Steam Enhanced Extraction (SEE) at the DOE LLNL Gas Pad Site and Visalia Wood Treater NPL site

The LLNL gasoline spill cleanup was the first large scale application of thermal remediation to NAPL contamination below the water table. Beginning in 1992, steam injection and electric heating were used to remove approximately 7000 gallons of gasoline which had been trapped at depths up to 40 ft below the water table. The NAPL product was removed from the approximately 100,000 cubic yard treatment zone following 14 weeks of operation in three phases over a year's time. Following NAPL removal, natural attenuation, physical oxidation, and continued pumping removed the much-larger dissolved plume. The site was formally closed in 1995. This collaborative effort between LLNL and UC Berkeley demonstrated that thermal remediation is effective on a large scale, and that many beneficial mechanisms operate simultaneously to improve efficiency. The removal of the dissolved plume is a good example of the benefits of source removal; natural attenuation works when the source is removed.