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' 11 February 2003 AGE-NC Project No. 98-0520 ' Page 7 of 21 „ Another disadvantage of excavation is the disruption of site use; however, the. site is not currently 1 being utilized except as temporary storage for discarded automobiles.'Other potential disadvantages include air pollution control concerns, backfilling and compaction costs. 6.1.3. Estimated Costs For Excavation At the site, AGE anticipates thatetroleum hydrocarbon- acted soil' >10 mg could be P Y excavated with traditional equipment. Approximately 10,780 cubic yards of soil would have to ' excavated from the former USTs and'surrounding areas (Figure 5);_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 is chosen. The cost for excavation, treatment/disposal and backfilling would probably be between $100 and $200 per cubic yard, depending upon hydrocarbon concentrations. Total costs for excavation and treatment or disposal, plus permitting fees, could therefore approach $1,078,000 to $2,156,000. 10 6.2. SOIL VAPOR EXTRACTION ' Soil vapor extraction(SVE) is a well-accepted method of treatment for hydrocarbon-impacted soil and has been used at numerous sites with an-excellent rate of success. The method is most effective ' on volatile bydrocarbons in permeable soil. 6.2.1. Principles 1. For most SVE systems, a vacuum blower is used to enhance volatilization of hydrocarbons in the vadose(unsaturated)zone and draw the vapor into extraction wells screened within the contaminant plume. The hydrocarbon vapor is drawn from the wells and "treated" in one of several possible treatment units (carbon canisters, internal combustion engines, thermal oxidizers and/or catalytic oxidizers). Air injection wells may be installed outside the contaminant plume to increase air flow to,the extraction unit. An internal-combustion(IC)system draws the vapor stream into a carburetor system of the internal- combustion engine and mixes the vapor with air before undergoing combustion.. Exhaust gasses (oxides of carbon and hydrogen) are further broken down in a catalytic' converter before being emitted to the atmosphere. These systems require supplemental fuel,such as propane or natural.gas, which can become expensive as vapor concentrations decrease below levels normally required for combustion. Typically,, internal combustion engines work effectively where in-situ hydrocarbon 1 Advanced GeoEnvironmental,Inc.