0.1
7.7
4.7
11.1
0.770
0.470
1.110
2,3,4,6,7,8­
HxCDF
0.1
4.4
2.6
5.1
0.440
0.260
0.510
1,2,3,7,8,9­
HxCDF
0.1
0.8
0.6
1.2
0.080
0.060
0.120
1,2,3,4,6,7,8­
HpCDF
0.01
8.3
4.6
11.1
0.083
0.046
0.111
1,2,3,4,7,8,9­
HpCDF
0.01
1.9
1.2
2.5
0.019
0.012
0.025
OCDF
0.0001
0
4.9
8.3
0.000
0.000
0.001
Total
TEQ
(
ng/
m3)
9.7
5.8
12.4
Percent
O
2
11.0
10.0
11.0
O
2
Correction
Factor
1.4
1.3
1.4
Total
TEQ
(
ng/
m3
at
7%
O2)
13.6
7.4
17.4
9
Table
B­
2.
Summary
of
TEQ
Results
­
US
Magnesium
(
May
2000)

Congener
WHO
TEFs
(
1998)
PCDD/
PCDF
(
ng/
m3)
TEQ
(
ng/
m3)

Run
2
Run
3
Run
4
Run
2
Run
3
Run
4
2,3,7,8
­
TCDD
1
0.04
0.06
0.03
0.040
0.060
0.030
1,2,3,7,8­
PeCDD
1
0.26
0.47
0.16
0.260
0.470
0.160
1,2,3,4,7,8­
HxCDD
0.1
0.18
0.29
0.05
0.018
0.029
0.005
1,2,3,6,7,8­
HxCDD
0.1
0.53
0.91
0.16
0.053
0.091
0.016
1,2,3,7,8,9­
HxCDD
0.1
0.44
0.74
0.13
0.044
0.074
0.013
1,2,3,4,6,7,8­­
HpCDD
0.01
0.97
1.86
0.27
0.010
0.019
0.003
OCDD
0.0001
0.78
1.17
0.14
0.000
0.000
0.000
2,3,7,8­
TCDF
0.1
7.64
9.82
5.67
0.764
0.982
0.567
1,2,3,7,8­
PeCDF
0.05
21.16
32.05
9.25
1.058
1.603
0.463
2,3,4,7,8­
PeCDF
0.5
12.12
21.08
8.45
6.060
10.540
4.225
1,2,3,4,7,8­
HxCDF
0.1
36.69
71.22
11.13
3.669
7.122
1.113
1,2,3,6,7,8­
HxCDF
0.1
21.33
39.79
6.15
2.133
3.979
0.615
2,3,4,6,7,8­
HxCDF
0.1
9.73
17.31
2.91
0.973
1.731
0.291
1,2,3,7,8,9­
HxCDF
0.1
8.45
15.31
2.48
0.845
1.531
0.248
1,2,3,4,6,7,8­
HpCDF
0.01
41.17
72.04
12.3
0.412
0.720
0.123
1,2,3,4,7,8,9­
HpCDF
0.01
17.41
30.9
3.12
0.174
0.309
0.031
OCDF
0.0001
124.15
185.83
18.13
0.012
0.019
0.002
Total
TEQ
(
ng/
m3)
16.5
29.3
7.9
Percent
O
2
11.4
9.6
10.4
O
2
Correction
Factor
1.5
1.2
1.3
Total
TEQ
(
ng/
m3
at
7%
O2)
24.2
36.0
10.5
