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Soil and Groundwater Investigation Report <br /> ARCO Facility No 6080 <br /> Lathrop, California <br /> • Page 4 <br /> Groundwater was encountered during drilling at approximately 11 feet bgs Static water <br /> levels in the monitoring wells were measured on June 21, 2000 to range from 7 73 to 8 47 <br /> feet bgs The groundwater flow direction for June 21, 2000 was calculated to be towards <br /> the northeast at an approximate gradient of 0 0026 ft/ft <br /> Analytical Results <br /> Soil and groundwater samples collected from each boring/monitoring well were <br /> submitted to Sequoia Analytical Inc in Sacramento, a Califorma state certified analytical <br /> laboratory, for chemical analysts Summaries of the soil and groundwater analyses are <br /> presented in Table 1 Certified laboratory reports are presented with the appropriate <br /> chain-of-custody documentation in Appendix C <br /> The samples were analyzed for TPHG and BTEX compounds using US Environmental <br /> Protection Agency (USEPA) Method 8015/8020 DHS/LUFT and for MTBE, TBA, <br /> DIPE, TAME, ETBE, 1,2 DCA and EDB using USEPA Method 8260A A composite <br /> sample of waste soil was collected and additionally analyzed for total lead using USEPA <br /> Method 6010 <br /> Petroleum hydrocarbons were detected in soil samples collected from boring/monitonng <br /> . well MW-1 and MW-2 Soil samples collected from boring/monitoring well MW-3 did <br /> not contain petroleum hydrocarbons TPHG was detected in the soil samples collected <br /> from boring/monitoring well MW-I and MW-2 at 11 feet bgs (near first encountered <br /> groundwater) at concentrations of 536 and 6 49 mg/kg, respectively Toluene and <br /> xylenes were also detected in the sample collected from I I feet bgs in boring/monitoring <br /> well MW-1 at concentrations of 290 and 2,250 µg/kg, respectively Concentrations of <br /> oxygenates, 1,2 DCA, EDB, benzene and ethylbenzene were below laboratory detection <br /> limits in all of the soil samples <br /> Groundwater samples collected from MW-1 and MW-2 contained MTBE at <br /> concentrations of 45 4 and 16 6 µg/l, respectively TPHG and benzene were below <br /> laboratory detection limits in all water samples <br /> Summary <br /> The following summarizes the results of the soil and groundwater investigation <br /> • Subsurface material encountered beneath the site consists predominately of fine to <br /> coarse grained sand, <br /> • Groundwater flow direction was calculated to be towards the northeast at a <br /> gradient of 0 0026 ft/ft Static groundwater levels were measured in the <br /> monitoring wells to be approximately 8 feet bgs, <br /> • • TPHG was detected in the soil samples collected from boring/monitoring well <br /> MW-1 and MW-2 during drilling at first encountered groundwater, but was not <br /> detected in the groundwater samples collected from the monitoring wells, <br />