In Situ Vacuum Extraction Process
TERRA VAC, INC.
(In Situ and Ex Situ Vacuum Extraction)
TECHNOLOGY DESCRIPTION:
In situ or ex situ vacuum extraction is a process that removes volatile organic compounds (VOC) and many semivolatile organic compounds (SVOC) from the vadose, or unsaturated, soil zone. These compounds can often be removed from the vadose zone before they contaminate groundwater. Soil piles also may be cleaned by ex situ extraction vacuum. An in situ and ex situ vacuum extraction process has been patented and licensed to Terra Vac, Inc. (Terra Vac), and others in the United States.
The extraction process uses readily available equipment, including extraction and monitoring wells, manifold piping, air/liquid separators, and vacuum pumps. Vacuum extraction systems may vent directly to the atmosphere or through an emission control device, such as activated carbon adsorption filters, internal combustion engines, or catalytic oxidizers. After the contaminated area is completely characterized, extraction wells are installed and connected by piping to the vacuum extraction and vapor treatment systems.
First, a vacuum pump draws the subsurface con-taminants from the extraction wells to the air-liquid separator. The vapor-phase contaminants may be treated with an activated carbon adsorption filter, a catalytic oxidizer, or another emission control system before the gases are discharged to the atmosphere. Subsurface vacuum and soil vapor concentrations are monitored with vadose zone monitoring wells.
The technology can be used in most hydro-geological settings and may reduce soil contaminant levels from saturated conditions to nondetectable. The process also works in fractured bedrock and less permeable soils (clays) with sufficient permeability. The process may be used to enhance bioremediation (bioven-ting). It also may be used in conjunction with dual vacuum extraction, soil heating, pneumatic fracturing, and chemical oxidation to recover a wide range of contaminants. The figure below illustrates one possible configuration of the process.
Typical contaminant recovery rates range from 20 to 2,500 pounds (10 to 1,000 kilograms) per day, depending on the degree of site contami-nation and the design of the vacuum extraction system.
WASTE APPLICABILITY:
The vacuum extraction technology may treat soils containing virtually any VOC and has successfully removed over 40 types of chemicals from soils and groundwater, including solvents and gasoline- and diesel-range hydrocarbons.
STATUS:
The vacuum extraction process was first demonstrated at a Superfund site in Puerto Rico in 1984. Terra Vac has since applied the technology at more than 20 additional Superfund sites and at more than 500 other waste sites throughout the United States, Europe, and Japan.
The process was demonstrated under the SITE Demonstration Program at the Groveland Wells Superfund site in Groveland, Massachusetts, from December 1987 through April 1988. The technology successfully remediated soils contaminated with trichloroethene (TCE). The Technology Evaluation Report (EPA/540/5-89/003a) and Applications Analysis Report (EPA/540/A5-89/003) are available from EPA.
DEMONSTRATION RESULTS:
During the Groveland Wells demonstration, four extraction wells pumped contaminants to the process system. During a 56-day period, 1,300 pounds of VOCs, mainly TCE, were extracted from both highly permeable strata and less permeable (10-7 centimeters per second) clays. The vacuum extraction process achieved nondetectable VOC levels at some locations and reduced the VOC concentration in soil gas by 95 percent. Average reductions of soil con-centrations during the demonstration program were 92 percent for sandy soils and 90 percent for clays. Field evaluations yielded the following conclusions:
·VOCs can be reduced to nondetectable levels; however, some residual VOC concentrations usually remain in the treated soils.
·Volatility of soils is a major consider-ation when applying this technology. Ideal measured permeabilities are 10-4 to 10-8 centimeters per second.
·Pilot demonstrations are necessary at sites with complex geology or contaminant distributions.
·Treatment costs are typically $40 per ton of soil but can range from $10 to $150 per ton of soil, depending on requirements for gas effluent or waste-water treatment.
·Contaminants should have a Henry's constant of 0.001 or higher.
FOR FURTHER INFORMATION:
EPA PROJECT MANAGER:
Mary Stinson
U.S. EPA
National Risk Management Research
Laboratory
2890 Woodbridge Avenue, MS-104
Edison, NJ 08837-3679
908-321-6683
Fax: 908-321-6640
TECHNOLOGY DEVELOPER CONTACTS:
Charles Pineo
Terra Vac, Inc.
1555 Williams Drive, Suite 102
Marietta, GA 30066-6282
770-421-8008
Fax: 770-421-8188
James Malot
Terra Vac, Inc.
356 Fortaleza Street
P.O. Box 1591
San Juan, PR 00902-1591
809-723-9171
Fax: 809-725-8750