At NASA’s Launch Complex 34 groundwater cleanup site on Cape Canaveral Air Force Station, a steam flood with coair injection was deployed to remove dense nonaqueous-phase liquid (DNAPL) trichloroethylene (TCE) from the subsurface. A steam flood, which is also referred to as Dynamic Underground Stripping (DUS), is an engineered combination of steam injection and vapor groundwater extraction. Hydrous Pyrolysis/Oxidation (HPO) is a secondary destruction mechanism that accompanies DUS. HPO initiates the destruction of underground contaminants through oxidation in the presence of injected steam. The purpose of the Launch Complex 34 demonstration was to test the effectiveness and evaluate the cost to deploy DUS/HPO with coair injection at a DNAPL-phase TCE-contaminated site.

Launch Complex 34’s geology consists of several stratigraphic units containing layered, heterogeneous lithology with permeability contrasts of up to two orders of magnitude. The aquifer has three distinct lithologic units for treatment: an Upper Sand Unit (USU), a Middle Fine-Grained Unit (MFGU), and a Lower Sand Unit (LSU). For a 120-day operating period, steam with coinjection of air was deployed at two depth intervals that targeted the USU and LSU within the aquifer. The MFGU was alternatively heated as buoyant steam rose to the surface.

During the deployment, steam was injected in the center of the 50- 75-foot plot at a maximum rate of 2,000 pounds per hour. Air was coinjected at a rate of 45 standard cubic feet per minute. Groundwater and vapor extraction wells were operated on the edges of the plot throughout the demonstration. Extracted groundwater and vapors laden with heated TCE were treated on the surface using a combination of stripping towers and onsite thermal oxidation units.

This demonstration was the first deployment of DUS with the coinjection of air in the United States. Previously, the use of air with steam injection had only been applied in the Czech Republic and Denmark. Conceptually, the mixture of steam and air produces a more controlled thermal front, with a large volume of air saturated with TCE rising to the surface under buoyancy influences. The controlled thermal front minimizes condensation of the contaminant and creation of nonaqueous-phase liquid on the edges of the heated zone, thereby minimizing the potential for its downward migration.

Key accomplishments:

• 2000: DUS/HPO design completed.
• 2001: DUS/HPO Remediation System constructed onsite. DUS/HPO Remediation System startup.
• Postdemonstration DUS/HPO Remediation System evaluation.