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C Ms. Lori Duncan A M B R I A September 9,2005 Assuming 7 years of SVE/AS operation and using the estimated average annual operational cost, the total SVE/AS operational cost will be$280,000. Groundwater monitoring is estimated to cost approximately $8,500 per year. Assuming 7 years of groundwater monitoring during SVE/AS and 3 years of groundwater monitoring following SVE/AS is required to reach clean-up levels, the total cost for groundwater monitoring is $85,000. The total estimated cost for this alternative is$575,000. SVE/AS will reduce groundwater concentrations by volatilizing hydrocarbons out of groundwater,but hydrocarbons in saturated soils will continue to dissolve into groundwater. Due to the continual dissolution of hydrocarbons in saturated soils into groundwater, operation of a © SVE/AS system will typically last longer than other active remedial alternatives. Recommendation: Although technically feasible, SVE/AS limitations have been identified in remediating hydrocarbons in saturated soils. Additionally, SVE/AS is not the most cost-effective remedial alternative. Therefore, Cambria does not recommend that SVE/AS be implemented at the site. DPE DPE is the process of applying high vacuum through an airtight well seal to simultaneously extract soil vapors from the vadose zone and groundwater from the saturated zone. The vacuum created by DPE can increase the groundwater yield from wells completed in low permeability formations. In addition, residual TPHg and BTEX in unsaturated and dewatered soils within the influence of the vacuum may be removed in the vapor phase. Groundwater extraction may provide hydraulic control of the hydrocarbon plume and reduce contaminant migration. Furthermore, extended dewatering of the saturated zone combined with vapor extraction can remediate residual hydrocarbons below the water table in the source area. A positive displacement blower or liquid-ring pump may be used to create the higher vacuum needed to extract groundwater and soil vapors simultaneously. Alternatively, a submersible groundwater pump can be used to extract groundwater, while a blower or liquid-ring pump is used solely to extract soil vapors. The extraction device is supplemented with a soil vapor treatment (oxidizer or carbon adsorption) system. Extracted groundwater can be treated and discharged to the local sanitary sewer or storm drain with the appropriate permits or off-hauled to a disposal facility. Feasibility and Cost-Effectiveness: Designing, permitting, and installing a DPE system at the site would cost an estimated $200,000 to $250,000. This estimate is based upon installing four extraction wells, installing underground piping, constructing a treatment compound, and installing the required equipment including an oxidizer for vapor treatment and GAC vessels for water treatment. DPE system operational cost for the first year is estimated at $75,000. The average annual operational cost is estimated at $50,000. DPE operation is assumed for a 16