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treatment, operation, and analytic costs The prevalence of low permeability materials in the unsaturated zone may limit the effectiveness of SVE Recommendation Because MTBE is a contaminant of concern and the low permeability conditions of the unsaturated soil and the capillary fringe at the site, SVE is not recommended as a remedial alternative Combined Soil Vapor and Ground Water Extraction This remedial technique uses GWE to enhance the vapor extraction of hydrocarbons in unsaturated soil, the capillary fringe and saturated soil For the same reasons discussed above, this alternative is not considered cost effective for this site Soil Vapor Extraction 1 Air Sparging Air sparging involves injecting ambient air via wells screened below the water table to volatilize aqueous-phase hydrocarbons Air sparging also supplies oxygen to indigenous microbes and stimulates naturally-occurring hydrocarbon biodegradation Hydrocarbon vapors are then typically captured and treated by a SVE system This technique is most effective for sites with hydrocarbons in permeable materials where the injected air is easily captured by SVE The low permeability materials in the unsaturated zone at the site should limit the effectiveness of air injection and vapor capture by an air sparging/SVE system With limited vapor capture, air sparging could cause hydrocarbon migration Air sparging is not an effective direct treatment for MTBE due to its high solubility Cost Effectiveness Since air sparging with SVE would require the installation of several air sparge wells, significant permitting, equipment installation, vapor treatment, operation, and analytic costs, and because SVE and air sparging are not effective for MTBE, this remediation technology is not as cost effective as other evaluated alternatives Recommendation Cambria does not recommend this remedial alternative at this time if research shows that this alternative is effective in the future, it will be evaluated at that time Bioventing 1 Biosparging Bioventing and biosparging are other new remedial techniques for cost effectively remediating site soil and ground water This technique involves injecting low flow rates of air beneath the water table in site wells that are screened both above and below the water table The injected air first stimulates hydrocarbon biodegradation in ground water, and then enters the vadose zone at low flow rates to encourage soil remediation Unlike air sparging, where air is injected directly into the formation at high rates to strip hydrocarbons, biospargzng uses low flow injection rates to minimize the potential for hydrocarbon vapor migration 240-0783 24