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DISCUSSION <br /> Results of this monitoring event indicated that levels of dissolved gasoline hydrocarbons areoc nsistent <br /> with levels detected during previous sampling events The groundwater gradient and direction of <br /> groundwater flow were also consistent with previous data Groundwater elevation decreased <br /> approximately 3 94 feet from the previous sampling event (May 1996) <br /> The SVE system is operating efficiently to reduce petroleum hydrocarbon impact to soil and <br /> groundwater A total of 1,150 pounds of TPHG was removed during the third quarter of 1996 A <br /> cumulative amount of 21,088 pounds of TPHG has been removed since commencing SVE activities (see <br /> Table 4) Figures 4 and 5 present the rate of TPHG concentration decline over time and the cumulative <br /> mass of TPHG removed over time, respectively A small increase in the concentration of TPHG was <br /> observed during this sampling event This increase in concentration is probably due to air sparging <br /> Air sparging was initiated towards the end of the first quarter and continued into the third quarter <br /> Sparging significantly increased the dissolved oxygen levels in air sparge wells AS-2 and AS-3 (see <br /> Table 5) EMCON will continue to monitor the effects of air sparging during the fourth quarter 1996 Air <br /> sparging has resulted in a small anticipated increase in influent TPHG concentration <br /> EMCON will continue to maintain and optimize the remediation system <br /> ATTACHMENTS <br /> • Table 1 Groundwater Monitoring Data <br /> • Table 2 Operational Uptime Information <br /> • • Table 3 Flow Rates and Results of Air Sample Analyses <br /> • Table 4 Extraction and Emission Rates <br /> • Table 5 Dissolved Oxygen Levels <br /> • Figure 1 Site Location Map <br /> • Figure 2 Generalized Site Plan <br /> • Figure 3 Groundwater Contour Map (September 18, 1996) <br /> • Appendix A Sampling and Analysis Procedures <br /> Appendix B Chain-of-Custody Records and Laboratory Analysis Records <br /> • Appendix C Field Data Sheets <br /> cc Elizabeth Thayer, California Regional Water Quality Control Board <br /> SACH\PJM80508051140 6CS-96\cjb 1 <br /> h <br />