SITE INFORMATION AND CORRESPONDENCE

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2-5% water vapor is considered necessary to avoid drying of the soil which would lead to a reduction in contaminant vapor extraction efficiency. The basic SVE system is composed of a blower or vacuum pump that draw contaminant vapors to one or more extraction wells and then through surface manifold piping, valves, and a vapor- water separator for subsequent delivery to a vapor treatment unit. Vapors may be captured or destroyed using thermal incineration, catalytic oxidation, internal combustion, carbon adsorption, and/or biofiltration. Bioventing employs the SVE system concept to promote the in- situ aerobic biodegradation of hydrocarbon contaminants within vadose soils. This is accomplished by using the SVE mediated movement of air through the area of soil contamination to deliver the large volume of oxygen required to develop and maintain the biomass necessary to accomplish the mineralization (thorough aerobic biodegradation) of fuel hydrocarbons. It has been suggested that using air as a mechanism to deliver oxygen to unsaturated soil could be 1 , 000 times more efficient than transferring it to water (Wilson and Ward, 1986) . A number of sources have reported that analysis of SVE systems indicate that 20-38% of hydrocarbon removal is by biodegradation, with the remainder occurring by volatilization. Nutrients (primarily nitrogen and phosphorus ) and moisture may also be added to increase biodegradation rates . The biological destruction component is particularly -appropriate to the remediation process when the hydrocarbon contaminant is formed, in part, of compounds that are essentially not volatile. In order to confirm the applicability of SVE to the subject site, it is proposed that a vacuum pump be installed and soil gases extracted from one of the on--site wells . Measurements would be made in the other two wells in order to determine the radius of influence that may be achieved, the probable rate of hydrocarbon removal, and the effectiveness of utilizing the existing monitoring wells as vapor extraction points . Pulse venting is expected .to enhance vapor removal efficiencies and will be studied by extracting vapors only periodically in order to allow contaminants to diffuse into large areas . In-Situ Bioremediation Technology Overviews Although contaminated soil at the subject site has been described as medium brown silty-clayey soil of low permeability, and biological treatment of extracted groundwater has already been proposed, there appears to have been no effort made to determine whether or not "joint" bioremediation of vadose soil 2 .