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k + <br /> - CreologicalTeckncicrfiu. <br /> Dual Phase Extraction Pilot Test Report Page; 12 <br /> Project No.723.2 <br /> { , November 5,.2004 <br /> 2. GTT estimated that approximately 485 lbs. or 173 gallons of petroleum hydrocarbons <br /> were removed by vapor extraction during the week long test. This amount includes <br /> Lhydrocarbons removed from groundwater during the liquid ring pump separation <br /> process. As shown in Table 2 the liquid q d nng pump vapor/liquid separation process <br /> reduces the contaminant concentrations in the extracted groundwater. The <br /> L groundwater samples taken after the liquid ring pump on the treatment trailer show an ' <br /> + order of magnitude reduction for BTEX and TPH-G constituents. <br /> 3. A sustained pumping rate of 3 gpm was achieved in well EW-1 for several days. This <br /> L well demonstrates that the site's soils are conducive to groundwater extraction <br /> technology. If the pumping was continued then the drawdown would produce a cone <br /> of depression further exposing soil to be influenced by vapor extraction. <br /> FI! <br /> 4. The amount of contamination removed by groundwater extraction during the test is <br /> estimated to be approximately 16.06 lbs. or 5.71 gallons of petroleum hydrocarbons <br /> I` 5. Wells VEW-1 & VEW-2 were completed with 20 feet of screen below the water <br /> table. These wells could be utilized in conjunction with well EW-1 for additional <br /> groundwater extraction capacity as well as vapor extraction. <br /> 6. The current well configuration should be adequate to support a remedial design plan <br /> " . to address the residual 'contamination in soils and shallow groundwater at the site. <br /> However, the contamination present in off site, down-gradient well MW-208 <br /> + indicates that the aquifer is impacted in its screened level of 76 feet bgs (or <br /> approximately 39 feet below the water table). An additional groundwater extraction <br /> well would be needed to remove water from this depth as no on site well intercepts <br /> this interval. <br /> (� 7. The five foot sampling methodology utilized at this site may have failed to intercept <br /> lithologic units of greater hydraulic conductivity. In addition, the plume remains <br /> undefined down gradient of the MW-8/-108/-208 well cluster. Additional site <br /> characterization is needed to develop a fall scale groundwater remedial system. <br /> GTI makes the following recommendations: <br /> 1. Perform interim remedial action by installing a high vacuum dual phase extraction <br /> unit to address the on site contamination. Extraction should be performed on the <br /> existing wells EW-1, VEW-1 & VEW-2 and a new extraction well set at a deeper <br /> depth as yet to be determined (refer to item #3 below). The treatment system should <br /> include air stripping and carbon filtration of extracted groundwater to be discharged <br /> to City of Stockton public treatment works. The placement of these components at <br /> the site will be problematic due to limited space. <br /> 2. Perform several CPT borings to further define the lithology at the site. A sand unit <br /> was identified in boring MW-101 at 70 - 77 feet bgs and determining if this unit is <br /> present as a preferential pathway to MW-208 is warranted. CPT methodology, in <br /> conjunction with SimulprobeTM technology, has been requested by SJC PHSIEHD in <br /> the past at this site. In GTI's opinion the use of CPT technology is warranted to fill <br /> - data gaps for site lithology. However, GTI does not feel that SimulprobeTM <br /> technology will be effective in deeper, heaving sands at.the site and recommends that <br /> 4J <br />