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consistent with previous data Groundwater elevation increased approximately 1 84 feet from the previous sampling event (August 1997) Per ARCO's request, oxygenates tertiary butanol, methyl tertiary butyl ether (MTBE), di-isopropyl ether, ethyl tertiary butyl ether, and tertiary amyl methyl ether were analyzed, using U S Environmental Protection Agency Method 8260, for the two monitoring wells with the highest concentrations of TPHG, benzene, toluene, ethylbenzene, and total xylenes (BTEX), and MTBE EMCON evaluated third quarter data and selected wells MW-2 and MW-5 to be analyzed for these oxygenates Well MW-5 contained 3 2 micrograms per liter of MTBE No other oxygenates were detected in the samples from wells MW-2 and MW-5 (see Table 2) The SVE system is operating to reduce petroleum hydrocarbon impact to soil and groundwater A total of 383 pounds of TPHG were removed during the fourth quarter of 1997 A cumulative amount of 25,184 pounds of TPHG have been removed since commencing SVE activities (see Table 5) Figures 4 and 5 present the rate of TPHG concentration over time and extraction rate and cumulative mass of TPHG removed over time, respectively 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 Air sparging was initiated on September 5, 1996, and continued through the first half of the fourth quarter 1997 Air sparge flow rates and DO concentrations are presented in Table 6 The DO readings were measured in the groundwater monitoring wells 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 techniques evaluation, the air sparge system will be restarted and operated at a low flow rate for bubbling and oxygen addition to the groundwater The addition of oxygen into the groundwater will enhance bioactivity at the site EMCON will continue to monrtor the effects of SVE system pulsing and air bubbling during the first quarter 1998 ATTACHMENTS: • Table 1 Groundwater Monrtonng Data • Table 2 Additional Groundwater Analytical Data • 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 Flow Rates and Dissolved Oxygen Levels • Figure 1 Site Location Map • Figure 2 Generalized Site Plan • Figure 3 Groundwater Contour Map (November 19, 1997) • Figure 4 TPHG Concentration Vs Time • Figure 5 Extraction Rate and Cumulative Mass of TPHG Removed Vs Time • 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 cc Elizabeth Thayer, California Regional Water Quality Control Board Bruce Tuter, San Joaquin Valley Unified Air Pollution Control District u SAC�N\P7U0805\08051140 8DS-97,cbell 1