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i ' 18 July 2002 AGE-NC Project No 96-0254 Page 7 of 17 511 Excavation All of the above-mentioned methods of ex-situ treatment require excavation of the impacted soil, which is generally the fastest and most effective method for soil remediation Once excavated, the Impacted soil is generally stockpiled on-site for treatment ortransported for disposal Ifsoll is treated on-site and the hydrocarbon concentrations can be 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 off-site, fill material must be Imported to backfill the excavation ' 5 1 2 Feasibility of Excavation iExcavation of Impacted soil,followed by ex-situ treatment and/or disposal is avery effective method ofremediation Theoretically,all or at least the majority of the impacted soil is removed In addition, ' longer-chain hydrocarbons are easily remediated with excavation while in-situ methods are slower or are ineffective However,excavation costs can be excessive if 1)the volume of the impacted soil is significant, or 2) the vertical extent of soil impact exceeds 20 feet or soil conditions require 1• shoring, resulting in the need for special equipment or shoring TPH-g-impacted soil on the subject site extends to depths of approximately 10 feet bsg in the vicinity of the former USTs and dispenser area, and the lateral extent of impacted vadose zone soil in the vicinity of former the USTs is limited(Figure 3),making excavation a viable alternative AGE does ' not anticipate that special equipment would be required to excavate to the depth of ground water at the subject site ' A primary disadvantage of excavation is the disruption of site use, the site is currently utilized as an auto dealership and space is not readily available for on-site treatment of excavated soil Other potential disadvantages Include air pollution control concerns,backfillmg and compaction costs 5 1 3 Estimated Costs For Excavation IAt the site, AGE anticipates that impacted soil could be excavated with traditional equipment Approximately 750 cubic yards of soil would have to excavated from the former USTs and I surrounding areas(Figure 7), very little "clean" overburden soil would likely need to be removed in the UST and surrounding areas Once excavated,the soil can then be treated on-site or transferred to an off-site disposal facility Replacement backfill material must be Imported if off-site disposal Iis chosen ' Advanced GeoEnvironmennl,Inc