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t Mr Travis Bryant Project 22605-101 01 October 30, 1997 Page 2 On February 25, 1997, an EMCON geologist observed V&W Drilling, Inc , of Rio Vista, California, drill three vertical soil bonngs (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 bonngs 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 4,400 ppb, respectively Benzene was detected in monitoring wells MW-1 and MW-2 at concentrations of 220 and 33 ppb, respectively GROUNDWATER MONITORING THIRD QUARTER 1997 On August 21, 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, Cahforrua. The groundwater samples were analyzed for TPHG and for benzene, toluene, ethylbenzene, and total xylenes (BTEX) using U S Environmental Protection Agency Modified Methods DHS/LUFT and 8020, respectively Copies of the chain-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 860 and 240 ppb, respectively Benzene was detected in monitoring wells MW-1 and MW-2 at concentrations of 130 and 20 ppb, respectively Results of laboratory analyses are presented in the table CONCLUSIONS I The typical gradient near the intersection of Charter way and Lincoln Street has generally been toward the northeast Groundwater elevations decreased approximately 0 79 foot from the previous sampling event (May 1997), and hydrocarbon concentrations in well MW-1 have continued to decrease since the • groundwater monitoring program began in March 1997 SAC\N\PJZ\2605\26051010 1 D5-97\r-jb 1