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q1 <br /> Work Plan for Additional Subsurface Assessment and Feasibility Study—Former Unocal Station#0187 <br /> September 14,2000 <br /> ADVANTAGES <br /> 1) Low annual cost <br /> DISADVANTAGES <br /> 1) Potential liability <br /> 2) No defined protect completion/closure <br /> 3) Potential migration of contamination <br /> CONCLUSION Not a suitable approach for this site at this time <br /> OPTION#2 -GROUNDWATER PUMP AND TREAT <br /> No aquifer tests have been completed at the site Much of the groundwater occurs within silt and clay <br /> zones of relatively low permeability However, the two mayor sand horizons may have relatively high <br /> permeability <br /> COST Medium to high <br /> TIME FRAME Long term <br /> ADVANTAGES <br /> 1) Potential for hydraulic control <br /> DISADVANTAGES <br /> 1) Extracted contaminants must be disposed of separately <br /> 2) Not cost-effective or productive for zones of relatively low permeability. <br /> 3) May not clean up the source of the contamination <br /> CONCLUSION Not effective remedial method for this site, more feasible methods are available <br /> OPTION 43—AIR SPARGEIVAPOR EXTRACTION <br /> Air sparging is an in situ remedial technology that reduces concentrations of volatile constituents in <br /> petroleum products that are adsorbed to soils and dissolved in groundwater This technology, which is <br /> also known as "in situ air stripping" and "in situ volatilization," involves the infection of contaminant-free <br /> air into the subsurface saturated zone, enabling a phase transfer of hydrocarbons from a dissolved state to <br /> a vapor phase The air is then vented through the unsaturated zone Air sparging is most often used <br /> together with soil vapor extraction(SVE), but it can also be used with other remedial technologies When <br /> air sparging is combined with SVE, the SVE system creates a negative pressure in the unsaturated zone <br /> through a series of extraction wells to control the vapor plume migration <br /> COST Moderate to high <br /> T1ME FRAME Long term due to low hydrocarbon extraction rate <br /> 240042 08 7 <br />