Essentially an enhancement to soil vapor extraction, SPSH is a rapid, cost-effective technique that steam-strips contaminants from soils in place, eliminating the need for excavation or soil pretreatment. The technology won an R&D 100 award in 1995. In Situ Corona is designed to destroy toxic materials such as chlorinated solvents, polychlorinated biphenyls, pesticides, and industrial fuel oils and lubricants. Both technologies promise faster, cheaper, and more effective cleanup of certain contaminated soils.

Theresa Bergsman, principal investigator, is currently on halftime entrepreneurial leave from PNNL to launch CES, which will initially focus on marketing SPSH and extending the development of In Situ Corona. Bergsman is enthusiastic about her involvement in the business. "Participation by a technology developer is really necessary for successful deployment," she says. "We’ve found that just licensing a technology and throwing it over the fence doesn’t work." Bergsman and three PNNL associates recently received 1998 Awards for Excellence in Technology Transfer from the Federal Laboratory Consortium, which gives up to 30 such awards each year to teams of federal lab employees for their success in transferring their research to private industry.

Soil vapor extraction has emerged as an improvement over soil excavation and pump-and-treat methods, but conventional SVE is ineffective if contaminants cannot be easily vaporized or if the soil is tightly bound, as in silts and clays. Electrical soil heating removes this obstacle by raising the temperature of the soil and contaminants, increasing the contaminants’ vapor pressure and thus their removal rate. Other heating methods, such as steam or hot-air injection, work only in permeable, unsaturated soil. Electrical soil heating actually relies on the indigenous soil moisture to raise the temperature of the soil internally through resistance. Electrical soil heating can also create an in situ source of steam to strip volatile and semivolatile contaminants from soils. The contaminated steam is removed through venting and treated aboveground. Since the steam is created directly in the soil, removal is more efficient. As the soil dries, its flow permeability rises, further increasing the rate of contaminant removal by simultaneous venting.

The unique feature of SPSH is that it splits standard three-phase ac electrical current into six separate electrical phases, each delivered to one of six electrodes placed in a circle, so that each conducts with all of the others. An electrically neutral pipe placed in the center is connected to a vacuum and used to vent the soil. Other electrical resistive soil heating techniques are frequently ineffective at heating bulk soil. Higher current densities at the electrodes can cause localized heating relative to the bulk soil. If the soil near the electrodes dries out, electrical conduction stops because dry soil is much more resistive. By delivering less power at the electrodes and more power to the bulk soil than other methods, the six-phase system generates more uniform heating, treats larger areas per array, and actually requires fewer electrodes per unit of soil. The system also uses conventional utility power transformers, requiring capital outlays as little as one-fifth to one-tenth those of higher frequency systems such as radio frequency or microwave heating.

Among the chief benefits of SPSH is its speed relative to alternative technologies. In a field demonstration at the Savannah River Site in 1993, the system treated more than 675 metric tons of soil contaminated with trichloroethylene and perchloroethylene, including organics suspended in a clay layer 9 meters below the surface. SPSH removed 99.7 percent of the contaminants within 25 days. A cost-benefit analysis by Los Alamos National Laboratory showed that SPSH could remediate a site 100 feet in diameter and 20 to 120 feet deep in 5 years for $88 per cubic yard. By comparison, the baseline SVE technology would require 50 years and cost $576 per cubic yard.

Subsequent improvements have made the system more field robust and cheaper to install, Bergsman says. Treatment costs vary with site geometry, soils, and contaminants, she cautions, but $40 to $80 per cubic yard, including treatment of secondary waste, is a fair range for the current system. The savings are largely the result of reduced treatment periods. SVE works well in permeable soils, but not where soil is less permeable, the water table is high, or the contaminants are less volatile. Such conditions are candidates for SPSH, which can remediate some sites 10 to 20 times faster than SVE or pump and treat. At an electronics manufacturing plant, SPSH removed nearly 5 metric tons of perchloroethylene from tight clay soil in a period of six months.

Thanks to a test sponsored in early 1997 by the Environics Directorate and supported by Armstrong Laboratory of Tyndall Air Force Base, SPSH is also proving to be an effective tool for the remediation of dense, nonaqueous phase liquids in saturated zones. DNAPLs tend to flow down to and then float atop less permeable layers. Bergsman says skeptics doubted the viability of heating a flowing aquifer to the boiling point, but SPSH took just 17 days to boil an aquifer flowing at 0.5 feet per day at a Dover Air Force Base test site.

In the second half of 1997, CES applied SPSH to saturated soil at Ft. Richardson, Alaska contaminated with chlorinated solvents, primarily 1,1,2,2 tetrachloroethane and trichloroethylene, at concentrations ranging up to 1,000 milligrams per kilogram of soil. Operating for six weeks with an active heating zone 10–40 feet below ground surface, the first array achieved a contaminant removal rate over 90 percent. Many contaminants were removed to nondetectable levels.

Currently, CES has two deployable 1-megawatt systems manufactured to specifications with off-the-shelf components. The systems use DOE-owned equipment available through a cooperative research and development agreement. With electrode arrays spanning 30–40 feet, these systems can treat up to 7,000 cubic yards of soil at a time. CES plans to add more systems as market conditions allow. Any profit will be split between Terra Vac and Battelle, which will return part of its share to the government.

For more information, contact Theresa Bergsman, Current Environmental Solutions, at (509) 943-8810 or (509) 376-3638, e-mail tm_bergsman@pnl.gov.