United States
Environmental Protection
Agency
•
SITE Technology Capsule
Arctic Foundations, Inc.
Freeze Barrier System
Introduction
In 1980, the U.S. Congress passed the Comprehensive
Environmental Response, Compensation, and Liability
Act (CERCLA), also known as Superfund, which
is committed to protecting human health and the
environment from uncontrolled hazardous waste sites.
CERCLA was amended by the Superfund Amendments
and ReauthorizationAcUSARA)in 1986. SARA mandates
cleaning up hazardous waste sites by implementing
permanent solutions and using alternative treatment
technologies or resource recovery technologies to the
maximum extent possible.
State and federal agencies and privateorganizationsare
exploring a growing number of innovative technologies
for treating hazardous wastes. These new technologies
are needed to remediate the more than 1,200 sites on
the National Priorities List. The sites involve a broad
spectrum of physical, chemical, and environmental
conditions requiring diverse remedial approaches.
The U.S. Environmental Protection Agency (EPA) has
focused on policy, technical, and informational issues
related to exploring and applying new technologies-
to Superfund site remediation. One EPA initiative to
accelerate the development, demonstration, and use
of innovative site remediation technologies is the
Superfund Innovative Technology Evaluation (SITE)
Program.
EPA SITE Technology Capsules summarize the
latest information available on selected innovative
technologies. The Technology Capsules assist EPA
remedial project managers, EPA on-scene coordinators,
contractors, and other remedial managers in evaluating
site-specific information to determine a technology's
applicability for site remediation.
This Technology Capsule provides information on the
Arctic Foundations, Inc. (API), freeze barrier system. API
developed the freeze barrier system to prevent migration
of contaminants in groundwater by completely isolating
contaminant source areas until appropriate remediation
techniques can be applied. Contaminants are contained
in situ with frozen native soils serving as the containment
medium.
The freeze barrier system was demonstrated from
September 1997 to July 1998 at the U. S. Department
of Energy {DOE} Oak Ridge National Laboratory (ORNL)
facility in Oak Ridge, Tennessee. The freeze barrier
system was installed to form a 75-foot by 80-foot box-
like structure around a former waste collection pond.
The pond formerly served as a collection and retention
basin for low-level radioactive wastes.
This Technology Capsule describes the API freeze
barrier system and summarizes results from the SITE
demonstration. The capsule includes the following
information:
Abstract
Site Background and System Construction
Technology Applicability
Site Requirements
Performance Data
Technology Status
Sources of Further Information
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Recycled/Recyclable
Printed with vegetable-based Ink on
paper Ihat contains a minimum of
50% post-consumer fiber content
processed chlorine free
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Abstract
API, of Anchorage, Alaska has developed a freeze barrier
system designed to prevent the migration of contaminants
in groundwater by completely isolating a contaminant
source area. The system can be used for long-term
containment of a source or temporary containment until
appropriate remediation techniques can be applied. With
this system, contaminants are contained in situ with frozen
native soils serving as the containment medium. The EPA
SITE Program evaluated the system at the DOE ORNL
facility in Oak Ridge, Tennessee from September 1997 to
July 1998.
For the demonstration, an array of freeze pipes called
"thermoprobes** was installed around a former waste
collection pond. The thermoprobes were installed vertically
to a depth of 32 feet below ground surface (bgs) and
anchored in bedrock. The thermoprobes were connected
to a refrigeration system by a copper piping network. A
cooled refrigerant (R404A) was circulated through the
system to remove heat from the soil. When the soil matrix
next to the pipes reached 0° C, soil particles bonded
together as the soil moisture froze. Cooling continued until
the frozen region around each thermoprobe began to
expand and build outward, coalescing with frozen regions
developed around other thermoprobes, until an
impermeable frozen soil barrier formed.
A great deal of the data for the demonstration were collected
by parties other than EPA, including AFI, DOE, and the
Tennessee Department of Environmental Conservation
(TDEC). Demonstration personnel collected independent
data to evaluate the technology's performance with respect
to primary and secondary objectives. Groundwater and
surface water samples were collected from locations
upgradient and downgradient of the barrier wall, and also
from locations within the barrier wall. The water samples
were analyzed for two tracer dyes, one of which was injected
into an upgradient monitoring well and the other injected
into a standpipe located within the barrier wall, to determine
the effectiveness of the freeze barrier system in isolating
the contaminant source area. Other data were collected to
determine the effects of the barrier wall on hydrogeologic
conditions and to monitor development of the frozen soil
barrier, as well as documenting installation and operating
parameters for the system.
After the barrier wall reached its design thickness of 12
feet, the groundwater level within the former pond dropped,
indicating that the barrier wall was effective in impeding
recharge into the former pond. Further, water levels
collected from within the former pond did not respond to
storm events compared to water levels collected from
locations outside the containment area, indicating that the
barrier wall was effective in impeding horizontal groundwater
flow through the former pond. Finally, the 1996 groundwater
tracing investigation indicated that groundwater flowed in a
radial pattern from the former pond area, which was not
the case during the demonstration groundwater tracing
investigation.
Sixteen days following tracer injection, tracer that was
injected into the standpipe located within the barrier was
detected outside the barrier in a standpipe located
northwest of the former pond, and was subsequently
detected in downgradient wells and standpipes located
north and west of the former pond. The tracer was first
detected at the standpipe adjacent to the northwest comer
of the former pond. Apparently, the tracer was later carried
to the other downgradient locations through the old drainage
ditches on the north and west sides of the former pond.
These drainage ditches were designed to contain any
overflow from the former pond and likely provided a
preferential pathway for tracer transport.
Historical information indicates that a subsurface pipe in
the northwest corner of the former pond may have been
left in place when the pond was closed. This indication is
further supported by a geophysical survey conducted prior
to the demonstration that detected an anomaly in the
northwest corner of the former pond, suggesting that a pipe
may exist. The alignment of the anomaly is very close to
the standpipe located northwest of the former pond where
dye was first detected. Although it cannot be determined
with certainty, it appears that the dye was transported from
the former pond through a breach in the northwest corner
that was most likely associated with a subsurface pipe in
the wall of the former pond. Available information also
indicates that the former pond is underlain by fractured
bedrock. Therefore, it is also possible that the breach was
associated with fractured bedrock underlying the former
pond.
Using information from the SITE demonstration, AFI, and
other sources, an economic analysis was conducted that
examined 12 cost categories for two different applications
of the freeze barrier system. The first case presents a cost
estimate for extending the use of the freeze barrier system
at DOE's HRE pond site over a 5-year period. The second
case is based on applying the freeze barrier system to a
Superfund site over a 10-year period. The cost estimate
for Case 2 assumes that site conditions were somewhat
similar to those encountered at the HRE pond site, with the
exception of the types of wastes in groundwater and size
of the containment area. Case 2 assumes that groundwater
is contaminated with radionuclides with a volume of 900,000
cubic feet requiring containment. Based on these
assumptions, the total cost per unit volume of frozen soil
was about $8.50 per cubic foot for Case 1 and $9.30 per
cubic foot for Case 2. The cost per unit volume of waste
isolated decreased with increased size of the containment
area, which was about $6.60 per cubic foot for Case 1 and
$3.10 per cubic foot for Case 2. Costs for applications of
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the freeze barrier system may vary significantly from these
estimates, depending on site-specific factors.
The AFI freeze barrier system demonstration, described in
detail in an Innovative Technology Evaluation Report, was
based on the nine decision-making criteria used in the
Superfund feasibility study process. Results of the
demonstration are summarized in Table 1.
Site Background and System
Construction
The SITE Program demonstration of the freeze barrier
system was conducted over a 5-month period from
February 1997 to July 1998. The system was demonstrated
at DOE's ORNL Waste Area Grouping 9 in Oak Ridge,
Tennessee. A former unlined surface impoundment known
as the HRE pond was the specific location for the system
demonstration. When it was operational, the HRE pond's
surface measured roughly 75 feet by 80 feet, with sides
sloping to a bottom measuring 45 feet by 50 feet. The HRE
pond was about 15 feet bgs.
From 1958 through 1961, the HRE pond served as a
retention/settling basin for low-level radioactive liquid wastes
with a radioactivity level equal to or less then 1,000 counts
per minute. High levels of fission products from a chemical
processing system and shield water containing about 340
curies (Ci) of beta-gamma activities were generated in a
reactor tank in the HRE Building; an influent line carrying
these wastes reportedly entered the northwest corner of
the HRE pond. Contaminants from these waste streams
were flocculated in the HRE pond, and treated water from
the pond was piped and discharged to a weir box located
about 40 feet southeast of the pond. The water was then
released from the weir box to a small nearby tributary. A
series of drainage ditches were also located on the north,
south, and west sides of the HRE pond to contain any
overflow from the waste streams. In 1970, the HRE pond
was (1) closed and backfilled with off-site soil containing
shale fragments, (2) combined with sodium borate, and (3)
capped with 8 inches of crushed limestone followed by an
asphalt cap.
In 1986, DOE conducted a soil and groundwater
characterization study in and around the former pond to
determine the concentrations of radiological contaminants.
As part of these activities, six soil borings were advanced
and a series of monitoring wells, piezometers, and
standpipes were installed. The monitoring wells,
piezometers, and standpipes were installed at depths
ranging from 10 to 40 feet bgs. The standpipes are 3-inch-
diameter steel pipes wfth 1 -inch-diameter holes drilled along
the length of the pipe. Analytical data from the soil borings
indicated that the primary radiological contaminants
detected in the former pond were cesium 137 (Cs) and
strontium 90 (Sr). A soil boring installed in the northwest
corner of the former pond yielded the highest radiological
level, with a portion of the core reading about 100 millirems
at a depth near the top of the former pond. Similar soil
patterns were encountered in each borehole installed within
the former pond. The stratification of each borehole
consisted of about 4 inches of asphalt at the surface, about
1 foot of crushed limestone below the asphalt cap, followed
by 5 feet of clay and shale fragments mixed with fill material
down to an elevation of 803 feet above mean sea level
(MSL), which is consistent with the bottom of the former
pond.
Predemonstration Activities
Predemonstration activities, including a groundwater tracing
investigation conducted by EPA in 1996 and two helium
gas tracer studies conducted by DOE in 1996 and 1997,
are discussed below.
1996 EPA Groundwater Tracing Investigation
EPA conducted a groundwater tracing investigation at
ORNL's HRE pond site between June 6,1996 and August
16,1996. The investigation was conducted to validate (1)
the suitability of the two injection points (monitoring well
MW1 [1109] and standpipe 12} proposed for use during the
demonstration groundwater tracing investigation; (2) the
functionality of the tracers prior to establishment of the
barrier wail; and (3) to identify viable groundwater and
surface water sampling locations for the demonstration
groundwater tracing investigation. The investigation was
also used as a baseline for comparing tracer transport
patterns to those observed during the demonstration
groundwater tracing investigation after the barrier wall was
in place.
The dyes rhodamine WT and eosine OJ were selected for
use during the groundwater tracing investigation. On June
7, 1996, 9.01 X 10Z grams of rhodamine WT dye was
injected into monitoring well MW1 (1109) located in the
northwest corner of the pond, and 9.89 X 102 grams of
eosine OJ dye was injected into standpipe 12 located near
the center of the asphalt cap covering the former pond.
Both dyes were flushed into the surrounding aquifer by a
slow injection of deionized water over a 5-day period. A
few days after dye injection, Oak Ridge received several
inches of rain, which also helped to mobilize the dyes.
During the groundwater tracing investigation, charcoal
packets and water samples were collected from
groundwater and surface water recovery points including
monitoring wells, standpipes, piezometers, springs, and a
nearby tributary (see Figure 1). Rhodamine WT was
detected at 16 recovery points and eosine OJ was detected
at 12 recovery points. Recovery points OLD, SBC, S3, S4,
S5, S6, and S7 showed detectable concentrations of
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Table 1. Feasibility Study Evaluation Criteria for the Freeze Barrier System
Criterion
Discussion
Overall Protection of Human Health
and the Environment
Compliance with Applicable or
Relevant and Appropriate
Requirements (ARAR)
Long-Term Effectiveness and
Permanence
Reduction of Toxlcity, Mobility, or
Volume Through Treatment
Short-Term Effectiveness
Implementabillty
Cost
Community Acceptance
State Acceptance
The technology is expected to protect human health and the environment by
preventing the further spread of waterborne contaminants until appropriate
remediation techniques can be applied.
Requires measures to protect workers during drilling and installation activities.
Requires compliance with RCRA storage and disposal regulations for
hazardous waste and pertinent Atomic Energy Act, DOE, and Nuclear
Regulatory Commission requirements for radioactive or mixed waste.
Drilling, construction, and operation of a ground freezing system may require
compliance with location-specific ARARs.
The treatment provides containment of wastes for as long as freezing
conditions are maintained or until remediation techniques can applied.
Human health risk can be reduced by sealing off a hazardous waste area,
thereby preventing the further spread of contaminants.
Periodic review of ground freezing system performance Is needed because
application of this technology to hazardous waste sites with contaminated
groundwater Is relatively recent.
A properly installed frozen soil barrier can isolate a contaminant source areas
without excavation, decreasing the potential for waste mobilization.
The barrier uses benign materials and does not create any reactions or by-
products in the subsurface area in which it is applied.
The speed of development of the barrier wall may vary depending on site
hydrogeology, topography, soil moisture content, soil type, and climate.
Hydrogeologic conditions should be well-defined prior to implementing this
technology. The technology is most easily implemented at shallow depths;
however, companies that employ this technology claim that barriers can be
established to depths of 1,000 feet or mom and can be used in both vadose
and saturated zones.
The site must be accessible to standard drilling equipment and delivery
vehicles.
The actual space requirements depend on the size of the containment area
and thickness of the barrier wall.
ice does not degrade or weaken over time and is repairable in situ. The
barrier wall is simply allowed to melt upon completion of containment needs
and thermoprabes are removed.
The formation of a frozen soil barrier In arid conditions may require a suitable
method for adding moisture to the soils to achieve saturated conditions prior to
barrier wall development.
For a full-scale frozen soil barrier applied to & site that is 150 feet by 200 feet
In size and operating for 10 years under some of the same general conditions
observed at the HRE pond site, total estimated fixed costs are estimated to be
about $2,124,600. Annual operating and maintenance costs, including those
for utilities, supplies, analytical services, labor, and equipment maintenance
are estimated to be about $67,000.
This criterion is generally addressed In the record of decision (ROD) after
community responses are received during the public comment period.
However, because communities are not expected to be exposed to harmful
levels of contaminants, noise, or fugitive emissions, community acceptance of
the technology Is expected to be high.
This criterion Is generally addressed in the ROD; state acceptance of the
technology will likely depend on the long-term effectiveness of the technology.
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rhodamine WT tracer between 2 and 5 days following dye
injection. Transport of rhodamine WT was also evident at
locations MW2 (1110), MW3 (1111), and MW4 (1112) 15
days following dye injection. Rhodamine WT was detected
at recovery point STSS, 22 days after dye injection. At
recovery points STP2, STP9, STP10, W898, and W674,
rhodamine WT arrived between 39 and 50 days following
dye injection.
Groundwater transport of eosine OJ tracer occurred
between 15 and 22 days following dye injection at recovery
points MW2 (1110), MW3 (1111), and MW4 (1112). Thirty-
nine to 50 days following dye injection, transport of eosine
OJ was also evident at recovery points STP2, STP9, STP10,
SBC, W898, and W674. At recovery points S3, S5, and
OLD, eosine OJ arrived between 50 and 56 days following
dye injection (ERA 1996). The eosine OJ results suggest
that a preferential pathway may exist on the north side of
the former pond because eosine OJ was detected in water
samples collected from the small tributary sooner then the
recovery points closest to the eosine OJ injection point,
MW1 {1109). The eosine OJ bypassed on-site monitoring
wells, standpipes, and piezometers and discharged directly
into the tributary within 2 to 4 days following injection. The
investigation also showed that groundwater transport out
of the former pond occurs in a radial pattern and is
hydraulically connected to the surrounding soils.
DOE Helium Gas Tracing Investigations
Following EPA's groundwater tracing investigation, DOE
conducted two independent gas tracing investigations using
helium in the summer of 1996 and winter of 1997. The
results of DOE'S investigations confirmed that groundwater
is transported in a radial pattern out of the former pond.
DOE also reported that transport out of the former pond
occurs under ambient conditions and not just under forced-
gradient conditions (water injection) as was the case with
the groundwater tracing investigation.
System Construction
Prior to system construction, an electromagnetic
geophysical survey of the former pond was conducted to
identify objects that could potentially disrupt drilling and
installation activities. According to DOE the survey Identified
three anomalies, one of which extended through the
northwest portion of the former pond that was consistent
with a subsurface pipe. The two other anomalies were
interpreted as possible buried scrap metal in the northwest
and southeast corners of the former pond. API's ground
freezing system was constructed from May through
September 1997. The system was constructed around the
top of the former pond, just southeast of the HRE building.
A total of 58 boreholes were drilled, using hollow-stem auger
and air rotary drilling methods, to a depth of about 32 feet
bgs into the underlying bedrock. Fifty thermoprobes,
spaced about 6 feet apart, were installed into the boreholes
with the base of each thermoprobe anchored in bedrock
(Figure 2). The annular space around each thermoprobe
was then filled with quartz sand. AFI also installed a
piezometer to a depth of about 7 feet bgs within the confines
of the barrier wall, just southeast of standpipe 12.
Eight temperature monitoring points were installed in the
remaining eight boreholes, using the same general
procedures used to install the thermoprobes (Figure 2). The
temperature monitoring points were placed at strategic
locations to monitor development of the frozen barrier wall.
Temperature monitoring points were set inside protective
casings to protect the instruments and allow replacement
without having to redrill.
Additional subsurface temperature data were collected from
platinum resistance temperature detectors (RTD) that were
installed on the external surface about midway down (15
feet bgs) each thermoprobe. The RTDs provide an
indication of the operating temperature of each
thermoprobe, and thus provided a means for AFI to evaluate
thermoprobe performance. AFI then wired each thermistor
and RTD to a datalogger for continuous collection of
subsurface temperature data.
Following placement of thermoprobes and temperature
monitoring points, cracks and voids in the asphalt cap over
the site surface were filled with an asphalt patching material.
An extruded polystyrene insulation material was then placed
over the asphalt surface and cut to fit securely around the
thermoprobes, piezometer, and temperature monitoring
points. A waterproofing membrane was placed over the
insulation to prevent infiltration of rain or surface water
(Figure 2), Concrete pavers were placed along the
perimeter of the membrane to prevent uplift from wind. Once
the waterproof membrane cured, the two refrigeration units,
an abovegrade copper piping network, and the electrical
connection were installed.
The two refrigeration units, each connected to 25
thermoprobes, were configured so that alternating
thermoprobes in the array surrounding the former pond was
plumbed to the same refrigeration unit. Before the system
was charged with refrigerant, the system underwent
pressure testing to ensure that there were no leaks or
blockages. The freeze barrier system was activated in mid-
September 1997.
Technology Applicability
AFI claims that its freeze barrier system can provide
subsurface containment for a variety of sites and wastes,
including the following: underground storage tanks;
nuclear waste sites; plume control; burial trenches, pits,
and ponds; in situ waste treatment areas; chemically
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contaminated sites; and spent fuel storage ponds, AFI
claims that the system is adaptable to any geometry;
drilling technology presents the only constraint.
Potential users of this system must consider the possibility
that formation of a soil barrier in arid conditions may
require a suitable method of adding and retaining moisture
in soils to achieve saturated conditions. An effective
means of homogeneously adding moisture to soils will be
required. The effectiveness of this system for containment
of contaminants in arid soils will require assessment. The
practicality of implementing this system at some sites may
be limited. As for most in situ containment systems, the
need for intrusive construction activities requires a
significant amount of open surface space, possibly
precluding the use of this system at certain sites.
Material handling requirements for the freeze barrier
system include those for the soil and water removed
during drilling activities. Groundwater removed from
boreholes during thermoprobe installation activities will
probably contain site-related contaminants. Soils
removed from below the water table in the vicinity of a
contaminant plume may have become contaminated by
contact with contaminated groundwater. For this reason,
soil and water generated during construction activities may
require handling, storage, and management as hazardous
wastes. Precautions may include availability of lined,
covered, roll-off boxes; drums; or other receptacles for the
soil; storage tanks or drums for the water; and appropriate
personal protective equipment for handling contaminated
materials. Contaminated soils should be stockpiled on site
separately from clean soils to minimize the amount of
material requiring management as potentially hazardous
waste.
Site Requirements
In addition to the hydrogeologic conditions that determine
the technology's applicability and design, other site
characteristics affect implementation of this system. The
amount of space required for a ground freezing system
depends on the thickness of the barrier wall and size of the
containment area. For the SITE demonstration, the array
of thermoprobes encompassed an area of about 75 feet by
80 feet, with an average frozen soil barrier wall thickness
of 12 feet. Thermoprobes are typically installed in a "V* or
"U" configuration to ensure complete encapsulation and
isolation of the waste source. At the HRE pond, the
thermoprobes were installed in a vertical position, with the
bottom of each thermoprobe anchored in bedrock.
The site must be accessible and have sufficient operating
and storage space for heavy construction equipment.
Access for a drill rig to install the thermoprobes and
temperature monitoring points for system operation is
required. A crane also may be necessary to install the
thermoprobes and to subsequently remove the
thermoprobes from the containment area following
remediation activities. Access for tractor trailers (for delivery
of thermoprobes, refrigeration units and associated piping,
construction supplies, and equipment) is preferable.
Underground utilities crossing the path of the proposed
system may require relocation if present, and overhead
space should be clear of utility lines to allow cranes and
drill rigs to operate. Construction around existing surface
structures also may be required.
Soil from drill cuttings at contaminated sites may require
management as a potentially hazardous waste. For this
reason, roll-off boxes or 55-gailon drums to store the soil,
and sufficient space near, but outside of the construction
area for staging, should be available. During drilling activities
at the HRE pond, radiation levels in soil cuttings were
continuously monitored and were classified as Category 1
(<1 milliradian [mRadJ/hour), Category 2 (>1 mRad/hour),
or Category 3 {>5 mRad/hour) waste to facilitate proper
disposition of the waste. A portable tank or tanker truck
also should be available for thermoprobe installation to
temporarily store water removed from the boreholes, if
necessary. Where soil type and site conditions are
appropriate, thermoprobes may be installed by pile driving
methods. This method eliminates handling drill cuttings
with limited environmental disturbance. A building or shed
may be necessary to protect the system control module
and instrumentation wiring, as well as for use by workers
during routine operation and maintenance activities.
Performance Data
EPA established primary and secondary objectives for the
SITE demonstration of the freeze barrier system. The
objectives were based on EPA's understanding of the freeze
barrier system, SITE Program demonstration goals, and
input from AFl. Primary objectives were considered critical
for the system demonstration, while secondary objectives
involved collecting additional data considered useful, but
not critical to the system demonstration. The objectives
also were selected to provide potential users of the freeze
barrier system with technical information to determine if
the system is applicable to other contaminated sites. The
SITE demonstration was designed to address one primary
objective and four secondary objectives for evaluation of
the freeze barrier system.
Primary Objective
The following was the primary (P) objective of the system
demonstration:
P1 - Determine the effectiveness of the freeze barrier
system in preventing hori2ontal groundwater flow beyond
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the limits of the frozen soil barrier through the performance
of a groundwater tracing investigation using a fluorescent
dye
The primary objective was established to evaluate the
freeze barrier system's ability to control hydrogeologic
conditions in the former pond. The barrier wall was
evaluated through the performance of a groundwater
tracing investigation that included injecting a fluorescent
dye {phloxine B) into standpipe 12, located in the center of
the former pond, and monitoring for the dye at groundwater
and surface water recovery points located within and
outside the former pond.
Secondary Objectives
The following were the secondary (S) objectives o! the
demonstration:
S1 • Verify whether flow pathways outside the former pond
were still open after placement of the freeze barrier wall
S2 - Evaluate the hydrogeologic isolation of the enclosed
former pond area before and after placement of the freeze
barrier wall
S3 - Monitor development of the freeze barrier wall
S4 - Document installation and operating parameters of
the freeze barrier wall
Secondary objective S1 was evaluated through the
performance of a second groundwater tracing investigation
that included adding a second fluorescent dye {eosine OJ)
to upgradient monitoring well MW1 (1109} and monitoring
for its presence at groundwater and surface water recovery
points within and outside the barrier wall. Objective S2
was evaluated through a comparison of water level data
obtained from standpipe 12 and monitoring wells MW1
(1109) and MW2 (1110). Objective S3 was evaluated by
collecting subsurface temperature data from a series of
temperature monitoring points located within and outside
the barrier wall in the southeast corner of the containment
area. Objective S4 was established to provide data for
estimating costs associated with use of the freeze barrier
system, and was based on observations made during the
demonstration, demonstration data, and data provided by
AR.
SITE Demonstration Results
This section summarizes the methods and procedures
used to collect and analyze samples for the critical
parameters during the SITE demonstration; the results of
the SITE demonstration, including the demonstration
background study; and evaluation of the primary and
secondary objectives.
Methods
Both the demonstration background study and
groundwater tracing investigation employed the use of
activated charcoal packets and grab sampling techniques
for the collection of groundwater and surface water
samples from potential tracer recovery points located
downgradient and across gradient from the two tracer
injection points (standpipe 12 and monitoring well MW1
[1109]). The samples were collected and analyzed in
accordance with the Freeze Barrier Technology
Demonstration QAPP.
The demonstration background study was conducted over
a 21-day period after the frozen soil barrier reached its
design thickness of 12 feet. A total of 22 charcoal packets
and 114 grab samples of water were collected from the
recovery points over the 21 -day period. The samples were
analyzed using a spectrofluorophotometer for any
residuals dyes from the 1996 groundwater tracing
investigation or natural background fluorescence.
The demonstration groundwater tracing phase of the
demonstration was conducted over a 5-month period after
the background study was completed. A total of 15
charcoal packets and 359 grab samples of water were
collected from the recovery points shown in Figure 1. The
samples were analyzed for the two dyes phloxine B and
eosine OJ, using a spectrofluorophotometer.
Results of the Demonstration Background Study
The demonstration background study was conducted in
January 1998 following establishment of the barrier wall.
Analytical results indicated the presence of residual
concentrations of the dyes eosine OJ and rhodamine WT
that were used during the 1996 groundwater tracing
investigation conducted by EPA. According to the analytical
laboratory, a green compound, which is a common
derivative of rhodamine WT, was identified in samples
collected from recovery points STP2, STP9, OLD, KL, and
MW1 (1109). Analytical results indicated that uranine was
present in water samples collected from recovery points
12, SBC, STP9, AFIP, MW4 (1112), S1, and S2. Uranine
also was present in samples collected from the same
recovery points during the 1996 groundwater tracing
investigation.
The highest concentration of fluorescence in background
samples in the range of the emission spectra for phloxine
B and eosine OJ was 1.30e-03 parts per billion (ppb). This
background concentration for phloxine B and eosin© OJ
was used as a baseline for comparison to demonstration
groundwater tracing investigation results. Therefore,
phloxine B and eosine OJ detected above the highest
background concentration was considered a detection at
any recovery point.
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During the demonstration background study, field personnel
interviewed Mr. IVtarlin Ritchey, a Lockheed Martin Energy
Systems Inc. engineer in charge of sump pumps in the
basement of the HRE building, located northwest
{upgradient} of the HRE pond. Mr. Ritchey was interviewed
in an attempt to identify a source for the uranine. Mr. Ritchey
stated that he had conducted a number of dye tracing
experiments from the basement of the HRE building, using
the dye uranine, during the period between the 1996
groundwater tracing investigation and the demonstration
background study. After discovering a potential source for
the uranine, it was unclear how uranine migrated from the
HRE building to standpipe 12 and piezometer AFIP located
within the containment area. Available information indicates
that piping connected to the HRE building entered the former
pond from the northwest and may have been left in place
after the pond closed. A geophysical survey conducted
prior to the demonstration refers to a subsurface pipe that
extends through the northwest wall of the former pond,
inferring that a pathway could exist between the former pond
and the HRE building. However, it is unknown whether this
pathway was open or closed after placement of the barrier
wall.
Evaluation of Objective P1
Determine the effectiveness of the freeze barrier system in
preventing horizontal groundwater flow beyond the limits
of the frozen soil barrier through the performance of a
groundwater tracing investigation using a fluorescent dye.
Phloxine B was detected outside the former pond at
recovery points STP10, AFIP, STP1, STP2, STP9, and MW4
(1112). Figure 3 shows the inferred migration pathway from
the phloxine B injection point at standpipe 12 to the recovery
points where phloxine B was detected. Phloxine B was
first recovered about 16 days after tracer injection at
recovery point STP10, which is located upgradient of
injection point 12. The concentration of phloxine B detected
at recovery point STP10 was 3.20e-01 ppb, well above the
highest concentration (1.30e-03 ppb} detected during the
demonstration background study. The recovery pattern at
STP10 shows a rapid increase in concentration of the
emission peak for phloxine B over time, with a lower
exponential decrease. The second detection of phloxine B
occurred 10 weeks after tracer injection at recovery point
AFIP.
The probability that piping may exist in the northwest portion
of the former pond cannot be discounted in relation to the
recovery of phloxine B at recovery point STP10. The
pathway from standpipe 12 to the area near standpipe
STP10 is close to the alignment of a geophysical anomaly
that was detected prior to the demonstration, which was
inferred to be a pipe. Although this is not the exact location
for the piping, there are no as-built diagrams available to
confirm their final location. Drilling activities associated with
installation of the ground freezing system revealed the
highest concentration of radionuclides in auger cuttings
collected in the northwest corner of the former pond, close
to where the geophysical anomaly was identified. This high
concentration is most likely associated with either a leak in
the influent pipe that extends from the HRE building to the
former pond or where the pipe emptied into the pond.
Water level data collected from standpipes 12 and STP10,
during water injection to mobilize the phloxine B dye,
revealed that the groundwater elevation in standpipe 12 was
anomalously high in comparison to that in standpipe STP10.
The hydrograph for standpipe 12 shows a rapid water level
increase and subsequent decrease during water injection
to mobilize the phloxine B dye. According to DOE, this
fluctuation was caused by groundwater mounding following
water injection at standpipe I2, which created a gradient
reversal in the direction of STP10. This gradient reversal
may have transported the phloxine B-laden groundwater
laterally through the subsurface pipe to the area near
standpipe STP10.
Phloxine B also was detected at concentrations above
background at recovery points STP1, STP2, MW4 (1112),
and STP9 between 69 and 126 days following tracer
injection, which was much later than the detection at STP10.
Based on the timing of the recoveries and decreased
concentrations with distance from recovery point STP10, it
does not appear that phloxine B migrated directly to any
other location. Available information also indicates that
recovery points STP10, STP1, STP2, STP9, and MW4
(1112) may be located within the drainage ditches on the
north and west sides of the former pond, outside the
containment area. The ditch locations and flow directions,
based on information provided by DOE, are shown in Figure
3. The drainage ditches, which are located around the
perimeter of the former pond, were designed to contain
any pond overflow and prevent release into the surrounding
groundwater system. The drainage ditches may have
provided a preferential pathway to transport the phloxine B
from STP10 to recovery points STP1, STP2, STP9, and
MW4 (1112), which were located downgradient of STP10.
Other data gathered during the demonstration period, with
the exception of the groundwater tracing investigation using
phloxine B, provide evidence that the ground freezing
system was effective in impeding horizontal groundwater
flow in the containment area. Based on available
information, the critical dye (phloxine B) injected into
standpipe 12 was transported beyond the limits of the frozen
soil barrier either through a breach in the barrier wall most
likely associated with a subsurface pipe or beneath the
barrier wall through fractured bedrock. According to DOE,
however, the slow drainage of the former pond following
establishment of the barrier wall likely would have resulted
in slower transport of phloxine B dye through fractured
bedrock to standpipe STP10 than what was observed during
10
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d"
671
LEGEND
r PHLOXINE B
\ INJECTION POINT
FORMER TOP OF POND
FORMER POND BOTTOM
LIMITS OF ASPHALT CAP
-S3 PHLOXINE B MIGRATION PATHWAY
•«• DRAINAGE DITCH CONFIGURATION
GROUND SURFACE
WATER WATER
RECOVERY POINT
t PHLOXINE B DETECTIONS
THERMOPROBE
TEMPERATURE MONITORING POINTS
Figure 3, System configuration and Inferred dye migration pathways.
11
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the demonstration. Supporting information is summarized
below:
Water level data and predemonstration groundwater tracing
data collected from locations within and outside the former
pond before emplacement of the barrier wall showed that
groundwater within and outside the pond was hydraulically
connected prior to construction of the barrier. However,
water level data collected from standpipe 12 within the
containment area following establishment of the barrier wall
showed that the water table dropped and did not respond
to storm events, compared to water levels collected outside
the containment area that did show responses to storm
events. These data indicated that the barrier wall was
effective in impeding groundwater recharge into the
containment area.
Subsurface temperature data collected from temperature
monitoring points T-1 and T-2, located in the northwest
corner of the barrier, showed that soil temperature from
the ground surface to about 30 feet bgs remained well below
32° F. Based on experience, however, AFI claims that the
barrier wall was frozen to a depth of about 36 feet bgs.
Results of the demonstration groundwater tracing
investigation compared to the 1996 groundwater tracing
investigation showed that the barrier wall disrupted
groundwater conditions within and outside the former pond
area. Phloxine B results from the demonstration
groundwater tracing investigation showed that transport out
of the former pond was limited to the northwest corner,
compared to the results of the 1996 investigation and DOE's
gas tracer studies that showed tracer transport in a more
radial pattern from standpipe 12. The demonstration
groundwater tracing investigation did not show tracer
transport directly to the on-site tributary as observed during
the 1996 groundwater tracing investigation, indicating that
the barrier was disrupting groundwater flow patterns in and
around the former pond area.
TDEC personnel collected surface water samples from the
weir box located about 40 feet southeast of the former pond,
during and after development of the barrier wall. Surface
water sampling results from July through September 1998
showed slightly lower levels of gross beta activity. According
to TDEC, however, sampling results should be qualified until
long-term results are made available because the samples
were collected during the dry season when gross beta
activity is generally lower.
Evaluation of Objectives S-1 and S2
Verify whether flow pathways outside the former pond were
still open after placement of the freeze barrier wall and
evaluate the hydrogeologic isolation of the former pond
before and after placement of the freeze barrier wall.
Information on water level results discussed in this section
is based on data gathered by DOE and presented in a report
entitled "HRE-Pond Cryogenic Barrier Technology
Demonstration: Pre- and Post-Barrier Hydrologic
Assessment" prepared by Dr. Gerilynn Moline, ORNL
Environmental Sciences Division. The following sections
describe the groundwater conditions encountered before
and after establishment of the barrier wall in the former
pond area.
Pre-Barrier Groundwater Conditions
Water level data collected from monitoring locations 12,
STP10, and MW2 (1110) compared to precipitation data,
indicates that all three monitoring points were responsive
to storm events prior to establishment of the frozen soil
barrier. The data also show that all three monitoring
locations exhibited the same types of water level oscillations
during storm events, providing evidence that groundwater
within and outside the former pond is hydraulically
connected. The rapid rise in groundwater elevations at
standpipe 12 during some storm events also suggests that
the water table may intersect the gravel layer beneath the
asphalt cap, thereby providing a pathway for migration of
contaminants out of the former pond through this highly
permeable layer. This relationship is apparent in the
hydrograph for standpipe 12, where the elevation of the
asphalt cap at standpipe 12 is 818.5 feet above MSL and
the groundwater elevation at standpipe 12 frequently
exceeded 817 feet above MSL during storm events,
assuming the asphalt cap is 1 foot thick.
The 1996 groundwater tracing investigation also shows that
groundwater within the former pond is hydraulically active
and connected to the surrounding soils, as evidenced by
the transport of tracers from within the former pond to areas
outside the former pond. The dye eosine OJ, injected into
center standpipe 12 under forced-gradient conditions during
water injection, was transported radially throughout the area
surrounding the former pond. The rhodamine WT dye
injected into monitoring well MW1 (1109) showed that a
preferential pathway may exist on the north side of the
former pond between monitoring well MW1 (1109) and the
tributary located just east of the pond. Rhodamine WT was
transported directly to the tributary and bypassed on-site
recovery points directly in line with the tributary.
Post-Barrier Groundwater Conditions
The water level within the HRE pond was significantly
impacted by the barrier wall. The water table elevation
exhibited a slow downward slope and did not respond to
storm events compared to locations outside the containment
area after freezing was initiated. According to AFI, the slow
decline in water levels at standpipe 12 is a result of soil
moisture being drawn to the frozen soil barrier. The slow
decline also may have been a result of slow seepage
12
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through fractured bedrock in the base of the former pond.
Figure 4 shows the hydrograph for standpipe 12, Analytical
results also show some distinct peaks just prior to the
demonstration groundwater tracing investigation that require
some explanation. According to DOE, the pressure
transducer was replaced just prior to Initiation of the
demonstration groundwater tracing investigation, which
reportedly displaced the water level in standpipe 12, resulting
in fluctuations in the hydrograph for standpipe 12, The only
other water level responses seen in the hydrograph for
standpipe 12 correspond to water injections that occurred
for 5 days following dye injection, even though there were
numerous storm events during this period.
Results of the eosine O J demonstration groundwater tracing
investigation suggest that the barrier wall also had an effect
on horizontal groundwater flow in the HRE pond area. Tracer
transport behavior during the demonstration groundwater
tracing investigation differed from the 1996 groundwater
tracing investigation. The 1996 groundwater tracing
investigation showed tracer transport from MW1 (1109) to
most of the downgradient recovery points including OLD,
SBC, MW2{1 \ 10), MW3 (1111), MW4 (1112), STSS, STP2,
STP9, STP10, W674, W898, and S3 through S7. The
eosine OJ dye, injected into monitoring well MW1 (1109)
during the demonstration groundwater tracing investigation,
only showed tracer transport to recovery points STP1,
STP2, STP9, MW4 (1112), and OLD. However, eosine OJ
was only detected at a concentration above background in
downgradient recovery point OLD (1.09e+03 ppb), 2 days
following dye injection. This change in transport behavior
Is likely due to diversion of dye-laden groundwater around
the barrier wall because concentrations in all samples, with
the exception of recovery point OLD, were below
demonstration background levels, indicating that peak
concentrations may not have been attained within the
demonstration period. This behavioral change is apparent
in the eosine OJ data for recovery point MW4 (1112), where
the highest concentration detected during the demonstration
groundwater tracing investigation did not occur until 2 weeks
prior to the end of the demonstration. However, this fact
cannot be determined with any certainty because samples
were not collected after the demonstration period ended.
Results from the 1996 investigation also show that tracer
was transported to the downstream locations (SBC and
S3 through S7) more rapidly than it was transported to the
locations closer to the pond (STP2, W898, W674, and OLD).
Tracer injected into monitoring well MW1 (1109) bypassed
the upgradient recovery points and discharged directly into
the tributary, indicating that a preferential pathway may exist
on the north side of the former pond. Tracer transport to
the tributary was not observed during the demonstration
groundwater tracing investigation, indicating that horizontal
groundwater flow may have been impeded as a result of
the barrier wall.
According to DOE, water table elevations downgradient of
the former pond also were affected by the frozen soil barrier.
DOE reported that the water level in standpipe STP5
dropped about 6.5 feet following barrier placement. DOE
also reported that water levels at standpipe STP6 were not
as responsive to storm events following barrier placement
and that only large storms produced the type of response
observed at STP6 prior to barrier placement. This effect
also shows that horizontal groundwater flow through the
former pond to these downgradient locations was impeded
or that flow was diverted around the barrier wall, resulting
in suppression of the water table at these locations.
Evaluation of Objective S-3
Monitor development of the freeze barrier wall.
Continuous subsurface temperature data were collected
from eight temperature monitoring points at various
locations and distances from the thermoprobes to monitor
the development of the frozen soil barrier wall. Six
temperature monitoring points installed in the southeast
corner of the containment area were used to monitor
development of the barrier wall. Each temperature
monitoring point was equipped with eight temperature
sensors installed at various depths to provide a vertical
profile of temperature conditions at each location.
The ground freezing system operated in three phases: initial
freeze-down, freezing to design thickness, and maintenance
freezing. During the freeze-down phase, which began in
mid-September 1997, the two refrigeration units operated
simultaneously, driving the 50 thermoprobes at
temperatures below -32° F. Gradually, the soil temperature
was reduced until the soil moisture around each
thermoprobe was frozen and began coalescing, which
occurred about mid-October 1997. According to AFI, this
process was continued until the frozen soil region around
each thermoprobe reached about 3 feet in thickness radially
and completely joined at the surface of the asphalt
pavement, which occurred about the first week of November
1997. This process, which is referred to as "freezing to
closure," occurred about 7 weeks following system start-
up.
Following closure, AFI reported that freezing was continued
until the frozen soil wall reached the design thickness of 12
feet, which occurred in mid-January 1998, or about 18
weeks following system startup. According to AFI, the
design thickness was selected based on API's past
experience using the thermoprobe placement configuration
similar to what was applied to the HRE pond site.
Subsurface temperatures at T-3 (located directly on the
centerline of the barrier) from the bottom of the insulation
to 30 feet bgs remained well below 32" F, from mid-January
through mid-July 1998.
13
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820
819
818
Replacement of
Pressure Transducers
Water Level
Manual w.l.
Peaks correspond to
dye/water injections
starting on 2/20/98
812
Jan-97
Mar-97
i i i I I
May-97 Jul-97 Sep-97 Nov-97 Jan-98
Mar-98 May-98 Jul-98
Figure 4. Hydrograph for Standpipe I2.
Once the design thickness was achieved, the maintenance
freezing phase began and the refrigeration units operated
on a 24-hour alternating run schedule to minimize power
consumption. Maintenance freezing required significantly
lower energy levels then the initial freezedown. According
to API, the barrier wall thickness remained fairly constant
during this phase and is expected to be maintained at the
HRE pond site until October 1,1999. The total volume of
soil frozen is about 134,000 cubic feet and the total volume
of soil contained is about 180,000 cubic feet.
In late September 1998, API simulated a power outage at
the HRE pond site. The refrigerant feed to the array of
thermoprobes was shut down for a period of 8 days while
subsurface temperature data were continuously collected.
AF! reported that ambient air temperatures during this
period averaged between 32° C and 35° C. The barrier
reportedly lost less than 2 percent of its design thickness
during this period, with the maximum loss at the top of the
barrier, just beneath the insulation. However, subsurface
temperature data showed that the centerline of the barrier
from the bottom of the insulation to 30 feet bgs remained
frozen throughout the 8-day testing period.
Evaluation of Objective S-4
Document installation and operating parameters of the
freeze barrier wall to determine costs.
Using information from the SITE demonstration, API, and
other sources, an economic analysis was conducted that
examined 12 cost categories for two different applications
of the freeze barrier technology. The first case presents a
cost estimate for extending the use of the freeze barrier
technology at the HRE pond site over a 5-year period. The
second case is based on applying the freeze barrier
technology to a Superfund site over a 10-year period. The
cost estimate for Case 2 assumes that site conditions were
somewhat similar to those encountered at the HRE pond
site, with the exception of the types of wastes in groundwater
and size of the containment area. Case 2 assumes that
groundwater is contaminated with radionuclides with a
volume of 900,000 cubic feet requiring containment. Based
on these assumptions, the total costs per unit volume of
frozen soil was about $8.50 per cubic foot for Case 1 and
$9.30 per cubic foot for Case 2. The cost per unit volume
of waste isolated decreased with increased size of the
containment area which was about $6.60 per cubic foot for
Case 1 and $3.10 per cubic foot for Case 2, Costs for
applications of the freeze barrier technology may vary
significantly from these estimates, depending on site-
specific factors.
Technology Status
To date, this SITE demonstration represents the first full-
scale application of the API frozen soil barrier system at a
14
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contaminated site. However, AFI has been developing,
designing, fabricating, and installing ground freezing
systems for about 30 years. AFI has used the system to
seal subsurface structures against flooding of groundwater;
to stabilize soils for excavation; and for foundation and
ground stabilization purposes. While the AFI ground
freezing system has been primarily used in arctic and
subarctic environments, such as Alaska, Canada, and
Greenland, the system can also be used in more temperate
locations as demonstrated at the HRE pond site.
Current plans for API's ground freezing at ORNL's HRE pond
site include maintaining the frozen soil barrier for at least 1
additional year beginning October 1,1998 to assess long-
term performance of the barrier wall. DOE also is
considering the use of the freeze barrier system for
containment of radiologically contaminated groundwater
plumes at two other DOE facilities, including Savannah River
and Hanford. The system also is being considered for
containment of a groundwater plume contaminated with
polychlorinated biphenyls and dense nonaqueous-phase
liquids at a site in Srnithville, Canada.
Sources of Further Information
Steve Rock
U.S. Environmental Protection Agency
Office of Research and Development
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, Ohio 45268
Telephone: (513)569-7149
FAX: (513)569-7879
E-mail: rock.steven & epamall epa.gov
Ed Yarmak
Project Manager
Arctic Foundations, Inc.
5621 Arctic Boulevard
Anchorage, Alaska 99518
Telephone: (907) 562-2741
FAX: (907)562-0153
E-mail: arcfnd®alaska.net
15
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United States
Environmental Protection
Agency
Office of Research and Development
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
EPA/540/R-Q3/5Q83
September 2004
wvwv.epa.gov
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