TECHNOLOGY UPDATE
Technology combination cuts DNAPL cleanup time at Superfund site By combining existing technologies, scientists from the Department of Energy's (DOE) Lawrence Livermore National Laboratory have significantly decreased the amount of time needed to clean up some of the country's most difficult-to-remediate sites. Jim Cummings of EPA's Technology Innovation Office believes that die technology could prove valuable for remediating contamination associated with wood treating, manufactured gas, and leaking underground storage tanks. In a full-scale evaluation at Southern California Edison's Visalia Pole Yard, a Superfund site where telephone poles were treated with rot-retarding chemicals for over 50 years, the technology is being used to remediate a groundwater plume containing creosote, pentachlorophenol, and diesel fuel. The cleanup began in June 1997, and by this April, researchers had removed 635,000 pounds of the dense nonaqueous phase liquid (DNAPL) mixture. Previously, the site ni3.n3.sers were able to remove only 10 pounds per week using conventional pumpand-treat technology The patented technology is actually a "treatment train" combining two existing remediation technologies, dynamic underground stripping and hydrous pyrolysis/oxidation. The treatment also incorporates advanced imaging using electrical resistance tomography. Dynamic underground stripping heats contaminated soil using steam and electrodes. Steam is injected into wells sunk into the site's permeable soil zones, and electrodes are used in less permeable soil. The heat and steam mobilize the contaminants and drive them toward extraction wells explained Robin Newmark a group leader at Lawrence Livermore's Earth
and Environmental Sciences Directorate. "Once you heat the soil up, wherever there is available oxygen, hydrous pyrolysis starts whether you like it or not," Newmark said. In hydrous pyrolysis/oxidation, dissolved contaminants in the groundwater are mineralized in situ by oxidation. The researchers increase the oxidization and degradation of residual contaminants by pumping air down into the heated ground. The researchers estimate that about 20% of
Robin Newmark of Lawrence Livermore National Laboratory (left) and Virgil Tackett of Southern California Edison stand atop a 17,000gallon tank containing the creosote mixture recovered from the Superfund site. (Courtesy Jacqueline McBride, LLNL)
the contaminants are destroyed in place; the rest is recovered and requires postremoval treatment. When the technology-intensive portion of the project is over, the researchers expect that bioremediation will begin as a byproduct of heating the soil. After an earlier test at a different site, they discovered that once the soil cooled down to below 80 °F, me warmed soil encouraged the growth of thermophilic microbes mat enhanced the bioremediation of residual diesel contaminants in that plume. Though technically a pilot because neither the California EPA, nor
0013-936X/98/0932-359AS15.00/0 © 1998 American Chemical Society
the U.S. EPA has officially agreed to a Record of Decision authorizing Edison to use this as the only cleanup technology, Edison nonetheless intends to use it to clean the entire 4.3-acre site. The utility had previously budgeted $45 million to pay for 30 years of pump-and-treat technology at the site, though senior engineer Craig Eaker believes that the process would actually take much longer due to the difficulties in estimating the extent of DNAPL contamination. "Now we optimistically estimate that it'll [cost] less than $14 million and we'll complete it within two years after the steaming is completed this year " he said This works out $45/yd 3 according to the researchers The technology is particularly effective for sites with DNAPLs, according to Roger Aines, who is also a group leader at the laboratory's Earth and Environmental Sciences Directorate. "We were looking at those problems for which there really are no conventional technologies," Newmark explained. The researchers estimate that the treatment will be most cost-effective at sites where contaminants have migrated below the water table or down more tfian 20 feet situations in which it is too expensive to excavate The scientists believe the technology could prove useful for remediating sites where organic compounds have migrated deep into the ground. They have conducted laboratory feasibility studies on its utility for removing PCE, TCE, carbon tetrachloride, PCB, naphthalene, and toluene, and estimate that it would cost less than $20/yd 3 to treat a site contaminated with chlorinated solvents if no surface treatment is required. The Lawrence Livermore scientists are currently researching the controlling factors associated with the technology including its thermodynamics and the rates of destruction of the Drimary contaminants of concern —KELLYN S. BETTS
AUG. 1, 1998 /ENVIRONMENTAL SCIENCE S TECHNOLOGY /NEWS " 3 5 9 A
