Frozen Soil Barrier Technology at the SEG Facilities, Oak Ridge, Tennessee (In Cooperation with the U.S. Department of Energy, Oak Ridge Operations)

Site Name:

Scientific Ecology Group Gallaher Road

Location:

Oak Ridge, Tennessee

Period of
Operation:

May 12 - October 10, 1994

Cleanup
Type:

Field demonstration

Vendor:

Rick Swatzell,
Principal Investigator,
Martin Marietta Energy Systems, Inc.
(615) 435-3126

Ray Peters,
SEG
(615) 376-819

Technology:
Frozen Soil Barrier

- Uses refrigeration to freeze soils and provide barrier/containment for hazardous and/or radioactive contaminants in soil and ground water.
- Demonstration facility was "V"-shaped, with dimensions of 56 by 56 feet outside and 33 by 33 feet inside; maximum depth was 28 feet
- Refrigerant pipes were installed around circumference of facility in a double-rowed configuration with an ice wall allowed to grow together between the pipes and forming a barrier.

Cleanup Authority:
None - demonstration conducted at a nonhazardous site

SIC Code:
Not Applicable
(not a contaminated site)
Point of Contact:
Jef Walker,
DOE
EM-50 Plumes
Focus Area Program Manager
(303) 903-7966

Contaminants:
None

- Surrogate solution (200 ppm Rhodamine-WT) were used to test the integrity characteristics of the barrier.

Waste Source:
Not Applicable (not a contaminated site)

Type/Quantity of Media Treated:
Soil

- Subsurface soils consisted of 13 to 22 feet of fill soils overlying residual soils. Fill soils consisted of stiff to hard red-brown silty clay, with varying amounts of chert fragments. Residual soils consisted of stiff to soft red-brown to brown silty clay and clayey silt, with varying amounts of chert fragments.
- Soil density measured as 108.8 lb/ft3.
- Average soil moisture content ranged from 26.5 to 33.9%.
- 8,175 cubic feet of soil contained by the frozen barrier.
- 35,694 cubic feet of soil composed frozen barrier.

Purpose/Significance of Application:
Frozen soil barrier technology has been demonstrated for controlling waste migration in soils.

Regulatory Requirements/Cleanup Goals:
No regulatory requirements or cleanup goals were identified for this demonstration because it was conducted at a nonhazardous site.

Results:
This demonstration was evaluated using the following four types of performance testing: 1) computer model validation; 2) soil movement testing, including heat grid tests; 3) barrier diffusion and leaking tank tests; and 4) barrier integrity testing. The barrier diffusion and leaking tank tests were used to demonstrate containment by the frozen barrier wall by releasing Rhodamine-WT from a tank inside the containment structure and measuring its potential diffusion across the barrier wall.

- Tests showed that Rhodamine was found only inside the barrier region, confirming barrier integrity.
- Tests showed that Rhodamine migrated approximately two feet in unfrozen soils, while essentially no Rhodamine was found below open-ended well casings within the freeze barrier.

Cost Factors:
- Total capital costs for the SEG demonstration were $481,427.
- Maintenance costs for the demonstration were estimated as $40,000 per year ($3322 per month).
- No additional details provided on components of capital or maintenance costs.
- Unit costs identified for this technology ranged from $4 to $14 per cubic foot of iced formed, and are compared with unit costs for grout systems ranging from $1 to $37 per cubic foot.
- Report authors indicated that a more realistic cost (i.e., for an actual remedial activity) for this type of technology would be $332,754, assuming that extra sensors and test support were not needed, if equipment were leased instead of purchased, and barrier thickness was decreased (which would mean less drilling, energy consumption, etc.)

Description:
Frozen soil barrier technology was demonstrated under the sponsorship of the U.S. DOE In Situ Remediation Integrated Demonstration Program at a nonhazardous site on SEG property at the Gallaher Road Facility in Oak Ridge Tennessee. Frozen soil barrier technology has been used for a number of years in large-scale civil engineering projects to seal tunnels, mine shafts, and other subsurface structures against flooding, and to stabilize soils during excavation. Advantages of frozen soil barrier technology include: 1) it can provide complete containment; 2) it uses benign material (water/ice) as a containment medium; 3) frozen barriers can be removed by thawing; and 4) frozen barriers can be repaired in situ (by injecting water into the leaking area).

At the SEG demonstration, a "V"-shaped containment structure was constructed 56 feet long by 56 feet wide by 28 feet deep. Refrigerant piping was used to create an area of frozen soil ranging from 5 to 15 feet thick. Several types of performance testing were performed, including barrier diffusion and leaking tank tests, based on use of a surrogate solution containing 200 ppm of Rhodamine-WT. The barrier diffusion and leaking tank tests showed that Rhodamine was found only inside the barrier region, confirming barrier integrity, and that Rhodamine migrated approximately two feet in unfrozen soils, while essentially no Rhodamine was found below open-ended well casings within the freeze barrier.

Determining the suitability of this technology for applications for arid/sandy environments will require development of methods for homogeneously adding and retaining moisture in the soils. In addition, technology applications in fine-grained soils around structures may be limited because of soil movement.