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Current Phase of Project: Monitoring Frequency of Groundwater Sampling: MW-1 through MW-4, and VW-3 = Quarterly Frequency of Groundwater Monitoring: Quarter) Sample Date: December 14 , 1998 Is Free Product (FP) Present on Site: No FP Recovered this Quarter: NA Cumulative FP Recovered to Date: NA Approximate Depth to Groundwater: 36.61 to 38.28 Direction of Groundwater Flow: East-northeast Groundwater Gradient: 0.002 DISCUSSION: Groundwater samples were analyzed for TPHG, BTEX, and the oxygenates tertiary butanol, MTBE, D1PE, ETBE, and TAME. Results of.this monitoring event indicated that dissolved gasoline hydrocarbons were generally consistent with previous monitoring events. The groundwater gradient and direction of groundwater flow (east-northeast) were generally consistent with the previous sampling events. Groundwater elevation increased 1.96 feet from the previous sampling event (September 1998). Groundwater samples were also analyzed for the oxygenates tertiary butanol, MTBE, di-isopropyl ether, ethyl tertiary butyl ether, and tertiary amyl methyl ether using USEPA Method 8260. MTBE was detected in wells MW-1, MW-4 and VW-3 at concentrations of 22.8 t g/L, 24.1 µg/L and 43.2 µg/L, respectively. MTBE by USEPA Method 8260 was below laboratory detection limits for wells MW-2 and MW-3. In addition, tertiary amyl methyl ether was detected at a concentration of 5.11 gg/L in well VW-3. All other oxygenates were below laboratory detection limits for all wells. The discreet groundwater sample collected from well MW-1 contained TPHG, benzene, toluene, ethylbenzene, and total xylenes concentrations of 7,170 µg/L, 424 �tg/L, 16.1 µg/L,'527 rtg/L, and 848 µg/L, respectively. MTBE was below laboratory detection limits by USEPA Method 8020, however, USEPA Method 8260 detected MTBE at a concentration of 31.4 µg/L. All other oxygenates were below laboratory detection limits for well MW-1. ATTACHMENTS: • Table 1 Groundwater Monitoring Data • Table 2 Groundwater Analytical Results for Oxygenates • Figure 1 Site Location Map • Figure 2 Groundwater Analytical Summary (Fourth Quarter 1998) • Figure 3 Groundwater Elevation Contours (Fourth Quartet 1998) • Appendix A Sampling and Analysis Procedures • Appendix B Laboratory Analysis Reports and Chain-of-Custody Records • Appendix C Field Data Sheets CP1H:1ARC012186IQTRLY12186Q498,DOC-981Esg:1 � e