Excavation of a 300,000 gallon frozen pond of radioactive waste located in the Melton Valley area of Oak Ridge National Laboratory on the Oak Ridge Reservation, in Oak Ridge, TN, began in early April 2005.
Bechtel Jacobs Company LLC, environmental management contractor for the U. S. Department of Energy’s (DOE) Oak Ridge Operations Office, subcontracted the $4 million pond project to Sevenson Environmental Services of Niagara Falls, NY, according to Bechtel Jacobs spokesman Dennis Hill.
“Preparation of the job site began in October 2004, and the entire project is expected to be completed by June 2005,” Hill said.
The waste pond was developed in the 1950s to receive radioactive waste from the Homogeneous Reactor Experiment, an old test nuclear reactor at Oak Ridge National Laboratory (ORNL). The waste includes strontium-90, a radioactive element that tends to concentrate in the bones if ingested by humans; cesium-137; tritium and transuranics.
“The facility has been inoperative since the mid-1960s and the frozen pond is in the ’backyard’ of the facility,” Hill said.
During the 1970s, the pond was backfilled with clay and shale and capped with asphalt. However, there were still concerns that nuclear waste would leach into the groundwater, soil and sediments and possibly migrate into nearby streams and ultimately into the reservoirs used for recreation and drinking supplies.
DOE officials decided in the mid-1990s to install a cyrogenic stabilization system at the waste pond, which was a series of thermo probes that froze the soil, groundwater and everything else to a depth of about 30 ft. (9.1 m), forming a barrier to the groundwater. This was designed as a temporary solution until the site could be excavated and the problem permanently solved. The cost for the cyrogenic stabilization system was $1.2 million, with annual maintenance costs of about $27,000.
“The cryogenic system, installed by Arctic Foundations, a company based in Alaska, worked better than expected” Hill said. “The ice barrier was up to 25 ft. thick, well beyond the 12-ft. thickness identified in the design.”
The cyrogenics system was shut down in February 2004 in preparation for system dismantling and pond excavation, however a thermal foam blanket remains around the frozen pond.
According to Hill, the foam insulates the underlying ground, keeping the soil cold, keeping the pond frozen until it can be excavated.
“Since the cooling system has been shut down, the thawing has been slow,” Hill said. “The earth is an excellent insulator. By the end of the summer of 2004, the ice barrier had only diminished by about 10 percent.”
Approximately 32 workers are on the site daily.
According to Hill, extensive preparation of the job site was required before excavation of the pond could begin.
“Preparation included substantial soil excavation in the areas surrounding the frozen pond. This soil contained lower levels of contamination than the pond itself, but enough contamination that it had to be removed. In all, approximately 10,000 cu. yds. of soil were removed from the surrounding areas,” Hill said.
Another 5,400 cu. yds. of soil (in-place volume) will be excavated from the pond itself.
“The excavated frozen soil will be stockpiled as necessary until it thaws,” Hill said. “Quicklime may be added to eliminate free liquids and accelerate the thawing process. The project [crew] is hoping the combination of warmer weather and sunny skies will also hasten the thawing.”
The excavated soil from the frozen pond will be sent to the DOE’s Environmental Management Waste Management Facility on another part of the Oak Ridge Reservation.
Roane Trucking will haul the material for Sevenson, using a variety of tri-axle dump trucks.
“After excavation of the pond is completed, the site will be backfilled with clean soil obtained from an offsite borrow area,” Hill said. “Common borrow will be placed in the excavated area and graded to drain. It will then be covered with topsoil and seeded.”
According to Hill, equipment at the job site includes two Caterpillar excavators (track hoes), a Cat 321C and a Cat 320C. Equipment is both owned and rented by Sevenson.
“Because the equipment is being exposed to radioactive waste, the equipment will have to be decontaminated at the conclusion of the job,” Hill said. “Precautions are being taken to minimize, to the extent feasible, the operation of the machines in areas with deep, soft sediment.”
Hill said the most challenging aspect of the job is that the waste is frozen and must be thawed before its disposal.
“No free liquids can be transported to or disposed of in the disposal facility,” Hill said.
The removal of the waste pond is part of a $165 million cleanup plan the DOE has implemented to clean up approximately 1,000 acres of the Melton Valley area of the Oak Ridge Reservation. For more than 50 years, this area was the site of production and research activities at ORNL, leaving in its wake a number of contaminated inactive facilities and waste disposal areas, including the frozen pond.
Melton Valley is also the location of Solid Waste Storage Areas (SWSA) 4 and 5, which during the 1950s and 1960s, were used as the Southeastern Regional Burial Ground for radioactive wastes from more than 50 other facilities, including other national laboratories operated by DOE’s predecessor agency, the Atomic Energy Commission. In addition to burial trenches located in SWSA 4 and 5, the area contains landfills, underground tanks, impoundments, liquid waste seepage pits and trenches, wells, pipelines and surface structures.
The DOE is remediating Melton Valley under the provisions of the comprehensive Environmental Response, Compensation and Liability Act. Cleanup of the area is now being performed on an accelerated schedule and will likely be completed by September 2006.
Bechtel Jacobs is responsible for the environmental cleanup and waste management for the entire Oak Ridge Reservation, including Melton Valley, along with Paducah, KY, and Portsmouth, OH.
Bechtel Jacobs Company also supports DOE in a re-industrialization program to find commercial uses for many Oak Ridge facilities that no longer have a mission.
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