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ge <br /> A S S O C I A T E S I N C <br /> cfin in addition to the air for a total flowrate of 6 cfin After 80 minutes of operation, helium was <br /> detected in well VW-5d but no helium was detected in well VW-4, seven feet away It was <br /> deterrmned that the injected air and helium were channeling through the subsurface to well VW- <br /> 5d At the direction of Mr Wong, the air sparge test was terminated to prevent the migration of <br /> the plume to the north <br /> Samples were submitted under cham-of-custody to Sequoia Analytical (FLAP #1210) and <br />' analyzed for TPHg and BTEX <br /> 4.4.2 Results <br /> Results and field readings from the short-term air sparge test performed on June 30, 1999 are <br /> summarized in Table 7 and contained in Appendix E <br />' Laboratory results of the groundwater samples collected from MW-1 before and after the test <br /> indicated that petroleum hydrocarbons increased during the test An injection rate of 4 cfin was <br /> attainable using two small air compressors Positive pressure was observed in well approximately <br /> t 20 feet away from the injection point, with the highest measurements in well VW-5d Helium was <br /> also detected in this well at 18% <br /> 4.4.3 Conclusions <br /> The helium detected in well VW-5d, 17 feet from the sparge well but not in VW-4, 7 feet from <br /> the sparge well indicated a preferential airflow pathway The elevated pressure measured in well <br /> VW-5d supports this conclusion <br /> 5.0 REMEDIAL ALTERNATIVES <br /> Based on the results of previous investigations, ATC has considered three remedial alternatives <br /> for soil and groundwater Soil and groundwater remedial alternatives include natural attenuation <br /> with groundwater monitoring, groundwater extraction with in-situ vapor extraction, and air <br /> sparging with in-situ vapor extraction The first alternative is a passive approach to site <br /> remediation and pilot testing has been completed for the second and third alternatives A <br /> summary of each alternative is presented below <br /> 5.1 Natural Attenuation with Groundwater Monitoring <br /> Natural attenuation, also known as passive bioremediation or intrinsic bioremediation, is a passive <br /> remedial approach that depends upon natural processes to degrade and dissipate petroleum <br /> constituents in soil and in groundwater Through biodegradation the actual reduction of <br /> petroleum constituent mass is realized <br /> Several detailed field studies have been performed examining indicators of intrinsic bioremediation <br /> and identify factors which significantly effect the rate and extent of bioremediation (Buscheck and <br /> W 162574 01\pilot-fs report doc 8 <br />