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1 ' <br /> 14 November 1995 _ <br /> AGE-NC Project No 95-0121 <br /> Page 10 of 20 , <br /> t , <br /> , <br />' 6 2 EX-SITU TREATMENT OF B PACTED SOIL <br /> Hydrocarbon-impacted soil can be excavated and treated on-site or transported off-site for disposal <br />' On-site treatment alternatives (ex-situ) include aeration, bioremediation, vapor extraction, and <br /> thermal destruction All are feasible methods for remediating sandy soil contaminated with gasoline <br /> However, increasing clay content limits the effectiveness of each method Off-site disposal generally <br />' involves the transportation of the impacted soil to a licensed treatment/disposal facility <br />' 6 2 1 EXCAVATION <br /> All of the mentioned methods of`ex-situ treatment require excavation of the impacted soil, which is <br />' generally the fastest and most effective method for soil remediation Impacted soil in the vadose and <br /> smear zones extend to a depth in excess of 30 feet bsg Therefore, soil would have to be excavated <br />' to depths greater than 30 feet (bsg) Once excavated, the impacted soil is generally stockpiled on-site <br /> for treatment or transportation for disposal If soil is treated on-site and the hydrocarbon <br /> concentrations can be reduced to concentrations set by the lead agency or to non-detectable <br /> concentrations, the soil can be used to backfill the excavation If the hydrocarbon-impacted soil is <br /> disposed of off-site, material must be imported to backfill the excavation <br /> Y <br /> 6 2 2 FEASIBILITY OF EXCAVATION <br /> Excavation of impacted soil, followed by ex-situ treatment and/or disposal is a yery effective method <br /> of remediation, non-detect (ND) can usually be achieved by excavation-since,'theoretically, all <br /> contaminated soil is removed However, excavation is usually too costly if the volume of impacted <br /> Isoil is very great or the impacted soil extends to depths requiring special equipment or extensive <br /> shoring No special equipment would be required for excavation at the subject site <br /> rThe primary disadvantage of excavation is-the disruption to'the site During excavation at the site, <br /> it is likely that present operations on the site would need to-be suspended for at least two to three <br /> weeks if off-site,disposal is selected, and as much as six to twelve months if on-site treatment and <br /> backfilling is selected Other disadvantages include air pollution control concerns, backfilling and <br /> compaction costs <br /> 6 2 3 ESTIMATED COSTS FOR EXCAVATION <br /> At the subject site, impacted soil could be excavated with traditional equipment APProximatelY <br /> 3,000 cubic yards of soil would have to excavated from the site, of which approximately 2,000 cubic <br /> } <br /> ' W <br />