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.l a . Mr Travis Bryant Project 22605-10102 January 28, 1998 Page 2 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 Based on analytical data collected from the soil borings, residual hydrocarbons were detected in soil 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 21 5 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 1n 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. FOURTH QUARTER 1997 On November 17, 1997, 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) EMCON used the data to evaluate changes in concentrations of dissolved gasoline hydrocarbons in the groundwater and changes in the gradient and direction of groundwater flow beneath the site EMCON's sampling and analysis procedures are presented In Appendix A 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 (BTE? ) using U S Environmental Protection Agency (USEPA) Modified Methods DHS/LUFT and 8020, respectively The groundwater samples were also analyzed for the oxygenates methyl tertiary butyl ether (MTBE), tertiary butanol, di-isopropyl ether (DIPE), 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 cham-of-custody records and laboratory analysis reports are presented in Appendix B The results of laboratory analyses indicated that dissolved hydrocarbons were present in the monitoring wells TPHG was detected in monitoring wells MW-1 and MW-2 at concentrations of 280 and 290 ppb, respectively Benzene was detected in monitoring wells MW-1 and MW-2 at concentrations of 56 and 48 ppb, respectively The results of laboratory analyses for the oxygenates MTBE, tertiary butanol, DIPS, ETBE, and TAME were all below laboratory detection limits Results of laboratory analyses are presented in Tables 1 and 2 • 5AC\N 1PJ212605126051010 2AB-9811baccus 1