ARCHIVED REPORTS XR0009959 - Laserfiche WebLink

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DISCUSSION The results of this monitoring event indicated that levels of dissolved gasoline hydrocarbons are consistent with levels detected during previous sampling events The groundwater gradient and direction of groundwater flow were also consistent with previous data Groundwater elevation increased approximately 2 30 feet from the previous sampling event (September 1996) The SVE system is operating efficiently to reduce petroleum hydrocarbon impact to soil and groundwater A total of 1,183 pounds of TPHG was removed during the fourth quarter of 1996 A cumulative amount of 22,271 pounds of TPHG has been removed since commencing SVE activities (see Table 4) Figures 4 and 5 present the rate of TPHG concentration over time and the cumulative mass of TPHG removed over time, respectively A small increase in the concentration of TPHG and benzene was observed dunng this sampling event This increase in concentration is probably due to air sparging Air sparging was initiated towards the end of the first quarter and continued into the fourth quarter Air sparge flow rates and dissolved oxygen concentrations are presented in Table 5 EMCON will continue to monitor the effects of air sparging during the first quarter 1997 Air sparging has resulted in an increase in influent TPHG concentration EMCON will continue to maintain and optimize the remediation system ATTACHMENTS • Table i Groundwater Monitoring Data • Table 2 Operational Uptime Information • Table 3 Flow Rates and Results of Air Sample Analyses • Table 4 Extraction and Emission Rates • Table 5 Air Sparge Flow Rates and Dissolved Oxygen Levels • Figure 1 Site Location Map • Figure 2 Generalized Site Plan • Figure 3 Groundwater Contour Map (November 26, 1996) • Figure 4 TPHG Concentration vs Time • Figure 5 Cumulative TPHG Removed vs Time • Appendix A Sampling and Analysis Procedures • Appendix B Chain-of-Custody Records and Laboratory Analysis Records • Appendix C Field Data Sheets cc Elizabeth Thayer, California Regional Water Quality Control Board I I SA(-\N\080"8051140 6US-97Nprz I