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i • • directly remediate contaminated groundwater beneath the site, and (e) is very expensive at properties where USTs are still in service Given the disadvantages of this method, this method is not seen as a viable remediation alternative for the site at this time 4.2 Air Stege and Sal Vaj or_ Extraction Soil vapor extraction remediation entails the removal of hydrocarbons from the ground in-situ These vapors are removed through vapor extraction wells placed in contaminated areas The vapors are removed through wells by a vacuum source and abated by one of several methods such as an internal combustion (IQ engine, a thermal oxidizer or carbon absorption Since the lithology of the sediments beneath the site is primarily sand of relatively high permeability, soil vapor extraction may be ideally suitable for remediation of contaminated soil in the source area The advantages of this form of remediation is that (a) It removes contamination from the ground which could act as a source for groundwater contamination, (b) it has a relatively low impact on the business at the site, (c) it is a proven . and effective technology, especially in high permeability soil, (d) it h a s relatively low impact on surrounding properties if designed to operate quietly, and (e) is generally less expensive than overexcavation when large volumes of soil must be remedied at an operational facility Vapor extraction technology is often used in conjunction with air sparging Air sparging is the infection of air beneath the water table, generally at the bottom of an unconfined aquifer Air bubbles rise through the saturated zone volatilizing hydrocarbons and forcing the hydrocarbons into the vadose (unsaturated) zone The hydrocarbons are then subsequently removed from the vadose zone using soil vapor extraction The addition of air through air sparging may also stimulate bioremediation Advantages of air sparging is that (a) it is relatively inexpensive, (b) it is a proven and effective technology, especially in high permeability soil, and (c) it has relatively low impact on the operation at the site and on surrounding properties Disadvantages of air sparging are that (a) the remediation must continue for months or years to remediate the site, (b) air sparging must be used in conjunction with soil vapor extraction, (c) air sparging may not be effective on MTBE in all cases (however, ASE has had success remediating MTBE with air sparging at . other sites), and (d) air sparging may not be as effective in areas where free-floating hydrocarbons are present Frank's One Stop Remedial Action Plan — August 2001 -14-