(In Situ Soil Treatment [Steam and Air Stripping])
TECHNOLOGY DESCRIPTION:
This technology treats contaminated soils and contained groundwater by the simultaneous in situ injection of treatment agents below ground during active mixing by augers or drilling blades (see figure below). The in situ injection of steam and air during mixing strips the volatile organic compounds (VOC) and semivolatile organic compounds (SVOC) from the soil and contained groundwater. The removed organics are captured at the surface and disposed of in an environmentally safe manner.
The technology is implemented by a drill unit that can consist of a single or double blade or auger mounted on a large crane or backhoe. The diameter of the drill or auger can vary from 5 to 8 feet, and it is mounted on a kelly that reaches depths of 60 feet.
The steam and air are carried down the center of the kelly(s) and injected into the ground through jets located on the blade or auger arms. The steam is supplied by an oil- or natural gas-fired boiler at 450 °F and 500 pounds per square inch gauge (psig). The air heated by the compressor is injected at 250 °F and 200 psig. The steam heats the contaminants in the soil and contained water, increasing the vapor pressure of the VOCs and SVOCs and increasing their removal rates. The direct application of the steam on the soil thermally desorbs the VOCs and SVOCs, increasing their removal percentage. Almost all the VOCs and SVOCs of interest form azeotropes with steam that boil below 212 °F and contain low concentrations (such as a few percent) of contaminants. These azeotropes significantly increase contaminant removal rates, especially for the higher-boiling-point SVOCs.
The VOC- and SVOC-laden air and steam vapor stream removes the contamination to the surface where it can be captured, if necessary, in a metal container. The container, which makes a tight seal to the ground surface, is connected to a process stream by piping. A suction blower draws the waste stream to the process stream where it is collected or destroyed. The blower creates a slight vacuum in the container and piping as well as a positive displacement inward to the collection or destruction system, thus protecting the outside environment from contamination.
The simplest form of the process system uses a catalytic oxidizer or thermal oxidizer to destroy the contamination before exhausting to the atmosphere. When treating chlorinated VOCs and SVOCs, an acid scrubber can be added if required by the amount of material being processed. Another simple process uses activated carbon to recover the contamination. For the carbon to work efficiently, a cooling system must precede the carbon bed, so the process must also treat contaminated water. If recovery and reuse of the contamination is important or economically desirable, a process system that condenses the gas stream can be used.
The in situ soil treatment technology has also treated contaminated soil by injecting and mixing other agents. Chemical injection processes include the stabilization and solidification of heavy metals, neutralization of acids and bases, and oxidation. The technology has been successfully used to perform bioremediation. The equipment is capable of injecting cement into the soil and making slurry walls. The technology has the unique feature of being able to inject two materials simultaneously or sequentially.
WASTE APPLICABILITY:
This technology can treat solid materials which do not contain obstructions, including soils, sludges, lagoons, and the liquids contained within, such as water and dense and light nonaqueous-phase liquids. The technology is applicable to most VOCs and SVOCs, including pesticides. It is particularly applicable to free product and removal of highly concentrated contamination. It is most effective for removals of 95 to 99 percent of the contamination as a result of the low temperature thermal desorption. After treatment is completed, the soil can meet construction engineering requirements by compacting or injecting small amounts of cement.
STATUS:
This technology was accepted into the SITE Demonstration Program in 1989. A SITE demonstration was performed in September 1989 at the Annex Terminal, San Pedro, California. Twelve soil blocks were treated for VOCs and SVOCs. Liquid samples were collected during the demonstration, and the operating procedures were closely monitored and recorded. In January 1990, six blocks that had been previously treated in the saturated zone were analyzed by EPA methods 8240 and 8270.
The Applications Analysis Report (EPA/540/A5-90/008) was published in June 1991. The technology remediated 30,000 cubic yards at the Annex Terminal after completion of the SITE demonstration and has been used at five other contaminated sites.
DEMONSTRATION RESULTS:
The SITE technology demonstration yielded the following results:
Removal efficiencies were greater than 85 percent for VOCs present in the soil.
Removal efficiencies were greater than 55 percent for SVOCs present in the soil.
Fugitive air emissions from the process were low.
No downward migration of contaminants resulted from the soil treatment.
The process treated 3 cubic yards of soil per hour.
FOR FURTHER INFORMATION:
EPA PROJECT MANAGER:
Paul dePercin
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7797
Fax: 513-569-7105
E-Mail:
dePercin.Paul@epamail.epa.gov
TECHNOLOGY DEVELOPER CONTACT:
Phil La Mori
NOVATERRA Associates
2419 Outpost Drive
Los Angeles, CA 90068-2644
213-969-9788
Fax: 213-969-9782
E-mail: NOVATERRA@aol.com