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GeologkOf 7CCWCS 11M Page 3 Interim Remedial Action Plan ..r Project No.723.2 March 7,2005 b� vacuum could be achieved at a distance of.46 feet from the extraction point (from EW-1 to MW-5). '--' r 2) GTI estimated that approximately 485 lbs. or 173 gallons of petroleum hydrocarbons were removed by vapor extraction during the week long test. This amount includes hydrocarbons removed from groundwater during the liquid ring pump separation process. As shown in Table 2, the liquid ring pump vapor/liquid separation process reduces the contaminant concentrations in the extracted groundwater. The groundwater samples taken after the liquid ring pump on the treatment trailer show an order of magnitude reduction for BTEX and TPH-G constituents. 3) A sustained pumping rate of.3 gpm was achieved in well EW-1 for several days. This well demonstrates that the site's soils are conducive to groundwater extraction technology. If the pumping was continued then the drawdown would produce a cone of depression further exposing soil to be influenced by vapor extraction. 4) The amount of contamination removed by groundwater extraction during the test is estimated to be approximately 16.06 lbs. or 5.71-,gallons of petroleum hydrocarbons 5) Wells VEW-1 & VEW-2 were completed with 20 feet of screen below the water table. These wells could be utilized in conjunction with well EW-1 for additional groundwater extraction capacity as well as vapor extraction. 6) The current well configuration should be adequate to support a remedial design plan to address the residual contamination in soils and shallow groundwater at the site. However, the contamination present in off site, down-gradient well MW-208 indicates that the aquifer is impacted in its screened level of 76 feet bgs (or approximately 39 feet below the water table). An additional groundwater extraction well would be needed to remove water from this depth as no on site well intercepts this interval. 7) The five foot sampling methodology utilized at this site may have failed to intercept lithologic units of greater hydraulic conductivity. In addition, the plume remains undefined down gradient of the MW-8/-108/-208 well cluster. Additional site characterization is needed to develop a full scale groundwater remedial system. Field evidence recorded during borehole installation indicates that contamination is present on the adjacent property across N. El Dorado Street — an active Shell service station. The data suggest that a co-mingled plume situation may exist and GTI recommends that the SJC PHS/EHD files be reviewed for the adjacent site to obtain well construction information and historical contaminant data. The file review will help clarify the site conceptual model. Because the lateral extent of the plume down gradient of the MW-8/108/208 well cluster has not been defined as noted in 7) above, the SJC PHS/EHD will probably require additional site definition. But concurrent with planning and executing additional site characterization, GTI recommends that interim remediation be implemented before this plume migrates any further and the cost for cleanup continues to increase. Interim remedial action can be initiated by installing a high vacuum dual phase extraction unit (as utilized during the pilot test) to address the on site contamination. Extraction should be performed on the existing wells EW- 1, VEW-1 & VEW-2 and a new extraction well set at a deeper depth (EW-2). The treatment system should include air stripping and granular activated carbon filtration of extracted