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ti i Mr Travis Bryant Project 22605-101 01 August 12, 1997 Page 2 hydrocarbon constituent detected in groundwater is gasoline The groundwater plume has not been delineated, but it extends downgradient 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 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) in 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 ppb and 33 ppb, respectively GROUNDWATER MONITORING SECOND QUARTER 1997 • On May 19, 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 Based on groundwater data obtained from adjacent properties, the groundwater flow direction has generally been toward the northeast Groundwater samples were collected from monitoring wells MW-1 and MW-2 and were analyzed at Columbia Analytical Services Laboratories in San Jose, California The groundwater samples were analyzed for TPHG and for benzene, toluene, ethylbenzene, and total xylenes using U S Environmental Protection Agency Modified Methods CA/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 7,300 ppb and 100 ppb, respectively Benzene was detected in monitoring well MW-1 at a concentration of 1,200 ppb, but was below laboratory detection limits in well MW-2 Results of laboratory analyses are presented in the table 0 SAC\lV\PJZ2605\2605 10 10 ICS-97\prz 1