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Beacon Station No 641 June 15, 2000 <br /> Stockton. California Results of Additional Subsurface Investigation <br /> Soil samples collected from the monitoring well MW-6, MW-7 and MW-8 borings at depths <br /> of 40 and 55 feet bsg were selected for analyses No TPHg or BTEX compounds were <br /> reported in soil samples collected from the monitoring well MW-6, MW-7 and MW-8 <br /> bonngs A concentration of 0 089 ppm MTBE was reported in the 55-foot soil sample from <br /> monitoring well MW-6 No other MTBE concentrations were reported in the soil samples <br /> from the monitoring well bonngs <br /> Analytical results of the soil stockpile sample indicate 0 019 ppm MTBE No TPHg or <br /> BTEX compounds were reported in the soil stockpile sample A total lead concentration of <br /> 6 7 ppm was also reported for the soil stockpile sample/ <br /> Analytical results of the initial groundwater sampling from monitoring well MW-6 indicated <br /> 890 ppb TPHg, 2 9 ppb ethylbenzene, 560 MTBE and 54 ppb TBA A TBA concentration <br /> of 23 ppb was reported for the initial groundwater sample collected from monitoring well <br /> MW-7 Analytical results of the initial groundwater sampling from monitoring well MW-8 <br /> indicated 810 ppb TPHg, 6 3 ppb benzene, 12 ppb toluene, 1 2 xylenes, 9 7 ppb TBA and <br /> 66 ppb ethanol <br /> Field screening and analytical results of the additional subsurface investigation soil samples <br /> indicate the extent of gasoline constituents in vadose zone soil is delineated to the north, east <br /> and south Analytical results of the groundwater samples collected in this investigation <br /> indicate the gasoline-impacted groundwater extends south and north of the UST basin to the <br /> locations of monitonng wells MW-6 and MW-8 The eastward extent of gasoline-impacted <br /> groundwater is effectively delineated by monitoring well MW-7 <br /> The data generated by previous work and this remedial investigation suggest the extent of <br /> gasoline-impacted groundwater is not delineated to the south and north Additionally, the <br /> extent of gasoline-impacted groundwater has not been delineated to the west because <br /> Ultramar was unable to obtain permission to install a groundwater monitoring well off site to <br /> the west (as proposed in the work plan) It is recommended that the project proceed with a <br /> 641 AddSbsrfcIvest5-00 doc 7 HORIZON ENVIRONMENTAL INC. <br /> 1641 14 <br />