CLEAN up a greasy kitchen spill with cold water and the going is slow. Use hot water instead, and progress improves markedly. So it makes sense that cleanup of greasy underground contaminants such as gasoline might go faster if hot water or steam were somehow added to the process. The Environmental Protection Agency named hundreds of sites to the Superfund list-sites that have been contaminated with petroleum products or petroleum products or solvents. Elsewhere across the country, thousands of properties not identified on federal cleanup lists are contaminated as well. Given that under current regulations, underground accumulations of solvent and hydrocarbon contaminants (the most serious cause of groundwater pollution) must be cleaned up, finding a rapid and effective method of removing them is imperative. In the early 1990s, in collaboration with the School of Engineering at the University of California at Berkeley, Lawrence Livermore developed dynamic underground stripping. (For an explanation of this method, see Energy & Technology Review, July 1992, pp. 1-7). This method for treating underground contaminants with heat is much faster and more effective than traditional treatment methods. More recently, Livermore scientists developed hydrous pyrolysis/oxidation, a process that converts contaminants in the ground to such benign products as carbon dioxide, chloride ions, and water. By introducing both heat and oxygen, this process has effectively destroyed all petroleum and solvent contaminants that have been subjected to laboratory tests. During the summer of 1997, both processes were used for cleanup of a four-acre site in Visalia, California, owned by Southern California Edison (Figure 1). The utility company had used the site for 80 years to treat utility poles by dipping them into creosote, a pentachlorophenol compound, or both. By the 1970s, these highly toxic substances had seeped into the subsurface to depths of approximately 100 feet (30 meters). The Visalia pole yard bore the distinction of being one of the original Superfund sites.

Southern California Edison and SteamTech Environmental Services of Bakersfield, California (the first commercial site licensee of the dynamic underground stripping technology), are cleaning up the Visalia site, with Livermore staff periodically on hand as operational consultants. During the first six weeks of operation, between June and August 1997, the team removed or destroyed in place approximately 300,000 pounds (135 metric tons) of contaminants, a rate of about 46,000 pounds (22 metric tons) per week (Figures 2 and 3). For nearly 20 years, Southern California Edison had been removing contaminants from the subsurface using the standard cleanup method, known as pump-and-treat, most recently at a rate of just 10 pounds (0.03 metric ton) per week. In contrast, the amount of hydrocarbons removed or destroyed in place in those six weeks was equivalent to 600 years of pump-and-treat, about 5,000 times the previous removal rate. Needless to say, the Visalia cleanup using dynamic underground stripping plus hydrous pyrolysis/oxidation is considered a wild success by everyone involved. Geophysicist Robin Newmark and geochemist Roger Aines are Lawrence Livermore project leaders for the work at Visalia. Says Aines, "No one really knew what was underground at Visalia. Through the winter of 1998, Southern California Edison and SteamTech have removed over 540,000 pounds (245 metric tons), and the job still isn't finished. However, contaminant concentrations in recovered groundwater continue to drop, so we know the end is in sight."

Finding a Better Way For years, scientists in Livermore's Earth and Environmental Sciences Directorate have been researching better methods to clean up soil and groundwater contamination, in part because both the Livermore site and Livermore's Site 300 are also Superfund sites as a result of U.S. Navy, Atomic Energy Commission, and DOE operations. Most contaminants at the Livermore sites are either petroleum distillates (e.g., gasoline, diesel fuel) or chlorinated hydrocarbons used as solvents. Existing methods to remove these compounds from soil and groundwater have halted their migration off the site, but cleanup will still take a decade or more to complete. For about 20 years, the traditional method of cleaning up contaminated groundwater has been the pump-and-treat method. Water is pumped from the water table to the ground surface, treated to remove or destroy contaminants, and returned underground. Huge amounts of water must be flushed through the contaminated area for years or even decades to clean it, and even then the contamination may not be completely removed. Says Newmark, "Some of the solvents and other contaminants have very low solubility. So very small amounts can pollute millions of gallons of water because contaminants leach out very slowly. When you try to clean them up with pump-and-treat, it's like trying to rinse a soapy sponge. You have to run vast amounts of water through the sponge before all the soap is finally out." Pump-and-treat systems are relatively inexpensive to operate, but they represent a long-term cost. They offer compliance in a regulatory sense, but the results are not very satisfying because the site is unlikely to be completely cleaned up. Boiling Off Contaminants The dynamic underground stripping technology developed by Livermore and the University of California was first demonstrated in the cleanup of an underground gasoline spill at the Livermore site in 1993 (see Energy & Technology Review, May 1994, pp. 11-21). Dynamic underground stripping was so successful in this cleanup that contaminants were removed 50 times faster than with the pump-and-treat process. The cleanup, estimated to take 30 to 60 years with pump-and-treat, was completed in about one year. In 1996, the Environmental Protection Agency and other regulators declared that no further remedial action was required. In this method, the area to be cleaned is ringed with wells for injecting steam at temperatures above 100°ree;C. Extraction wells in the central area are used to vacuum out vaporized contaminants. To ensure that thick layers of less permeable soils are heated sufficiently, electrode assemblies are sunk into the ground and the ground is heated, which forces trapped liquids to vaporize and move to the steam zone for removal by vacuum extraction. These combined processes achieve a hot, dry, contaminant-free zone of earth surrounded by cool, damp, untreated areas. Steam injection and heating cycles are repeated as long as underground imaging shows that cool (and therefore untreated) regions remain. Although the initial capital outlay for dynamic underground stripping is higher than for pump-and-treat systems, the process saves money in the long run because it is completed much more quickly. Most of the equipment, such as boilers for generating steam, can be rented. Up-front costs include installing the heating wells, renting the equipment, and operating the system intensively for a short period of time. There are no long-term operation and maintenance costs. That 1993 field trial of dynamic underground stripping cost about $110 per cubic yard ($140 per cubic meter), although Livermore scientists believe they could repeat the project for about $65 per cubic yard ($85 per cubic meter). Because contamination at the gasoline spill at the Livermore site migrated downward 40 meters, digging up the contaminated soil and disposing of it would have cost almost $300 per cubic yard ($400 per cubic meter). Soil removal and disposal costs are more typically in the range of $100 to $200 per yard ($130 to $260 per cubic meter); pump-and-treat method costs are as high as or higher than soil removal costs. Unexpected Help The Livermore team discovered an unexpected benefit of dynamic underground stripping: it encourages bioremediation. Heating the soil at the gasoline spill site to temperatures above 100°ree;C was expected to sterilize it, with the microorganisms that use petroleum products as food expected to return slowly as the soil cooled. But soil samples taken soon after completion of the cleanup revealed large numbers of microbes that thrive in high temperatures (known as thermophiles), apparently because predators and competition had been eliminated. Bioremediation is an important final step in soil and groundwater cleanups because the microorganisms destroy residual contaminants missed during the initial cleanup process. Oxygen Is Key to Approach With dynamic underground stripping, the contaminants are vaporized and vacuumed out of the ground, leaving them still to be destroyed elsewhere. In fact, about half the cost of a typical cleanup is in treating the recovered groundwater and hauling away and disposing of the contaminated material that is brought to the surface. "Livermore's hydrous pyrolysis/oxidation technology takes the cleanup process one step further," explains Aines, "by eliminating the treatment, handling, and disposal requirements and destroying the contamination in the ground." The Visalia pole yard cleanup is the only application of this method to date, but indications are that large-scale cleanups with hydrous pyrolysis/oxidation could cost as little as $25 per cubic yard ($33 per cubic meter), an enormous savings over current methods. Best of all, the end product of a hydrous pyrolysis/oxidation cleanup with bioremediation as a final step is expected to be a truly clean site. The hydrous pyrolysis/oxidation process builds on the team's experience with heating large amounts of soil that was gained during earlier work with dynamic underground stripping. To provide the oxygen, steam and air are injected in parallel pipes, building a heated, oxygenated zone in the subsurface. When injection is halted, the steam condenses and contaminated groundwater returns to the heated zone. The groundwater then mixes with the condensed steam and oxygen, which destroys dissolved contaminants. This process avoids many of the mixing problems encountered in other in situ oxidation schemes. In such processes, an oxidizing reagent is typically injected into the subsurface, resulting in the displacement of the contaminant. Without a return process such as steam condensation, the contaminant and oxidant never mix or mix poorly at best. During the heating process in hydrous pyrolysis/oxidation, the dense, nonaqueous-phase liquids and dissolved contaminants are destroyed in place without surface treatment. The technique improves the rate and efficiency of remediation by rendering the hazardous materials benign by a completely in situ process. Hydrous pyrolysis/oxidation also takes advantage of the large increase in mobility that occurs when the subsurface is heated and makes contaminants more available for destruction. Many remediation processes are limited by the access of the reactants to the contaminant, making the lack of mobility the bane of remediation efforts in low-permeability materials such as clays. Most early Livermore experiments on the hydrous pyrolysis/oxidation process, funded by DOE, were with trichloroethylene (TCE), a solvent that was widely used in degreasing and other industrial processes. TCE is the most common groundwater contaminant in the DOE complex and in most industrial areas. Unlike gasoline, TCE and similar solvents are heavier than water, which means that they can sink below the water table, making cleanup extremely difficult, if not impossible, with conventional methods. "The oxidation process occurs naturally, but without heat it is very slow," explains Kevin Knauss, the Livermore geochemist who leads the effort in the laboratory, "so we needed to know how hot the soil had to be." The team learned that with TCE, just a few degrees can make an enormous difference in how quickly the breakdown occurs. At 90°ree;C, it takes a few weeks; at 100°ree;C, it takes a few days; and at 120°ree;C, it occurs in just a few hours. Laboratory results indicated that the contaminants at Visalia would react at similar rates. Experiments with dissolved oxygen showed that the oxygen in air is sufficient to degrade the contaminants. Because oxygen is corrosive, pumping pure oxygen into the ground could very quickly damage the piping system, but the less concentrated oxygen from the air is less corrosive and easy to introduce. The demonstration of hydrous pyrolysis/oxidation at Visalia confirmed the effectiveness of this technology for dense, heavier-than-water groundwater pollutants such as creosote and pentachlorophenol. The method has also been tested successfully in the laboratory on contaminants resistant to cleanup in the past-for example, carbon tetrachloride, a chemical used as a refrigerant and a dry-cleaning solvent, and polychlorinated biphenyls (PCBs), a chemical used in electrical transformers and capacitors. Project co-leader Aines notes, "This new technology could also be used to mop up methyl tert butyl ether (MTBE), a gasoline additive that has begun showing up in California groundwater." The method can also be used to clean up groundwater and soils to almost any depth. Controlling the Process Several geophysical techniques were used at Visalia to monitor the underground movement of steam and the progress of heating. One technique was electrical resistance tomography, a technology developed at Livermore, applied during the 1993 gasoline cleanup, and now available commercially. Electrical resistance tomography is an imaging method like a CAT scan that provides near-real-time images of the underground processes between pairs of monitoring wells (Figure 4). Soil electrical properties vary with temperature, soil type, and fluid saturation. For example, higher electrical resistivity is found in more permeable sand and gravel soils. Conversely, less permeable clay soils show lower resistivity (higher conductivity). Baseline measurements with electrical resistance tomography are used to characterize a site and to predict steam pathways. During treatment at Visalia, daily resistivity measurements supplied a picture of the progress of the steam front and the heated zones. Monitoring the progress of the heating fronts ensured that all soil was treated. Temperature measurements made in monitoring wells revealed details of the complex heating phenomena in the individual soil layers.

To evaluate the progress of the chemical destruction of contaminants in situ, the team also developed field methods for sampling and analyzing hot water for contaminants, oxygen, intermediate products, and products of reaction. Because hydrous pyrolysis/oxidation is an aqueous-phase reaction, capturing and evaluating the fluid in that phase is essential. At elevated temperatures, many of the key constituents are sufficiently volatile that traditional sampling techniques are not suitable. The Livermore team developed high-temperature systems that can deliver a pressurized, isolated fluid stream to the surface, where in-line analysis can be performed. Building on Livermore's experience in using noble-gas tracers to track water movement (see S&TR, November 1997, pp. 12-17), Bryant Hudson designed tracer experiments to help verify hydrous pyrolysis/oxidation in the field. Noble-gas tracers-including helium, neon, krypton, and xenon-were added to injected water and steam to track the movement of the steam (and subsequent condensation to liquid water) and the movement of other gases initially present in the steam (Figure 5). Naturally occurring dissolved gases (nitrogen and argon) provided measurements of atmospheric and native groundwater interaction. Once a "packet" of water had been tagged with gas tracers, it could later be identified by the types and amounts of tracers in it. The tracers thus assisted with many tasks, including: Following the injected steam-water- oxygen pattern from each injection well. Determining how much mixing occurred. Determining oxygen consumption, carbon dioxide production, and transport. Correlating the intermediate hydrous pyrolysis/oxidation destruction products with temperature and oxygen. Identifying the overall isotopic content of the extracted carbon with regard to carbon-14 (14C) and carbon-13 (13C). In soil-gas and water samples, evidence of the progress of hydrous pyrolysis/oxidation (Figure 6) was found in a number of sources, including the disappearance of dissolved oxygen (consumed through the hydrous pyrolysis/oxidation reactions), the appearance of oxidized intermediate products, and the production of carbon dioxide (the final product of this process). Important information on the isotopic content of the carbon in the carbon dioxide was obtained from Livermore's Center for Accelerator Mass Spectrometry. The ratios of 14C/12C and of 13C/12C in carbon dioxide from the subsurface were more similar to those of the petroleum-based contaminants than to those of groundwater in the area, indicating that the contamination was being destroyed and converted to carbon dioxide.

Modeling to Predict/Evaluate The team used NUFT, a widely used three-dimensional groundwater modeling code developed several years ago at Livermore, to model such important process parameters as mixing of steam, air, and groundwater. In general, simulations with models such as NUFT provide a diagnostic means for anticipating the results of a decontamination scheme in complicated soil environments and, later, for evaluating field results. In the case of a cleanup such as the one at Visalia, where much of the decontamination occurs in situ and is therefore not directly observable, the noble-gas tracers provide data critical for validating initial modeling results. "Modeling proved invaluable at Visalia and remarkably accurate as well, compared with results from monitoring wells," explains Newmark. "Livermore models predicted steam and tracer movement to within an hour or two in most instances." (See Figure 7.) Modeling also effectively predicted the time of thermal breakthrough, which occurs when sufficient heat has built up in the subsurface for vaporization of contaminants to begin, and steam collapse, which is the opposite phenomenon. The team found that the ratio of tracer gas to natural air mixed into water was much greater than predicted by the model's initial assumption of no mixing of the atmosphere and steam zone. These data demonstrate that mixing is important and the process is more efficient than envisioned.

From Liability to Asset In short order, just months after laboratory experiments were completed, the new hydrous pyrolysis/ oxidation method succeeded at the Visalia site. The project team had brought together Livermore's expertise in underground imaging, noble-gas-tracer monitoring, supercomputer modeling, and accelerator mass spectrometry to create and verify the field results of a technology to transform the groundwater and soil cleanup process. Far faster than other techniques, the technology provides a relatively inexpensive way to clean up difficult contaminants that plague dozens of sites across the country. For their efforts, the team was recognized with the Laboratory Director's Performance Award in December 1997. The project team was mindful of the need to make the techniques simple for others to operate and maintain. Integrated Water Technologies of Santa Barbara, California, recently became the first nationwide licensee of Livermore's new cleanup technologies. The company plans to begin using them this year to clean up several Superfund sites. Work at Visalia is not yet complete. The best estimates today are that cleanup will be completed in a year, with another four years of monitoring the site. Southern California Edison had expected to meet Environmental Protection Agency requirements in about 120 years with traditional pump-and-treat technology combined with enhanced bioremediation. Instead, a piece of real estate that had been a major liability will soon become a valuable asset. - Katie Walter

Key Words: dynamic underground stripping, electrical resistance tomography, groundwater contamination, hydrous pyrolysis/oxidation, modeling, noble-gas tracers, NUFT code, remediation, soil contamination.

For further information contact Robin Newmark (925) 423-3644 (newmark1@llnl.gov) or Roger Aines (925) 423-7184 (aines1@llnl.gov.)

ROBIN L. NEWMARK, leader of the Applied Geology and Geophysics Group in the Earth and Environmental Sciences Directorate, has been at Livermore since 1985. Her early work focused primarily on borehole geophysics applications. Since 1990, she has been involved in the development of thermal remediation methods and subsurface detection and imaging techniques essential for monitoring and process control of in situ environmental remediation. She earned a B.S. in earth and planetary sciences from Massachusetts Institute of Technology in 1978, an M.S. in marine geophysics from the University of California at Santa Cruz in 1980, and a Ph.D. in marine geophysics from Columbia University in 1985. Author of many papers, reports, and patents, Newmark is associate editor of Geophysics, the journal of the Society of Exploration Geophysicists.


ROGER D. AINES came to the Laboratory in 1984 and is currently leader of the Geochemistry Group in the Earth and Environmental Sciences Directorate. Since 1990, he has been working on the development of thermal remediation methods. Earlier, he gained experience centered on geochemical research and modeling for the Yucca Mountain nuclear waste repository project. Roger received a B.A. in chemistry from Carleton College in 1978 and a Ph.D. in geochemistry in 1984 from California Institute of Technology. He is an author of many papers, patents, and reports related to disposal of nuclear waste and thermal remediation of contaminated groundwater.