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� v <br /> A Ss OCIATES ING <br /> the airstream prevented additional measurements In addition, injection flowrates of 6 cfm <br /> resulted in detectable concentrations of helium in wells wells MW2, V W 1, MW3, and V W2 <br /> ' located 30 to 44 feet away from injection well MW1 Using the concentration of TPHg in vapor <br /> samples collected prior to the combination pilot test and the above calculations, approximately <br /> 0 89 pounds of TPHg was removed during the combination pilot test <br /> ' 4.1.3 Conclusions <br /> ons <br /> ' Vctio pilottesting performed at the site indicated that a radius of influence (ROI) of up <br /> feet was achieved with air flowrates ranging fro 8 3 to 12 2 cf and wellhead vacuums <br /> ranging 210 to 23 4 inches of mercury Air sparge clot testing performed at the site <br /> indicated that an ROI of a 1mately 30 feet was achieve with an injection flowrate of 6 cfm <br /> and an injection pressure f 6 0 to 6ps�f <br /> Vapor extraction/air sparge testing combination testing performed at the site indicated that a ROI of <br /> up to 38 feet was achieved with air flowrates ranging from 5 8 to 7 2 cfm when operated in <br />' conjunction ith air sparging The vapor extraction/air sparge testing combination testing also <br /> resulted in an ROI of approximately 38 feet was achieved with an injection flowrate of 6 cfm when <br /> operated in conjunction with air sparging <br /> The actual radius of influence for each vapor extraction well and air <br /> p sparge well will vary <br /> depending on subsurface geologic conditions, the extent and distribution of hydrocarbon-impacted <br />' soil, the effect of concurrently operating the VES/AS systems, and site-specific operating <br /> conditions of the VES/AS The effective radius of influence should be evaluated following long- <br /> term operation of the VES/AS <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 third alternative A groundwater <br />' extraction pilot test has not been completed for the second alternative A summary of each <br /> alternative is presented in the following sections <br /> 5.1 Natural Attenuation with Groundwater Monitoring <br /> Natural attenuation, also known as passive bioremediation or intrinsic bioremediation, is a <br /> passive remedial approach that depends upon natural processes to degrade and dissipate <br /> ? petroleum constituents in soil and in groundwater Through biodegradation the actual reduction <br /> of petroleum constituent mass is realized <br /> W 1625961reportslpdotcap doe 7 <br /> , J <br />