MEMORANDUM
SUBJECT:
Review
of
Chat
Used
as
Minefill
TO:
File
FROM:
Bonnie
Robinson
OSW,
USEPA
DATE:
December
13,
2005
I
reviewed
the
use
of
chat
as
minefill
in
the
Tri­
State
Mining
District
states
of
Kansas,
Missouri,
and
Oklahoma.
The
initial
purpose
of
the
study
was
to
determine
if
chat
has
been
amended
with
cement
and
concrete
for
use
as
minefill.
I
found
no
evidence
that
chat
has
been
or
is
currently
being
mixed
with
cement
and
concrete
fro
use
as
minefill.

In
July
2000,
Governor
Keating's
Tar
Creek
Task
Force
Subsidence
Subcommittee
concluded
that
a
slurry
of
chat
and
fly
ash
could
be
used
to
backfill
and
seal
open
mine
connections
to
prevent
the
chat
material
from
moving
into
open
mine
workings
at
the
bottom
of
the
shaft
or
pit
as
occurred
in
the
Picher
Mining
Field
in
Oklahoma
(
Gov.
Keating,
2000b,
pp.
26­
27).
An
Oklahoma
DEQ
study
recommended
conducting
an
evaluation
of
amendments,
or
additives
to
mix
with
the
chat
fill,
that
may
reduce
the
generation
of
dissolved
solids
concentrations
in
the
shallow
ground
water
(
e.
g.,
fly
ash,
lime,
limestone
fines,
organic
matter)
(
OkDEQ,
2005b).

EPA
Regions
6
and
7
used
chat
to
backfill
open
mine
pits
and
mine
shafts
in
the
Tri­
State
Mining
District
states
of
Kansas
and
Oklahoma.
The
Missouri
Department
of
Transportation,
in
consultation
with
the
U.
S.
Bureau
of
Mines,
developed
plans
to
use
chat
as
minefill
in
a
2001
construction
project.

EPA
and
other
agencies
have
expressed
concerns
about
the
environmental
and
health
effects
of
placing
chat
materials
underground
or
below
the
water
table
due
to
suspected
high
levels
of
lead,
zinc,
and
cadmium
that
may
be
released
from
the
materials.
(
Gov.
Keating,
2000b,
pp.
26­
27)

The
Agency's
findings
regarding
the
current
use
of
chat
as
minefill
in
the
Tri­
State
Mining
District
are
summarized
below.

Kansas
EPA
Region
7
used
chat
to
fill
mine
shafts
near
Galena
in
the
Cherokee
County,
Kansas
Superfund
Site
(
US
EPA,
1989).
The
selected
remedy
was
to
selectively
place
waste
rock
and
chat
in
open
subsidences,
pits
and
shafts.
This
action
would
eliminate
human
exposure
via
ingestion
and
reduce
long­
term
shallow
ground
water
and
surface
water
metals
loading
(
p.
19).
Mining
wastes
were
segregated
and
wastes
less
than
1,000
ppm
lead
were
placed
at
the
surface
2
with
more
impacted
wastes
placed
at
depth
or
used
as
fill
material
for
open
dry
shafts.
Low
concentration
wastes
or
bull
rock
were
used
to
fill
shafts
that
contained
water
(
US
EPA,
2000,
p.
5).
As
of
the
2nd
5­
year
review
in
2000,
leaching
of
heavy
metals
to
the
ground
water
system
has
been
reduced,
filled
shafts
remain
closed,
and
ecological
improvement
has
been
identified
(
p.
11).
EPA
and
other
agencies
have
expressed
concerns
about
the
environmental
and
health
effects
of
placing
chat
materials
underground
or
below
the
water
table
due
to
suspected
high
levels
of
lead,
zinc
and
cadmium
that
may
be
released
from
the
materials.
An
EPA
Region
7
Mine
Waste
Fact
Sheet
cautions
that
"
placement
of
fill
material
which
comes
in
contact
with
freestanding
water
in
an
excavation
or
with
surface
water"
may
present
a
threat
to
human
health
or
the
environment
(
US
EPA,
2003,
p.
3).

Missouri
In
2001,
the
Missouri
Department
of
Transportation
conducted
an
intensive
investigation
to
plan
the
location
of
a
highway
in
the
Tri­
State
Mining
District.
Open
mine
shafts
as
deep
as
60
meters
could
not
be
avoided
and
their
threat
to
the
future
highway
had
to
be
mitigated.
In
consultation
with
the
U.
S.
Bureau
of
Mines,
MoDOT
decided
to
seal
the
shafts
with
polyurethane
foam
plugs
followed
by
3
meters
of
reinforced
concrete.
The
remainder
of
the
shafts
were
to
be
filled
with
chat.
Construction
was
scheduled
for
August
2001.
It
is
not
known
if
these
plans
were
implemented.
(
Hatheway,
et.
al.,
2001)

Oklahoma
The
Oklahoma
DEQ
used
chat
to
fill
mine
shafts
in
the
Picher
Field
in
Ottawa
County,
Oklahoma.
The
results
showed
that
chat
has
a
high
probability
of
moving
into
open
mine
workings
at
the
bottom
of
the
shaft
or
pit.
"
Removal
of
chat
(
with
high
lead,
cadmium,
and
zinc
concentrations)
from
the
surface
to
native
soil
and
placement
in
the
subsurface
removes
the
hazards
to
human
health
and
ecological
toxicity
by
breaking
the
exposure
pathways.
However,
if
the
chat
is
placed
in
the
subaqueous
environment,
contamination
of
the
shallow
ground
water
will
occur
with
release
of
dissolved
solids
to
the
already
metals
rich
ground
water
of
the
mine
pool.
Estimation
of
the
extent
and
degree
of
contamination
of
the
shallow
ground
water
is
the
basis
for
monitoring
the
McNeely­
Green
site
and
evaluation
of
the
water
quality
results."
(
OkDEQ,
2005b,
p.
10)
The
study's
recommendations
include
the
following:

­
Evaluate
amendments
(
additives
to
mix
with
the
chat
fill)
that
may
reduce
the
generation
of
elevated
dissolved
solids
concentrations
in
the
shallow
ground
water
(
e.
g.,
fly
ash,
lime,
limestone
fines,
organic
matter
 
chicken
litter,
wood
chips,
etc.).
(
p.
11)

­
Evaluate
the
application
of
subaqueous
placement
of
chat
where
water­
filled
subsidences
occur
near
streams
or
points
of
shallow
ground
water
discharge.
(
p.
11)

­
Evaluate
the
effect
on
water
quality
of
the
mine
pool
resulting
from
subaqueous
placement
of
chat
directly
into
the
mine
workings
through
mine
shafts
or
drilled
holes.
3
(
p.
12)

Excerpts
of
relevant
sections
from
Governor
Keating's
Tar
Creek
Task
Force
Reports
From
the
Subsidence
Subcommittee
Report
(
Gov.
Keating,
2000b):

"
Chat
material
has
been
used
in
some
cases
to
backfill
open
mine
pits.
Chat
tends
to
move
into
open
mine
workings
if
used
without
a
more
stable
base
material.
If
the
bottom
of
the
subsidence
pit
is
sealed
from
the
remaining
mine
workings,
chat
is
an
excellent
fill
material.
Chat
is
also
much
cheaper
to
use
as
fill
material
than
most
other
materials.
Some
concern
exists
regarding
the
potential
health
effects
from
placing
chat
underground
due
to
the
levels
of
lead,
zinc
and
cadmium
contained
in
the
chat.
Nevertheless,
there
are
many
advantages
to
using
chat
as
a
fill
material."
(
p.
7)

"
Chat
can
be
used
as
a
cost
effective
material
to
fill
subsidence
areas
if
certain
stabilization
techniques
are
used.
In
the
early
1990'
s,
the
EPA
Region
VII
utilized
chat
to
fill
mine
shafts
in
Galena,
Kansas
in
the
Cherokee
County,
Kansas
Superfund
Site.
The
shafts
were
filled
for
engineering
efficiency
in
mitigating
the
threatened
release
of
hazardous
substances
in
the
surface
mine
wastes.
The
purpose
of
that
cleanup
action
was
to
reduce
the
loading
of
heavy
metals
to
ground
water
and
surface
bodies
due
to
runoff
and
infiltration
from
the
surface
mine
wastes
in
order
to
protect
aquatic
life.
Also,
by
containing
the
surface
mine
wastes
in
shafts
and
subsidences,
the
direct
contact
threat
to
humans
and
terrestrial
life
due
to
exposure
to
hazardous
substances
in
the
waste
was
significantly
reduced
or
eliminated.
Their
goal
was
not
to
fill
shafts
and
subsidences
to
reduce
the
physical
hazards
associated
with
open
mine
shafts;
however,
such
was
a
beneficial
consequence
of
the
work."
(
p.
10)

Considerations
regarding
use
of
chat
to
fill
mine
shafts
or
collapsed
areas
(
pp.
26­
27):

(
1)
"
Chat
has
a
high
probability
of
moving
into
open
mine
workings
at
the
bottom
of
the
shaft
or
pit.
Numerous
examples
exist
in
the
Picher
Mining
Field
where
chat
was
used
to
fill
open
mine
shafts
and
collapse
pits
only
to
find
later
that
the
chat
had
moved
into
the
open
mine
workings
at
the
bottom
and
reopened
the
shaft
and
pit."

(
2)
"
The
connections
to
any
open
mine
workings
at
the
bottom
of
the
pit
must
be
sealed
in
order
to
use
chat
as
a
fill
material."
Any
connections
should
be
"
sealed
to
prevent
the
movement
of
the
chat
material.
Sealing
open
mine
connections
could
be
accomplished
by
backfilling
with
mine
debris
(
mill
foundations
and/
or
boulders)
or
using
a
fly
ash/
chat
slurry.
Some
of
the
water
in
the
collapse
area
may
require
removal
prior
to
backfilling
with
chat
to
prevent
overflow
as
chat
is
being
added.
Once
filled
near
the
surface,
layers
4
of
clay
and
soil
could
be
added
and
graded
to
prevent
water
from
draining
into
the
filled
area."

(
3)
"
EPA
and
other
agencies
have
expressed
concerns
about
the
environmental
and
health
effects
of
placing
chat
materials
underground
or
below
the
water
table
due
to
suspected
high
levels
of
lead,
zinc
and
cadmium
that
may
be
released
from
the
materials."

"
The
advantages
of
using
chat
as
a
fill
material
are:
­
Encapsulating
large
volumes
of
chat,
thereby
reducing
the
potential
health
hazard
­
Trucking
costs
for
chat
would
be
minimal
­
Preventing
surface
water
from
draining
into
the
subsided
areas
­
Reducing
the
amount
of
acid
water
reaching
the
surface
­
Providing
a
nearby
location
for
disposal
of
chat
fines
which
currently
exist
and
for
chat
fines
that
may
be
generated
in
the
future
through
chat
washing/
screening
­
Reclaiming
many
acres
of
land
­
Providing
a
disposal
location
for
material
removed
from
drainage
channels
(
Tar
and
Lytle
Creeks)"
(
p.
27)

The
Task
Force
recommendations
include:
­
"
Fill
selected
open
mine
shafts
to
reduce
the
occurrence
of
new
subsidence
in
the
Tar
Creek
Superfund
Site,"
and
­
"
The
use
of
chat
should
be
given
serious
consideration
for
backfilling
subsidence
features."
(
p.
37)

Mine
subsidence
abatement
techniques
are
described
in
Appendix
F
of
the
Subcommittee
Report.

From
the
Mine
Shaft
Subcommittee
Report
(
Gov.
Keating,
2000a):

The
Mine
Shaft
Subcommittee
recommended
closing
open
mine
shafts
in
the
Oklahoma
Picher
Field
area
using
backfill
as
the
preferred
method
of
sealing
shafts
which
open
into
cavities
that
are
less
than
20
ft.
high.
(
p.
23).
A
Bureau
of
Mines
1986
study
recommended
waste
rock,
not
chat,
as
an
initial
fill
material
in
the
Picher
Field
mine
shafts.
(
p.
12)
The
viability
of
using
chat
as
fill
material
in
mine
shafts
is
still
being
debated
by
OkDEQ.
Economic
and
environmental
factors
will
ultimately
determine
if
chat
will
be
used.
(
p.
17)
The
backfill
method
uses
a
range
of
gradations
of
fill
material,
from
the
coarsest
at
the
bottom
to
the
finest
at
the
top.
The
OkDEQ
will
determine
chat
use
guidelines
based
on
a
risk
assessment
of
its
use
as
a
fill
material.
(
p.
17)
Appendix
B
of
the
Subcommittee
Report
contains
examples
of
backfill
methods
and
cases
where
these
techniques
have
been
used.

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