The Paducah plant hopes the six-phase heating system will speed removal of hazardous degreaser that taints the groundwater.
By Joe Walker firstname.lastname@example.org
The "six-phase heating" system, activated about 10 a.m. Friday after months of preparation, uses electrical resistance to heat the ground far below the surface and vacuum out vaporized contamination for carbon-filter treatment. Six hexagonally arrayed electrodes are buried 100 feet deep near the southwest corner of a cleaning building, called C-400, where the now-banned hazardous degreaser trichloroethylene (TCE) was used extensively for decades to clean uranium-enrichment machinery.
Historic spills have left almost 180,000 gallons of TCE beneath the building, some at concentrations more than 20,000 times greater than the federal safe drinking water standard of 5 parts per billion. That level, at which municipal water systems must treat to remove TCE, is equivalent to five kernels of corn in a silo 45 feet high and 15 feet wide. Molasses-like globs of the hidden, heavier-than-water chemical have lodged in underground rock fissures, feeding traces of TCE into the aquifer almost indefinitely.
Although the six-phase system has worked well in other parts of the nation, the aquifer beneath the plant is uniquely deep and rapid, flowing at roughly a foot a day, said Gary Bodenstein, Department of Energy project manager.
"We're pushing the edge of the technology to see if it will work," he said. "Everybody is very confident that it will, so let's prove it."
Digging up soil is impractical because much of the contamination is under the building, which is still in use. DOE and lead environmental firm Bechtel Jacobs expect the test to show the electrode process can remove 99 percent of the solvent from soil and groundwater.
Monitoring wells will calculate the effectiveness. A successful run would mean installing 72 more electrodes, expanding the cleanup twelvefold on an ongoing basis, Bodenstein said.
Other cleanup techniques have been used with mixed results. One soil-heating process called Lasagna worked well at about half the depth of the aquifer beneath the building. A second system — injecting iron filings into a gummy base of food material in the ground to form a filter — had viscosity problems in cold weather.
Two ongoing pump-and-treat systems on the northeastern and northwestern plant boundaries help control the heaviest concentrations of TCE. But they aren't the answer to cleanup because their average daily yield is only enough solvent to fill about a two-liter bottle. Bechtel Jacobs spokesman Greg Cook said the systems would take "hundreds of years" to clean up TCE at the rate it dissolves.
"This (electrode) technology, if it works, will allow us to finally get to the main source of the groundwater contamination," he said. "That's what makes this so important."
Bodenstein said the six-phase system was "the most promising technology" to come out of lengthy brainstorming at the plant two years ago by industry experts, as well as researchers from DOE and state and federal regulatory agencies.