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iDISCUSSION" 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-2 was below method reporting limits for TPHG, benzene, and total xylenes TPHG was detected in well MW-5 at a concentration of 57 1 micrograms per liter { g/I), and toluene and total xylenes were below method reporting limits TPHG and benzene were below method reporting limits in well MW-6 Total xylenes were below method reporting limits in well MW-10 MTBE was detected in wells MW-2, MW-5, and MW-10 at concentrations of 2 89 [.g/I, 4 93 µg11, and 5 95 �tg/I, respectively, using USEPA Method 8020, however wells MW-2 and MW-10 were below method reporting limits using USEPA Method 8260 The groundwater gradient and direction of groundwater flow (north to southeast) were generally consistent with previous data Groundwater elevation increased approximately 3 99 feet from the previous sampling event(December 1999) The oxygenates, tertiary butanol, MTBE, DIPS, ETBE, and TAME were analyzed to samples collected from groundwater monitoring wells MW-1 through MW-7, and MW-10 using USEPA Method 8260 Well MW-5 contained an MTBE concentration of 2 96 gg/l, respectively No other oxygenates were detected in the wells EMCON shut down the SVE system on November 24, 1997, due to low soil vapor concentrations and is currently pulsing the system on a periodic basis The SVE system remained shut down during the first quarter 2400 The air sparge system was shut down on November 24, 1997, along with the SVE system to evaluate feasible remediation alternatives Based on data and remediation technique evaluation, the air sparge system was restarted on January 20, 1998, and operated at a low flow rate for bubbling and oxygen addition to the groundwater The addition of oxygen into the groundwater will help to promote biodegradation of petroleum hydrocarbons in impacted groundwater at the site As a result of air bubbling in air sparge wells AS-1, AS-2, and AS-3, since January 1998, dissolved oxygen levels in monitoring wells MS-1(s), MS-2(s), MS-3(s), and MW-2 have increased significantly as shown in Table 5 The effects of the SVE system pulsing and air bubbling during the second quarter 2000 will continue to be monitored ARCO will transfer this project to another consultant The new consultant will begin providing services during the second quarter 2000 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 (First Quarter 2000) • Figure 2 Groundwater Elevation Contours (First Quarter 2000) • Appendix A Sampling and Analysis Procedures • Appendix B Chain-of-Custody Records and Laboratory Analysis Records • Appendix C Operation and Maintenance and Groundwater Monitoring Field Data Sheets CP\N\CamPk\DataWchiveWr-o121301Qtrly12130Q100 DOC-971at 2 IT Corporation 06/06/00