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i I REMEDIAL ACTION PLAN USA STATION#65 - LODI NOVEMBER, 1995 6.1 OPTION I - Passive Soil Remediation Passivesoil remediation relies on the principle that hydrocarbon compounds will naturally degrade or attenuate over time. Such degradation and/or attenuation can be attributed in part to metabolic and co-metabolic processes occurring between indigenous microorganisms found in soil and the hydrocarbon compounds of concern. Under proper circumstances, passive,remediation can be an appropriate choice. Sites with soils having adequate populations of hydrocarbon degrading bacteria,nutrients, and oxygen levels may be a good choice for this alternative. Additionally, sites in areas which pose little risk or threat for potential human contact may also be amenable to this alternative. Although hydrocarbon compounds observed in site soils do not appear to present a significant human or environmental health threat,regulatory acceptance is unlikely. Option I was not retained for further consideration. i � 6.2 OPTION II- Soil Vapor Extraction With Off-Gas Treatment i Soil vapor extraction (SVE) is designed to volatilize and remove TPH compounds present i beneath the Site as: • vapor in the vadose zone; ' volatile liquid phase hydrocarbon floating on the groundwater table and in { the capillary fringe; and a • to a limited degree,dissolved TPH in the groundwater. Hydrocarbons beneath the site appear to the confined to a relatively small area immediately surrounding the tank cluster; therefore, it appears that the TPH impacted zones beneath the site should be'accessible by the use of soil vapor extraction. Analytical laboratory results of soil and groundwater samples collected from previously installed wells indicate that the TPH compounds { are present as gasoline. Analytical results of soil samples collected during previous investigations have failed to detect significant concentrations of hydrocarbons; however,results of the VES testing yielded relatively high concentrations. TPH impacted soil is anticipated to extend to the water table approximately 47 to 50-bgs. Therefore,by using the wells in the area immediately surrounding the tank cluster, it should be possible effectively remediate the site using vapor extraction. 6