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• Ms Margaret Lagorio,SJCPHS September 28,2004 Dual Phase Extraction Test Re ort Joe's Truck Plaza,Lathrop,California Page 8 • Based on soil vapor flow rates and concentrations, the average soil vapor mass extraction rates for TPHG, benzene, and MTBE were estimated to be approximately 0 11 pounds per day (lbs/day), less than 0 001 lbs/day, and approximately 0 02 lbs/day, respectively (Table 4) • Based on the analytical results of influent groundwater samples and the average groundwater extraction rate of 7 2 gpm, the average mass extraction rates for TPHG, benzene, and MTBE were estimated to be less than 0 004 lbs/day, 0 00004 lbs/day and 0 008 lbs/day, respectively DISCUSSION AND RECOMMENDATIONS The purpose of the test was to evaluate the performance of DPE and its viability to be used as a long-term remedial alternative to mitigate the subsurface petroleum hydrocarbon impact DPE resulted in good groundwater and soil vapor extraction rates Since induced vacuums greater than 1 percent of the applied vacuum were not observed during the test, soil vapor ROI could not be established Based on drawdowns observed in wells MWO-1X, MW-2, and MW-1, the ROI for groundwater extraction is estimated to be approximately 30 feet The influent concentrations of petroleum hydrocarbons and fuel oxygenates in both extracted groundwater and soil vapors were relatively low, resulting in low mass extraction rates Given the groundwater and soil vapor flow rates, DPE appears to be a technically viable remedial alternative However, due to the low concentration of petroleum hydrocarbons and resulting low mass extraction rates, DPE is not a cost effective remedial alternative LIMITATIONS This report was prepared in general accordance with accepted standards of care that existed at the time this work was performed No other warranty, expressed or implied, is made Conclusions and recommendations are based on field observations and data obtained from this work and previous investigations It should be recognized that definition and evaluation of geologic conditions is a difficult and inexact art Judgments leading to conclusions and recommendations are generally made with an incomplete knowledge of the subsurface conditions present More extensive studies may be performed to reduce uncertainties This report is solely for the use and information of our client unless otherwise noted �i P Woe's Truck Plaza\Reports\DPE TestUoes Truck DPE Test Report doc 5TRA W5