1
Peer
Review
Comments
on:

Technical
Background
Document:
Mercury
Wastes
Evaluation
of
Treatment
of
Bulk
Elemental
Waste
January
24,
2003
Submitted
by:

Science
Applications
International
Corporation
Engineering
and
Environmental
Management
Group
11251
Roger
Bacon
Drive
Reston,
Virginia
20190
Submitted
to:

U.
S.
Environmental
Protection
Agency
Ariel
Rios
Building
Office
of
Solid
Waste
1200
Pennsylvania
Avenue,
N.
W.
Washington,
D.
C.
20460
EPA
Contract
No.
68­
W0­
0122
Work
Assignment
No.
1­
2
SAIC
Project
No.
06­
0758­
08­
2889­
000
2
Evaluation
of
Treatment
of
Bulk
Elemental
Mercury
In
order
to
help
evaluate
whether
EPA
could
propose
treatment
and
disposal
alternatives
to
the
current
land
disposal
restriction
(
LDR)
treatment
standard
of
mercury
retorting,
EPA
conducted
a
study
on
the
treatment
of
bulk
elemental
mercury.
The
study
was
performed
to
assess
conditions
that
affect
the
stability
of
waste
residues
resulting
from
the
treatment
of
bulk
elemental
mercury.
The
results
of
the
study
were
submitted
for
formal,
independent
peer
review
by
three
national
experts
with
significant
technical
expertise
in
hazardous
waste
leaching.
These
peer
reviewers
have
no
prior
association
with
this
study,
and
have
no
perceived
or
actual
conflict
with
any
impact
of
the
study
results.
The
members
of
the
peer
review
panel
were
tasked
with
evaluating
the
adequacy
of
the
experimental
design,
conduct,
and
conclusions
of
the
study.
The
peer
review
panel
also
provided
information
on
how
the
study
can
be
used
to
provide
a
framework
to
determine
whether
additional
protective
measures
are
required
to
prevent
loss
of
mercury
to
the
environment
from
the
treatment
and
co­
disposal
of
mercury­
bearing
wastes
in
landfills.
Additionally,
the
members
of
the
peer
review
panel
were
asked
if
additional
studies
were
warranted
for
other
factors
that
impact
solubility
(
e.
g.,
liquid/
solid
ratio,
redox
conditions,
leachate
composition)
or
affect
ability
to
leach
(
such
as
use
of
macroencapsulation).
The
specific
questions
asked
of
the
peer
reviewers
are
provided
in
this
document,
along
with
the
peer
reviewer's
comments,
and
EPA's
responses
to
those
comments.

Charge
Question
1:
Was
the
experimental
design
of
the
study
appropriate?

Reviewer
#
1:
Yes.
This
study
was
conducted
with
well­
defined
objectives
and
a
carefully
generated
study
design.
The
test
protocols
and
operating
instructions
were
well
developed.
This
study
conducted
controlled
laboratory
testing
of
elemental
mercury
stabilization
offered
by
commercially
available
methods
and
vendors.
The
stabilized
samples
were
tested
for
leaching
in
the
laboratory
in
a
replicated
manner.

Reviewer
#
2:
The
design
followed
neither
EPA
guidance
nor
requirements
for
the
use
of
Data
Quality
Objectives.
3
Response:
EPA
has
developed
the
DQOs
process
as
the
Agency's
recommended
planning
process
when
environmental
data
are
used
to
select
between
two
opposing
conditions,
such
as
achieving
or
not
achieving
a
numerical
standard.
The
DQOs
process
is
used
to
develop
qualitative
and
quantitative
statements
of
the
overall
level
of
uncertainty
that
a
decision­
maker
is
willing
to
accept
in
results
or
decisions
derived
from
environmental
data,
i.
e.,
Data
Quality
Objectives.
The
DQOs
process
entails
a
seven
step
systematic
procedure
for
defining
the
criteria
that
a
data
collection
design
should
satisfy,
including
when
to
collect
samples,
where
to
collect
samples,
the
tolerable
level
of
decision
error
for
the
study,
and
how
many
samples
to
collect,
balancing
risk
and
cost
in
an
acceptable
manner.
When
this
process
is
not
directly
applicable
(
i.
e.,
the
experimental
objective
is
estimation,
research,
or
any
other
objective
that
does
not
select
between
two
distinct
conditions),
the
Agency
recommends
the
use
of
a
systematic
planning
method
for
defining
performance
criteria.
For
this
research
project,
a
systematic
planning
method
was
used.
A
Quality
Assurance
Project
Plan
(
QAPP)
was
developed
by
EPA
and
was
followed
throughout
the
project.
EPA
believes
that
the
project
objectives
and
criteria
were
logical,
given
the
intended
end­
use
of
the
data,
well­
defined,
and
achievable.

I
could
not
find
the
QAPP
for
this
project
(
the
included
QAPP
appeared
identical
to
the
QAPP
for
the
surrogate
sludge
project),
but
it
apparently
dealt
with
only
laboratory
QA/
QC
and
not
the
larger
issues
of
decisions
to
be
made,
decision
error,
and
optimizing
the
plan.
Had
this
been
done,
the
problems
of
treated
waste
inhomogeneity,
sub­
sampling,
numbers
of
samples,
and
optimizing
data
collection,
e.
g.,
using
composite
samples,
could
have
been
incorporated
into
the
study
design.
In
particular,
a
clear
statement
of
the
decisions
could
have
noted
the
importance
of
leaching
solids
up
to
at
least
pH
12.5,
the
regulatory
limit
for
hazardous
waste.
Perhaps
more
important,
a
statement
of
acceptable
errors
should
have
been
included,
e.
g.,
a
treatment
technology
must
be
effective
on
90%
of
wastes
with
a
90%
confidence.
Without
such
a
statement,
it
is
difficult
to
decide
when
a
technology
is
good
enough.

Response:
EPA
added
the
study
on
stabilization
of
bulk
elemental
mercury
to
an
on­
going
study
on
the
stabilization
of
mercury­
contaminated
surrogate
waste.
The
study
was
added
because
of
concerns
about
long­
term
disposition
of
the
Defense
Logistics
Agency
(
DLA)
mercury
stockpile,
and
was
intended
to
mirror
the
on­
going
study,
both
in
experimental
design
and
study
goals.
Because
of
this
similarity
in
design
and
goals,
the
very
limited
amount
of
time
remaining
in
the
contract,
as
well
as
budget
limitations,
the
decision
was
made
to
operate
the
bulk
elemental
study
under
the
surrogate
study
QAPP.
The
heterogeneity
issues
experienced
during
the
bulk
elemental
mercury
study
were
very
similar
to
those
experienced
during
the
surrogate
study
­
they
were
not
predicted
during
the
planning
phase
of
either
study,
and
would
not
have
been
better
identified
in
a
separate
planning
document.
The
study
was
intended
to
evaluate
how
well
the
available
treatment
technologies
performed
on
a
level
playing
field,
not
to
determine
if
the
treatment
technologies
could
meet
a
certain
performance
standard.
Therefore,
a
statement
of
acceptable
error
would
have
been
inappropriate.
4
The
design
of
leaching
waste
treated
with
mercuric
selenide
was
not
consistent
with
the
other
leaching
tests
and
only
included
leaching
at
two
pHs.
As
a
result,
the
conclusion
regarding
the
effect
of
chloride
could
not
be
compared
with
the
effect
of
pH
over
a
larger
range.

Response:
A
technology
is
available
that
threats
waste
with
selenium,
forming
mercuric
selenide
as
the
stable
(
insoluble)
treatment
residual.
During
the
stabilization
evaluation,
the
solubility
of
mercuric
selenide
in
the
presence
of
chloride
ions
was
evaluated
using
a
computer
model
(
Minteq).
The
results
of
that
modeling
exercise
indicated
that
mercuric
selenide
becomes
soluble
when
exposed
to
chloride
ions
for
some
unknown
period
of
time.
This
finding
prompted
EPA
to
add
an
evaluation
of
the
stability
of
mercuric
selenide
in
the
constant­
pH
leaching
test,
with
and
without
chloride
ions,
to
evaluate
solubility
in
the
short
term.
This
experiment
was
not
intended
to
be
comparable
to
the
larger­
pH
range
leaching
tests
conducted
for
the
other
treatment
technologies.

Reviewer
#
3:
The
experimental
design
was
generally
appropriate.
One
exception
was
the
failure
to
confirm
that
waste
loadings
(
elemental
mercury
loadings)
were
as
reported
by
the
vendors.
The
report
does
not
present
any
data
supporting
the
reported
waste
loadings.
The
experimental
plan
calls
for
mercury
concentrations
in
the
waste
forms
to
be
determined,
but
these
data
are
not
presented.
These
concentrations
would
be
a
check
on
the
reported
waste
loadings
and
should
be
reported.

Response:
That
analytical
plan
called
for
the
determination
of
waste
loadings
using
SW­
846
Method
7470A,
Mercury
in
Liquid
Waste
(
Manual
Cold­
Vapor
Technique).
This
analytical
approach
yielded
poor
recoveries
because
the
treatment
residual
was
difficult
to
digest,
making
it
impossible
to
dissolve
the
mercury
and
make
it
available
for
analysis.
As
a
result,
the
waste
loadings
reported
by
the
vendors
could
not
be
verified.

Identifying
the
concentrations
of
mercury
in
the
waste
forms
among
the
raw
data
in
Appendix
B
is
difficult.
However,
an
attempt
was
made
to
identify
these
concentrations
and
it
appears
that
the
mercury
contents
of
treated
solids
from
some
vendors
were
much
lower
than
expected
from
reported
waste
loadings.
The
highest
concentration
reported
for
a
solid
from
vendor
A
(
samples
01
to
10,
p
B­
98)
is
16,400
mg/
kg,
compared
to
a
concentration
of
330,000
mg/
kg
expected
from
the
reported
waste
loading
of
33%.
The
highest
concentration
found
for
a
solid
treated
by
Vendor
B
(
samples
34
to
43
on
p
B­
154,
B­
155)
is
285,000
mg/
kg
compared
to
concentrations
of
550,000
mg/
kg
and
440,000
mg/
kg
expected
for
waste
loadings
of
55%
(
Phase
I)
and
44%
(
Phase
II).
Other
concentrations
are
reported
in
this
group
that
are
much
lower.
The
highest
concentration
found
for
a
solid
treated
by
Vendor
C
is
10,700
mg/
kg
(
samples
9
to
13,
p.
B­
67)
compared
to
a
concentration
of
201,000
mg/
kg
expected
for
a
waste
loading
of
20.1%.

Response:
The
reported
concentration
are
from
the
analyses
with
incomplete
digestion
discussed
previously,
and
are
recognized
to
be
lower
than
the
"
true"
values.
The
reported
waste
loadings
are
theoretical
values,
based
on
the
known
masses
of
mercury
added
to
know
masses
of
additives
in
the
treatment
process.
5
Recoveries
of
metals
from
treated
wastes
are
often
less
than
expected.
Low
recoveries
can
be
the
result
of
inadequate
analytical
procedures
for
measuring
metals
in
solids
that
have
been
treated
with
the
intent
to
reduce
the
availability
of
the
metal.
No
information
was
given
concerning
the
dissolution
procedures
used
on
the
treated
wastes
to
solubilize
mercury
prior
to
analysis.
The
only
procedure
specified
(
SW
846
Method
7470A)
is
a
method
for
analyzing
mercury
in
aqueous
solutions.
Therefore,
there
is
no
way
to
determine
if
the
dissolution
procedure
could
be
expected
to
reliably
recover
mercury.
Regardless
of
the
reason
for
the
low
recoveries
for
treated
wastes
submitted
by
Vendors
A
and
C,
they
are
so
low
that
they
cast
doubt
on
the
meaningfulness
of
the
results
of
leaching
tests.

Response:
The
sample
digestion
protocol
used
for
the
solid
samples
is
described
in
Appendix
B,
pages
207­
213.
This
digestion
procedure
follows
the
first
digestion
option
provided
in
SW­
846
Method
7471A
Mercury
in
Solid
or
Semi­
solid
Waste
(
Manual
Cold­
Vapor
Technique).
The
determinative
portions
of
the
two
procedures
are
identical.
Therefore,
we
can
assume
that
the
procedure
could
be
expected
to
reliably
recover
mercury.

All
spike
recovery
measurements
of
the
leachates
achieved
quantitative
recoveries
between
84%
and
109%.
Thus,
there
is
no
evidence
of
a
problem
with
the
analysis
of
mercury
in
the
leachates.
We
believe
this
is
because
the
mercury
was
in
solution,
and
therefore,
available
for
analysis.

Charge
Question
2:
Was
the
study
conducted
properly?

Reviewer
#
1:
Most
likely
yes,
although
there
are
possible
heterogeneity
present
in
the
stabilized
wastes
as
indicated
by
large
variability
in
concentrations
in
replicates
subjected
to
leaching
tests.
My
review
of
the
material
in
the
report
suggests
that
the
vendors
and
laboratories
properly
carried
out
the
preparation
of
stabilized
waste
forms
and
the
leaching
tests
required
on
the
stabilized
samples.
Appropriate
QA/
QC
and
reporting
of
results
have
been
accomplished.

Reviewer
#
2:
The
lab
procedures
appear
acceptable,
although
I
could
not
find
detailed
sampling
and
sub­
sampling
procedures.
The
procedures
appear
to
have
been
carried
out
correctly.

Response:
General
sampling
procedures
are
provided
in
Section
4.0
of
the
QAPP.
Specific
sampling
and
sub­
sampling
procedures
were
not
provided,
as
the
physical
form
and
characteristics
of
the
treated
waste
forms
was
not
well­
defined
before
the
treatment
took
place.
Each
vendor
was
charged
with
using
best
professional
judgement
and
skill
at
ensuring
that
the
treated
waste
form
submitted
was
representative
of
the
bulk
of
the
entire
treated
waste
form.
In
subsampling
the
waste
form
for
testing
purposes,
the
engineers
conducting
the
testing
were
similarly
charged.

Reviewer
#
3
The
study
was
conducted
properly,
with
the
exception
of
assuring
that
waste
loadings
were
as
reported
by
the
vendors.

Response:
As
discussed
earlier,
the
analytical
plan
called
for
the
determination
of
waste
6
loadings
using
SW­
846
Method
7470A,
Mercury
in
Liquid
Waste
(
Manual
Cold­
Vapor
Technique).
This
analytical
approach
yielded
poor
recoveries
because
the
treatment
residual
was
difficult
to
digest,
making
it
impossible
to
dissolve
the
mercury
and
make
it
available
for
analysis.
As
a
result,
the
waste
loadings
reported
by
the
vendors
could
not
be
verified.

Charge
Question
3:
Were
the
stated
objectives
adequately
met?

Reviewer
#
1:
Yes.
The
report
specifies
two
major
objectives
as
(
1)
to
evaluate
alternative
treatment
processes
for
elemental
mercury
to
meet
a
TCLP
treatment
goal
of
0.025
mg/
L
or
less,
and
(
2)
to
empirically
test
and
compare
new
leaching
protocols
to
the
standard
TCLP
method.
This
study
included
testing
of
pellets
and
crushed
samples
of
the
stabilized/
treated
elemental
mercury.
In
addition,
limited
evaluation
was
conducted
to
examine
the
effects
of
chloride
in
leaching
solution
on
leaching
of
mercury
from
stabilized
materials.
The
results
and
graphs
presented
in
this
report
clearly
show
that
there
are
significant
differences
in
the
effectiveness
of
the
various
treatment
technologies.
The
constant
pH
leaching
test
results
indicate
that
leaching
of
mercury
from
the
stabilized
elemental
mercury
is
a
pH
dependent
phenomenon.
For
example,
Vendor
B
stabilized
material
shows
a
monotonic
increase
in
mercury
leaching
as
the
leaching
fluid
pH
is
increased
from
highly
acidic
to
highly
alkaline.
Vendor
C
stabilized
elemental
mercury
shows
a
decreasing
leaching
pattern
when
leaching
fluid
pH
is
increased
from
acidic
pH
of
2.
The
Vendor
A
results
are
more
variable.
The
leaching
test
results
indicate
that
Vendor
B
treatment
performs
the
best
and
meets
the
treatment
goal
of
0.025
mg/
L
leachate
concentration
for
pH
range
of
2
to
at
least
10.
The
Vendor
C
stabilized
material
does
not
yield
results
that
are
0.025
mg/
L
and/
or
lower.
Vendor
A
does
produce
stabilized
material
that
meets
the
leaching
goal
only
at
pH
2.
Therefore,
this
study
report
should
recognize
that
all
treatment
technologies
that
were
tested
are
not
equally
effective,
and
that
Vendor
B
technology
provides
the
most
effective
method
for
a
large
range
of
pH
conditions.
This
report
also
needs
to
conclude
that
the
new
leaching
test
protocols
yield
significantly
different
leaching
concentrations
than
the
TCLP
test.
This
is
not
surprising,
particularly
when
elemental
mercury
is
being
reacted
to
form
a
sulfide
solid
phase
compound
that
is
known
to
have
pH
dependent
solubility.

Response:
The
intent
of
this
study
was
to
evaluate
the
stability
of
treatment
residuals
from
commercially
available
technologies
against
bench
mark
standards,
and
not
to
compare
the
technologies
to
each
other.
Therefore,
EPA
believes
that
it
is
inappropriate
to
reach
the
relative
conclusions
suggested
by
the
reviewer.
The
final
test
conditions
of
the
TCLP
were
shown
to
be
vary
from
waste
to
waste.
However,
TCLP
leachate
concentrations
were
consistent
with
the
concentration
gradients
as
a
function
of
pH
indicated
by
the
constant
pH
measurements.
Thus,
in
general,
the
two
test
procedures
provided
similar
results
when
compared
at
the
same
pH
level.

Reviewer
#
2:
The
first
review
objective
was
to
"
evaluate
the
effectiveness
of
alternative
treatments
to
obtain
a
goal
of
0.025
mg/
L
TCLP
over
a
range
of
pH
2
to
pH
12."
I
assume
the
reference
to
TCLP
is
a
mistake,
and
the
objective
is
to
review
the
results
of
the
constant
pH
extraction.
With
this
assumption,
the
data
collected
were
adequate
to
do
the
evaluation,
with
the
exception
of
an
apparent
sample
heterogeneity
problem.
7
The
second
review
objective
was
to
compare
constant
pH
protocol
results
to
standard
TCLP
results.
The
data
were
adequate
for
this
comparison,
with
the
exception
of
sample
heterogeneity.

Response:
EPA
agrees
that
sample
heterogeneity
was
a
recurring
issue,
albeit
a
minor
one.
We
believe
that
the
sample
heterogeneity
is
inherent
in
the
nature
of
both
the
untreated
and
treated
materials,
and
difficult
to
control.
As
the
study
was
intended
to
evaluate
the
treatment
residuals
from
the
stabilization
technologies
as
they
are
used
commercially,
we
believe
that
this
heterogeneity
is
a
variable
that
must
be
considered.

The
third
review
objective
was
to
evaluate
the
effects
of
increased
chloride
concentration
of
mercuric
selenide
at
constant
pH
conditions.
These
data
were
not
adequate
since
only
two
pHs
and
two
chloride
concentrations
were
used;
the
results
were
inadequate
to
quantitatively
compare
the
chloride
effect
with
the
pH
effect.

Response:
As
previously
discussed,
EPA
added
a
resource­
limited
evaluation
of
the
stability
of
mercuric
selenide
in
the
constant­
pH
leaching
test,
with
and
without
chloride
ions,
to
evaluate
solubility
in
the
short
term.
This
experiment
was
not
intended
to
be
comparable
to
the
larger­
pH
range
leaching
tests
conducted
for
the
other
treatment
technologies.
These
limited
data
suggest
to
us
that
the
presence
of
chloride
ions
could
be
an
important
factor
in
the
leaching
behavior
of
stabilized
mercury
wastes.
Therefore,
we
would
suggest
any
future
studies
in
this
area
include
chloride
as
a
variable.

Reviewer
#
3:
a)
Effectiveness
of
meeting
goal
of
0.025
mg/
L
in
leaching
tests
i)
TCLP
Test
The
treated
material
prepared
by
Vendor
A
did
not
generally
meet
the
goal
of
0.025
mg/
L
mercury
in
the
TCLP
test,
although
one
sample
of
the
palletized
material
met
the
goal
by
a
small
margin.
This
behavior
was
generally
confirmed
by
the
CPLT,
which
showed
similar,
but
generally
higher,
concentrations
interpolated
to
the
pH
values
measured
in
the
TCLP.

The
treated
material
prepared
by
Vendor
B
did
meet
the
treatment
goal
and
it
did
so
by
a
substantial
margin
(
all
concentrations
below
0.01
mg/
L).
The
total
mercury
analysis
for
the
material
supplied
by
this
vendor
may
have
been
high
enough
to
support
the
reported
waste
loading
(
see
response
to
question
1,
above).
The
behavior
in
the
TCLP
was
supported
by
similar
behavior
in
the
CPLT
near
the
pH
of
the
TCLP
test.

The
treated
material
prepared
by
Vendor
C
did
meet
the
TCLP
goal,
but
not
by
a
substantial
margin.
Concentrations
measured
in
all
samples
were
below
0.025
mg/
L,
but
above
0.010
mg/
L.
However,
the
reproducibility
was
very
good,
with
a
coefficient
of
determination
of
9%.
The
behavior
in
the
TCLP
was
partially
confirmed
by
the
CPLT.
The
concentration
at
the
TCLP
pH
(
pH
6.7)
interpolated
from
data
from
the
CPLT
was
similar,
but
somewhat
higher.
The
interpolated
concentration
in
the
CPLT
was
strongly
influenced
by
the
CPLT
data
point
at
pH
6,
which
was
somewhat
lower
than
those
measured
at
pH
4
and
pH
8.
The
ability
of
this
treated
8
material
to
reliably
pass
the
TCLP
goal
is
also
brought
into
question
by
indications
that
concentrations
of
total
mercury
may
have
been
measured
in
the
treated
material
that
are
much
lower
than
what
would
be
expected
from
the
reported
waste
loading
(
see
response
to
question
1,
above).

ii)
Constant
pH
test
The
treated
material
prepared
by
Vendor
A
did
not
meet
the
goal
of
0.025
mg/
L
in
the
CPLT
except
at
pH
2
(
pellets
and
crushed
samples)
and
pH
11
(
pellets).
The
behavior
in
the
CPLT
was
generally
confirmed
by
that
in
the
TCLP
when
concentrations
are
compared
near
the
pH
of
the
TCLP.
However,
interpolated
concentrations
in
the
CPLT
tended
to
be
generally
higher
than
those
measured
in
the
TCLP.

The
treated
material
prepared
by
Vendor
B
did
meet
the
goal
in
the
CPLT,
except
at
pH
12.
The
behavior
in
the
CPLT
was
generally
confirmed
by
that
in
the
TCLP
when
compared
by
interpolating
CPLT
data
to
the
pH
of
the
TCLP.

The
treated
material
prepared
by
Vendor
C
generally
did
not
meet
the
goal
in
the
CPLT.
Two
samples
at
pH
12
had
concentrations
(
0.0251
mg/
L
and
0.0249
mg/
L)
that
were
substantially
the
same
as
the
treatment
goal.
The
concentrations
measured
in
the
TCLP
at
pH
6.7
were
similar
to
that
measured
in
the
CPLT
at
pH
6,
but
substantially
lower
than
that
measured
at
pH
8.

Response:
Observations
are
correctly
summarized.

Supplementary
Information
Question
1:
Are
you
aware
of
any
other
data/
studies
that
are
relevant
to
the
assessment
of
stabilized
mercury­
bearing
wastes
and
the
behavior
of
these
wastes
in
the
environment?

Reviewer
#
1:
No,
I
am
not
aware
of
any
other
data/
studies
pertinent
to
this
study.

Reviewer
#
2:
This
report
does
not
have
a
list
of
references,
so
the
question
is
very
broad.
A
start
would
be
the
studies
for
EPA
or
used
by
EPA
in
previous
rule­
making.
Second
would
be
a
literature
review
using
appropriate
keywords.

Response:
A
bibliography
(
provided
by
Reviewer
#
3)
was
included
in
a
final
revision
of
the
report.

Reviewer
#
3:
Reviewer
No.
3
provided
an
extensive
list
of
articles
relevant
to
both
studies.

Response:
A
bibliography
(
provided
by
Reviewer
#
3)
was
included
in
a
final
revision
of
the
report.

Question
2:
With
regard
to
the
disposal
of
treated
mercury
wastes,
are
additional
studies
9
warranted
for
other
factors
that
impact
solubility
or
affect
ability
to
leach,
such
as
use
of
macroencapsulation?
If
you
believe
that
additional
studies
are
needed,
please
explain
why.

Reviewer
#
1
No.
This
study
has
achieved
the
goals
of
the
project
and
has
generated
scientifically
sound
results.
This
study
does
show
that
there
is
at
least
one
treatment
technology
that
should
be
effective
over
a
large
range
of
leaching
fluid
pH.
If,
however,
there
are
additional
technologies
that
emerge
then
similar
testing
is
desirable
to
evaluate
the
expected
effectiveness
of
the
new
technology.

Reviewer
#
2:
An
additional
study
is
needed
to
fill
the
holes
in
this
report,
particularly
extractions
up
to
at
least
pH
12.5.
If
the
mercuric
selenide
process
is
considered
a
viable
technology,
then
mercuric
selenide
waste
should
be
evaluated
over
the
range
of
pH
2­
12.5
and
with
varied
chloride
content
in
the
leachate.
Additional
studies
on
other
factors
could
be
done,
but
the
priorities
seem
to
be:
pH
effects
(
2­
12.5),
chloride
effects,
and
redox
effects.

Response:
EPA
does
not
agree
that
additional
studies
are
warranted
for
this
pH
range,
as
few
landfills
have
been
shown
to
maintain
pH
conditions
in
excess
of
pH
12.
EPA
does
agree
that,
if
additional
resources
become
available,
it
would
be
useful
to
further
investigate
the
stability
of
mercuric
selenide
across
a
wider
range
of
pH
values.
We
also
agree
that
varying
chloride
content
across
the
pH
range
for
all
wasteforms
would
be
a
useful
study,
and
would
provide
additional
information
on
the
potential
effects
of
chloride
content
in
landfill
leachate.

Reviewer
#
3:
These
studies
have
adequately
demonstrated
that
a
goal
of
0.025
mg/
L
in
the
TCLP
can
be
met
by
existing
stabilization
technologies,
both
for
a
surrogate
waste
containing
various
forms
of
mercury
at
a
total
concentration
of
5,000
mg/
kg
and
for
elemental
mercury.
However,
meeting
this
goal
does
not
insure
that
adequate
protection
of
human
health
and
the
environment
is
assured
for
all
conditions
of
waste
disposal.
However,
this
statement
is
not
limited
to
mercury
wastes,
but
is
a
limitation
of
the
TCLP
for
all
hazardous
constituents.
Therefore,
additional
studies
are
not
warranted
to
determine
if
existing
technologies
can
meet
a
TCLP
goal
of
0.025
mg/
L
for
wastes
that
contain
mercury
at
concentrations
above
260
mg/
kg.
However,
additional
studies
are
warranted
to
develop
characterization
methods
and
analytical
techniques
that
will
insure
safe
disposal
of
hazardous
wastes
containing
toxic
materials
including
mercury
under
a
range
of
site­
specific
disposal
conditions.

Response:
The
additional
studies
proposed
by
the
Reviewer
will
be
considered
as
additional
resources
become
available.

Question
3
(
a):
Do
you
agree
that
the
following
statements
are
supported
by
the
research
results?

Site­
specific
disposal
conditions
must
be
considered
along
with
appropriate
treatment
technology
as
decisions
are
made
about
disposal
of
mercury
wastes.
10
Reviewer
#
1:
Based
on
the
review
of
the
results
reported,
it
seems
that
pH
was
the
only
environmental
parameter
tested.
For
the
Vendor
B
technology
it
appears
that
disposal
sites
with
leaching
fluid
of
greater
than
pH
10
should
be
avoided
for
disposing
the
stabilized
wastes
and
all
other
sites
below
pH
10
will
be
appropriate
for
disposing
of
stabilized
waste.
Therefore,
I
believe
that
statement
in
(
a)
as
written
is
more
stringent
than
supported
by
the
research
results
and
should
be
therefore
modified.

Response:
pH
was
the
only
environmental
variable
evaluated
in
this
study.
EPA
acknowledges
that
there
are
other
variables,
but
believes
that
pH
is
certainly
a
significant
variable.
The
Reviewer
acknowledges
that
the
pH
of
the
leachate
in
the
landfill
cell,
a
site­
specific
condition,
must
be
considered
when
selecting
a
technology.
EPA
believes
that
this
supports
the
conclusion
that
"
Site­
specific
disposal
conditions
must
be
considered
along
with
appropriate
treatment
technology
as
decisions
are
made
about
disposal
of
mercury
wastes."

Reviewer
#
2:
No.
The
study
provides
useful
data
on
pH
and
chlorides,
but
it
does
not
provide
adequate
support
for
an
absolute
requirement
for
site­
specific
data.
An
alternative
to
using
sitespecific
conditions
is
a
robust
treatment
standard
which
addresses
the
most
important
variables.
A
major
implementation
problem
with
requiring
site­
specific
conditions
is
the
regulatory
feasibility
of
using
site­
specific
information.
For
any
disposal
of
hazardous
wastes,
treated
or
untreated,
it
is
scientifically
preferable
to
use
site­
specific
conditions
as
well
as
the
waste
properties.
It
is
misleading,
however,
to
pursue
this
path
unless
the
regulatory
system
has
the
flexibility
to
implement
efficiently
to
provide
the
necessary
protection
to
public
health
and
the
environment.

Response:
We
agree
that
it
is
scientifically
preferable
to
use
site­
specific
conditions
as
well
as
the
waste
properties
to
assess
disposal
options.
EPA
believes
that
consideration
of
site­
specific
disposal
conditions
along
with
appropriate
treatment
technology
information
is
the
best
alternative
when
making
environmentally
sound
decisions
about
the
disposition
of
these
high
mercury
stabilized
wastes.
As
the
reviewer
correctly
notes,
implementation
of
such
requirements
into
a
regulatory
framework
would
be
problematic.
We
believe
that
the
reviewer's
suggestion
of
using
a
robust
treatment
standard
that
addresses
only
the
most
important
variables
would
be
equally
problematic
to
implement
on
a
national
basis.

Reviewer
#
3:
:
These
research
results
do
support
this
statement,
because
they
demonstrate
that
pH
can
have
an
important
impact
on
the
amount
of
mercury
leached
from
treated
wastes.
The
pH
of
a
leaching
fluid
can
be
very
different
under
different
disposal
conditions.
However,
the
research
results
do
not
prove
the
statement,
because
there
could
be
conditions
under
which
a
waste
could
be
characterized
so
that
site­
specific
disposal
conditions
would
not
be
required
to
insure
a
reasonable
degree
of
confidence
in
protection
of
human
health
and
the
environment.

Response:
EPA
acknowledges
the
difference
noted
by
the
Reviewer
between
data
"
supporting"
and
"
proving"
a
premise.
The
Agency
does
not
anticipate
having
sufficient
resources
available
11
to
investigate
all
of
the
characterizations
conditions
possible
in
order
to
definitively
prove
or
disprove
the
hypothesis.

Question
3(
b):
Do
you
agree
that
the
following
statements
are
supported
by
the
research
results?

The
presence
of
chloride
ions
in
a
given
disposal
environment
may
significantly
impact
the
release
from
a
treated
waste
form
(
mercury
selenide).

Reviewer
#
1:
The
limited
data
developed
and
presented
in
this
report
do
support
the
statement
in
(
b).
However,
it
would
be
desirable
to
generate
empirical
results
using
a
number
of
chloride
concentrations
in
leaching
fluid
to
establish
correlation
between
chloride
concentrations
and
leachability
of
mercury
converted
to
mercuric
selenide.
These
experiments
will
provide
a
basis
for
deriving
the
lower
limit
of
chloride
concentration
that
should
not
be
exceeded
in
the
leaching
fluids.

Response:
The
additional
studies
proposed
by
the
Reviewer
will
be
considered
as
additional
resources
become
available.

Reviewer
#
2:
Yes,
the
data
in
the
report
do
support
this
statement.
However,
there
is
no
comparison
with
other
variables,
not
even
an
adequate
comparison
with
pH,
which
shows
the
relative
importance
of
chloride
concentration.

Response:
EPA
agrees
that
if
additional
studies
were
planned,
it
would
be
useful
to
further
investigate
mercuric
selenide
or
elemental
mercury
treated
to
a
mercuric
selenide
composition
across
a
wider
range
of
pH
values.
We
also
agree
that
varying
chloride
content
across
the
pH
range
for
all
wasteforms
would
be
a
useful
study,
and
would
provide
additional
information
on
the
potential
effects
of
chloride
content
in
landfill
leachate.

Reviewer
#
3:
This
statement
is
supported
by
the
research
results,
because
a
leaching
solution
with
500
mg/
L
chloride
did
result
in
higher
concentrations
of
mercury
being
leached
at
pH
7
and
10.
However,
the
data
reported
is
not
sufficient
to
conclude
that
chloride
will
(
rather
than
may)
significantly
impact
release
of
mercury
under
a
range
of
disposal
conditions.
Sufficient
data
exists
on
formation
of
mercury­
chloride
soluble
complexes
to
strongly
suggest
that
chloride
will
tend
to
increase
mercury
release,
but
specific
conclusions
on
the
impact
of
particular
levels
of
chloride
in
different
disposal
scenarios
would
require
additional
research.

Response:
A
previously
noted,
EPA
agrees
that
if
additional
studies
were
planned,
it
would
be
useful
to
further
investigate
mercuric
selenide
or
elemental
mercury
treated
to
a
mercuric
selenide
composition
across
a
wider
range
of
pH
values.
We
also
agree
that
varying
chloride
content
across
the
pH
range
for
all
wasteforms
would
be
a
useful
study,
and
would
provide
additional
information
on
the
potential
effects
of
chloride
content
in
landfill
leachate.
12
Question
4:
Do
you
have
any
other
comments?

Reviewer
#
1:
No.

Reviewer
#
2:
Some
minor
editing
was
needed
for
the
final
reports,
i.
e.,
spaces
and
placement
of
hyphens.
Data
on
the
quantities
of
listed
wastes
would
have
been
useful
to
understand
the
magnitude
of
various
waste
treatment
problems.

Response:
The
editorial
corrections
suggested
by
the
reviewer
were
incorporated
in
a
final
revision
to
the
report.

Reviewer
#
3:
The
following
corrections
should
be
made
to
the
report:
C
(
Various
places)
The
relationship
of
ALTER
and
the
University
of
Cincinnati
should
be
clarified.
It
appears
that
the
two
are
used
interchangeably.
C
(
p.
3­
2)
It
would
be
helpful
to
the
reader
to
make
more
clear
here
that
the
"
waste"
being
treated
is
elemental
mercury.
C
(
p.
3­
4,
line
5
from
bottom
and
elsewhere)
Provide
units
for
liquid/
solid
ratio.
C
(
p.
5­
1,
Table
5­
1
and
others)
Percentages
should
be
reported
with
no
more
significant
digits
than
the
measurements
upon
which
they
are
based.
C
(
p.
5­
1,
Table
5­
1
and
others)
The
leaching
fluid
used
in
the
TCLP
tests
should
be
specified.
C
(
p.
5­
4,
Table
5­
3)
Standard
deviation
of
TCLP
results
for
Phase
II
should
be
0.00160.
C
(
p.
5­
6,
Figure
5­
3)
TCLP
data
are
missing
from
this
figure.

Response:
The
editorial
corrections
suggested
by
the
reviewer
were
incorporated
in
a
final
revision
to
the
report.
