ARCHIVED REPORTS XR0008636 - Laserfiche WebLink

Home Browse Search

1 2.3 Ex-Situ Vapor Extraction Ex-situ soil vapor extraction uses slotted PVC piping within the stockpiled soil to remove volatile organic compounds (VOC) from the soil matrix, similar to ex-situ I bioremediation, only nutrients and moisture are not required A vacuum is applied to the piping, typically by means of a blower, and VOC vapors contained within soil pore spaces are extracted from the material Ex-situ vapor extraction has been shown to I effectively remove volatile, lighter-chain hydrocarbons (e g gasoline) from soil In general, the extracted vapors will require treatment, unless contaminant concentrations are low Various soil vapor treatment options include, in order of decreasing contaminant concentration thermal incineration, thermal oxidation, catalytic oxidation, carbon adsorption, and direct discharge (no treatment) The type of vapor treatment is determined by local air discharge regulations, cost, contaminant types, and concentrations 1 2.4 Incineration On Site Incineration of hydrocarbon-bearing soil at the site requires excavation of soil and contracting for a temporary soil incineration unit on site Typically, these units consist Iof a combustion chamber and a vapor-treatment system Soil is introduced into the chamber and heated sufficiently to volatilize and destroy the hydrocarbons present Fumes generated by the process may be collected and treated by various means Typically, on-site units may treat approximately 500 cubic yards of soil per day to "non-detectable" levels If the soil is treated on site it may be feasible to reclaim the material as backfill for the excavation(s) Currently, there are a limited number of units permitted in the western United States that incinerate soil Costs generally range from $70 to $110 per ton I1 3 In-Situ Methods I1 3 1 In-Situ Bioremediation In-situ bioremediation consists of creating an environment in the subsurface to allow for organic compounds to be degraded by indigenous bacteria Creation of the environment is achieved by maintaining and monitoring adequate oxygen, pH, moisture, and nutrient levels in the soil Nutrient and hydrocarbon levels in groundwater should also be monitored Oxygen levels in the soil can be maintained with the use of air spargers, oxygen spargers, air infiltration (vapor extraction or injection systems), or hydrogen peroxide infiltration To implement a bioremediation technology, the site must have soils with high intrinsic hydraulic conductivity to compensate for the decrease in hydraulic conductivity due to the increase in the bacteria population Typically, the hydraulic conductivity becomes a concern at a Ivalue less than 2 8 feet per day