\,EPAUnited States Environmental Protection

Agency

SITE Technology Capsule

Arctic Foundations, Inc.

Freeze Barrier Syste m

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 th e

environment from uncontrolled hazardous waste sites .

CERCLA was amended by the Superfund Amendment s

and Reauthorization Act (SARA) in 1986 . SARA mandates

cleaning up hazardous waste sites by implementin g

permanent solutions and using alternative treatmen t

technologies or resource recovery technologies to th e

maximum extent possible .

State and federal agencies and private organizations ar e

exploring a growing number of innovative technologie s

for treating hazardous wastes . These new technologie s

are needed to remediate the more than 1,200 sites o n

the National Priorities List . The sites involve a broa d

spectrum of physical, chemical, and environmenta l

conditions requiring diverse remedial approaches .

The U.S . Environmental Protection Agency (EPA) ha s

focused on policy, technical, and informational issue s

related to exploring and applying new technologies

to Superfund site remediation . One EPA initiative t o

accelerate the development, demonstration, and use

of innovative site remediation technologies is th e

Superfund Innovative Technology Evaluation (SITE )

Program.

EPA SITE Technology Capsules summarize th e

latest information available on selected innovativ e

technologies . The Technology Capsules assist EPA

remedial project managers, EPA on-scene coordinators ,

contractors, and other remedial managers in evaluatin g

site-specific information to determine a technology's

applicability for site remediation .

This Technology Capsule provides information on th e

Arctic Foundations, Inc. (AFI), freeze barrier system. AFI

developed the freeze barrier system to prevent migratio n

of contaminants in groundwater by completely isolatin g

contaminant source areas until appropriate remediatio n

techniques can be applied . Contaminants are containe d

in situ with frozen native soils serving as the containmen t

medium .

The freeze barrier system was demonstrated fro m

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 boxlike 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 AFI freeze

barrier system and summarizes results from the SIT E

demonstration . The capsule includes the followin g

information:

• Abstract

• Site Background and System Constructio n

• Technology Applicabilit y

• Site Requirement s

• Performance Data

• Technology Statu s

• Sources of Further Informatio n

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SUPERFUND INNOVATIVE

TECHNOLOGY EVALUATION

Recycled/Recyclable

Printed with vegetable-based ink o n

paper that contains a minimum of

50% post-consumer fiber content

processed chlorine free
Abstract

AFI, of Anchorage, Alaska has developed a freeze barrie r

system designed to prevent the migration of contaminant s

in groundwater by completely isolating a contaminan t

source area. The system can be used for long-ter m

containment of a source or temporary containment unti l

appropriate remediation techniques can be applied . With

this system, contaminants are contained in situ with froze n

native soils serving as the containment medium . The EPA

SITE Program evaluated the system at the DOE ORN L

facility in Oak Ridge, Tennessee from September 1997 to

July 1998.

For the demonstration, an array of freeze pipes calle d

"thermoprobes" was installed around a former wast e

collection pond. The thermoprobes were installed verticall y

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 th e

system to remove heat from the soil . When the soil matrix

next to the pipes reached 0° C, soil particles bonde d

together as the soil moisture froze. Cooling continued unti l

the frozen region around each thermoprobe began to

expand and build outward, coalescing with frozen region s

developed around other thermoprobes, until a n

impermeable frozen soil barrier formed .

A great deal of the data for the demonstration were collecte d

by parties other than EPA, including AFI, DOE, and the

Tennessee Department of Environmental Conservatio n

(TDEC). Demonstration personnel collected independent

data to evaluate the technology's performance with respec t

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 sample s

were analyzed for two tracer dyes, one of which was injected

into an upgradient monitoring well and the other injecte d

into a standpipe located within the barrier wall, to determin e

the effectiveness of the freeze barrier system in isolatin g

the contaminant source area. Other data were collected to

determine the effects of the barrier wall on hydrogeologi c

conditions and to monitor development of the frozen soi l

barrier, as well as documenting installation and operatin g

parameters for the system .

After the barrier wall reached its design thickness of 1 2

feet, the groundwater level within the former pond dropped ,

indicating that the barrier wall was effective in impedin g

recharge into the former pond . Further, water level s

collected from within the former pond did not respond t o

storm events compared to water levels collected fro m

locations outside the containment area, indicating that th e

barrier wall was effective in impeding horizontal groundwate r

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 no t

the case during the demonstration groundwater tracin g

investigation.

Sixteen days following tracer injection, tracer that wa s

injected into the standpipe located within the barrier wa s

detected outside the barrier in a standpipe located

northwest of the former pond, and was subsequentl y

detected in downgradient wells and standpipes locate d

north and west of the former pond. The tracer was firs t

detected at the standpipe adjacent to the northwest corner

of the former pond . Apparently, the tracer was later carrie d

to the other downgradient locations through the old drainag e

ditches on the north and west sides of the former pond .

These drainage ditches were designed to contain an y

overflow from the former pond and likely provided a

preferential pathway for tracer transport .

Historical information indicates that a subsurface pipe i n

the northwest corner of the former pond may have bee n

left in place when the pond was closed . This indication is

further supported by a geophysical survey conducted prio r

to the demonstration that detected an anomaly in th e

northwest corner of the former pond, suggesting that a pip e

may exist . The alignment of the anomaly is very close t o

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 fro m

the former pond through a breach in the northwest corne r

that was most likely associated with a subsurface pipe i n

the wall of the former pond. Available information also

indicates that the former pond is underlain by fracture d

bedrock. Therefore, it is also possible that the breach was

associated with fractured bedrock underlying the forme r

pond.

Using information from the SITE demonstration, AFI, an d

other sources, an economic analysis was conducted tha t

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 syste m

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 estimat e

for Case 2 assumes that site conditions were somewhat

similar to those encountered at the HRE pond site, with th e

exception of the types of wastes in groundwater and siz e

of the containment area. Case 2 assumes that groundwate r

is contaminated with radionuclides with a volume of 900,00 0

cubic feet requiring containment. Based on thes e

assumptions, the total cost per unit volume of frozen soi l

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 an d

$3.10 per cubic foot for Case 2. Costs for applications of

2
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, wa s

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 Syste m

Construction

The SITE Program demonstration of the freeze barrie r

system was conducted over a 5-month period from

February 1997 to July 1998. The system was demonstrate d

at DOE's ORNL Waste Area Grouping 9 in Oak Ridge,

Tennessee. A former unlined surface impoundment know n

as the HRE pond was the specific location for the syste m

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 HR E

pond was about 15 feet bgs .

From 1958 through 1961, the HRE pond served as a

retention/settling basin for low-level radioactive liquid waste s

with a radioactivity level equal to or less then 1,000 count s

per minute . High levels of fission products from a chemica l

processing system and shield water containing about 34 0

curies (Ci) of beta-gamma activities were generated in a

reactor tank in the HRE Building ; an influent line carryin g

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 fro m

the pond was piped and discharged to a weir box locate d

about 40 feet southeast of the pond . The water was the n

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 an y

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 groundwate r

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, an d

standpipes were installed . The monitoring wells ,

piezometers, and standpipes were installed at depth s

ranging from 10 to 40 feet bgs . The standpipes are 3-inchdiameter steel pipes with 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 northwes t

corner of the former pond yielded the highest radiologica l

level, with a portion of the core reading about 100 millirem s

at a depth near the top of the former pond . Similar soi l

patterns were encountered in each borehole installed withi n

the former pond . The stratification of each borehol e

consisted of about 4 inches of asphalt at the surface, abou t

1 foot of crushed limestone below the asphalt cap, followe d

by 5 feet of clay and shale fragments mixed with fill materia l

down to an elevation of 803 feet above mean sea level

(MSL), which is consistent with the bottom of the forme r

pond.

Predemonstration Activities

Predemonstration activities, including a groundwater tracin g

investigation conducted by EPA in 1996 and two heliu m

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 wel l

MW1 [1109] and standpipe 12) proposed for use during th e

demonstration groundwater tracing investigation ; (2) the

functionality of the tracers prior to establishment of th e

barrier wall; and (3) to identify viable groundwater an d

surface water sampling locations for the demonstratio n

groundwater tracing investigation . The investigation was

also used as a baseline for comparing tracer transport

patterns to those observed during the demonstratio n

groundwater tracing investigation after the barrier wall wa s

in place.

The dyes rhodamine WT and eosine OJ were selected fo r

use during the groundwater tracing investigation . On June

7, 1996, 9.01 X 102 grams of rhodamine WT dye was

injected into monitoring well MW1 (1109) located in th e

northwest corner of the pond, and 9 .89 X 102 grams of

eosine OJ dye was injected into standpipe 12 located nea r

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 severa l

inches of rain, which also helped to mobilize the dyes .

During the groundwater tracing investigation, charcoa l

packets and water samples were collected fro m

groundwater and surface water recovery points includin g

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 DLD, SBC, S3, S4 ,

S5, S6, and S7 showed detectable concentrations o f

3
INJECTION POIN T

STP 1

MW 1

1109)

OSTP2

OW671 W2

1110) S30

STSS

SBC

/

/ OW673

STP5

SIP 1 0

TP9

OSTP8

(1111 )

OMW3

MW 4

O(1112) STP6

0

W675

LEGEND

FORMER TOP OF POND

FORMER POND BOTTO M

LIMITS OF ASPHALT CA P

GROUND SURFACE

WATER WATER

O RECOVERY POINT

15' 0 15I

' 3o '

SCALE : 1" - 30'

Figure 1 . Dye injection and recovery points.

4
Table 1 . Feasibility Study Evaluation Criteria for the Freeze Barrier Syste m

Criterion Discussio n

Overall Protection of Human Health

and the Environment

• The technology is expected to protect human health and the environment b y

preventing the further spread of waterborne contaminants until appropriate

remediation techniques can be applied .

• Requires measures to protect workers during drilling and installation activities .

Compliance with Applicable or

Relevant and Appropriate

• Requires compliance with RCRA storage and disposal regulations fo r

hazardous waste and pertinent Atomic Energy Act, DOE, and Nuclea r

Requirements (ARAR) Regulatory Commission requirements for radioactive or mixed waste .

• Drilling, construction, and operation of a ground freezing system may requir e

compliance with location-specific ARARs .

Long-Term Effectiveness and

Permanence

• The treatment provides containment of wastes for as long as freezin g

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 becaus e

application of this technology to hazardous waste sites with contaminate d

groundwater is relatively recent .

Reduction of Toxicity, Mobility, or

Volume Through Treatment

• 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 .

Short-Term Effectiveness • The speed of development of the barrier wall may vary depending on sit e

hydrogeology, topography, soil moisture content, soil type, and climate .

Implementability • Hydrogeologic conditions should be well-defined prior to implementing thi s

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 more 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 are a

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 thermoprobes 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 t o

barrier wall development.

Cost • For a full-scale frozen soil barrier applied to a site that is 150 feet by 200 fee t

in size and operating for 10 years under some of the same general condition s

observed at the HRE pond site, total estimated fixed costs are estimated to be

about $2,124,600. Annual operating and maintenance costs, including thos e

for utilities, supplies, analytical services, labor, and equipment maintenanc e

are estimated to be about $67,000 .

Community Acceptanc e • This criterion is generally addressed in the record of decision (ROD) afte r

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 o f

the technology is expected to be high .

State Acceptance • This criterion is generally addressed in the ROD ; state acceptance of the

technologv will likely depend on the long-term effectiveness of the technology .

5
rhodamine WT tracer between 2 and 5 days following dye

injection . Transport of rhodamine WT was also evident a t

locations MW2 (1110), MW3 (1111), and MW4 (1112) 1 5

days following dye injection. Rhodamine WT was detecte d

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 followin g

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) . Thirtynine to 50 days following dye injection, transport of eosin e

OJ was also evident at recovery points STP2, STP9, STP10 ,

SBC, W898, and W674. At recovery points S3, S5, an d

DLD, eosine OJ arrived between 50 and 56 days followin g

dye injection (EPA 1996) . The eosine OJ results suggest

that a preferential pathway may exist on the north side o f

the former pond because eosine OJ was detected in wate r

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 monitorin g

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 i s

hydraulically connected to the surrounding soils .

DOE Helium Gas Tracing Investigation s

Following EPA's groundwater tracing investigation, DO E

conducted two independent gas tracing investigations usin g

helium in the summer of 1996 and winter of 1997. The

results of DOE's investigations confirmed that groundwate r

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 wit h

the groundwater tracing investigation .

System Construction

Prior to system construction, an electromagneti c

geophysical survey of the former pond was conducted t o

identify objects that could potentially disrupt drilling and

installation activities. According to DOE the survey identified

three anomalies, one of which extended through th e

northwest portion of the former pond that was consisten t

with a subsurface pipe. The two other anomalies wer e

interpreted as possible buried scrap metal in the northwes t

and southeast corners of the former pond . AFI's ground

freezing system was constructed from May throug h

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 borehole s

with the base of each thermoprobe anchored in bedroc k

(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 confine s

of the barrier wall, just southeast of standpipe 12 .

Eight temperature monitoring points were installed in th e

remaining eight boreholes, using the same genera l

procedures used to install the thermoprobes (Figure 2) . The

temperature monitoring points were placed at strategi c

locations to monitor development of the frozen barrier wall .

Temperature monitoring points were set inside protectiv e

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 (1 5

feet bgs) each thermoprobe . The RTDs provide a n

indication of the operating temperature of eac h

thermoprobe, and thus provided a means for AFI to evaluat e

thermoprobe performance. AFI then wired each thermisto r

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 ove r

the site surface were filled with an asphalt patching material .

An extruded polystyrene insulation material was then place d

over the asphalt surface and cut to fit securely around th e

thermoprobes, piezometer, and temperature monitorin g

points. A waterproofing membrane was placed over th e

insulation to prevent infiltration of rain or surface wate r

(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 electrica l

connection were installed .

The two refrigeration units, each connected to 2 5

thermoprobes, were configured so that alternatin g

thermoprobes in the array surrounding the former pond was

plumbed to the same refrigeration unit . Before the syste m

was charged with refrigerant, the system underwent

pressure testing to ensure that there were no leaks o r

blockages . The freeze barrier system was activated in midSeptember 1997.

Technology Applicability

AFI claims that its freeze barrier system can provid e

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

6
WATERPROOFING MEMBRAN E

LIMITS OF ASPHALT CA P

FORMER TOP OF PON D

FORMER POND BOTTOM

♦ THERMOPROBE

® TEMPERATURE MONITORING POINTS

+ MW = Monitoring Well

• SIP, I Standpipe

• W Piezorneter

N

Active System Suction Lin e

Active System Liquid Lin e

Passive Refrigerant Valve

+%671

Top Pressure Cap of Thermoprobe

Membrane Boot

Lugs on Thermoprobe

Riser Clam p

\STP6

MW4

+W67 1112)

41675

PLAN VIEW OF

SYSTEM CONFIGURATION

LEGEND NOT TO SCALE

PROFILE VIEW OF

THERMOPROB E

NOT TO SCALE

Figure 2 . Plan view of system configuration and profile view of thermoprobe .
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 possibilit y

that formation of a soil barrier in arid conditions may

require a suitable method of adding and retaining moistur e

in soils to achieve saturated conditions . An effective

means of homogeneously adding moisture to soils will b e

required. The effectiveness of this system for containmen t

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, th e

need for intrusive construction activities requires a

significant amount of open surface space, possibl y

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 fro m

boreholes during thermoprobe installation activities wil l

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 hazardou s

wastes. Precautions may include availability of lined ,

covered, roll-off boxes ; drums ; or other receptacles for th e

soil; storage tanks or drums for the water; and appropriat e

personal protective equipment for handling contaminate d

materials. Contaminated soils should be stockpiled on sit e

separately from clean soils to minimize the amount o f

material requiring management as potentially hazardou s

waste.

Site Requirement s

In addition to the hydrogeologic conditions that determine

the technology's applicability and design, other sit e

characteristics affect implementation of this system . The

amount of space required for a ground freezing syste m

depends on the thickness of the barrier wall and size of th e

containment area . For the SITE demonstration, the array

of thermoprobes encompassed an area of about 75 feet b y

80 feet, with an average frozen soil barrier wall thicknes s

of 12 feet. Thermoprobes are typically installed in a "V" or

"U" configuration to ensure complete encapsulation an d

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 an d

temperature monitoring points for system operation is

required. A crane also may be necessary to install the

thermoprobes and to subsequently remove th e

thermoprobes from the containment area followin g

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 propose d

system may require relocation if present, and overhea d

space should be clear of utility lines to allow cranes an d

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 thi s

reason, roll-off boxes or 55-gallon drums to store the soil ,

and sufficient space near, but outside of the constructio n

area for staging, should be available . During drilling activitie s

at the HRE pond, radiation levels in soil cuttings were

continuously monitored and were classified as Category 1

(<1 milliradian [mRad]/hour), Category 2 (>1 mRad/hour),

or Category 3 (>5 mRad/hour) waste to facilitate prope r

disposition of the waste . A portable tank or tanker truck

also should be available for thermoprobe installation t o

temporarily store water removed from the boreholes, if

necessary. Where soil type and site conditions ar e

appropriate, thermoprobes may be installed by pile driving

methods. This method eliminates handling drill cutting s

with limited environmental disturbance . A building or shed

may be necessary to protect the system control modul e

and instrumentation wiring, as well as for use by worker s

during routine operation and maintenance activities .

Performance Data

EPA established primary and secondary objectives for th e

SITE demonstration of the freeze barrier system . The

objectives were based on EPA's understanding of the freez e

barrier system, SITE Program demonstration goals, and

input from AFI . Primary objectives were considered critical

for the system demonstration, while secondary objective s

involved collecting additional data considered useful, bu t

not critical to the system demonstration . The objectives

also were selected to provide potential users of the freez e

barrier system with technical information to determine i f

the system is applicable to other contaminated sites . The

SITE demonstration was designed to address one primar y

objective and four secondary objectives for evaluation o f

the freeze barrier system.

Primary Objective

The following was the primary (P) objective of the syste m

demonstration:

P1 - Determine the effectiveness of the freeze barrie r

system in preventing horizontal groundwater flow beyon d

8
the limits of the frozen soil barrier through the performanc e

of a groundwater tracing investigation using a fluorescen t

dye

The primary objective was established to evaluate th e

freeze barrier system's ability to control hydrogeologi c

conditions in the former pond. The barrier wall was

evaluated through the performance of a groundwate r

tracing investigation that included injecting a fluorescen t

dye (phloxine B) into standpipe 12, located in the center o f

the former pond, and monitoring for the dye at groundwate r

and surface water recovery points located within an d

outside the former pond.

Secondary Objectives

The following were the secondary (S) objectives of th e

demonstration:

Si - 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 enclose d

former pond area before and after placement of the freez e

barrier wall

S3 - Monitor development of the freeze barrier wal l

S4 - Document installation and operating parameters o f

the freeze barrier wall

Secondary objective S1 was evaluated through th e

performance of a second groundwater tracing investigatio n

that included adding a second fluorescent dye (eosine OJ )

to upgradient monitoring well MW1 (1109) and monitorin g

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 dat a

obtained from standpipe 12 and monitoring wells MW 1

(1109) and MW2 (1110). Objective S3 was evaluated by

collecting subsurface temperature data from a series o f

temperature monitoring points located within and outsid e

the barrier wall in the southeast corner of the containmen t

area. Objective S4 was established to provide data fo r

estimating costs associated with use of the freeze barrie r

system, and was based on observations made during th e

demonstration, demonstration data, and data provided by

AFI.

SITE Demonstration Results

This section summarizes the methods and procedures

used to collect and analyze samples for the critica l

parameters during the SITE demonstration ; the results of

the SITE demonstration, including the demonstration

background study ; and evaluation of the primary an d

secondary objectives .

Methods

Both the demonstration background study an d

groundwater tracing investigation employed the use o f

activated charcoal packets and grab sampling technique s

for the collection of groundwater and surface wate r

samples from potential tracer recovery points locate d

downgradient and across gradient from the two trace r

injection points (standpipe 12 and monitoring well MW 1

[1109]) . The samples were collected and analyzed in

accordance with the Freeze Barrier Technology

Demonstration ()AP R

The demonstration background study was conducted ove r

a 21-day period after the frozen soil barrier reached it s

design thickness of 12 feet. A total of 22 charcoal packet s

and 114 grab samples of water were collected from th e

recovery points over the 21-day period . The samples were

analyzed using a spectrofluorophotometer for any

residuals dyes from the 1996 groundwater tracin g

investigation or natural background fluorescence .

The demonstration groundwater tracing phase of the

demonstration was conducted over a 5-month period afte r

the background study was completed . A total of 1 5

charcoal packets and 359 grab samples of water wer e

collected from the recovery points shown in Figure 1 . The

samples were analyzed for the two dyes phloxine B an d

eosine OJ, using a spectrofluorophotometer.

Results of the Demonstration Background Stud y

The demonstration background study was conducted i n

January 1998 following establishment of the barrier wall .

Analytical results indicated the presence of residua l

concentrations of the dyes eosine OJ and rhodamine W T

that were used during the 1996 groundwater tracin g

investigation conducted by EPA. According to the analytical

laboratory, a green compound, which is a commo n

derivative of rhodamine WT, was identified in samples

collected from recovery points STP2, STP9, DLD, KL, and

MW1 (1109). Analytical results indicated that uranine was

present in water samples collected from recovery point s

12, SBC, STP9, AFIP, MW4 (1112), S1, and S2 . Uranine

also was present in samples collected from the sam e

recovery points during the 1996 groundwater tracin g

investigation.

The highest concentration of fluorescence in backgroun d

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 eosine O J

was used as a baseline for comparison to demonstratio n

groundwater tracing investigation results . Therefore,

phloxine B and eosine OJ detected above the highes t

background concentration was considered a detection a t

any recovery point .

9
During the demonstration background study, field personne l

interviewed Mr. Marlin Ritchey, a Lockheed Martin Energy

Systems Inc . engineer in charge of sump pumps in th e

basement of the HRE building, located northwes t

(upgradient) of the HRE pond. Mr. Ritchey was interviewe d

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, usin g

the dye uranine, during the period between the 199 6

groundwater tracing investigation and the demonstratio n

background study. After discovering a potential source fo r

the uranine, it was unclear how uranine migrated from th e

HRE building to standpipe 12 and piezometer AFIP locate d

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 plac e

after the pond closed . A geophysical survey conducte d

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 thi s

pathway was open or closed after placement of the barrie r

wall .

Evaluation of Objective P 1

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 a t

recovery points STP10, AFIP, STP1, STP2, STP9, and MW4

(1112) . Figure 3 shows the inferred migration pathway fro m

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 a t

recovery point STP10, which is located upgradient o f

injection point 12. The concentration of phloxine B detecte d

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 lowe r

exponential decrease . The second detection of phloxine B

occurred 10 weeks after tracer injection at recovery poin t

AFIP.

The probability that piping may exist in the northwest portio n

of the former pond cannot be discounted in relation to th e

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 wa s

inferred to be a pipe . Although this is not the exact locatio n

for the piping, there are no as-built diagrams available t o

confirm their final location . Drilling activities associated with

installation of the ground freezing system revealed th e

highest concentration of radionuclides in auger cutting s

collected in the northwest corner of the former pond, clos e

to where the geophysical anomaly was identified . This high

concentration is most likely associated with either a leak i n

the influent pipe that extends from the HRE building to th e

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 wa s

anomalously high in comparison to that in standpipe STP10.

The hydrograph for standpipe 12 shows a rapid water leve l

increase and subsequent decrease during water injection

to mobilize the phloxine B dye . According to DOE, this

fluctuation was caused by groundwater mounding followin g

water injection at standpipe 12, which created a gradient

reversal in the direction of STP10 . This gradient reversal

may have transported the phloxine B-laden groundwate r

laterally through the subsurface pipe to the area nea r

standpipe STP10 .

Phloxine B also was detected at concentrations abov e

background at recovery points STP1, STP2, MW4 (1112) ,

and STP9 between 69 and 126 days following trace r

injection, which was much later than the detection at STP10 .

Based on the timing of the recoveries and decrease d

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 th e

north and west sides of the former pond, outside th e

containment area. The ditch locations and flow directions ,

based on information provided by DOE, are shown in Figur e

3 . The drainage ditches, which are located around th e

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, an d

MW4 (1112), which were located downgradient of STP10 .

Other data gathered during the demonstration period, wit h

the exception of the groundwater tracing investigation usin g

phloxine B, provide evidence that the ground freezin g

system was effective in impeding horizontal groundwate r

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 froze n

soil barrier either through a breach in the barrier wall mos t

likely associated with a subsurface pipe or beneath th e

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 STP1 0 than what was observed durin g

10
S7

THERMOPROB E

O TEMPERATURE MONITORING POINTS

OTCP

4671

LEGEND

FORMER TOP OF PON D

FORMER POND BOTTOM

LIMITS OF ASPHALT CAP

PHLOXINE B MIGRATION PATHWAY

DRAINAGE DITCH CONFIGURATION

GROUND SURFACE

WATER WATER

0 RECOVERY POIN T

PHLOXINE B DETECTIONS

Figure 3 .. System configuration and inferred dye migration pathways

11
the demonstration . Supporting information is summarize d

below:

Water level data and predemonstration groundwater tracin g

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 hydraulicall y

connected prior to construction of the barrier. However,

water level data collected from standpipe 12 within the

containment area following establishment of the barrier wal l

showed that the water table dropped and did not respon d

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 temperatur e

monitoring points T-1 and T-2, located in the northwes t

corner of the barrier, showed that soil temperature fro m

the ground surface to about 30 feet bgs remained well belo w

32° F. Based on experience, however, AFI claims that th e

barrier wall was frozen to a depth of about 36 feet bgs .

Results of the demonstration groundwater tracin g

investigation compared to the 1996 groundwater tracin g

investigation showed that the barrier wall disrupte d

groundwater conditions within and outside the former pond

area . Phloxine B results from the demonstratio n

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 durin g

the 1996 groundwater tracing investigation, indicating that

the barrier was disrupting groundwater flow patterns in an d

around the former pond area .

TDEC personnel collected surface water samples from th e

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 199 8

showed slightly lower levels of gross beta activity. According

toTDEC, however, sampling results should be qualified unti l

long-term results are made available because the sample s

were collected during the dry season when gross beta

activity is generally lower.

Evaluation of Objectives S-1 and S 2

Verify whether flow pathways outside the former pond were

still open after placement of the freeze barrier wall an d

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 sectio n

is based on data gathered by DOE and presented in a report

entitled "HRE-Pond Cryogenic Barrier Technolog y

Demonstration : Pre- and Post-Barrier Hydrologi c

Assessment" prepared by Dr. Gerilynn Moline, ORN L

Environmental Sciences Division . The following section s

describe the groundwater conditions encountered before

and after establishment of the barrier wall in the forme r

pond area.

Pre-Barrier Groundwater Condition s

Water level data collected from monitoring locations 12 ,

STP10, and MW2 (1110) compared to precipitation data ,

indicates that all three monitoring points were responsiv e

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 oscillation s

during storm events, providing evidence that groundwate r

within and outside the former pond is hydraulically

connected . The rapid rise in groundwater elevations at

standpipe 12 during some storm events also suggests tha t

the water table may intersect the gravel layer beneath th e

asphalt cap, thereby providing a pathway for migration of

contaminants out of the former pond through this highl y

permeable layer. This relationship is apparent in the

hydrograph for standpipe 12, where the elevation of th e

asphalt cap at standpipe 12 is 818 .5 feet above MSL and

the groundwater elevation at standpipe 12 frequentl y

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 b y

the transport of tracers from within the former pond to area s

outside the former pond. The dye eosine OJ, injected int o

center standpipe 12 under forced-gradient conditions durin g

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 th e

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 containmen t

area after freezing was initiated . According to AFI, the slow

decline in water levels at standpipe 12 is a result of soi l

moisture being drawn to the frozen soil barrier . The slow

decline also may have been a result of slow seepag e

12
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 th e

demonstration groundwater tracing investigation that require

some explanation. According to DOE, the pressure

transducer was replaced just prior to initiation of th e

demonstration groundwater tracing investigation, whic h

reportedly displaced the water level in standpipe 12, resultin g

in fluctuations in the hydrograph for standpipe 12 . The only

other water level responses seen in the hydrograph fo r

standpipe 12 correspond to water injections that occurre d

for 5 days following dye injection, even though there wer e

numerous storm events during this period .

Results of the eosine OJ demonstration groundwater tracin g

investigation suggest that the barrier wall also had an effec t

on horizontal groundwater flow in the HRE pond area . Tracer

transport behavior during the demonstration groundwate r

tracing investigation differed from the 1996 groundwate r

tracing investigation. The 1996 groundwater tracin g

investigation showed tracer transport from MW1 (1109) to

most of the downgradient recovery points including DLD,

SBC, MW2(1110), 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 DLD . However, eosine OJ

was only detected at a concentration above background i n

downgradient recovery point DLD (1 .09e+03 ppb), 2 day s

following dye injection . This change in transport behavio r

is likely due to diversion of dye-laden groundwater aroun d

the barrier wall because concentrations in all samples, with

the exception of recovery point DLD, were below

demonstration background levels, indicating that pea k

concentrations may not have been attained within th e

demonstration period . This behavioral change is apparen t

in the eosine OJ data for recovery point MW4 (1112), wher e

the highest concentration detected during the demonstration

groundwater tracing investigation did not occur until 2 week s

prior to the end of the demonstration. However, this fac t

cannot be determined with any certainty because sample s

were not collected after the demonstration period ended .

Results from the 1996 investigation also show that trace r

was transported to the downstream locations (SBC an d

S3 through S7) more rapidly than it was transported to th e

locations closer to the pond (STP2, W898, W674, and DLD) .

Tracer injected into monitoring well MW1 (1109) bypasse d

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 demonstratio n

groundwater tracing investigation, indicating that horizonta l

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 STP 5

dropped about 6.5 feet following barrier placement. DOE

also reported that water levels at standpipe STP6 were no t

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 th e

former pond to these downgradient locations was impeded

or that flow was diverted around the barrier wall, resultin g

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 variou s

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 monito r

development of the barrier wall . Each temperature

monitoring point was equipped with eight temperatur e

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 i n

mid-September 1997, the two refrigeration units operate d

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, whic h

occurred about mid-October 1997. According to AFI, thi s

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 asphal t

pavement, which occurred about the first week of Novembe r

1997. This process, which is referred to as "freezing t o

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 1 2

feet, which occurred in mid-January 1998, or about 1 8

weeks following system startup . According to AFI, the

design thickness was selected based on AFI's pas t

experience using the thermoprobe placement configuration

similar to what was applied to the HRE pond site .

Subsurface temperatures at T-3 (located directly on th e

centerline of the barrier) from the bottom of the insulatio n

to 30 feet bgs remained well below 32° F, from mid-January

through mid-July 1998 .

13
Replacement of

Pressure Transducers

Freezin g

initiated 9/8/97

-WaterLevel

O Manual w.l .

Peaks correspond to

dye/water injections

starting on 2/20/98

I I

Jan-97 Mar-97 . May-97 Jul-97 Sep-97 Nov-97 Jan-98 Mar-98 May-98 Jul-98

Figure 4. Hydrograph for Standpipe 12 .

Once the design thickness was achieved, the maintenance

freezing phase began and the refrigeration units operate d

on a 24-hour alternating run schedule to minimize powe r

consumption. Maintenance freezing required significantly

lower energy levels then the initial freezedown . According

to AFI, the barrier wall thickness remained fairly constan t

during this phase and is expected to be maintained at th e

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, AFI simulated a power outage a t

the HRE pond site. The refrigerant feed to the array of

thermoprobes was shut down for a period of 8 days whil e

subsurface temperature data were continuously collected .

AFI reported that ambient air temperatures during thi s

period averaged between 32° C and 35° C. The barrier

reportedly lost less than 2 percent of its design thicknes s

during this period, with the maximum loss at the top of th e

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 remaine d

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, AFI, an d

other sources, an economic analysis was conducted that

examined 12 cost categories for two different application s

of the freeze barrier technology. The first case presents a

cost estimate for extending the use of the freeze barrie r

technology at the HRE pond site over a 5-year period . The

second case is based on applying the freeze barrie r

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 o f

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 th e

containment area which was about $6 .60 per cubic foot fo r

Case 1 and $3.10 per cubic foot for Case 2 . Costs for

applications of the freeze barrier technology may var y

significantly from these estimates, depending on sitespecific factors.

Technology Statu s

To date, this SITE demonstration represents the first full -

scale application of the AFI frozen soil barrier system at a

14
contaminated site . However, AFI has been developing,

designing, fabricating, and installing ground freezin g

systems for about 30 years . AFI has used the system t o

seal subsurface structures against flooding of groundwater;

to stabilize soils for excavation ; and for foundation an d

ground stabilization purposes. While the AFI ground

freezing system has been primarily used in arctic an d

subarctic environments, such as Alaska, Canada, an d

Greenland, the system can also be used in more temperat e

locations as demonstrated at the HRE pond site .

Current plans for AFI's ground freezing at ORNL's HRE pon d

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 i s

considering the use of the freeze barrier system fo r

containment of radiologically contaminated groundwater

plumes at two other DOE facilities, including Savannah Rive r

and Hanford . The system also is being considered fo r

containment of a groundwater plume contaminated wit h

polychlorinated biphenyls and dense nonaqueous-phas e

liquids at a site in Smithville, Canada .

Sources of Further Informatio n

Steve Roc k

U .S. Environmental Protection Agency

Office of Research and Development

National Risk Management Research Laboratory

26 West Martin Luther King Driv e

Cincinnati, Ohio 45268

Telephone: (513) 569-7149

FAX: (513) 569-7879

E-mail : rock.steven@epamail.epa.gov

Ed Yarmak

Project Manage r

Arctic Foundations, Inc.

5621 Arctic Boulevard

Anchorage, Alaska 9951 8

Telephone: (907) 562-2741

FAX: (907) 562-0153

E-mail : arcfnd@a/aska .net

15
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United State

A

s

Environmental Protectio n

Agency

Office of Research and Developmen t

National Risk Managemen t

Research Laboratory

Cincinnati, OH 45268

Official Business

Penalty for Private Us e

$300

EPA/540/R-03/508a

September 200 4

www.epa.gov .

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