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electrons). There are several compounds that can serve as electron acceptors including oxygen, nitrate, iron oxides, sulfate, water, and carbon dioxide (Borden and others, 1995). Aerobic microorganisms use oxygen as the electron acceptors. Anaerobic microorganisms use other compounds such as nitrate, iron oxides(ferric iron), and sulfate as electron acceptors. In order to determine the effectiveness of natural attenuation with groundwater, monitoring, a groundwater monitoring -program would have to be `initiated at the site that would require monitoring for these parameters for at least one year. Monitoring at the site would have to continue until concentrations of petroleum hydrocarbons reached acceptable levels. 662 Air Sparging with Soil Vapor Extraction Air sparging with soil vapor extraction has proven effective in reducing volatile organic compounds (VOCs) and certain semi-volatile compounds: In brief, air is .injected.into the saturated zone. The air forms bubbles that rise to the unsaturated zone, carrying trapped and dissolved contaminants. Vapor extraction wells in the unsaturated zone capture sparged air. If necessary the effluent air can be treated using a variety of vapor treatment options. This method also stimulates biodegradation by increasing the supply of oxygen in the subsurface. The advantages of in-situ air sparging with soil vapor extraction include: • Short treatment times; usually I to 3 years under optimal conditions. • Readily available equipment and easy installation: ._ • Implementation with minimal disturbance to aboveground activities. • Requires no removal,treatment, storage, or discharge considerations for groundwater. • Cost competitive. • Can be used under buildings and other locations that cannot be excavated. In order to determine the effectiveness of air sparging and soil vapor extraction, pilot testing to . evaluate the effectiveness of both methods sould be performed at the site 6_3 Soil Vapor Extraction with Groundwater Extraction and Treatment Soil vapor extraction (SVE) has proven effective in reducing VOCs and certain semi-volatile compounds in soil. In brief, air is extracted from the saturated zone. If necessary,the effluent air can be treated using a variety of vapor.treatment options. SVE performed in conjunction with groundwater extraction and treatment is even more effective. A dedicated pump is placed in a groundwater monitoring well and groundwater is extracted 24 hours a 'day, treated, and then discharged. The extraction of the groundwater effectively lowers the groundwater 'elevation exposing impacted soils,which can be remediated by SVE. SA22493\n:pons\CAP.doc 7