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Thrifty Oil Co Station # 172 for the past several years from approximately 50 feet below surface grade to 42 feet below surface grade A summary of historical groundwater laboratory analytical results are presented in Table 1, and a benzene groundwater isoconcentration plume map is presented in Figure 8. The table indicated that groundwater concentrations have fluctuated on site with a majority of this occurring in the Vicinityof MW-11 Figure 8 indicates that the plume is confined to the site, due to the outer wells being either ND or very low hydrocarbon concentrations 6.0 REMEDIAL ALTERNATIVES The following remedial alternatives have been evaluated as options to remediate hydrocarbon affected soil and groundwater beneath the site 6.1 No Action This alternative is no-action and allow remaining hydrocarbons in soil to degrade naturally The NO-ACTION alternative is not viable for this site because concentrations generally exceed allowable levels for petroleum hydrocarbons in soil and groundwater S6.2 Excavation and Landfill Disposal Hydrocarbon impacted soil remains beneath the new tanks at depths ranging from 20 to 55 feet below surface grade Excavation and removal of this contamination would involve a mayor site reconstruction effort that would, at a minimum, require removal of the existing tanks The cost of removing, handling and transporting of soil in this type of program would cost approximately $500,000 This estimate does not include site reconstruction A detailed cost breakdown is included in Attachment B These costs and interruption of business operations are considered to be prohibitive 6.3 Groundwater Removal and Soil Vapor Extraction Insitu Soil vapor extraction is a recognized and effective technology for the treatment of subsurface soil affected by volatile compounds The process facilitates the removal of hydrocarbons by continually circulating air through soil, enhancing evaporation and desorption of volatile from unsaturated soils into the vapor stream Soil vapor extraction will operate in conjunction with a groundwater removal system The purpose of the groundwater removal system is to reduce the migration of dissolved hydrocarbons in groundwater and lower groundwater elevations in order to expose hydrocarbon impacted soil to vapor extraction The cost associated with the remedial option is estimated at$170,000 A detailed cost breakdown is included in Attachment B This option best suits the specific issues related to this site and meets anticipated regulatory needs i 8