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' Former Manna Pro Site <br /> Page 10 <br /> Project No 207 3 <br /> Remedial Feasibility Study <br /> • <br /> 6.0 VAPOR EXTRACTION WITH GROUNDWATER PUMPING <br /> Past work performed by Groundwater Technology Inc (GTI) in 1994 documented pilot level <br /> field-testing of a remedial concept involving simultaneous vapor extraction and groundwater <br /> pumping This work concluded that soil vapor extraction used in conjunction with <br /> groundwater pumping is a feasible method of remediation <br /> The GTI report went on to propose a conceptual remedial action plan The plan proposed <br />' that 3 groundwater extraction wells and 20 vapor extraction wells be constructed to facilitate <br /> the extraction of gasoline In concept, groundwater would be removed via the three <br /> groundwater pumping wells in order create a groundwater depression This depression is <br /> intended to prevent the escape of dissolved-phase hydrocarbons from the treatment area As <br /> a side benefit, the small decrease in groundwater level would also expose more unsaturated <br /> zone to vapor extraction The principal remedial mechanism in the GTI proposal is vapor <br />' extraction The groundwater pumping is intended principally to prevent lateral spread of <br /> contamination die to groundwater "mounding" resulting from application of a vacuum <br /> associated with vapor extraction <br /> The GTI proposal did not include any estimate of the time needed to complete the extraction <br /> process, nor did it estimate the rate of hydrocarbon removal over the life of the project <br />'• The groundwater extraction data collected b GTI make it <br /> g y apparent, that based on the recent <br /> high levels of groundwater, the reduction in elevation of groundwater due to pumping would <br /> not be adequate to expose the more intensely contaminated interval (35 to 45 feet bgs) The <br /> data also seems to clearly show that it is unlikely that this method would be substantially <br /> more effective in hydrocarbon removal than vapor extraction alone, unless the groundwater <br /> tsurface falls rather dramatically For reasons described above, this remedial method does not <br /> appear to be feasible at this time <br /> 1 <br />' 2937 Veneman Ave,#13240 Geo-Phase Environmental Inc Phone (209)569-0293 <br /> Modesto,CA 95356 Fax(209)569-0295 <br /> r <br />