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Ms Margaret Lagono,SJCPHS September 28,2004 i Dual Phase Extraction Test Report Joe's Truck Plaza,Lathrop,California Page 7 DPE Test Analysis The induced vacuum and drawdown data collected were evaluated in relation to the applied vacuum to estimate radius of influence (ROI) The effective ROI has been defined as the radial distance from a vapor extraction well at which recorded vacuum Ievels suggest that subsurface air flow occurs and is presumed to be sufficient for remediation (P C Johnson et al, 1990) For the purpose of this test, the soil vapor ROI is defined as the distance from the well at which I percent of the applied wellhead vacuum occurs, and the groundwater ROI is identified as the distance at which a minimum of 2 percent drawdown is observed compared to drawdown in the extraction well DPE Test Results Field data collected from extraction well MW-7 and from the observation wells are summarized in Tables 1 through 4 and a summary of the test results are presented below • The applied wellhead vacuum during the test ranged from 23 to 27 5 inches Hg (or approximately 312 8 to 374 inches WC), with influent soil vapor flow rates in • the range of 86 to 88 cubic feet per minute (cfm), and an average groundwater extraction rate of 7 2 gallons per minute (gpm) • Induced vacuum in the range of 0 inches WC to 0 04 inches WC was observed in only one well (MW-2), located approximately 30 feet from well MW-7 These induced vacuum observations are less than 1% of applied wellhead vacuum • The maximum groundwater drawdown in all the observation wells during the test was in the range of 0 15 to 0 37 feet The highest decrease in groundwater elevation was observed in well MWO-1X, located approximately 30 feet from well MW-7 Figure 3 illustrates the drawdown with time at the observation wells during the DPE test Greater than 2 percent drawdown was observed in wells MWO-1X and MW-2 • The influent soil vapor concentrations of MTBE were reported at 17 milligrams per cubic meter (mg/m)(June 15, 2004) and 2 9 mg/m3 (June 16, 2004) TPHG was reported at 14 mg/m3 in the influent air sample collected on June 16, 2004, while benzene was not reported any of the samples collected on June 15 and 16, 2004 (Table 2) • The influent groundwater concentrations of MTBE were reported at 90 µg/L (June 14, 2004) and 96 µg/L (June 16, 2004) TPHG or benzene were not reported in the influent groundwater samples collected June 14 and June 16, 2004 (Table 3) P Woe s Truck Plaza\Reports\DPE Testlloes Truck DPE Test Report doc 5 7-RA rus