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C A M B R I A Ms.Lori Duncan September 9,2005 Feasibility and Cost-Effectiveness: Natural attenuation is a fairly effective means of remediating TPHg and benzene, which are the primary CDCs. It is also very cost effective since it allows hydrocarbons to degrade naturally and does not require active remediation. Natural attenuation of hydrocarbons to the specified clean-up levels would take a significantly long time. Monitoring (including secondary indicators), sampling, and reporting costs for monitored natural attenuation are estimated at approximately $9,500 per year. Assuming that 20 years of groundwater monitoring would be required to reach clean-up levels, the total monitoring cost for this alternative is $190,000. To verify soil clean-up, confirmation soil borings would be required. The cost of four confirmation soil borings is estimated at $10,000. The total cost for this alternative would be$200,000. © Recommendation: While natural attenuation may be a cost-effective alternative, other active remedial alternatives can more readily remediate the soil and groundwater. MNA also does not address hydraulic control. While we do not recommend monitored natural attenuation at this time,this remedial alternative may be appropriate in the future as a final remedial approach. In-Situ Chemical Oxidation Injection of hydrogen peroxide can reduce hydrocarbon mass through in-situ chemical oxidation in two ways. In the presence of metals that are commonly found in the subsurface, the chemical reaction known as Fenton's Reagent produces a hydroxyl radical that is a strong oxidizer and ultimately oxidizes hydrocarbons to water and carbon dioxide. This reaction is strongly exothermic and results in increased soil and groundwater temperatures when used in-situ. Additionally, after introducing the solution into the subsurface, it also produces elevated DO concentrations in groundwater that can accelerate naturally occurring hydrocarbon biodegradation. The combination of chemical hydrocarbon oxidation within the treatment zone and enhanced biodegradation as DO migrates in groundwater away from the injection area can rapidly reduce hydrocarbon mass. One method to apply hydrogen peroxide to a well would be to use a siphon pump and allow the hydrogen peroxide to infiltrate into the aquifer. Following the addition of the hydrogen peroxide, a slug of tap water would be added to the well to help facilitate hydrogen peroxide infiltration into the aquifer. The amount of hydrogen peroxide and tap water added to each well would be based on the well diameter, depth to groundwater, water temperature, and soil permeability. Multiple applications are usually required. To obtain background values, "sentry"wells would be monitored for DO prior to initiating hydrogen peroxide injection. Once hydrogen peroxide injection is initiated, DO levels would be monitored routinely in the treatment wells and sentry wells. Monitoring of bioparameters and petroleum constituent concentrations would be conducted to determine the effectiveness of the hydrogen peroxide treatment. 13