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AMBRIA same as the September 2003 event, except pressure transducers were not used for monitoring groundwater levels and barometric pressure readings were not collected A total of 5,371 gallons of groundwater were extracted from MW-4 over 5,953 minutes (99 2 hours) The flow rate averaged 0 90 gpm Approximately 1 7 pounds of MTBE were removed The initial groundwater sample collected from MW-4 on October 27 contained 9,000 ppb MTBE and 94,000 ppb TBA The subsequent groundwater samples collected from MW-4 on October 29 contained 47,000 ppb MTBE and 39,000 ppb TBA The final groundwater samples collected from MW4 on October 31 contained 30,000 ppb MTBE and 29,000 ppb TBA Certified analytical reports are provided in Appendix A December 2003 GWE Event. Cambria conducted the third batch GWE event on well MW-4 from December 1 through 5, 2003 The GWE equipment and procedures for this event were the same as the October 2003 event A total of 4,801 gallons of groundwater were extracted from MW-4 over 6,015 minutes (100 3 hours) The flow rate averaged 0 80 gpm Approximately 15 pounds of MTBE were removed The initial groundwater sample collected from MW4 on December 1 contained 10,000 ppb MTBE and 97,000 ppb TBA The final groundwater samples collected from MW-4 on December 5 contained 39,000 ppb MTBE and 25,000 ppb TBA Certified analytical reports are provided in Appendix A Conclusions- The GWE data suggest that interim remediation was effective Approximately --19,850 gallons of groundwater has been extracted, removing 8 04 pounds of MTBE''l;he second quarter 2004 groundwater contour/chemical concentration map`, showing thee-current MTBE concentrations in all monitoring wells is included as Figure 3 Figure 4 presents a graph of MTBE and TBA concentrations in monitoring well MW-4 versus time The MTBE concentrations in well MW-4 have decreased approximately two orders of magnitude since the outset of GWE Similar decreasing MTBE concentration trends are observed in other source area monitoring wells and piezometers Figure 5 presents graphs of MTBE and TBA concentrations versus time for well MW-1 and piezometers P-1 and P-2, showing this trend of decreasing MTBE concentrations The data suggest that MTBE is being remediated b two mechanisms Mass removal b GWE<^ gg � Y Y has decreased the magnitude of the MTBE plume in the source area Additionally, it appears that natural biodegradation of MTBE is occurring TBA is a byproduct of MTBE degradation 0955 7