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' 15 June 1999 • AGE-NC Project No 98-0450 ' Page 8 of 27 ' 4 14 Estimated Cost In general, the cost for excavation, disposal, and backfill activities ranges from $170,000 to ' $210,000 Cost associated with confirmation soil sampling and analysis, would range from $15,000 to$20,000 The total cost for soil removal, disposal, and backfilling activities are estimated to cost from $185,000 and $230,000 42 SOIL VAPOR EXTRACTION ' Soil vapor extraction (SVE) is a well accepted method of treatment for hydrocarbon-impacted soil , ' and has been used at various UST sites with an excellent rate of success The method is most effective on volatile hydrocarbons in permeable soil ' 4 2 1 Principles For most SVE systems, a vacuum blower is used to volatilize 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 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 the carbul etor system of theengine ' and mixes the vapor with air prior to 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 greatly increase ' expenses as vapor concentrations decrease below levels normally required for combustion Typically, internal combustion engines work effectively where in-situ hydrocarbon concentrations approach the 40,000 parts per million by volume (ppmv) required for peak performance of the ' engine As concentrations decrease below 20,000 ppmv, supplemental fuel is required for maximum hydrocarbon destruction Monitoring of supplemental fuel requirements Lan become burdensome Another disadvantage of these systems is the noise generated by the engine, however, this can be mitigated by placing the unit inside an enclosure A carbon-canister system operates by routing hydrocarbon vapor through activated carbon filters ' where adsorption of hydrocarbons onto carbon takes place, removing the hydrocarbons from the vapor stream. This type of system works best for low concentrations of hydrocarbons and becomes expensive when high concentrations of hydrocarbon vapor necessitate frequent canister replacement Advanced CcoEnvironmental,Inc .1 i