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to a depth of 16 feet bgs Soil samples collected from beneath the tanks were submitted to CWL ' for analysis All soil samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg) and total petroleum hydrocarbons as diesel (TPHd) by EPA method 8020, and benzene, toluene, ' and total xylenes (BTX) by EPA method 8020 Selected samples were analyzed for ethylene dibrorrude (EDB) by EPA method 8010, and total lead Analytical results indicated low levels of PHCs detected in the initial soli samples, primarily in the samples collected at the south ends of the ' tanks where petroleum product odor was detected However, PHC concentrations in the follow up samples collected approximately 5 feet below the initial samples, were significantly attenuated relative to the initial concentrations m the samples No EDB was detected in any of the samples Lead was detected at 6 to 12 4 mg/kg in the initial samples from the north ends of both tanks, but was not detected in the follow up samples at 16 feet bgs ' 2.2.2 Initial Subsurface Investigation ' No PHCs were detected in the uppermost soil samples collected from 10 to 11 feet bgs, or in the two lowermost samples collected at 35 and 40 feet bgs, in any of the three borings PHCs in soils were first detected at 16 feet bgs in boring B3-2, and at 20 feet bgs in borings B3-1 and B3-3 ' (Figure 2) The highest levels of PHCs in sorts were detected in the sample collected from 15 5 to 16 0 feet bgs in boring B3-2 Tlus sample contained 2,100 mg/kg TPHg and 8 4 mg/kg benzene Uppermost groundwater samples were collected at 12 and 13 feet bgs in borings B3-3 and B3-2 , respectively The sample from B3-2 contained trace amounts of PHCs (0 00042 mg/1 benzene), ' while no PHCs were detected in the sample from B3-3 Groundwater sampled from boring B3-1 at 22 feet bgs, within the zone of strong petroleum product odor, contained the highest concentrations of PHCs in groundwater samples, with 1,600 mg/P TPHg The depth-discrete ' groundwater sample collected from 31 to 35 feet bgs in boring B3-2 contained 2 7 mg/Q TPHg and 0 060 mg/2 benzene, indicating that dissolved phase PHCs are present in the coarser-grained sediments below the zone ofPHC-impacted soils ' 2.3 GEOLOGIC AND HYDROLOGIC CHARACTERISTICS ' The site is located on the delta of the San Joaquin River, approximately 2 miles east of the confluence of the San Joaquin and Calaveras Rivers The subsurface geology consists of a thick sequence of alluvial deposits of late Tertiary to Holocene Age, overlying sedimentary rocks of ' Cretaceous to Tertiary age, which in turn overlie crystalline basement rocks (Bartow and Nilsen, 1990) Data from nearby studies within the Port area indicate a soil profile to a depth of about 20 feet bgs comprised of interbedded sands and clays, mostly under reduced conditions (Sierra-Pacific ' Groundwater Consultants [SPDC], 1994) ' kladftv vqm 3 PHILIP P. Ross, R.G.