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C A M B R I A Ms. Lori Duncan September 9,2005 Another method to apply hydrogen peroxide to the subsurface would be to install temporary, direct-push probes to the desired depth intervals instead of using permanent groundwater monitoring wells. The hydrogen peroxide can be injected into the probes using a pump to provide maximum infiltration of the solution into the subsurface. This method can be used to remediate unsaturated soils. If this method is used, confirmation borings would be required. Feasibility and Cost-Effectiveness: Implementing hydrogen peroxide injection at the site using the siphon method would cost an estimated$35,000 to$40,000 for the first year. This estimate is C'L(� based upon installing three additional wells and/or direct-push probes to be used as injection n points in areas of remaining source material. These proposed wells and existing wells VEW-2 1` and MW-3 would be injected with hydrogen peroxide on a monthly basis for 1 year. One well © volume of 7.5% hydrogen peroxide solution would be injected per well per month. Based on monitoring data results, follow-up injections or additional injection points could be required to meet the approved groundwater clean-up goals. To verify soil clean-up,confirmation soil borings would be required. The cost of four confirmation soil borings is estimated at$10,000. Hydrogen peroxide injection may provide hydrocarbon mass reduction at a relatively low cost. The addition of a liquid solution of hydrogen peroxide to soil may potentially cause leaching of hydrocarbons in soils to groundwater. Finally, the effectiveness of hydrogen peroxide injection has been demonstrated in bench-scale studies at other sites, but the reliability and costs remain uncertain when compared to other technologies. Additionally, hydrogen peroxide injections alone would not address migration of the groundwater plume beneath the site. Recommendation: With the uncertainties regarding effectiveness, potential hydrocarbon leaching to groundwater, total costs, and the lack of hydraulic control, the potential drawbacks do not justify the estimated lower cost. We do not recommend this remedial alternative. SVE with AS SVE is a common remediation technology applied to address gasoline fuel impacts to unsaturated soil at UST sites. SVE is most effective in moderate to high permeability soils. SVE involves applying a vacuum to wells to extract hydrocarbon-bearing vapors from the vadose zone and capillary fringe area. Extracted hydrocarbons are typically treated by granular activated carbon (GAC), catalytic or thermal oxidizers, or internal combustion engines. Additionally, SVE can improve or protect groundwater quality by removing source area hydrocarbons, by encouraging hydrocarbon diffusion from groundwater, and by delivering oxygen to the subsurface. Increased oxygen concentrations can stimulate naturally occurring hydrocarbon biodegradation in soil and groundwater. SVE system components would include appropriately constructed SVE wells, vapor conveyance piping, a vapor and liquid separator, a vapor extraction device, and a vapor treatment device. The vapor extraction device (blower) would be sized based on the radius of influence and applied 14