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DEMONSTRATION BULLETIN: IN-SITU VACUUM EXRACTION: TERRA VAC, INC.
Citation:
U.S. EPA. DEMONSTRATION BULLETIN: IN-SITU VACUUM EXRACTION: TERRA VAC, INC. U.S. Environmental Protection Agency, Washington, DC, EPA/540/M5-89/003, 1989.
Impact/Purpose:
to inform the public
Description:
This in-situ vacuum extraction technology is a process for the removal and venting of volatile organic compounds (VOCs) from the vadose or unsaturated zone of soils. Often, these compounds can be removed from the vadose zone before they have a chance to contaminate groundwater. In using this technology, subsurface organic contaminants are "vacuumed up" via a well, vapor/liquid separated, and then exposed to activated carbon before the "vapor" is allowed to be released into the atmosphere. The technology uses readily available components such as extraction and monitoring well(s), manifold piping, vapor/liquid separator, vacuum pump, and emission control equipment, such as activated carbon canisters. Once a contaminated area is completely defined, an extraction well (or wells) is installed (depending upon the extent of contamination) and is connected by piping to a vapor/liquid separator device (Figure 1). A vacuum pump draws the subsurface contaminants through the well, separator device, and an activated carbon canister before discharge of the air streams is allowed to the atmosphere. Subsurface vacuum and soil vapor concentration are monitored via vadose zone monitoring wells. The technology does not require highly trained operators or soil excavation, and it also is not depth limited. The technology works best when it is applied towards the remediation at sites which are contaminated by liquids having high vapor pressures. However, the process is limited in applicability; diffusion rates through dense soils (such as compacted clays) are much lower than through sandy soils, and if activated carbon is used, then spent carbon must be processed. In addition, depending on the soil type and the depth to groundwater, the radius of influence of a single extraction well can range from tens to hundreds of feet. Typical contaminant recovery rates also range between 20 and 2500 pounds per day and are a function of volatility of the organic compound recovered. Therefore, the more volatile the organic compound, the faster the process works. The developer also states that the process is more cost effective where contaminated soils are predominantly above the water table, although systems have been designed for vapor and groundwater recovery.