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
Oxygen Is Key to Approach
Controlling the Process
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:
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
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 (firstname.lastname@example.org) or Roger Aines (925) 423-7184 (email@example.com.)
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.