UN~
TED
STATES
ENVIRONME~~
TAL
PROTEGT~
ON
AGENCY
WASHINGTON,
D.
C.
20460
OFFIGE
OF
AIR
AND
RnoMTlON
Dr.
H.
Gregor
Rigo,
President
H
G
Rig0
&
Associates,
Inc,
Columbia
Road
Is,
OH
44138­
2206
Dear
Dr.
Rigo:

Thank
you
for
your
letter
dated
December
28,2001.
In
your
letter,
you
conclude
that
the
wtitation
(
PLQ)
for
Method
23,
the
Environmental
Protection
Agency's
test
method
for
measuring
polychlorinated
dibenzodioxins
(
PCDD's)
and
polychlorinated
dibenzofurans
(
PCDF's),
is
higher
than
the
emission
limits
for
PCDD's
and
the
various
regdations
limiting
the
emission
of
these
compounds
itom
municipal
Again,
according
to
your
letter,
this
is
important
because
the
EPA's
Method
"
that
under
the
current
regulatory
scheme,
test
results
can
only
be
used
for
they
are
above
the
practical
quantification
limit."

While
I
share
your
concern
about
measurement
uncertainty,
there
is
no
requirement
in
any
other
EPA
compliance
test
method
to
establish
a
PLQ
or
to
prohibit
the
use
ata
that
fall
below
the
PLQ.
The
procedure
in
Method
301
for
determiping
the
eled
as
an
"
optional"
procedure
and
not
a
required
one,
as
proposed
in
the
Federal
Register
on
June
13,1991
In
the
Preamble
to
the
final
rulemaking
for
Method
301,,
we
responded
to
several
comments
suggesting
the
EPA
revise
the
proposed
method
to
include
specific
procedures
to
defrne
the
meas
comments
noted
that
Method
301
re
level
of
the
pollutant
in
the
waste
s
limit
or
require
the
tester
to
estabIi
301
"
provided'
cedures
for
dete
I
t
range
of
the
method.
EPA's
ester
to
validate
measurement
methods
at
the
t
declined
to
set
an
absolute
lower
measurement
it.
Our
response
also
pointed
out
that
Method
g
a
limit
of
quantitation
and
that
it
`
advocated"
the
use
to
help
defrne
a
method's
measurement
range.
It
did
not
choose
to
make
I
regret
any
confusion
that
this
may
have
caused
and
appreciate
the
oppo
irements
of
Method
301.

Although
Metbod
301
does
not
require
that
a
tester
determine
the
PLQ
of
a
method,
it
does
have
limits
on
the
allowabie
precision
for
a
compliance
test
method.
As
defined
in
Section
6.3.1.1,
the
precision
of
a
method
is
unacceptable
if
the
relative
standard
deviation
is
equal
to
or
greater
than
50%.
Based
on
your
analysis
and
that
of
the
American
Society
of
Mechanical
,

h
Committee
on
Reference
Method
Accuracy
and
Precision,
the
relative
n
ofMethod
23
was
always
less
than
50%
over
the
entire
range
of
emission
Internet
A&
ress
(
URL)
http:
l/
www­
epagov
Rffiycle&
RecycbWe
Prtnled
with
Vegetable
OII
Based
inks
on
Recycled
Peper
(
Minimum
30%
Postconsumer)

­­­­­­~­­
­
