United States
Environmental Protection
Agency
Hazardous Waste Engineering Researj?hVs><
Laboratory - .
Cincinnati OH 45268 •A"J
Research and Development
EPA/600/S2-85/021 May 1985
ŁEPA Project Summary
Using Mined Space for
Long-Term Retention of
Nonradioactive Hazardous
Waste
R. B. Stone, K. A. Covell, T. R. Moran, L. W. Weyand, and C. U. Sparkman
A project was undertaken to assess
the current status of using mined space
for long-term retention of nonradio-
active hazardous waste. The full report
consists of two volumes. Volume 1
updates studies conducted in 1974,
reviews recent literature on the subject,
determines the involvement of govern-
ment agencies, reviews regulatory and
permitting requirements, and identifies
existing mines for a potential demon-
stration project. Volume 2 investigates
the use of solution-mined salt caverns
for storing hazardous wastes. This vol-
ume examines the extent of salt depos-
its in the continental United States,
their proximity to the U.S. EPA waste-
generating regions, salt chemistry, con-
struction, design, and operation of the
solution-mined caverns, environmental
considerations, projects proposed by
industry, advantages, and needed re-
search.
This Project Summary was developed
by EPA's Hazardous Waste Engineering
Research Laboratory, Cincinnati. OH,
to announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
A national hazardous waste manage-
ment program was formed with the
enactment of the 1976 Resource Conser-
vation and Recovery Act (RCRA) and the
Hazardous Waste regulations promul-
gated by the U.S. Environmental Protec-
tion Agency (EPA). The presently accepted
methods of hazardous waste disposal are
deep-well disposal, engineered landfills,
land treatment, and incineration. How-
ever, these methods yield a certain
amount of untreatable hazardous waste
that must be dealt with in an environ-
mentally acceptable manner. Permanent
storage of such wastes in underground,
mined space appears to provide a tech-
nically and economically feasible method
for dealing with them. Among the advan-
tages of this method are the following:
1. The waste would be below drinking
aquifers in deep mines.
2. Wastes would be isolated from the
public and the surface ecology.
3. Security can be readily maintained.
4. Minimum maintenance is required
in a sealed mine.
5. The mine could be used as a long-
term warehouse if retrievability is
desired.
The purpose of this two-volume project
was to update the state-of-the-art of using
mined space for hazardous waste storage
in the United States and to determine the
feasibility of conducting a limited demon-
stration project. Specifically, Volume 1
examines the following subjects: (1) the
literature produced on mined storage
activities in the past decade, (2) involve-
ment of government agencies, (3) various
regulatory and permitting requirements
for storing waste in mines, and (4) selec-
tion of candidates for a potential demon-
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stration project. Volume 2 investigates
the use of solution-mined salt caverns for
storing hazardous wastes. Subjects cov-
ered in this volume include: (1) the extent
of salt deposits in the continental United
States and their proximity to waste-gen-
eration by EPA regions, (2) salt chemistry,
(3) construction, design, and operations
of solution-mined caverns, (4) environ-
mental considerations, (5) projects pro-
posed by industry, (6) advantages of
solution-mined caverns, and (7) needed
research.
Literature Review
The literature review was based on a
search to identify past and present re-
search, government activities, develop-
ment of commercial facilities, and foreign
use of underground caverns for storing
wastes. Citations were retrieved for liter-
ature published since 1974.
Foreign Activities
Recent foreign activities include the
Herfa-Neurode facility in the Republic of
West Germany. This operation continues
to run satisfactorily 13 years after its
start-up in 1972. About 270,000 tons of
hazardous wastes were placed in the
mine in 10 years, and the present annual
volume is 35,000 to 40,000 tons. Reuse
of stored waste is possible, and more than
1,000 tons have been retrieved by a
waste producer and returned to the
originator for further use.
India has conducted studies to evaluate
the concept of storing hazardous waste in
mined space.
United States Activities
Empak, Inc., of Houston, Texas, applied
for a state permit to build a hazardous
waste facility in solution-mined caverns
at the Vinton Salt Dome in southwest
Louisiana. However, a state law was
subsequently passed forbidding such a
project for 2 years. The delay was to allow
the state time to evaluate the proposed
use.
United Resource Recovery, Inc., of
Houston, Texas, has an application pend-
ing for a state permit to store hazardous
waste in the Boling Salt Dome in Texas.
This request has triggered a geological
study to evaluate the acceptability of
using salt domes in Texas for waste
disposal and to recommend guidelines for
such storage. Work is being done by the
Texas Bureau of Economic Geology.
The University of Minnesota conducted
a 1982 study of the subsurface isolation
of hazardous wastes. The study was
sponsored by the Minnesota Waste Man-
agement Board and was oriented to deep
geologic disposal in crystalline bedrock
within the state. Five sites were selected
for further investigation, but the crystal-
line rock concept was dropped from
further consideration because of its high
cost.
The PPG Industries, Inc., limestone
mine in Barberton, Ohio, was proposed
for use as a waste storage facility in
1981-82, but the project was dropped
because of economic conditions in the
United States.
Research Activities
EPA has sponsored several studies in
recent years on encapsulation container-
ization, and fixation technologies. Data
from these projects apply directly to the
use of mined space for storage of hazard-
ous wastes.
The American Society for Testing and
Materials (ASTM) has been working on a
hazardous waste compatibility guide.
After acceptable methodology has been
developed for mined space storage, the
compatibility of waste with a salt envi-
ronment must be established.
Public Reaction
The public has become increasingly
aware of the potential danger of hazard-
ous waste through continuing commen-
tary by the media. This public awareness
does not include a concern for the nation-
al consequences of failing to develop final
treatment and storage methods.
Involvement of Government
Agencies
Every phase of a hazardous waste
storage facility, from conception to clo-
sure, requires the involvement of govern-
ment agencies at all levels—federal,
state, and local. These agencies and the
extent of their involvement will vary with
location and time as new legislation is
passed and programs are implemented.
Siting of hazardous waste facilities re-
quires approval from all levels of govern-
ment and public concern is making ap-
proval of permits more difficult to obtain.
Regulatory and Permitting
Requirements
A reasonably uniform hazardous waste
management program is being conducted
throughout the United States as a result
of RCRA regulations. These regulations
provide that a state agency may be
authorized to administer a hazardous
waste program in that state in lieu of a
federally administered program. Many
states have developed and manage their
own hazardous waste programs under
EPA regulatory guidelines. EPA is admin-
istering the programs of those states that
have not completed development of their
hazardous waste management plans.
Presently neither EPA nor individual
states have developed regulations spec-
ifically pertaining to hazardous waste
storage in mined space. Thus, such
facilities will have to be designed, sited,
and evaluated through interpreting the
intent of existing regulations.
Current Applicable RCRA
Permitting Requirements
Permitting of new hazardous waste
facilities is regulated by EPA in 40 CFR
Section 270. This regulation requires a
two-part application for approval of the
proposed facilities. Present permitting
requirements do not include specific
terms related to storage of wastes in
mined space but they are comprehensive
enough to secure the information for
such a permit application.
State Hazardous Waste
Permitting Requirements
States authorized by the EPA to admin-
ister a hazardous waste program have
developed and are using permitting regu-
lations. States without EPA authorization
are using EPA regulations.
In general, all authorized states now
have regulations and permitting practices
that conform to EPA hazardous waste
management regulations and administra-
tive criteria. Differences in storage regu-
lations and permitting procedures do not
specifically relate to hazardous waste
storage in subsurface mines.
The 1976 RCRA does not prescribe
requirements for the siting of new haz-
ardous waste management facilities.
Present policies consider this task the
responsibility of each state.
In the past, several states gave various
agencies the permitting authority for
hazardous waste facilities. The state then
ruled on the permit after analyzing the
applications and holding public hearings.
However, public opposition to new facil-
ities resulted in very few approved per-
mits; as a result, most states now specify
procedures for site selection, provide for
public participation, and establish the
responsibility of state and local agencies.
Selecting Candidate Mines for a
Demonstration Project
The object was to select three candi-
date mines with good potential for use as
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a demonstration facility for storing non-
radioactive hazardous wastes.
The basic criteria were as follows:
• The preferred candidates were to be
salt mines, but other types were not
ruled out.
• The mine should have been mined by
the room and pillar method.
• Existing engineering, geological, and
other information should indicate that
the mine is suitable for the purpose.
• An industrial organization must exist
that is willing to cooperate in a limited
demonstration of the concept.
Additional criteria included the follow-
ing:
• Hazardous wastes to be stored must
be packaged, encapsulated or solid-
ified, nonreactive, dry, noncombust-
ible, and untreatable by current tech-
nology or the end product of current
treatment technology.
• Limestone mines mined by the room
and pillar method were included in this
report.
The approach to mine selection consist-
ed of (1) identification of all known salt
mines in the United States, (2) a prelim-
inary screening of 30 potential candidate
mines to eliminate obviously unsuitable
subjects, (3) a geographical screening to
match mine locations with EPA Regions
in which hazardous wastes are produced,
(4) a final subjective screening of the
seven remaining mines to determine
hydrology, geology, marketing, socio-
political factors, accessibility, location,
previous studies, and owner interest, and
(5) visits to the three selected facilities
and discussions of the proposed demon-
stration with the owners/operators.
The three selected salt mines were in
Michigan, Ohio, and Texas. The alter-
native limestone mine was in Ohio. One
mine was withdrawn from consideration
when the operators indicated that it was
not in their best interest to participate.
Another mine was rejected because it
was the subject of adverse public reaction
to a recent attempt to establish a com-
mercial hazardous waste storage facility
in the mine. Such recent efforts were
considered likely to strengthen public
resistance and reduce the probability of
obtaining a state permit. The third mine
was the highest ranked of the original
three candidates, andthe owner indicated
willingness to participate in the demon-
stration. In this case, the state has
jurisdiction for hazardous waste facility
siting, and their regulations are equal to
or more stringent than those required by
the 1976 RCRA. The proposed demon-
stration facility must undergo the same
permitting procedures as any other haz-
ardous waste facility in the state.
As an alternative limestone mine was
ranked numerically at the top of the list
and illustrates the possibility of using
mines in types of rock other than salt. But
because this mine would require an
expensive hoisting system to be installed,
it was not considered further.
The third salt mine discussed has an
operating hoisting system and was equal
in rating. Thus, the third mine was
selected as the best candidate for a
demonstration facility.
Solution-Mined Storage
Solution-mined caverns could provide
suitable containment facilities for haz-
ardous wastes and good isolation from
the environment. After the waste slurry
cavern has been plugged with cement,
the plastic nature of the salt under strata
pressure will provide an effective seal.
Many large salt deposits in the United
States are located near a number of the
major hazardous waste generation areas,
a factor which would minimize transpor-
tation and handling cost.
Basic Requirements for
Solution-Mined Storage
Caverns
Any solution-mined storage facility
must have three characteristics for suc-
cessful cavern construction:
1. asufficientthicknessof structurally
sound salt at a proper depth without
excess interbedded insolubles,
2. an adequate supply of rawwaterfor
leaching the salt, and
3. an environmentally acceptable and
economical means of disposing of
the resulting brine.
Salt Dome Leaching
Techniques
The basic technique for developing a
salt dome cavern is to drill into a salt mass
and to pump fresh or low-salinity water
into the hole. The salt is then dissolved
and carried to the surface as a brine
solution. The hole within the exposed salt
gradually enlarges and eventually forms
a useful cavern.
Bedded Salt Leaching
Techniques
The basic principles of leaching are the
same in bedded salt as in a salt dome, but
bedded salt presents an additional prob-
lem because of the thinness of the salt
resource and the tendency of large, inter-
bedded shale layers to collapse and
damage the leaching casing strings.
These bedded salt insolubles tend to fall
to the bottom of the cavern as a pile of
large rocks rather than as fine sand, as is
the case in a salt dome cavern.
Locations of Waste
Generators and Sa/t Deposits
Four EPA Regions (III, IV, V, and VI)
produced 78% of the Nation's total haz-
ardous waste in 1980. Regions IV and VI,
with 25% and 26% of the total, respec-
tively, both have salt domes that could be
used for the emplacement of hazardous
waste. Regions III and V, with 11 % and
16% respectively, both have bedded salt
that could be used. These caverns would
be smaller and more numerous than the
salt dome caverns, but reduced shipping
costs might make them cost-effective if a
method for brine disposal can be devel-
oped.
Methods for Storing Hazardous
Wastes in Solution-Mined Salt
Caverns
Several methods exist for storing haz-
ardous wastes in solution-mined caverns.
Each is discussed here briefly.
Brine-Balanced Cavern with
Brine Discharge During Waste
Injection
In a brine-balanced cavern, the product
to be stored is injected with a pump,
displacing brine up the casing string and
over to a brine holding pond. Caverns
using this concept have a very long life,
because the range of stress on the salt is
small. The main advantage of using this
method for hazardous wastes is that it
permits the use of very large caverns. If
the hazardous waste slurry is significantly
lighter than saturated brine, the waste
can be injected into the top of the cavern,
displacing saturated brine up the casing
string. If the specific gravity of the waste
is close to or greater than that of the
saturated brine, the waste slurry must be
weighted so that it is significantly heavier
than the brine and remains on the bottom
of the cavern. The floating brine would
then be displaced from the top of the
cavern and directed to disposal wells.
Brine contamination is possible with
this method.
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Gas-Balanced Cavern with Zero
Discharge
In a gas-balanced cavern, the brine is
displaced by an inert gas and injected into
a remote brine disposal well. The cavern
is sealed at the minimum design pressure,
then liquid and slurry wastes are injected
into the cavern until the inert gas reaches
the maximum design pressure. Gas bal-
ancing permits the use of a smaller cavern
than the brine balancing and a larger
cavern than the atmospheric method
(which is discussed in the following
section). Gas balancing eliminates the
possibility of brine contamination and the
need for a scrubber and flare unless they
are needed by the surface plant.
Atmospheric Cavern with
Controlled Gas Discharge During
Waste Injection
In an atmospheric cavern, the brine is
pumped out by a means of a submersible
pump and directed to disposal. Chemical-
ly compatible liquid and pumpable slurry
wastes are then inserted into the cavern.
Displaced vapors or gases are collected
and either sent through a scrubber or
burned in an approved flare.
A cavern exposed to atmospheric pres-
sure would be limited in size to maintain
structural integrity. No brine contamina-
tion would occur, but a scrubber and flare
would be required.
In Situ Solidified Waste Storage
Hazardous wastes can be mixed with a
cement or polymer slurry before injection
into a cavern to provide permanent solid-
ified storage for liquid and slurry wastes
and to reduce risks from earthquakes or
inadvertent drilling into a hazardous-
waste-filled cavern. Such a cavern would
be limited in size to maintain structural
integrity during the period it is exposed to
atmospheric pressure.
String-of-Pearls-Waste Storage
Caverns
The string-of-pearl method consists of
constructing a series of caverns, one
above the other, from one deep solution
well in a salt dome. Each cavern is sealed
by the installation of a cement plug in the
top neck of the cavern before starting
construction of the cavern above it. The
brine from the first (bottom) cavern is
removed by submersible pump and direc-
ted to the remote brine wells. This cavern
will remain structurally stable because of
its small size and because it is filled with
waste quickly, thus reducing the time it is
exposed to near-atmospheric pressure.
For maximum structural integrity, all the
hazardous waste could be mixed with a
cement slurry so that the entire cavern
would solidify. A small middle cavern
(and later a top cavern) can then be
constructed.
Environmental, Sociological, and
Economic Consideration for
Solution-Mined Facilities
A hazardous waste retention facility
must protect all aspects of the environ-
ment at all times. Solution mining has the
potential for meeting this requirement.
A minimum of land surface is required,
and many salt domes are relatively free of
population and industry.
Site operation should have no adverse
effect on water quality, since there is no
discharge to surface waters. The clean,
saturated brine produced by cavern con-
struction can be injected into deep dis-
posal wells.
Air emission sources are limited to the
diesel blanket storage tank and vapors
displaced from the caverns. The latter
would be chemically scrubbed or burned
in an approved flare.
Careful siting of the facility will ensure
that nowildlife habitat isdisrupted. Major
facilities would be located in areas already
relatively clear of vegetation. The storage
facility should not be located in a wetlands
area.
The proposed project should not inter-
fere with oil and gas production or any
scenic or other natural resource.
Needed Research
Industry has used solution-mined salt
caverns for storage and disposal of certain
hazardous wastes for many years, but the
practice has been limited to compatible
chemicals known to be nonreactive to
each other and to the salt. The hazardous
waste industry faces a nearly infinite mix
of chemicals. When a commercial haz-
ardous waste facility has many clients,
the potential for adverse reactions is
multiplied many times if their wastes are
mixed together for disposal. Thus, more
research must be conducted for each
combination of waste streams. Research
is also needed to determine the compat-
ibility of salt core with anticipated waste
streams.
Solidifying waste in situ would enhance
the use of solution-mined caverns even
more. Research is thus needed to develop
slurries of salt-saturated hazardous
wastes and cement or polymer that will
remain fluid during emplacement and
remain sufficiently strong, long-lived, and
economical when solidified in the cavern.
After the waste has been emplaced, a
method is also needed for flushing the
surface piping and well tubing before
solidification occurs.
Preliminary feasibility studies are need-
ed for solution-mined hazardous waste
retention facilities using both dome and
bedded salt formations. These studies
should include the following items
• Conceptual designs.
• Order-of-magnitude cost estimates for
facilities in both dome and bedded salt
formations
• Evaluations of the waste form—solu-
tion, slurry, and/or solidification.
• Viable schemes for handling the most
difficult-to-manage wastes (those that
remain after all economical means
have been used to prevent, reduce,
neutralize, or otherwise render them
nonhazardous).
The full report was submitted in fulfill-
ment of Contract No. 68-03-3191 by
Fenix & Scisson, Inc., under the sponsor-
ship of the U.S. Environmental Protection
Agency.
•&U. S. GOVERNMENT PRINTING OFFICE: 1985/559 111/10835
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R. B, Stone, K. A. Cove//, T. R. Moran, L W. Weyand, andC. U. Spark/nan are with
Fenix and Scisson, Inc.. Tulsa. OK 74119.
Car/ton C. Wiles is the EPA Project Officer (see below).
The complete report consists of two volumes, entitled "Using Mined Space for
Long-Term Retention of Nonradioactive Hazardous Waste:"
"VolumeI. ConventionalMines,"(OrderNo. PB85-177111/AS;Cost:$ 13.00)
"Volume/I. Solution Mined Salt Caverns," (Order No. PB85-177 129/AS;Cost:
$10.00)
The above reports will be available only from: (costs subject to change)
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
(. 0-
Official Business
Penalty for Private Use $300
OC00329 PS
U S ENV1R PROTECTION *GINCY
CHICAGO
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