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GEOMATRIX <br /> Vapor extraction would not be effective in removing residual petroleum hydrocarbons in the <br />' saturated zone Air injection to enhance in situ bioremediation or aur sparging to strip the <br /> VOCs from affected groundwater would not be technically feasible since the majority of the <br /> residual petroleum hydrocarbons are adsorbed to the laterally extensive clay/silt layer beneath <br /> the site In addition, the clay/silt layer might promote lateral migration of vapor containing <br />' VOCs beneath the layer as a result of the air injection or air sparging The uncertainty in the <br /> lateral migration of vapor containing gasoline constituents in the unsaturated zone would be <br /> difficult to control and might pose potential health and safety risks to the site <br /> 6.0 CONCLUSION AND RECOMMENDATIONS <br />' Based on the data and the evaluation, the site can be classified as a low-risk groundwater case <br /> because <br />' • There is no continuing source of PHC at the site The source, (i.e , USTs and <br /> 180 cubic yards of affected soil), was removed from the site in 1988 <br /> • There is no measurable separate-phase product at the site <br /> s Confirmed results of EDB, 1213CA, and oxygenates have not been detected in <br /> samples collected from the site <br />' ® The concentrations of TPHg and BTEX appear stable in the groundwater samples <br /> collected from the existing wells <br /> • There are no known municipal or supply wells located within a 2,000-foot radius <br /> of the site <br /> 1 • The site lithology and hydrogeology are well understood <br /> 0 The limited vertical and lateral extent of affected soil and groundwater is <br />' delineated <br /> • The best available technologies, (i e , excavation, enhanced in situ bioremediation, <br />' vapor extraction, air sparging, and air injection) are not technically and/or <br /> economically feasible due to site conditions <br /> 0 The PID readings (0 to 3 ppmv) and analytical results of soil samples collected <br /> from 10 feet bgs or shallower do not indicate potential risks of vapor exposure to <br /> on-site workers In addition, the site is covered with asphalt and concrete <br /> pavement <br /> 1\KOJECI160WMA37 00016437-08 doe l 5 <br />