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1 1 20 March 1996 AGE-NC Project No 95-0130 Page 12 of 23 ' 6 1 5 ESTIMATED COST OF SOIL VAPOR EXTRACTION The costs for vapor extraction systems vanes greatly, depending upon the particular system utilized for the destruction of the extracted hydrocarbon vapors (thermal destruction, carbon adsorption, etc) For the TFS site, the cost to operate, maintain, monitor and sample an SVE system will likely ' average between$75,000 to $125,000 per year Rental/lease costs will likely comprise approximately $35,000 to $60,000 per year Maintenance costs can vary significantly, depending upon the specific ' unit utilized ' 62 EX-SITU TREATMENT OF "ACTED SOIL Hydrocarbon-impacted soil can be excavated and treated on-site or transported off-site for disposal ' On-site treatment alternatives (ex-situ) include aeration, bioremediation, vapor extraction, and thermal destruction All are feasible methods for remediating sandy soil contaminated with gasoline However, increasing clay content limits the effectiveness of each method Off-site disposal generally involves the transportation of the impacted soil to a licensed treatment/disposal facility 6 2 1 EXCAVATION All of the mentioned methods of ex-situ treatment require excavation of the impacted soil, which is ' generally the fastest and most effective method for soil remediation Impacted soil in the vadose and smear zones extends to a depth in excess of 55 feet bsg, therefore, soil would have to be excavated to depths greater than 55 feet bsg Once excavated, the impacted soil is generally stockpiled on-site ' for treatment or for transportation for disposal If soil is treated on-site and the hydrocarbon concentrations are reduced to concentrations set by the lead agency or to non-detectable concentrations, the soil can be used to backfill the excavation If the hydrocarbon-impacted soil is ' disposed of off-site, material must be imported to backfill the excavation ' 6 2 2 FEASIBILITY OF EXCAVATION Excavation of impacted soil, followed by ex-situ treatment and/or disposal is a very effective method of remediation, non-detect (ND) can usually be achieved by excavation since, theoretically, all contaminated soil is removed However, excavation is usually too costly if the volume of impacted soil is very great or the impacted soil extends to depths requinng special equipment or extensive shoring Special equipment would be required for excavation at the subject site The pnmary disadvantage of any remediation scheme involving excavation is the disruption to the site During excavation at the site, it is likely that present operations on the site would need to be