United
States
Environmental
Protection
Agency
Office
of
Water
4303
EPA
821­
R­
01­
023
March
2001
Guidance
for
Implementation
and
Use
of
EPA
Method
1631
for
the
Determination
of
Low­
Level
Mercury
(
40
CFR
part
136)
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
i
Table
of
Contents
Chapter
1
Introduction
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1­
1
Subjects
addressed
in
this
guidance
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1­
1
Chapter
2
Use
of
"
Clean"
Techniques
to
Preclude
Contamination
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2­
1
What
is
the
contamination
control
philosophy
behind
EPA
Method
1631
?
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2­
1
What
are
"
clean"
techniques
and
how
are
they
used
?
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2­
1
What
level
of
contamination
control
is
required
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2­
2
What
level
of
contamination
control
and
clean
techniques
should
be
required
for
compliance
monitoring
under
National
Pollutant
Discharge
Elimination
System
("
NPDES")
permits
?
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2­
3
How
will
I
know
if
my
sample
is
contaminated
?
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2­
4
What
"
clean"
techniques
are
necessary
in
the
laboratory
?
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2­
4
How
can
I
determine
if
the
laboratory
and
my
analytical
system
is
sufficiently
clean
?
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2­
5
Can
I
use
off­
the­
shelf
bottles
from
a
bottle
supplier
and
still
comply
with
Method
1631,
Section
4.3.7.1
?
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2­
6
How
can
I
prevent
contamination
of
my
laboratory
from
samples
containing
high
concentrations
of
mercury
?
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2­
6
What
other
documents
address
contamination
control
issues
?
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2­
6
Chapter
3
Matrix
Interferences
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3­
1
What
are
the
known
matrix
interferences
in
the
determination
of
mercury
using
Method
1631
?
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3­
1
How
can
I
determine
that
a
matrix
interference
exists
?
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3­
1
Can
dilution
be
used
to
overcome
matrix
interferences
?
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3­
1
How
can
I
overcome
a
matrix
interference
?
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3­
2
What
is
the
nature
of
the
iodide
interference
and
how
can
it
be
overcome
?
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3­
3
Is
it
possible
to
overcome
an
interference
from
gold
in
the
sample
?
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3­
3
What
if
high
concentrations
of
organic
matter
are
present
?
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3­
4
What
are
the
specific
procedures
for
use
of
additional
BrCl
and
UV
photo­
oxidation
?
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3­
4
Can
the
non­
homogeneity
of
a
sample
containing
high
solids
result
in
failure
of
the
MS/
MSD
?
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.
3­
5
How
can
I
demonstrate
that
my
inability
to
meet
the
QC
acceptance
criteria
in
EPA
Method
1631
is
attributable
to
a
matrix
interference
rather
than
a
laboratory
performance
deficiency
?
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.
.
3­
5
Shouldn't
EPA
allow
regulatory
relief
when
a
matrix
interference
is
demonstrated
?
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.
3­
6
How
can
I
expect
EPA
Method
1631
to
perform
in
the
presence
of
matrix
interferences
?
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3­
6
What
permit
relief
is
there
if
I
cannot
achieve
the
MDL
and
ML
in
my
matrix
?
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3­
7
Chapter
4
Flexibility
in
EPA
Method
1631
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4­
1
Is
there
flexibility
in
EPA
Method
1631
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.
4­
1
What
types
of
modifications
may
I
make
to
Method
1631
?
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4­
1
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
ii
How
can
I
demonstrate
equivalent
or
superior
performance
for
a
modification
?
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4­
2
May
I
eliminate
one
of
the
gold
traps
specified
in
EPA
Method
1631
?
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4­
2
Section
9.1.2
of
the
Method
allows
use
of
flow
injection.
We
encountered
a
problem
with
flow
injection
when
we
analyzed
an
effluent
containing
high
concentrations
of
organic
materials.
Can
a
flow
injection
system
continue
to
be
used
for
this
effluent
?
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4­
2
Method
1631
states
that
a
cold
vapor
atomic
adsorption
spectrometry
(
CVAAS)
detector
can
be
used.
Can
I
achieve
the
Method
detection
and
quantitation
limits
using
CVAAS
?
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4­
3
Section
9.3.4.1
states
that
few
interferences
have
been
encountered
with
Method
1631.
Would
you
expect
this
statement
to
be
true
when
CVAAS
is
used
?
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.
4­
3
What
is
the
status
of
EPA
Method
245.7
"
Determination
of
Ultra­
trace
Level
(
ng
Hg/
L)
Total
Mercury
in
Water
by
Cold
Vapor
Atomic
Fluorescence
Spectrometry"
and
can
it
be
used
?
.
.
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.
.
4­
3
Chapter
5
Frequently
Asked
Questions
(
FAQs)
Concerning
EPA
Method
1631
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5­
1
General
Questions
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.
5­
1
When
should
I
use
EPA
Method
1631
for
measurement
of
mercury
?
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.
5­
1
Is
use
of
EPA
Method
1631
required
?
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.
5­
1
How
rigorously
must
EPA
Method
1631
be
followed
?
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.
5­
2
Do
you
have
analytical
methods
for
determination
of
elemental
mercury
(
Hg0)
and
methyl
mercury
(
CH3Hg)
?
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.
.
5­
2
Is
Method
1631
for
total
mercury
or
for
dissolved
and
total
recoverable
mercury
?
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.
5­
2
Sampling
Questions
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.
5­
2
Should
samples
in
which
dissolved
mercury
is
to
be
determined
be
filtered
in
the
field
or
in
the
laboratory
?
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.
5­
2
Does
EPA
Method
1631
allow
use
of
continuous
versus
grab
sampling
?
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.
.
5­
3
Can
plastic
containers
other
than
fluoropolymer
be
used
for
collection
of
samples
for
mercury
?
.
.
.
.
.
5­
3
Is
borosilicate
glass
(
Section
6.1)
really
OK
?
The
sampling
method
does
not
allow
glass
for
mercury;
only
fluoropolymer.
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.
5­
3
Can
I
digest
samples
in
polyethylene
or
polypropylene
vessels
?
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.
5­
3
The
sampling
procedures
in
the
Method
and
in
the
Sampling
Guidance
are
not
explicit
in
stating
the
exact
steps
that
are
required
for
sample
collection.
Can
you
provide
further
guidance
in
this
area
?
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.
.
5­
4
Must
I
preserve
samples
in
the
field
?
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.
5­
4
Early
versions
of
Method
1631
allowed
a
holding
time
of
6
months.
Why
was
it
changed
?
.
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.
.
5­
4
Why
is
it
necessary
to
test
the
pH
of
samples
to
ensure
that
they
have
been
properly
preserved,
as
stated
in
Section
8.2
of
the
Method
?
Oxidation
with
BrCl
is
more
important
than
preservation,
and
ensures
that
the
samples
will
be
at
pH
<
2.
.
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.
.
5­
5
Is
placing
a
serial
number
on
each
sample
bottle
a
good
idea
?
.
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.
.
5­
5
Why
is
a
sample
preservation
temperature
of
0
E
C
specified
?
This
temperature
may
cause
an
aqueous
sample
to
freeze
and
a
glass
sample
bottle
to
break.
.
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.
5­
5
Is
there
really
a
need
to
refrigerate
samples
?
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.
.
5­
5
Can
you
offer
any
other
helpful
tips
on
sampling
?
.
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.
5­
5
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
iii
Blanks
Questions
.
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.
5­
6
Is
the
bubbler
blank
the
same
as
a
laboratory
(
method)
blank
?
i.
e.,
does
it
cover
the
entire
system
?
Also,
what
about
field
blanks
and
equipment
blanks
?
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.
5­
6
What
is
the
required
frequency
for
field
blanks
?
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.
5­
7
How
are
field
blanks
collected
if
the
sample
is
collected
from
a
closed
plumbing
system
?
.
.
.
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.
.
5­
7
Is
it
necessary
to
run
a
sampler
check
blank
(
Section
9.4.4.2)
on
each
piece
of
sampling
equipment
that
will
be
used
in
the
field
?
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.
5­
7
Can
I
subtract
field
or
equipment
blank
results
from
results
for
samples
?
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.
5­
7
Can
we
use
field
blank
correction
?
(
Section
12.4.2
of
EPA
Method
1631
does
not
specifically
state
that
it
is
allowed.)
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5­
8
Can
I
apply
blank
correction
when
multiple
blanks
are
collected,
as
detailed
in
Section
9.4.3.3
of
EPA
Method
1631
?
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.
5­
8
How
should
we
interpret
results
from
the
analyses
of
field
blanks
?
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.
5­
8
Are
field
samples
results
void
when
field
and
equipment
blanks
do
not
meet
the
requirements
in
Section
9.4,
in
the
same
way
that
they
are
void
when
results
for
reagent
blanks
do
not
meet
these
requirements
?
.
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.
5­
9
We
have
found
that
a
minimum
of
triplicate
reagent
blanks
are
required
daily
for
reliable
low­
level
mercury
measurements.
Can
multiple
blanks
be
used
?
.
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.
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.
5­
9
Quality
Control
(
QC)
Questions
.
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.
.
5­
10
What
quality
control
tests
are
required
by
Method
1631
and
what
performance
criteria
must
be
met
?
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.
5­
10
Can
the
QC
be
adjusted
for
measurements
at
high
levels
?
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.
5­
11
How
do
QC
requirements
differ
as
applied
to
an
analytical
batch
and
to
a
specific
discharge
?
.
.
.
.
.
5­
11
How
do
we
combine
batch­
specific
and
matrix­
specific
QC
requirements
?
.
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.
5­
12
We
operate
a
commercial
laboratory
that
receives
samples
from
multiple
clients.
What
spiking
levels
are
required
for
the
MS/
MSD
in
a
given
batch
?
.
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.
.
5­
13
Must
we
use
the
regulatory
compliance
limit
as
the
spike
level
for
both
influents
and
effluents
?
.
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.
5­
14
If
two
analytical
batches
of
20
or
fewer
samples
are
run
in
the
same
day,
must
there
be
a
total
of
6
bubbler
blanks,
2
OPRs,
and
2
QCSs
?
.
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.
.
5­
14
What
frequency
is
required
for
the
OPR
?
.
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.
5­
14
Laboratories
are
not
always
in
contact
with
field
sampling
teams.
Why
should
we
have
to
communicate
that
the
sampling
precision
is
inadequate,
as
stated
in
Section
9.7
of
the
Method
?
.
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.
5­
14
Miscellaneous
Questions
.
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.
5­
15
How
much
should
I
be
concerned
about
contamination
from
the
bromine
monochloride
(
BrCl)
and
other
reagents
?
.
.
.
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.
.
5­
15
How
safe
is
bromine
monochloride
?
It
seems
dangerous
to
us.
.
.
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.
.
.
5­
15
How
do
I
know
when
enough
BrCl
has
been
added
to
an
opaque
sample
?
.
.
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.
.
5­
15
Method
1631
uses
calibration
factors
and
the
relative
standard
deviation
of
calibration
factors
and
the
relative
standard
deviation
of
calibration
factors
for
establishing
calibration
linearity.
Nearly
all
other
metals
methods
use
linear
regression.
Why
is
EPA
Method
1631
different
?
.
.
.
5­
15
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
iv
Can
we
use
the
slope,
intercept,
and
correlation
coefficient
method
of
calibrating
and
calculating
results,
provided
that
we
demonstrate
equivalency
?
.
.
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.
.
.
.
.
.
.
.
5­
16
Why
doesn't
EPA
make
every
effort
to
communicate
its
expectations
on
weighted
regression
to
manufacturers
of
instruments
?
.
.
.
.
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.
.
.
.
.
.
5­
16
Why
doesn't
EPA
require
dilution
when
the
concentration
in
a
sample
is
greater
than
90
percent
of
the
linear
dynamic
range
(
LDR),
as
with
some
other
EPA
metals
methods
?
.
.
.
.
.
.
.
.
.
.
.
.
.
5­
16
The
highest
ambient
criterion
for
mercury
is
12
ng/
L.
Why
is
calibration
performed
to
100
ng/
L
?
.
.
5­
17
Must
our
laboratory
discard
the
secondary
standard
on
the
expiration
date
even
if
it
is
still
within
the
control
limits
of
EPA
Method
1631
?
.
.
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.
5­
17
Sections
7.9
and
7.10
state
that
the
working
standards
"
should"
be
replaced
monthly.
Does
the
word
"
should"
imply
that
it
is
the
laboratory's
discretion
?
.
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.
.
.
.
.
5­
17
How
expensive
is
it
to
set
up
EPA
Method
1631
?
.
.
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.
.
5­
17
What
criteria
should
I
use
in
selecting
a
laboratory
?
.
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.
.
.
5­
17
What
data
can
and
cannot
be
reported
for
regulatory
compliance
purposes,
and
is
it
the
laboratory
or
discharger's
responsibility
to
make
the
determination
?
.
.
.
.
.
.
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.
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.
.
.
.
.
.
.
.
5­
18
Are
reporting
requirements
in
Section
12.4
of
Method
1631
the
laboratory's
responsibility
or
the
discharger's
?
.
.
.
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.
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.
.
.
5­
18
Can
laboratories
report
results
below
the
ML
for
field
samples
?
.
.
.
.
.
.
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.
.
.
.
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.
.
5­
18
Chapter
6
Sources
of
Information
.
.
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.
.
.
.
6­
1
Regulatory
Background
.
.
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.
.
.
.
6­
1
Data
Gathering
for
EPA
Method
1631
.
.
.
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.
.
.
6­
1
Documents
Supporting
EPA
Method
1631
.
.
.
.
.
.
.
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.
.
.
6­
1
Documents
on
Compliance
Monitoring
and
Methods
.
.
.
.
.
.
.
.
.
.
.
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.
.
6­
2
Source
for
Documents
.
.
.
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.
6­
2
Chapter
7
Where
to
Get
Additional
Help
.
.
.
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.
.
.
.
.
.
.
.
7­
1
EPA
contact
for
questions
specifically
related
to
EPA
Method
1631
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Websites
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7­
1
APPENDIX
A:
Standard
Operating
Procedure
for
Collection
of
Ambient
Water
and
Wastewater
Samples
for
Determination
of
Mercury
Using
EPA
Method
1631
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A­
1
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
v
Acknowledgments
This
guidance
document
was
developed
under
the
direction
of
William
A.
Telliard
and
Maria
Gomez­
Taylor
of
the
Engineering
and
Analysis
Division
(
EAD)
within
the
U.
S.
Environmental
Protection
Agency's
(
EPA's)
Office
of
Science
and
Technology
(
OST).
EPA
expresses
appreciation
to
Roger
Stewart
of
the
Virginia
Department
of
Environmental
Quality
(
DEQ),
Paul
Boothe
of
Albion
Environmental
Laboratories,
Beverly
van
Buuren
and
Nicolas
Bloom
of
Frontier
Geosciences,
Mark
Hoeke
of
the
Association
of
Metropolitan
Sewerage
Agencies,
and
representatives
of
the
Alliance
of
Automobile
Manufacturers,
the
American
Chemistry
Council,
the
Utility
Water
Act
Group,
and
the
American
Forest
and
Paper
Association
for
providing
technical
assistance
and
review
during
document
development.

Disclaimer
This
Guidance
for
Implementation
and
Use
of
EPA
Method
1631
for
Determination
of
Low­
Level
Mercury
(
the
"
Guidance")
is
provided
to
help
implement
national
policy
on
the
use
of
EPA
Method
1631.
The
material
presented
is
intended
solely
for
guidance
and
does
not
alter
any
statutory
requirements.
This
guidance
does
not
substitute
for
Clean
Water
Act
(
CWA)
requirements
or
EPA
regulations,
nor
is
it
a
regulation
itself.
Thus,
it
cannot
impose
legally
binding
requirements
on
EPA,
States,
Tribes,
or
the
regulated
community
and
may
not
apply
to
a
particular
situation
based
upon
case­
specific
circumstances.
EPA
and
State
decision
makers
retain
the
discretion
to
adopt
approaches
on
a
case­
by­
case
basis
that
differ
from
this
guidance
where
appropriate.
This
guidance
may
be
changed
based
on
any
future
information
made
available
to
EPA.

This
guidance
has
been
reviewed
by
the
U.
S.
EPA
Office
of
Water
and
approved
for
publication.
Mention
of
commercial
organizations,
trade
names,
or
commercial
products
does
not
constitute
endorsement
or
recommendation
for
use.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
vi
Foreword
The
latest
recommended
water
quality
criteria
(
WQC)
published
by
the
U.
S.
Environmental
Protection
Agency
(
EPA)
are
those
listed
in
the
National
Toxics
Rule
(
58
FR
60848)
and
the
Stay
of
Federal
Water
Quality
Criteria
for
Metals
(
60
FR
22228),
and
codified
at
40
CFR
131.36.
In
addition
to
the
WQC
published
at
131.36,
EPA
has
established
WQC
for
protection
of
aquatic
life,
human
health,
and
wildlife
in
the
Water
Quality
Guidance
for
the
Great
Lakes
System
at
40
CFR
132.
The
lowest
WQC
for
mercury
is
a
criterion
for
protection
of
wildlife
of
1.3
ng/
L.
EPA
developed
Method
1631
to
specifically
address
State
needs
for
the
reliable
measurement
of
mercury
at
WQC
levels.

Measurement
of
mercury
by
Method
1631
is
accomplished
by
oxidation
of
mercury
with
bromine
monochloride
(
BrCl),
sequential
reduction
with
ammonium
hydroxide
and
stannous
chloride
to
convert
Hg(
II)
to
volatile
Hg(
0),
purge
of
Hg(
0)
from
water
onto
a
gold­
coated
sand
trap,
thermal
desorption
from
the
trap,
and
detection
by
cold­
vapor
atomic
fluorescence
spectrometry
(
CVAFS).
Tests
of
the
initial
version
of
Method
1631
were
directed
at
making
measurements
in
ambient
waters
at
WQC
levels.
In
data
gathering,
EPA
found
that
Method
1631
also
could
be
applied
to
effluents
and
other
matrices.
These
applications
were
supported
by
data
from
laboratories
within
the
U.
S.
and
overseas
and
by
a
comprehensive
survey
of
waters
in
the
State
of
Maine
(
Maine
DEP,
Mercury
in
Wastewater:
Discharges
to
the
Waters
of
the
State).
Method
1631
was
validated
initially
in
four
single­
laboratory
studies,
and
the
resulting
performance
specifications
were
validated
in
an
interlaboratory
validation
involving
twelve
participant
laboratories
and
one
referee
laboratory.
The
highest
method
detection
limit
(
MDL)
determined
by
all
laboratories
in
reagent
water
was
1.8
ng/
L.
Results
from
these
studies
indicate
that
the
Method
is
capable
of
producing
reliable
measurements
of
mercury
in
aqueous
matrices
at
WQC
levels.

In
May
1998,
EPA
proposed
Method
1631
at
40
CFR
part
136
for
use
in
determining
mercury
at
ambient
WQC
levels
in
EPA's
CWA
programs,
and
subsequently
published
a
Notice
of
Data
Availability
(
64
FR
10596)
that
included
additional
data
supporting
application
of
the
Method
to
effluent
matrices.
On
June
8,
1999,
EPA
responded
to
numerous
public
comments
on
the
proposed
method
and
promulgated
EPA
Method
1631,
Revision
B:
Mercury
in
Water
by
Oxidation,
Purge
and
Trap,
and
Cold
Vapor
Atomic
Fluorescence
Spectrometry
at
40
CFR
part
136
for
use
in
EPA's
CWA
monitoring
programs.

The
purpose
of
this
guidance
is
to
assist
regulatory
agencies,
control
authorities,
dischargers,
generators,
industrial
users,
and
laboratories
in
the
application
of
EPA
Method
1631
to
ambient
water
and
wastewater,
provide
information
on
the
use
of
"
clean
techniques"
to
preclude
contamination,
give
details
on
how
to
overcome
matrix
interferences,
and
answer
frequently
asked
questions
(
FAQs).
We
trust
that
this
guidance
will
assist
you
in
using
Method
1631
to
produce
reliable
measurements
of
mercury
at
the
levels
necessary
to
address
EPA
and
State
water
quality
criteria.

Following
publication
of
this
Guidance,
EPA
is
planning
to
promulgate
Method
1631,
Revision
C
to
clarify
requirements
for
the
reporting
and
use
of
field
blank
results.
This
Guidance
addresses
those
requirements.
In
addition,
EPA
plans
to
sign
a
notice
of
proposed
rulemaking
by
September
30,
2001
of
specific
requirements
for
clean
techniques
and
quality
control
to
be
used
in
conjunction
with
Method
1631.
The
proposal
should
be
published
in
the
Federal
Register
by
October
2001.
The
proposed
requirements
will
be
based
on
comments
received
from
several
stakeholders
since
promulgation
of
Method
1631,
Revision
B.
After
proposal
and
review
and
consideration
of
comments
received
during
the
public
comment
period,
EPA
would
take
final
action
during
2002
on
the
proposed
revisions
to
Method
1631
addressing
clean
technique
and
quality
control
requirements.
At
that
time,
EPA
may
revise
this
Guidance
in
accordance
with
any
new
requirements.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
1­
1
Chapter
1:
Introduction
This
guidance
is
intended
to
provide
assistance
to
the
analytical
community
in
the
application
and
use
of
Method
1631
and
to
include
more
detailed
information
on
certain
aspects
of
the
Method.
This
guidance
also
explains
the
flexibility
allowed
within
the
scope
of
Method
1631
and
answers
frequently
asked
questions
(
FAQs)
about
the
Method.
To
help
in
this
process,
this
Guidance
is
divided
into
the
following
topics:

#
Chapter
1
discusses
the
purpose
and
contents
of
this
document
and
provides
background
information
concerning
the
development
of
Method
1631
and
its
application
to
ambient
and
effluent
waters.

#
Chapter
2
discusses
the
use
of
"
clean"
techniques
to
prevent
and
control
contamination.

#
Chapter
3
discusses
known
matrix
interferences
and
provides
suggestions
as
to
how
you
can
overcome
these
and
other
interferences.

#
Chapter
4
discusses
flexibility
in
Method
1631.

#
Chapter
5
presents
responses
to
frequently
asked
questions
(
FAQs)
by
the
analytical
community
regarding
use
of
Method
1631.

#
Chapter
6
provides
a
list
of
information
sources
pertaining
the
regulatory
background
and
data
gathering
for
Method
1631.

#
Chapter
7
provides
sources
of
information
and
EPA
contacts
that
may
help
you
answer
any
remaining
questions
you
may
have
regarding
Method
1631.

Subjects
addressed
in
this
guidance
Use
of
"
clean"
and
"
ultra­
clean"
techniques
The
terms
"
clean"
and
"
ultra­
clean"
have
been
applied
to
the
techniques
needed
to
reduce
or
eliminate
contamination
in
trace
metals
determinations.
However,
these
terms
are
not
well
defined,
and
their
meaning
varies
widely
among
researchers
and
other
users
of
the
techniques.
For
example,
the
U.
S.
Geological
Survey's
(
USGS's)
Water
Quality
Laboratory
has
defined
"
clean"
to
mean
measurements
to
a
concentration
of
0.1
F
g/
L
and
"
ultra­
clean"
to
mean
measurements
to
a
concentration
of
0.01
F
g/
L.
The
method
detection
limit
(
MDL;
40
CFR
136,
Appendix
B)
in
Method
1631
is
0.0002
F
g/
L
(
0.2
ng/
L),
well
below
these
levels.
As
a
result,
the
terms
"
clean"
and
"
ultra­
clean"
are
not
used
in
Method
1631.
However,
in
response
to
requests
from
the
analytical
community,
this
guidance
addresses
"
clean"
and
"
ultra­
clean"
techniques.
In
this
guidance,
the
term
"
clean"
refers
to
the
suite
of
techniques
needed
to
reduce
or
eliminate
contamination
when
Method
1631
is
used.
The
term
ultra­
clean
is
not
employed.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
1­
2
Potential
matrix
interferences
The
proposed
version
of
Method
1631
contained
the
statement
that
there
were
no
observed
interferences
in
determination
of
mercury
by
Method
1631.
Commenters
on
the
proposal
pointed
out
that
precious
metals
(
primarily
gold),
were
interferents,
and
that
high
concentrations
of
iodide
and
organic
matter
could
be
interferents.
After
consideration
and
confirmation
of
the
comments,
EPA
revised
the
language
in
Method
1631
to
state
that
gold
and
iodide
were
known
interferents.
This
guidance
provides
suggestions
for
overcoming
potential
interferences,
procedures
for
demonstrating
that
a
matrix
interference
exists,
and
procedures
for
calculating
matrix­
specific
MDL/
MLs.

Frequently
asked
questions
This
guidance
also
gives
details
concerning
the
flexibility
inherent
in
Method
1631
and
provides
answers
to
frequently
asked
questions
(
FAQs).
For
ease
of
use,
Chapters
2
through
5
are
presented
in
question
and
answer
format.
In
each
question,
the
pronouns
"
I"
and
"
we"
refer
to
the
questioner
whereas
the
pronoun
"
you"
refers
to
EPA.
In
the
answers,
the
pronouns
"
we,"
"
us,"
and
"
our"
refer
to
EPA
whereas
the
pronouns
"
you"
and
"
your"
refer
to
the
questioner
and
to
other
users
of
Method
1631.

While
this
guidance
attempts
to
address
issues
and
situations
pertinent
to
Method
1631,
it
also
identifies
and
references
other
analytical
methods
and
sampling
techniques
and
provides
a
list
of
EPA
and
other
authorities
to
contact
for
additional
information
and
guidance.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
2­
1
Chapter
2:
Use
of
"
Clean"
Techniques
to
Preclude
Contamination
This
chapter
discusses
the
techniques
that
may
be
used
to
preclude
contamination,
how
to
determine
if
contamination
exists,
and
how
to
evaluate
the
effects
of
contamination
on
results.
For
information
on
the
specific
contamination
control
techniques
required
for
use
with
Method
1631,
refer
to
Guidelines
Establishing
Test
Procedures
for
the
Analysis
of
Pollutants;
Measurement
of
Mercury
in
Water
(
Method
1631,
Revision
B);
Final
Rule
at
40
CFR
part
136,
published
in
the
Federal
Register
(
64
FR
30417;
June
8,
1999).
For
additional
information
on
the
techniques
that
may
be
helpful
in
precluding
contamination
when
Method
1631
is
used,
refer
to
the
Sampling
Guidance
(
EPA
Method
1669:
Sampling
Ambient
Water
for
Trace
Metals
at
EPA
Water
Quality
Criteria
Levels,
EPA­
821­
R­
96­
011)
and
video
(
Sampling
Ambient
and
Effluent
Waters
for
Trace
Metals,
EPA
821­
V­
97­
001).

What
is
the
contamination
control
philosophy
behind
Method
1631
?

The
philosophy
behind
contamination
control
is
to
reduce
or
eliminate
contamination
in
order
to
produce
a
reliable
result.
The
basis
of
this
philosophy
is
given
in
the
Sampling
Guidance
(
EPA
Method
1669):
"
The
philosophy
behind
contamination
control
is
to
ensure
that
any
object
or
substance
that
contacts
the
sample
is
nonmetallic
and
free
from
any
material
that
may
contain
metals
of
concern."
This
means
that
mercury
in
the
sample
bottle,
reagents,
laboratory,
and
labware
is
eliminated
or
reduced
to
a
level
that
will
not
compromise
the
measurement.
It
also
means
that
mercury
is
eliminated
or
reduced
from
air
in
the
laboratory
and
must
be
prevented
from
entering
the
sample
at
the
sampling
site.

Laboratories
that
have
been
conducting
measurements
with
Method
1631
for
years,
such
as
those
that
participated
in
EPA's
validation
studies
(
see
Interlaboratory
Validation
Study
Report
in
the
Water
Docket
for
proposal
of
Method
1631),
have
addressed
the
laboratory
aspects
of
contamination
control.
These
laboratories
demonstrated
in
the
method
validation
study,
that
they
were
capable
of
controlling
contamination
to
levels
that
would
not
compromise
reliable
mercury
determinations.
For
a
laboratory
that
is
just
preparing
to
conduct
measurements
using
Method
1631,
we
have
made
several
documents
available.
These
documents
are
Method
1631
itself,
the
Sampling
Guidance
(
EPA
Method
1669),
Guidance
on
Establishing
Trace
Metals
Clean
Rooms
in
Existing
Facilities
(
EPA
821­
B­
95­
001;
colloquially
known
as
the
"
Clean
Spaces
Guidance"),
and
a
document
produced
under
contract
to
EPA
by
the
Research
Triangle
Institute
(
RTI)
titled
"
Trace
Metal
Cleanrooms"
(
RTI/
6302/
04­
02
F).
These
documents,
in
combination,
will
impart
the
philosophy
needed
to
allow
your
laboratory
to
make
reliable
mercury
determinations
at
levels
as
low
as
can
be
measured
by
Method
1631.

What
are
"
clean"
techniques
and
how
are
they
used
?

As
stated
in
Chapter
1
of
this
guidance,
"
clean"
is
not
a
specific
set
of
steps
or
procedures,
but
rather
a
philosophy
of
field
and
laboratory
techniques
designed
to
preclude
contamination.
Specific
techniques
may
vary
among
laboratories
or
sites,
but
when
appropriately
applied,
clean
techniques
result
in
contaminantfree
measurements.
Some
specific
requirements
for
controlling
contamination
are
given
in
Method
1631
and
further
suggestions
are
provided
in
the
Sampling
Guidance
(
EPA
Method
1669).

The
greatest
risk
from
contamination
in
sampling
and
analysis
for
mercury
occurs
during
sample
collection
because
the
sample
container
is
opened
and
filled
in
an
uncontrolled
environment.
The
Sampling
Guidance
identifies
the
precautions
that
can
be
taken
to
avoid
sample
contamination,
and
includes
a
detailed
description
of
the
"
clean
hands/
dirty
hands"
technique
commonly
used
by
researchers
when
collecting
water
samples
that
will
be
analyzed
for
mercury.
This
technique
is
demonstrated
in
the
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
2­
2
Trace
Metals
Sampling
video
(
EPA­
821­
V­
97­
001).
In
this
technique,
a
person
designated
as
"
clean
hands"
handles
all
operations
involving
direct
contact
with
the
sample
bottle.
"
Dirty
hands"
is
responsible
for
all
activities
that
do
not
involve
direct
contact
with
the
sample
bottle.
(
See
Section
8.2.3
of
the
Sampling
Guidance.)
This
division
of
responsibility
precludes
contamination
by
controlling
how
the
sample
is
handled
during
collection
and
preparation
for
shipment
to
the
laboratory.

It
is
also
possible
for
sample
contamination
to
occur
from
the
sampling
equipment
used
or
in
the
laboratory.
The
sample
collection
team
must
use
collection
bottles
and
equipment
that
have
been
demonstrated
to
be
clean
(
Section
9.4.4).
The
laboratory
should
demonstrate
that
the
laboratory
equipment
is
free
of
contamination
and
also
must
demonstrate
that
the
reagents
used
are
free
of
contamination
(
Section
9.4.2)
The
laboratory
environment
can
be
controlled
and
made
free
from
mercury
by
using
steps
described
in
Method
1631
and
in
the
Clean
Spaces
and
Trace
Metal
Cleanroom
guidance
documents
cited
previously
and
referenced
in
Chapter
6
of
this
Guidance.

What
level
of
contamination
control
is
required
?

The
terms
"
shall"
and
"
must"
in
Method
1631,
Revision
B
define
procedures
that
are
required
for
producing
reliable
data.
The
terms
"
should"
and
"
may"
indicate
optional
steps
that
may
be
modified
or
omitted
if
the
laboratory
can
demonstrate
that
the
modified
method
produces
equivalent
or
superior
results.
The
following
clean
techniques
are
requirements
of
Method
1631,
Revision
B:

C
Sampling
personnel
must
wear
clean,
non­
talc
latex
gloves
during
all
operations
involving
handling
of
the
Apparatus,
samples,
and
blanks
(
Section
4.3.6).
Non­
talc
vinyl
or
polyethylene
gloves
may
be
substituted
to
avoid
allergic
reactions
to
latex
and
to
sample
for
metals
other
than
mercury,
provided
that
the
gloves
would
not
compromise
measurement
of
mercury
at
the
levels
required.
C
All
apparatus
used
for
determination
of
mercury
at
ambient
water
quality
criteria
levels
must
be
nonmetallic,
or
free
of
material
that
may
contain
metals,
or
both
(
Section
4.3.7).
C
All
materials
that
will
directly
or
indirectly
contact
the
sample
must
be
cleaned
using
the
procedures
in
Method
1631
and
must
be
known
to
be
clean
and
mercury­
free
before
proceeding
(
Sections
4.3.7.1
and
6.0).
C
Sampling
must
not
proceed
if
it
is
possible
that
the
Apparatus
is
contaminated
(
Section
4.3.7.3).
C
Use
clean
fluoropolymer
or
glass
sample
bottles
(
Section
4.3.7.1).
C
Reagent
blanks
must
be
analyzed
for
contamination
prior
to
use.
If
reagent
blanks
are
contaminated,
a
new
batch
of
reagents
must
be
prepared
(
Section
4.3.8.5)
C
Each
laboratory
must
perform
and
meet
the
minimum
requirements
of
Method
1631
Quality
Control
(
Section
9.0).
For
details
on
these
requirements,
see
the
answer
to
the
FAQ
"
What
quality
control
(
QC)
tests
are
required
by
Method
1631
and
what
performance
criteria
must
be
met?"

The
following
additional
techniques
may
further
aid
in
identifying
or
precluding
contamination:

°
Sampling
personnel
should
be
trained
in
techniques
for
sampling
mercury
at
low
levels.
°
Collect
samples
using"
Clean
Hands/
Dirty
Hands"
sampling
techniques
described
in
Method
1669.
°
The
frequency
of
blank
samples
can
be
increased
beyond
that
required
by
Method
1631
(
e.
g.,
field
blanks
may
be
collected
at
each
site
immediately
before
and
after
sample
collection,
reagent
blanks
can
be
analyzed
daily).
°
Establish
and
maintain
a
laboratory
QA
program
with
control
limits
to
monitor
laboratory
air,
reagent
water,
acid
vats,
and
work
surfaces.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
2­
3
The
extent
of
contamination
control
that
may
be
necessary
varies.
For
example,
while
observing
sampling
for
mercury
and
other
metals
in
San
Francisco
Bay,
EPA
noted
that
researchers
were
able
to
use
precleaned
and
double­
bagged
equipment
and
non­
talc
latex
gloves
as
their
only
form
of
contamination
control.
In
contrast,
we
also
evaluated
techniques
in
which
sampling
technicians
led
by
Dr.
Carl
Watras
wore
precleaned
wind
suits,
hats,
shoulder­
length
gloves,
and
latex
gloves
to
collect
samples
from
Trout
Lake
Station,
Wisconsin.
Each
group
of
researchers
used
contamination
control
techniques
that
had
been
demonstrated
(
through
repeated
collection
of
clean
field
blanks)
to
be
appropriate
for
the
environment
being
sampled.
Later,
we
retained
Dr.
Watras
for
a
1994
study
that
required
sampling
several
publicly­
owned
treatment
works
(
POTWs)
in
the
Great
Lakes
Basin.
In
this
study,
sampling
crews
wore
precleaned
suits,
hats,
and
shoulder­
length,
non­
talc
latex
gloves.
The
only
sample
that
demonstrated
contamination
was
collected
during
a
rainstorm.
In
a
later
study
conducted
during
1996
and
1997,
we
collected
samples
from
two
POTWs
in
the
Great
Lakes
Basin
to
evaluate
several
types
of
clean
sampling
techniques.
This
evaluation
included
a
comparison
of
samples
collected
when
wearing
only
latex
gloves
vs.
the
use
of
gloves
and
precleaned
wind
suits.
In
general,
we
found
that
latex
gloves
were
necessary
and
that
the
wind
suits
did
make
some
difference.
(
Recognizing
that
some
people
can
be
sensitive
to
latex,
use
of
clean,
non­
talc
gloves
made
from
other
materials;
e.
g.,
vinyl
or
polyethylene,
may
also
be
acceptable.)
Results
from
the
1994
study
and
the
1996/
1997
study
are
presented
in
separate
reports
referenced
at
the
end
of
this
guidance
(
An
Analytical
Survey
of
Nine
POTWs
from
the
Great
Lakes
Basin,
12/
15/
94
and
Evaluating
Field
Techniques
for
Collecting
Effluent
Samples
for
Trace
Metals
Analysis,
EPA
821­
R­
98­
008).

What
level
of
contamination
control
and
clean
techniques
should
be
required
for
compliance
monitoring
under
National
Pollutant
Discharge
Elimination
System
("
NPDES")
permits
?

EPA
believes
that
the
use
of
clean
techniques
is
necessary
when
analyzing
samples
at
low
water
quality
criteria
levels
such
as
those
established
in
the
Great
Lakes
Guidance.
For
this
reason,
we
recommend
that
state
and
federal
agencies
measuring
ambient
water
quality
for
compliance
with
water
quality
standards
at
very
low
concentrations
should
require,
as
a
matter
of
internal
agency
protocol,
that
their
personnel
use
clean
techniques.
However,
we
have
avoided
specifying
an
exact
suite
of
protocols
that
must
be
employed
in
every
NPDES
compliance
monitoring
situation
because
some
of
these
protocols
may
vary
according
to
the
experience
of
the
sampling
teams
and
analytical
laboratory,
the
environment
from
which
the
sample
is
collected,
and
the
permit
limit
(
some
water
quality­
based
permit
limits
are
higher
than
others).

EPA
suggests
that
NPDES
permits
specify
the
use
of
clean
techniques,
on
a
permit­
by­
permit
basis,
depending
on
the
measurement
level
of
concern,
upon
request
by
the
permit
applicant.
For
discharger
or
facilities
required
to
meet
the
ambient
criterion
of
12
ng/
L
in
the
National
Toxics
Rule
(
58
FR
60848;
40
CFR
131.36)
or
lower,
a
prudent
course
would
be
to
institute
all
of
the
clean
techniques
recommended
in
Method
1631
and
in
this
Guidance.

EPA
is
planning
to
propose
additional
requirements
for
clean
techniques
by
October
2001.
Following
review
of
public
comments,
EPA
will
take
final
action
to
establish
any
additional
requirements
by
October
2002.
At
that
time,
EPA
may
revise
this
Guidance
in
accordance
with
the
new
requirements.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
2­
4
How
will
I
know
if
my
sample
is
contaminated
?

In
general,
if
the
performance
criteria
specified
in
Method
1631
are
met,
samples
can
be
considered
uncontaminated
and
collection
and
analytical
clean
techniques
can
be
considered
sufficient.
The
best
way
to
determine
if
contamination
has
occurred
during
sampling
is
to
collect
a
sufficient
number
of
field
blanks
and
equipment
blanks.
Section
9.4.3.1
of
Method
1631
requires
collection
of
at
least
one
field
blank
for
each
set
of
samples
(
samples
collected
from
the
same
site
at
the
same
time,
to
a
maximum
of
ten
samples).
The
Method
also
requires
analysis
of
sampling
equipment
blanks
(
Section
9.4.4).
Field
blanks
are
produced
by
transferring
reagent
water
that
is
carried
to
the
site
into
a
sample
bottle
at
the
same
time
(
within
minutes)
that
the
sample
is
collected
and
using
the
same
techniques
that
were
used
to
collect
the
sample.
Equipment
blanks
are
produced
by
rinsing
the
sampling
equipment
with
reagent
water
prior
to
use
and
collecting
the
rinse
water.

If
mercury
is
present
in
the
field
or
equipment
blanks
at
levels
that
would
compromise
reliable
measurement
of
mercury
in
the
sample,
you
should
assume
that
the
sample
was
contaminated
during
collection
or
transit.
If
the
level
in
the
associated
blank(
s)
is
equal
to
or
greater
than
the
ML
or
greater
than
1/
5
the
level
in
the
associated
sample,
whichever
is
higher
(
see
Section
9.4.3
of
Method
1631),
assume
that
the
sample
is
contaminated.
If
the
sample
is
contaminated
during
collection
or
transit,
you
should
eliminate
any
source
of
contamination
that
has
been
identified
and
re­
sample
the
site.
Additional
guidance
concerning
the
interpretation
of
blank
data
is
provided
in
Guidance
on
the
Documentation
and
Evaluation
of
Trace
Metals
Data
Collected
for
Clean
Water
Act
Compliance
Monitoring,
which
is
referenced
in
Chapter
6
of
this
document.

Samples
also
may
be
contaminated
during
laboratory
processing
activities.
You
can
determine
if
your
sample
was
contaminated
in
the
laboratory
by
examining
results
from
the
field,
reagent,
and
bubbler
blanks.
Field
blanks,
reagent
blanks
and
bubbler
blanks
are
required
by
Method
1631
at
Section
9.4.
Please
refer
to
the
question
"
How
can
I
determine
if
the
laboratory
and
my
analytical
system
are
sufficiently
clean?"
below
for
more
information
on
this
subject.

What
"
clean"
techniques
are
necessary
in
the
laboratory
?

The
contamination
control
philosophy
described
above
applies
in
the
laboratory
as
well
as
in
the
field.
Controlling
contamination
in
the
laboratory
starts
with
the
facility.
It
is
best
to
use
a
facility
that
is
not
constructed
of
metal
or
to
build
an
isolated,
non­
metallic
facility
within
the
metallic
facility.
Method
1631
states
that
the
ideal
environment
for
processing
samples
is
a
class­
100
clean
room.
If
such
a
room
is
not
available,
samples
should
be
prepared
in
a
class­
100
clean
bench
or
a
nonmetal
glove
box
fed
by
mercuryand
particle­
free
air
or
nitrogen.
EPA
cautions
that
sample
digestion
with
BrCl
and
mineral
acids
in
a
clean
bench
can
pose
a
significant
health
risk
if
the
bench
blows
air
outward,
toward
the
analyst.
Sample
digestion
should
be
done
in
an
exhaust
hood
that
is
monitored
for
atmospheric
mercury.

Existing
facilities
can
be
made
acceptable
for
use
by
following
the
suggestions
in
the
Clean
Spaces
Guidance
(
EPA
821­
B­
95­
001).
One
suggestion
is
to
paint
the
walls
with
metal­
free
paint
(
epoxy­
or
latex­
based)
to
which
has
been
added
a
small
amount
of
sulfur
powder
to
react
with
mercury
that
could
diffuse
out
of
the
underlying
surfaces.
To
the
extent
practicable,
all
metal
fixtures
and
appliances
should
be
replaced
with
non­
metal
counterparts.
For
new
laboratories
or
laboratories
being
renovated,
non­
metal
cabinetry
is
now
available.
If
any
former
use
of
the
facility
involved
handling
mercury,
the
mercury
has
likely
adsorbed
or
been
amalgamated
into
all
parts
of
the
facility.
In
this
situation,
it
may
be
impossible
to
reduce
the
contamination
to
levels
low
enough
to
allow
measurements
at
the
method
detection
limit
(
MDL)
and
minimum
level
of
quantitation
(
ML)
in
Method
1631
(
0.2
ng/
L
and
0.5
ng/
L,
respectively).
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
2­
5
The
clean
techniques
that
are
currently
required
or
necessary
in
the
laboratory
are
described
above
and
include
equipment
cleaning,
use
of
non­
metallic
areas
and
apparatus,
and
analysis
of
quality
control
samples.
The
following
additional
laboratory
clean
techniques
are
further
recommended,
but
currently
not
required,
for
use
with
Method
1631:

°
Perform
operations
in
a
clean
room
or
clean
bench
(
Section
4.3.3
and
Section
8.5.3).
°
Minimize
exposure
of
the
apparatus
to
potential
sources
of
mercury
(
Section
4.3.4).
°
Clean
all
work
surfaces
in
which
samples
will
be
processed
with
a
lint­
free
cloth
or
wipe
soaked
with
reagent
water
(
Section
4.3.5).
°
When
an
unusually
concentrated
sample
is
encountered,
immediately
analyze
a
bubbler
and
blank
the
traps
to
check
for
carryover
(
Section
4.3.8.1
and
Section
11.2.4).
°
Samples
known
or
suspected
to
contain
the
lowest
concentration
of
mercury
should
be
analyzed
first
followed
by
samples
containing
higher
levels
(
Section
4.3.8.1).
°
Monitor
reagent
water
for
Hg
(
Section
7.1).
°
Samples
known
to
contain
high
levels
of
mercury
(
greater
than
100
ng/
L)
should
be
diluted
prior
to
bringing
them
into
the
clean
room
or
area
(
Section
4.3.8.2).
°
Process
samples
as
far
as
possible
from
sources
of
airborne
contamination
(
Section
4.3.8.4).
°
Bring
outside
air,
which
is
very
low
in
mercury,
directly
into
the
clean
room
air
intake
(
Section
7.2).
°
Avoid
condensation
of
water
in
gold
traps
by
predrying
the
traps
and
discarding
traps
that
absorb
large
quantities
of
water
vapor
(
Section
4.4.3).
°
Pass
the
effluent
from
the
CVAFS
through
either
a
column
of
activated
charcoal
or
a
trap
containing
gold
or
sulfur
to
amalgamate
or
react
mercury
vapors
(
Section
5.3.6).
°
Store
sample
bottles
in
clean
(
new)
polyethylene
bags
until
sample
analysis
(
Section
8.6).

In
summary,
the
best
way
to
control
contamination
is
to
completely
avoid
exposure
of
the
samples
and
the
sample
processing
and
analysis
equipment
to
contamination
in
the
first
place.

How
can
I
determine
if
the
laboratory
and
my
analytical
system
are
sufficiently
"
clean"
?

Determining
that
the
laboratory,
including
the
equipment,
is
sufficiently
clean
involves
running
bubbler
blanks,
reagent
blanks,
and
equipment
blanks
as
necessary,
depending
on
the
suspected
mercury
source.
If
a
blank
is
found
to
contain
mercury
at
a
level
that
could
compromise
measurements,
the
source
of
mercury
contaminating
that
blank
should
be
pursued
and
eliminated
or
reduced
until
the
mercury
emanating
from
that
source
is
sufficiently
controlled.
Section
9.4
of
Method
1631
requires
analysis
of
at
least
three
bubbler
blanks
per
analytical
batch
and
one
reagent
blank
per
batch
of
reagents
with
verification
in
triplicate
each
month
and
provides
levels
of
mercury
contamination
that
could
compromise
reliable
measurements.
EPA's
Guidance
on
the
Documentation
and
Evaluation
of
Trace
Metals
Data
Collected
for
Clean
Water
Act
Compliance
Monitoring
provides
detailed
recommendations
concerning
the
use
and
interpretation
of
laboratory
blank
results.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
2­
6
Can
I
use
off­
the­
shelf
bottles
from
a
bottle
supplier
and
still
comply
with
Method
1631,
Section
4.3.7.1
?

Clean
sample
bottles
play
a
critical
role
on
the
credibility
of
analytical
results.
You
may
use
bottles
"
off
the
shelf"
from
a
bottle
supplier
provided
the
supplier
cleans
the
bottles
using
the
procedures
in
Section
6.1.2.1
or
by
another
procedure
that
will
result
in
bottles
that
will
not
contaminate
samples
(
i.
e.,
result
in
Hg
levels
less
than
the
ML
or
less
than
or
equal
to
one­
fifth
the
Hg
level
of
the
associated
samples).
You
or
the
bottle
supplier
must
run
bottle
blanks
to
demonstrate
that
the
bottles
are
clean
(
Section
9.4.4).
A
representative,
randomly
selected
subset
of
a
lot
should
be
tested
to
show
that
the
bottles
in
the
lot
are
contamination
free.
We
recommend
you
test
a
minimum
of
one
bottle
per
cleaned
batch
or
lot
of
up
to
20
bottles.

How
can
I
prevent
contamination
of
my
laboratory
from
samples
containing
high
concentrations
of
mercury
?

It
would
be
prudent
to
pre­
screen
each
sample
known
or
suspected
to
contain
a
high
concentration
of
Hg
or
in
which
the
Hg
concentration
is
unknown.
Screening
could
be
either
by
cold
vapor
atomic
absorption
spectrometry
(
CVAAS)
or
by
dilution
of
the
sample
by
a
large
factor
(
e.
g.,
100
to
10,000)
and
analysis
by
EPA
Method
1631.

What
other
documents
address
contamination
control
issues
?

This
guidance
is
not
intended
to
be
comprehensive
in
covering
the
subject
of
contamination
control.
For
greater
detail,
see
the
suggestions
in
Method
1631,
Method
1669,
the
Clean
Spaces
Guidance,
"
Trace
Metal
Cleanrooms,"
and
the
additional
references
listed
in
Chapter
6
of
this
guidance.
The
National
Aeronautics
and
Space
Administration,
the
U.
S.
Department
of
Energy,
the
U.
S.
Geological
Survey,
and
other
Government
and
private
sector
organizations
also
have
addressed
the
issue
in
great
detail
over
the
years
and
have
established
systems
based
on
the
contamination
to
be
controlled.
The
philosophy
and
details
of
those
systems
are
incorporated
in
documents
that
are
referenced
in
Methods
1669
and
1631,
and
have
been
used
by
the
authors
of
some
of
the
documents
referenced
in
this
Guidance.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
3­
1
Chapter
3:
Matrix
Interferences
In
the
context
of
EPA
Method
1631,
matrix
interferences
are
non­
mercury
substances
in
a
sample
that
can
interfere
with
or
compromise
reliable
measurement
of
mercury.
Because
EPA
Method
1631
is
performance
based,
the
laboratory
is
permitted
to
modify
the
Method
to
overcome
interferences
provided
performance
criteria
are
met.
This
chapter
discusses
how
matrix
interferences
can
be
identified
and
reduced
or
eliminated.

What
are
the
known
matrix
interferences
in
the
determination
of
mercury
using
Method
1631
?

Section
4.4.1
of
Method
1631
states
"
At
the
time
of
promulgation
of
this
method,
gold
and
iodide
were
known
interferences."
EPA
has
also
received
comments
suggesting
that
high
concentrations
of
organic
matter
may
compromise
measurements
at
low
levels
(<
1
ng/
L)
of
mercury.

How
can
I
determine
that
a
matrix
interference
exists
?

The
best
way
to
determine
that
a
matrix
interference
exists
is
to
analyze
the
matrix
spike/
matrix
spike
duplicate
(
MS/
MSD)
as
described
in
Section
9.3
of
the
Method.
A
recovery
outside
of
the
MS/
MSD
QC
acceptance
criteria
limits
suggests
the
presence
of
an
interference.
If
results
of
the
MS/
MSD
are
similar
but
fail
the
QC
acceptance
criteria
for
recovery,
and
if
results
for
the
initial
precision
and
recovery
(
IPR)
and
ongoing
precision
and
recovery
(
OPR)
tests
are
within
their
respective
QC
acceptance
criteria,
suggestions
in
the
Method
for
reducing
or
eliminating
interferences
should
be
applied.

Another
means
to
determine
if
a
matrix
interference
exists,
particularly
at
low
levels
approaching
the
ML
in
Method
1631,
is
to
analyze
the
sample
in
duplicate.
If
the
relative
percent
difference
(
RPD)
does
not
meet
the
QC
acceptance
criteria
in
Method
1631,
a
matrix
interference
may
be
present.

If
a
sample
is
expected
to
contain
an
interference,
you
may
wish
to
screen
the
sample
prior
to
analysis
for
mercury.
For
gold,
we
estimate
that
a
concentration
roughly
equivalent
to
the
concentration
of
Hg
being
determined
could
interfere.
Gold
can
be
determined
at
the
mg/
L
level
by
sample
concentration
and
ICP/
MS;
iodide
can
be
determined
by
EPA
Method
345.1
(
titrimetry);
and
the
organic
content
can
be
determined
by
TOC
measurement
using
EPA
Method
415.1.

Can
dilution
be
used
to
overcome
matrix
interferences
?

EPA
recognizes
dilution
as
a
means
to
overcome
matrix
interferences
(
see
EPA's
Guidance
on
Evaluation,
Resolution
and
Documentation
of
Analytical
Problems
Associated
with
Compliance
Monitoring;
EPA
821­
B­
93­
001)
and
EPA
Method
1631
does
not
preclude
sample
dilution
to
overcome
matrix
interferences.
Dilution
is,
in
fact,
necessary
for
samples
in
which
the
concentration
of
mercury
exceeds
the
range
of
the
analytical
system.
For
example,
if
a
sample
is
known
or
suspected
to
contain
a
concentration
of
Hg
greater
than
100
ng/
L,
the
sample
can
be
diluted
to
bring
the
concentration
into
the
analytical
range
and
to
avoid
carryover
of
Hg
into
a
subsequent
sample.

Dilution
would
be
inappropriate,
however,
if
the
sample
is
diluted
to
a
mercury
concentration
below
the
minimum
level
of
quantitation
(
ML)
or
the
level
needed
to
determine
regulatory
compliance,
whichever
is
higher.
To
overcome
a
matrix
interference,
a
good
rule
of
thumb
is
to
dilute
the
sample
by
the
minimum
amount
necessary.
If
further
dilution
is
necessary
to
overcome
a
matrix
interference,
do
not
dilute
below
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
3­
2
the
ML.
Samples
can
be
screened
for
dilution
levels
by
analyzing
aliquot
volumes
and
dilution
levels
along
with
MS/
MSD
analyses
until
the
MS/
MSD
results
are
satisfactory.

EPA
believes
that
if
dilution
is
performed
carefully,
the
mercury
concentration
can
remain
within
the
analytical
range
(
above
the
ML)
while
the
effects
of
the
matrix
interference
are
minimized.
For
example,
if
mercury
needs
to
be
measured
at
the
ambient
water
quality
criterion
(
WQC)
of
12
ng/
L
in
the
National
Toxics
Rule,
dilution
of
a
sample
by
a
factor
of
10
would
allow
reliable
measurement
at
this
level.
This
is
because
the
ML
in
Method
1631
is
0.5
ng/
L
and
dilution
of
the
sample
by
a
factor
of
10
would
raise
the
ML
to
5
ng/
L
(
10
x
0.5
ng/
L).
This
ML
is
still
well
below
the
12
ng/
L
required.

In
recognition
that
matrix
characteristics
can
change,
EPA
cautions
that
the
need
for
sample
dilution
should
not
only
be
matrix­
specific,
but
also
should
be
determined
each
time
a
sample
from
a
particular
site
is
analyzed.
It
is
also
possible
that
the
matrix
characteristics,
including
matrix
interferences,
may
remain
constant
with
time.
If
two
consecutive
samples
from
a
given
discharge
require
the
same
amount
of
dilution
to
meet
the
QC
acceptance
criteria,
subsequent
samples
should
be
diluted
to
that
level,
unless
there
is
an
indication
that
the
matrix
characteristics
have
changed
and
dilution
would
not
be
sufficient
or
needed
to
overcome
a
matrix
interference.

For
those
instances
in
which
dilution
is
inappropriate,
specific
procedures
given
in
EPA
Method
1631
and
presented
below
for
overcoming
interferences
should
be
applied.

How
can
I
overcome
a
matrix
interference
?

Because
every
situation
is
different,
we
can
not
specify
a
single
detailed
or
rigorous
protocol
for
overcoming
every
matrix
interference.
The
following
general
suggestions
are
offered
to
guide
the
laboratory
in
attempting
to
overcome
the
interference:

The
first
step
should
be
to
evaluate
the
effect
of
dilution
on
the
level
that
needs
to
be
measured.
For
example,
if
the
regulatory
compliance
level
is
5
ng/
L,
the
sample
can
be
diluted
by
as
much
as
a
factor
of
10
and
reliable
measurements
can
still
be
made
because
the
ML
will
be
raised
to
5
ng/
L.
To
make
the
most
reliable
measurement,
the
minimum
amount
of
dilution
should
be
used.
Continuing
with
the
example,
if
dilution
by
a
factor
of
2
would
eliminate
the
interference
(
as
determined
by
MS/
MSD
recoveries
within
the
QC
acceptance
criteria
in
EPA
Method
1631),
this
minimum
amount
of
dilution
should
be
used.
We
suggest
dilution
in
successive
factors
of
2
until
the
QC
acceptance
criteria
for
the
MS/
MSD
are
met,
followed
by
dilution
by
an
additional
factor
of
2
(
as
additional
assurance),
provided
that
the
concentration
remains
above
the
ML.

Another
means
for
overcoming
matrix
interferences
is
the
method
of
standard
additions
(
MSA).
MSA
is
described
in
Methods
for
Chemical
Analysis
of
Water
and
Waste
(
EPA­
600/
4­
79­
020,
Revised
March
1983;
NTIS
PB84­
123677)
and
in
Standard
Methods
for
the
Examination
of
Water
and
Wastewater.
For
MSA,
a
minimum
of
5
separate
concentrations
within
the
linear
range
of
the
analytical
system,
including
one
unspiked
sample,
is
recommended.

If
dilution
or
MSA
are
unsuccessful,
there
should
be
an
attempt
to
determine
the
cause
of
the
interference.
If
the
interference
is
caused
by
iodide,
gold,
or
biota,
these
can
be
overcome
using
the
procedures
recommended
in
Method
1631
and
presented
in
response
to
the
questions
below.
In
this
Guidance,
we
have
attempted
to
provide
the
latest
techniques
successfully
being
used
to
overcome
the
few
interferences
that
are
known
regarding
the
use
of
Method
1631.
If
the
interference
cannot
be
identified
and
overcome,
the
technical
literature
and
experts
in
the
field
of
trace
mercury
determinations
using
EPA
Method
1631
can
be
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
3­
3
consulted.
As
technology
develops,
the
literature
and
these
experts
would
have
the
latest
information
for
overcoming
matrix
interferences.
In
general
these
experts
reside
in
the
laboratories
that
participated
in
EPA's
inter­
laboratory
validation
study
of
EPA
Method
1631
("
Results
of
the
EPA
Method
1631
Validation
Study,"
February,
1998,
available
from
the
EPA
Sample
Control
Center,
6101
Stevenson
Ave,
Alexandria,
VA,
22304;
703­
461­
2100;
SCC@
dyncorp.
com).
We
also
suggest
performance
of
an
intercomparison
study
with
one
of
these
laboratories
to
confirm
the
presence
of
the
matrix
effect.

If
the
matrix
interference
remains
intractable,
regulatory
relief
may
be
appropriate.
For
a
discussion
of
regulatory
relief,
please
see
the
response
to
the
question
"
How
can
I
demonstrate
that
my
inability
to
meet
the
QC
acceptance
criteria
for
the
MS/
MSD
is
attributable
to
a
matrix
interference
rather
than
a
laboratory
performance
deficiency?"

What
is
the
nature
of
the
iodide
interference
and
how
can
it
be
overcome
?

Section
4.4.1
of
Method
1631
states:
"
At
a
mercury
concentration
of
2.5
ng/
L
and
at
increasing
iodide
concentrations
from
30
to
100
mg/
L,
test
data
have
shown
that
mercury
recovery
will
be
reduced
from
100
to
0
percent.
At
iodide
concentrations
greater
than
3
mg/
L,
the
sample
should
be
pre­
reduced
with
SnCl2
(
to
clarify
the
brown
color),
and
additional
SnCl2
should
be
added
to
the
bubbler.
If
samples
containing
iodide
concentrations
greater
than
30
mg/
L
are
analyzed,
it
may
be
necessary
to
clean
the
analytical
system
with
4
N
HCl
after
the
analysis."

Another
means
for
overcoming
an
iodide
interference
was
given
in
an
attachment
to
a
comment
on
proposal
of
Method
1631.
In
this
case,
a
discharger's
laboratory
observed
that
mercury
was
being
complexed
by
high
(
30
­
40
mg/
L)
concentrations
of
iodide
in
the
wastewater
when
using
EPA
Method
245.1.
The
laboratory
added
a
small
amount
of
sodium
tetrahydroborate
to
aid
in
the
reduction
of
mercury
so
that
the
mercury
could
be
purged
from
solution
and
determined.

Is
it
possible
to
overcome
an
interference
from
gold
in
the
sample
?

No.
Free
mercury
in
the
wastewater
will
amalgamate
with
gold
and
cannot
be
separated
by
the
techniques
in
Method
1631.
This
interference
can
occur
in
precious
metals
mining
operations.
Permitting
authorities
should
work
with
permittees
on
a
case­
by­
case
basis
to
determine
appropriate
actions
and
regulatory
controls
when
gold
interferences
are
present.

Because
the
atomic
weights
of
gold
and
mercury
are
nearly
identical,
a
concentration
of
gold
in
a
sample
equal
to
the
mercury
concentration
could,
potentially,
amalgamate
all
of
the
Hg
and
prevent
the
mercury
from
being
released
and
purged
in
EPA
Method
1631.
If
the
concentration
of
a
sample
is
not
being
checked
against
a
limit,
the
spike
level
for
the
MS/
MSD
is
5
ng/
L
(
Method
1631,
Section
9.3.1).
Therefore,
potentially,
5
ng/
L
of
gold
could
prevent
the
QC
acceptance
criteria
for
the
MS/
MSD
from
being
met.
If
an
interference
from
gold
is
suspected,
the
method
of
standard
additions
may
aid
in
determining
that
gold
is
amalgamating
mercury
and
causing
reduced
recovery
of
the
MS/
MSD.

The
laboratory
is
responsible
for
controlling
gold
interference
that
may
be
the
result
of
laboratory
contamination.
EPA
Method
1631
recommends
that
care
be
taken
to
prevent
gold
contamination
of
samples
by
protecting
gold
traps
from
free
halogens
or
overheating,
and
replacing
the
traps
or
gold
air
filters
if
they
are
degrading.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
3­
4
What
if
high
concentrations
of
organic
matter
are
present
?

A
symptom
of
an
interference
caused
by
a
sample
containing
a
high
concentration
of
organic
matter
is
that
the
sample
may
foam
when
purged.
If
this
indication
of
an
organic
interference
is
encountered,
purge
a
fresh
charge
of
reagent
water
in
the
bubbler
for
at
least
10
minutes
and
discard
the
water.

One
technique
for
overcoming
an
organic
interference
is
by
diluting
a
smaller
sample
aliquot
with
reagent
water.
If
necessary
to
measure
at
a
compliance
level,
a
large
volume
of
this
diluted
aliquot
can
be
used.
Sections
11.1.1.1
and
11.1.1.2
of
Method
1631
also
recommend
that
samples
containing
high
concentrations
of
organic
matter,
such
as
biota,
be
oxidized
with
additional
BrCl
in
order
to
release
mercury
that
may
be
bound
to,
or
complexed
with,
the
organic
materials.

Method
1631,
Sections
3.1
and
11.1
suggests
that
recovery
of
mercury
bound
within
microbial
cells
may
require
increased
BrCl,
elevated
temperatures,
or
the
additional
step
of
photo­
oxidation
with
ultra­
violet
(
UV)
light.
Specific
procedures
for
using
the
techniques
are
provided
in
response
to
the
question
below.
An
attachment
to
a
comment
on
the
proposal
of
Method
1631
gave
an
example
in
which
a
laboratory
determined
that
an
increased
amount
of
BrCl
and
heat
could
be
used
successfully
to
oxidize
organic
matter
present
in
a
particular
effluent.

As
of
the
date
of
this
Guidance,
EPA
is
not
aware
of
matrices
for
which
Method
1631
procedures
or
these
additional
oxidation
techniques
have
not
been
sufficient
for
overcoming
organic
interferences,
and
for
this
reason,
EPA
does
not
have
data
which
indicate
levels
of
organic
matter
that
may
exceed
the
capability
of
Method
1631.
It
is
important
to
remember
that
if
additional
reagents,
heat,
or
photo­
oxidation
are
used
for
complete
oxidation
of
samples,
the
corresponding
quality
control
samples
and
the
initial
demonstration
of
capability
(
IPR
and
MDL)
tests
also
should
include
the
additional
amounts
of
reagents,
heat,
or
photooxidation

What
are
the
specific
procedures
for
use
of
additional
BrCl
or
UV
photo­
oxidation
?

Section
11.1.1.1
of
Method
1631
states
that
the
amount
of
BrCl
added
to
a
clear
or
filtered
100­
mL
sample
is
0.5
mL
(
see
Section
7.6
of
Method
1631
for
details
of
the
BrCl
solution)
and
the
amount
added
to
a
brown
or
turbid
sample
is
1.0
mL.
Section
11.1.1.2
of
Method
1631
suggests
addition
of
up
to
5
mL
of
BrCl
solution
for
highly
organic
samples.
This
additional
solution
is
added
to
a
100­
mL
sample
in
the
sample
bottle
(
see
Method
11.1.1
of
Method
1631).
If
necessary,
more
BrCl
can
be
added.
A
commenter
on
this
Guidance
warns
that
a
high
concentration
of
BrCl
in
the
bubbler
can
ruin
the
soda
lime
and
gold
traps
and
show
up
as
a
matrix
interference
itself.
For
this
reason,
it
is
important
to
make
sure
that
all
BrCl
is
reduced
prior
to
purging
(
if
possible).
If
this
is
not
possible,
then
an
analytical
spike
should
be
performed
to
show
that
the
system
is
free
from
interference
(
see
Section
11.2
of
Method
1631).
Because
the
sample
is
thoroughly
purged
during
the
purge­
and­
trap
step,
the
additional
volume
associated
with
the
BrCl
should
have
no
effect
on
purge
efficiency.

During
photo­
oxidation,
samples
are
placed
in
quartz
or
thin­
walled
fluoropolymer
bottles
and
then
placed
in
a
UV­
oxidation
chamber
for
6
to
8
hours.
Following
oxidation,
the
samples
are
allowed
to
cool
to
room
temperature
prior
to
analysis.
Samples
containing
significant
particulate
matter
may
be
periodically
shaken,
or
the
chamber
placed
on
an
orbital
shaker,
to
keep
the
particles
in
the
photon
flux.
Alternatively,
samples
in
quartz
bottles
containing
a
fluoropolymer
stirring
bar
are
placed
adjacent
to
a
high­
intensity
(>
100
F
watt/
cm2)
UV
lamp
and
oxidized
for
a
minimum
of
2
hours
until
oxidation
is
complete.
Oxidation
is
considered
complete
for
samples
in
which
a
yellow
color
remains
following
photo­
oxidation,
but
disappears
with
the
addition
of
the
hydroxylamine
hydrolchloride
(
NH2OH.
HCl).
If
however,
the
yellow
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
3­
5
color
disappears
during
photo­
oxidation,
additional
BrCl
should
be
added,
and
the
sample
returned
to
the
UV­
oxidation
chamber.
Complete
oxidation
can
also
be
assessed
using
starch
iodide
indicating
paper
to
test
for
residual
free
oxidizer
(
Method
1631,
Section
11.1.2).

Again,
if
additional
reagents
or
UV
photo­
oxidation
are
used
for
complete
oxidation
of
samples,
the
corresponding
quality
control
samples
and
the
IPR
and
MDL
tests
also
should
include
the
additional
amounts
of
reagents
or
UV
photo­
oxidation
steps.

Can
the
non­
homogeneity
of
a
sample
containing
high
solids
result
in
failure
of
the
MS/
MSD
?

If
the
MS/
MSD
RPD
for
a
high­
solids
matrix
does
not
meet
the
RPD
performance
criterion,
there
may
be
a
problem
with
sample
preparation
or
homogenization.
Section
11.1.1
of
Method
1631
requires
thorough
shaking
to
homogenize
the
sample.
As
of
the
date
of
this
Guidance,
we
have
not
had
reports
that
high
solids
have
presented
a
problem
in
meeting
the
MS/
MSD
precision
and
recovery.

How
can
I
demonstrate
that
my
inability
to
meet
the
QC
acceptance
criteria
for
the
MS/
MSD
is
attributable
to
a
matrix
interference
rather
than
a
laboratory
performance
deficiency
?

The
initial
precision
and
recovery
(
IPR),
ongoing
precision
and
recovery
(
OPR),
blank,
matrix
spike
and
matrix
spike
duplicate
(
MS/
MSD),
and
quality
control
sample
(
QCS)
tests
in
Section
9
of
Method
1631
allow
separation
of
these
variables.
In
general,
if
the
blank
and
IPR/
OPR
tests
are
failed,
there
is
a
laboratory
performance
deficiency,
and
the
laboratory
is
responsible
for
identifying
and
correcting
the
deficiency
and
repeating
the
blank
and
IPR/
OPR
tests
(
Method
1631,
Section
9.2).
If
results
for
the
blank
and
IPR/
OPR
tests
are
within
the
QC
acceptance
criteria,
and
the
relative
percent
difference
(
RPD)
QC
acceptance
criterion
for
the
MS/
MSD
test
is
failed,
the
problem
is
likely
attributable
to
a
sample
that
is
insufficiently
homogenized
or
to
imprecise
aliquotting
or
spiking
of
the
MS/
MSD.
In
this
case,
the
laboratory
should
evaluate
the
cause,
correct
the
problem,
and
re­
spike
the
MS/
MSD.
If
the
RPD
for
the
MS/
MSD
remains
above
the
QC
acceptance
criterion,
the
laboratory
should
run
a
duplicate
OPR
to
assure
that
precision
is
being
controlled.
If
the
RPD
for
the
duplicate
OPR
is
within
the
QC
acceptance
criterion
for
the
MS/
MSD,
the
laboratory
should
dilute
the
sample
in
successive
factors
of
2
to
determine
if
a
matrix
interference
is
causing
the
imprecision.

If
the
blank,
IPR,
OPR,
and
MS/
MSD
precision
are
within
their
respective
QC
acceptance
criteria
and
the
MS
and
MSD
recoveries
are
not,
a
matrix
interference
is
present,
and
the
matrix
interference
needs
to
be
overcome.
If
the
matrix
interference
cannot
be
overcome,
results
of
associated
samples
may
not
be
reported
or
used
for
permitting
or
regulatory
compliance
purposes
(
Section
9.3.4.1).

If
all
suggestions
given
in
EPA
Method
1631
and
this
Guidance
are
unsuccessful
in
overcoming
the
interference,
the
discharger/
permittee
should
submit
the
following
information
to
the
regulatory/
control
authority
to
demonstrate
that
regulatory
relief
may
be
appropriate:

C
MDL,
IPR,
and
blank
data
demonstrating
that
the
laboratory
can
perform
Method
1631
C
Field,
equipment,
and
reagent
blank
data
demonstrating
that
the
sampling
and
analysis
systems
are
free
from
contamination
at
the
levels
required
for
reliable
determination
of
mercury.
Such
blank
data
should
be
associated
with
the
sample
under
evaluation.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
3­
6
C
MS/
MSD
data
demonstrating
that
a
potential
matrix
interference
exists
because
the
recoveries
and
precision
are
not
within
the
QC
acceptance
criteria
of
the
Method
C
Confirmation
of
the
out­
of­
specification
MS/
MSD
recovery
by
a
second
laboratory
C
Steps
taken
to
attempt
to
mitigate
the
interference
(
e.
g.,
dilution;
addition
of
a
greater
amount
of
BrCl;
addition
of
NH2OH.
HCl;
use
of
UV
photo­
oxidation;
etc.)

Once
these
data
are
received
by
the
regulatory/
control
authority,
the
authority
may
make
a
determination
that
Method
1631
indeed
does
not
produce
reliable
results
for
the
measurement
of
mercury
in
that
test
sample
matrix
and
that
regulatory
relief
may
be
appropriate.
An
example
of
possible
relief
that
is
used
in
other
EPA
methods,
is
to
dilute
the
sample
with
reagent
water
until
the
QC
acceptance
criteria
are
met.
In
cases
where
dilution
results
in
an
increased
MDL/
ML
level,
compliance
would
be
evaluated
at
the
least
dilute
level
at
which
the
QC
acceptance
criteria
could
be
met.
EPA
would
provide
assistance
to
the
regulatory/
control
authority,
upon
request,
to
assist
in
this
determination
in
the
event
that
the
regulatory/
control
authority
does
not
have
the
technical
expertise
to
make
the
determination.

Shouldn't
EPA
allow
regulatory
relief
when
a
matrix
interference
is
demonstrated
?

Method
1631
is
performance­
based.
This
means
the
laboratory
is
permitted
to
modify
the
Method
to
overcome
interferences
or
lower
the
cost
of
measurement
provided
that
all
performance
criteria
are
met.
EPA
supports
solutions
for
overcoming
matrix
interference
problems
so
that
mercury
can
be
measured
at
levels
that
could
have
an
adverse
effect
on
human
health
and
the
environment.

EPA
believes
that
an
automatic
allowance
for
matrix
effects
is
inappropriate
and
would
provide
a
disincentive
for
addressing
interferences
that
may
be
overcome
easily
using
the
procedures
recommended
in
Method
1631.
EPA
has
also
provided
suggestions
in
Guidance
on
Evaluation,
Resolution,
and
Documentation
of
Analytical
Problems
Associated
with
Compliance
Monitoring
(
EPA
821­
B­
93­
001)
and
in
this
Guidance
to
aid
dischargers
and
laboratories
in
overcoming
matrix
interference
problems.
We
also
believe
that
a
given
discharger
is
most
familiar
with
its
wastewater
and
can
find
solutions
to
matrix
interference
problems.
Some
examples
for
overcoming
interferences
were
submitted
to
EPA
in
attachments
to
comments
on
Method
1631
proposal
and
were
discussed
earlier
as
techniques
for
overcoming
iodide
and
organic
interferences.

A
site­
specific
or
facility­
specific
allowance
may
be
warranted
after
all
efforts
to
remove
interferences
have
been
exhausted,
and
should
be
handled
on
a
case­
by­
case
basis
by
the
regulatory/
control
authority.
See
the
response
to
the
preceding
question,
the
questions
below,
and
the
FAQs
for
further
information
on
what
may
be
appropriate
regulatory
relief
when
a
matrix
interference
has
been
demonstrated
and
all
attempts
at
overcoming
this
interference
have
been
made.

How
can
I
expect
Method
1631
to
perform
in
the
presence
of
matrix
interferences
?

Statements
of
the
performance
of
Method
1631
are
estimates
based
on
EPA's
evaluation
in
various
Method
1631
performance
studies
using
reagent
water,
fresh
water,
marine
water,
and
wastewater
matrices.
Section
1.5
of
Method
1631
states:
"
The
detection
limit
and
minimum
level
of
quantitation
in
this
Method
usually
are
dependent
on
the
level
of
interferences
rather
than
instrumental
limitations."
We
believe
most
interferences
can
be
overcome
by
procedures
recommended
in
the
Method
and
in
this
Guidance,
however,
it
is
possible
that
the
Method
may
not
achieve
these
performance
characteristics
in
every
sample
matrix.

The
Method
1631
MDL
was
determined
to
be
0.2
ng/
L
when
no
interferences
are
present.
Therefore,
the
MDL
and
ML
should
be
treated
as
"
presumptive"
performance
characteristics,
and
may
vary
depending
on
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
3­
7
the
presence
of
an
interference
and
on
the
measurement
concentration
of
interest.
The
40
CFR
136,
appendix
B
procedures
for
determining
MDL
state
that
a
sample
may
be
used
for
determining
the
MDL
if
the
analyte
level
does
not
exceed
10
times
the
MDL
of
the
analyte
in
reagent
water.
The
variance
of
the
analytical
method
changes
as
the
analyte
concentration
increases
from
the
MDL,
hence
the
MDL
determined
under
these
circumstances
may
not
truly
reflect
method
variance.

What
permit
relief
is
there
if
I
cannot
achieve
the
MDL
and
ML
in
my
matrix
?

EPA
suggests
that
the
discharger/
permittee
attempt
to
achieve
the
MDL
and
ML
stated
in
Section
1.5
of
Method
1631,
in
the
presence
of
matrix
interferences,
using
the
interference­
reducing
procedures
in
EPA's
Guidance
on
Evaluation,
Resolution,
and
Documentation
of
Analytical
Problems
Associated
with
Compliance
Monitoring
(
EPA
821­
B­
93­
001)
and
contained
in
Method
1631
and
this
Guidance.
These
procedures
include
use
of
a
higher
BrCl
level,
dilution,
heat,
UV
photo­
oxidation,
extra
caution
in
sample
handling,
the
method
of
standard
additions,
and
the
interference­
reducing
procedures
given
in
Section
4.4
of
the
Method.
Use
of
a
larger
sample
volume
may
also
be
particularly
useful
when
the
MDL
in
Method
1631
cannot
be
achieved,
because
the
concentration
of
Hg
will
be
moved
higher
into
the
analytical
range
and
away
from
the
increased
error
that
occurs
in
the
region
of
the
MDL.
We
are
aware
of
laboratories
that
use
sample
volumes
as
large
as
1000
mL,
10
times
larger
than
the
sample
volume
specified
in
Method
1631.
If
a
larger
volume
is
used,
the
instrument
would
need
to
be
calibrated
at
this
larger
volume,
all
performance
tests
(
IPR,
Blank,
OPR,
MS/
MSD)
performed
at
this
larger
volume,
and
all
QC
acceptance
criteria
met.
This
approach
also
may
be
of
use
to
dischargers
and
regulatory
authorities
as
EPA
and
States
develop
policies
for
interim
permitting
and
total
maximum
daily
loads
(
TMDLs)
for
mercury
in
ambient
waters
and
other
applications
of
ambient
WQC
for
mercury.

Use
of
a
gold
wire
to
remove
mercury
selectively
and
the
use
of
oxidation
also
have
been
suggested
for
determining
an
MDL
in
the
sample
matrix
with
high
mercury
concentration.
However,
EPA
cautions
that
mercury
in
environmental
samples
can
be
complexed
with
colloids
and
unavailable
for
amalgamation
with
gold.
Releasing
the
mercury
using
BrCl
oxidation
followed
by
reduction
with
SnCl2
would
modify
the
matrix,
thereby
defeating
the
purpose
of
the
gold
wire.

When
a
discharger/
permittee
demonstrates
that
a
different
MDL/
ML
is
appropriate
for
its
effluent
matrix
based
on
the
statement
in
Section
1.5
of
Method
1631
and
the
MDL
procedure
in
40
CFR
136,
appendix
B,
it
is
possible
that
a
permit
could
specify
a
different
detection
or
quantitation
level.
If
the
discharger/
permit
applicant
demonstrates
that
Method
1631
cannot
achieve
the
presumptive
detection
and
quantitation
limits
on
an
effluent­
specific
basis,
the
discharger/
permittee
and
regulatory/
control
authority
could
work
cooperatively
to
establish
a
higher
reporting
threshold
using
a
procedure
such
as
that
given
at
40
CFR
132,
appendix
F,
Procedure
8
and
to
establish
an
alternative
ML
using
the
procedures
for
developing
an
interim
ML
as
in
EPA's
draft
National
Guidance
for
the
Permitting,
Monitoring,
and
Enforcement
of
Water
Quality­
based
Effluent
Limitations
Set
Below
Analytical
Detection/
Quantitation
Levels
(
available
from
the
EPA
Sample
Control
Center).
EPA
recommends
that
such
procedures
be
applied
by
dischargers/
permittees
and
regulatory/
control
authorities
when
such
interferences
are
demonstrated
in
the
measurement
of
mercury
generally.

The
regulatory
authority
should
take
into
account
the
procedures
used
to
attempt
to
achieve
the
Method
1631
MDL
in
allowing
establishment
of
a
higher
reporting
threshold
based
on
an
inability
to
achieve
the
MDL
and
ML
in
Method
1631.
In
other
words,
EPA
expects
a
discharger
to
make
all
reasonable
attempts
to
reduce
any
interference
problems
before
seeking
approval
of
a
higher
MDL
and
ML.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
4­
1
Chapter
4:
Flexibility
in
EPA
Method
1631
This
chapter
discusses
the
flexibility
inherent
in
EPA
Method
1631
and
the
process
of
demonstrating
equivalent
performance
when
the
Method
is
modified.
This
discussion
is
summarized
from
Method
1631
and
from
Guidance
on
Evaluation,
Resolution,
and
Documentation
of
Analytical
Problems
Associated
with
Compliance
Monitoring
(
EPA
821­
B­
93­
001).

Is
there
flexibility
in
Method
1631
?

Yes.
Method
1631
is
"
performance­
based."
This
means
you
may
modify
the
Method
provided
you
demonstrate
that
your
modification
achieves
performance
equivalent
or
superior
to
the
performance
of
Method
1631.
See
the
FAQ
"
How
can
I
demonstrate
equivalent
or
superior
performance
for
a
method
modification?"
for
details.

What
types
of
modifications
may
I
make
to
Method
1631
?

The
typical
changes
that
would
make
it
easier
for
you
to
practice
the
Method
without
compromising
performance
or
safety
are
allowed.
For
example,
change
of
a
beaker
to
an
Erlenmeyer
flask
or
change
of
a
round
purge
vessel
to
a
cylinder
would
be
allowed,
after
a
demonstration
of
equivalency,
because
they
would
not
be
expected
to
adversely
affect
method
performance.
Changes
that
would
adversely
affect
performance
or
safety
are
not
allowed.
(
Refer
to
Section
9.1.2
of
Method
1631,
excerpted
below).
Any
modification
to
the
Method
beyond
those
expressly
permitted,
is
considered
a
major
modification
and
is
subject
to
application
and
approval
of
alternate
test
procedures
under
40
CFR
136.4
and
136.5.

If
the
modification
is
to
be
permanent
in
the
laboratory
and
the
performance
of
the
analytical
system
could
be
adversely
affected
by
interferents
(
e.
g.,
a
change
in
the
design
of
the
gold
traps
or
a
change
in
the
detector),
the
effect
of
interferents
on
the
performance
of
the
system
should
be
evaluated.

As
stated
in
Section
9.1.2
of
Method
1631,
the
purpose
of
allowing
changes
to
the
Method
is
to
improve
Method
performance
or
lower
the
cost
of
measurements.
Section
9.1.2
states:

In
recognition
of
advances
that
are
occurring
in
analytical
technology,
the
laboratory
is
permitted
certain
options
to
improve
results
or
lower
the
cost
of
measurements.
These
options
include
automation
of
the
dual­
amalgamation
system,
single­
trap
amalgamation
(
Reference
18),
direct
electronic
data
acquisition,
calibration
using
gas­
phase
elemental
Hg
standards,
changes
in
the
bubbler
design
(
including
substitution
of
a
flow­
injection
system),
or
changes
in
the
detector
(
i.
e.,
CVAAS)
when
less
sensitivity
is
acceptable
or
desired.
Changes
in
the
principle
of
the
determinative
technique,
such
as
the
use
of
colorimetry,
are
not
allowed.
If
an
analytical
technique
other
than
the
CVAFS
technique
specified
in
this
Method
is
used,
that
technique
must
have
a
specificity
for
mercury
equal
to
or
better
than
the
specificity
of
the
technique
in
this
Method.

You
are
also
required
to
maintain
records
of
modifications
made
to
the
Method,
including
the
reason
for
the
modification
and
results
of
quality
control
tests.
Minimum
requirements
for
these
records
are
detailed
in
Method
1631,
Section
9.1.2.2.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
4­
2
How
can
I
demonstrate
equivalent
or
superior
performance
for
a
modification
?

You
can
demonstrate
equivalent
or
superior
performance
by
showing
that
results
produced
by
your
modification
are
equal
or
superior
to
results
produced
by
the
unmodified
Method.
The
performance
of
a
modified
method
is
measured
by
precision
and
recovery
(
bias),
and
can
be
extended
to
include
detection
limit
as
well
as
other
measures
of
method
performance.
You
must
perform
the
method
detection
limit
(
MDL)
and
initial
precision
and
recovery
(
IPR)
tests
prior
to
practicing
Method
1631.
These
tests
are
described
in
detail
in
Section
9
of
the
Method.
If
you
modify
the
method,
you
must
use
those
modifications
when
performing
IPR
studies,
and
you
must
repeat
the
MDL
test
using
the
modifications.
Your
modification
is
permitted
if
all
QC
acceptance
criteria
are
met,
including
calibration,
blank,
MS/
MSD,
and
QCS
tests,
as
well
as
the
IPR
and
MDL
tests.

May
I
eliminate
one
of
the
gold
traps
specified
in
Method
1631
?

Yes,
provided
that
you
repeat
the
IPR,
blank,
and
MS/
MSD
tests
and
meet
the
QC
acceptance
criteria
in
the
Method.
If
the
MDL
will
be
affected
by
elimination
of
the
trap,
you
must
also
achieve
an
MDL
less
than
or
equal
to
one­
third
the
regulatory
compliance
level.
See
Section
9.1.2
and
Section
9.1.2.1
in
Method
1631
for
details
of
the
demonstration.

Although
Method
1631
allows
you
to
perform
analyses
without
both
of
the
gold
traps,
the
reason
for
using
both
gold
traps
are
(
1)
to
preclude
water
from
reaching
the
atomic
fluorescence
detector,
and
(
2)
to
sharpen
the
mercury
peak
so
that
low
levels
of
mercury
can
be
measured
reliably.
EPA
strongly
cautions
that
elimination
of
one
or
both
of
these
traps
may
not
allow
the
Method
precision,
recovery,
and
detection
limit
to
be
achieved.

Section
9.1.2
of
the
Method
allows
use
of
flow
injection.
We
encountered
a
problem
with
flow
injection
when
we
analyzed
an
effluent
containing
high
concentrations
of
organic
materials.
Can
a
flow
injection
system
continue
to
be
used
for
this
effluent
?

The
flow
injection
system
can
continue
to
be
used
provided
that
(
1)
you
have
performed
the
initial
precision
and
recovery
(
IPR)
test
and
met
the
QC
acceptance
criteria
with
the
flow
injection
system
as
an
integral
part
of
the
analytical
system
(
Section
9.2
of
Method
1631),
(
2)
you
have
demonstrated
that
the
MDL
achieved
with
the
flow
injection
system
as
an
integral
part
of
the
analytical
system
is
less
than
or
equal
to
one­
third
the
regulatory
compliance
level
or
less
than
or
equal
to
the
MDL
of
the
Method,
whichever
is
greater
(
Sections
9.1.2.2
and
9.2),
(
3)
you
have
recalibrated
the
instrument
if
the
change
affected
calibration
(
Section
9.1.2.2),
and
(
4)
you
have
assessed
the
performance
of
the
Method
on
the
sample
matrix
using
the
MS/
MSD
test
in
Section
9.3
of
Method
1631
and
have
met
the
QC
acceptance
criteria
for
this
test.

The
MS/
MSD
test
is
most
critical
for
this
assessment.
If
the
presence
of
organic
or
biological
materials
affects
recovery
or
precision
of
the
MS/
MSD
to
the
point
at
which
the
QC
acceptance
criteria
cannot
be
met,
the
flow
injection
system
cannot
be
used
on
that
sample.
If
the
QC
acceptance
criteria
are
met,
use
of
the
flow
injection
system
is
acceptable.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
4­
3
Method
1631
states
that
a
cold
vapor
atomic
adsorption
spectrometry
(
CVAAS)
detector
can
be
used.
Can
I
achieve
the
Method
detection
and
quantitation
limits
using
CVAAS
?

No,
the
detection
and
quantitation
limits
specified
in
Method
1631
cannot
be
achieved
using
CVAAS.
The
allowance
for
use
of
CVAAS
in
Method
1631
(
Section
9.1.2)
was
in
response
to
requests
from
commenters
on
the
proposal
of
the
Method.
Some
commenters
claimed
that
detection
limits
on
the
order
of
1
­
3
ng/
L
could
be
achieved
using
CVAAS.
If
a
CVAAS
detector
is
used,
Method
1631
states
that
you
must
demonstrate
that
an
MDL
less
than
or
equal
to
one­
third
the
regulatory
compliance
level
or
less
than
or
equal
to
the
Method
MDL,
whichever
is
greater,
can
be
achieved
(
Method
1631,
Section
9.1.2.1).

Section
9.3.4.1
states
that
few
interferences
have
been
encountered
with
Method
1631.
Would
you
expect
this
statement
to
be
true
when
CVAAS
is
used
?

Although
we
would
expect
it
to
be
true,
we
have
not
thoroughly
investigated
the
issue.
If
matrix
interference
problems
are
encountered
in
the
use
of
CVAAS
that
would
not
be
encountered
with
use
of
cold­
vapor
atomic
fluorescence
spectrometry
(
CVAFS),
CVAAS
would
not
be
considered
equivalent
to
CVAFS
and
CVAFS
would
be
required.

What
is
the
status
of
EPA
Method
245.7
"
Determination
of
Ultra­
trace
Level
(
ng
Hg/
L)
Total
Mercury
in
Water
by
Cold
Vapor
Atomic
Fluorescence
Spectrometry"
and
can
it
be
used
?

We
currently
believe
that
EPA
Method
245.7
is
capable
of
reliably
analyzing
for
mercury
in
water
at
levels
as
low
as
1
­
3
ng/
L
and
are
evaluating
EPA
Method
245.7
for
inclusion
in
the
test
methods
at
40
CFR
part
136.
Until
this
evaluation
is
complete,
EPA
Method
245.7
is
not
approved
for
use
in
EPA's
Clean
Water
Act
programs.
However,
a
discharger
may
seek
approval
for
use
of
EPA
Method
245.7
under
the
alternate
test
procedure
(
ATP)
program
at
40
CFR
136.4
and
136.5
or
may
negotiate
its
use
in
new
permits
if
the
permitting/
control
authority
is
willing
to
allow
it.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
1
Chapter
5:
Frequently
Asked
Questions
(
FAQs)
Concerning
EPA
Method
1631
The
questions
below
are
those
that
we
have
been
asked
most
frequently
or
those
that
have
caused
uncertainty
in
how
the
Method
is
to
be
used.
Following
proposal
of
Method
1631
and
associated
notices,
commenters
raised
more
than
100
questions
and
issues
concerning
the
Method.
We
included
written
comments
and
our
responses
in
the
Water
Docket
to
support
the
final
rule.
We
urge
dischargers/
generators/
industrial
users,
regulatory/
control
authorities,
laboratories,
and
others
that
have
questions
concerning
Method
1631
to
review
the
comments
and
responses
in
the
administrative
record
at
the
Water
Docket.
Chapter
7,
Where
to
Get
Additional
Help,
provides
contact
information
for
the
Water
Docket.

General
Questions
When
should
I
use
Method
1631
to
measure
mercury
?

If
a
method
is
not
specified
in
your
NPDES
permit,
you
should
use
the
Method
when
it
is
necessary
to
measure
mercury
concentrations
in
the
range
of
0.5
to
100
ng/
L.
Method
1631
can
be
used
for
measurements
above
this
100
ng/
L
range
by
dilution
of
the
sample,
but
use
of
one
of
the
other
methods
approved
at
40
CFR
part
136
may
be
more
cost
effective.

Is
use
of
Method
1631
required
?

If
Method
1631
is
specifically
required
by
the
NPDES
permit,
then
it
must
be
used
for
all
compliance
monitoring
activities.

EPA
regulations
(
Part
122
and
Part
136)
require
use
of
Part
136
methods
in
the
NPDES
program,
and
in
general,
any
of
the
methods
approved
for
use
at
40
CFR
part
136
for
determination
of
mercury
concentrations
may
be
used
under
EPA's
Clean
Water
Act
programs.
Where
there
are
two
or
more
methods
in
Part
136
for
a
pollutant
(
as
is
the
case
for
mercury),
the
regulations
do
not
specify
that
the
most
sensitive
method
automatically
be
used.
Instead,
EPA
expects
that
permitting
authorities
would
use
their
best
professional
judgment
to
choose
the
most
appropriate
method
for
the
situation.
For
example,
if
a
permit
writer
needed
to
choose
a
method
to
monitor
compliance
with
an
effluent
limit,
the
method
should
be
adequate
"
to
assure
compliance
with
permit
limitations"
according
to
40
CFR
122.44(
i)(
1).
Accordingly,
if
permit
limitations
require
a
permittee
to
achieve
very
low
concentrations
of
a
pollutant,
the
permitting
authority
should
require
the
specific
sample
collection
techniques
and
analytical
methods
that
would
produce
sufficiently
precise
results
to
assess
compliance
with
that
limit.
When
an
effluent
limitation
is
specified
in
a
permit
at
higher
levels,
other
less
sensitive
test
methods
could
be
incorporated
and
still
assure
that
measurements
are
representative
of
that
monitored
activity
and
adequate
to
assess
compliance.

The
Agency
developed
EPA
Method
1631
to
enable
reliable
measurement
of
water
samples
at
the
levels
established
in
water
quality
criteria.
Consequently,
EPA
expects
that
when
the
measurement
sensitivity
of
EPA
Method
1631
is
necessary
to
assess
and
implement
effluent
limitations
that
are
at
or
near
the
water
quality
criteria
values,
Method
1631
will
be
used.
If
and
when
other
methods
for
measuring
mercury
are
promulgated
in
Part
136
or
approved
under
the
procedures
at
136.3
that
are
also
capable
of
measuring
at
these
levels,
the
permitting
authority
would
have
the
discretion
to
determine
which
method
is
most
appropriate
under
the
circumstances.
(
Please
note
that
EPA
recognizes
that
some
States
may
need
to
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
2
follow
State
procedures
to
adopt
changes
to
Part
136
before
they
can
require
use
of
a
newly
promulgated
method
and
allows
States
a
reasonable
time
to
accomplish
this.
See
40
CFR
123.62(
e).

How
rigorously
must
Method
1631
be
followed
?

You
must
follow
the
Method
rigorously.
However,
you
are
allowed
to
modify
the
Method
under
the
performance­
based
allowances
provided
that
you
perform
the
equivalency
demonstration
and
meet
the
QC
acceptance
criteria
for
the
performance
tests.
See
Chapter
4,
Flexibility
in
EPA
Method
1631,
for
guidance
in
making
method
modifications.

Do
you
have
analytical
methods
for
determining
elemental
mercury
(
Hg0)
and
methyl
mercury
(
CH3Hg)
?

We
have
drafted
procedures
for
each
of
these
forms
of
mercury
but
have
not
proposed
these
procedures
for
general
use.
For
a
copy
of
these
draft
procedures,
please
contact
the
EPA
Sample
Control
Center
at
the
address
or
phone
number
given
in
Chapter
6,
Sources
of
Information.

Is
Method
1631
for
total
mercury
or
for
dissolved
and
total
recoverable
mercury
?

Method
1631
is
for
determination
of
"
total,"
"
total
recoverable,"
or
"
dissolved"
mercury.
Confusion
continues
over
use
of
the
terms
"
total"
and
"
total
recoverable."
For
determinations
of
mercury
using
Method
1631,
and
for
other
EPA
methods
for
determination
of
metals,
the
terms
"
total"
and
"
total
recoverable"
are
synonymous.
For
total/
total
recoverable
measurements,
the
sample
is
not
filtered
prior
sample
processing.
Therefore,
if
a
"
total"
or
"
total
recoverable"
mercury
concentration
is
reported,
you
should
understand
that
the
result
represents
the
determined
concentration
of
mercury
in
the
combined
dissolved
and
suspended
fractions
of
the
sample.

The
"
dissolved"
measurement
applies
to
total/
total
recoverable
mercury
that
exists
in
the
filtrate
of
a
sample
that
has
been
passed
through
a
0.45
micron
filter.
(
See
EPA
Method
1669
for
a
discussion
of
the
details
of
a
filter
and
for
sampling
for
dissolved
mercury.)

Sampling
Questions
(
also
refer
to
Chapter
2,
which
discusses
the
use
of
clean
techniques)

Should
samples
in
which
dissolved
mercury
is
to
be
determined
be
filtered
in
the
field
or
in
the
laboratory
?

To
preclude
interchange
of
mercury
between
the
dissolved
and
suspended
forms,
you
should
filter
samples
for
dissolved
mercury
in
the
field
at
the
time
of
collection
(
40
CFR
136.3,
Table
II,
footnote
7).
Because
field
filtration
increases
the
risk
of
contamination,
the
field
sampling
team
should
be
trained
in
the
sampling
techniques
that
will
preclude
contamination
at
the
levels
required
to
be
measured.
The
use
of
inline
filtration,
described
in
Method
1669,
can
reduce
contamination
resulting
from
sample
filtration
and
the
associated
increased
sample
handling.
A
reviewer
of
this
Guidance
suggests
that
it
may
be
better
to
ship
the
sample
to
the
laboratory
and
filter
the
sample
before
preservation
and
within
24
hours
of
collection
under
controlled
conditions.
Samples
may
be
filtered
in
the
laboratory
prior
to
preservation
if
they
are
collected
in
fluoropolymer
or
glass
bottles,
filled
to
the
top
with
no
head
space,
capped
tightly,
and
maintained
at
0­
4
E
C
until
preservation
(
Method
1631,
Section
8.5).
Filtered
and
unfiltered
samples
must
be
preserved
within
48
hours
after
sample
collection.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
3
Does
Method
1631
allow
use
of
continuous
versus
grab
sampling
?

Section
8.3
of
Method
1631
suggests
use
of
the
procedures
found
in
EPA
Method
1669
(
the
Sampling
Guidance).
EPA
Method
1669
gives
four
procedures
for
sampling.
Continuous
(
composite)
sampling
is
not
among
these
procedures.
However,
in
tests
performed
at
the
Hampton
Roads
Sanitary
District
in
Virginia,
and
in
other
locations,
researchers
have
been
able
to
construct
continuous
sampling
systems
that
control
contamination
below
levels
that
would
compromise
reliable
measurement
of
mercury.

The
NPDES
program
regulations
at
40
CFR
122
require
collection
of
a
24­
hour
composite
sample,
but
also
recognize
that
composite
sampling
may
be
waived
for
any
outfall
for
which
the
applicant
demonstrates
that
the
use
of
an
automatic
sampler
is
infeasible
and
that
the
minimum
of
4
grab
samples
will
be
a
representative
sample
of
the
effluent
being
discharged
(
see
40
CFR
122.21(
g)(
7)).
The
Pretreatment
regulations
at
40
CFR
part
403
contain
similar
requirements.

To
date,
we
have
not
collected
a
sufficient
amount
of
data
to
demonstrate
that
composite
sampling
systems
can
collect
mercury
samples
that
are
free
of
contamination
and
that
do
not
lose
mercury
via
volatilization.
For
this
reason,
EPA
strongly
suggests
that
samples
for
mercury
be
collected
using
one
of
the
four
sampling
procedures
given
in
Section
8.2
of
Method
1669.
If
a
composite
measurement
is
needed,
four
(
or
more)
samples
(
as
required
by
the
regulations
or
in
the
permit)
should
be
collected.
These
samples
should
be
composited
in
the
laboratory
or,
alternatively,
the
grab
samples
may
be
analyzed
individually,
and
the
results
mathematically
composited.

Can
plastic
containers
other
than
fluoropolymer
be
used
for
collection
of
samples
for
mercury
?

Not
at
present.
Mercury
has
been
shown
to
diffuse
in
and
out
of
polyethylene
and
polypropylene
containers.
If
another
type
of
plastic
container
can
be
found
that
would
not
result
in
a
loss
or
gain
of
mercury
to
the
sample,
EPA
would
consider
allowing
such
a
container
under
the
ATP
program.

Is
borosilicate
glass
(
Section
6.1)
really
OK
?
The
sampling
method
does
not
allow
glass
for
mercury;
only
fluoropolymer.

Sections
4.2.2.3.1
and
6.3
of
the
Sampling
Guidance
(
EPA
Method
1669)
explicitly
allow
for
use
of
glass
for
mercury.
Only
the
earliest
drafts
(
before
April
1995)
of
the
guidance
would
have
precluded
the
use
of
glass.
It
has
also
been
suggested
that
flint
glass
bottles
may
be
acceptable,
if
properly
cleaned.
EPA
currently
has
no
data
to
support
use
of
sample
bottles
other
than
fluoropolymer
or
borosilicate
glass.

Can
I
digest
samples
in
polyethylene
or
polypropylene
vessels
?

You
must
collect,
preserve
and
store
samples
in
a
fluoropolymer
or
borosilicate
glass
bottle
(
Section
8.2).
A
polyethylene
or
polypropylene
sample
bottle
must
not
be
used
because
Hg
may
diffuse
in
or
out
of
the
bottle
during
transport
or
storage.
However,
you
may
use
polyethylene
or
another
material
for
sample
digestion
provided
the
digestion
vessel
is
demonstrated
to
be
free
of
contamination,
and
you
repeat
the
initial
demonstration
of
method
performance
in
Section
9.2
and
meet
the
QC
acceptance
criteria
for
the
performance
tests.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
4
The
sampling
procedures
in
the
Method
and
in
the
Sampling
Guidance
are
not
explicit
in
stating
the
exact
steps
that
are
required
for
sample
collection.
Can
you
provide
further
guidance
in
this
area
?

As
stated
in
Chapter
2
of
this
document,
the
Sampling
Guidance
(
Method
1669)
provides
guidance
for
site­
specific
determination
of
what
techniques
are
necessary
to
collect
water
samples
for
reliable
measurement
of
mercury.
The
exact
procedures
required
are
dependent
on
the
level
of
mercury
expected
in
the
sample
and
on
the
degree
of
potential
contamination.
However,
to
assist
dischargers
and
others
that
need
to
make
mercury
measurements
in
the
low­
to
sub­
ppt
range,
Frontier
Geosciences
Inc.
has
developed
a
standard
operating
procedure
(
SOP)
for
sampling
that
it
provides
to
its
customers.
This
SOP
has
been
modified
to
be
consistent
with
the
requirements
in
EPA
Methods
1631
and
1669
and
is
presented
in
Appendix
A
to
this
guidance.
This
procedure
should
be
viewed
as
containing
the
minimum
steps
necessary
for
reliable
sampling,
and
some
of
the
additional
measures
in
the
Sampling
Guidance
may
be
necessary
to
preclude
contamination
at
some
sampling
sites.

The
Virginia
Department
of
Environmental
Quality
(
VA­
DEQ)
has
also
developed
an
SOP
for
sampling
water
titled
Collection
of
Freshwater,
Saltwaters,
and
Wastewaters
for
the
Determination
of
Trace
Elements
(
Revision
#:
20001105,
December
7,
2000).
This
SOP
is
currently
available
from
VA­
DEQ,
629
E.
Main
Street,
Richmond,
VA
23219,
attn:
Roger
Stewart,
or
call
804­
698­
4449.

In
addition
to
the
Sampling
Guidance
and
these
SOPs,
we
recommend
that
persons
conducting
sampling
for
mercury
be
trained
in
the
"
Clean
Hands/
Dirty
Hands"
sampling
technique.
We
also
recommend
a
demonstration
of
proficiency
by
sampling
personnel
prior
to
collection
of
a
sample
for
regulatory
compliance,
consisting
of
collection
of
field
and
equipment
blanks
to
show
that
samples
will
not
be
contaminated.
Field
audits
also
could
be
performed
to
ensure
that
proper
sample
collection
procedures
are
being
followed.

EPA
has
conducted
trace
metals
workshops
that
have
provided
"
hands­
on"
training
for
this
purpose.
In
addition,
EPA
and
State
agencies
are
sponsoring
training
workshops
titled
Mercury
Collection
and
Analysis
in
Ambient
and
Effluent
Waters
Using
EPA
Method
1631.
The
workshops
will
be
held
throughout
the
year
2001
in
various
EPA
Region
V
states
and
at
EPA's
Annual
Conference
on
the
Analysis
of
Pollutants
in
the
Environment
on
May
8­
10,
2001
in
Portsmouth,
VA.

Must
I
preserve
samples
in
the
field
?

Samples
may
be
shipped
to
the
laboratory
unpreserved
if
they
are
(
1)
collected
in
fluoropolymer
or
glass
bottles,
(
2)
filled
to
the
top
with
no
head
space,
(
3)
capped
tightly,
and
(
4)
maintained
at
0
­
4
E
C
from
the
time
of
collection
until
preservation.
The
samples
must
be
acid­
preserved
within
48
hours
after
sampling.
Otherwise,
samples
must
be
preserved
in
the
field.
(
See
Section
8.5
of
Method
1631.)
Samples
for
dissolved
mercury
must
be
filtered
upon
collection
and
prior
to
preservation.
The
acid
used
for
preservation
must
be
demonstrated
to
be
free
of
mercury
at
levels
that
would
compromise
reliable
measurement
of
mercury.

Early
versions
of
Method
1631
allowed
a
holding
time
of
6
months.
Why
was
it
changed
?

The
holding
time
was
changed
because
the
holding
time
table
(
Table
II)
at
40
CFR
136.3(
e)
specified
a
holding
time
of
28
days
for
mercury.
Commenters
on
the
proposal
of
Method
1631
pointed
out
the
conflict
between
the
holding
time
in
the
Method
and
in
Table
II.
We
searched
for
holding
time
data
that
would
support
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
5
6
months
and
could
not
find
data
that
would
support
the
longer
holding
time.
Therefore,
the
holding
time
of
28
days
in
Table
II
was
required
in
Revision
B
of
Method
1631,
which
was
promulgated
on
June
8,
1999.

Why
is
it
necessary
to
test
the
pH
of
samples
to
ensure
that
they
have
been
properly
preserved,
as
stated
in
Section
8.2
of
the
Method
?
Oxidation
with
BrCl
is
more
important
than
preservation,
and
ensures
that
the
samples
will
be
at
pH
<
2.

The
purpose
of
determining
the
pH
is
to
verify
that
samples
were
preserved
in
the
field,
thereby
confirming
the
48­
hour
holding
time
prior
to
preservation
has
not
been
exceeded.

Is
placing
a
serial
number
on
each
sample
bottle
a
good
idea
?

Yes,
placing
a
serial
number
on
each
sample
bottle
and
on
each
piece
of
apparatus
used
in
the
analysis
is
a
good
idea.
That
way,
if
a
sample
containing
a
high
concentration
of
mercury
is
encountered,
the
sample
bottle
and
other
pieces
of
apparatus
that
the
sample
touched
can
be
readily
identified
and
decontaminated
without
contaminating
the
remainder
of
the
apparatus
or
laboratory.
In
addition,
serial
numbers
can
be
used
to
identify
samples
that
are
associated
with
any
equipment
that
has
been
determined
to
be
contaminated.
The
best
means
for
serializing
sample
bottles
and
each
piece
of
apparatus
is
engraving
prior
to
cleaning.
EPA
cautions
that
indelible
inks
may
contain
mercury
and
contaminate
the
sample.

Why
is
a
sample
preservation
temperature
of
0
E
C
specified
?
This
temperature
may
cause
an
aqueous
sample
to
freeze
and
a
glass
sample
bottle
to
break.

The
preservation
temperature
specified
is
0
­
4
E
C.
Water
can
exist
in
both
liquid
and
solid
phases
at
0
E
C.
The
purpose
of
allowing
0
E
C
is
to
allow
samples
to
be
partially
frozen
so
that
the
heat
capacity
of
ice
can
be
used
to
extend
the
shipping
time,
if
desired.
See
the
SOP
in
Appendix
A
for
additional
details
Is
there
really
a
need
to
refrigerate
samples
?

The
original
draft
of
Method
1631
contained
the
requirement
to
cool
samples
to
1­
4
E
C
from
the
time
of
collection
until
preservation.
Recognizing
that
it
would
be
near
impossible
to
maintain
a
sample
temperature
in
this
range
during
shipment,
EPA
wrote
the
requirement
as
0­
4
E
C.
Until
data
demonstrate
that
refrigeration
is
not
necessary,
unpreserved
samples
must
be
maintained
at
0­
4
E
C.

Please
note
that
this
requirement
is
from
the
time
of
collection
until
preservation.
If
samples
are
collected
and
preserved
in
the
field,
refrigeration
is
not
required
for
shipment
or
subsequent
storage
at
the
laboratory.

Can
you
offer
any
other
helpful
tips
on
sampling
?

°
Do
not
use
sample
containers
that
have
not
been
demonstrated
to
be
clean
(
See
Section
4.3.7
of
Method
1631
and
Section
4.2.2.3
of
EPA
Method
1669).
°
Either
do
not
sample
when
it's
raining
or
prevent
rainwater
from
falling
into
the
sampling
container.
°
Face
upstream
and
upwind
(
See
Section
8.2.2
of
EPA
Method
1669).
°
Avoid
all
sources
of
potential
contamination
including
improperly
cleaned
equipment,
atmospheric
inputs,
and
human
contact.
°
Do
not
breathe
into
the
sample
bottle
if
you
have
mercury
amalgam
fillings
in
your
teeth
(
See
Section
4.2
of
Method
1631
and
Section
4.1.2
of
EPA
Method
1669).
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
6
°
Do
not
sample
under
or
near
a
bridge
or
other
metal
structure.
Metals
particles
can
slough
off
of
the
structure
and
contaminate
the
sample
(
See
Section
4.1.2
of
EPA
Method
1669).
°
Do
not
sample
when
the
wind
could
blow
metal,
debris,
or
dust
particles
into
the
sample
bottle
(
See
Section
4.3.8.4
of
Method
1631
and
Section
4.2.2.4.4
of
EPA
Method
1669).
°
In
general,
the
more
blank
samples
that
are
collected
and
analyzed,
the
better
the
assessment
of
whether
or
not
contamination
has
occurred.
Method
1631
includes
the
minimum
requirements
for
field
and
equipment
blanks
when
collecting
samples
for
mercury
analysis
at
water
quality
criteria
concentration
levels.
°
Train
the
sampling
team
in
the
use
of
the
sampling
techniques
in
EPA
Methods
1631
and
1669.
°
Put
on
more
than
one
pair
of
gloves
and
strip
off
or
change
gloves
frequently.

Blanks
Questions
(
also
refer
to
Chapter
2,
which
discusses
the
use
of
clean
techniques)

Is
the
bubbler
blank
the
same
as
a
laboratory
(
method)
blank
(
i.
e.,
does
it
cover
the
entire
system)
?
Also,
what
about
field
blanks
and
equipment
blanks
?

The
bubbler
blank
is
not
the
same
as
a
method
blank
in
that
it
does
not
include
a
fresh
aliquot
of
the
reagents.
Method
1631,
Section
9.4.1
states
that
bubbler
blanks
are
analyzed
to
demonstrate
freedom
from
system
contamination.
Bubbler
blanks
are
analyzed
immediately
after
analyzing
a
sample
by
placing
a
clean
gold
trap
on
the
bubbler
and
purging
the
water
in
the
bubbler
a
second
time.

Field
and
equipment
blanks
are
used
to
demonstrate
freedom
from
contamination
in
the
sampling
equipment
and
sample
collection
techniques.
Use
of
field
and
equipment
blanks
is
addressed
in
Sections
9.4.3
and
9.4.4
of
Method
1631,
in
Sections
9.3
and
9.4
of
the
Sampling
Guidance
(
EPA
Method
1669),
and
in
Chapter
2
of
this
guidance.

Definitions
for
various
blanks
are
as
follows:

Bubbler
Blank
­
A
Bubbler
Blank
(
see
Section
9.4.1
of
Method
1631)
is
used
to
demonstrate
freedom
from
system
contamination.
At
least
three
bubbler
blanks
must
be
run
per
analytical
batch
by
placing
a
clean
gold
trap
on
the
bubbler
immediately
following
analysis
of
a
sample,
and
analyzing
the
sample
a
second
time.

Field
Blank
­
A
Field
Blank
(
see
Section
9.4
of
EPA
Sampling
Method
1669)
is
generated
by
filling
a
large
carboy
or
other
appropriate
container
with
reagent
water
in
the
laboratory,
transporting
the
filled
container
to
the
sampling
site,
processing
the
reagent
water
through
each
of
the
sample
processing
steps
and
equipment
(
e.
g.,
tubing,
sampling
devices,
filters,
etc.)
that
will
be
used
for
sample
collection,
collecting
the
reagent
water
in
a
sample
bottle,
and
shipping
the
sample
bottle
to
the
laboratory
for
analysis
in
accordance
with
Method
1631.
Field
blanks
are
used
to
identify
contamination
from
the
sampling
equipment,
from
sampling,
and
from
transporting
the
sample
to
the
laboratory.

Equipment
Blank
­
A
Bottle
Blank
or
Sampler
Check
Blank
(
see
Section
9.4.4
of
Method
1631).
Equipment
blanks
are
used
to
identify
contamination
from
sample
bottles
and
the
sampling
equipment.

Bottle
Blank
(
see
Section
9.4.4.1
of
Method
1631)
­
A
Bottle
Blank
is
generated
by
filling
a
sample
bottle
with
reagent
water
acidified
to
pH
<
2,
capping
the
bottle,
allowing
the
bottle
to
stand
for
a
minimum
of
24
hours,
and
the
analyzing
the
water.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
7
Sampler
Check
Blank
(
see
Section
9.4.4.2
of
Method
1631)
­
A
Sampler
Check
Blank
is
generated
at
the
laboratory
or
equipment
cleaning
facility
by
filling
a
large
carboy
or
other
container
with
reagent
water,
processing
the
reagent
water
through
the
sampling
equipment
using
the
same
procedures
that
will
be
used
in
the
field,
and
collecting
and
analyzing
the
water.

Reagent
Blank
­
A
Reagent
Blank
(
see
Section
9.4.2
of
Method
1631)
is
generated
by
adding
aliquots
of
BrCl,
NH2OH,
and
SnCl2
to
previously
purged
reagent
water
in
the
bubbler
and
analyzing
the
reagent
water.
Reagent
blanks
are
used
to
identify
contamination
from
the
reagents.

Method
Blank
(
Laboratory
Blank)
­
An
aliquot
of
reagent
water
that
is
treated
exactly
as
a
sample
including
exposure
to
all
glassware,
equipment,
solvents,
and
reagents
that
are
used
with
samples.
The
laboratory
blank
is
used
to
determine
if
analytes
or
interferences
are
present
in
the
laboratory
environment,
the
reagents,
or
the
apparatus.
Method
blanks
are
not
required
in
EPA
Method
1631;
however,
we
strongly
suggest
that
the
laboratory
run
at
least
one
method
blank
with
each
batch
of
samples.

What
is
the
required
frequency
for
field
blanks
?

Method
1631
requires
that
a
minimum
of
1
field
blank
accompany
each
set
of
samples
collected
at
a
given
site
(
i.
e.,
sampling
point)
at
the
same
time,
to
a
maximum
of
10
samples.
If
one
sample
is
collected
at
a
given
site
at
a
given
time,
a
minimum
of
one
field
blank
must
be
collected
for
that
sample;
if
one
sample
is
collected
at
a
given
site
at
two
different
times,
a
minimum
of
one
field
blank
must
be
collected
for
each
of
the
two
samples;
if
a
sample
is
collected
at
two
different
sites
at
the
same
time,
a
minimum
of
one
field
blank
must
be
collected
for
each
of
the
two
samples.

How
are
field
blanks
collected
if
the
sample
is
collected
from
a
closed
plumbing
system
?

Collection
of
the
field
blank
should
simulate,
as
closely
as
possible,
collection
of
the
sample.
For
example,
if
a
sample
from
a
closed
plumbing
system
is
collected
by
opening
a
valve
in
the
system,
the
field
blank
should
be
collected
by
pouring
the
reagent
water
carried
to
the
field
into
a
sample
bottle
adjacent
to
the
sampling
valve.
In
this
way,
any
mercury
in
the
atmosphere
at
the
valve
that
could
contaminate
a
sample
would
contaminate
the
field
blank.

Is
it
necessary
to
run
a
sampler
check
blank
(
Section
9.4.4.2)
on
each
piece
of
sampling
equipment
that
will
be
used
in
the
field
?

All
sampling
equipment
(
bottles,
tubing,
dipper,
transfer
vessel,
etc.)
that
will
contact
the
sample
in
the
field
must
be
checked
for
contamination.
Each
piece
may
be
tested
individually
or
in
combination
as
a
whole
sampling
apparatus.
You
may
test
a
representative
number
of
the
bottles
and
tubing
as
described
in
Section
9.4.4.3
of
Method
1631.
If
a
representative
number
of
bottles
and
tubing
are
shown
to
be
clean,
the
lot
of
bottles
cleaned
at
the
same
time
using
the
same
procedure
are
assumed
to
be
clean.

Can
I
subtract
field
or
equipment
blank
results
from
results
for
samples
?

If
blank
correction
is
requested
or
required,
you
may
subtract
the
results
from
field
or
equipment
blanks
(
but
not
both)
provided
that
the
results
for
the
blanks
meet
the
requirements
in
Section
9.4
of
Method
1631.
If
the
result
from
a
field
or
equipment
blank
is
subtracted,
you
may
not
additionally
subtract
the
reagent
blank
result
because
the
reagents
also
are
used
for
the
determination
of
mercury
in
the
field
and/
or
equipment
blanks;
i.
e.,
subtraction
of
one
blank
only,
among
the
reagent
blank,
field
blank,
or
equipment
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
8
blank
is
allowed.
The
laboratory
must
also
report
results
for
the
sample
and
the
reagent,
field,
and
equipment
blanks
separately
so
that
the
data
user
can
judge
the
appropriateness
of
blank
subtraction,
if
blank
subtraction
was
performed.
Again,
results
for
all
blanks
must
meet
the
specifications
in
Section
9.4
of
Method
1631
before
blank
subtraction
may
be
performed.
If
results
for
all
blanks
meet
the
respective
specifications,
the
choice
of
which
blank
to
subtract
is
at
the
discretion
of
the
discharger/
permittee
and
its
laboratory.

Can
we
use
field
blank
correction
?
(
Section
12.4.2
of
Method
1631
does
not
specifically
state
that
it
is
allowed.)

Even
though
Method
1631,
Revision
B
specifically
addresses
correction
of
test
sample
results
for
reagent
blanks,
silence
on
field
blanks
does
not
mean
that
field
blank
correction
is
precluded.
The
preamble
to
the
final
rule
promulgating
Method
1631B
states:
"
There
is
no
prohibition
against
reporting
blank­
subtracted
results,
provided,
of
course
that
results
for
blanks
and
samples
are
reported
separately"
(
64
FR
30427).

EPA
is
planning
to
promulgate
Method
1631,
Revision
C
during
June
2001
to
clarify
that
field
blank
results
must
be
reported
separately
and
that
field
blank
correction
must
be
performed
if
requested
or
required
by
a
regulatory
authority
or
in
a
permit.

Can
I
apply
blank
correction
when
multiple
blanks
are
collected
for
a
particular
type
of
blank,
as
detailed
in
Section
9.4.3.3
of
Method
1631
?

Section
9.4.3.3
allows
subtraction
of
the
average
concentration
of
multiple
field
blanks
(
a
minimum
of
three).
This
subtraction
may
be
performed
for
either
the
reagent,
the
field,
or
the
equipment
blank
samples,
provided
that
results
for
the
blanks
and
samples
also
are
reported
separately
and
all
the
blanks
being
averaged
are
of
the
same
type.

How
should
we
interpret
results
from
the
analyses
of
field
blanks
?

Section
9.4.3.2
of
Method
1631
states
that
if
Hg
or
any
potentially
interfering
substance
is
found
in
the
field
blank
at
a
concentration
equal
to
or
greater
than
the
ML,
or
greater
than
one­
fifth
the
level
in
the
associated
sample,
whichever
is
greater,
results
for
associated
samples
may
be
the
result
of
contamination
and
may
not
be
reported
or
otherwise
used
for
regulatory
compliance
purposes.

The
criteria
for
field
blanks
in
Method
1631,
Section
9.3.4.2
and
the
table
provided
in
this
Guidance
in
response
to
"
What
quality
control
tests
are
required
by
Method
1631
and
what
performance
criteria
must
be
met?,"
can
be
interpreted
to
mean
that
a
blank
containing
Hg
just
below
the
ML
of
0.5
ng/
L
is
acceptable
for
a
sample
result
in
the
range
of
1­
5
times
the
ML
(
0.5­
2.5
ng/
L).
This
interpretation
is
not
intended.
Section
12.4.1
of
EPA
Method
1631
requires
reporting
of
results
for
Hg
in
field
blanks
to
the
level
of
the
MDL
(
0.2
ng/
L).
If
a
sample
result
is
in
the
range
of
1­
2.5
ng/
L
and
the
field
blank
is
less
than
the
MDL,
the
concentration
is
likely
not
the
result
of
contamination
because
the
level
in
the
blank
is
less
than
one­
fifth
the
level
in
the
sample.
If
the
sample
result
is
in
the
range
of
0.5
ng/
L,
it
would
be
prudent
to
analyze
a
larger
sample
volume
(
200­
1000
mL)
or
to
make
measurements
to
a
lower
MDL
to
demonstrate
that
the
concentration
of
Hg
in
the
blank
is
less
than
one­
fifth
the
concentration
in
the
sample.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
9
Are
field
sample
results
void
when
field
and
equipment
blanks
do
not
meet
the
requirements
in
Section
9.4,
in
the
same
way
that
they
are
void
when
results
for
reagent
blanks
do
not
meet
these
requirements
?

Generally
speaking,
yes.
Sample
results
must
not
be
allowed
to
be
compromised
by
contaminated
blanks.
Samples
that
are
associated
with
field
or
equipment
blanks
not
meeting
the
requirements
in
Section
9.4
may
not
be
reported
or
otherwise
used
for
permitting
or
regulatory
compliance
purposes.
However,
field
sample
results
that
are
associated
with
contaminated
blanks,
but
also
are
still
below
the
regulatory
compliance
threshold,
may
be
used
to
demonstrate
permit
compliance.
Please
refer
to
EPA's
Guidance
on
the
Documentation
and
Evaluation
of
Trace
Metals
Data
Collected
for
Clean
Water
Act
Compliance
Monitoring,
referenced
in
Chapter
6
of
this
Guidance.

We
have
found
that
a
minimum
of
triplicate
reagent
blanks
are
needed
daily
for
reliable
low­
level
mercury
measurements.
Can
multiple
blanks
be
used
?

Nothing
in
Method
1631
precludes
a
laboratory
from
exceeding
the
QC
requirements
in
the
Method,
and
EPA
applauds
such
actions.
Therefore,
a
greater
number
of
blanks,
replicates,
and
spikes
than
required
by
the
Method
may
be
used.
However,
Method
1631
also
requires
that
results
of
all
blanks
and
samples
be
reported
separately,
unless
otherwise
requested
or
required
by
a
regulatory
authority
or
a
permit.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
10
Quality
Control
Questions
What
quality
control
(
QC)
tests
are
required
by
Method
1631
and
what
performance
criteria
must
be
met
?

Method
1631
requires
the
following
QC
tests
and
performance
criteria:

Test
Spike
Amount
Minimum
Frequency
Criteria
Method
Detection
Limit
(
MDL)
Follow
40
CFR
136,
Appendix
B
Initial
demonstration
#
0.2
ng/
L
or
one­
third
the
regulatory
compliance
limit,
whichever
is
greater
Initial
Precision
and
Recovery
(
IPR)
5
ng/
L
Initial
demonstration
4
replicates
Average
percent
recovery
=
79
­
121
Relative
standard
deviation
#
21%

Matrix
Spike/
Matrix
Spike
Duplicate
(
MS/
MSD)
Compliance
limit
or
1­
5x
background,
whichever
is
greater
10%
from
a
given
sampling
site
or
discharge
Percent
recovery
=
71
­
125
Relative
Percent
Difference
#
24
Bubbler
Blanks
NA
1
after
each
OPR
At
least
3
per
batch
Each
bubbler
blank
#
50
pg
Mean
of
3
bubbler
blanks
<
25
pg
Standard
deviation
of
3
<
10
pg
Reagent
Blanks
NA
Each
new
batch
of
reagents,
and
in
triplicate
each
month
#
25
pg
Field
Blanks
NA
10%
from
same
site
at
same
time
<
0.5
ng/
L
or
#
one­
fifth
Hg
in
associated
sample(
s),
whichever
is
greater
Bottle
Blanks
NA
1
per
cleaning
batch
<
0.5
ng/
L
or
#
one­
fifth
Hg
in
associated
sample(
s),
whichever
is
greater
Sampler
Check
Blank
NA
1
following
each
cleaning
<
0.5
ng/
L
or
#
one­
fifth
Hg
in
associated
sample(
s),
whichever
is
greater
Ongoing
Precision
and
Recovery
(
OPR)
5
ng/
L
Prior
to
and
after
analysis
of
each
analytical
batch
Percent
recovery
=
77
­
123
Quality
Control
Sample
(
QCS)
Within
calibration
range
1
per
batch
No
specification;
follow
specification
provided
by
supplier
The
type,
frequency
and
criteria
of
the
QC
samples
presented
in
the
above
table
are
the
minimum
required
by
Method
1631.
Laboratories
may
wish
to
increase
the
level
of
QC
to
ensure
reliable
measurements
of
mercury.
An
increase
in
QC
may
be
desirable,
for
instance,
for
commercial
laboratories
conducting
a
large
number
of
low
level
analyses.
For
example,
such
laboratories
may
want
to
analyze
one
or
more
reagent
blanks
each
day
that
low
level
mercury
analyses
are
conducted
rather
than
perform
the
minimum
requirement
of
verification
in
triplicate
each
month.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
11
Can
the
QC
be
adjusted
for
measurements
at
high
levels
?

The
IPR,
OPR,
and
blank
levels
are
fixed
in
Method
1631
to
allow
measurement
of
mercury
at
low­
and
sub­
ng/
L
levels.
When
Method
1631
was
developed,
we
did
not
consider
that
laboratories
would
desire
to
make
measurements
in
the
10
to
100
ng/
L
range
only.
Therefore,
we
specified
IPR
and
OPR
spiking
levels
at
5.0
ng/
L,
and
did
not
allow
higher
levels
of
mercury
in
blanks,
that
would
be
consistent
with
higher
levels
of
Hg
in
samples.
Currently,
the
levels
specified
in
the
Method
must
be
used
and
the
QC
criteria
met
to
address
these
levels.

We
want
to
caution
that
mixing
use
of
Method
1631
at
low
and
high
levels
establishes
a
system
that
can
be
confusing
to
analysts
and
would
be
more
susceptible
to
mistakes
than
a
system
dedicated
to
low­
level
measurements
because
allowing
blank
contamination
to
a
level
of
0.2
ng/
L
is
vastly
different
than
allowing
contamination
to
10
ng/
L.

How
do
QC
requirements
differ
as
applied
to
an
analytical
batch
and
to
a
specific
discharge
?

Requirements
for
batch­
and
discharge­
specific
QC
are
different,
but
overlap.

Batch­
specific
QC
Batch­
specific
QC
is
required
to
demonstrate
the
analytical
process
is
in
control
during
the
12­
hour
shift
in
which
samples,
blanks,
and
standards
will
be
analyzed.
An
"
analytical
batch"
is
defined
in
the
Glossary
at
the
end
of
Method
1631
as:
"...
up
to
20
samples
that
are
oxidized
with
the
same
batch
of
reagents
and
analyzed
during
the
same
12­
hour
shift.
Each
analytical
batch
must
also
include
at
least
three
bubbler
blanks,
an
OPR,
and
a
QCS.
If
only
1
sample
is
analyzed,
the
batch
size
is
1;
if
20
samples
are
analyzed,
the
batch
size
is
20.
In
addition,
MS/
MSD
samples
must
be
prepared
at
a
frequency
of
10%
per
analytical
batch
(
one
MS/
MSD
for
every
10
samples)."

Discharge­
specific
QC
Discharge­
specific
QC
is
required
to
assure
the
method
is
continuously
applicable
to
a
specific
discharge.
Method
1631,
Section
9.3
states
"...
the
laboratory
must
spike,
in
duplicate,
a
minimum
of
10%
from
a
given
sampling
site
or,
if
for
compliance
monitoring,
form
a
given
discharge."
The
definition
of
"
discharge"
is
synonymous
with
"
matrix
type,"
or
wastewater
stream
in
a
given
industrial
subcategory.
(
Industrial
subcategories
are
defined
in
the
wastewater
regulations
at
40
CFR
parts
400­
699.)
"
Matrix
type"
or
"
discharge"
means
a
sample
medium
with
common
characteristics
across
a
given
industrial
subcategory.
Examples
include:
C­
stage
effluents
from
chlorine
bleach
mills
in
the
Pulp,
Paper,
and
Paperboard
industrial
category;
effluents
from
the
continuous
casting
subcategory
of
the
Iron
and
Steel
industrial
category;
publicly
owned
treatment
work
(
POTW)
sludges;
and
effluents
being
discharged
to
POTWs
from
plants
in
the
Atlantic
and
Gulf
Coast
Hand­
shucked
Oyster
Processing
subcategory.

Discharge­
specific
QC
is
applicable
on
the
basis
of
matrix
type
and
is
intended
for
routine
monitoring
of
the
same
discharge.
For
example,
if
a
commercial
laboratory
were
analyzing
C­
stage
effluents
from
several
chlorine
bleach
mills
in
the
Pulp,
Paper,
and
Paperboard
industrial
category,
it
would
be
necessary
to
analyze
an
MS/
MSD
from
any
one
of
the
C­
stage
effluents
only.
The
reason
that
a
single
MS/
MSD
pair
can
be
used
to
represent
a
particular
wastewater
stream
is
that
a
given
wastewater
stream
from
the
same
process
can
be
expected
to
have
the
same
characteristics.
Analysis
of
a
discharge
must
have
an
MS/
MSD
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
12
performed
on
the
1st,
11th,
21st,
etc.
sample
(
or
more
frequently)
to
demonstrate
that
the
nature
of
the
discharge
has
not
changed.

For
application
of
discharge­
specific
QC,
consider
the
following
example:
A
laboratory
receives
two
samples
of
different
matrices,
each
from
one
of
two
clients.
Client
A's
regulatory
compliance
limit
is
12
ng/
L
and
Client
B's
is
5
ng/
L.
Both
samples
have
a
background
concentration
of
2
ng/
L
of
mercury..
Which
sample
must
be
spiked
at
what
level
?
If
neither
matrix
has
had
an
MS/
MSD
performed
before,
the
MS/
MSD
must
be
performed
on
both.
If
either
matrix
has
not
had
an
MS/
MSD
performed
within
the
last
10
samples,
the
MS/
MSD
must
be
performed
for
this
matrix.
Method
1631
Sections
9.3.1.1
and
9.3.1.2
require
that
the
concentration
be
at
the
regulatory
compliance
limit,
at
1­
5
times
the
background
concentration
of
mercury
in
the
sample,
or
at
1­
5
times
the
ML
in
Method
1631
(
i.
e,
0.5
­
2.5
ng/
L),
whichever
is
greater.
(
See
also
the
response
to
the
question
"
What
spiking
levels
are
required
for
the
MS/
MSD
in
a
given
batch?")
For
this
example,
the
MS/
MSD
spike
for
Client
A
would
be
12
ng/
L,
the
regulatory
compliance
limit.
For
Client
B,
the
spike
would
be
in
the
range
of
5
ng/
L
(
regulatory
compliance
limit)
­
10
ng/
L
(
5
times
the
background
concentration).

We
recognize
that
the
discharge­
specific
QC
can
be
troublesome
for
commercial
laboratories
that
may
not
know
that
the
sample
is
from
a
particular
discharge,
the
regulatory
compliance
limit
for
the
industrial
subcategory,
or
the
last
time
that
an
MS/
MSD
was
performed.
Therefore,
it
would
be
prudent
for
laboratories
to
obtain
extra
sample
for
the
MS/
MSD
to
meet
the
frequency
requirement
of
10
percent
(
1
in
10
samples).
However,
it
is
the
discharger's
responsibility
to
make
sure
that
the
requirements
in
EPA
Method
1631
are
followed,
that
all
QC
is
performed,
and
that
all
QC
acceptance
criteria
are
met.
It
is
advisable
for
a
discharger
to
inform
the
laboratory
of
the
particular
matrix
and
the
discharge­
specific
QC
requirements
so
that
the
QC
requirements
in
Method
1631
can
be
met.

How
do
we
combine
batch­
specific
and
matrix­
specific
QC
requirements
?

EPA
recognizes
the
possibility
that
requiring
MS/
MSD
pairs
to
represent
an
analytical
batch
and
a
matrix
type
may
force
laboratories
to
analyze
more
than
one
MS/
MSD
pair
per
ten
samples.
Although
it
may
not
be
possible
to
avoid
this
situation,
EPA
suggests
the
following
tips
to
help
mitigate
the
occurrence:

°
Where
possible,
consider
holding
(
and
properly
storing)
samples
to
increase
the
analytical
batch
size
relative
to
the
QC
frequency.
This
approach
can
be
implemented
only
to
the
extent
that
sampling
holding
times
and
reporting
thresholds
are
not
compromised.
°
Maintain
control
charts
that
track
the
frequency
of
MS/
MSD
pairs
by
batch
and
by
matrix
type.
Because
EPA
allows
any
of
the
samples
in
an
analytical
batch
to
be
used
for
MS/
MSD
purposes,
laboratories
that
routinely
analyze
multiple
matrix
types
can
stagger
MS/
MSD
analyses
so
that
an
MS/
MSD
pair
for
each
matrix
type
is
analyzed
in
different
analytical
batches.
In
determining
which
matrix
should
be
spiked
for
a
particular
batch,
the
laboratory
can
consult
the
control
chart
and
determine
which
matrix
type
needs
to
be
spiked
in
order
to
stay
within
the
10%
frequency.

To
illustrate,
let's
consider
the
case
of
a
laboratory
planning
to
analyze
8
samples
during
a
12­
hour
shift.
Four
of
these
samples
are
POTW
effluents,
two
are
effluents
from
the
Pulp,
Paper,
and
Paperboard
Industry,
one
is
an
effluent
from
the
Iron
and
Steel
Industry's
continuous
casting
subcategory,
and
the
remaining
sample
is
ambient
water
collected
from
Lake
Michigan.
The
laboratory
consults
its
control
chart
and
determines
that
it
has
analyzed
only
three
POTW
effluent
samples
since
the
last
POTW
effluent
MS/
MSD
pair.
In
this
case,
the
laboratory
can
analyze
the
four
POTW
samples
without
needing
another
MS/
MSD
pair.
Similarly,
the
laboratory
has
analyzed
only
six
pulp
and
paper
effluent
samples
since
its
last
MS/
MSD
pair
for
that
matrix,
so
the
two
pulp
and
paper
effluent
samples
do
not
require
another
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
13
MS/
MSD
pair.
The
laboratory
determines
that
nine
effluents
from
the
continuous
casting
subcategory
were
analyzed
following
the
last
MS/
MSD
pair
for
that
discharge
type,
so
an
MS/
MSD
pair
for
one
of
the
two
samples
scheduled
could
meet
the
10%
frequency.
Similarly,
the
laboratory
has
analyzed
10
ambient
water
samples
from
Lake
Michigan
since
it
last
performed
an
MS/
MSD
pair
for
that
matrix
type.
In
this
situation,
the
laboratory
has
two
matrix
types
that
require
MS/
MSD
analysis
but
fewer
than
ten
samples.
The
laboratory
consults
it's
scheduling
log
and
determines
that
it
is
due
to
receive
several
more
Lake
Michigan
samples
during
the
week.
Therefore,
this
laboratory
can
choose
to
properly
store
the
Lake
Michigan
sample,
and
run
the
remaining
seven
samples
during
the
current
shift
using
one
of
the
iron
and
steel
effluents
to
analyze
an
MS/
MSD
sample
pair.

We
operate
a
commercial
laboratory
that
receives
samples
from
multiple
clients.
What
spiking
levels
are
required
for
the
MS/
MSD
in
a
given
batch
?

The
required
MS/
MSD
spiking
level
is
defined
in
Section
9
of
the
Method
as
follows:

9.3.1.1
If,
as
in
compliance
monitoring,
the
concentration
of
Hg
in
the
sample
is
being
checked
against
a
regulatory
compliance
limit,
the
spiking
level
shall
be
at
that
limit
or
at
1
 
5
times
the
background
concentration
of
the
sample,
whichever
is
greater.

9.3.1.2
If
the
concentration
of
Hg
in
a
sample
is
not
being
checked
against
a
limit,
the
spike
shall
be
at
1
 
5
times
the
background
concentration
or
at
1­
5
times
the
ML
in
Table
2,
whichever
is
greater.

The
"
background
concentration"
is
the
concentration
of
mercury
in
the
unspiked
sample.
This
concentration
is
determined
by
analysis
of
an
aliquot
of
unspiked
sample
using
the
procedure
in
Section
11
of
EPA
Method
1631
(
see
Sections
9.3.2
and
11
of
EPA
Method
1631).
Once
the
background
concentration
is
determined,
the
MS
and
MSD
are
spiked
in
the
range
of
1­
5
times
this
concentration
and
analyzed.
You
may
accompany
analysis
of
the
MS/
MSD
with
analysis
of
another
aliquot
of
unspiked
sample,
if
desired,
so
that
all
analyses
are
conducted
at
the
same
time
in
order
to
produce
the
most
accurate
results.
Spiking
requirements
are
also
provided
in
response
to
the
question
"
How
do
QC
requirements
differ
as
applied
to
an
analytical
batch
and
to
a
specific
discharge
?

To
minimize
error
in
spiking,
the
volume
of
the
spike
should
be
minimized
so
that
the
volume
of
the
sample
plus
spike
is
not
appreciably
greater
than
the
volume
of
the
unspiked
sample
(
nominally
100
mL
in
Method
1631),
although
the
purge­
and­
trap
system
is
relatively
insensitive
to
volume
changes.
Also,
the
concentration
and
volume
of
the
spike
should
be
known
and
measurable
to
within,
ideally,
less
than
one
percent,
so
that
the
error
associated
with
spiking
is
minimized.
If
there
is
doubt
about
the
concentration
and
volume
of
the
spiking
solution,
test
the
solution
using
reagent
water
to
make
sure
that
the
MS/
MSD
recovery
and
precision
can
be
achieved
using
the
concentration
and
volume
selected.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
14
Must
we
use
the
regulatory
compliance
limit
as
the
spike
level
for
both
influents
and
effluents
?

If
there
is
a
regulatory
compliance
limit
for
both
an
influent
and
an
effluent
(
an
unlikely
occurrence),
the
spike
level
must
be
appropriate
to
each
matrix
type.
For
the
influent,
the
spike
level
must
be
at
the
regulatory
compliance
limit
for
the
influent,
provided
that
the
regulatory
compliance
limit
for
the
influent
is
greater
than
1­
5
times
the
background
concentration
of
mercury
in
the
sample.
Otherwise,
the
spike
level
must
be
at
1­
5
times
the
background
concentration
of
mercury
in
the
influent
sample.
Similarly,
for
the
effluent,
the
spike
level
must
be
at
the
regulatory
compliance
limit
for
the
effluent,
provided
that
the
regulatory
compliance
limit
for
the
effluent
is
greater
than
1­
5
times
the
background
concentration
of
mercury
in
the
sample.
Otherwise,
the
spike
level
must
be
at
1­
5
times
the
background
concentration
of
mercury
in
the
effluent
sample.

The
specific
level
in
the
1­
5
range
is
dependent
on
the
level
at
which
the
sample
will
be
spiked.
If
the
sample
will
be
spiked
at
2
times
the
background
concentration
of
mercury,
the
regulatory
compliance
limit
would
need
to
be
greater
than
2
times
the
background
concentration
in
order
for
the
sample
to
be
spiked
at
the
regulatory
compliance
limit
rather
than
at
2
times
the
background
concentration.

If
two
analytical
batches
of
20
or
fewer
samples
are
run
in
the
same
day,
must
there
be
a
total
of
6
bubbler
blanks,
2
OPRs,
and
2
QCSs
?

No,
there
must
be
3
bubbler
blanks,
2
OPRs
(
one
at
the
beginning
and
one
at
the
end)
and
a
QCS
associated
with
each
batch,
as
required
by
Section
9.1.7
of
the
Method.

What
frequency
is
required
for
the
OPR
?

The
OPR
must
be
run
at
the
beginning
and
end
of
each
batch
of
20
or
fewer
samples.
If
there
is
only
one
sample
in
the
batch,
an
OPR
must
be
run
before
and
after
the
sample.
See
Section
9.5.1
of
Method
1631.
The
purpose
of
requiring
an
OPR
before
and
after
the
batch
is
to
assure
that
the
analytical
system
remains
in
calibration
during
the
period
that
samples
are
run.
The
OPR
at
the
end
of
one
batch
of
samples
can
serve
as
the
OPR
at
the
beginning
of
the
following
batch
of
samples,
so
long
as
the
12­
hour
shift
for
the
batch
(
Method
1613B,
Section
9.1.7)
is
not
exceeded.

Laboratories
are
not
always
in
contact
with
sampling
teams.
Why
should
we
have
to
communicate
that
sampling
precision
is
inadequate,
as
stated
in
Section
9.7
of
the
Method?

Section
9.7
of
the
method
states
that
the
laboratory
may
be
required
to
analyze
field
duplicates
if
needed
for
specific
program
requirements.
It
also
states
that,
when
these
are
analyzed,
the
relative
percent
difference
(
RPD)
between
field
duplicates
should
be
<
20%
and
that
the
laboratory
should
notify
the
sampling
team
if
the
RPD
exceeds
20%.
The
words
"
should"
in
Section
9.7
convey
that
the
action
is
recommended
and
is
not
required.
The
reason
for
the
suggestion
to
communicate
inadequate
sampling
precision
to
the
sampling
team
was
to
alert
the
team
that
samples
were
not
being
collected
precisely.
This
would
allow
the
team
to
study
its
collection
activities
and
attempt
to
determine
why
duplicate
samples
either
were
not
collected
correctly
or
resulted
in
different
levels
of
mercury.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
15
Miscellaneous
Questions
How
much
should
I
be
concerned
about
contamination
from
the
bromine
monochloride
(
BrCl)
and
other
reagents
?

Method
1631
requires
analysis
of
at
least
one
reagent
blank
(
with
monthly
verification
in
triplicate)
for
each
new
batch
of
reagents.
The
degree
of
concern
is
based
on
the
level
of
mercury
to
be
measured
and
on
the
amount
of
reagent
required
for
complete
oxidation.
The
amount
of
reagent
used
depends
on
the
matrix
being
analyzed
(
for
example,
samples
that
are
high
in
organic
material
may
require
additional
BrCl).
The
way
in
which
you
can
make
sure
that
any
reagent
used
in
the
analysis
will
not
contaminate
a
sample
is
to
test
that
reagent
using
the
reagent
blank
procedure
in
Section
9.4.2
of
Method
1631.
We
suggest
that
laboratories
test
the
reagents
daily.
If
a
method
blank
is
run
with
each
batch,
the
method
blank
can
serve
this
purpose
(
see
the
subsection
on
the
method
blank
under
the
question
"
Is
the
bubbler
blank
the
same
as
a
laboratory
(
method)
blank?")

How
safe
is
bromine
monochloride
?
It
seems
dangerous
to
us.

BrCl
is
dangerous,
as
are
the
hot
acid
vat
and
the
acids
suggested
for
use
in
labware
cleaning
in
Method
1631.
Precautions
for
handling
these
materials
are
given
in
Section
5.0
and
Section
7.0
and
are
further
noted
in
various
sections
throughout
the
Method.
Laboratory
personnel
should
be
trained
in
safe
handling
of
these
reagents
and
materials.
See
Section
5.0
(
Safety)
in
Method
1631.

How
do
I
know
when
enough
BrCl
has
been
added
to
an
opaque
sample
?

Method
1631
requires
the
addition
of
0.5
mL
BrCl
solution
to
clear
samples
and
1.0
mL
BrCl
solution
to
brown
or
turbid
samples.
There
are
matrices,
particularly
those
with
high
organic
content,
that
may
require
additional
BrCl,
elevated
temperatures,
or
photo­
oxidation.
Method
1631
requires
addition
of
BrCl
(
or
complete
oxidation)
until
a
yellow
color
persists
or
until
starch
iodide
paper
indicates
the
presence
of
residual
BrCl
oxidizer
(
see
Section
11.1.1
of
Method
1631).

Method
1631
uses
calibration
factors
and
the
relative
standard
deviation
of
calibration
factors
for
establishing
calibration
linearity.
Nearly
all
other
metals
methods
use
linear
regression.
Why
is
Method
1631
different
?

The
calibration
factor
approach
is
the
simplest
form
of
weighted
regression
that
we
have
been
able
to
devise.
It
assumes
that
a
straight
line
through
the
origin
is
most
representative
for
most
instruments
and
analytical
systems.
We
have
studied
various
approaches
to
calibration
over
the
past
several
years
and
have
worked
with
statisticians
to
resolve
the
proper
means
of
establishing
calibration.
Nearly
all
statisticians
and
knowledgeable
analytical
chemists
now
agree
that,
for
nearly
all
analytical
systems
and
instruments,
a
weighted
regression
is
the
proper
form.
Recently,
the
International
Union
of
Pure
and
Applied
Chemistry
(
IUPAC)
came
to
the
same
conclusion
(
see
Pure
and
Applied
Chemistry
70,
993­
1014
(
1998)).

For
Method
1631,
laboratories
in
our
inter­
laboratory
method
validation
study
had
little
difficulty
using
the
calibration
factor
approach
or
in
meeting
the
relative
standard
deviation
(
RSD)
criterion
of
15
percent
in
the
calibration
factor
approach.
Therefore,
the
15
percent
criterion
was
retained
in
Method
1631.

Regarding
the
regression
used
in
nearly
all
metals
methods,
this
regression
is
unweighted;
i.
e.,
it
assumes
that
the
standard
deviation
is
the
same
at
all
concentrations.
An
unweighted
regression
is
incorrect
for
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
16
nearly
all
instruments
and
analytical
systems.
Weighting
should
be
inversely
proportional
to
concentration
for
nearly
all
analytical
systems
and
instruments
as
we
and
IUPAC
have
learned
(
pH
would
be
an
exception).
Therefore,
we
have
required
use
of
the
simplest
form
of
weighted
regression
in
Method
1631.

Can
we
use
the
slope,
intercept,
and
correlation
coefficient
method
of
calibrating
and
calculating
results,
provided
that
we
demonstrate
equivalency
?

As
stated
above,
we
have
found
that
a
weighted
regression
is
most
appropriate
for
analytical
chemistry
measurements,
and
that
the
calibration
factor
approach
is
the
simplest
form
of
weighted
regression.
Therefore,
only
a
weighted
regression
would
be
considered
equivalent
to
the
CF
approach.
The
slope,
intercept,
and
correlation
coefficient
method
traditionally
used
for
metals
measurements,
and
that
uses
an
unweighted
regression,
may
not
be
used.

Recently,
EPA
allowed
use
of
a
"
linear
calibration"
for
automated
calculations
in
metals
methods.
This
"
linear
calibration"
can
be
used
for
automated
calculations
provided
that
the
linear
calibration
is
weighted.

Why
doesn't
EPA
make
every
effort
to
communicate
its
expectations
on
linear
regression
to
manufacturers
of
instruments
?

The
calibration
factor
and
weighted
linear
regression
approach
to
calibration
have
been
in
existence
for
more
than
25
years
and
have
been
used
in
automated
GC/
MS
data
systems
since
that
time.
Therefore,
instrument
manufacturers
have
known
about
this
approach
for
some
time.
EPA
proposed
Method
1631
in
May
of
1998
and
published
the
final
rule
in
June
of
1999.
The
calibration
factor
approach
was
included
in
the
proposal,
giving
instrument
manufacturers
more
than
a
year
to
implement
the
calibration
factor/
weighted
regression
approach.

EPA
reviewed
a
study
performed
by
Tekran,
Inc.,
one
of
the
manufacturers
of
instruments
for
determination
of
mercury
using
EPA
Method
1631,
that
used
both
the
calibration
factor/
weighted
regression
(
CF/
WR)
and
unweighted
regression
approaches.
The
calibration
included
a
data
point
at
the
Method
1631
MDL
(
0.2
ng/
L).
The
RSD
for
the
CF/
WR
approach
was
7.8
percent.
The
coefficient
of
determination
(
r2)
for
the
unweighted
approach
was
1.000,
indicating
no
error
in
calibration.
The
reason
for
the
indication
of
zero
error
is
that
the
low
calibration
points
are,
essentially,
unweighted.
Therefore,
the
unweighted
regression
is
equivalent
to
a
single­
point
calibration
at
the
highest
calibration
point.
We
do
not
believe
that
this
form
of
calibration
is
consistent
with
the
best
science.

Why
doesn't
EPA
require
dilution
when
the
concentration
in
a
sample
is
greater
than
90
percent
of
the
linear
dynamic
range
(
LDR),
as
with
some
other
EPA
metals
methods
?

The
LDR
for
Method
1631
is
to
100
ng/
L.
You
may
dilute
the
sample
when
90
percent
of
the
LDR
is
exceeded,
if
desired.
The
reason
that
we
did
not
require
dilution
of
the
sample
when
this
level
is
exceeded
is
that
all
of
the
laboratories
in
EPA's
interlaboratory
validation
study
of
Method
1631
were
able
to
demonstrate
linearity
to
100
ng/
L.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
17
The
highest
ambient
criterion
for
mercury
is
12
ng/
L.
Why
is
calibration
performed
to
100
ng/
L
?

The
range
of
Method
1631
was
established
by
the
technology
used.
In
initial
tests
it
was
found
that
the
linear
range
extended
to
100
ng/
L.
This
range
was
verified
in
the
interlaboratory
validation
study.
If
you
chose
to
use
a
lesser
range,
you
may
dilute
samples
into
the
region
of
the
ambient
criterion.
However,
you
must
calibrate
to
100
ng/
L
and
demonstrate
linearity
to
this
level.

Must
our
laboratory
discard
the
secondary
standard
on
the
expiration
date
even
if
it
is
still
within
the
control
limits
of
Method
1631
?

Yes.
The
secondary
standard
(
typically
1.00
F
g/
mL
Hg)
must
be
discarded
(
Section
7.8
of
the
Method)
.
The
reason
is
that
there
is
error
associated
with
testing
the
standard.
If
the
results
of
testing
show
that
the
standard
is
barely
within
the
high
or
low
control
limit,
the
results
of
sample
analyses
could
be
inaccurate.
To
preclude
generation
of
waste
containing
mercury,
the
amount
of
the
secondary
standard
prepared
should
be
consistent
with
the
amount
that
will
be
required
during
the
life
of
the
standard.
Section
14.1
of
Method
1631
states:
"
Standards
should
be
prepared
in
volumes
consistent
with
laboratory
use
to
minimize
the
disposal
of
excess
volumes
of
expired
standards."

Sections
7.9
and
7.10
state
that
the
working
standards
"
should"
be
replaced
monthly.
Does
the
word
"
should"
imply
that
it
is
the
laboratory's
discretion
?

Yes.
As
defined
in
the
Glossary
at
the
end
of
Method
1631,
"
should"
means
that
a
given
action,
activity,
or
procedure
is
suggested,
but
not
required.
However,
if
it
is
later
shown
that
a
working
standard
held
for
more
than
one
month
was
inaccurate,
the
intended
objective
of
ensuring
reliable
measurements
of
mercury
by
Method
1631
would
not
have
been
met.
It
is
the
laboratory's
responsibility
to
assure
that
measurements
made
are
reliable.

How
expensive
is
it
to
set
up
Method
1631
?

Depending
on
how
many
analyses
are
to
be
performed
and
whether
new
or
used
materials
will
be
used
for
construction,
costs
can
range
from
thousands
to
hundreds
of
thousands
of
dollars.
The
Clean
Spaces
Guidance
can
assist
you
in
cost
minimization.
This
document
describes
how
costs
to
establish
a
trace
metals
laboratory
at
the
University
of
California
Santa
Cruz
were
minimized
to
a
few
thousand
dollars.
For
a
complete,
new,
clean
room
for
mercury
analyses,
we
estimate
the
cost
at
approximately
$
150,000
and
the
costs
for
equipment
and
instrumentation
at
$
50,000.
If
one
or
only
a
few
samples
are
to
be
analyzed,
the
most
cost­
effective
means
is
to
contract
through
a
laboratory
routinely
determining
mercury
at
the
levels
required.

What
criteria
should
I
use
in
selecting
a
laboratory
?

As
with
other
analyses,
selection
should
be
based
on
the
experience
of
the
laboratory
in
making
the
particular
measurement,
the
knowledge
and
skill
of
laboratory
personnel
with
the
particular
technology,
the
quality
assurance/
quality
control
applied
to
the
analysis,
the
documented
history
of
performance
of
the
laboratory
in
making
the
measurements,
and
to
a
lesser
extent,
the
fee
charge
by
the
laboratory.
For
determination
of
mercury
using
Method
1631,
particularly
for
making
measurements
at
or
near
1
ng/
L,
a
documented
history
of
freedom
from
contamination
and
recovery
of
OPRs
and
MS/
MSDs
within
the
QC
acceptance
criteria
of
Method
1631
provides
an
indication
that
the
analyses
are
being
performed
reliably.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
5­
18
EPA
believes
that
the
laboratories
that
participated
in
the
interlaboratory
validation
of
Method
1631
are
all
capable
of
performing
mercury
determinations
reliably.
However,
the
user
should
review
the
performance
of
these
and
other
laboratories
in
the
context
of
the
objectives
of
any
study.

What
data
can
and
cannot
be
reported
for
regulatory
compliance
purposes,
and
is
it
the
laboratory
or
discharger's
responsibility
to
make
the
determination
?

In
general,
only
sample
results
that
are
associated
with
QC
data
that
meet
the
QC
requirements
in
Method
1631
may
be
reported
or
used
for
permitting
or
regulatory
compliance
purposes.
See
Sections
9.3.4.1,
9.3.4.2,
9.4.3.2,
and
13.2
of
Method
1631.

If
the
data
are
to
be
used
for
permitting
or
regulatory
compliance
under
a
permit,
all
data
are
the
responsibility
of
the
discharger/
permittee.
It
is
the
laboratory's
responsibility
to
make
sure
that
all
QC
acceptance
criteria
are
met.
An
exception
would
be
if
a
matrix
interference
could
not
be
overcome
and
precluded
the
MS/
MSD
recovery
and
precision
criteria
from
being
met.
See
the
chapter
on
Matrix
Interferences
in
this
guidance
for
the
action
to
be
taken
when
a
matrix
interference
is
encountered.

In
addition,
a
laboratory
cannot
be
responsible
for
activities
over
which
it
has
no
control.
If
a
discharger
collects
samples
and
a
field
blank,
and
the
field
blank
is
contaminated,
it
is
the
discharger's
responsibility.
If,
however,
a
reagent
or
laboratory
blank
is
contaminated
and
the
associated
field
blank
is
contaminated,
it
is
possible
that
the
laboratory
contaminated
the
field
blank.
In
this
case,
the
contaminated
field
blank
would
be
the
laboratory's
responsibility.
Regardless
of
whose
responsibility
it
is,
the
result
for
a
sample
associated
with
a
contaminated
field
blank
generally
may
not
be
reported
or
otherwise
used
for
permitting
or
regulatory
compliance
purposes
(
see
Section
9.4.3.2
of
Method
1631),
unless
the
contamination
has
no
negative
effect
on
the
objective
of
the
monitoring
program.
For
example,
sample
results
that
are
associated
with
contaminated
field
blanks,
but
also
are
still
below
the
regulatory
compliance
threshold,
may
be
used
to
demonstrate
permit
compliance.
Additional
guidance
concerning
the
possible
use
of
data
associated
with
certain
types
of
QC
failures
is
provided
in
Guidance
on
the
Documentation
and
Evaluation
of
Trace
Metals
Data
Collected
for
Clean
Water
Act
Compliance
Monitoring,
which
is
referenced
in
Chapter
6
of
this
document.

Are
reporting
requirements
in
Section
12.4
of
Method
1631
the
laboratory's
responsibility
or
the
discharger's
?

For
permitting
or
regulatory
compliance
purposes,
the
reporting
requirements
are
the
responsibility
of
the
discharger/
permittee.
However,
the
discharger/
permittee
can
only
report
results
as
reliable
as
those
produced
by
the
laboratory.
In
addition,
the
laboratory
is
closest
to
the
analysis
and,
therefore,
most
familiar
with
the
data
being
reported
to
the
discharger/
permittee.
To
the
extent
possible,
the
laboratory
should
provide
data
to
the
discharger/
permittee
that
will
satisfy
the
requirements
in
Section
12.4
and
the
permit.

Can
laboratories
report
results
below
the
ML
for
field
samples
?

Yes.
There
is
nothing
in
Method
1631
that
precludes
laboratories
from
reporting
results
in
ways
different
from
those
specified
in
Section
12.4,
provided
that
the
results
are
also
reported
as
specified
in
Section
12.4.
Section
12.4
requires
that
laboratories
report
results
below
the
ML
as
<
0.5
ng/
L
or
as
required
by
the
regulatory
authority
or
in
the
permit.
However,
if
a
regulatory/
control
authority
or
the
permit
requires
reporting
of
results
without
censoring
at
the
ML
or
MDL
(
i.
e.,
at
as
low
a
level
as
possible),
the
result
must
be
reported
without
censoring.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
6­
1
Chapter
6:
Sources
of
Information
This
section
provides
sources
of
information
related
to
the
final
guidelines
establishing
test
procedures
for
measurement
of
mercury
in
water.
Specifically,
this
section
provides
a
listing
of
documents
pertaining
to
the
regulatory
background
and
data
gathering
for
EPA
Method
1631.

Regulatory
Background
Act
Clean
Water
Act
(
CWA)
­
Public
Law
92­
500,
et.
seq.;
33
U.
S.
C.
1251
et.
seq.

Analytical
methods
under
CWA
Sections
301,
304,
and
501
History:
see
Federal
Register,
February
7,
1991
(
56
FR
5090)
Support
for
effluent
guidelines:
see
Federal
Register,
October
18,
1995
(
60
FR
53988).
Proposal
of
Method
1631:
See
Federal
Register,
May
26,
1998
(
64
FR
28867).
Promulgation
of
Method
1631,
Revision
B:
See
Federal
Register,
June
8,
1999
(
64
FR
30417)

Data
Gathering
for
EPA
Method
1631
Proposal
See
Federal
Register,
May
26,
1998
(
64
FR
28867)
See
the
administrative
record
in
the
Water
Docket
(
Docket
W­
98­
15)
for
reports
supporting
the
proposal
of
Method
1631.

Notice
of
data
availability
(
NODA)
See
Federal
Register,
March
5,
1999
(
64
FR
10596)

Data
received
from
commenters
See
the
administrative
record
in
the
Water
Docket
(
Docket
W­
98­
15)
for
the
final
rule
Final
rule
See
Federal
Register,
June
8,
1999
(
64
FR
30417)
See
the
administrative
record
in
the
Water
Docket
(
Docket
W­
98­
15)
for
reports
supporting
the
promulgation
of
Method
1631,
Revision
B.

Documents
Supporting
EPA
Method
1631
°
Bloom,
Nicolas,
Draft
Total
Mercury
in
Aqueous
Media,
Frontier
Geosciences,
Inc.,
September
7,
1994.
°
Method
1669:
Sampling
Ambient
Water
for
Trace
Metals
at
EPA
Water
Quality
Criteria
Levels,
EPA
821­
R­
96­
011,
July
1996
°
Sampling
Ambient
and
Effluent
Waters
for
Trace
Metals,
EPA­
821­
V­
97­
001,
1997
°
Results
of
the
EPA
Method
1631
Interlaboratory
Validation
Study,
Available
from
the
EPA
Sample
Control
Center
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
6­
2
°
Guidance
on
Establishing
Trace
Metal
Clean
Rooms
in
Existing
Facilities
("
Clean
Spaces
Guidance"),
EPA­
821­
B­
96­
001,
April
1995
°
Trace
Metal
Cleanroom,
RTI/
6302/
04­
02
F,
Research
Triangle
Institute,
October
1995.
°
An
Analytical
Survey
of
Nine
POTWs
from
the
Great
Lakes
Basin,
Draft
Report,
US
EPA
Office
of
Science
and
Technology,
Analytical
Methods
Staff,
December
15,
1994
°
Evaluating
Field
Techniques
for
Collecting
Effluent
Samples
for
Trace
Metals
Analysis,
EPA
821­
R­
98­
008,
June
1998
°
Guidance
on
the
Documentation
and
Evaluation
of
Trace
Metals
Data
Collected
for
Clean
Water
Act
Compliance
Monitoring,
EPA
821B­
96­
004,
July
1996
See
also
the
references
at
the
end
of
EPA
Method
1631
Documents
on
Compliance
Monitoring
and
Methods
Guidance
on
Evaluation,
Resolution,
and
Documentation
of
Analytical
Problems
Associated
with
Compliance
Monitoring,
EPA­
821­
B­
93­
00,
June
1993.

Source
for
Documents
The
documents
listed
in
this
guidance
may
be
viewed
at
or
obtained
from
the
Water
Docket
(
see
the
address
below).
Nearly
all
documents
are
also
available
from
the
EPA
Sample
Control
Center:

EPA
Sample
Control
Center
EPA
Water
Docket
DynCorp
I&
ET
Waterside
Mall
6101
Stevenson
Avenue
401
M
Street,
Southwest
Alexandria,
VA
22304­
3540
Washington,
DC
Tel:
(
703)
461­
2100
Tel:
(
202)
260­
3027
Fax:
(
703)
461­
8056
E­
mail:
SCC@
DynCorp.
com
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
7­
1
Chapter
7:
Where
to
Get
Additional
Help
This
section
lists
reference
locations
and
EPA
contacts
that
may
provide
additional
information
related
to
the
final
guidelines
establishing
test
procedures
for
measurement
of
mercury
using
EPA
Method
1631.

EPA
contact
for
questions
specifically
related
to
Method
1631
Maria
Gomez­
Taylor
Engineering
and
Analysis
Division
(
4303)
U.
S.
EPA
Ariel
Rios
Building
1200
Pennsylvania
Avenue,
N.
W.
Washington,
DC
20460
Tel:
(
202)
260­
1639
Fax:
(
202)
260­
7185
E­
Mail:
gomez­
taylor.
maria@
epa.
gov
Water
Docket
The
administrative
record
(
public
comments,
EPA
responses,
and
all
supporting
documents
for
Method
1631,
including
those
listed
below)
are
available
for
review
at
the
Water
Docket.
For
access
to
docket
materials,
phone
the
Water
Docket
between
9:
00
a.
m.
and
3:
30
p.
m.
for
an
appointment.
The
address
below
is
for
the
physical
location
of
the
Water
Docket
and
is
not
a
mailing
address.
For
the
EPA
mailing
address,
see
the
address
for
the
EPA
contact
above.

EPA
Water
Docket
Waterside
Mall
401
M
Street,
Southwest
Washington,
DC
Tel:
(
202)
260­
3027
Websites
EPA's
home
page
on
the
World
Wide
Web:
http://
www.
epa.
gov
EPA's
Office
of
Science
and
Technology's
analytical
methods
and
water
documents
pages
on
the
World
Wide
Web:
http://
www.
epa.
gov/
OST/
Methods
(
water
methods)
http://
www.
epa.
gov/
ost/
guide
(
water
documents)
Guidance
­
EPA
Method
1631,
March
2001
1
This
Standard
Operating
Procedure
is
based
on
a
procedure
provided
by
Frontier
Geosciences,
Inc.
Guidance
­
Method
1631
A­
1
APPENDIX
A
Standard
Operating
Procedure
for
Collection
of
Ambient
Water
and
Wastewater
Samples
for
Determination
of
Mercury
Using
EPA
Method
1631
1
Note:
This
procedure
should
be
viewed
as
containing
the
minimum
steps
necessary
for
reliable
sampling.
Some
of
the
additional
measures
in
the
Sampling
Guidance
(
EPA
Method
1669)
may
be
necessary
to
preclude
contamination
at
some
sampling
sites.
EPA
Methods
1631
and
1669
are
referenced
throughout
this
SOP.
Advice
on
training,
equipment,
and
sampling
technique
is
also
available
from
laboratories
analyzing
samples
using
EPA
Method
1631.

1.0
Scope
and
Application
1.1
This
standard
operating
procedure
(
SOP)
gives
details
for
collection
of
grab
samples
of
ambient
water
and
wastewater
for
the
determination
of
low­
level
mercury.
Adherence
to
this
SOP
can
be
expected
to
minimize
contamination
from
the
sample
bottle
and
external
sources.
1.2
This
SOP
is
for
collection
of
a
grab
sample
directly
into
the
sample
bottle
(
e.
g.,
effluents,
rapidly
flowing
streams/
rivers)
(
Method
1669,
Section
8.2.5).
If
transfer
containers
(
e.
g.,
dippers)
or
other
equipment
(
sampling
pumps,
etc.)
are
required
to
obtain
samples,
including
composite
samples,
refer
to
EPA
Method
1669
for
detailed
guidance.

2.0
Sample
bottle
requirements
2.1
Sample
bottles
may
be
either
fluoropolymer
that
has
been
cleaned,
tested,
and
double
bagged
in
a
Class­
100
clean
bench
(
Method
1631,
Section
6.1.2.1
and
Method
1669,
Section
6.3),
or
borosilicate
glass
with
fluoropolymer­
lined
lids
obtained
from
a
supplier
that
certifies
cleanliness
for
metals
sampling
(
e.
g.,
I­
Chem,
Series
200
or
equivalent).
If
sample
bottles
are
from
a
bottle
lot,
a
statistically
relevant
number
of
bottles
in
the
lot
should
be
tested
to
demonstrate
freedom
from
contamination
at
levels
that
could
compromise
results
(
Method
1613B,
Section
9.4.4.1).
Untested
sample
bottles
must
not
be
used
as
they
may
be
the
source
of
possible
contamination
(
Method
1613B,
Section
9.4.4.1).
2.2
Sample
bottles
may
also
be
obtained
in
kit
form
from
the
laboratory.
A
kit
would
consist
of
double­
bagged
sample
bottles,
reagent
water
for
the
field
blank(
s),
gloves,
and
ice.
Blue
Ice
may
be
obtained
from
the
laboratory
or
locally;
wet
ice
should
be
obtained
locally.
3.0
Sample
collection
3.1
Collection
of
samples
is
performed
using
the
"
clean
hands­
dirty
hands"
technique
(
Method
1669,
Section
2.4).
Bottles
are
sealed
tightly
and
re­
bagged
using
the
opposite
series
of
steps
as
were
used
to
open
them.
Samples
are
either
preserved
immediately
upon
collection,
or
bottles
are
shipped
to
the
analytical
laboratory
via
overnight
courier
for
preservation
and
analysis.
3.2
Ideally,
at
least
two
persons
each
wearing
fresh
cleanroom
gloves
(
Method
1631,
Section
4.3.6
and
Method
1669,
Section
4.2.2.2)
are
required
on
a
sampling
crew.
Cleanroom
gloves
should
be
worn
at
all
times
when
handling
samples
or
sampling
equipment.
3.3
One
person
(
designated
"
dirty
hands")
removes
a
bagged
bottle
from
the
box
or
cooler,
and
opens
the
outer
bag,
avoiding
touching
the
inside
surface
of
that
bag.
3.4
The
other
person
(
designated
"
clean
hands")
reaches
in,
opens
the
inner
bag,
and
removes
the
sample
bottle.
"
Clean
hands"
should
not
touch
anything
but
the
outside
surface
of
the
sample
bottle
and
cap,
and
the
water
being
sampled.
If
anything
other
than
the
sample
bottle,
cap,
or
water
is
touched,
"
clean
hands"
must
change
gloves.
Guidance
­
EPA
Method
1631,
March
2001
Guidance
­
Method
1631
A­
2
3.5
"
Clean
hands"
opens
the
sample
bottle
and
holds
the
bottle
in
one
hand
and
the
cap
in
the
other.
If
it
is
necessary
to
set
the
cap
down,
it
should
be
placed
in
the
inner
bag
from
which
the
sample
bottle
was
removed.

Note:
The
person
collecting
the
sample
should
be
wary
of
disturbing
the
flow
upstream
of
the
sampling
point.
The
insertion
of
the
bottle
into
a
flowing
stream,
or
standing
in
the
flow
downstream
of
the
sampling
point,
creates
eddies
(
disturbances
in
the
upstream
flow)
that
can
resuspend
solids
near
the
sampling
point.
Entry
of
such
re­
suspended
solids
into
the
sample
may
produce
a
non­
representative
sample
and
could
increase
the
mercury
concentration.

3.6
Rinse
the
sample
bottle
and
inside
surface
of
the
cap
three
times
with
sample
water,
and
fill
the
bottle
to
the
top
with
sample
(
Method
1669,
Section
8.2.5.5).
Replace
the
cap
and
tighten
securely.

Note:
If
the
person
collecting
the
sample
cannot
directly
reach
the
water
to
be
sampled,
a
poletype
sampler
may
be
attached
to
the
sample
bottle
to
extend
the
reach
for
sample
collection.
The
pole
and
bottle
clamp
should
be
made
of
plastic
and/
or
stainless
steel
and
the
mouth
of
the
bottle
should
be
held
facing
upstream
of
the
pole.
The
use
of
a
transfer
vessel
should
be
avoided.

3.7
Re­
bag
the
bottle
in
the
opposite
order
that
it
was
removed.
3.8
Cleanroom
gloves
should
be
changed
between
samples
and
whenever
anything
not
known
to
be
trace
metal
clean
is
touched.

4.0
Collection
of
field
blanks
4.1
EPA
Method
1631
requires
collection
of
a
field
blank
with
every
10
samples
from
a
given
site
(
Method
1631,
Section
9.4.3.1).
A
sample
bottle
for
the
field
blank
should
be
requested
from
the
laboratory
when
the
sampling
kit
is
requested
(
Section
2.2
of
this
SOP).
A
separate
sample
bottle
as
well
as
a
bottle
filled
with
reagent
water
are
used
to
collect
the
field
blank.
4.2
To
collect
the
field
blank,
open
an
empty
sample
bottle
using
the
"
clean
hands­
dirty
hands"
techniques
described
above.
Also
open
the
bottle
containing
the
reagent
water.
4.3
Pour
the
reagent
water
into
the
empty
sample
bottle.
This
is
now
the
field
blank.
4.4
Re­
bag
the
field
blank
in
the
opposite
order
that
it
was
removed.

5.0
Preservation,
packing,
refrigeration,
and
shipment
of
samples
5.1
Following
collection,
samples
must
either
be
preserved
(
Method
1631,
Section
8.5)
or
may
be
shipped
unpreserved
if
they
are
(
1)
collected
in
glass
or
fluoropolymer
bottles,
(
2)
filled
to
the
top
with
no
head
space,
(
3)
capped
tightly,
and
(
4)
maintained
at
0
 
4
E
C
from
the
time
of
collection
until
preservation.
The
samples
must
be
acid­
preserved
within
48
h
after
sampling
(
Method
1631,
Section
8.5.1).
5.2
Pack
sample
bottles
upright
to
prevent
the
area
around
the
bottle
cap
from
becoming
wet.
Wrap
glass
sample
bottles
with
bubble­
type
packing
to
prevent
breakage
during
shipment.
5.3
Blue
Ice
or
wet
ice
may
be
used
to
refrigerate
sample
bottles.
The
Blue
Ice
must
be
frozen
prior
to
sampling.
If
the
sample
in
a
glass
sample
bottle
is
cooled
to
0
E
C
prior
to
shipment
and
packed
in
frozen
blue
ice,
the
sample
may
freeze
and
rupture
the
bottle.
Wet
ice
avoids
this
problem
but
increases
the
potential
for
mercury
contamination
because
the
sample
bottle
may
become
immersed
in
water
from
the
melting
ice.
Packaging
the
wet
ice
in
multiple
plastic
bags
will
preclude
water
from
melted
ice
from
reaching
the
sample
bottle.
