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it (t DISCUSSION Results of this monitoring event indicate that concentrations of dissolved gasoline hydrocarbons in wells MW-1 through MW-7 and MW-10 are consistent with levels detected in previous sampling events, with the following exceptions Well MW-1 was below method reporting limits for benzene TPHG and benzene concentrations in well MW-2 decreased to 79 1 micrograms per Mer (µg11) and 4 25 FEg/l, respectively, and ethylbenzene was below method reporting limits MTBE was detected in well MW-10 at a concentration of 9 08 gg/I using USEPA Method 8020, but was below method reporting limits using USEPA Method 8260 The groundwater gradient and direction of groundwater flow (north-northeast to southeast) were generally consistent with previous data Groundwater elevation increased approximately 1 84 feet from the previous sampling event (September 1999) The oxygenates, tertiary butanol, MTBE, DIPE, ETBE, and TAME were analyzed in samples collected from groundwater monitoring wells MW-1 through MW-7, and MW-10 using USEPA Method 8260 Wells MW-2 and MW-5 contained MTBE concentrations of 4 12 Rg/1 and 2 68 �Lg/l, respectively No other oxygenates were detected in the wells ATTACHMENTS • Table 1 Groundwater Monitoring Data • Table 2 Groundwater Analytical Results for Oxygenates • Table 3 Operational Uptime Information of the Soil Vapor Extraction System • Table 4 Flow Rates and Results of Air Sample Analyses • Table 5 Extraction and Emission Rates • Table 6 Air Sparge/Air Bubbling Flow Rates and Dissolved Oxygen Levels • Figure 1 Groundwater Analytical Summary (Fourth Quarter 1999) • Figure 2 Groundwater Elevation Contours (Fourth Quarter 1999) • Appendix A Sampling and Analysis Procedures • Appendix B Cham-of-Custody Records and laboratory Analysis Records • Appendix C Operation and Maintenance and Groundwater Monitoring Field Data Sheets I Cf'1C ICommoa\QMR1ARC014thQ94121300499 DOC-98\sg i IT Corporation 02/07/00