From Tech Trends November 1994

Vacuum Extraction/Air Sparging with Bioremediation for Organics

By Paul dePercin, Risk Reduction Engineering Laboratory

The Subsurface Volatilization and Ventilation System (SVVS ) is an in situ vacuum extraction/air sparging and bioremediation technology for the treatment of subsurface organic contamination in soil and ground water. The primary objective of the SITE (Superfund Innovative Technology Evaluation) Program evaluation of SVVS at the Electro-Voice, Incorporated (EV) facility in Buchanan, Michigan was to determine the effectiveness of SVVS in reducing volatile organic contamination in the vadose zone. The demonstration met the objective.

Historical activities at the EV facility included painting, electroplating and assembling of components associated with the manufacture of audio equipment. In 1964 EV implemented an automated painting system; and, a dry well was installed to handle some of the liquid wastes generated from the paint shop. A remedial investigation discovered a sludge-like material beneath the dry well area contaminated with aromatic hydrocarbons and halogenated and non-halogenated volatile and semi-volatile compounds. Some of these organic contaminants have migrated to underlying strata. The SITE chose seven of these contaminants to demonstrate the effectiveness of the SVVS system. These contaminants and their initial average concentrations were the BTEX compounds -- benzene at 0.01 parts per million (ppm), toluene at 92 ppm, ethylbenzene at 37.4 ppm and xylenes at 205 ppm -- and tetrachloroethene at 5.4 ppm, trichlorethene at 0.36 ppm and 1,1-dichloroethene at 0.01 ppm. The overall reductions in contaminants ranged from 71% to over 99%, which greatly exceed the developer's claim of a projected 30% reduction.

The SVVS technology, developed by Billings and Associates, Inc., and operated under a licensing agreement by Brown & Root Environmental, utilizes vapor extraction and biostimulation to remove and destroy organic contaminants from the subsurface. Vapor extraction removes the easily strippable volatile components from the soil and/or ground water. This removal mechanism is dominant during the early phases of the remediation. Biostimulation processes dominate the later phases of the remediation and are used to accelerate the in situ destruction or organic compounds in the soil and ground water. The developer claims that remediation using the combination of vapor extraction and biostimulation is more rapid than the use of biostimulation alone. The SITE demonstration tests indicate that the technology stimulated biodegradative processes at the site and that the early phase of the remediation was characterized by higher concentrations of volatile organics in the extracted vapor stream. In addition, SVVS can remediate contaminants that would not be remediated by vapor extraction alone (chemicals with lower volatilities and/or chemicals that are tightly sorbed). These benefits translate into lower costs and faster remediations.

The technology consists of a network of injection and extraction wells plumbed to one or more compressors or vacuum pumps, respectively. The vacuum pumps create negative pressure to extract contaminant vapors. Air compressors simultaneously create positive pressures across the treatment area to deliver oxygen for enhanced aerobic biodegradation. The system is maintained at a vapor control unit that houses pumps, control valves, gauges and other process control hardware. The operation of SVVS is custom designed to meet specific site conditions. The number and spacing of the wells depends upon the results of a model, as well as the physical, chemical and biological characteristics of the site.

According to the developer, the SVVS is applicable to sites contaminated with gasoline, diesel fuels and other hydrocarbons, including halogenated compounds. The developer claims that the SVVS is very effective in treating soils contaminated with virtually any material that exhibits some volatility or is biodegradable. The technology can be applied to contaminated soil, sludges, free-phase hydrocarbon product and ground water.

A one-year time frame was chosen for SITE testing purposes at the EV site. However, other sites may require longer or shorter remedial cleanup time.

For more information, call Paul dePercin at EPA's Risk Reduction Engineering Laboratory at 513-569-7797. An Innovative Technology Evaluation Report describing the complete demonstration will be available in early 1995.