Frozen Soil Barrier at Oak Ridge National Laboratory, Oak Ridge, Tennessee

Site Name:

Oak Ridge National Laboratory

Location:

Oak Ridge, Tennessee

Period of
Operation:

September 1996 to September 1998

Cleanup
Type:

Field demonstration

Vendor:

Edward Yarmak
Chief Engineer
Arctic Foundations Inc.
(907) 562-2741

Technology:
Frozen Soil Barrier
- The demonstration used an array of 50 sealed thermocouples installed around the perimeter of the impoundment, on 6 ft centers to a depth of approximately 30 ft bgs
- The thermocouples were fabricated from 6 inch schedule 40 steel pipe, and used carbon dioxide as a working fluid, with an above-ground refrigeration system, to freeze the soil
- The refrigeration system used R-404A, and thermal expansion valves, to control the amount of freezing
- The frozen soil barrier was established in 18 wks, had a length of 300 linear ft, depth of 30 ft, thickness of 12 ft, frozen soil volume of 108,000 ft3, and contained a volume of 168,750 ft3
- A two-part polyurea coating was spray applied over a non-woven geotextile fabric to prevent surface water from entering the isolated area
- The system was operated first in a freeze-down phase, where the frozen soil barrier was created; subsequent operation was in maintenance phasend Services Module - used to control and monitor equipment operation

Cleanup Authority:
NRC

Technical Contacts:
Elizabeth Phillips
Principal Investigator
DOE Oak Ridge
(423) 241-6172

Michael Harper
Co-Principal Investigator
Bechtel Jacobs Company, LLC
(423) 574-7299

Steven Rock
EPA SITE
(513) 569-7149
DOE Contact:
Scott McMullin
DOE Savannah River
(803) 725-5608

Contaminants:
Radionuclides
- Initial concentrations in sediment included strontium 90 - 75 Curies (Ci) and cesium 137 - 16 Ci

Waste Source:
Nuclear processing operations

Type/Quantity of Media Treated:
Soil, Sediment, Groundwater
- Depth to groundwater is 2 to 9 ft bgs
- Groundwater discharges to surface water at several locations around the impoundment

Purpose/Significance of Application:
Demonstrate frozen soil barrier for containment of contaminated surface impoundment

Regulatory Requirements/Cleanup Goals:
- Evaluate performance of the barrier for isolating and containing contaminants
- No specific cleanup goals were identified

Results:
- Performance was evaluated based on groundwater level monitoring, dye tracer studies, and operation tests
- Groundwater level monitoring and dye tracer studies (eosine and phloxine dies) showed hydraulic isolation of the impoundment
- A 7-day loss of power test showed that the barrier maintained its integrity during a power outage

Cost Factors:
- The actual cost for the demonstration was $1,809,000, consisting of $43,000 for site infrastructure, surveys, and maintenance; $1,253,000 for system design, fabrication, procurement, installation, and start-up; $274,000 for ORNL site support; and $239,000 for barrier verification
- A review of projected costs for frozen soil barriers to grouted barriers showed that frozen soil is less costly for initial installation and operation, with a break-even point of 8 to 9 yrs

Description:
The demonstration site is a former unlined, earthen impoundment used from 1958 through 1961 for retention/settling of liquid radioactive wastes generated from operation of a Homogeneous Reactor Experiment (HRE) at DOE's Oak Ridge facility. The impoundment was 75 ft long by 80 ft wide by 10 ft deep, with a capacity of approximately 310,000 gallons. In 1970, the impoundment was backfilled with local soils, covered with 8 inches of crushed stone, and capped with asphalt. A 1986 study found that sediments buried in the impoundment contained strontium 90 and cesium 137, and that groundwater that moved through this area transported contaminants to surrounding locations, including surface waters.

For the demonstration, a frozen soil barrier was constructed using thermocouple technology. The barrier had a length of 300 linear ft, depth of 30 ft, thickness of 12 ft, frozen soil volume of 108,000 ft3, and contained a volume of 168,750 ft3. Groundwater level monitoring and dye tracer studies showed that the barrier provided for hydraulic isolation of the impoundment, and a 7-day loss of power test showed that the barrier maintained its integrity during this time. A cost analysis comparing projected costs for frozen soil barriers to grouted barriers showed that frozen soil barriers are less costly for initial installation and operation, with a break-even point of 8 to 9 years.