Soil Remediation by Steam Enhanced Extraction

Superfund Basic Research Program

Hazardous substances that reach the subsurface from leaking underground storage tanks, accidental spills, or improper disposal pose a significant challenge for remediation scientists and site managers. Traditional methods of cleanup, such as pump and treat, have proven to be inefficient, costly, and slow in removing contaminants from groundwater and unsaturated zones in the subsurface.  In response to the need for a technology that can remove volatile hydrocarbons from above, below, and in the water table, as well as from areas of relatively impermeable clays, Dr. Kent Udell developed a process called Steam Enhanced Extraction (SEE). This SBRP-funded research generated a new national and international industry, and a solid technical basis for U.S. Environmental Protection Agency (EPA) policy on source removal for soil and groundwater cleanup.

Working with the University of California-Berkeley SBRP, Dr. Udell designed SEE to remove organic compounds from contaminated soils without the need for excavation. The in-situ steam enhanced extraction process involves the injection of steam into subsurface soils to mobilize contaminants and application of a vacuum at the extraction wells to help direct the steam toward the extraction wells.  Vertical steam injection wells are placed within the region of contamination and extraction wells are placed within and around the region. Some of the contaminant is pushed ahead of the condensing steam front and into the extraction wells. In the steam zone, the residual contaminant is volatilized at the elevated temperature and swept toward the extraction well by the flowing steam. After the entire soil mass under treatment has reached the steam temperature, the flow of steam continues only intermittently with a constant vacuum applied to the extraction wells. The vacuum extraction removes much of the remaining contamination. As the soil in the high permeability region cools, the steam remaining in the low permeability region evaporates the contaminants. Proper process operation procedures must be followed to prevent downward movement of high density solvents.

Dr. Udell conducted a very successful full-scale demonstration of SEE at Lawrence Livermore National Laboratory. A demonstration at the Visalia Pole Yard in Visalia, California, one of the first sites placed on the National Priority List, showcased SEE's industrial application. This work was considered to be a break-through application of remediation technology, and earned the first and only EPA Remediation Technology Development Award for "technical excellence in the development of in situ thermal treatment technologies." For a cost of about $15 million, the application of SEE at the Visalia Pole Yard site decreased the financial liability of the site by $85 million, demonstrating a clear financial incentive for publicly owned corporations to take a more aggressive approach to environmental restoration.

Steam injection was also applied at Cape Canaveral at Launch Complex 34.  This site is particularly important in that the steam technology was the third technique to be demonstrated in adjacent plots. The use of steam injection at that site was also unique in its application through the co-injection of air with the steam. Dr. Udell developed the theoretical underpinning of the value of air co-injection with the steam in the elimination of accumulation of the non-aqueous phase liquids (NAPL) at the steam condensation front. Such accumulation has been shown to be the requisite step leading to uncontrolled downward migration of the non-aqueous phase liquid during thermally enhanced cleanup operations. In all cases, including controlled two dimensional laboratory experiments, the simultaneous injection of air and steam increased the NAPL compound removal rate beyond that which could be achieved by either pure steam injection or pure air sparging.

Other SEE applications at Superfund sites include:

• Loring Air Force Base in Maine where steam was injected into fractured rock that is contaminated by NAPL trapped in the fractures.  This is a large project where both the State of Maine and the EPA are actively engaged in the application and evaluation of the potential of Steam Enhanced Extraction to remediate fractured geologies.
  
  
• Wyckhoff Superfund site adjacent to Eagle Harbor near Seattle where SEE was included as the selected cleanup remedy in the Record of Decision.  A pilot test of the technology, consisting of about 10 injection and 10 extraction wells is now underway.
  
  
• Baxter and McCormick Superfund site near Stockton, California where SEE is being considered for the remediation with a full-scale design completed in sufficient detail for costing purposes. The project is now under funding consideration by the EPA. This site is one of the largest wood treating chemical spills in the country and defies all other techniques for remediation in any reasonable time frame.

International application is also gaining momentum. Dr. Udell has applied his expertise at a PCE- and kerosene-contaminated site in Denmark with success, and SEE is used routinely in the Czech Republic, including the first successful remediation of a fractured bedrock site. Also of interest is the successful pilot demonstration of the technology at the Pancevo site in the former Yugoslavia, now Serbia, which experienced a catastrophic release of millions of pounds of the highly toxic chemical, 1,2 DCA due to the NATO bombings in 1999.

This work demonstrates that many sites previously considered as untreatable can be remediated with reasonable cost and acceptable certainty using thermal remediation techniques. The SEE technology is applicable to hydrocarbon mixtures (gasoline, jet fuel, diesel) and dense solvents such as trichloroethylene (TCE), trichloroethane (TCA), or perchloroethylene (PCE). The benefits of this technology are the drastically reduced volumes of contaminated fluid to be treated on the surface, order-of-magnitude decreases in the time for remediation, applicability to liquid contaminants both above and below the water table, and potential for recycling recovered separate phase contaminants. The process can be implemented with standard boilers, fluid cooling and separation equipment. To apply this process to contaminated soils near the surface, a cap may be required. Otherwise, the applicability of the technique is broad.

Dr. Udell's work was highlighted in an EPA Ground Water Issue on Steam Injection for Soil and Aquifer Remediation (EPA/540/S-97/505) (http://www.epa.gov/tio/tsp/download/steaminj. pdf)  (633 KB)

Additional information is available in Alternatives for Ground Water Cleanup (http://books.nap.edu/books/0309049946/html/in dex.html) - National Academies Press.

Currently, Steamtech Environmental Services, Inc. performs commercial applications of this technology.