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0 • facilitate removal by "stripping" of the volatile contaminants out of the groundwater. In addition, in biosparging, pure oxygen may be used instead of air. To apply biosparging at this site, air or pure oxygen would be injected under pressure into the groundwater in typically one -inch diameter wells or sparge points. As in air sparging, an air compressor would be required to provide the pressurized air but at a lower injection rate. Injection might also be implemented on a timer; the timed cycle would be determined based on results of respiration tests. Such tests would be conducted onsite as part of a field pilot test for the design of the full-scale treatment system. One advantage of biosparging over air sparging/SVE is that neither vapor emission control nor separated liquid handling would be needed. In addition to the sparge depth (anticipated to be more than 30 feet), the generally low air or oxygen injection rate would typically not result in driving the volatile contaminants from the groundwater into the vadose zone, as would be the case in air sparging; therefore, no soil vapor capture would be necessary. As such, no treatment or control of vapor emission and separated liquid would be required. Addition of nutrient, such as nitrate and phosphate, may be needed if oxygen alone would not be sufficient to sustain microbial biodegradation of the hydrocarbons. The requirement for nutrient supplement would be determined based on groundwater quality data from baseline and during treatment. 4.3.1 Technical Effectiveness As the organic contaminants are amenable to aerobic biodegradation, biosparging has the capability of reducing the bulk mass of TPH-g and BTEX in the groundwater. The current onsite groundwater conditions indicate low oxygen content (less than 1 milligram per liter [mg/L]) within the contaminant plume; introducing oxygen via biosparging should stimulate microbial biodegradation of the organics. As in the previous two alternatives, the presence of silty and clayey soils would limit the effectiveness of biosparging to achieve a complete removal of the hydrocarbons from the subsurface. It is expected that this process would take as much time as in the other two alternatives. The overall effectiveness of this alternative is therefore considered moderate. 4.3.2 Implementability Biosparging is easy to implement. Biosparge equipment is commercially available and simple to install. Because a biosparge system does not produce contaminated soil vapor or liquid, no additional aboveground treatment will be required. As such, permitting for air emissions or liquid discharge to POTW will not be necessary. If oxygen were to be used, a building permit for housing an oxygen generator as hazardous material might be required. Such a requirement FS -Onsite Petroleum Hydrocarbon Remediation.doc 4-6 Shaw Environmental, Inc.