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CV ATc A S S O C I A T E S I N C LW ♦ Criterion 7: Of all the alternatives, the passive remediation approach is the easiest to implement. Groundwater monitoring activities would continue to ensure natural attenuation is occurring. When concentrations have reduced to levels acceptable to the regulatory agencies or an apparent decreasing trend is evident, a closure plan will be submitted. Well destruction permits t' would be obtained from the appropriate agencies and the wells would be destroyed by overdrilling the well casing and sand pack and pressure grouting the boring to the surface when concentrations have been reduced to an acceptable level. ♦ Criterion 8: Minimal activity would be conducted at the site. Because petroleum hydrocarbon impacted groundwater has likely migrated off-site, the impact on the community may be significant to the businesses located on the site and nearby. 5.22 Alternative 2- Dual-Phase Groundwater and Soil Vapor Extraction �. ♦ Criterion 1: This alternative has minimal health-based risks. If concentrations warrant treatment, petroleum hydrocarbons are removed from extracted groundwater and vapor prior to discharge to the municipal sewer system and the atmosphere, respectively, reducing the risk of exposure to humans. Groundwater would be monitored periodically to ensure that reduction is occurring. The potential fire or explosion hazard is minimal with a properly designed system and regularly �- scheduled monitoring and maintenance. ♦ Criterion 2: ` Dual-phase groundwater and vapor extraction would reduce the level of toxicity and volume of contaminants in the soil and groundwater to levels acceptable to regulatory agencies. In addition, this method also should reduce the potential for groundwater to become impacted with higher concentrations of petroleum hydrocarbons. ♦ Criterion 3: This alternative can be implemented within regulatory guidelines. ♦ Criterion 4: The dual-phase groundwater and soil vapor extraction alternative could be implemented with a portable remediation system utilizing the existing wells. A thermal oxidizing unit or catalytic oxidizing unit can be used initially for the treatment of off-gases but may be changed to vapor- phase carbon after concentrations are reduced. A granular-activated carbon system can be used for the treatment of extracted groundwater prior to discharge to the municipal sewer rV system. Additional costs to the client would be incurred for permitting, leasing, and mobilizing the dual-phase groundwater and vapor extraction equipment. The cost of this alternative is ..• estimated to be between$70,000 and$100,000. S:IEnvironmental162577VSCMCAPAdddoc 8