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~5 • Mr Travis Bryant Project 22605-10103 August 18, 1998 Page 2 groundwater is gasoline The groundwater plume has not been delineated, but it extends downgradient (eastward) as far as Van Buren Street On February 25, 1997, an EMCON geologist observed V&W Drilling, Inc , of Rio Vista, California, drill three vertical soil borings (B-1, B-2, and B-3) Soil boring B-1 was converted to vapor extraction well VW-1, and borings B-2 and B-3 were converted to groundwater monitoring wells MW-1 and MW-2, respectively Residual hydrocarbons were detected in soil samples collected from borings B-1 through B-3 The highest concentrations were detected in soil boring B-1, drilled beneath the former UST Residual petroleum hydrocarbons were not detected in the vadose zone (0 to 215 feet below ground surface) soil borings B-2 and B-3, but were detected in the saturated zone Analytical results of groundwater indicated dissolved hydrocarbons were detected in monitoring wells MW-1 and MW-2 (EMCON, August 4, 1997) TPHG was detected in monitoring wells MW-1 and MW-2 at concentrations of 18,000 parts per billion (ppb) and 220 ppb, respectively Benzene was detected in monitoring wells MW-1 and MW-2 at concentrations of 4,400 and 33 ppb, respectively GROUNDWATER MONITORING: SECOND QUARTER 7998 On May 21, 1998, an EMCON technician was on site to measure depths to groundwater and collect groundwater samples from wells MW-1 and MW-2 for subjective and laboratory analyses Floating product was not observed in groundwater monitoring wells (see Table 1) EMCON's sampling and analysis procedures are presented in Appendix A At the time of the monitoring event, groundwater levels were 18 56 and 18 65 feet below ground surface in wells MW-1 and MW-2, respectively These levels are approximately 2 9 feet higher than the February 1998 monitoring event levels Groundwater samples were collected from monitoring wells MW-1 and MW-2 and were analyzed at Sequoia Analytical in Sacramento, California The groundwater samples were analyzed for TPHG, benzene, toluene, ethylbenzene, and total xylenes (BTEX) using U S Environmental Protection Agency (USEPA) Modified Method DHS/LOFT and 8020, respectively The groundwater samples were also analyzed for the oxygenates methyl tertiary butyl ether (MTBE), tertiary butanol, di-isopropyl ether (DIPS), ethyl tertiary butyl ether (ETBE), and tertiary amyl methyl ether (TAME) using USEPA Method 8260 (according to the California Regional Water Quality Control Board requirements) Copies of the chain-of-custody records and laboratory analysis reports are • presented in Appendix B SACC IDMS11BC11BCST0CK QW-Mma i sEmcQn Rev 0,8/18/98